Functional Human Physiology for the Exercise and Sport Sciences The Nervous System Jennifer L. Doherty, MS, ATC Department of Health, Physical Education,

Functional Human Physiologyfor 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) Brain

2) Spinal Cord

The peripheral nervous system (PNS)1) Afferent Division

2) Efferent Division Somatic Nervous System Autonomic Nervous System

Functional Divisions of the PNS Afferent = Sensory

1) Somatic sensory

2) Visceral sensory Efferent = Motor

1) Somatic motor

2) Visceral motor


Divisions of the PNS according to type of control

Somatic nervous system 1) Voluntary

Autonomic nervous system1) 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) Oligodendrocytes = form myelin in the CNS

2) Schwann Cells = form myelin in the PNS

3) Microglia Cells = macrophages of the CNS

4) Ependymal Cells = line cerebral ventricles

5) Astrocytes = develop neuronal connections


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 bone1) Dura Mater2) Arachnoid mater3) Pia Mater


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


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


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

Interneurons Also call Association / Internuncial neurons Function: link between afferent and efferent

neurons1) 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



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 butterfly-shaped interior region of the spinal cord

Ventral Horn Contains Efferent Neurons

1) Interneurons2) Cell bodies3) 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 between1) Different levels of the spinal cord, or2) 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 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.


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

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 - Basal Nuclei

The Brain – Diencephalon (Forebrain)

The diencephalon includes two structures:1) Thalamus

2) Hypothalamus

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

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

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.

Hypothalamus

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

Limbic System

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


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


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

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

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


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


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 Physiologyfor the Exercise and Sport Sciences

The Nervous System: Sensory Systems




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 Sensitive to tissue damage

Thermoreceptors Sensitive to temperature, either to heat or cold

Mechanoreceptors Sensitive to changes in mechanical energy such as pressure or the

movement of fluids1) Baroreceptors detect the blood pressure in certain arteries and veins. 2) Stretch receptors are sensitive to changes in the amount of inflation in the

lungs.3) 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 Tract1) 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




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


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


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 Neurons1) Neurons that travel from the ganglion to the effector

organ

Sympathetic Nervous System

Thoracolumbar Division Arises from the ventral roots of all thoracic spinal nerves Arises from the ventral roots of lumbar spinal nerves 1-3

Preganglionic Neurons 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 Arises from the cranial nerve nuclei in the brain stem Arises from the ventral roots of sacral spinal cord

Preganglionic Neurons 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 Release Acetylcholine

Cholinergic Receptors Nicotinic receptors

1) Excitatory

2) Opens Na+ and K+ channels

Muscarinic receptors1) Excitatory or Inhibitory

2) Uses G-proteins to open specific ion channels

Adrenergic Neurons 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

Functional Human Physiology for the Exercise and Sport Sciences The Nervous System Jennifer L. Doherty, MS, ATC Department of Health, Physical Education,

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