Human Anatomy & Physiology I Lecture 4 PDF

PHM 10402 HUMAN ANATOMY & PHYSIOLOGY I LECTURE 4 DR. CHE KU DAHLAN CHE KU DAUD FACULTY OF PHARMACY, UniSZA. Kemaskini: Oktober 2024 Pathways of the Nervou...

PHM 10402 HUMAN ANATOMY & PHYSIOLOGY I LECTURE 4 DR. CHE KU DAHLAN CHE KU DAUD FACULTY OF PHARMACY, UniSZA. Kemaskini: Oktober 2024 Pathways of the Nervous System CNS communicates with body structures via pathways. sensory or motor information processing and integration occur continuously Pathways travel through the white matter of the spinal cord. Connect various CNS regions with peripheral nerves. Pathways of the Nervous System Consists of a tract and a nucleus. Tracts are groups or bundles of axons that travel together in the CNS. Each tract may work with multiple nuclei groups in the CNS. A nucleus is a collection of neuron cell bodies located within the CNS. Nervous System Pathways Ascending pathways carry sensory information from the peripheral body to the brain Descending pathways transmit motor information from the brain or brainstem to muscles or glands Pathway crosses over from one side of the body to the other side at some point in its travels. The left side of the brain processes information from the right side of the body, and vice versa. Nervous System Pathways Most exhibit a precise correspondence between a specific area of the body and a specific area of the CNS. Pathways that connect these parts of the primary motor cortex to a specific body part exhibit somatotopy. Nervous System Pathways All pathways are composed of paired tracts. A pathway on the left side of the CNS has a matching tract on the right side of the CNS. Both left and right tracts are needed to innervate both the left and right sides of the body. Pathways are composed of a series of two or three neurons that work together. Nervous System Pathways Sensory pathways have primary neurons, secondary neurons, and sometimes tertiary neurons that facilitate the pathway’s functioning conduct information about limb position and the sensations of touch, temperature, pressure, and pain Motor pathways use an upper motor neuron and a lower motor neuron the cell bodies are located in the nuclei associated with each pathway  Nervous System Pathways Somatosensory pathways process stimuli received from receptors within the skin, muscles, and joints Viscerosensory pathways process stimuli received from the viscera Sensory Receptors Detect stimuli and then conduct nerve impulses to the CNS Sensory pathway centers within either the spinal cord or brainstem process and filter the incoming sensory information. They determine whether the incoming sensory stimulus should be transmitted to the cerebrum or terminated. More than 99% of incoming impulses do not reach the cerebral cortex and our conscious awareness. Primary (First-Order) Neuron Sensory pathways utilize a series of two or three neurons to transmit stimulus information from the body periphery to the brain. The first neuron is the primary (first-order) neuron The dendrites are part of the receptor that detects a specific stimulus. The cell bodies reside in the posterior root ganglia of spinal nerves or the sensory ganglia of cranial nerves. Secondary (Second-Order) Neuron The axon of the primary neuron projects to a secondary neuron within the CNS. Is an interneuron. The cell body resides within either the posterior horn of the spinal cord or a brainstem nucleus. The axon projects to the thalamus, where it synapses with the tertiary neuron. Tertiary (Third-Order) Neuron Also an interneuron. Its cell body resides within the thalamus. The thalamus is the central processing and coding center for almost all sensory information. Posterior Funiculus-Medial Lemniscal Pathway Projects through the spinal cord, brainstem, and diencephalon before terminating within the cerebral cortex. tracts within the spinal cord posterior funiculus tracts within the brainstem medial lemniscus Conducts sensory stimuli concerned with proprioceptive information about limb position and discriminative touch, pressure, and vibration sensations. Anterolateral Pathway Located in the anterior and lateral white funiculi of the spinal cord. anterior spinothalamic tract lateral spinothalamic tract Axons projecting from primary neurons enter the spinal cord and synapse on secondary neurons within the posterior horns. Axons entering these pathways conduct stimuli related to crude touch and pressure as well as pain and temperature. Axons of the secondary neurons cross over and relay stimulus information to the opposite side of the spinal cord before ascending toward the brain. Spinocerebellar Pathway Conducts proprioceptive information to the cerebellum for processing to coordinate body movements. Composed of anterior and posterior spinocerebellar tracts. the major routes for transmitting postural input to the cerebellum Sensory input is critical for regulation of posture and balance and coordination of skilled movements. These are different from the other sensory pathways in that they do not use tertiary neurons. they only have primary and secondary neurons Motor Pathways Descending pathways in the brain and spinal cord that control the activities of skeletal muscle. Formed from the cerebral nuclei, the cerebellum, descending projection tracts, and motor neurons. Regulate the activities of skeletal muscle.  Corticobulbar Tracts Originate from the facial region of the motor homunculus within the primary motor cortex. Axons extend to the brainstem, where they synapse with lower motor neuron cell bodies that are housed within brainstem cranial nerve nuclei. Axons of these lower motor neurons help form the cranial nerves.  Corticobulbar Tracts Transmit motor information to control: eye movements (via CN III, IV, and VI) cranial, facial, pharyngeal, and laryngeal muscles (via CN V, VII, IX, and X) some superficial muscles of the back and neck (via CN XI) intrinsic and extrinsic tongue muscles (via CN XII) Corticospinal Tracts Descend from the cerebral cortex through the brainstem and form a pair of thick bulges in the medulla called the pyramids. Continue into the spinal cord to synapse on lower motor neurons in the anterior horn of the spinal cord. Role of the Cerebral Nuclei Receive impulses from the entire cerebral cortex, including the motor, sensory, and association cortical areas, as well as input from the limbic system. Most of the output goes to the primary motor cortex. Do not exert direct control over lower motor neurons. Provide the patterned background movements needed for conscious motor activities by adjusting the motor commands issued in other nuclei. 27  Somatic Motor Control Several regions of the brain participate in the control of motor activities. Motor programs require conscious directions from the frontal lobes. Movement is initiated when commands are received by the primary motor cortex from the motor association areas. The cerebellum is critically important in coordinating movements because it specifies the exact timing of control signals to different muscles.  Levels of Processing and Motor Control Simple reflexes that stimulate motor neurons represent the lowest level of motor control. The nuclei controlling these reflexes are located in the spinal cord and the brainstem. Brainstem nuclei also participate in more complex reflexes. Initiate motor responses to control motor neurons directly. Oversee the regulation of reflex centers elsewhere in the brain. Cerebral Cortex Control highly variable and complex voluntary motor patterns. Occupy the highest level of processing and motor control. Motor commands may be conducted to specific motor neurons directly. May be conveyed indirectly by altering the activity of a reflex control center.  Cerebral Cortex Higher-order mental functions: consciousness, learning, memory, and reasoning involve multiple brain regions connected by complicated networks and arrays of axons conscious and unconscious processing of information are involved in higher-order mental functions may be continually adjusted or modified Cerebral Lateralization Each hemisphere tends to be specialized for certain tasks. Higher-order centers in both hemispheres tend to have different but complementary functions. Cerebral Lateralization Left hemisphere is the categorical hemisphere and it functions in categorization and symbolization. contains Wernicke’s area and the motor speech area specialized for language abilities important in performing sequential and analytical reasoning tasks (science and mathematics) appears to direct or partition information into smaller fragments for analysis Cerebral Lateralization Right hemisphere is called the representational hemisphere. concerned with visuospatial relationships and analyses the seat of imagination and insight, musical and artistic skill, perception of patterns and spatial relationships, and comparison of sights, sounds, smells, and tastes Both cerebral hemispheres remain in constant communication through commissures, especially the corpus callosum, which contains hundreds of millions of axons that project between the hemispheres. 39  Nerves Bundles of axons in the PNS Sensation: The conscious or subconscious awareness of external or internal stimuli. Perception: The conscious awareness and the interpretation of meaning of sensations.  Peripheral sensory receptors By location: Exteroceptors – Sensitive to stimuli arising from outside body Interoceptors – Or visceroreceptors, from internal viscera Proprioceptors – Monitor degree of stretch in skeletal muscles, tendons, joints and ligaments General Senses vs. Special Senses Pain Taste Temperature Smell Light touch Vision Pressure Hearing Sense of body Balance and limb position  Mechanoreceptors Thermoreceptors Photoreceptors Chemoreceptors Nociceptors Osmoreceptors  Unencapsulated Encapsulated Nerve vs Nerve Endings Endings Free nerve endings skin, bones, internal organs, joints Deeper tissue, muscles Encapsulated nerve endings Free Nerve Endings Pain & Temperature Merkel’s Discs Light Touch & Pressure Root Hair Plexuses Light Touch  Meissner’s Corpuscles Discriminative Touch in Hairless Skin Areas Pacinian Corpuscles Deep Pressure Krause’s End-Bulbs Discriminative Touch in Mucous Membranes Ruffini’s Corpuscles Deep Pressure & Stretch (Proprioception)  Merkel cell Merkel Cells- slow mechanoreceptors (basal layer) free nerve endings Merkel disc Meissner’s corpuscles Ruffini corpuscle root hair plexus Pacinian corpuscles  Proprioceptors Muscle Spindles - Skeletal Muscle Stretching Golgi Tendon Organs - Tendon Stretching Joint kinesthetic receptors – monitors stretch in synovial joints; sends info to cerebellum and spinal reflex arcs – to cerebrum, – cerebellum and – spinal reflex arcs  Stimulus & Modalities A stimulus is a change detectable by the body. Stimuli exist in a variety of energy forms, or modalities, such as heat, light, sound, pressure, and chemical changes. Sometimes we perceive sensory signals when they reach a level of consciousness, but other times they are processed completely at the subconscious level. All the information regarding all these senses is send to the CNS via AFFERENT NEURONS.  Because the only way afferent neurons can transmit information to the CNS about stimuli is via action potential propagation, these forms of energy must be converted into electrical signals. THE CONVERSION OF STIMULUS ENERGY INTO A GRADED POTENTIAL IS CALLED SENSORY TRANSDUCTION AND IS DONE BY SENSORY RECEPTORS. Receptors are sensory afferent nerve endings that terminate in periphery as either part of a neuron or in the form of specialized capsulated structures. They act as biological transducers and convert various forms of energy acting on them into action potentials. SENSORY RECEPTORS Classification of Receptors Receptors are present in the skin, the mucous membranes, fascia and deeper parts of the body. They are responsible for 4 different sensations: 1. Touch-pressure 2. Cold 3. Warmth and 4. Pain The receptors are: 1. Encapsulated receptors: consist of multilayered capsules of connective tissue which surround a core of cells in which axons end after losing their myelin sheath. - Meissner’s corpuscle: sensitive to light touch & are rapidly adapting. Are present just below the epidermis in the palmer surface of fingers, lips, margins of the eyelids. - Pacinian Corpuscle: respond to vibration & deep pressure & is rapidly adapting. Present in deeper tissues and also in pleura, peritoneum, external genitalia and walls of many viscera. Also present in periostium, ligaments and joint capsules. - Krause’s end bulbs: occur in conjunctivae, papillae of lips and tongue. 2. Expanded tips on sensory nerve endings: - Merkel’s discs: which detects light, sustained touch and texture, and is slowly adapting. Present in hairless skin e.g. fingertips. - Riffini’s end organs: in deeper layer of skin and deeper tissues, e.g. periostium, ligaments and joint capsules. They respond to deep, sustained pressure and stretch of the skin, such as during a massage, and are slowly adapting. 3. Naked or free nerve endings: are the most widely distributed receptors in the body and can be excited by touch, cold, warmth and pain.  SENSORY RECEPTORS Pacinian Corpuscle Free nerve ending’s  General properties of receptors The following are the properties of the Sensory Receptors: 1. Receptor Potential. 2. Specificity of stimulus & the Adequate stimulus. 3. Effect of strength of stimulus. 4. Adaptation (also Desensitization). 5. Muller’s doctrine of specific nerve energies 6. Law of projection. 7. Threshold. 8. Sensory unit 9. Receptive field. 1. RECEPTOR POTENTIAL THE CHANGES IN SENSORY RECEPTOR MEMBRANE POTENTIAL IS A GRADED POTENTIAL CALLED THE RECEPTOR POTENTIAL.  SENSORY TRANSDUCTION Transduction is the conversion of stimulus energy into information that can be processed by the nervous system, which is an action potential. Stimulus ↓ Receptor (SENSORY TRANSDUCTION) ↓ Graded Potential (RECEPTOR POTENTIAL) ↓ Afferent Neuron ↓ Action Potential  How is a physical or a chemical stimulus converted into a change in membrane potential? Stimulus (chemical/ mechanical/ thermal) ↓ Receptor which is either: 1. Specialized ending of the afferent neuron, OR 2. A separate receptor cell associated with a peripheral nerve ending. ↓ Membrane permeability altered (usually by opening of ligand-gated or stimulus sensitive cation channels) ↓ A graded potential is generated. It is called RECEPTOR POTENTIAL. ↓ There is summation, and if the stimulus is strong, it leads to a greater permeability change in the receptor which leads to a large Receptor potential. ↓ If the Receptor Potential is large enough ↓ An Action Potential is generated (by opening of the voltage-gated Na channels in the afferent neuron next to the receptor)  THE INITIATION OF THE ACTION POTENTIAL The initiation site of action potentials in an afferent neuron differs from the site in an efferent neuron or interneuron. In the other two types of neurons (interneuron & the efferent neuron), action potentials are initiated at the axon hillock located at the start of the axon next to the cell body. However, in the afferent neuron, action potentials are initiated at the peripheral end of fiber next to the receptor, a long distance from the cell body. 2. SPECIFICITY OF STIMULUS & ADEQUATE STIMULUS If all stimuli are converted to action potentials in sensory neurons and all action potentials are identical, how can the central nervous system tell the difference between heat and pressure, or between a pinprick to the toe and one to the hand? All stimuli once received by the receptor are converted into action potentials and all of them are carried by the afferent neurons. This means that the CNS must distinguish four properties of a stimulus to be able to specify a stimulus: (1) its nature, or modality and (2) its location (3) Intensity (4) Duration  Adequate Stimulus Each sensory receptor has an adequate stimulus, a particular form of energy to which it is most responsive. For example, thermoreceptors are more sensitive to temperature changes than to pressure, and mechanoreceptors respond preferentially to stimuli that deform the cell membrane, receptors in the eye are sensitive to light, receptors in the ear to sound waves, and warmth receptors in the skin to heat energy. Because of this differential sensitivity of receptors, we cannot “see” with our ears or “hear” with our eyes. Some receptors can respond weakly to stimuli other than their adequate stimulus, but even when activated by a different stimulus, a receptor still gives rise to the sensation usually detected by that receptor type. They respond to most other forms of energy if the intensity is high enough. Photoreceptors of the eye respond most readily to light, for instance, but a blow to the eye may cause us to “see stars”, an example of mechanical energy of sufficient force to stimulate the photoreceptors. Sensory receptors can be incredibly sensitive to its preferred stimulus.  Modality/ Nature of the stimulus The 1:1 association of a receptor with a sensation is called labeled line coding. Stimulation of a cold receptor is always perceived as cold, whether the actual stimulus was cold or an artificial depolarization of the receptor. The blow to the eye that causes us to see a flash of light is another example of labeled line coding. A blow to the eye is seen as “white light” as the photoreceptors were stimulated.  3. Effect of Strength & Duration of Stimulus: For individual sensory neurons, intensity discrimination begins at the receptor. If a stimulus is below threshold, the primary sensory neuron does not respond. Once stimulus intensity exceeds threshold, the primary sensory neuron begins to produce action potentials. As stimulus intensity increases, the receptor potential amplitude (strength) increases in proportion, and the frequency of action potentials in the primary sensory neuron increases, up to a maximum rate. Similarly, the duration of a stimulus is coded by the duration of action potentials in the sensory neuron. In general, a longer stimulus generates a longer series of action potentials in the primary sensory neuron 4. ADAPTATION also called Desensitization. It is the decrease in response of receptors on being continuously stimulated. When a stimulus persists continuously, some receptors adapt, or cease to respond. Thus, the receptor “adapts” to the stimulus by no longer responding to it to the same degree. Receptors fall into one of two classes, depending on how they adapt to continuous stimulation: 1. Tonic receptors 2. Phasic receptors 5. MULLER’S DOCTRINE OF SPECIFIC NERVE ENERGIES THE NATURE OF PERCEPTION OF A STIMULUS BY THE CNS IS DEFINED BY THE PATHWAY OVER WHICH THE SENSORY INFORMATION IS CARRIED. HENCE, THE ORIGIN OF THE SENSATION IS NOT IMPORTANT. 6. LAW OF PROJECTION STIMULATION OF NERVE FIBER ANYWHERE ALONG ITS COURSE PRODUCES THE SPECIFIC SENSATION IN THE AREA OF THE BODY FROM WHERE IT ORIGINATED. 6. THRESHOLD ALL RECEPTORS NEED A MINIMUM STRENGTH OF STIMULUS TO START SHOWING ACTIVITY; THIS STRENGTH IS CALLED THE THRESHOLD. 7. SENSORY UNIT THE SENSORY UNIT IS A SINGLE PRIMARY AFFERENT NERVE INCLUDING ALL ITS PERIPHERAL BRANCHES. 8. RECEPTIVE FIELD. THE AREA OF THE BODY WHOSE SENSORY NERVE SUPPLY COMES FROM A SINGLE SENSORY UNIT IS CALLED A RECEPTIVE FIELD.  SENSORY CLASSIFICATION OF THE NERVE FIBERS Type A fibers are the typical large and medium-sized myelinated fibers of spinal nerves. Type C fibers are the small unmyelinated nerve fibers that conduct impulses at low velocities. The C fibers constitute more than one half of the sensory fibers in most peripheral nerves, as well as all the postganglionic autonomic fibers. Note that a few large myelinated fibers can transmit impulses at velocities as great as 120 m/sec, a distance in 1 second that is longer than a football field. Conversely, the smallest fibers transmit impulses as slowly as 0.5 m/sec, requiring about 2 seconds to go from the big toe to the spinal cord. ____Cranial nerves attach to brain ___Spinal nerves attach to spinal cord 12 pair 31 pair III. Cranial Nerves- These nerves serve the head and neck; they originate in the brain and most of them exit the skull through cranial foramina not vertebral foramina. They are numbered I – XII rostrally to caudally.  A. Olfactory nerve I- sensory nerve for smell, it runs below the frontal lobe, purely sensory, cerebrum – B. Optic nerve II- a brain tract exiting through the optic chiasma, it sends signals of images to the brain, purely sensory, cerebrum C. Oculomotor nerve III- caudal to optic chiasma it innervates internal eye muscles to move the eye (superior, inferior, lateral, medial rectus) and eyelids. It adjust the pupil and lens. Motor nerve, visceral motor, and proprioceptive, midbrain D. Trochlear nerves IV- (pulley) it inervates the superior oblique muscles of the eye. Motor nerve, midbrain E. Trigeminal nerves V – (three fold)- it has three branches that carry sensory information from the face (superficial and internal) and motor information for chewing muscles. Mixed, pons F. Abducens nerves VI- innervates a muscle that abducts the eye (lateral rectus), motor nerve, pons G. Facial nerves VII- innervates muscles of facial expression, activates facial glands, conveys sensory from taste buds. Mixed and visceral motor, pons H. Vestibulocochlear nerves VIII- sensory nerve for hearing and equilibrium, purely sensor, medulla oblongata I. Glossopharyngeal nerves IX. innervates the tongue and pharynx, controls a muscle used for swallowing, activates salivary gland, conducts taste, and other facial sensory. Mixed and visceral motor, medulla oblongata J. Vagus Nerves X- (wanders) controls muscles of swallowing extends beyond the face and neck into the thorax and abdomen to innervate internal organs for motor and sensory impulses, some sensory near ear area. Mixed and visceral motor, medulla oblongata. K. Accessory nerves XI- accessory for the vagus nerve- it joins it, and controls muscles that moves the head and some of the same as the vagus. Motor and visceral motor, medulla oblongata. L. Hypoglossal nerves XII- (below the tongue) runs below the tongue and innervates the tongue muscles, motor nerves, medulla oblongata. III. Spinal Nerves- There are 31 pairs of nerves exiting the spinal column: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. They innervate the body in sections as seen on page 426. Each nerve has a dorsal (sensory) and ventral root (motor) that attach to the spinal cord at the rootlets. Each spinal nerve also has dorsal and ventral ramus that carries motor and sensory nerves. The ventral ramus connects to rami commicantes that connect to symphathetic chain ganglia. The dorsal rami supplies the posterior parts of the body and ventral rami supplies the lateral and anterior sides of the body. A. Innervation of the back- the nerves follow a neat and simple pattern. B. Innervation of the anterior thoracic an abdominal wall- supply intercostals muscles, skin or anterior and lateral thorax and abdomen. Introduction to nerve plexuses- these are networks of nerve clusters formed by ventral rami from different spinal nerves. Plexuses serve the limbs and are designed to prevent paralysis of a limb muscle by the distruction of just one spinal nerve. 1. The cervical plexus and innervation of the neck- formed by C1-C4 nerves, most branches are cutaneous nerves and anterior neck muscles and diaphragm. Anatomy of the Spinal Cord Upper limbs lower limbs  Peripheral motor endings Innervation of skeletal muscle Innervation of visceral muscles and glands  Motor axons innervate skeletal muscle fibers at neuromuscular junctions = motor end plates All muscles in Motor unit: motor neuron & all motor unit contract the muscle fibers it innervates together when neuron fires Stimulation of single motor unit causes weak contraction of entire muscle (spread out)  Innervation of visceral muscles & glands Near end organ visceral motor axon swells = presynaptic terminals (vesicles with neurotransmitters): action slow (NT diffuses) Somatic Pain-results from injuries to skin, muscle, joints, tendon vs. Visceral Pain- pain in body organs  Mature neurons are amitotic If the soma of a damaged nerve is intact, axon will regenerate Involves coordinated activity among: – Macrophages—remove debris – Schwann cells—form regeneration tube and secrete growth factors – Axons—regenerate damaged part Endoneurium Schwann cells 1 The axon Droplets becomes of myelin fragmented at the injury site. Fragmented axon Site of nerve damage Figure 13.4 (1 of 4)  2 Macrophages Schwann cell Macrophage clean out the dead axon distal to the injury. Figure 13.4 (2 of 4)  Aligning Schwann cells 3 Axon sprouts, form regeneration tube or filaments, grow through a regeneration tube formed by Schwann cells. Fine axon sprouts or filaments Figure 13.4 (3 of 4)  Schwann cell Site of new 4 The axon myelin sheath regenerates and formation a new myelin sheath forms. Single enlarging axon filament Figure 13.4 (4 of 4) On Old Olympus Towering Tops A Fat Voracious German Viewed A Hop 1. Olfactory- smell 2. Optic- vision 3. Oculomotor- 4 of the 6 extrinsic eye muscles 4. Trochlear- extrinsic eye muscles 5. Trigeminal- sensory fibers to the face and motor fibers to the chewing muscles 6. Abducens- controls eye muscles that turn the eye laterally 7. Facial- facial expression 8. Vestibulocochlear- hearing and balance 9. Glosopharyngeal- tongue and pharynx 10.Vagus- parasympathetic control of heart, lungs & abdominal organs 11.Accessory- accessory part of vagus nerve, neck & throat muscles 12.Hypoglossal- moves muscles under tongue Olfactory tract Olfactory bulb Filaments of olfactory nerve Olfactory receptor cell Nerve Pathways into the Spinal Cord sensory pathway motor pathway Spinal nerves  Spinal nerves Dorsal roots – sensory fibers arising from cell bodies in dorsal root ganglia Ventral roots – motor fibers arising from anterior gray column of spinal cord Ventral root ganglia  Dorsal and ventral roots join in an intervertebral foramen forming spinal nerve Outside foramen, re-branch as rami (sing., ramus): Dorsal and ventral rami (somatic) Rami communicantes (visceral) Spinal nerve  Dorsal rami serve the muscles and skin of the posterior trunk – Back, from neck to sacrum, innervated in a neatly segmented pattern: horizontal strip at same level as emergence from spinal cord Ventral rami serve the muscles and skin of the lateral and anterior trunk – In thorax only, a simple segmented pattern as intercostal nerves – Also serve the limbs Cross section of thorax showing main roots and branches of a spinal nerve – In the thorax, each ventral ramus continues as an intercostal nerve Dorsal ramus Ventral ramus Intercostal nerve  REFLEXES Rapid, predictable response to a stimulus. Unlearned, involuntary, "hard-wired" into our neuroanatomy at the cellular & tissue level. The simplest type of nerve circuit regulates a reflex (or autonomic response) and is called a reflex arc. Methods of Classifying Reflexes  sensory neuron motor neuron stretch interneuron receptor motor neuron patellar Spinal Reflex ligament Arc 1 Quadriceps strongly contracts. Golgi tendon organs are activated. Interneurons Quadriceps (extensors) Spinal cord Golgi tendon organ Hamstrings (flexors) + Excitatory synapse – Inhibitory synapse 1 Quadriceps strongly 2 Afferent fibers synapse contracts. Golgi tendon with interneurons in the organs are activated. spinal cord. Interneurons Quadriceps (extensors) Spinal cord Golgi tendon organ Hamstrings (flexors) + Excitatory synapse – Inhibitory synapse 1 Quadriceps strongly 2 Afferent fibers synapse contracts. Golgi tendon with interneurons in the organs are activated. spinal cord. Interneurons Quadriceps (extensors) Spinal cord Golgi tendon organ Hamstrings (flexors) 3a The motor neurons (red) send activating + Excitatory synapse impulses to the – Inhibitory synapse quadriceps causing it to contract, extending the knee. 1 Quadriceps strongly 2 Afferent fibers synapse contracts. Golgi tendon with interneurons in the organs are activated. spinal cord. Interneurons Quadriceps (extensors) Spinal cord Golgi tendon organ Hamstrings (flexors) 3a 3b The interneurons (green) make The motor neurons (red) send activating inhibitory synapses with ventral horn neurons (purple) + Excitatory synapse impulses to the that prevent the antagonist – Inhibitory synapse quadriceps causing it to contract, extending the muscles (hamstrings) from knee. resisting the contraction of the quadriceps. Reflex Arc  Baby Reflexes Palmar Grasp reflex Suckling reflex Rooting reflex Babinski/plantar reflex Pupillary Reflex  Mammalian Dive Reflex An automated response system for diving in cold water (less than about 21C / 70F). 1. Bradycardia 2. Vasoconstriction to extremities 3. Apnea  CENTRAL NERVOUS SYSTEM (CNS) A HIERARCHY OF DOMAINS CEREBRAL CORTEX lower -------------------------------- higher telencephalon BASAL FOREBRAIN FOREBRAIN HIPPOCAMPUS diencephalon THALAMUS HYPOTHALAMUS MIDBRAIN mesencephalon MIDBRAIN NUCLEI CEREBELLUM metencephalon HINDBRAIN PONS myelencephalon MEDULLA cervical SPINAL thoracic CORD lumbar sacral  THE CEREBRAL CORTEX THE HOME OF CONSCIOUSNESS CONSCIOUSNESS --- Property of self-awareness and awareness of one’s place in the environment CEREBRAL CORTEX --- The highest brain center; different portions perform different functions, but the SUM of these activities defines conscious state ELECTROENCEPHALOGRAM (EEG) --- Measures electrical activity in cerebral cortex. FAST ASYNCHRONOUS EEG --- observed in awake individuals SLOW SYNCHRONOUS EEG --- observed in deep sleep and coma  ASCENDING SENSORY PATHWAYS A SOMATOTOPIC REPRESENTATION OF THE BODY IN THE CEREBRAL CORTEX DESCENDING PATHWAYS FROM THE MOTOR CORTEX SOME CORTICAL NEURONS PROJECT AXONS THAT SYNAPSE ON SPINAL MOTOR NEURONS  THE CEREBELLUM AND BASAL FOREBRAIN COORDINATION AND CONSISTENCY OF MOTOR TASKS CEREBELLUM --- BRAIN’S “INTERNAL GUIDANCE SYSTEM” FOR MOTOR TASKS 1) receives input on motor task to be performed and progress of ongoing task, and provides corrective signals to keep task on target 2) adapts with repetition to provide better guidance BASAL FOREBRAIN --- ENSURES MOTOR TASKS ARE EXECUTED SMOOTHLY AND AT DESIRED SPEED DISEASES OF THE BASAL FOREBRAIN: Parkinson’s Disease ……. Slowed movement with tremor Huntington’s Disease ….. Hyperkinesis with tremor  THE HIPPOCAMPUS ESSENTIAL CENTER FOR SPATIAL LEARNING AND MEMORY Lesions in hippocampus result in inability to create new spatial and verbal long-term memories  THE BRAIN STEM CONTROL CENTER OF WAKEFULNESS AND REFLEXIVE BEHAVIORS Brain stem serves as on/off switch to control cortical activity and consciousness Brain stem and its associated cranial nerves control many stereotyped involuntary motor tasks: Rhythmic breathing Heartbeat modulation Swallowing Sneezing Involuntary facial Major Divisions of CNS expressions  THE HYPOTHALAMUS SMALL CONTROL CENTER IN BRAIN STEM COORDINATING PHYSIOLOGICAL AND BEHAVIORAL RESPONSES TO PHYSICAL AND EMOTIONAL STATES EXAMPLES 1. Thirst and hunger urges are induced by hypothalamus in response to visceral sensory inputs of hyperosmolarity and hypoglycemia 2. Sweating, flushness of skin, and urge to seek out cooler environment are induced by hypothalamus in response to hyperthermia caused by hot weather, exertion or fever 3. Secretion of pituitary hormones which regulate sexual functions and behavior are coordinated by commands from the hypothalamus 4. Physical expression of emotions orchestrated by hypothalamus  THE LIMBIC SYSTEM A NETWORK OF BRAIN CENTERS WHICH PRODUCE EMOTIONAL, MOTIVATIONAL, AND ADDICTIVE STATES Best understood limbic center is the AMYGDALA AMYGDALA is required for experiencing both fearful and pleasurable responses and is required for generating memories associated with emotional experiences