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Functional Human Physiology for the Exercise and Sport Sciences The Nervous System Jennifer L. Doherty, MS, ATC Department of Health, Physical Education, and Recreation Florida International University Overview of the Nervous System Two major anatomical divisions The central nervous system (CNS) 1) 2) Brain Spinal Cord The peripheral nervous system (PNS) 1) 2) Afferent Division Efferent Division Somatic Nervous System Autonomic Nervous System Overview of the Nervous System Functional Divisions of the PNS Afferent = Sensory 1) Somatic sensory 2) Visceral sensory Efferent = Motor 1) Somatic motor 2) Visceral motor Overview of the Nervous System Divisions of the PNS according to type of control Somatic nervous system 1) Voluntary Autonomic nervous system 1) Involuntary 2) Further divided according to the overall effect on the organs: Sympathetic division = “Fight or Flight” Parasympathetic division = “Rest and Repair” Functions of the Nervous System Collecting information Peripheral Nervous System 1) Sensory or afferent input Evaluation and decision making Central Nervous System Integration and comparison to: Homeostatic ranges Previous or learned experiences Elicits responses Peripheral Nervous System 1) Motor or efferent output General Anatomy of the CNS Glial Cells Supporting cells for neurons in the CNS 5 types 1) 2) 3) 4) 5) Oligodendrocytes = form myelin in the CNS Schwann Cells = form myelin in the PNS Microglia Cells = macrophages of the CNS Ependymal Cells = line cerebral ventricles Astrocytes = develop neuronal connections General Anatomy of the CNS Cranium/Skull Protects this soft tissue of the brain Vertebral Column Protects the spinal cord Meninges Connective tissue membranes that separate the soft tissue of the CNS from surrounding bone 1) Dura Mater 2) Arachnoid mater 3) Pia Mater General Anatomy of the CNS Cerebrospinal Fluid (CSF) Clear, watery fluid that bathes the CNS Acts as a shock absorber to prevent injury Provides nutrients to glial cells Removes waste products Maintains normal ionic concentrations surrounding neurons General Anatomy of the CNS The CNS requires an abundant blood supply due to the high metabolic rate of neuronal tissue Brain accounts for 20% of all O2 used Brain accounts for 50% of all glucose used Blood-Brain Barrier A physical barrier between the CSF and blood This semi-permeable membrane functions to protect the environment surrounding the neurons in the CNS General Anatomy of the CNS Classification of Neurons Classified according to the direction that the nerve impulse travels in relation to the central nervous system. Sensory / Afferent Neurons Receptors: located in the periphery 1) sensitive to changes inside or outside of the body Nerve impulses: travel toward the CNS General Anatomy of the CNS Interneurons Also call Association / Internuncial neurons Function: link between afferent and efferent neurons 1) Relay information from one part of the CNS to another for processing, interpreting, and eliciting a response Motor / Efferent Neurons Nerve impulses: travel away from the CNS toward effector organs General Anatomy of the CNS Gray Matter Areas of the CNS consisting primarily of: 1) Cell bodies 2) Dendrites 3) Axon terminals Area where synaptic transmission and neural integration occurs White Matter Areas in the CNS consisting primarily of myelinated axons 1) Function to rapidly transmit action potentials over relatively long distances The Spinal Cord Cylinder of nervous tissue Continuous with the lower portion of the brain Branches into 31 pairs of spinal nerves Cervical nerves (C1 – C8) Thoracic nerves (T1 – T12) Lumbar nerves (L1 – L5) Sacral nerves (S1 – S5) Coccygeal nerve (C0) The Spinal Cord Gray matter: concentrated in the butterflyshaped interior region of the spinal cord Ventral Horn Contains Efferent Neurons 1) Interneurons 2) Cell bodies 3) Dendrite Dorsal Horn Contains Afferent Neurons 1) Axon terminals The Spinal Cord Afferent Nerve Fibers Cell bodies are located outside the spinal cord in clusters called dorsal root ganglia These fibers form the dorsal roots Efferent Nerve Fibers Cell bodies are located in the spinal cord These fibers for the ventral roots The Spinal Cord Spinal Nerves Contain both afferent and efferent axons Joining of the dorsal root and the ventral root Called Mixed Nerves Spinal Cord White Matter: consists of Tracts providing communication between 1) Different levels of the spinal cord, or 2) The brain and various levels of the spinal cord Ascending Tracts Transmit information from the spinal cord to the brain Descending Tracts Transmit information from the brain to the spinal cord The Brain Forebrain Largest and most superior portion of the brain Divided into right and left hemispheres Consists of the Cerebrum and Diencephalon Cerebellum Located inferior to the forebrain Functions include motor coordination, balance, and feedback systems Brainstem Connects the forebrain and cerebellum to the spinal cord Consists of the Midbrain, Pons, and Medulla Oblongata The Brain – Cerebrum (Forebrain) Cerebral Cortex Thin, highly convoluted layer gray matter Responsible for conscious initiation of voluntary movements Regions of the Cerebral Cortex Frontal Lobes Parietal Lobes Temporal Lobes Occipital Lobe The Brain – Cerebrum (Forebrain): Areas of Specialized Function Primary Somatosensory Cortex Involved in processing somatic sensory information associated with: 1) Somesthetic sensations such as touch, temperature and pain perception 2) Proprioception which is the awareness of muscle tension, joint position, and limb position Primary Motor Cortex Initiates voluntary movement The Brain – Cerebrum (Forebrain) The cerebral cortex is topographically organized Areas may be mapped according to function Called somatotopic organization Motor and Sensory Homunculi Map of the cerebral cortex corresponding to the part of the body served by a particular region The size of the body part on the homunculus is proportional to the amount of brain dedicated to that body part 1) For Example, the hand is very large on both the sensory and motor homunculus because it has many sensory receptors and requires very fine motor control. The Brain – Cerebrum (Forebrain) Subcortical Nuclei Regions of gray matter within the cerebrum Includes the Basal Nuclei (Basal Ganglia) Masses of gray matter scattered deep within the cerebral hemispheres Components of the basal nuclei include: 1) The caudate nucleus 2) The putamen 3) The globus pallidus Important role in modifying movement The Brain - Basal Nuclei Normally inhibit motor function thereby controlling muscle activity Receive input from: The entire cerebral cortex Other subcortical nuclei 1) Such as the subthalamic nucleus of the diencephalon, substantia nigra, and the red nucleus No direct connections with the motor pathways Send information to the Primary Motor Cortex through the thalamus The Brain - Basal Nuclei Complex role in motor control Important in starting, stopping, and monitoring movements executed by the primary motor cortex It is particularly involved in slow, sustained, or stereotyped movements 1) Examples: arm swing during gait, riding a bicycle, or eating Inhibit antagonistic (unnecessary) movements Enhances the ability to perform several tasks at once Impairment results in: Disturbances in muscle tone and posture Tremors Abnormally slow movement The Brain – Diencephalon (Forebrain) The diencephalon includes two structures: 1) Thalamus 2) Hypothalamus Thalamus Referred to as the “gateway” to the cerebral cortex Most afferent neurons synapse with at least one of the thalamic nuclei The major relay station for all sensory input (except smell) A relay station for impulses that regulate emotion Also a relay station for motor impulses from the cerebellum and basal ganglia Thalamus Consists of many separate groups of nuclei Each receiving a certain kind of information Information is sent from the thalamic nuclei to a particular region of the cortex Nuclei of the Thalamus Ventral Posterolateral Nucleus Ventral Lateral Nucleus Medial and Lateral Geniculate Bodies Thalamus The Ventral Posterolateral Nucleus Receives somatic sensory information (touch, pressure, pain) Relays information to the somatosensory region of the cerebral cortex The Ventral Lateral Nucleus Receives motor information from the basal nuclei and cerebellum Relays information to the motor region of the cerebral cortex The Medial and Lateral Geniculate Bodies The medial geniculate body sends auditory information from the auditory receptors to the auditory region of the cerebral cortex The lateral geniculate body sends visual information to the occipital region of the cerebral cortex Hypothalamus Located inferior to the thalamus and superior to the brain stem It is interconnected to the cerebral cortex, thalamus, and other parts of the brain stem It consists of a collection of many different nuclei. The Supraoptic Nucleus The Paraventricular Nucleus The Preoptic Nucleus The Ventromedial Nucleus Hypothalamus The hypothalamus has many roles in regulating homeostasis It senses the chemical and thermal qualities of the blood It is involved in: Regulation of heart rate and arterial blood pressure; Control of movements and glandular secretions of the stomach and intestines; Regulation of respiratory rate; Regulation of water and electrolyte balance; and Control of hunger and regulation of body weight. Limbic System A diverse collection of closely associated cerebral cortical regions Encircle the upper part of the brain stem lending is name, limbus (refers to ring) The structures of the limbic system include: The hippocampus The mammillary bodies of the diencephalon The hypothalamus The anterior nucleus of the thalamus The amygdaloid body Several gyri and fiber tracts (fornix) that have not yet been specifically identified Limbic System Controls the emotional aspects of behavior Connected to the cerebral cortex and brain stem Allows for perception and response to a wide variety of stimuli Communicates with the prefrontal lobes to elicit a relationship between feelings and thoughts. This explains why emotions sometimes override thoughts and why reason can override emotion when an emotional response would be inappropriate. Part of the system, the hippocampus and the amygdaloid body are involved in memory The Brain - Cerebellum Located inferior to the forebrain and posterior to the brainstem Functions: Coordination of muscular activity 1) Skilled movements, posture, and balance Regulate muscle tone The cerebellum has no direct connections with muscles It functions at an unconscious level The Brain - Cerebellum Receives a variety of information Information about voluntary muscle activity from the motor region of the cerebral cortex Sensory information from proprioceptors throughout the body Information from the visual and equilibrium pathways Integrates this information and determines how to integrate the sensory information with the motor functions to elicit a coordinated response Sends its coordination plan to the primary motor cortex The primary motor cortex then signals the muscles to elicit the desired response The Brain - Cerebellum Cortical Control of Voluntary Movement Pyramidal Tracts Direct pathways from the primary motor cortex to the spinal cord, called Corticospinal tracts Control small groups of muscles that contract independently of each other Extrapyramidal Tracts Indirect connections between the brain and spinal cord Includes all motor control pathways outside the pyramidal system Control large groups of muscles that contract together to maintain posture and balance Pyramidal Tracts Axons of neurons in these tracts terminate in the ventral horn of the spinal cord Called Upper Motor Neurons Axons of neurons in these tracts cross over to the opposite side of the CNS in the area of the medulla Called Medullary Pyramids Pyramidal Tracts Lateral and Ventral Corticospinal Tracts Carry nerve impulses for skilled, voluntary contraction of the skeletal muscles Large motor pathways that descend from the cerebral motor cortex to the motor neurons in the ventral horn of the spinal cord The largest and most important motor tracts in the body Pyramidal Tracts The Lateral Corticospinal tracts cross over in the region of the medulla, called the medullary pyramids The Ventral Corticospinal tracts cross over in the spinal cord Pyramidal Tracts From the medulla, the corticospinal tracts descend to the spinal cord level of the muscle to be innervated Both lateral and ventral corticospinal tracts synapse with either: 1) Interneurons, or 2) Motor neurons in the ventral horn of the spinal cord Interneurons synapse with lower motor neurons that travel directly to the neuromuscular junction of the skeletal muscle the CNS wants to activate Pyramidal Tracts The Corticospinal Tracts connect the left cerebral motor cortex with the muscles on the right side of the body and vice versa For example: The brain has received and processed sensory information that causes it to direct the biceps muscles to contract to lift a weight The brain sends impulses down the corticospinal tracts to the C5-C7 levels of the spinal cord to synapse with the appropriate motor neurons The nerve impulse is propogated along the ventral roots of the brachial plexus, to the musculocutaneous nerve, which innervates the biceps The biceps muscle contracts to lift the weight Extrapyramidal Tracts Motor control pathways outside of the pyramidal system Indirect connections between the brain and spinal cord Neurons in these tracts do NOT form synapses with motor neurons Include two tracts Reticulospinal tracts Rubrospinal tracts Extrapyramidal Tracts Reticulospinal Tracts The Lateral, Anterior, and Medial Reticulospinal tracts are motor (efferent, descending) Descend from the reticular formation, which is located in the pons and medulla Elicits involuntary motor responses Functions: Facilitate extensor motor neurons (promotes muscle tone) Facilitate visceral motor function, and Control unskilled movements Extrapyramidal Tracts Rubrospinal tracts Motor (efferent, descending) tracts descending from the red nucleus (rubro-) of the midbrain These tracts cross over in the brain stem Elicits involuntary motor responses Functions: Synapse with motor neurons that will transmit impulses to the neuromuscular junction of the muscle that will contract Result in muscle contractions that maintain muscle tone in the flexor muscles on the opposite side of the body Functional Human Physiology for the Exercise and Sport Sciences The Nervous System: Sensory Systems Jennifer L. Doherty, MS, ATC Department of Health, Physical Education, and Recreation Florida International University Sensory Receptors Specialized neuronal structures that detect a specific form of energy in either the internal or external environment Energy is detected by the dendritic end organs of sensory (afferent) neurons This information is transmitted to the CNS Receptors may change one form of energy to another For example, chemical to electrical at the NMJ Types of Sensory Receptors Chemoreceptors Sensitive to chemical concentrations such as in smell and taste Nociceptors or pain receptors Thermoreceptors Sensitive to tissue damage Sensitive to temperature, either to heat or cold Mechanoreceptors Sensitive to changes in mechanical energy such as pressure or the movement of fluids 1) 2) 3) Baroreceptors detect the blood pressure in certain arteries and veins. Stretch receptors are sensitive to changes in the amount of inflation in the lungs. Proprioceptors are sensitive to changes in tension in the muscles, tendons, and ligaments. Photoreceptors Sensitive to light intensity and are found only in the eyes. Sensory Transduction Sensory impulses are generated by receptors The energy of the stimulus is absorbed The energy is then transduced into an electrical signal Receptor potential A stimulus that exceeds the threshold intensity Graded potential The electrical signal that is produced when threshold is reached Propagation of a nerve impulse Sensation The awareness of a stimulus Perception The brain’s interpretation of the sensory information provided by the sensory receptors Since all nerve impulses are the same, the only differences are: The type of receptor that was stimulated, and The region of the brain to which the receptor is connected. For example, 1) When heat receptors in the 2nd finger of the right hand are stimulated by a lit match, the region of the brain corresponding to that part of the body will perceive pain 2) If light receptors were transplanted to the region of the brain that senses smell, then stimulation of the light receptors would result in an odor being perceived Sensory Adaptation Sensory adjustment that occurs when receptors are continuously stimulated Sensory Coding Receptors respond to continuous stimulation by firing at slower and slower rates Eventually the receptors may fail to send any signal at all The sense of smell is particularly subject to sensory adaptation For example When you are in a room with a strong odor you will notice that soon you cannot smell the odor, or it is much reduced The smell receptors have adapted and are not stimulated again until the stimulus changes Clothing against skin is another example The Somatosensory System The Somatosensory Cortex Postcentral Gyrus of Cerebrum 1) Sensory homunculus 2) Somatic sensory and proprioception The Somatosensory System Somatosensory Pathways Dorsal Column-Medial Lemniscus 1) Transmit sensory impulses from mechanoreceptors and proprioceptors to the thalamus 2) Crosses over in the region of the medulla Spinothalamic Tract 1) Transmits sensory impulses from thermoreceptors and nocioceptors to the thalamus after crossing to the other side in the spinal cord 2) Crosses over in the spinal cord Spinothalamic Tracts The Lateral and Anterior Spinothalamic Tracts are sensory (afferent, ascending) Travel from the spinal cord to the thalamus Receive sensory input from the receptors for: Pain (from free nerve endings) Temperature (from Pacinian corpuscles) Deep pressure (from Meissners corpuscles) Touch (from End bulbs of Krause ) Spinothalamic Tracts Sensory information crosses to the opposite side in the spinal cord The sensory information ascends to the thalamus A synapse occurs with one of the thalamic nuclei The sensory information is sent from the thalamus to sensory cortex of the cerebrum Located in the post central gyrus For example: A heat receptor (free nerve ending) located in the L3 dermatome on the anterior thigh is stimulated by the heating pad you have put on the quadriceps muscle group of your sore right thigh The impulse travels along the peripheral nerve through the sensory neuron in the dorsal root ganglion and on to a synapse with an internuncial neuron in the dorsal horn of segment L3 From there the fiber carrying the next impulse crosses over to the left side of the spinal cord to the lateral spinothalamic tract, and ascends to the thalamus. Another synapse occurs in the thalamus and the next impulse is sent to the sensory cortex of the cerebrum where the brain will perform its integrative and decision making functions. A decision will be made whether to instruct the muscles of your hands and arms to remove the heating pad because it is too hot or leave it in place. Pain Perception Mediated primarily through free nerve endings Sensitive to a variety of painful or noxious stimuli Changes in chemical composition of body fluids, such as decreased pH or accumulation of metabolic wastes can stimulate pain receptors. Adaptation to pain is practically non-existent Pain sensation can be triggered by a single stimulus and is longer lasting than many other types of stimuli, such as hot, cold, or smell Pain Pathways Pain impulses are transmitted through the ascending pathways of the spinal cord, primarily the lateral spinothalamic tracts to the brain Nocioceptors (pain receptors) located in the skin When stimulated, send pain information along a first order neuron First order neurons Deliver sensory impulses from the receptor to the dorsal horn of the spinal cord where it synapses on a second order neuron Second order neruons Travel in the spinothalamic tract to the thalamus which relays the information to the appropriate area of the primary somatosensory cortex Pain Pathways Within the brain most of the pain sensation terminates in the reticular formation and are processed by the thalamus, hypothalamus and the cerebral cortex The brain, after evaluating the extent of the pain, sends information back along a designated motor tract to the muscles that require contraction to move the limb away from the source of pain Visceral Pain Usually not very well localized It may feel as though it is coming from another part of the body than from the organ actually affected Referred pain Results from common nerve pathways that bring sensory information from skin or muscles of another part of the body in addition to that of an organ. For Example, Pain impulses from the heart are conducted along the same neural pathways as pain from the left arm and shoulder Thus, the brain interprets heart pain as the more familiar shoulder and arm pain Modulation of Pain Signals In cases of extreme pain, impulses are capable of stimulating the release of biochemicals that can block pain impulses Among these biochemicals are: Neuropeptides Serotonin Enkephalin Endorphins These biochemicals can bind to pain receptors and block the sensation of severe or acute pain The Nervous System: Autonomic and Motor Systems Jennifer L. Doherty, MS, ATC Department of Health, Physical Education, and Recreation Florida International University The Autonomic Nervous System Peripheral Nervous System Somatic NS Autonomic NS 1) Sympathetic 2) Parasympathetic The involuntary part of the PNS Operates without conscious control Primary function is to maintain homeostasis The Autonomic Nervous System Controls the following: Smooth muscle of the blood vessels; Abdominal and thoracic viscera; Certain glands; and Cardiac muscle. Serves an important role in maintaining: Heart rate Blood pressure Breathing Body temperature The Autonomic Nervous System Dual Innervation of the ANS The sympathetic division of the ANS is responsible for readying the body for strenuous physical activity or emotional stress Fight or Flight Response Prepares the body to deal with disturbances to homeostasis (threatening situations) Anatomy of the ANS The ANS consists of efferent pathways Each efferent pathway contains 2 neurons that are arranged in series to each other Provides communication between the CNS and the effector organ Anatomy of the ANS Autonomic Ganglia Provide communication pathways via synapses between neurons Preganglionic Neurons Travel from the CNS to the ganglia 1) Sympathetic chain ganglion, 2) Collateral ganglion, or 3) Parasympathetic ganglion Postganglionic Neurons 1) Neurons that travel from the ganglion to the effector organ Sympathetic Nervous System Thoracolumbar Division Preganglionic Neurons Arises from the ventral roots of all thoracic spinal nerves Arises from the ventral roots of lumbar spinal nerves 1-3 Originate in the Lateral Horn of the spinal cord Cell bodies are located in the thoracic and upper lumbar regions of the spinal cord Short Myelinated Axons Postganglionic Neurons Synpase with preganglionic neurons in the Sympathetic Chains (Trunks) Long Unmyelinated Axons Sympathetic Nervous System Sympathetic Chains (Trunks) Where preganglionic and postganglionic neurons synapse in the Sympathetic NS Comprised of sympathetic nerves that are connected to a string of nerve cell bodies Called the Sympathetic (Paravertebral) Chain Ganglia These interconnected ganglia are located close to the spinal cord Far away from the structures it innervates Parasympathetic Nervous System Craniosacral Division Preganglionic Neurons Arises from the cranial nerve nuclei in the brain stem Arises from the ventral roots of sacral spinal cord Those originating in the cranial nerve nuclei travel with axons of cranial nerves and terminate in ganglia near the effector organ Those originating in the sacral spinal cord synapse with other parasympathetic preganglionic neurons to form pelvic nerves that terminate near the effector organ Long Myelinated Axons Postganglionic Neurons Travel to the effector organ Short Unmyelinated Axons Mixed Composition of ANS Nerves Both systems function utilizing two neurons that communicate through a ganglion Preganglionic nerve fibers arise in the CNS Myelinated axon leaves the CNS as part of a cranial nerve or spinal nerve Travels to an autonomic nervous system ganglion Preganglionic nerve fibers synapse with the postganglionic nerve fibers in the ganglion Postganglionic nerve fibers travel to the appropriate effector organ Effects of the ANS The two divisions have opposite effects on the organs and structures innervated Sympathetic Nervous System Acetylcholine = neurotransmitter at the synapse with the ganglion Norepinephrine = neurotransmitter at the synapse with the effector organ Parasympathetic Nervous System Acetylcholine = neurotransmitter at both synapses Effects of the ANS Cholinergic Neurons Adrenergic Neurons Release Acetylcholine Cholinergic Receptors Nicotinic receptors 1) Excitatory 2) Opens Na+ and K+ channels Muscarinic receptors 1) Excitatory or Inhibitory 2) Uses G-proteins to open specific ion channels Release Norepinephrine Adrenergic Receptors Alpha receptors 1) Excitatory Beta receptors 1) Excitatory or Inhibitory Effects of the ANS The sympathetic division generally produces a whole body response when stimulated. The overall function of the sympathetic division is the fight or flight response. The parasympathetic division generally produces a single response at a specific effector organ. The overall function of the parasympathetic division is rest and repair. Comparison: Somatic and Autonomic Nervous Systems