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🏃‍♂️ Motor Pathways 🏃‍♂️ The motor pathway is responsible for transmitting signals from the brain to the muscles to initiate movement. This pathway can be divided into two main parts: the upper motor neuron and the lower motor neuron. Upper Motor Neuron The upper motor neuron starts in the primar...

🏃‍♂️ Motor Pathways 🏃‍♂️ The motor pathway is responsible for transmitting signals from the brain to the muscles to initiate movement. This pathway can be divided into two main parts: the upper motor neuron and the lower motor neuron. Upper Motor Neuron The upper motor neuron starts in the primary motor cortex of the brain and travels down through the internal capsule, brainstem, and medulla before crossing to the opposite side of the body. It then descends in the spinal cord until it reaches the anterior horn cell in the gray matter of the spinal cord. Lower Motor Neuron The lower motor neuron starts at the anterior horn cell and ends in the muscles of the body. These fibers are responsible for transmitting the signal from the upper motor neuron to the muscles to initiate movement. Characteristics of Motor Fibers Motor fibers have the following characteristics: Thick and myelinated: This allows for faster transmission of nerve impulses. Fast: Motor fibers can transmit nerve impulses at speeds of up to 100 meters per second. Alpha fibers: These are the fastest and most myelinated type of motor fiber. 🤔 Somatic vs. Autonomic Fibers 🤔 Somatic Fibers Somatic fibers start at the anterior horn cell in the gray matter of the spinal cord. They are responsible for transmitting signals to skeletal muscles to initiate movement. Autonomic Fibers Autonomic fibers start at the lateral horn cell in the spinal cord. They are responsible for transmitting signals to smooth muscles and glands to regulate various bodily functions. Key Differences Somatic Fibers Autonomic Fibers Starting point Anterior horn cell Lateral horn cell Transmit signals to skeletal Transmit signals to smooth muscles and Function muscles glands Type of muscle Skeletal muscle Smooth muscle 📚 Embryology of the Nervous System 📚 The nervous system develops from the ectoderm layer of the embryo. The ectoderm differentiates into two subtypes: surface ectoderm and neuroectoderm. Surface Ectoderm The surface ectoderm gives rise to the epidermis of the skin. Neuroectoderm The neuroectoderm gives rise to the central nervous system (CNS) and peripheral nervous system (PNS). Development of the CNS and PNS The CNS develops from the neural tube, while the PNS develops from the neural crest. Key Structures Structure Origin Function Neural tube Neuroectoderm Gives rise to the CNS  Structure Origin Function Neural crest Neuroectoderm Gives rise to the PNS Provides support and induces differentiation of the Notochord Mesoderm neuroectoderm 📝 Definitions 📝 Central nervous system (CNS): The part of the nervous system that consists of the brain and spinal cord. Peripheral nervous system (PNS): The part of the nervous system that consists of nerves and ganglia outside of the CNS. Ganglion: A collection of cell bodies in the PNS. Nerve: A collection of axons in the PNS. Tract: A collection of axons in the CNS.## Embryonic Development and the Nervous System The three primary germ layers in embryonic development are: Ectoderm: gives rise to the nervous system Mesoderm: gives rise to the notochord, bones, and cartilage Endoderm: not mentioned in this lecture, but it gives rise to the lining of the digestive tract and other internal organs "The ectoderm is always behind, and the mesoderm is always in front of the ectoderm." Intervertebral Discs and Herniation 🌀 The nucleus pulposus is a gel-like substance in the center of the intervertebral disc.  When the nucleus pulposus bulges, it can cause neuropathic pain and is known as disc herniation. Disc herniation can cause sciatica. Neurons and Myelination 🧠 All neurons have a neural sheath that allows for regeneration. Some neurons are myelinated, while others are not. Myelinated fibers include A and B fibers, while unmyelinated fibers are C fibers. Fiber Type Myelination Speed A Myelinated 100 m/s B Myelinated 10 m/s C Unmyelinated 1 m/s Myelin Production 🧬 In the central nervous system (CNS), myelin is produced by oligodendrocytes. In the peripheral nervous system (PNS), myelin is produced by Schwann cells. Spinal Cord Structure 🌀 The spinal cord has white matter on the outside and gray matter on the inside, forming an H shape. The gray matter is divided into different regions, including the anterior horn and posterior horn. Motor and Sensory Roots 🔄 The motor or efferent root is also known as the ventral root or ramus. The sensory or afferent root is also known as the dorsal root or ramus. The autonomic nervous system is always motor and is located in the lateral horn. Reflex Arc 🔄 A reflex arc is a neural pathway that allows for a rapid response to a stimulus. The reflex arc involves the following steps: Sensory input enters the spinal cord through the dorsal root. The signal is relayed to the anterior horn. The signal is transmitted to the muscles through the ventral root. Somatic and Autonomic Nervous Systems 🔄 The somatic nervous system is responsible for voluntary movements and has the following characteristics: Fast transmission speed Thick, myelinated fibers (A alpha) No ganglia One neurotransmitter (acetylcholine) Voluntary control The autonomic nervous system is responsible for involuntary movements and has the following characteristics: Slower transmission speed Thinner, myelinated fibers (B and C) Ganglia present Multiple neurotransmitters (acetylcholine and norepinephrine) Involuntary control  Somatic Autonomic Transmission Speed Fast Slow Fiber Type A alpha B and C Ganglia No Yes Neurotransmitters Acetylcholine Acetylcholine and norepinephrine Control Voluntary Involuntary Overview of Motor Pathways and Functions Autonomic Nervous System 🧠 The autonomic nervous system is a division of the peripheral nervous system that controls involuntary actions, such as heart rate, digestion, and breathing. Divisions of the Peripheral Nervous System The peripheral nervous system is divided into two main divisions: Sensory Division (Afferent Division): carries sensory information from the body to the brain Motor Division (Efferent Division): carries signals from the brain to the body to control movement and other functions The motor division is further divided into:  Somatic Nervous System: controls voluntary movements, such as walking and talking Autonomic Nervous System: controls involuntary actions, such as heart rate and digestion Autonomic Nervous System Structure The autonomic nervous system is divided into two main divisions: Sympathetic Division: responsible for the "fight or flight" response, increasing heart rate and blood pressure in emergency situations Parasympathetic Division: responsible for "rest and digest" actions, promoting relaxation and reducing stress Key Differences between Somatic and Autonomic Nervous Systems Somatic Nervous System Autonomic Nervous System Muscle Type Skeletal muscle Smooth muscle and cardiac muscle Myelination Heavily myelinated Lightly myelinated or non-myelinated Acetylcholine (always Acetylcholine or norepinephrine Neurotransmitters stimulatory) (stimulatory or inhibitory) Two-neuron chain (preganglionic and Neuron Structure Single neuron postganglionic neurons) Functions of the Sympathetic Division Regulates sweating to control body temperature Influences metabolism Regulates kidney activity Prepares the body for emergency situations (fight or flight response) Functions of the Parasympathetic Division "Rest and digest" actions, promoting relaxation and reducing stress Directs the digestion of food and the expulsion of waste Maintains regular bodily functions, such as heart rate and blood pressure Anatomy of the Autonomic Nervous System Parasympathetic Fibers: originate in the brain and sacral region of the spinal cord, with long preganglionic fibers and short postganglionic fibers Sympathetic Fibers: originate in the thoracic and lumbar regions of the spinal cord, with short preganglionic fibers and long postganglionic fibers Regulation of the Autonomic Nervous System The autonomic nervous system is regulated by components of the central nervous system, ensuring that the body's automatic functions are properly controlled and coordinated. Understanding the Autonomic Nervous System Motor Neurons and Reflexes 🤖 The Motor Pathway The motor pathway is a two-neuron system that allows the brain to control muscle movement. The pathway begins in the motor cortex, a region of the brain that maps the body. When a muscle is contracted, a signal is sent from the motor cortex to the upper motor neuron, which carries the signal down to the lower motor neuron. The lower motor neuron then sends the signal to the muscle, causing it to contract. Upper and Lower Motor Neurons Upper Motor Neuron: The upper motor neuron is responsible for carrying the signal from the motor cortex to the lower motor neuron. It plays an important role in initiating muscle contraction and also has an inhibitory function, telling the lower motor neuron to stop contracting. Lower Motor Neuron: The lower motor neuron is responsible for carrying the signal from the upper motor neuron to the muscle. Its primary function is to contract the muscle. Reflexes A reflex is an automatic response to a stimulus that occurs without the need for conscious thought. Reflexes occur at the level of the spinal cord and are mediated by the lower motor neuron. "A reflex is a rapid, automatic response to a stimulus that occurs without the need for conscious thought." The Patellar Tendon Reflex The patellar tendon reflex is an example of a reflex that occurs when the tendon below the kneecap is stretched. This stretching stimulates the stretch receptors in the tendon, which send a signal to the lower motor neuron. The lower motor neuron then sends a signal to the muscle, causing it to contract. Damage to Motor Neurons Effect on Muscle Effect on Muscle Effect on Effect on Muscle Type of Damage Mass Power Reflexes Tone Upper Motor Hypertonia Neuron Damage Minimal loss Reduced Hyperreflexia (spasticity) Lower Motor Hypotonia Neuron Damage Significant loss Reduced Hyporeflexia (flaccidity) Spinal Cord Injuries Spinal cord injuries can result in damage to either the upper or lower motor neurons, depending on the location of the injury. For example, a cervical spinal cord injury can result in: Lower motor neuron damage to the arm, leading to loss of mass, power, and reflexes, and flaccidity Upper motor neuron damage to the leg, leading to reduced mass and power, hyperreflexia, and spasticity Motor Neurons and Reflex Mechanisms 🌀 Vestibular System Overview The vestibular system is responsible for the body's equilibrium, maintaining balance and providing awareness of the body's spatial orientation. Vestibular Reflex Pathways Vestibular sensory organs detect changes in the head's positions and movements, and transmit this information to various regions of the brain. Projections to the brain stem trigger reflex pathways that lead to compensatory actions to maintain stability or reestablish equilibrium. Examples of vestibular reflex pathways include: Vestibulo-ocular reflex: controls eye muscles to keep visual objects in focus while the head is moving Vestibulo-spinal reflex: senses a potential loss of balance and activates body muscles to keep the body from falling 🗺️ Vestibular System Structure The sensory part of the vestibular system is located in the inner ear on each side of the body. It consists of: 3 semicircular canals that sense rotational movements 2 otolithic organs that sense head positions and straight line motions Semicircular Canals Canal Plane of Motion Movement 1 Horizontal Turning left and right 2 Sagittal Nodding up and down 3 Frontal Tilting to a side Each canal has an enlargement at one end called an ampulla, which contains a fluid called endolymph. Within the ampulla, there are hair cells embedded in a gel-like structure named cupula. Otolithic Organs The 2 otolithic organs are: Saccule: vertical, senses head positions and movements in the vertical plane Utricle: horizontal, senses head positions and movements in the horizontal plane The cilia of these cells are embedded in a gel-like layer, sprinkled with calcium carbonate crystals called otoconia (commonly known as ear rocks). 🔄 Vestibular Sensory Mechanism "Vestibular sensory organs detect not the motion itself, but changes in the rate of motion, specifically, acceleration or deceleration." When the head turns, the ducts that are located on the same plane of motion rotate, but the fluid lags behind because of inertia. This causes the fluid to briefly move in the opposite direction as the head, and either push or pull on the cupula, bending the cilia on the hair cells, and thus, activating them to send nerve impulses to the brain. The direction of the bend determines if the signals generated are excitatory or inhibitory. Because the two sides of the head are mirror images, a head turn generates excitatory signals on one side and inhibitory signals on the other. Vestibular System: Balance and Orientation Tactile Sense The sense of touch, or tactile sense, is the perception of objects that come into contact with the skin. Mechanism of Tactile Perception Mechanical stimuli such as pressure, stretch, vibration, or movement cause physical deformation in tactile receptors, which are essentially nerve endings of sensory neurons. The deformation typically leads to opening of ion channels, allowing ions to flow in or out of the cells, resulting in cellular depolarization. If the stimulus is strong enough, action potentials are generated and sent to the brain. Types of Tactile Receptors Tactile receptors can be classified based on their anatomical structure and functional properties. Type Description Encapsulated Wrapped in connective tissue Unencapsulated Not wrapped in connective tissue Rapidly Adapting Generate action potentials when first stimulated, then quickly adapt and reduce or stop generating signals Slowly Adapting Keep generating signals for a longer time “Rapidly adapting receptors respond to changes and therefore detect movements and sequence of events rather than static objects. Slowly adapting receptors carry messages about steady pressure on the skin and sense objects’ texture, edges, and shapes.” Sensitivity of Tactile Receptors Tactile receptors also differ in their sensitivity. Some respond to light touch, while others sense only heavy pressure. Receptive Fields A sensory neuron receives signals from an area called its receptive field. Any touch within a receptive field stimulates one sensory neuron, transmitting one single signal to the brain. Receptive Field Size Sensitivity Vibration Frequency Response Small High Low frequencies Large Low High frequencies Touch Sensory Pathway A touch sensory pathway involves three neurons. First-order neurons: Touch receptors that form sensory fibers that enter the spinal cord via the dorsal root of spinal nerve. Second-order neurons: Receive signals from first-order neurons and cross over to the other side of the cord before ascending to the thalamus. Third-order neurons: Conduct information from the thalamus to the sensory cortex. Organization of the Sensory Cortex The sensory cortex is spatially organized so that its adjacent areas represent neighboring regions of the body. The size of the cortical area representing a certain body region is proportional to the number of sensory receptors it has. Body Region Cortical Representation Fingers Large Face Large Trunk Small Understanding the Tactile Sense Pain Mechanism 🤕 Pain is a defense mechanism that warns the body about potential or actual injuries or diseases, prompting protective actions. Pain Pathway The pain pathway involves the following steps: Noxious signals send impulses to the spinal cord The spinal cord relays the information to the brain The brain interprets the information as pain, localizes it, and sends back instructions for the body to react Pain Receptors (Nociceptors) Pain receptors, or nociceptors, are specialized nerve endings that detect and respond to painful stimuli. Nociceptors are present in the skin, superficial tissues, and virtually all organs, except for the brain. They are the nerve endings of first-order neurons in the pain pathway. Types of Nociceptors Type Characteristics Function Initial sharp pain perceived at the time of A fibers Myelinated, fast conduction speed injury C Unmyelinated, slow conduction fibers speed Longer lasting, dull, diffusing pain Pain Transmission First-order neurons travel by way of spinal nerves to the spinal cord, where they synapse with second-order neurons in the dorsal horn. These second-order neurons cross over to the other side of the cord before ascending to the brain. Pain Pathways to the Brain There are two major pathways that carry pain signals from the spinal cord to the brain: Spinothalamic Tract: involved in localization of pain Second-order neurons travel up to the thalamus, where they synapse with third-order neurons Third-order neurons project to their designated locations in the somatosensory cortex Spinoreticular Tract: responsible for the emotional aspect of pain Second-order neurons ascend to the reticular formation of the brainstem before running up to the thalamus, hypothalamus, and the cortex Specialized Pain Pathways Pain signals from the face follow a different route to the thalamus: First-order neurons travel mainly via the trigeminal nerve to the brainstem, where they synapse with second-order neurons  Second-order neurons ascend to the thalamus Types of Pain Somatic Pain: pain from the skin, muscles, and joints Visceral Pain: pain from internal organs Referred Pain Visceral pain is often perceived at a different location due to the convergence of pain pathways at the spinal cord level. For example, pain from a heart attack may be felt in the left shoulder, arm, or back rather than in the chest where the heart is located. This occurs because the brain cannot distinguish between pain signals from different sources that converge at the same spinal segment. Understanding Pain Mechanisms and Pathways 🌿 The Olfactory System The olfactory system is responsible for the sense of smell or olfaction. It is a complex process that involves the detection of airborne molecules emitted by an odorant source. Olfactory Sensory Neurons Olfactory sensory neurons are located at the roof of the nasal cavity and are responsible for converting chemical stimuli into electrical signals. These neurons: Express a single type of protein receptor Have cilia that bind to odorant molecules Send signals to the olfactory bulb via the olfactory nerve (also known as cranial nerve 1) Odorant Molecules and Receptors "Odorant molecules are first dissolved in the mucus secreted by the olfactory epithelium, which guides them to the cilia of olfactory neurons." There are approximately 400 different odorant receptors in humans Each receptor can bind to multiple odorant molecules Each odorant molecule can bind to multiple receptors This enables the olfactory system to recognize an enormous number of odorants Signal Transduction Odorant receptors are G protein-coupled receptors Upon binding to an odorant, a signaling cascade is activated, leading to membrane depolarization When the olfactory stimulus is strong enough, action potentials are generated and conducted along the axon to the olfactory bulb Olfactory Bulb and Cortex Structure Description Receives axons from olfactory sensory neurons and synapses with Olfactory Bulb second-order neurons (mitral and tufted cells) within glomeruli Mitral and Receive excitatory input from sensory neurons and inhibitory feedback Tufted Cells from the cerebral cortex Olfactory Formed by the axons of mitral and tufted cells, project directly to Tracts the primary olfactory cortex Primary Located on the base of the frontal lobe and inferior surface of Olfactory the temporal lobe, projects to other areas of the brain mediating different Cortex aspects of odor recognition and response Olfactory System Maintenance and Disorders Olfactory neurons are replaced more often than other neurons due to exposure to the external environment Stem cells in the epithelium differentiate into new olfactory neurons Factors that destroy all olfactory neurons at once can result in permanent anosmia Anosmia can also be caused by illnesses that cause inflammation of the nasal mucosa Loss of smell can affect the taste experience, as taste and smell are the two aspects of flavor  The ability to smell decreases with normal aging, but anosmia is also an early sign of several neurodegenerative disorders Understanding the Olfactory System 👀 The Anatomy of the Human Eye The Outer Layer 🌐 The outer layer of the eye is composed of the cornea and the sclera. The sclera is the white visible portion of the eyeball. The cornea is a dome-shaped structure that forms from the transparent part of the sclera at the front of the eye. The cornea is the first optical component of the eye machinery, providing 70% of the eye's focusing power. The Middle Layer 🔍 The middle layer of the eye is composed of the choroid, ciliary body, lens, and iris. Structure Description A thin, blood-rich membrane that supplies blood to the eye, especially to the Choroid retina. Ciliary Body A structure that helps adjust the shape of the lens to focus light.  Structure Description Lens A transparent structure that focuses light onto the retina. A circular, pigmented structure that regulates the amount of light entering the Iris eye. The iris acts like the aperture of a camera, constricting the pupil in bright light and dilating it in low light. The Iris and Pupil 👀 The pupil is a dark-colored opening at the center of the iris that allows light to pass through. The iris regulates the amount of light entering the eye by adjusting the size of the pupil. The Inner Layer 📺 The innermost layer of the eye is the retina. The retina can be imagined as the wall on which images are projected. The retina is made up of two types of cells: rod cells and cone cells. These cells, also called photoreceptors, convert light into electrical signals that are transferred to the brain through the optic nerve. The Vitreous Cavity 🌀 The vitreous cavity is a space between the lens and the back of the eye. The cavity is filled with a jelly-like transparent fluid called vitreous humor.  The vitreous humor helps maintain the round shape of the eye. Understanding the Human Eye's Anatomy Taste and the Sense of Taste 🍴 The Process of Taste Taste, also known as gestation, is a special sense that helps us evaluate what we eat or drink. The process of taste involves the activation of taste receptor cells in the mouth by certain food molecules dissolved in saliva. These chemical stimuli are then converted into electrical signals and sent via several nerves to the brain, where they are interpreted as tastes. Taste Buds and Papillae Taste buds are groups of taste receptor cells that are present most abundantly on the tongue but also on other parts of the mouth. On the tongue, taste buds are located on small visible bumps called papillae. There are different types of papillae on different parts of the tongue, but the taste buds that they contain are all similar in structure. Structure of Taste Buds Each taste bud is composed of about 50 taste cells with microvilli at the top, projecting into a pit called the taste pore. This is where taste molecules bind to their receptors. Taste cells synapse with sensory nerve fibers at the base of taste buds. Types of Taste Receptors There are 5 main types of taste receptors corresponding to 5 major taste sensations in humans: Taste Receptor Description Salty Receptors Detect sodium and salt  Taste Receptor Description Sweet Receptors Bind to a number of sugars and sugar substitutes Sour Receptors Activated by acids Umami Receptors Elicit a meaty taste, particularly by glutamates Bitter Associated with spoiled foods, natural toxins, and substances such as Receptors quinine and caffeine Distribution of Taste Receptors Each taste cell has receptors for only one type of taste, but a taste bud is typically composed of a variety of cells detecting different tastes. All primary tastes can be perceived throughout the tongue, but some regions are more sensitive to a certain taste than others. Thresholds for Detection The threshold for detection is the minimum amount of a substance required to elicit a taste response. The thresholds for detection differ among chemicals that taste the same. Sweet and salty substances generally have high thresholds, while bitter compounds typically have very low thresholds. Supertasters Some people are supertasters, meaning they have more taste buds on their tongue and are therefore able to detect certain subtle tastes at very low concentrations. Signaling Pathways Depending on the type of taste sensation, binding of taste molecules to their specific receptors results in either depolarization or activation of G protein and second messenger signaling in taste cells. In either case, the activated taste cells release neurotransmitters, which generate action potentials in sensory nerve fibers. Transmission of Taste Signals Depending on the location of the taste buds, nerve fibers carrying taste signals move along cranial nerves 7, 9, or 10 to the solitary nucleus of the brain stem. From there, 2nd order neurons project to 2 destinations: The thalamus, where they synapse with 3rd order neurons, which continue to higher cortical taste centers The hypothalamus and amygdala, where they trigger autonomic reflexes such as salivation, gagging, vomiting, and provide input for regulation of eating behaviors Understanding the Sense of Taste 🌀 Vestibular System Overview The vestibular system is responsible for the body's equilibrium, maintaining balance and providing awareness of the body's spatial orientation. Vestibular Reflex Pathways Vestibular sensory organs detect changes in the head's positions and movements, and transmit this information to various regions of the brain. Projections to the brain stem trigger reflex pathways that lead to compensatory actions to maintain stability or reestablish equilibrium. Vestibulo-ocular reflex: controls eye muscles to keep visual objects in focus while the head is moving by moving the eyes in the opposite direction as the head. Vestibulo-spinal reflex: senses a potential loss of balance and activates body muscles to keep the body from falling. 🗺️ Vestibular System Structure The sensory part of the vestibular system is located in the inner ear on each side of the body. It consists of:  3 semicircular canals: sense rotational movements, such as when the head is turning. 2 otolithic organs: sense head positions, as well as straight line motions, such as when riding in a car or elevator. Semicircular Canals Canal Plane of Motion 1 Turning left and right 2 Nodding up and down 3 Tilting to a side Each canal has an enlargement at one end called an ampulla, which contains a fluid called endolymph. Within the ampulla, there are hair cells embedded in a gel-like structure named cupula. Otolithic Organs The 2 otolithic organs are 2 patches of hair cells oriented nearly perpendicular to each other: Saccule: vertical Utricle: horizontal The cilia of these cells are embedded in a gel-like layer, sprinkled with calcium carbonate crystals called otoconia, commonly known as ear rocks. 🔄 How Vestibular Sensory Organs Work Vestibular sensory organs detect not the motion itself, but changes in the rate of motion, specifically, acceleration or deceleration. When the head turns, the ducts that are located on the same plane of motion rotate, but the fluid lags behind because of inertia. This causes the fluid to briefly move in the opposite direction as the head, and either push or pull on the cupula, bending the cilia on the hair cells, and thus, activating them to send nerve impulses to the brain. The direction of the bend determines if the signals generated are excitatory or inhibitory. Because the two sides of the head are mirror images, a head turn generates excitatory signals on one side and inhibitory signals on the other. 🚗 Examples of Vestibular Sensory Organs in Action When a person is sitting in a car that starts to move, the heavy gel-like layer of the utricle lags behind at first, bending the cilia back, activating the hair cells. The more sudden the car starts, the greater the stimulation. Similar events occur in the saccule during an elevator ride up or down. Understanding the Vestibular System 🗣️ Auditory Transduction Auditory transduction is the process by which the ear converts sound waves in the air into electrical impulses that can be interpreted by the brain. The External Auditory Canal and Tympanic Membrane The external auditory canal is the passage through which sound enters the ear. The sound then meets the tympanic membrane, a cone-shaped structure that vibrates in response to sound waves. The tympanic membrane is a thin, semi-transparent membrane that separates the external auditory canal from the middle ear. The vibrations of the tympanic membrane are influenced by the frequency and amplitude of the sound waves: Lower frequency sounds produce slower vibrations Lower amplitude sounds produce less dramatic vibrations Higher frequency sounds produce faster vibrations The Auditory Ossicles The tympanic membrane articulates with a chain of three bones called the auditory ossicles:  Ossicle Description Malleus Incus Stapes Moves with a piston-like action, sending vibrations into the bony labyrinth The Bony Labyrinth and Cochlea The stapes sends vibrations into the bony labyrinth, a structure filled with a fluid called paralynth. The vibrations are able to displace the paralynth due to the flexibility of the round window membrane. The cochlea is the spiral portion of the bony labyrinth where the vibrations are drawn into the spiral system and return to meet the round window. The cochlea is divided into three structures: Structure Description Scala Vestibuli The ascending portion of the passage  Structure Description Scala Tympani The descending portion of the passage Cochlear Situated between the scala vestibuli and scala tympani, filled Duct with endolymph The Organ of Corti and Hair Cells The organ of Corti is a specialized structure situated on the basilar membrane, which vibrates in response to the vibrations traveling up the scala vestibuli. The organ of Corti sends nerve impulses to the brain via the cochlear nerve. The hair cells are specialized cells within the organ of Corti that generate the nerve impulses. They are closely covered by the tectorial membrane, and as the basilar membrane vibrates, the tiny clusters of hairs are bent against the tectorial membrane, triggering the hair cells to fire. Tonotopic Organization The basilar membrane does not vibrate simultaneously. Instead, specific areas along the basilar membrane move variably in response to different frequencies of sound. This arrangement is known as tonotopic organization: Lower frequencies vibrate the basilar membrane closer to the apex of the cochlea Higher frequencies produce vibrations closer to the base Understanding Auditory Transduction Process Peripheral Nervous System 🧠 The peripheral nervous system (PNS) is a part of the nervous system that consists of the nerves and ganglia outside of the brain and spinal cord. The PNS is everything that's not the brain, brainstem, and spinal cord. Functional Subdivisions of the Peripheral Nervous System The PNS has two main functional subdivisions: Autonomic Nervous System (ANS): controls involuntary functions, such as heart rate, digestion, and breathing. Somatic Nervous System (SNS): controls voluntary functions, such as movement and sensation. Cranial Nerves 🧠 The cranial nerves are 12 pairs of nerves that arise from the brain and brainstem. They are responsible for controlling various functions, such as sensation, movement, and involuntary functions. Mnemonic for Remembering Cranial Nerves O, O, O, to touch and feel very good velvet a heaven. Cranial Nerve Name Function I Olfactory Sense of smell (sensory) II Optic Vision (sensory) III Oculomotor Movement of eye (motor) Cranial Nerve Name Function IV Trochlear Movement of eye (motor) V Trigeminal Sensation of face, movement of jaw (both) VI Abducens Movement of eye (motor) VII Facial Movement of face, taste (both) VIII Vestibulocochlear Balance, sound (sensory) IX Glossopharyngeal Swallowing, taste (both) Sensory and motor functions, including heart rate and X Vagus digestion (both)  Cranial Nerve Name Function XI Accessory Movement of shoulders (motor) XII Hypoglossal Movement of tongue (motor) Mnemonic for Remembering Cranial Nerve Functions Some say marry money, but my brother says big brains matter most. Letter Function S Sensory M Motor B Both Spinal Nerves 🧠 The spinal nerves are 31 pairs of nerves that arise from the spinal cord. They are responsible for controlling various functions, such as sensation, movement, and involuntary functions. Divisions of the Spinal Cord The spinal cord can be divided into five regions: Cervical (8 pairs of nerves) Thoracic (12 pairs of nerves) Lumbar (5 pairs of nerves) Sacral (5 pairs of nerves) Coccygeal (1 pair of nerves) Mnemonic for Remembering Spinal Nerve Divisions 8 AM, 12 PM, 5 PM, 5, 1 Autonomic Nervous System 🧠 The autonomic nervous system has two subdivisions: Sympathetic Nervous System: responsible for "fight or flight" responses, such as increased heart rate and blood pressure. Parasympathetic Nervous System: responsible for "rest and digest" responses, such as decreased heart rate and blood pressure. Parasympathetic Nervous System The parasympathetic nervous system has fibers that arise from the cranial nerves and sacral nerves. Cranial nerves: III, VII, IX, X Sacral nerves: S2-S4 Sympathetic Nervous System The sympathetic nervous system has fibers that arise from the thoracic and lumbar nerves. Thoracic nerves: T1-T12 Lumbar nerves: L1-L2 Overview of the Peripheral Nervous System 🧠 The Limbic System: An Overview The limbic system is a complex network of brain structures that play a crucial role in our emotional, cognitive, and behavioral responses. The term "limbic" comes from the Latin word "limbus," meaning border or edge, as it is situated at the border between the brain stem and the neocortex. Why is it called a System? The limbic system is referred to as a system because its various structures interact with each other to produce a specific output. This output can be behavioral, emotional, or cognitive. Think of it like a pinball machine, where different parts of the limbic system communicate with each other to create a response to sensory input. 🤔 Major Structures of the Limbic System The following are some of the major structures that make up the limbic system: Structure Function Amygdala Emotional response, emotions (e.g., fear, anger, joy) Hippocampus Memory formation, encoding and processing of memories Homeostasis, maintaining internal balance (e.g., hunger, thirst, Hypothalamus sleep)  Structure Function Thalamus Filter of the brain, relay center for sensory information Cingulate Gyrus Memory, emotions, pain perception, error recognition Nucleus Accumbens Reward processing, pleasure and motivation The Amygdala The amygdala is often referred to as the emotional center of the brain. It plays a crucial role in processing emotions, such as fear, anger, and joy. The Hippocampus The hippocampus is involved in the formation of new memories, particularly those related to emotions and experiences. It does not store memories, but rather helps to encode and process them. The Hypothalamus The hypothalamus is responsible for maintaining homeostasis, or internal balance, in the body. It regulates basic needs such as hunger, thirst, and sleep. The Thalamus The thalamus acts as a filter for sensory information, deciding what information to focus on and what to ignore. It also serves as a relay center, directing sensory information to the appropriate part of the brain for processing. The Cingulate Gyrus The cingulate gyrus is involved in a variety of functions, including memory, emotions, pain perception, and error recognition. It is connected to the hippocampus via the fornix. The Nucleus Accumbens The nucleus accumbens is responsible for processing rewards and pleasure. It plays a key role in motivation and is often referred to as the "reward center" of the brain.## Limbic System Structures The limbic system is a complex network of brain structures that play a crucial role in emotions, motivation, and memory. The following are some of the major structures of the limbic system: Nucleus Accumbens: associated with pleasure and reward Olfactory Bulb: deals with smell and is connected to the limbic system Amygdala: plays a key role in emotional response and fear Hippocampus: involved in memory formation and consolidation Hypothalamus: regulates the body's autonomic nervous system and endocrine system Pituitary Gland: releases hormones that stimulate the adrenal glands to produce stress hormones Prefrontal Cortex: responsible for rational thought and decision-making Emotional Response 🚨 The amygdala is the center of emotional response in the limbic system. It detects threats and triggers a fear response, which activates the body's sympathetic nervous system and releases stress hormones. The Amygdala's Role in Emotional Response Detects threats through visual, auditory, or olfactory input Triggers a fear response, which activates the body's sympathetic nervous system  Communicates with the hypothalamus, pituitary gland, and hippocampus to coordinate the body's response The Body's Response to Threat Response Description Sympathetic Nervous System Activation increases heart rate, breathing, and blood pressure cortisol, norepinephrine, and adrenaline are released to Stress Hormone Release prepare the body for "fight or flight" the hippocampus forms a memory of the event to help the Memory Formation body learn from the experience Memory and Learning 📚 The hippocampus is the center of memory and learning in the limbic system. It plays a crucial role in forming and consolidating memories, especially explicit memories. The Hippocampus's Role in Memory and Learning Forms memories of events, especially those that are emotionally charged Consolidates memories from short-term to long-term storage Communicates with the fornix and cingulate gyrus to encode and store memories Memory Formation and Consolidation "Memory formation is the process of creating new memories, while memory consolidation is the process of strengthening and stabilizing those memories over time." Memory Formation: the process of creating new memories, especially explicit memories Memory Consolidation: the process of strengthening and stabilizing memories over time, making them easier to retrieve and recall## Limbic System Functions The limbic system is a complex network of brain structures that play a crucial role in various functions, including memory, emotions, motivation, and homeostasis. Memory and Learning 📚 The process of strengthening neural connections is called long-term potentiation. The hippocampus and amygdala work together to create emotional memories. The olfactory bulb is also involved in emotional memories, particularly those associated with smells. "Long-term potentiation is a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons." Motivation and Reward 🏆 The ventral tegmental area (VTA) is a structure deep within the midbrain that is packed with dopaminergic neurons. Dopaminergic neurons release an excess supply of dopamine, a neurotransmitter that controls pleasure, reward, and motor function. The VTA projects to the nucleus accumbens, which deals with pleasure. Structure Function Ventral Tegmental Area (VTA) Releases dopamine, controls pleasure and reward Nucleus Accumbens Deals with pleasure  Structure Function Neurotransmitter that controls pleasure, reward, and motor Dopamine function Sex Motivation 🚫 The hypothalamus is involved in sex motivation and releases hormones such as oxytocin and testosterone. The hypothalamus is often referred to as the "king" or "queen" of the brain. Homeostasis 🏥 The hypothalamus controls homeostasis, which is the body's internal balance. The hypothalamus has two parts: the lateral hypothalamus, which makes us hungry, and the ventromedial hypothalamus, which makes us full. Structure Function Hypothalamus Controls homeostasis, internal balance Lateral Hypothalamus Makes us hungry Ventromedial Hypothalamus Makes us full Other structures that play a role in homeostasis include:  Fat cells, which release leptin to make us full Pancreas, which releases insulin to help glucose enter cells Stomach, which releases ghrelin to make us hungry "Homeostasis is the ability to maintain a stable internal environment despite changes in the external environment." Overview of the Limbic System Central Nervous System 🧠 The central nervous system (CNS) is made up of the brain and the spinal cord. It is central anatomically, as it sits in the middle of the body, and functionally, as it is the site of information integration. Protective Layers of the Brain 🧬 Above the brain, but below the skull, there are three protective layers called the meninges or meningeal layers. Layer Description The layer most adherent to the brain, meaning "soft mother". It is like tissue Pia Mater paper stuck to the brain. The layer with projections down to the pia mater, resembling a spider's web, Arachnoid meaning "spider mother". Cerebrospinal fluid floats through the space Mater between the arachnoid and pia mater.  Layer Description The tough outer layer, meaning "tough mother", with a consistency like a Dura Mater paper bag. Brain Structure 🧠 The brain is made up of the cerebrum, cerebellum, and brain stem. Cerebrum The cerebrum is the largest part of the brain and is divided into lobes or cortices. The cortex is the outer layer of the cerebrum, made up of grey matter, where information is processed and we become consciously aware. Lobe Function Frontal Lobe Site of the motor cortex, responsible for conscious movement. Location of the somatosensory cortex, responsible for processing Parietal Lobe sensation. Occipital Lobe Site of the visual cortex, responsible for processing visual information.  Lobe Function Temporal Lobe Site of the auditory cortex, responsible for processing sound. Cerebellum The cerebellum, or "little brain", plays a role in maintaining: Tone (muscle contraction) Posture Balance Brain Stem The brain stem is made up of three parts: the midbrain, pons, and medulla oblongata. It is responsible for: Housing cranial nerves Regulating respiratory and cardiovascular rhythms Controlling reflexes, such as: Blink reflex Cough reflex Vomiting reflex Jaw jerk reflex Grey and White Matter 🧬 Grey matter is composed of neuron cell bodies, where information is processed and integrated. White matter is composed of axons, which are insulated with fat and transmit information.  Grey Matter White Matter Composition Neuron cell bodies Axons Function Information processing and integration Information transmission Appearance Grey White (due to fatty insulation) Central Nervous System Overview and Structure Sensory Receptors 🧠 Sensory receptors are specialized nerve endings that detect changes in the environment and send signals to the brain. They can be categorized into different types based on their location and function. Types of Sensory Receptors Mechanoreceptors: detect mechanical pressure, stretch, and vibration Thermal receptors: detect changes in temperature Pain receptors: detect painful stimuli Taste receptors: detect chemicals in food and drinks Smell receptors: detect chemicals in the air Vision receptors: detect light and color How Sensory Receptors Work Sensory receptors work by detecting a stimulus and generating a receptor potential. The receptor potential is a change in the electrical potential of the nerve cell that is proportional to the strength of the stimulus. If the receptor potential is strong enough, it can trigger an action potential, which is a rapid change in the electrical potential of the nerve cell that travels down the length of the nerve fiber. "The receptor potential is like a messenger that tells the nerve cell whether the stimulus is strong enough to trigger an action potential." The Pathway of Sensory Information Sensory information travels from the sensory receptors to the brain through a series of nerve fibers. The pathway of sensory information can be divided into three levels: Level Location Function First-order Sensory receptor to spinal cord or Detects stimulus and generates neuron medulla oblongata receptor potential Second-order Spinal cord or medulla oblongata neuron to thalamus Transmits information to thalamus Third-order Thalamus to somatosensory Transmits information to neuron cortex somatosensory cortex for processing Touch Receptors Touch receptors are specialized nerve endings that detect mechanical pressure, stretch, and vibration. There are several types of touch receptors, including: Pacinian corpuscles: detect deep pressure and vibration Meissner's corpuscles: detect light touch and pressure Merkel's discs: detect pressure and texture The Somatosensory Cortex The somatosensory cortex is the part of the brain that processes sensory information from the body. It is located in the parietal lobe and is responsible for processing information from touch, pressure, temperature, and pain. "The somatosensory cortex is like a map of the body, with different areas corresponding to different parts of the body." Sensory Pathways There are two main sensory pathways that transmit information from the body to the brain: Medial lemniscus: transmits information from touch, pressure, and proprioception (position and movement) Spinothalamic tract: transmits information from pain, temperature, and coarse touch Pathway Function Location Transmits information from Medial touch, pressure, and Spinal cord to medulla oblongata to lemniscus proprioception thalamus to somatosensory cortex Spinothalamic Transmits information from pain, Spinal cord to thalamus to tract temperature, and coarse touch somatosensory cortex Autonomic Functions Some sensory information does not need to reach the conscious brain and is processed at the level of the brain stem. This includes: Temperature regulation: the brain stem regulates body temperature without conscious input Hunger and thirst: the brain stem regulates hunger and thirst without conscious input## Sensory Input and Special Senses The human body has a unique way of processing sensory input from different parts of the body. The somatosensory cortex is responsible for processing senses from various body parts, with some areas having more receptors than others. Body Parts with High Sensory Input Fingers: have a lot of receptors, allowing for fine touch Tongue: has a high concentration of receptors, making it sensitive to taste Nose of a rat, rabbit, and cat: highly sensitive areas Taste 👅 Taste is one of the special senses that is closely related to smell. It is responsible for quality assurance of food intake. How Taste Works Specialized receptor cells in the epithelium of the tongue connect to the first-order afferent nerve Taste buds are found all over the tongue, with different areas sensitive to different tastes Saliva dissolves chemicals in food, which then bind to taste receptors in the taste pores Types of Taste Sweet Umami (glutamine) Salty Sour Bitter The Gustatory Pathway Pathway Description 1. Taste buds Specialized receptor cells in the epithelium of the tongue 2. First-order afferent nerve Connects to the medulla  Pathway Description 3. Medulla Connects to the thalamus 4. Thalamus Connects to the gustatory cortex (part of the sensory cortex) Projections to Other Parts of the Brain Limbic system: involved in emotions, memory, and instincts Hypothalamus: involved in regulating hunger and thirst Smell 👃 Smell is closely related to taste and is also involved in quality assurance of food intake. How Smell Works Specialized epithelial cells in the nose detect chemicals in the air Air movement carries chemicals to the olfactory epithelium Chemicals are dissolved in the mucus layer and bind to receptors on the cilia of the first-order neurons The Olfactory Pathway Pathway Description 1. Olfactory epithelium Specialized epithelial cells in the nose 2. First-order neurons Connect directly to the olfactory bulb  Pathway Description Second-order neurons connect to the cerebral cortex or limbic 3. Olfactory bulb system Comparison of Olfactory Epithelium in Different Species Species Number of Receptors Dog 250,000,000 Mouse 50,000,000 Human 6,000,000 "Smell is a powerful trigger for memories and emotions, and is closely linked to the limbic system."## The Importance of Smell in Animal Behavior Smell is a crucial sense for most animals, including humans. Animals can detect human scent even before they see them. Hand sanitizer can be particularly problematic, as it can leave a strong scent on surfaces and equipment. 👀 The Eye: A Complex Organ The eye is part of the brain and is formed from the neural tube during embryonic development. The retina is neuroepithelium and is closely related to the central nervous system. Infections in the eye can easily spread to the central nervous system and cause meningitis. 📚 The Tunicas of the Eye Tunic Description Structures Tunica Fibrosa Outermost layer, fibrous, and strongest layer Sclera, Cornea Tunica Vascularized layer, produces different structures Ciliary body, Iris, Vasculosa within the eye Choroid Innermost layer, nervous layer, and part of the Tunica Interna brain Retina 👀 The Cornea The cornea is a strong and transparent structure that allows light to pass through. It is composed of: Stratified squamous epithelium (protective layer) Bowman's membrane (basal membrane) Stroma (connective tissue with regular and parallel collagen fibers) Descemet's membrane (thin membrane) Endothelium (innermost layer) "The cornea is transparent because the collagen fibers in the stroma are aligned in parallel, allowing light to pass through. If the fibers are misaligned, the light is scattered, and the cornea becomes opaque." 👀 The Sclera The sclera is a white and fibrous layer that provides structure and protection to the eye. It is composed of irregular connective tissue, which scatters light and makes it appear white. 👀 The Iris The iris is a beautiful structure that determines eye color. It is composed of: Stroma (connective tissue with pigment) Epithelium (on the back side of the iris) Muscle bundles (for dilation and constriction of the pupil) "The iris is lined by an epithelium on one side, and the stroma is fully exposed on the front side. The pigment in the stroma determines the eye color." 👀 The Ciliary Body and Choroid The ciliary body and choroid are part of the tunica vasculosa and provide blood flow to the eye. The choroid is the rest of the tunica vasculosa that continues on the back of the eye.## The Iris and Pupil The iris is a part of the tunica vasculosa, a vascular layer of the eye. It is located between the cornea and the lens. Function of the Iris The iris has two main functions: Regulates the amount of light entering the eye by adjusting the size of the pupil Divides the eye into the anterior chamber and the posterior chamber Structure of the Iris The iris is composed of: Stroma: a layer of connective tissue with a lot of pigments Epithelium: a layer of cells that covers the back of the iris Musculature: muscles that control the size of the pupil How the Pupil Changes Size When the constrictor papillae muscle constricts, the pupil becomes smaller, reducing the amount of light entering the eye. When the dilator papillae muscle constricts, the pupil becomes larger, allowing more light to enter the eye. The Ciliary Body 🌐 The ciliary body is another part of the tunica vasculosa. It is located behind the iris and is connected to the lens. Function of the Ciliary Body The ciliary body has two main functions: Accommodation: changing the shape of the lens to focus on objects at different distances Production of aqueous humor: producing a fluid that nourishes the eye and helps maintain its shape Structure of the Ciliary Body The ciliary body is composed of: Musculature: muscles that control the shape of the lens Ciliary processes: fine fibers that attach to the lens and help change its shape Epithelium: a layer of cells that produces aqueous humor How the Ciliary Body Works When the ciliary muscles constrict, the ciliary processes pull on the lens, causing it to change shape. This allows the eye to focus on objects at different distances. Muscle Contraction Lens Shape Focus Ciliary muscles constrict Lens becomes more rounded Near vision Ciliary muscles relax Lens becomes flatter Far vision Aqueous Humor and Eye Pressure 💧 Aqueous humor is a fluid produced by the ciliary body that nourishes the eye and helps maintain its shape. Function of Aqueous Humor Aqueous humor: "is a clear, watery fluid that fills the anterior and posterior chambers of the eye, providing nutrients and oxygen to the cornea and lens, and helping to maintain the eye's shape" How Aqueous Humor Affects Eye Pressure The amount of aqueous humor produced and drained from the eye determines the eye pressure. If the production of aqueous humor exceeds the drainage, the eye pressure increases. The Vitreous Body 🌌 The vitreous body is a gelatinous structure that fills the space between the lens and the retina. Function of the Vitreous Body The vitreous body: "is a clear, gel-like substance that fills the center of the eye, giving it shape and helping to maintain its pressure" Structure of the Vitreous Body The vitreous body is composed of: Gelatinous material: a clear, gel-like substance Fibers: fine fibers that help maintain the shape of the vitreous body The Lens 🔍 The lens is a clear, flexible structure that changes shape to focus on objects at different distances. Function of the Lens The lens: "is a clear, flexible structure that changes shape to focus light on the retina, allowing us to see objects at different distances" Structure of the Lens The lens is composed of: Lens fibers: long, thin fibers that make up the lens Lens capsule: a thin, transparent membrane that surrounds the lens Epithelium: a layer of cells that lines the lens capsule How the Lens Changes Shape The lens changes shape when the ciliary muscles constrict or relax, causing the lens fibers to become more or less compact. The Retina 📸 The retina is the innermost layer of the eye, responsible for detecting light and transmitting visual information to the brain. Function of the Retina The retina: "is the innermost layer of the eye, responsible for detecting light and transmitting visual information to the brain" Structure of the Retina The retina is composed of: Photoreceptors: specialized cells that detect light and transmit visual information to the brain Rods and cones: two types of photoreceptors that detect different types of light Optic nerve: the nerve that transmits visual information from the retina to the brain## The Eye Structure The Vascular Layer and Sclera The choroid is a highly vascularized part of the eye with dense, irregular connective tissue. The sclera, on the other hand, is a fibrous layer that provides protection to the eye. The Retina The retina consists of several layers, including the photoreceptor layer. Photoreceptors are specialized cells that convert light into electrical signals. There are two types of photoreceptors: Rods: responsible for black and white vision Cones: responsible for color vision These photoreceptors connect to bipolar cells, which are the first sensory cells in the retina. The bipolar cells then connect to the optic nerve, which is the second-order neuron. The Retinal Pigment Epithelium (RPE) The RPE is a layer of pigmented epithelial cells that plays a crucial role in maintaining the health of the retina. It absorbs light that passes through the photoreceptors, preventing it from reflecting back and causing blurry vision. "The RPE is like a dark layer that absorbs light, preventing it from reflecting back and causing blurry vision. This is important for maintaining sharp vision." The Tapetum Lucidum Some animals, such as dogs and cats, have a reflective layer called the tapetum lucidum. This layer reflects light back onto the photoreceptors, allowing the animal to see better in low light conditions. However, this comes at the cost of reduced sharp vision. The Optic Nerve The optic nerve is the second-order neuron that collects all the nerve fibers from the retina and exits the eye through the optic disc. The optic disc is also known as the blind spot, as it does not contain any photoreceptors. The Vitreous Body The vitreous body is a gelatinous substance that fills the eye and gives it its shape. It is composed of hyaluronic acid, which is also found in connective tissue. 👂 The Ear Structure The External Ear The external ear consists of the ear pinna and the ear canal. The ear canal is a narrow passage that can be prone to infections such as otitis externa. The Middle Ear The middle ear consists of the ossicles, which are the smallest bones in the body. These bones transmit sound waves from the eardrum to the oval window, enhancing the sound signal. Structure Description Ear Pinna The outer part of the ear Ear Canal A narrow passage that leads to the eardrum Ossicles The smallest bones in the body, responsible for transmitting sound waves Eardrum A thin membrane that separates the external ear from the middle ear Oval Window A small opening that transmits sound waves to the inner ear External Ear The external ear, also known as the ear pinna, is covered in skin and contains cartilage. The ear canal is lined with squamous stratified epithelium and contains sebaceous glands and ceruminous glands. "Cerumen is a waxy substance produced by the ceruminous glands that has antimicrobial properties and helps to protect the ear canal from infection."  The ear canal also contains hair cells and ceruminous glands that produce a healthy flora in the external ear canal. Cleaning the ears too much can remove the natural antibiotic layer of the skin and is not recommended. Middle Ear The middle ear contains the tympanic membrane (eardrum), ossicles (malleolus, incus, and stapes), and the oval window. Structure Description Tympanic membrane A thin membrane that vibrates in response to sound waves Small bones that transmit sound waves from the tympanic membrane Ossicles to the oval window A small opening that transmits sound waves from the ossicles to the Oval window inner ear The middle ear is connected to the pharynx through the Eustachian tube, which helps to equalize pressure in the ear. The middle ear can be prone to infection, especially if the tympanic membrane is damaged. Inner Ear The inner ear consists of a bony labyrinth and a membranous labyrinth. "The bony labyrinth provides protection for the membranous labyrinth, similar to a cast around a broken arm." The inner ear contains the utricle and saccule, which are responsible for providing information about balance and spatial orientation. The semicircular canals are three-dimensional canals that are arranged at 90- degree angles to each other and provide information about angular movement. Structure Description A structure that provides information about balance and spatial Utricle orientation A structure that provides information about balance and spatial Saccule orientation Semicircular Three-dimensional canals that provide information about angular canals movement The inner ear also contains hair cells that are connected to afferent neurons and are responsible for transmitting information about sound and balance to the brain. Cochlea The cochlea is a spiral-shaped structure that is responsible for converting sound waves into electrical signals that can be interpreted by the brain.  Structure Description Scala vestibuli A duct in the cochlea that contains fluid and helps to transmit sound waves Scala media A duct in the cochlea that contains fluid and helps to transmit sound waves Scala tympani A duct in the cochlea that contains fluid and helps to transmit sound waves The cochlea contains hair cells that are connected to afferent neurons and are responsible for transmitting information about sound to the brain. Understanding Sensory Receptors and Functions 🌟 Efferent Nervous System: Autonomic Nervous System The autonomic nervous system is a part of the efferent nervous system that controls involuntary actions, such as heart rate, digestion, and breathing. It is responsible for the body's "fight or flight" response and "rest and digest" response. Definition of Key Terms Efferent: A response or signal that is sent out from the central nervous system to the rest of the body. Afferent: A signal or information that is sent to the central nervous system from the rest of the body. Autonomic: Involuntary, unconscious, and automatic. Autonomic Nervous System Overview The autonomic nervous system is divided into two main branches:  Sympathetic Nervous System: responsible for the "fight or flight" response, which prepares the body for immediate action. Parasympathetic Nervous System: responsible for the "rest and digest" response, which promotes relaxation and restoration. How the Autonomic Nervous System Works The autonomic nervous system collects information from sensory receptors and sends signals to the central nervous system, which processes the information and sends signals back to the body through two neurons: Preganglionic Neuron: sends signals from the central nervous system to the ganglion. Postganglionic Neuron: sends signals from the ganglion to the target organ. Parasympathetic Nervous System Location: starts in the brain stem and sacral area. Effect: promotes relaxation and restoration. Transmitters: uses acetylcholine as a transmitter. Receptors: uses nicotinic receptors between pre and postganglionic neurons, and muscarinic receptors between postganglionic neurons and target organs. Organ Effect of Parasympathetic Stimulation Heart Decreased heart rate Digestive Tract Increased digestion Lungs Increased respiration  Organ Effect of Parasympathetic Stimulation Eyes Increased tear production Sympathetic Nervous System Location: starts in the thoracic and lumbar areas. Effect: prepares the body for immediate action. Transmitters: uses acetylcholine between pre and postganglionic neurons, and noradrenaline (norepinephrine) between postganglionic neurons and target organs. Receptors: uses nicotinic receptors between pre and postganglionic neurons, and alpha and beta receptors between postganglionic neurons and target organs. Organ Effect of Sympathetic Stimulation Heart Increased heart rate Digestive Tract Decreased digestion Lungs Increased respiration Eyes Increased pupil dilation Comparison of Parasympathetic and Sympathetic Nervous Systems Parasympathetic Sympathetic Location Brain stem and sacral area Thoracic and lumbar areas Effect Relaxation and restoration Preparation for immediate action Transmitters Acetylcholine Acetylcholine and noradrenaline Receptors Nicotinic and muscarinic Nicotinic, alpha, and beta Why Two Different Receptors? The use of two different receptors, nicotinic and muscarinic, allows for more precise control over the target organs. Nicotinic receptors are always excitatory, while muscarinic receptors can be either excitatory or inhibitory. This allows for more nuanced control over the body's responses.## Autonomic Nervous System Receptors Sympathetic Nervous System Receptors The sympathetic nervous system uses different receptors to transmit information to the effector organs. These receptors include: Alpha 1 (α1): always excites the organs Alpha 2 (α2): always inhibits the organs Beta 1 (β1): always excites the organs Beta 2 (β2): always inhibits the organs  Receptor Effect α1 Excites organs α2 Inhibits organs β1 Excites organs β2 Inhibits organs Why Multiple Receptors? The sympathetic nervous system has multiple receptors to allow for a range of responses to different stimuli. This allows the body to fine-tune its response to different situations. Inhibitory Pathways in the Sympathetic Nervous System The sympathetic nervous system also has inhibitory pathways that can affect the parasympathetic nervous system. This allows the body to balance the two systems and prevent over-activation. Take-Home Message The key point to understand is that the sympathetic nervous system uses different receptors to transmit information to the effector organs, and that these receptors can be manipulated by pharmaceuticals. 📚 Pharmacology and the Autonomic Nervous System 📚 Adrenergic and Cholinergic Drugs Drugs can be either adrenergic (acting on the sympathetic nervous system) or cholinergic (acting on the parasympathetic nervous system). These drugs can either enhance or inhibit the activity of the respective system. Agonists and Antagonists Drugs can be classified as either agonists (enhancing the activity of a receptor) or antagonists (inhibiting the activity of a receptor). 📚 Consciousness and the Brain Stem 📚 Definition of Consciousness Consciousness is the state of being aware of one's surroundings, thoughts, and feelings. The Thalamus and Consciousness The thalamus is the gateway between the conscious and unconscious mind. It relays sensory information to the cortex, allowing us to perceive the world around us. The Reticular Formation and Consciousness The reticular formation is a network of neurons in the brain stem that regulates consciousness and alertness. It influences the thalamus and the sensory input that reaches the cortex. The Readiness Response The readiness response is a state of heightened alertness and arousal that prepares the body for action. It is characterized by increased muscle tone, enhanced sensory input, and increased reflexes. Effects of the Readiness Response Increased muscle tone Enhanced sensory input Increased reflexes Increased heart rate and blood pressure Increased respiration rate Example: Watching a Scary Movie When watching a scary movie, the reticular formation is activated, leading to a state of heightened alertness and arousal. This can cause a range of physiological responses, including increased heart rate, blood pressure, and respiration rate.## Brain Activity and Sleep Brain activity can be measured through brainwaves, which are different in various activity levels of the brain. These brainwaves are typically described through human medicine, but can also be applied to veterinary medicine. Brainwave Patterns Brainwave Pattern Description Very small, high-frequency waves associated with alertness and Beta Waves attention Slower and larger waves associated with relaxation and decreased Alpha Waves alertness Delta Waves Large, slow waves associated with deep sleep Sleep Stages Sleep is divided into two main stages: Non-Rapid Eye Movement (NREM) sleep and Rapid Eye Movement (REM) sleep. Non-Rapid Eye Movement (NREM) Sleep Characterized by slow brainwaves and low arousal threshold Easily awakened Dominated by the parasympathetic nervous system Rapid Eye Movement (REM) Sleep Characterized by fast brainwaves and high arousal threshold Difficult to awaken  Dominated by the sympathetic nervous system REM Sleep in Different Species Species REM Sleep Duration Predators (e.g. fox, humans, monkeys, cats) Longer REM sleep duration Prey Species (e.g. rabbits, cows) Shorter REM sleep duration Unihemispheric slow-wave sleep (one half of the brain sleeps Marine Mammals while the other half remains awake) Manipulating Consciousness 💊 Consciousness can be manipulated through various means, including sedation, anesthesia, and tranquilizers. Definitions Sedation: A mild reduction in awareness and consciousness, often used for less invasive procedures. Anesthesia: A state of unconsciousness, often used for more invasive procedures. Tranquilizers: Pharmaceuticals that reduce emotional response, often used in pets. States of Consciousness State Description Sedation Reduced awareness and consciousness, but still responsive to stimuli  State Description Anesthesia Unconsciousness, unresponsive to stimuli Tranquilization Reduced emotional response, but still conscious Reduced responsiveness to the environment, but still able to respond to Depression input Stupor Depressed consciousness, arousal is possible but difficult Coma Unconscious state, unresponsive to stimuli Regulation of Consciousness Consciousness is regulated by the Reticular Activating System (RAS) in the brain stem. Pharmaceuticals that manipulate consciousness often act on this area. Effects of Brain Stem Injuries Small injuries to the brain stem can cause massive changes in responsiveness Trauma to the brain stem can lead to coma Injuries to other areas of the brain, such as the prefrontal cortex, may not affect consciousness as significantly## Learning and Memory Types of Learning Habituation: the process of becoming less responsive to a stimulus after repeated exposure Sensitization: the process of becoming more responsive to a stimulus after repeated exposure Imprinting: a type of learning that occurs during a critical period in an animal's development, where they form a strong bond with the first moving object they encounter  Classical Conditioning: a type of learning in which a neutral stimulus is paired with an unconditioned stimulus to elicit an unconditioned response Memory Short-term Memory: a type of memory that holds information for a short period of time, typically seconds or minutes Long-term Memory: a type of memory that holds information for an extended period of time, typically hours, days, or years "Repetition is key to forming long-term memories. The more we repeat information, the more likely it is to be stored in our long-term memory." The Limbic System The limbic system is a network of brain structures that play a crucial role in emotion, motivation, and memory The limbic system includes the hippocampus, amygdala, and hypothalamus 🐾 Urinary System Anatomy 🐾 Functional Bladder Anatomy Structure Description Detrusor a smooth muscle layer that surrounds the bladder and contracts to expel Muscle urine Ureters tubes that carry urine from the kidneys to the bladder a small triangular area on the posterior wall of the bladder where the Trigone ureters enter Neural Components of Micturition The neural components of micturition include the spinal cord, brainstem, and peripheral nerves  The spinal cord receives and integrates information from the bladder and urethra to control the micturition reflex Nerves Involved in Micturition Nerve Function Pudendal Nerve carries sensory information from the urethra and bladder to the spinal cord carries motor information from the spinal cord to the detrusor muscle and Pelvic Nerve urethral sphincter 📚 Key Concepts 📚 Micturition: the process of storing and expelling urine Urination: the act of expelling urine from the bladder Voiding: the act of emptying the bladder of urine## Urinary System Anatomy The urinary system consists of the kidneys, ureters, bladder, and urethra. The bladder is a hollow, muscular organ that stores urine. Internal and External Sphincters Internal Sphincter: A continuation of the detrusor muscle, made of smooth muscle and elastic tissue, located at the bladder neck. External Sphincter: A skeletal muscle under voluntary control by the nervous system, also known as the urethralis muscle. "The internal sphincter is part of the detrusor muscle, which is a smooth muscle that needs to be in a normal tone to allow the filling of the bladder." Urinary System Function 🔄 The urinary system involves the coordinated interaction of the autonomic and somatic nervous systems. Filling and Voiding Filling: The bladder fills with urine, and the internal sphincter relaxes to allow urine to enter the bladder. Voiding: The bladder empties, and the internal sphincter contracts to prevent urine from entering the urethra. Nervous System Control Somatic Nervous System: Controls the external sphincter, a skeletal muscle that is under voluntary control. Autonomic Nervous System: Controls the internal sphincter and the detrusor muscle, which are smooth muscles that are not under voluntary control. Nervous System Function Somatic Controls external sphincter (skeletal muscle) Autonomic Controls internal sphincter and detrusor muscle (smooth muscle) Peripheral Nerves Pudendal Nerve: A somatic nerve that controls the external sphincter. Hypogastric Nerve: A sympathetic nerve that controls the bladder wall and internal sphincter. Pelvic Nerve: A parasympathetic nerve that controls the bladder wall and internal sphincter. Reflexes and Control Centers 🔄 Reflexes: The sympathetic and parasympathetic nervous systems work together to control the filling and voiding of the bladder. Control Centers: The sacral and lumbar areas of the spinal cord, as well as the pontine section of the midbrain, control the reflexes.  Reflex Function Sympathetic Relaxes muscle to fill bladder Parasympathetic Contracts muscle to empty bladder Disorders 🚨 Urethral Obstruction: A blockage in the urethra that prevents urine from flowing out of the bladder. Prolonged Bladder Extension: A condition in which the bladder is stretched for an extended period, leading to muscle damage and urinary incontinence. Urethral Mucoid Plugs: A blockage in the urethra caused by a mucous plug. Prostate Tumors: A tumor in the prostate gland that can put pressure on the urethra and prevent urine from flowing out of the bladder. Trauma: A physical injury that can damage the urinary system and lead to urinary incontinence.## Lower Motor Neuron Damage Lower motor neuron damage can result in a flaccid bladder, which is characterized by a loss of bladder tone and function. This can occur due to damage to the sacral segments of the spinal cord, which innervate the bladder and rectal area. "A flaccid bladder is a condition where the bladder muscle is weak and unable to contract properly, leading to urinary incontinence and other bladder problems." Causes of lower motor neuron damage include: Tail pull injuries in cats Prolapsed discs in the sacral region Damage to the nerve fibers in the sacral segments of the spinal cord Upper Motor Neuron Damage 🐕 Upper motor neuron damage, on the other hand, can result in a spastic bladder, which is characterized by an overactive bladder muscle. This can occur due to damage to the brain or spinal cord above the level of the sacral segments. "A spastic bladder is a condition where the bladder muscle is overactive and contracts too frequently, leading to urinary incontinence and other bladder problems." Causes of upper motor neuron damage include: Blocked cap or prolapsed disc in the thoracic or lumbar region Damage to the brain or spinal cord above the level of the sacral segments Pharmacological Interventions 💊 Pharmacological interventions can be used to assist with bladder problems caused by lower or upper motor neuron damage. These interventions can include: Medication Action Effect Agonist Stimulates the receptor Increases bladder tone and function Antagonist Blocks the receptor Decreases bladder tone and function Cauda Equina Syndrome 🐴 Cauda equina syndrome is a condition that occurs when the lumbosacral joint is unstable, causing compression of the spinal nerve roots. This can lead to a range of symptoms, including: Urinary incontinence Fecal incontinence Pain in the lower back and legs  Weakness in the legs "Cauda equina syndrome is a condition where the spinal nerve roots are compressed, leading to a range of symptoms including urinary and fecal incontinence." Causes of cauda equina syndrome include: Prolapsed discs in the lumbosacral region Instability of the lumbosacral joint Compression of the spinal nerve roots Anatomy of the Lumbosacral Region 📚 The lumbosacral region is supported by the abdominal muscles, which can make it prone to mobility issues. The thoracic region, on the other hand, is supported by the ribs, which provides more stability. Region Support Prone to Mobility Issues Lumbosacral Abdominal muscles Yes Thoracic Ribs No Clinical Signs of Cauda Equina Syndrome 🐕 Clinical signs of cauda equina syndrome can include: Urinary incontinence Fecal incontinence Pain in the lower back and legs Weakness in the legs  Decreased reflexes in the legs "Cauda equina syndrome can present with a range of clinical signs, including urinary and fecal incontinence, pain, and weakness in the legs."## Spinal Cord Anatomy The spinal cord is a long, thin, tube-like structure made up of nervous tissue that extends from the base of the brain down to the lower back. It is protected by the vertebral column and is responsible for transmitting messages between the brain and the rest of the body. Conus Medullaris and Filum Terminale The conus medullaris is the lower end of the spinal cord, which is cone-shaped and located at the level of the first or second lumbar vertebra. The filum terminale is a thin filament of connective tissue that extends from the tip of the conus medullaris to the coccyx (tailbone). "The filum terminale is like a terminal thread that runs from the end of the spinal cord to the coccyx, providing a connection between the spinal cord and the tailbone." Cauda Equina The cauda equina is a bundle of nerve roots that arise from the lower end of the spinal cord and extend down to the coccyx. The cauda equina is formed by the nerve roots that arise from the lumbar and sacral spinal cord segments. Spinal Cord Segment Nerve Roots Lumbar (L1-L5) L1-L5 nerve roots Sacral (S1-S5) S1-S5 nerve roots Development of the Spinal Cord During embryonic development, the spinal cord and vertebral column grow at different rates, resulting in the formation of the cauda equina. "As the embryo grows, the spinal cord and vertebral column grow at different rates, causing the nerve roots to become stretched and form the cauda equina." Clinical Signs of Spinal Cord Disease 🐕 Lower back pain Reluctance to jump or exercise Weakness or incoordination Proprioceptive deficits (loss of sense of position and movement) Urinating in inappropriate places Dropping feces Diagnosis of Spinal Cord Disease 🧬 MRI (Magnetic Resonance Imaging): the most accurate diagnostic tool for spinal cord disease Radiographs (x-rays): may show bony changes, but not soft tissue changes Orthopedic examination: to rule out other causes of clinical signs, such as hip dysplasia or arthritis Treatment of Spinal Cord Disease 🏥 Exercise modification and rest Anti-inflammatory medication Physical therapy Acupuncture Laser therapy Shockwave therapy Hydrotherapy  Treatment Description Exercise modification and Reducing exercise and activity to allow the spinal cord to rest heal Anti-inflammatory medication Reducing inflammation and pain Physical therapy Improving mobility and flexibility Acupuncture Stimulating healing and reducing pain Laser therapy Reducing inflammation and promoting healing Shockwave therapy Stimulating healing and reducing pain Hydrotherapy Improving mobility and flexibility Surgical interventions can be performed to relieve pressure on the spinal cord and alleviate symptoms. One such procedure is a laminectomy, which involves removing the top part of the vertebra (dorsal laminectomy) to relieve pressure on the spinal cord. Laminectomy Procedure A laminectomy can be performed to: Relieve pressure on the spinal cord Decompress nerve roots Stabilize the spine Degenerative Myelopathy 🐕 Degenerative myelopathy is a disease that affects older animals, causing progressive loss of function in the hind limbs. It is characterized by: Loss of coordination and balance Weakness in the hind limbs Difficulty walking Eventual paralysis "Degenerative myelopathy is a disease that's not reversible, seen in our older animals, and clinically presents itself as loss of function to that back end is progressive." Clinical Signs of Degenerative Myelopathy Walking on tiptoes Scuffing of the nails Shortening of the nails Eventual paralysis Lumbar Sacral Disease 🤕 Lumbar sacral disease is a condition that affects the lower back and can cause symptoms such as: Sciatica Compression of the spinal cord Inflammation "Symptoms come and go. It's awful. Yeah. And you know, I was good for you until I got on a plane just recently, and now I'm in the back again." Causes of Lumbar Sacral Disease Cause Description Slipped disc A herniated disc that puts pressure on the spinal cord Arthritis Inflammation of the joints that can cause compression of the spinal cord Treatment for Lumbar Sacral Disease Physiotherapy Pain medication Surgery (in some cases) Cutaneous Trunk 🤔 The cutaneous trunk is a nerve that branches off from the spinal nerve and supplies sensation to the skin. Nerve Description Cutaneous trunk Supplies sensation to the skin  Nerve Description Branches off from the spinal cord and supplies sensation and motor Spinal nerve function to the body Lesion Location 📍 When stimulating the cutaneous trunk, the lesion is typically located at the point where the nerve exits the spinal cord. Lesion Location Description Green area The actual problem area where the lesion is located Normal area The area where the nerve is functioning normally Understanding the Relationship Between Stimulation and Response When stimulating a specific area of the spinal cord, the actual region being tested is two vertebrae in front of the stimulation point. This is because the sensation is reflexive and involves the spinothalamic tract. The Spinothalamic Tract The spinothalamic tract is a pathway in the spinal cord that transmits sensory information from the body to the brain. The spinothalamic tract is responsible for transmitting information about pain, temperature, and crude touch. It is an afferent pathway, meaning it carries information from the body to the brain. Afferent vs. Efferent Pathways Pathway Definition Function Afferent Carries information from the body to the brain Transmits sensory information Efferent Carries information from the brain to the body Transmits motor information Interneurons and the Spinal Cord Interneurons are specialized neurons that are found within the spinal cord. They play a crucial role in processing and integrating sensory information. Interneurons are usually found in the spinal cord and are involved in the processing and integration of sensory information. Central vs. Peripheral Nervous System System Definition Function Central Nervous Consists of the brain and spinal Processes and integrates System (CNS) cord sensory information Peripheral Nervous Consists of nerves that connect the Transmits sensory and System (PNS) CNS to the rest of the body motor information In the context of the spinothalamic tract, the pathway that goes up to the brain is considered part of the central nervous system, while the pathway that goes to the muscles is considered part of the peripheral nervous system. Key Points to Remember When stimulating a specific area of the spinal cord, the actual region being tested is two vertebrae in front of the stimulation point. The spinothalamic tract is an afferent pathway that transmits sensory information from the body to the brain. Interneurons are specialized neurons that are found within the spinal cord and play a crucial role in processing and integrating sensory information. Understanding the Autonomic Nervous System 🧠 Nervous System Overview The nervous system is a complex system that controls and coordinates the body's functions. It is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). Central Nervous System (CNS) The CNS is the master control unit of the body, responsible for processing information and controlling the body's functions. The CNS consists of the brain and spinal cord. Brain The brain is the control center of the body, responsible for processing information and controlling the body's functions. It is divided into different regions, including: Cerebrum: the largest part of the brain, responsible for processing sensory information and controlling movement Cerebellum: responsible for coordinating movement and balance Brainstem: connects the cerebrum to the spinal cord and regulates basic functions such as breathing and heart rate Spinal Cord The spinal cord is a long, thin, tube-like structure that extends from the base of the brain down to the lower back. It plays a crucial role in the transmission of nerve impulses between the brain and the rest of the body. Peripheral Nervous System (PNS) The PNS is the part of the nervous system that connects the CNS to the rest of the body. The PNS consists of nerves that transmit information between the CNS and the rest of the body. Nerves A nerve is a bundle of neurons that transmit information between the CNS and the rest of the body