9 - 1 copyright the mcgraw-hill companies, inc. permission required for reproduction or display....

9 - 1

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

*See PowerPoint image slides for all figures and tables pre-inserted into PowerPoint without notes”.

Chapter 9Lecture Outlines*

Hole’s Essentials of HumanAnatomy & Physiology

David ShierJackie ButlerRicki Lewis

Created by Lu Anne Clark Professor of Science, Lansing Community College

9 - 2

Chapter 9Nervous System


9 - 3

Introduction: A. The nervous system is composed of

neurons and neuroglia.1. Neurons transmit nerve impulses along nerve fibers to other neurons.2. Nerves are made up of bundles of nerve fibers.3. Neuroglia carry out a variety of functions to aid and protect components of the nervous system.


9 - 4

B. Organs of the nervous system can be divided into the central nervous

system (CNS), made up of the brain and spinal cord, and the peripheral nervous system (PNS), made up of peripheral nerves that connect the CNS to the rest of the body.


9 - 5

C. The nervous system provides sensory, integrative, and motor

functions to the body.1. Motor functions can be

divided into the consciously controlled somatic nervous system and the unconscious autonomic system.


9 - 6

General Functions of the Nervous System A. Sensory receptors at the ends of peripheral nerves gather information and convert it into nerve impulses.B. When sensory impulses are integrated in the brain as perceptions, this is the integrative function of the nervous system.C. Conscious or subconscious decisions follow, leading to motor functions via effectors.


9 - 7


9 - 8

Neuroglial Cells A. Classification of Neuroglial Cells

1. Neuroglial cells fill spaces, support neurons, provide structural

frameworks, produce myelin, and carry on phagocytosis. Four are in the CNS and the last in the PNS.

2. Microglial cells are small cells that phagocytize bacterial cells and cellular debris.


9 - 9

3. Oligodendrocytes form myelin in the brain and spinal cord.

4. Astrocytes are near blood vessels and support structures, aid in metabolism, and respond to brain

injury by filling in spaces.


9 - 10

5. Ependyma cover the inside of ventricles and form

choroid plexuses within the ventricles.

6. Schwann cells are the myelin-producing neuroglia of

the peripheral nervous system.


9 - 11


9 - 12

Neuron Structure A. A neuron has a cell body with

mitochondria, lysosomes, a Golgi apparatus, chromatophilic substance

(Nissl bodies) containing rough endoplasmic reticulum, and neurofibrils.


9 - 13


9 - 14

B. Nerve fibers include a solitary axon and numerous dendrites.

1. Branching dendrites carry impulses from other

neurons (or from receptors) toward the cell body.

2. The axon transmits the impulse away from the axonal hillock of the cell body and may give off side branches.


9 - 15

3. Larger axons are enclosed by sheaths of myelin provided by Schwann cells and are myelinated fibers.a. The outer layer of myelin is surrounded by a neurilemma (neurilemmal sheath) made up of the cytoplasm and nuclei of the Schwann cell.b. Narrow gaps in the myelin sheath between Schwann cells are called nodes of Ranvier.


9 - 16


9 - 17

4. The smallest axons lack a myelin sheath and

are unmyelinated fibers.

5. White matter in the CNS is due to myelin

sheaths in this area.6. Unmyelinated nerve tissue

in the CNS appears gray.


9 - 18

7. Peripheral neurons are able to regenerate because of the neurilemma, but the CNS axons are myelinated by oligodendrocytes, thus lacking

neurilemma, and usually do not regenerate.


9 - 19

Classification of NeuronsA. Neurons can be grouped in

two ways: on the basis of structural differences (bipolar, unipolar, and multipolar neurons), and by functional differences

(sensory neurons, interneurons, and motor neurons).


9 - 20


9 - 21

B. Classification of Neurons 1. Bipolar neurons are found in the eyes, nose, and ears, and have a single axon and a single dendrite extending from opposite sides of the cell body.2. Unipolar neurons are found in

ganglia outside the CNS and have an axon and a dendrite arising from a single short fiber extending from

the cell body.


9 - 22

3. Multipolar neurons have many nerve fibers arising from their cell bodies and are

commonly found in the brain and spinal cord.

4. Sensory neurons (afferent neurons) conduct impulses from peripheral receptors to the CNS and are usually

unipolar, although some are bipolar neurons.


9 - 23

5. Interneurons are multipolar neurons lying within the CNS that form links between other neurons.

6. Motor neurons are multipolar

neurons that conduct impulses from the CNS to effectors.


9 - 24

9 - 25

Cell Membrane Potential A. A cell membrane is usually

polarized, with an excess of negative charges on the inside of the membrane; polarization is

important to the conduction of nerve impulses.


9 - 26

At rest – slightly more negative inside the cell membrane than outside

9 - 27


9 - 28

B. Distribution of Ions 1. The distribution of ions is determined by the membrane channel proteins that are selective for certain ions.2. Potassium ions pass through the membrane more readily than do sodium ions, making potassium ions a major contributor to membrane polarization.


9 - 29

C. Resting Potential 1. Due to active transport, the cell maintains a greater concentration of sodium ions outside and a greater concentration of potassium ions inside the membrane.2. The inside of the membrane has excess negative charges, while the outside has more positive charges.3. This separation of charge, or potential difference, is called the resting potential.


9 - 30

D. Potential Changes 1. Stimulation of a membrane can

locally affect its resting potential.2. When the membrane potential

becomes less negative, the membrane is depolarized.

3. If sufficiently strong depolarization occurs, a threshold potential is achieved as ion channels open.


9 - 31


9 - 32

4. At threshold, action potential is reached.

5. Action potential may be reached when a

series of subthreshold stimuli summate and reach threshold.


9 - 33

9 - 34

E. Action Potential 1. At threshold potential,

membrane permeability to sodium suddenly changes in the region of stimulation.

2. As sodium channels open, sodium ions rush in, and the membrane potential changes and becomes depolarized.


9 - 35

When stimulated past threshold (about –30mV in humans), sodium channels open and sodium rushes into the axon, causing a region of positive charge within the axon. This is called depolarization

9 - 36

3. At the same time, potassium channels open to allow

potassium ions to leave the cell, the membrane becomes

repolarized, and resting potential is reestablished.

4. This rapid sequence of events is the action potential.5. The active transport

mechanism then works to maintain the original concentrations of sodium and

potassium ions.


9 - 37

The region of positive charge causes nearby voltage gated sodium channels to close. Just after the sodium channels close, the potassium channels open wide, and potassium exits the axon, so the charge across the membrane is brought back to its resting potential. This is called

repolarization.

9 - 38

9 - 39

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

• http://www.biology4all.com/resources_library/source/63.swf

9 - 41

Nerve Impulse

A. A nerve impulse is conducted as action potential is reached at the trigger zone and spreads by a local current flowing down the fiber, and adjacent areas of the membrane

reach action potential.


9 - 42

A nerve impulse is self-propagating. At the leading edge

of an action potential, sodium gates open, allowing sodium ions to flow into the cell. This flow of ions triggers more sodium gates

to open, causing the action potential to move.

At the trailing edge of an action potential, potassium gates open, allowing positive ions to flow out, and restoring the resting

potential of the neuron.

9 - 43

B. Impulse Conduction 1. Unmyelinated fibers conduct

impulses over their entire membrane surface.

2. Myelinated fibers conduct impulses from node of Ranvier

to node of Ranvier, a phenomenon called saltatory conduction.

3. Saltatory conduction is many times faster than conduction on

unmyelinated neurons.


9 - 44

C. All-or-None Response 1. If a nerve fiber responds

at all to a stimulus, it responds completely by conducting an impulse (all-or-none response).

2. Greater intensity of stimulation triggers more

impulses per second, not stronger impulses.


9 - 45

The Synapse

A. Nerve impulses travel from neuron to neuron along complex nerve pathways.

B. The junction between two communicating neurons is

called a synapse; there exists a synaptic cleft between them across which the impulse must be conveyed.


9 - 46

C. Synaptic Transmission 1. The process by

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


9 - 47

9 - 48

2. When an impulse reaches the synaptic knobs of an axon,

synaptic vesicles release neurotransmitter into the synaptic cleft.3. The neurotransmitter reacts with specific receptors on the postsynaptic membrane.


9 - 49

D. Excitatory and Inhibitory Actions1. Neurotransmitters that increase postsynaptic membrane permeability to sodium ions may trigger impulses and are thus excitatory.2. Other neurotransmitters may decrease membrane permeability to sodium ions, reducing the chance that it will reach threshold, and are thus inhibitory.


9 - 50

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

activated.


9 - 51

9 - 52

E. Neurotransmitters1. At least 50 kinds of

neurotransmitters are produced by the nervous system, most of which are synthesized in the cytoplasm

of the synaptic knobs and stored in synaptic vesicles.

2. When an action potential reaches the synaptic knob,

calcium ions rush inward and, in response, some synaptic vesicles fuse with the

membrane and release their contents to the synaptic cleft.


9 - 53

3. Enzymes in synaptic clefts and on postsynaptic membranes rapidly decompose the neurotransmitters after their release.

4. Destruction or removal of neurotransmitter

prevents continuous stimulation of the postsynaptic neuron.


9 - 54

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.


9 - 55

C. Facilitation 1. A particular neuron of a

pool may receive excitatory or inhibitory stimulation; if

the net effect is excitatory but subthreshold, the neuron becomes more excitable to incoming stimulation (a condition called

facilitation).


9 - 56

D. Convergence 1. A single neuron within a

pool may receive impulses from two or more fibers

(convergence), which makes it possible for the neuron to summate impulses from different sources.


9 - 57

E. Divergence 1. Impulses leaving a

neuron in a pool may be passed into several output fibers (divergence), a pattern that

serves to amplify an impulse.


9 - 58


Convergence

Divergence

9 - 59

• http://www.pbs.org/wgbh/nova/sciencenow/video/3204/q01.html

9 - 60

Types of NervesA. A nerve is a bundle of nerve

fibers held together by layers of connective tissue.

B. Nerves can be sensory, motor, or mixed, carrying both sensory and motor fibers.


9 - 61

Nerve PathwaysA. The routes nerve impulses travel are called pathways, the simplest of which is a reflex arc.B. Reflex Arcs 1. A reflex arc includes a sensory receptor, a sensory neuron, an interneuron in the spinal cord, a motor neuron, and an effector.


9 - 62

• http://www.sumanasinc.com/webcontent/animations/content/reflexarcs.html

9 - 63

C. Reflex Behavior 1. Reflexes are automatic, subconscious responses to stimuli that help maintain homeostasis (heart rate, blood pressure, etc.) and carry out automatic responses (vomiting, sneezing, swallowing, etc.).


9 - 64

2. The knee-jerk reflex (patellar tendon reflex) is an example

of a monosynaptic reflex (no interneuron).

3. The withdrawal reflex involves sensory neurons,

interneurons, and motor neurons.

a. At the same time, the antagonistic extensor muscles are inhibited.


9 - 65


9 - 66

Meninges A. The brain and spinal cord are

surrounded by membranes called meninges that lie between the bone and the soft tissues.


9 - 67


9 - 68

B. The outermost meninx is made up of tough, white dense connective tissue, contains many blood vessels, and is called the dura mater.1. It forms the inner periosteum of the skull bones.2. In some areas, the dura mater forms partitions between lobes of the brain, and in others, it forms dural sinuses.3. The sheath around the spinal cord is separated from the vertebrae by an epidural space.


9 - 69

C. The middle meninx, the arachnoid mater, is thin and lacks blood vessels.

1. It does not follow the convolutions of the

brain.2. Between the arachnoid and

pia maters is a subarachnoid space containing cerebrospinal fluid.


9 - 70

D. The innermost pia mater is thin and contains many blood vessels and nerves.

1. It is attached to the surface of the brain and spinal cord and follows their contours.


9 - 71

9 - 72

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.


9 - 73


9 - 74

B. Structure of the Spinal Cord 1. The spinal cord consists of

31 segments, each of which gives rise to a pair of spinal nerves.

2. A cervical enlargement gives rise to nerves leading to the upper limbs, and a lumbar enlargement gives rise to those innervating the lower limbs.


9 - 75

3. Two deep longitudinal grooves (anterior median fissure and posterior median sulcus)

divide the cord into right and left halves.

4. White matter, made up of bundles of myelinated nerve fibers (nerve tracts), surrounds a butterfly-shaped

core of gray matter housing interneurons.

5. A central canal contains cerebrospinal fluid.


9 - 76

Cerebrospinal Fluid

77

•Cerebrospinal fluid is a fluid that circulates throughout the CNS. •located between the brain and skull and in the subarachnoid space of the spinal cord

78

•Cerebrospinal fluid has 2 important benefits to the central nervous system:

1. Circulation • delivers nutrients to the structures of the

nervous system • the cerebrospinal fluid removes wastes from

the brain and spinal cord, detoxifying the environment of the nervous system

2. Shock absorption • protects the brain and spinal cord from

trauma/injury caused by movement, falls, blows, etc.

79

Spinal Tap

•a procedure to collect cerebrospinal fluid to check for the presence of disease or injury

Reasons for doing a spinal tap… to diagnose various conditions in the

Nervous system, including:•viral and bacterial infections, such as meningitis and encephalitis•tumors or cancers of the nervous system •syphilis, a sexually transmitted disease • bleeding (hemorrhaging) around the brain and spinal cord • multiple sclerosis, a disease that affects the myelin coating of the nerve fibers of the brain and spinal cord • Guillain-Barré syndrome, an inflammation of the nerves

80

.

9 - 81

Anatomy of the Spine

Region Spinal Segment

Vertebral Bodies

Nerves

Neck Cervical C1-C7 C1-C8

Upper and mid-back

Thoracic T1-T12 T1-T12

Low back Lumbar L1-L5 L1-L5

Tail Sacral S1-S5 (fused)

S1-S5

9 - 83

C. Functions of the Spinal Cord 1. The spinal cord has two

major functions: to transmit impulses to and

from the brain, and to house spinal reflexes.

2. Tracts carrying sensory information to the brain are

called ascending tracts; descending tracts carry

motor information from the brain.


9 - 84

3. The names that identify tracts are based on

the origin and the termination of the fibers in the tract.

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


9 - 85

Spinal Nerves• 31 pairs – contain thousands of nerve

fibers• Connect to the spinal cord• Named for point of issue from the spinal

cord– 8 pairs of cervical nerves (C1-C8)

– 12 pairs of thoracic nerves (T1-T12)

– 5 pairs of lumbar nerves (L1-L5)

– 5 pairs of sacral nerves (S1-S5)

– 1 pair of coccygeal nerves (Co1)

9 - 86

Spinal Nerves Posterior View

Figure 14.9

9 - 87

Structural Organization of PNS in Region of a Spinal Nerve

Figure 14.2

9 - 88

Innervation of the Skin: Dermatomes

• Dermatome – an area of skin – Innervated by cutaneous branches of

a single spinal nerve

• Upper limb – skin is supplied by nerves of the brachial plexus

• Lower limb – Lumbar nerves – anterior surface– Sacral nerves – posterior surface

9 - 89

Dermatomes:

– TrigeminalTrigeminal– CervicalCervical– ThoracicThoracic– LumbarLumbar– SacralSacral

9 - 90

Map of Dermatomes – Anterior View

Figure 14.17a

9 - 91

Map of Dermatomes – Posterior View

Figure 14.17b

9 - 92

Spinal cord Injuries

9 - 93

Spinal Cord Injury Epidemiology

• Age at injury increasing– Mean 32 years– More people 60 years+ at time of injury

• 80% male• Etiology

– 34% MVC, 19% falls, 17% GSW, 7% diving– MVC #1 cause if <45 years– Falls #1 cause if >45 years

9 - 94

9 - 95

The extent of the impairment is determined by the location of the injury

9 - 96

Spinal Cord Injury Epidemiology

• Neurologic level and completeness (ASIA)– Cervical 50.7%– Thoracic 35.1%– Lumbosacral 11%

• C5 > C4 > C6 > T12 > C7 > L1

9 - 97

Types of Spinal Cord Paralysis• Depending on the location and the extent of

the injury different forms of paralysis can occur.

• Monoplegia- paralysis of one limb• Diplegia- paralysis of both upper or lower

limbs• Paraplegia- paralysis of both lower limbs• Hemiplegia- paralysis of upper limb, torso

and lower leg on one side of the body• Quadraplegia- paralysis of all four limbs

9 - 98

Spinal Cord Paralysis LevelsC1-C3 • All daily functions must be totally assisted• Breathing is dependant on a ventilator• Motorised wheelchair controlled by sip and puff or chin

movements is requiredC4• Same as C1-C3 except breathing can be done without a

ventilatorC5• Good head, neck, shoulder movements, as well as elbow flexion• Electric wheelchair, or manual for short distancesC6• Wrist extension movements are good• Assistance needed for dressing, and transitions from bed to

chair and car may also need assistanceC7-C8• All hand movements• Ability to dress, eat, drive, do transfers, and do upper body

washes

9 - 99

Spinal Cord Paralysis LevelsT1-T4 (paraplegia)• Normal communication skills• Help may only be needed for heavy household

work or loading wheelchair into carT5-T9• Manual wheelchair for everyday living• Independent for personal careT10-L1• Partial paralysis of lower bodyL2-S5• Some knee, hip and foot movements with

possible slow difficult walking with assistance or aids

• Only heavy home maintenance and hard cleaning will need assistance

9 - 100

Complete and IncompleteSpinal Cord Syndromes can be classified into

either complete or incomplete categories• Complete – characterized as complete loss

of motor and sensory function below the level of the traumatic lesion

• Incomplete – characterized by variable neurological findings with partial loss of sensory and/or motor function below the lesion

9 - 101

Spina Bifida

• A birth defect that results in incomplete development of the spinal cord or its coverings

• In mild cases it often goes undetected.

•

9 - 102

• In more severe cases this can result in the spinal cord and its covering membranes protruding out of an affected infant's back

• Depending on severity, varying degrees of paralysis and incontinence

• Treatment can be surgical

• http://www.youtube.com/watch?v=DF04XPBj5uc&NR=1

9 - 104


9 - 105

Brain A. The brain is the largest, most complex

portion of the nervous system, containing about 100 billion multipolar neurons.

B. The brain can be divided into the cerebrum (largest portion and associated

with higher mental functions), the diencephalon (processes sensory input), the cerebellum (coordinates muscular

activity), and the brain stem (coordinates and regulates visceral activities).


9 - 106

C. Structure of the Cerebrum1. The cerebrum is the largest portion

of the mature brain, consisting of two cerebral hemispheres.

2. A deep ridge of nerve fibers called the corpus callosum connects the hemispheres.3. The surface of the brain is marked by convolutions, sulci, and fissures.


9 - 107

4. The lobes of the brain are named according to the bones they underlie and include the

frontal lobe, parietal lobe, temporal lobe, occipital lobe,

and insula.5. A thin layer of gray matter,

the cerebral cortex, lies on the outside of the cerebrum and

contains 75% of the cell bodies in the nervous system.


9 - 108


9 - 109

6. Beneath the cortex lies a mass of white matter made up of myelinated nerve fibers

connecting the cell bodies of the cortex with the rest of the

nervous system.


9 - 110

D. Functions of the Cerebrum1. The cerebrum provides

higher brain functions, such as interpretation of sensory input, initiating voluntary muscular movements, memory, and integrating information for reasoning.


9 - 111

2. Functional Regions of the Cerebral Cortex a. The functional areas of the brain

overlap, but the cortex can generally be divided into

motor, sensory, and association areas.

b. The primary motor areas lie in the frontal lobes, anterior to the

central sulcus and in its anterior wall.


9 - 112

c. Broca's area, anterior to the primary motor cortex, coordinates muscular

activity to make speech possible.d. Above Broca's area is the frontal

eye field that controls the voluntary movements of the eyes and eyelids.

e. The sensory areas are located in several areas of the cerebrum and

interpret sensory input, producing feelings or sensations.


9 - 113

f. Sensory areas for sight lie within the occipital lobe.

g. Sensory and motor fibers alike cross over in the spinal cord or brain stem so centers in the right hemisphere are interpreting or controlling the left side of the body, and vice versa.


9 - 114

h. The various association areas of the brain analyze and interpret sensory impulses and function in reasoning, judgment, emotions, verbalizing

ideas, and storing memory.


9 - 115

i. Association areas of the frontal lobe control a number of higher

intellectual processes. j. A general interpretive area is

found at the junction of the parietal, temporal, and occipital lobes, and plays the primary role in complex thought processing.


9 - 116

3. Hemisphere Dominancea. Both cerebral hemispheres function

in receiving and analyzing sensory input and sending motor impulses

to the opposite side of the body.b. Most people exhibit hemisphere

dominance for the language-related activities of speech, writing, and reading.

http://www.web-us.com/BRAIN/braindominance.htm


9 - 117

c. The left hemisphere is dominant in 90% of the population, although some individuals have the right hemisphere as dominant, and others show equal dominance in

both hemispheres.d. The non-dominant hemisphere

specializes in nonverbal functions and controls emotions and intuitive thinking.


9 - 118

e. The basal ganglia are masses of gray matter located deep within the cerebral hemispheres that relay motor impulses from the cerebrum

and help to control motor activities by producing inhibitory

dopamine.


9 - 119

E. Ventricles and Cerebrospinal Fluid 1. The ventricles are a series of connected cavities within the cerebral hemispheres and brain stem.2. The ventricles are continuous with the central canal of the spinal cord, and are filled with cerebrospinal fluid.


9 - 120


9 - 121

3. Choroid plexuses, specialized capillaries from the pia mater,

secrete cerebrospinal fluid.

a. Most cerebrospinal fluid arises in the lateral ventricles.

4. Cerebrospinal fluid has nutritive as well as protective (cushioning)

functions.


9 - 122

F. Diencephalon1. The diencephalon lies above

the brain stem and contains the thalamus and

hypothalamus.2. Other portions of the

diencephalon are the optic tracts and optic chiasma, the

infundibulum (attachment for the pituitary), the posterior pituitary, mammillary bodies, and

the pineal gland.


9 - 123

3. The thalamus functions in sorting and directing

sensory information arriving from other parts of the nervous system, performing the services of both messenger

and editor.


9 - 124

4. The hypothalamus maintains homeostasis by regulating a wide variety of visceral activities and by linking the endocrine system with the nervous system.

a. The hypothalamus regulates heart rate and arterial

blood pressure, body temperature, water and electrolyte balance, hunger

and body weight, movements and secretions of the digestive

tract, growth and reproduction, and sleep and wakefulness.


9 - 125

5. The limbic system, in the area of the diencephalon, controls emotional experience and expression.a. By generating pleasant or unpleasant feelings about experiences, the limbic system guides behavior that may enhance the chance of survival.


9 - 126

G. Brain Stem 1. The brain stem,

consisting of the midbrain, pons, and medulla oblongata, lies at the base of the cerebrum, and

connects the brain to the spinal cord.


9 - 127

2. Midbraina. The midbrain, located

between the diencephalon and pons, contains bundles of myelinated nerve fibers that convey impulses to and from

higher parts of the brain, and masses of gray matter that serve as reflex centers.

b. The midbrain contains centers for auditory and visual reflexes.


9 - 128

3. Pons a. The pons, lying between

the midbrain and medulla oblongata, transmits

impulses between the brain and spinal cord, and contains centers that regulate the rate and depth of breathing.


9 - 129

4. Medulla Oblongata a. The medulla oblongata

transmits all ascending and descending impulses between

the brain and spinal cord.


9 - 130

b. The medulla oblongata also houses nuclei that

control visceral functions, including the cardiac center that controls heart rate, the

vasomotor center for blood pressure control, and the respiratory center that works, along with the pons, to control the rate and depth of breathing.


9 - 131

c. Other nuclei in the medulla oblongata are associated with coughing, sneezing, swallowing, and vomiting.


9 - 132

5. 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.


9 - 133

b. Decreased activity in the reticular formation

results in sleep; increased activity results in wakefulness.

c. The reticular formation filters incoming sensory impulses.


9 - 134

H. Cerebellum 1. The cerebellum is made up

of two hemispheres connected by a vermis.

2. A thin layer of gray matter called the cerebellar

cortex lies outside a core of white matter.


9 - 135


9 - 136

3. The cerebellum communicates with

other parts of the central nervous system through cerebellar peduncles.

4. The cerebellum functions to integrate sensory

information about the position of body parts and coordinates skeletal muscle activity and maintains posture.


9 - 137

Peripheral Nervous SystemA. The peripheral nervous system

(PNS) consists of the cranial and spinal nerves that come from the central nervous system and travel to the remainder of the body.

B. The PNS is made up of the somatic nervous system that oversees voluntary activities, and the

autonomic nervous system that controls involuntary activities.


9 - 138

C. Cranial Nerves1. There are twelve pairs of cranial nerves that arise from the underside of the brain, most of which are mixed nerves.2. The 12 pairs are designated by number and name and include the olfactory, optic, oculomotor, trochlear, trigenimal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, and hypoglossal nerves.


9 - 139


9 - 140

3. Refer to Figure 9.31 and Table 9.6 for cranial nerve number, name, type, and function.


9 - 141

D. Spinal Nerves1. There are Thirty-one pairs of

mixed nerves make up the spinal nerves.

2. Spinal nerves are grouped according to the level from which they

arise and are numbered in sequence, beginning with those in the cervical region.

3. Each spinal nerve arises from two roots: a dorsal, or sensory,

root, and a ventral, or motor, root.


9 - 142


9 - 143

4. The main branches of some spinal nerves form plexuses.

5. Cervical Plexusesa. The cervical plexuses lie on either side of the neck

and supply muscles and skin of the neck.

6. Brachial Plexusesa. The brachial plexuses arise from lower cervical and

upper thoracic nerves and lead to the upper limbs.


9 - 144

7. Lumbrosacral Plexusesa. The lumbrosacral

plexuses arise from the lower spinal cord and lead to the lower abdomen, external

genitalia, buttocks, and legs.


Peripheral Nervous System

Skeletal(Somatic)

Sympathetic Parasympathetic

Autonomic

Peripheral Nervous System

Skeletal (Somatic) System• Nerves to/from

spinal cord– control muscle

movements– somatosensory

inputs

• Both Voluntary and reflex movements

• Skeletal Reflexes– simplest is spinal

reflex arcMuscle

MotorNeuron

Interneuron

Skin receptors

SensoryNeuron

Brain

9 - 147

Autonomic Nervous SystemA. The autonomic nervous

system has the task of maintaining homeostasis of visceral activities without

conscious effort.


9 - 148

B. General Characteristics1. The autonomic nervous system includes two divisions: the sympathetic and parasympathetic divisions, which exert opposing effects on target organs.a. The parasympathetic division operates under normal conditions.b. The sympathetic division operates under conditions of stress or emergency.


Sympathetic• “ Fight or flight” response• Release adrenaline and

noradrenaline • Increases heart rate and

blood pressure• Increases blood flow to

skeletal muscles• Inhibits digestive

functions

CENTRAL NERVOUS SYSTEMBrain

Spinalcord

SYMPATHETIC

Dilates pupil

Stimulates salivation

Relaxes bronchi

Accelerates heartbeat

Inhibits activity

Stimulates glucose

Secretion of adrenaline,nonadrenaline

Relaxes bladder

Stimulates ejaculationin male

Sympatheticganglia

Salivaryglands

Lungs

Heart

Stomach

Pancreas

Liver

Adrenalgland

Kidney

9 - 150

C. Autonomic Nerve Fibers 1. In the autonomic motor

system, motor pathways include two fibers: a preganglionic fiber that leaves the CNS, and a postganglionic fiber that controls the effector.


9 - 151

2. Sympathetic Divisiona. Fibers in the sympathetic division arise from the thoracic

and lumbar regions of the spinal cord, and

synapse in paravertebral ganglia close to the vertebral column.

b. Postganglionic axons lead to an effector

organ.


9 - 152


9 - 153

3. Parasympathetic Divisiona. Fibers in the parasympathetic division arise from the brainstem

and sacral region of the spinal cord, and synapse

in ganglia close to the effector organ.


9 - 154


9 - 155

4. Autonomic Neurotransmitters a. Preganglionic fibers of

both sympathetic and parasympathetic divisions release acetylcholine.b. Parasympathetic postganglionic fibers are

cholinergic fibers and release acetylcholine.


9 - 156

c. Sympathetic postganglionic fibers are adrenergic and

release norepinephrine.d. The effects of these two divisions, based on the

effects of releasing different neurotransmitters to the

effector, are generally antagonistic.


9 - 157

5. Control of Autonomic Activitya. The autonomic nervous

system is largely controlled by reflex centers

in the brain and spinal cord.b. The limbic system and cerebral cortex alter the

reactions of the autonomic nervous system through

emotional influence.


Parasympathetic

• “ Rest and digest ” system

• Calms body to conserve and maintain energy

• Lowers heartbeat, breathing rate, blood pressure

CENTRAL NERVOUS SYSTEMBrain

PARASYMPATHETIC

Spinalcord

Stimulates salivation

Constricts bronchi

Slows heartbeat

Stimulates activity

Contracts bladder

Stimulates erectionof sex organs

Stimulates gallbladder

Gallbladder

Contracts pupil

Summary of autonomic differencesAutonomic nervous system controls physiological arousal

Sympatheticdivision (arousing)

Parasympatheticdivision (calming)

Pupils dilate EYES Pupils contract

Decreases SALVATION Increases

Perspires SKIN Dries

Increases RESPIRATION Decreases

Accelerates HEART Slows

Inhibits DIGESTION Activates

Secrete stresshormones

ADRENALGLANDS

Decrease secretionof stress hormones

9 - 1 copyright the mcgraw-hill companies, inc. permission required for reproduction or display....

Documents

nervous system copyrightthe

somatic nervous system

peripheral nervous system

central nervous system

unconscious autonomic

bacterial cells

small cells

microglial cells