hole’s essentials of human anatomy &...

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Chapter 9

Hole’s Essentials of HumanAnatomy & Physiology

David ShierJackie ButlerRicki Lewis

Created by Dr. Melissa Eisenhauer Trevecca Nazarene University

Amended by John Crocker

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Chapter 9

Nervous System

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1) What are the functions of the nervous system?2) Describe each of the five types of neuroglial cells.3) Describe the structure of a nerve fiber.4) Describe the groupings of neurons by structural differences.and by functional differences.5) Compare and contrast resting potential and action potential.6) How does a nerve impulse travel the length of a nerve? How is this process different in myelenated

fibers and unmyelinated fibers?7) Describe the process of synaptic transmission.8) Compare and contrast exitatory and inhibitory actions by neurons.9) What are neurotransmitters? Where are they synthesized and stored? How do they act?10) compare and contrast facilitatation, convergence, and divergence.11) What is a reflex arc? What steps are involved?12) What are reflex behaviors?13) What are meninges? Describe the three types.14) Describe the structure of the spinal chord.15) Compare and contrast white matter and gray matter.16) What are the functions of the spinal chord?17) Describe each of the functional divisions of the brain.18) Describe the functional regions of the cerebral cortex.19) What is hemisphere dominance? What functions are performed by the dominant hemisphere? What

functions are performed by the non-dominant hemisphere?20) What are the functions of the thalamus and hypothalamus?21) What is the limbic system and what does it do?22) List the components of the brain stem and describe the functions of each.23) What are the functions of the cerebellum.24) What are plexuses?25) Compare and contrast the sympathetic and parasympathetic nervous systems.

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Introduction: A. The nervous system is composed of neurons and

neuroglia.1. Neurons are typically divided into:

a) cell bodyb) axon c) dendrites

2. Neurons transmit nerve impulses along nerve fibers to other neurons.

3. Neuroglia carry out a variety of functions to aid and protect components of the nervous system.

4. Nerves are made up of bundles of nerve fibers.

CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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A. Organs of the nervous system can be divided into 1. Central nervous system (CNS)

a) Brain b) Spinal cord

2. Peripheral nervous system (PNS)a) Peripheral nervesb) Connect the CNS to the rest of the body

B. The nervous system provides 1. Sensory2. Integrative3. Motor functions

a) Somatic nervous system - consciously controlled b) Autonomic system - unconscious


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General Functions of the Nervous System A. Sensory receptors

1. At the ends of peripheral nerves 2. Gather information 3. Convert it into nerve impulses

B. Sensory impulses are integrated in the brain as perceptions (integrative function)

C. Conscious or subconscious decisions follow D. Lead to motor functions via effectors


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Supporting cells A. Function of Neuroglial Cells

1. Fill spaces2. Support neurons3. Provide structural frameworks4. Produce myelin5. Carry on phagocytosis

B. Classification of Neuroglial Cells 1. Four are in the CNS and the last in the PNS2. Microglial cells

a) Smallb) Phagocytize bacterial cells and cellular debris


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1. Oligodendrocytes a) Form myelin in the brain and spinal cord

2. Astrocytes a) Near blood vessels and support structuresb) Aid in metabolismc) Respond to brain injury by filling in spaces.

3. Ependyma a) Cover the inside of ventricles b) Form choroid plexuses within the ventricles.

4. Schwann cells a) Peripheral nervous system onlyb) Produce myelin


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Neuron Structure A. Cell body contains:

1. Mitochondria 2. Lysosomes 3. Golgi apparatus 4. Chromatophilic substances called Nissl bodies

containing: a) rough endoplasmic reticulumb) neurofibrils


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A. Nerve fibers include: A. Numerous dendrites

1. Branching2. Carry impulses from other neurons (or from

receptors) toward the cell bodyB. A solitary axon

1. Transmits the impulse away from the axonal hillock of the cell body

2. May give off side branches


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1. Larger axons are enclosed by sheaths of myelina) Provided by Schwann cells b) Outer layer of myelin surrounded by a

neurilemma (neurilemmal sheath) made up of the cytoplasm and nuclei of the Schwann cell.

c) Narrow gaps in the myelin sheath between Schwann cells are called nodes of Ranvier.

2. The smallest axons lack a myelin sheath and so are called unmyelinated fibers.


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1. White matter in the CNS is due to myelin sheaths in this area

2. Unmyelinated nerve tissue in the CNS comprise the gray matter.

3. Peripheral neurons are able to regenerate because of the neurilemma

4. CNS axons are myelinated by oligodendrocytes thus lacking neurilemma and usually do not regenerate


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Classification of NeuronsA. Neurons can be grouped in two ways:

1. Structural differences a) Bipolar neurons

a) found in the eyes, nose, and earsb) have a single axon and a single dendrite extending

from opposite sides of the cell body.b) Unipolar neurons

a) found in ganglia outside the CNS b) have an axon and a dendrite arising from a single

short fiber extending from the cell bodyc) Multipolar neurons

a) found in the brain and spinal cord b) have many nerve fibers arising from their cell bodies


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1. Functional differencesa) Sensory neurons (afferent neurons)

a) usually unipolarb) some bipolarc) conduct impulses from peripheral receptors to the CNS

b) Interneuronsa) multipolar neurons b) within the CNS c) form links between other neurons

c) Motor neuronsa) multipolar neurons b) conduct impulses from the CNS to effectors


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Cell Membrane Potential A. A cell membrane is usually polarized

1. Excess of negative charges on the inside of the membrane

2. Polarization is important to the conduction of nerve impulses


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A. Distribution of Ions 1. Distribution of ions is determined by the membrane

channel proteins 2. MCPs selective for certain ions3. Potassium ions (K+) pass through the membrane

more readily than do sodium ions (Na+)

4. Potassium ions a major contributor to membrane polarization


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A. Resting Potential 1. Due to active transport

a) Cells maintain a greater concentration of sodium ions outside

b) Greater concentration of potassium ions inside the membrane

2. Inside the membrane - excess negative charge3. Outside - excess positive charge4. This separation of charge, or potential difference,

is called the resting potential


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A. Potential Changes 1. Stimulation of a membrane can locally affect its

resting potential2. When the membrane potential becomes less

negative, the membrane is depolarized3. If sufficiently strong depolarization occurs, a

threshold potential is achieved as ion channels open4. At threshold, an action potential is reached5. Action potentials may be reached when a series of

subthreshold stimuli combine to reach threshold


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A. Action Potential 1. At threshold potential

a) Na+ channels open b) Membrane permeability to Na+ quickly changes in the

region of stimulation.c) Na+ rushes ind) Membrane potential changes and becomes depolarized.e) K+ channels open allowing K+ to leave the cellf) The membrane becomes repolarizedg) Resting potential is reestablished.

2. This rapid sequence of events is the action potential.3. Active transport mechanisms then restore the original

concentrations of Na+ and K+


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Nerve Impulse A. A nerve impulse is conducted as an action

potential is reached at the trigger zone. B. This spreads by a local current flowing down the

fiber, and adjacent areas of the membrane reach action potential.


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A. Impulse Conduction 1. Unmyelinated fibers conduct impulses over their

entire membrane surface.2. Myelinated fibers conduct impulses from one

Node of Ranvier to the next (saltatory conduction)3. Saltatory conduction is many times faster

conduction over the complete membrane surface


A. All-or-None Response 1. Nerve fibers respond to a stimulus completely by

conducting an impulse or not at all 2. Greater intensity of stimulation triggers more

impulses per second, not stronger impulses.

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The Synapse A. Nerve impulses travel from neuron to neuron along

complex nerve pathways.B. The junction between two communicating neurons is

called a synapseC. A synaptic cleft is the space between them across which

the impulse must be conveyed.


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A. Synaptic Transmission 1. When an impulse reaches the synaptic knobs of an

axon, synaptic vesicles release a neurotransmitter into the synaptic cleft

2. The neurotransmitter from the presynaptic neuron reacts with specific receptors on the postsynaptic membrane

3. This process by which the impulse in the presynaptic neuron is transmitted across the synaptic cleft to the postsynaptic neuron is called synaptic transmission


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A. Excitatory and Inhibitory Actions1. Neurotransmitters that increase postsynaptic

membrane permeability to Na+ may trigger impulses and are thus excitatory

2. Other neurotransmitters may decrease membrane permeability to Na+, reducing the chance that it will reach threshold, and are thus inhibitory

3. The effect on the postsynaptic neuron depends on which presynaptic knobs are activated


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A. Neurotransmitters1. 50+ different neurotransmitters are produced by

the nervous systema) most are synthesized in the cytoplasm of synaptic knobs b) stored in synaptic vesicles.

2. When an action potential reaches the synaptic knoba) calcium ions rush inward b) in response some synaptic vesicles fuse with the

membrane releasing their contents to the synaptic cleft

3. Synaptic cleft and on postsynaptic membrane enzymes rapidly decompose the neurotransmitters

4. Removal of the neurotransmitter prevents continuous stimulation of the postsynaptic neuron


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Impulse Processing A. How impulses are processed is dependent upon how

neurons are organized in the brain and spinal cord.B. Neuronal Pools

1. Neurons within the CNS are organized into neuronal pools with varying numbers of cells.

2. Each pool receives input from afferent nerves and processes the information according to the special characteristics of the pool.


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A. Facilitation1. A particular neuron of a pool may receive excitatory

or inhibitory stimulation2. If the net effect is excitatory but subthreshold, the

neuron becomes more excitable to incoming stimulation (facilitation).

B. Convergence 1. A single neuron within a pool may receive impulses

from two or more fibers (convergence) 2. Makes it possible for the neuron to summate

(combine) impulses from different sources.


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A. Divergence 1. Impulses leaving a neuron in a pool may be

passed into several output fibers (divergence) 2. This pattern serves to amplify an impulse.


39Convergence Divergence

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Types of NervesA. A nerve is a bundle of nerve fibers held together

by layers of connective tissue.B. Nerves can be:

1. Sensory2. Motor3. Mixed, carrying both sensory and motor fibers.


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Nerve PathwaysA. The routes nerve impulses travel are called

pathways, the simplest of which is a reflex arc.B. Reflex Arcs include:

1. Sensory receptors 2. Sensory neurons3. Interneurons in the spinal cord4. Motor neurons5. Effectors


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A. Reflex Behavior 1. Reflexes are automatic subconscious responses to

stimuli 2. Help maintain homeostasis (heart rate, blood

pressure, etc.) 3. Carry out automatic responses (vomiting, sneezing,

swallowing, etc.) 4. The knee-jerk reflex (patellar tendon reflex) is an

example of a monosynaptic reflex (no interneuron)5. The withdrawal reflex involves

a) Sensory neuronsb) Interneuronsc) Motor neuronsd) Simultaneously the antagonistic extensor muscles are

inhibited


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Meninges A. The brain and spinal cord are surrounded by

membranes called meninges B. Meninges lie between the bone and the soft tissues. C. Dura mater

1. Outermost meninx 2. Tough, white dense connective tissue3. Contains many blood vessels4. Forms the inner periosteum of the skull bones.5. Forms partitions between lobes of the brain6. Forms dural sinuses.7. The sheath around the spinal cord is separated

from the vertebrae by an epidural space.


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A. Arachnoid mater1. The middle meninx2. Thin and lacks blood vessels3. Does not follow the convolutions of the brain4. Subarachnoid space

a) Between the arachnoid and pia mater b) Contains cerebrospinal fluid

B. Pia mater 1. Innermost2. Thin and contains many blood vessels and nerves3. Attached to the surface of the brain and spinal cord4. Follows the contours of the brain and spinal cord


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Spinal Cord A. The spinal cord begins at the base of the brain and

extends as a slender cord to the level of the intervertebral disk between the first and second lumbar vertebrae.

B. Structure of the Spinal Cord 1. The spinal cord consists of 31 segments2. Each gives rise to a pair of spinal nerves3. Cervical enlargement gives rise to nerves leading to

the upper limbs4. Lumbar enlargement gives rise to nerves innervating

the lower limbs


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1. Two deep longitudinal grooves divide the cord into right and left halvesa) anterior median fissureb) posterior median sulcus

2. White mattera) Bundles of myelinated nerve fibers (nerve tracts) b) Surrounds a butterfly-shaped core of gray matter housing

interneurons

3. A central canal contains cerebrospinal fluid


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A. Functions of the Spinal Cord 1. The spinal cord has two major functions:

a) to transmit impulses to and from the brainb) to house spinal reflexes

2. Nerve tracts are identified by the origin and termination of the fibers in the tract

3. Ascending tracts tracts carry sensory information to the brain

4. Descending tracts carry motor information from the brain

5. Many spinal reflexes also pass through the spinal cord.


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Brain A. The brain is the largest most complex portion of the

nervous systemB. Contains 100 billion multipolar neuronsC. Can be divided into the:

1. Cerebrum a) largest portion b) associated with higher mental functions

2. Diencephalon - processes sensory input3. Cerebellum - coordinates muscular activity4. Brain stem - coordinates and regulates visceral

activities


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A. Structure of the Cerebrum1. Largest portion of the mature brain2. Consists of two cerebral hemispheres.3. The corpus callosum, a deep ridge of nerve fibers,

connects the hemispheres.4. The surface of the brain is marked by convolutions,

sulci, and fissures.5. Lobes of the brain named according to the bones

they underlie a) frontal lobeb) parietal lobec) temporal lobed) occipital lobee) insula


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1. The cerebral cortexa) A thin layer of gray matterb) Lies on the outside of the cerebrum c) Contains 75% of the cell bodies in the nervous system

2. Beneath the cortex lies a mass of white mattera) Made up of myelinated nerve fibers b) Connects the cell bodies of the cortex with the rest of the

nervous system


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A. Functions of the Cerebrum - higher brain functions1. Interpretation of sensory input2. Initiating voluntary muscular movements3. Memory4. Integrating information for reasoning


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A. Functional Regions of the Cerebral Cortex 1. The functional areas of the brain overlap2. The cortex can, however, generally be divided into

a) Motor areasb) Sensory areasc) Association areas

3. The primary motor areas lie in the frontal lobes, anterior to the central sulcus and in its anterior wall.

4. Broca’s areaa) Anterior to the primary motor cortexb) Coordinates muscular activity for speech


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1. The frontal eye field a) Above Broca’s areab) Controls the voluntary movements of the eyes and

eyelids

2. The sensory areasa) located in several areas of the cerebrum b) interpret sensory input, producing feelings or sensations

3. Sensory areas for sight lie within the occipital lobe4. Sensory and motor fibers cross over in the spinal

cord or brain stem a) centers in the right hemisphere interpret and control the

left side of the bodyb) centers in the left hemisphere interpret and control the

right side of the body


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1. The various association areas of the brain a) Analyze and interpret sensory impulses b) Function in reasoning, judgment, emotions,

verbalizing ideas, and storing memory

2. Association areas of the frontal lobe control a number of higher intellectual processes

3. A general interpretive area found at the junction of the parietal, temporal, and occipital lobes plays the primary role in complex thought processing


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A. Hemisphere Dominance1. Both cerebral hemispheres function in receiving

and analyzing sensory input and sending motor impulses to the opposite side of the body.

2. Most people exhibit hemisphere dominance for the language-related activities of speech, writing, and reading.

3. The left hemisphere is dominant in 90% of the population

4. The non-dominant hemisphere specializes in nonverbal functions and controls emotions and intuitive thinking


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1. Basal ganglia a) Masses of gray matter b) Located deep within the cerebral hemispheres c) Relay motor impulses from the cerebrum d) Help to control motor activities by producing

inhibitory dopamine2. Basal ganglia include:

a) Caudate nucleusb) Putamenc) Globus pallidus.


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A. Ventricles and Cerebrospinal Fluid 1. Ventricles

a) Series of connected cavities within the cerebral hemispheres and brain stem

b) Continuous with the central canal of the spinal cordc) filled with cerebrospinal fluid

2. Choroid plexusesa) Specialized capillaries from the pia materb) Secrete cerebrospinal fluidc) Most cerebrospinal fluid arises in the lateral ventricles.d) Cerebrospinal fluid has nutritive as well as protective

(cushioning) functions


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A. Diencephalon1. Lies above the brain stem 2. Composed of the:

a) Thalamusb) hypothalamus c) optic tracts d) optic chiasma e) infundibulum (attachment for the pituitary)f) posterior pituitaryg) mammillary bodiesh) pineal gland


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1. The thalamusa) functions in sorting and directing sensory information

arriving from other parts of the nervous systemb) performing the services of both messenger and editor

2. The hypothalamus a) maintains homeostasis by regulating a wide variety of

visceral activities including:1) heart rate and arterial blood pressure2) body temperature3) water and electrolyte balance4) hunger and body weight5) movements and secretions of the digestive tract6) growth and reproduction7) sleep and wakefulness

b) Links the endocrine system with the nervous system


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1. The limbic systema) In the area of the diencephalonb) Controls emotional experience and expressionc) Generates pleasant or unpleasant feelings about

experiencesd) Guides behavior that may enhance the chance of

survival using these feelings


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A. Brain Stem1. Lies at the base of the cerebrum2. Connects the brain to the spinal cord 3. Consists of the:

a) Midbrainb) Ponsc) Medulla oblongata


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1. Midbraina) Located between the diencephalon and ponsb) Contains bundles of myelinated axons that convey

impulses to and from higher parts of the brainc) Masses of gray matter that serve as reflex centers,

including centers for auditory and visual reflexes.2. Pons

a) lies between the midbrain and medulla oblongatab) transmits impulses between the brain and spinal cordc) contains centers that regulate the rate and depth of

breathing


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1. Medulla Oblongataa) transmits all ascending and descending impulses

between the brain and spinal cordb) houses nuclei that control visceral functions, including

1) the cardiac center that controls heart rate2) the vasomotor center for blood pressure control3) the respiratory center that works, along with the

pons, to control the rate and depth of breathing4) Other nuclei associated with coughing, sneezing,

swallowing, and vomiting


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1. Reticular Formationa) Throughout the brain stem, hypothalamus,

cerebrum, cerebellum, and basal ganglia, is a complex network of nerve fibers connecting tiny islands of gray matter; this network is the reticular formation.

b) Decreased activity in the reticular formation results in sleep; increased activity results in wakefulness.

c) The reticular formation filters incoming sensory impulses


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A. Cerebellum 1. Two hemispheres connected by a vermis2. The cerebellar cortex is a thin layer of gray matter

that lies outside a core of white matter3. Communicates with other parts of the CNS via

cerebellar peduncles4. Integrates sensory information about the position

of body parts 5. Coordinates skeletal muscle activity and maintains

posture


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Peripheral Nervous SystemA. The peripheral nervous system (PNS) consists of the

cranial and spinal nerves that arise from the central nervous system and travel to the remainder of the body.

B. Includes two components1. The somatic nervous system that oversees

voluntary activities2. The autonomicautonomic nervous system that controls

involuntary activities.


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A. Cranial Nerves1. arise from the underside of the brain2. most are mixed nerves3. Twelve pairs designated by number and name 4. include the:

I. Olfactory nerves VII. Facial nervesII. Optic nerves VIII. Vestibulocochlear nervesIII. Oculomotor nerves IX. Glossopharyngeal nervesIV. Trochlear nerves X. Vagus nervesV. Trigenimal nerves XI. Accessory nervesVI. Abducens nerves XII. Hypoglossal nerves


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A. Spinal Nerves1. Thirty-one pairs of mixed nerves 2. Grouped according to the level from which they

arise 3. Numbered in sequence beginning in the cervical

region4. Each spinal nerve arises from two roots:

a) a dorsal root (sensory root)b) a ventral root (motor root)


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1. The main branches of some spinal nerves form plexuses.a) Cervical plexuses

1) Lie on either side of the neck 2) Supply muscles and skin of the neck

b) Brachial plexuses 1) Arise from lower cervical and upper thoracic nerves 2) Lead to the upper limbs

c) Lumbrosacral plexuses1) arise from the lower spinal cord2) Lead to the lower abdomen, external genitalia,

buttocks, and legs


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Autonomic Nervous SystemA. The autonomic nervous system (ANS) maintains

the homeostasis of visceral activities without conscious effort

B. General Characteristics1. Motor pathways include two fiber types:

a) preganglionic fibers leave the CNSb) postganglionic fibers innervate the effectors


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1. Includes two divisions exerting opposing effects on target organs: a) sympathetic

1) operates under conditions of stress or emergency2) Fibers arise from the thoracic and lumbar regions of

the spinal cord3) synapse in paravertebral ganglia close to the vertebral

column4) Postganglionic axons lead to an effector organ

b) Parasympathetic1) operates under normal conditions2) Fibers arise from the brainstem and sacral region of

the spinal cord3) synapse in ganglia close to the effector organ


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Sympathetic Parasympathetic

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1. Autonomic Neurotransmitters a) Preganglionic fibers of both sympathetic and

parasympathetic divisions release acetylcholine.b) Parasympathetic postganglionic fibers are

cholinergic fibers and release acetylcholinec) Sympathetic postganglionic fibers are adrenergic

and release norepinephrined) The effects of these two divisions are generally

antagonistic due to the effects of releasing different neurotransmitters to the effector


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1. Control of Autonomic Activitya) largely controlled by reflex centers in the

brain and spinal cordb) The limbic system and cerebral cortex alter

the reactions of the autonomic nervous system through emotional influence


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