Neurology Introduction PDF

# Neurology Introduction ## Terminology - **Afferent:** Information that enters the nervous system. - **Efferent:** Information that leaves the nervous system. - **Neurotransmitters:** Chemical messengers that transmit signals between neurons/synapse. - **Neuron:** Elongated cell that detects and...

# Neurology Introduction ## Terminology - **Afferent:** Information that enters the nervous system. - **Efferent:** Information that leaves the nervous system. - **Neurotransmitters:** Chemical messengers that transmit signals between neurons/synapse. - **Neuron:** Elongated cell that detects and transmits messages as nerve impulses. - **Nerve:** Bundle of axons that carries information to and from CNS. - **Afferent (IN):** Carries information from the periphery to the CNS. - **Efferent (OUT):** Carries information from the CNS to the periphery. - **Ganglia:** Concentration of neuronal bodies outside CNS. - **Nuclei:** Concentration of neuronal bodies within brain parenchyma. - **Myelination:** Process of forming a fatty insulating layer around the axon, allowing for faster transmission. - **Myelinated:** Affects the speed of transmission, typically large. - **Unymyelinated:** Typically small. - **Synapse:** Gap between two neurons where chemical signals are transmitted. ## Nervous System Composed of two main parts: - **Central Nervous System (CNS):** - **Control Center of Body:** Responsible for processing information, controlling movements, and regulating various bodily functions. - **Spinal Cord:** Long, thin, tube-like structure that extends from the medulla oblongata to the lower back, crucial role in transmitting messages between the brain and the rest of the body. Encased in bone, divided into segments (vertebrae). - **Optic Nerve:** Cranial nerve that transmits visual information from the eye to the brain. - **Peripheral Nervous System (PNS):** - **Responsible for transmitting information between CNS and the body.** - **Includes:** - **Sensory Nerves (Afferent):** - **Motor Nerves (Efferent):** - **Somatic Nervous System:** Voluntary control. - **Visceral/Autonomic Nervous System:** Involuntary control, Heart Rate + Digestion. - **Sympathetic:** Fight or Flight. - **Parasympathetic:** Rest and Digest. ## The Vagus Nerve Cranial nerve that plays a key role in parasympathetic nervous system. ## Central Nervous System - 100,000,000 nerve cells (neurons) each with 1,000 connections. - Supported by _neuroglia_: - Provide nourishment, insulation, protection to neurons. ## Types of Neurons - **Multipolar:** Multiple dendrite areas and one axon. - **Bipolar:** One dendrite and one axon. - **Unipolar:** Dendrite and axon are continuous, with nerve cell body on side. ## Functions of Neurons - **Sensory Neurons**: Receive and transmit sensory input. - **Motor Neurons:** Carry motor information. - **Interneurons:** Connect CNS and facilitate communication between parts of brain/spinal cord. ## Neuroglia - **Astrocytes:** Star-shaped cells that produce blankets and sheets around blood vessels, forming the blood-brain barrier. - **Oligodendrocytes:** Cells that myelinate axons of CNS, one produces myelin for multiple axons. - **Microglia:** Small, phagocytic cells that clean up debris and waste in CNS. - **Ependymal Cells:** Line the central canal and ventricles of CNS, produce cerebrospinal fluid (CSF). - **Schwann Cells:** Cells that myelinate peripheral nerves, can only wrap around a single axon. | Cell Type | CNS | PNS | |---|---|---| | Myelinating | Oligodendrocyte | Schwann Cell | | Phagocytic | Microglia | Macrophage | | Barrier Cell | Astrocyte | None | | CSF producing | Ependymal | None | | Nodes of Ranvier | Schwann cells | None | | | Allow for rapid transmission of nerve impulses. | - **Satellite Cells:** Specialized cells that surround cell bodies in PNS (particularly ganglia), support and protect cell bodies. ## Grey vs White Matter | Matter Type | Description | Location | |---|---|---| | Grey Matter | Composed of cell bodies of nerve cells, darker in colour. | Typically found on the outside of the cerebrum and cerebellum. | | White Matter | Composed of myelinated axons, which appear white due to the myelin sheath surrounding axons. | Typically found in the middle. | ### Specific Brain Areas - **Cerebrum:** Grey matter found on the outside with cell bodies of nerve cells. White matter found in the middle, with myelinated axons. - **Molecular Layer:** Outermost layer, with few cell nuclei. - **Purkinje Cells:** Large, pretty cells found in the cerebellum. - **Cerebellum:** Grey matter is found on the outside with cell bodies of nerve cells. White matter is found in the center, with myelinated axons. - **Molecular Layer:** Outermost layer with few cell nuclei. - **Purkinje Cells:** Large, pretty cells found in the cerebellum. - **Granular Cells:** Produce a granular layer. - **Brain Stem:** Grey matter comes in clusters, with cell bodies of nerve cells. White matter found throughout, with myelinated axons. - **Nuclei:** Clusters of cell bodies that have their own specific location. - **Spinal Cord:** White matter found on the outside, with myelinated axons. Grey matter found in the center with cell bodies of motor neurons and interneurons. - **Dorsal Horn:** Receives information and communicates with the ventral horn to provide a response. - **Interneurons:** Crucial role in reflexes, allow for immediate responses without involving the cerebrum. ## Proprioception - Sense of self. - Incorporates sight, hearing, and muscle strength. - Key components: - Muscle strength - Tension - Position - Degree of compromise ## Reflex Arc - A neural pathway that allows for rapid responses to stimuli. - Consists of: - **Sensory Receptors:** Specialized receptors that detect specific stimuli (e.g. mechanoreceptors, thermoreceptors, nociceptors). - **Sensory Neuron (Dorsal Root)/fibres:** Brings information into CNS from sensory receptors. - **Interneurons:** Process and integrate information in CNS. - **Motor Neurons/fibres:** Transmits signals from the CNS to muscles or glands. - **Effectors:** Muscles or glands that respond to motor neuron signals. - **Dorsal Horn:** Contains cell bodies of sensory neurons in spinal cord (sensory fibres enter spinal cord). - **Ventral Horn:** Contains cell bodies of motor neurons in spinal cord (motor fibres exit spinal cord). - **Motor Response:** Final output of the reflex arc, results in muscle contraction or relaxation. ## Spinal Reflexes & Withdrawal Reflex - Occur at the level of spinal cord, involving lower motor neurons. - **Withdrawal Reflex:** Reflex that occurs within the spinal cord, without involving the brain. - Rapid response to a stimulus. - **Pain Sensory Fibres:** Brings pain information into the CNS. - **Dorsal Horn:** Contains cell bodies of sensory neurons in the spinal cord. - **Interneuron:** Synapses with motor neurons to produce a motor response. - **Motor Response:** Final output of the reflex arc, resulting in muscle contraction or relaxation. ## Components of the Brain - **Cerebrum:** - Largest part. - Responsible for processing sensory information, controlling movement, thought, emotion, memory. - Left and Right hemispheres. - Has gyri (increase surface area and allow for more efficient processing of information). - **Cerebellum:** - Located at the base of the brain. - Coordinates movement, balance, and posture. - Involved in learning, memory, and motor skills. - **Brainstem:** - Connects the cerebrum to the spinal cord. - Regulates breathing, heart rate, and blood pressure. - Consists of the midbrain, pons, and medulla oblongata. ## Meninges - Cover and protect the brain and spinal cord. - Three layers of connective tissue: - **Dura Mater:** - Outermost layer, adherent to bone. - Inner layer lines the inner surface of the brain. - Provides tough, protective covering, contains sinuses. - Thick, dense, non-elastic. - Fibrous sac. - **Arachnoid Mater:** - Middle layer, spider-like appearance (trabeculae). - Absorbs CFS. - Plays a crucial role in the flow of cerebrospinal fluid. - Subarachnoid space between arachnoid layer and innermost layer. - Contains CSF. - **Pia Mater:** - Innermost layer. - Attached to the surface of the brain and spinal cord. - Contains choroid plexus, produces CSF from blood plasma and epithelial cells. ## Thalamus - Crucial role in relaying sensory information to the cerebral cortex. ## Ventricular System - Network of cavities within the brain that contain CSF. - Includes: - **Lateral Ventricles (left and right):** Contains CFS. - **Third Ventricle:** Contain CFS and surrounds the thalamus. - **Fourth Ventricle:** Contains CFS and connects to the aqueduct. - **Aqueduct:** Transmits CFS from the third to the fourth ventricle. ## Cranial Nerves - 12 cranial nerves that arise from the brain and are part of the PNS. | Cranial Nerve | Function | Origin | Tests | Brainstem Connection | Innervates | |---|---|---|---|---|---| | Olfactory (I) | Smell | Forebrain | Smell response (non-irritant scent) | No | Nasal epithelium | | Optic (II) | Vision | Diencephalon | Menace response, PLR | No | Retina | | Oculomotor (III) | Eye movement, pupil constriction | Midbrain | PLR, eye position | Yes (Midbrain) | Most eye muscles, pupil | | Trochlear (IV) | Eye movement (downward/inward) | Midbrain | Eye position (look for strabismus) | Yes (Midbrain) | Superior Oblique Muscle | | Trigeminal (V) | Sensory to face, motor to chewing muscles | Pons | Palpebral reflex, jaw tone, corneal reflex | Yes (Pons/Medulla) | Face, masticatory muscles | | Abducent (VI) | Lateral eye movement | Pons/Medulla Junction | Eye movement, strabismus | Yes (Pons/Medulla) | Lateral rectus muscle | | Facial (VII) | Facial expression, taste, salivation, lacrimation | Medulla | Menace response, palpebral reflex | Yes (Medulla) | Facial muscles, tongue (taste), glands | | Vestibulocochlear (VIII) | Hearing, balance | Medulla | Hearing Test, observe balance and nystagmus | Yes (Medulla) | Cochlea, vestibular apparatus | | Glossopharyngeal (IX) | Taste, swallowing, salivation | Medulla | Gag reflex, eating/drinking observation | Yes (Medulla) | Pharynx, tongue (taste), salivary glands | | Vagus (X) | Autonomic to heart, lungs, digestive system | Medulla | Gag reflex, voice changes, heart rate | Yes (Medulla, Spinal Cord) | Viscera, larynx | | Accessory (XI) | Neck and shoulder movement | Medulla, Spinal Cord | Head/neck movement, muscle tone | Yes (Medulla) | Sternocleidomastoid, trapezius muscles | | Hypoglossal (XII) | Tongue movement | Medulla | Tongue movement, eating/drinking observation | Yes (Medulla) | Tongue muscles | ## Cell Bodies of Cranial Nerves Cell bodies are located in nuclei within brain tissue. - **Schwann Cells:** Covers cranial newves. - **Examples:** - Trigeminal nerve has a ganglion externally + nuclei within brain parenchyma. - Optic nerve is brain tissue with oligodendrocytes. - **Nuclei:** - Crucial for receiving and sending information. - Nuclei for cranial nerves III-XII are located in the midbrain area. - Nuclei for cranial nerves I and II are located in the epithelium of the sensory organs (e.g. olfactory bulb). ## Eye Muscles - **Superior Rectus:** Upward movement. - **Inferior Rectus:** Downward movement. - **Medial Rectus:** Inward movement. - **Lateral Rectus:** Outward movement. ## Eye Conditions - **Mydriasis:** Condition characterized by abnormally large pupil. - **Miosis:** Condition characterized by abnormally small pupil. - **Anisocoria:** Condition characterized by uneven pupil size. - **Nystagmus:** Involuntary eye movement. - **Strabismus:** Crossed eyes. ## Trigeminal Nerve - Largest cranial nerve. - Sensory and motor function. - Three main branches: - **Ophthalmic:** Sensation in the eye area, including the medial canthus. - **Maxillary:** Sensation in the external part of the face, including the lateral canthus of the eye. - **Mandibular:** Sensation in the lower face, including the lower lip, motor function for masticatory muscles. - **Lingual Branch:** Responsible for sensory input. - **Hypoglossal Branch:** Motor component. ## Facial Nerve - Controls the muscles of facial expression. - Transmits sensory information from the face to the brain. ## Facial Nerve Assessment - **Corneal Reflex:** Function of the ophthalmic branch. - **Nasal Sensation:** Function of the maxillary branch. - **Lower Lip Sensation:** Function of the mandibular branch. - **Facial Muscle Function:** Function of the facial nerve. ## Glossopharyngeal Nerve (CN IX) - Swallowing and sensory. ## Functions - **Sensory:** Visceral sensory coming in from the carotid body associated with the heart, parasympathetic glandular functions. - **Motor:** Involved in swallowing. ## Vagus Nerve - Heart rate, swallowing, gag reflex. - **Sensory:** Visceral sensory, associated with internal organs. - **Motor:** Involved in swallowing, gag reflex, and heart rate regulation. - **Parasympathetic:** Associated with the nervous system. ## Laryngeal Paralysis - Condition where the larynx (voice box) is paralyzed - **Causes:** - Damage to the recurrent laryngeal nerve, which innervates the larynx. - Infection or inflammation of the larynx. - Trauma to the neck or throat. - Congenital defects. - **Symptoms:** - Difficulty breathing. - Stridor (high-pitched sound while inhaling). - Coughing or gagging. - Blue-tinged gums and tongue. ## Accessory Nerve - Cranial nerve. - **Cranial Internal Branch:** - **Cervical Branch:** - Controls movement of trapezius and brachiocephalicus. ## Hypoglossal Nerve - Innervates muscles of the tongue for protrusion, retraction, and food manipulation. - Originates in the brainstem and travels down to the tongue. ## Sound and the Ear - **Sound:** Vibration of an object through a medium, e.g. air, water, and solid objects. - **Pressure Waves:** - **Pitch:** Highness or lowness of a sound, determined by the frequency of the sound wave. - **Intensity:** Loudness of a sound, determined by the amplitude of the sound wave. - **Quality:** Clarity or tone of a sound, determined by the presence of overtones. - **Ear:** Sound wave travels through air and enters the ear through the pinna (outer ear). - Passes through the ear canal and hits the eardrum, causing it to vibrate. - Vibrations transmitted through the middle ear and into the inner ear where they are converted to electrical signals. - **Cochlea:** Spiral-shaped structure in the inner ear. - Responsible for converting sound waves into electrical signals. - **Three Ducts:** - **Scala Vestibuli:** Connected to the oval window, filled with _perilymph_. - **Scala Media:** Filled with _endolymph_, contains the organ of Corti. - **Scala Tympani:** Connected to the round window, filled with _perilymph_. - **Organ of Corti:**Structure within the scala media. - Contains specialized epithelial receptor cells = Hair cells. - Converts vibrations of sound waves into electrical signals. - **Sound Recognition:** - **Intensity:** Movement of hair cells proportional to the amplitude of the sound wave. - **Pitch:** Location of the hair cells that are stimulated by the sound wave. - High-frequency sounds stimulate hair cells closer to the base of the cochlea. - Low-frequency sounds stimulate hair cells closer to the apex. - **Basilar Membrane:** Flexible structure that runs along the length of the cochlea. - Stiffer and narrower at the base and more flexible and wider at the apex. - High-frequency: More vibrations at the base. - Low-frequency: More vibrations at the apex. - **Hair Cells:** Have a resting potential and are bent by the motion of endolymph in the cochlear duct. - **Hair towards kinocilia:** Depolarized, action potential occurs. - **Hair away from kinocilia:** Hyperpolarize. ## Hair Cell Structure - **Stereocilia:** Hair-like structures on the surface of hair cells that detect sound waves. - **Kinocilia:** Longest stereocilia on a hair cell, which determines the direction of bending. - **Endolymph:** Fluid in the cochlear duct that moves in response to sound waves, bending hair cells. ## Balance - **Vestibular System:** Responsible for detecting changes in head position and movement. - **Semicircular Canals:** Three canals in the inner ear that detect angular movement. - Oriented at 90° angles to each other and are filled with endolymph. - When the head rotates, the endolymph in the canals lags, bending heir cells and triggering action potential. - **Utricle:** Detects horizontal acceleration. - **Saccule:** Detects vertical acceleration. - Both filled with a gelatinous layer. - Contain hair cells that are bent by the movement of calcium carbonate crystals. - Both in the inner ear that detect linear acceleration. ## Vision - Eye sending visual information to the brain. - **Image:** Received at the back of the eye and upside down and distorted. - **Visual Cortex:** At the back of the head processes the image and corrects it. - **Retina:** Light-sensitive tissue at the back of the eye that receives visual information. - **Optic Nerve:** Nerve that carries visual information from the eye to the brain. ## Sensory Receptors - Specialized nerve endings that detect changes in the environment and send signals to the brain. - **Types:** - **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 air. - **Vision Receptors:** Detect light and color. ## Receptor Potential - Change in the electrical potential of a nerve cell that is proportional to the _strength of the stimulus_. - If the receptor potential is strong enough, this causes an **Action Potential**. ## Action Potential - Rapid change in the electrical potential of a nerve cell that travels down the _length_ of a nerve fiber. ## Pathway of Sensory Information 1. **First-Order Neuron:** Sensory receptor to the spinal cord or medulla oblongata. - Detects the stimulus, and generates the receptor potential. 2. **Second-Order Neuron:** Spinal cord or medulla oblongata to the thalamus. - Transmits information to the thalamus. 3. **Third-Order Neuron:** Thalamus to the somatosensory cortex. - Transmits information to the somatosensory cortex for processing. ## Touch Receptors - Specialized nerve endings. - Detect mechanical pressure, stretch, and vibration. - **Pacinian Corpuscles:** Detect deep pressure and vibration. - **Meissner's Corpuscles:** Detect light touch and pressure. - **Merkel's Discs:** Detect pressure and texture. ## Somatosensory Cortex - Part of the brain that processes sensory information from the body. - Touch, pressure, temperature, and pain. - Located in the **Parietal Lobe**. ## Medial Lemniscus - Transmits information from touch, pressure, and proprioception. - Location: Spinal cord to medulla oblongata → thalamus → somatosensory cortex. ## Spinothalamic Tract - Transmits information from pain, temperature, and coarse touch. - Location: Spinal cord → thalamus → somatosensory cortex. ## Autonomic Function - Sensory information doesn't reach conscious brain but processed at the brainstem. - Temp, hunger, thirst. ## Taste - Specialized receptor cells in the epithelium of the tongue connect to first-order afferent nerves. - Saliva dissolves chemicals in food, which then bind to taste receptors in taste pores. - **Types of Taste:** - Sweet - Umami (glutamine) - Salty - Sour - Bitter ## Gustatory Receptor - Taste buds. - Specialized receptor cells in the epithelium of the tongue. - **First-order afferent nerve:** Connects to the medulla. ## Medulla - Connects to the thalamus. - Connects to the gustatory complex (part of the sensory cortex). ## Smell - Specialized epithelial cells in the nose. - Detect chemical in the air. - Air movement carries chemicals to the olfactory epithelium, chemicals dissolved in the mucus layer and bind to receptors on cilia of first-order neurons. ## Olfactory Epithelium - Specialized epithelial cells in the nose. - Dog: 250,000,000 - Mouse: 50,000,000 - Human: 6,000,000 ## First and Second-Order Neurons - **First-order neurons:** Connect directly to the olfactory bulb. - **Second-order neurons:** Connect to the cerebral cortex or limbic system. ## Eye - Part of the brain. - Formed from the neural tube during embryonic development. - **Neuroepithelium:** Closely related to CNS. - **Tunicas of the Eye:** - **Tunica Fibrosa:** Outermost layer. - **Fibrous:** Strongest layer. - **Sclera & Cornea:** Ciliary body, iris, choroid. - **Tunica Vasculosa:** Vascularized layer, produces different structures within the eye. - **Tunica Interna:** Innermost layer, nervous layer. - **Cornea:** Strong, transparent structure that allows light to pass through. - **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) - If any fibers misaligned, light becomes scattered and the cornea opaque. - **Sclera:** White, fibrous layer that provides structure and protection. - **Composed of:** Irregular connective tissue, scatters light and makes it appear white. - **Iris:** Determines eye color (stroma). - **Composed of:** - Stroma (connective tissue with pigment, fully exposed on the front side) - Epithelium (on the back side of the iris) - Muscle bundles (for dilation and constriction of the pupil) - Part of the tunica vasculosa. - Located between cornea and the lens. - **Two main functions:** - Regulates the amount of light entering the eye adjusting the size of the pupil., - Divides the eye into the anterior and posterior chambers. ## How Pupils Change Size - **Constrictor papillae muscle:** Contracts, making pupils smaller and reducing light entering. - **Dilator papillae muscle:** Contracts, and the pupil becomes larger, increasing light entering. ## Ciliary Body & Choroid - Part of the tunica vasculosa. - Provides blood flow to the eye. - **Choroid:** Rest of the tunica vasculosa that continues to the back of the eye. ## Ciliary Body - Located behind the iris and connected to the lens. - Two main functions: - **Accommodation:** Changing shape of the lens to focus at different distances. - **Production of aqueous humor:** Producing a fluid that nourishes the eye and helps maintain shape. ## Ciliary Body Composition - **Musculature:** Muscle that controls the shape of the lens. - **Ciliary Processes:** Fine fibers that attach to the lens and help change its shape. - **Epithelium Layer:** ## Neuro Exam - **Upper Motor Neuron:** Originates in the brain and spinal cord. - Connects to either interneurons or lower motor neurons (controlled by the UMNs). - Inhibitory and excitatory influence. - Controls muscle activity. - Regulates posture. - Maintains muscle tone. - **UPN Pathway:** - **Reticulospinal:** Influences reflex arc and lower motor neurons. - **Corticospinal:** Main influencer of the lower motor neuron, with a dominating negative inhibitory influence. - **Lower Motor Neuron:** Connects to muscle (effector organ) and originates in the spinal cord and PNS. - Also called Alpha motor neuron, has its cell body in the ventral horn. - Innervates skeletal muscles and transmits signals to muscles and glands. - Maintains muscle tone and regulates posture. - **Interneurons:** Inhibitory and excitatory influence from the same side and other sides. - **Sensory Stimuli:** Direct influence from the dorsal horn, e.g., skin temperature, touch. - **Reflex Arc:** Pathway that allows for a rapid response to sensory stimuli, involves lower motor neurons and interneurons. - **Neurolocalization:** Process of using reflex responses to localize lesions in the nervous system. ## Spinal Cord Lesions - **Upper Motor Neuron (corticospinal pathway):** - **Hypertonia:** Increased muscle tension, increased reflexes. - **Lower Motor Neuron:** - **Hypotonia:** Decreased muscle tension, decreased reflexes. - **Atonia:** No muscle tension, no reflexes. | Location | Effect on Upper Motor Neuron | Effect on Lower Motor Neuron | |---|---|---| | A (C1-C5) | Damage to upper motor neuron, leading to spasticity and over-reflexing. | No effect on lower motor neuron. | | B (Brachial Plexus) | No effect on upper motor neuron. | Damage to lower motor neuron, leading to weakness and paralysis. | | C (Thoracic Area) | Damage to upper motor neuron, leading to spasticity and over-reflexing. | No effect on lower motor neuron. | | D (Lumbosacral Plexus) | No effect on upper motor neuron. | Damage to lower motor neuron, leading to weakness and paralysis. | ## Upper Motor Neuron Damage - **Spasticity:** - **Over-reflexing:** - **Loss of inhibition:** ## Lower Motor Neuron Damage - **Weakness:** - **Flaccid muscles:** - **Paralysis:** ## Pupillary Light Reflex - Involves optic nerve (CN II) and oculomotor nerve (CN III). - **Light in one eye:** Pupillary constriction in both eyes. - **Optic nerve (CN II) → Visual cortex → Oculomotor nerve (CN III).** - **Localization of Damage:** - No constriction in either eye = Damage to optic nerve (CN II). - No constriction in the opposite eye = Damage to the oculomotor nerve (CN III). ## Palpebral Reflex - Involves the trigeminal nerve (CNV) and facial nerve (CN VII). - **Touching the skin around the eyelid:** Blinking. - **Trigeminal nerve (CNV) ** → **Facial Nerve (CN VII).** - **Branches:** - **Ophthalmic:** Sensory, involved in the palpebral reflex. - **Maxillary:** Sensory, involved in the palpebral reflex. ## Corneal Reflex - Involves the trigeminal nerve (CNV) and facial nerve (CN VII). - **Touching the cornea:** Blinking and retraction of the eye. - **Trigeminal nerve (CN V)** ← **Facial Nerve (CN VII)** and **Abducens nerve (CN VI).** ## Menace Response - Learned response, not a reflex. - Involves higher brain and cerebellum. - **Seeing something coming toward them:** Blinking, reflect, and head movement. ## Nasal Mucosa - Involves sensation of the trigeminal nerve (CN V). - Ophthalmic and maxillary are responsible. ## Lip Pinch Reflex - Acts on sensory component, specifically the mandibular branch. - **Pinching the lower lip:** Twitch in the lip muscles. - **Motor component:** Mediated by the facial nerve. ## Gag Reflex - Involves intrinsic muscles of the larynx and vagus nerve. - **Stimulation of the pharyngeal area:** Elevation of the soft palate and pharyngeal muscle contraction. - **Key role played by the Vagus Nerve.** ## Patellar Reflex - **Sensory Input:** Lengthening of the quadriceps muscle detected by the intrafusal muscle spindle. - **Intrafusal Muscle Spindle:** Receptor that measures muscle length. - **Afferent Neuron:** Sensory information transmitted to the spinal cord through the afferent neuron. - **Alpha Motor Neuron:** Spinal cord sends a signal to the alpha motor neuron, which contracts the muscle. - **Gamma Motor Neuron:** Adjusts the sensitivity of the muscle spindle. - **Involves:** Femoral nerve and the quadriceps muscle. - **Tapping patellar tendon:** Stifle extension. - **Sensory Input:** Femoral nerve. - **Motor Component:** Quadriceps muscle. - **Sustained Contraction of Muscles:** ## Tonic Stretch (Golgi Tendon Reflex) - Reflex that regulates muscle tension by detecting changes in tendon tension. - **Involves:** - **Golgi Apparatus:** Detects changes in tendon tension. - **Afferent Neuron:** Transmits sensory _information_ to the spinal cord. - **Interneurons:** Process sensory _information_ and send signals to the muscle. - **Muscle:** Contracts or relaxes in response to sensory information. - **Helps prevent muscle rupture by releasing tension in the tendon.** - **Provides excitatory input to the opposing muscle group to maintain balance.** ## Withdrawal Reflex - Involves: - **Flexor Muscles:** Contracting to withdraw the limb. - **Extensor Muscles:** Relaxing to allow the limb to move away from the stimulus. - **Opposing Muscles:** Contracting to maintain balance and prevent falling. ## Crossed Extensor Reflex - Helps maintain balance and prevent falling. - **Normal in standing animals, pathological in animals lying on their side.** ## Tongue Reflex - Involves the lingual nerve (branch of the trigeminal nerve). - **Stimulation of the tongue:** Movement/sensation. ## Cutaneous Trunci Reflex - Involves the cutaneous trunci muscle and lateral thoracic nerve. - **Pinching the skin on either side of the spinal column:** Contraction of the cutaneous trunci muscle. ## Ulnar and Median Nerve Reflexes - Involve the sensation on the skin of the palmar surface of the forelimb. - **Ulnar Nerve:** Dermatome = lateral toe. - Sensation on the skin of the palmer surface. - **Median Nerve:** Dermatome = Palmer surface of the forelimb. - Sensation on the skin of the palmer surface. ## Dermatomes - Areas of skin that are innervated by nerves that arise from specific spinal nerve roots. ## Quadrants - Divisions of limbs that help further localize sensations. - **C5:** Radial (front) - **C6:** Radial (front) - **C7:** Radial (front) - **C8:** Ulnar (back) - **T1:** Ulnar (back) ## Nerve Assessment - **Radial Nerve:** Assesses the front limb. - **Sciatic Nerve:** Assesses the back leg. - **Pudendal Nerve:** Assesses the pelvic area. ## Embryonic Development of Nervous System - **Nervous System:** Develops from: - **Neuroplate:** Originates from _ectoderm_. - **Neural Tube:** Folds together to form a neural tube. - **Neural Tube:** - **Three Main Structures:** - **Forebrain:** Divides into _telencephalon_ and _diencephalon_. - **Midbrain:** Divides into _mesencephalon_. - **Hindbrain:** Divides into _metencephalon_ and _myelencephalon_. - **Develop into:** - **Cerebrum:** - **Thalamus & Hypothalamus:** - **Brainstem:** - **Cerebellum:** ## Synaptic Tuning - Process of strengthening or weakening synapses based on use. - **Important for shaping behavior and personality**. ## Evolution of Brain Development - **Dogs + Cats:** Large cerebrum. - **Birds:** Smaller cerebrum. ## Cerebrum - **Largest part of the brain.** - **Responsible for conscious behaviors and calculations.** - **Two parts:** - **Allocortex:** Small, primitive part of the cerebrum responsible for instinctive functions, e.g., emotions, motivation, feeding, and reproductive. - **Neocortex:** Large, more developed part of the cerebrum responsible for higher cognitive skills, e.g., problem-solving, learning, habituation, memory, processing sensory information, fine motor skills. - **Consists of:** - Visual cortex: Processes visual information. - Auditory cortex: Processes auditory information. - Motor cortex: Controls movement. - Somatosensory cortex: Processes sensory information form the body. ## Hypothalamus - Involved in regulating hunger and thirst. ## Limbic System - Network of structures connecting _neocortex_ and _allocortex_. - Responsible for motivation, memory, and emotional responses. - Located on the border between _neocortex_ and _allocortex_. - Crucial role in: - Connecting internal drives and motivation with goal-directed behavior, - Overriding instinctive decisions. ## Thalamus - Regulates the flow of information to the cerebrum. - Acts as a relay center for _sensory_ information. - Can shut off the flow during rest and recovery. ## Cerebellum - Coordinates and regulates movement, balance, and posture. - **Consists of three areas:** - **Vestibular Cerebellum:** Connected to the inner ear. - Responsible for maintaining balance and spatial orientation. - Constantly checks the head and body position. - Adjusts muscle tone to prevent falls. - **Spinal Cerebellum:** Controls movement. - Defines muscle tone. - Communicates with the spinal cord to coordinate muscle activity. - Responsible for reflexes and automatic movements. - Refines movements. - **Cerebral Cerebellum:** Communicates with the cerebrum to plan and refine movements. - Responsible for fine motor skills and coordination. - Works with the cerebrum. ## Brainstem - Responsible for unconscious responses: - Breathing - Heart Rate - Body Temperature - Digestion. - Respiration. ## Brainstem Parts - **Three Main Parts:** - **Midbrain:** Controls auditory and visual processing. - **Pons:** Connects the cerebellum to the rest of the brain. - **Medulla Oblongata:** Regulates autonomic functions, e.g., heart rate and breathing. ## Reticular Formation - Network of nuclei in the brainstem that activates/regulates consciousness and alertness. - "Net" that filters and processes information. ## Spinal Cord - Network of nerves that carries information from the body to the brain. - Responsible for transmitting _sensory_ information and _motor_ signals. - Divided into: - **Sensory Pathways:** Carry information from the body to