Download CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE

UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
LEARNING OUTCOMES:
11.1
Introduction
1.
11.2
Meninges
2.
11.3
11.5
11.6
Describe the coverings of the brain and spinal cord.
Ventricles and Cerebrospinal Fluid
3.
11.4
Describe the relationship among the brain, brainstem, and spinal cord.
Discuss the formation and function of cerebrospinal fluid.
Spinal Cord
4.
Describe the structure of the spinal cord and its major functions.
5.
Describe a reflex arc and reflex behavior.
Brain
6.
Describe the development of the major parts of the brain and explain the functions
of each part.
7.
Distinguish among sensory, association, and motor areas of the cerebral cortex.
8.
Discuss hemisphere dominance.
9.
Explain the stages in memory storage.
10.
Explain the functions of the limbic system and the reticular formation.
Peripheral Nervous System
11.
Distinguish between the major parts of the peripheral nervous system.
12.
Describe the structure of a peripheral nerve and how its fibers are classified.
13.
Identify the cranial nerves and list their major functions.
14.
Explain how spinal nerves are named and their functions.
1
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
LEARNING OUTCOMES:
11.7
11.8
Autonomic Nervous System
15.
Characterize the autonomic nervous system.
16.
Distinguish between the sympathetic and the parasympathetic divisions of the
autonomic nervous system.
17.
Compare sympathetic and parasympathetic nerve pathways.
18.
Explain how the autonomic neurotransmitters differently affect visceral effectors.
Life-Span Changes
19.
Describe aging-associated changes in the nervous system.
2
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.1
INTRODUCTION
A.
The central nervous system (CNS) organs include the brain and spinal cord.
1.
Brain
a.
largest most complex part of nervous system. It includes:
○
○
○
○
2.
b.
includes 100 billion multi-polar neurons
c.
oversees functions of the entire body
d.
provides characteristics like personality
Spinal Cord
a.
B.
two cerebral hemispheres
the diencephalon
the brain stem (attaches the brain to the spinal cord)
the cerebellum
provides two-way communication between the CNS and the
peripheral nervous system (PNS).
The CNS organs are protected (surrounded) by bones, membranes, and fluid.
1.
Bones
a.
b.
The brain is encased by eight skull bones (i.e. cranium; name the
eight bones).
The spinal cord is encased by 26 bones that make up the vertebral
column.
2.
Membranes (see 11.2 below)
3.
Fluid (see 11.3 below)
3
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.2
MENINGES
A.
The membranes around the brain and spinal cord are called "meninges".
Three distinct layers.
1.
Brain: See Figure 11.1, page 391.
a.
Dura mater ("white" in Fig 11.1):
o
outermost membrane that is attached to the inner
periosteum of the skull
o
tough, white fibrous CT
o
contains many blood vessels & nerves
o
Note: Dura mater splits into two layers where it encloses
the dural sinuses (that collect venous blood from the brain).
b.
Arachnoid Mater ("violet" in Fig 11.1):
o
middle layer
o
thin net-like membrane
o
beneath the arachnoid mater lies a wide space called the
sub-arachnoid space
This space is filled with cerebrospinal fluid (CSF) and
serves as a cushion for the brain.
2.
c.
Pia Mater ("salmon" in Fig 11.1):
o
inner layer that clings to brain surface
o
very thin delicate CT
o
many nerves & blood vessels = nourishment
o
dips into grooves & contours
*
See boxes on page 391 concerning subdural hematoma and
meningitis.
Spinal Cord: See Fig 11.2, page 392.
a.
Note that the dura mater is not attached to bone of the vertebra (as
in the brain where it is attached to the skull).
b.
The space between the dura mater and the bone is called the
epidural space and is filled with loose CT and fat.
c.
CSF fills the subarachnoid space and central canal.
4
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.3
VENTRICLES AND CEREBROSPINAL FLUID (CSF)
A.
In addition to filling the subarachnoid space, CSF fills the ventricles
(interconnected cavities) within the cerebral hemispheres and brain
stem. See Figure 11.3, page 393.
B.
The Ventricles:
1.
2.
3.
C.
Secretion and Circulation of CSF See Figure 11.4, page 394.
1.
2.
3.
4.
D.
CSF is secreted by specialized capillaries called choroid plexuses. The
CSF is secreted into the lateral ventricles (ventricles 1 & 2).
CSF circulates down into the 3rd & then 4th ventricle and then into
either:
a.
the central canal of spinal cord
b.
the subarachnoid space of meninges.
CSF is reabsorbed back into the bloodstream through arachnoid
granulations that project into dural sinuses.
CSF movement is aided by cilia of ependymal cells.
CSF
1.
2.
*
are continuous with central canal of spinal cord
are filled with cerebrospinal fluid (CSF)
are lined by ependymal cells (recall this neuroglial cell in CNS)
Total volume in above spaces = 150 mL.
a.
About 1 liter is secreted daily to replenish the circulating 150 ml
every 3-4 hours.
Functions:
a.
mechanical protection (i.e. cushion)
b.
chemical protection (i.e. ions, hormones, neurotransmitters)
See Clinical Application 11.1, page 395 concerning Cerebrospinal Fluid Pressure.
5
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.4
SPINAL CORD
The spinal cord is a nerve column that passes downward from brain into the vertebral
canal. Recall that it is part of the CNS. Spinal nerves extend to/from the spinal cord and
are part of the PNS.
A.
B.
Structure of the Spinal Cord: Longitudinal
See Fig 11.5, page 396.
1.
Length = about 17 inches.
a.
Start = foramen magnum
b.
End = tapers to point called the conus medullaris, and terminates
near the intervertebral disc that separates the 1st - 2nd lumbar (L1L2) vertebrae.
2.
contains 31 segments (and therefore gives rise to 31 pairs of spinal
nerves).
3.
Note cervical and lumbar enlargements.
4.
Note cauda equina (“horse’s tail”) in which the lower lumbar and sacral
nerves travel downward (i.e. lower spinal nerves must “chase” their points
of exit).
5.
Note filum terminale that represents distal portion of the tail (pia mater).
Structure of the Spinal Cord: Cross-Sectional: See Figure 11.6, page 397.
A cross-section of the spinal cord resembles a butterfly with its wings outspread
(gray matter) surrounded by white matter.
1.
Gray matter or "butterfly" = bundles of (interneuron) cell bodies:
a.
b.
c.
2.
posterior (dorsal) horns,
lateral horns, and
anterior (ventral) horns.
Note location of:
a.
b.
c.
d.
central canal (lined by ependymal cells),
gray commissure,
anterior median fissure,
posterior median sulcus.
6
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.4
SPINAL CORD
B.
Structure of the Spinal Cord: Cross-Sectional:
3.
White matter = myelinated (interneuron) axons:
a.
4.
Locations:
o
posterior (dorsal) funiculi or white columns,
o
lateral funiculi or white columns, and
o
anterior (ventral) funiculi or white columns.
Other Important Features:
a.
b.
c.
5.
See Figure 11.6, page 397.
ventral root
dorsal root
o
dorsal root ganglion (DRG).
1.
Ganglion = a bundle of cell bodies outside the CNS
(i.e. in the PNS).
2.
DRG contains the cell bodies of sensory (afferent)
neurons bringing impulses into the spinal
cord/CNS.
The fusion of the dorsal and ventral roots designates the beginning
of the spinal nerve, which then passes through its intervertebral
foramen.
Summary sketch:
7
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.4
SPINAL CORD
C.
Functions of the Spinal Cord
The functions of the spinal cord are two-fold. The spinal cord provides spinal
reflexes and serves as a conduit for nerve impulses to and from the brain.
1.
Spinal Reflexes
a.
b.
c.
occur in gray matter of spinal cord
Recall that is Nerve Pathway is the route traveled by a nerve
impulse through the nervous system.
A Reflex Arc is the simplest demonstration of a nerve pathway.
See Figure 11.7, page 398.
o
o
o
o
d.
involves 2-3 neurons
involuntary response
does not involve the brain
Examples include:
1.
knee-jerk or patellar reflex. Fig 11.8, page 399.
2.
withdrawal. Fig 11.9, page 399 and Fig 11.10, page
400.
3.
sneezing.
4.
blinking.
Components of a Reflex arc:
See Table 11.2, page 398.
o
o
o
o
o
e.
A sensory receptor, which reacts to a stimulus
A sensory neuron, that conducts the afferent (sensory)
impulses to the CNS
The integration center, consisting of one to several
synapses in the CNS
A motor neuron that conducts the efferent (motor) impulses
from the CNS to an effector
An effector, the muscle fibers or glands that respond to the
motor impulse by contracting a muscle.
Uses of Reflexes: See Clinical Application 11.2, page 400.
o
o
to insure proper transmission of an impulse from sensory
receptor through the nervous system and to the effector.
to prevent tissue damage.
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UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.4
SPINAL CORD
C.
Functions of the Spinal Cord
2.
Conduit for nerve impulse to and from the brain: Nerve Tracts
a.
Ascending and Descending Tracts
o
The white matter of the spinal cord represents the location
of our major nerve pathways called "nerve tracts".
o
o
b.
provide a 2-way system of communication:
See Figures 11.11-11.13, pages 401-402 and Table 11.3,
page 403.
o In general, ascending tracts are located in the posterior
(dorsal) columns and conduct sensory (afferent) impulses
from body parts up to the brain.
o In general, descending tracts are located in the anterior
(ventral) columns and conduct motor (efferent) impulses
from the brain down to effectors.

General characteristics of nerve tracts:
a.
Most cross over
b.
Most consist of 2-3 successive neurons
c.
Most exhibit somatotropy (i.e. tracts from/to
upper body are located on outside, tracts
from/to lower body on inside)
All pathways are paired (right and left).
Ascending Tracts
o
Fasciculus gracilis and fasciculus cuneatus
1.
Location = posterior column.
2.
Information carried = touch, pressure, movement.
o
Spinothalamic tracts
1.
Location:
o
lateral tract in lateral column
o
anterior tract in anterior column
2.
Information carried:
o
lateral tract = pain and temperature
o
anterior tract = touch and pressure
o
Spinocerebellar tracts
1.
Location:
o
anterior = anterior superficial lateral column
o
posterior = posterior superficial lateral
column
2.
Information carried = sensation of movement of
lower limbs.
9
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.4
SPINAL CORD
C.
Functions of the Spinal Cord
2.
Conduit for nerve impulse to and from the brain: Nerve Tracts
c.
*
*
*
11.5
Descending Tracts
o
Corticospinal tracts
1.
Location:
o
anterior tract in anterior column
o
lateral tract in lateral column
2.
Information carried = control of skeletal muscles
o
Reticulospinal tracts
1.
Location:
o
anterior tract in anterior column
o
lateral tract in lateral column
2.
Information carried = control muscle tone and sweat
glands.
o
Rubrospinal tracts
1.
Location = lateral deep column.
2.
Information carried = control of posture.
ALS – Amyotrophic Lateral Sclerosis. See box on page 403.
Hemi-lesion of the spinal cord. See box on page 403.
Spinal Cord Injuries. See Clinical Application 11.3, page 404.
BRAIN
The brain is the largest and most complex portion of the nervous system. It occupies the
cranial cavity and is composed of one hundred billion multipolar neurons. The brain
oversees the function of the entire body and also provides characteristics like personality.
The brain is composed of 4 major portions, including the cerebrum, cerebellum,
diencephalon, and brain stem.
See Figure 11.15, page 406.
A.
Brain Development
1.
Embryonic neural tube expands and hollows cranially.
*
See box on page 405 re: anencephaly.
2.
Three vesicles develop that split and become four adult ventricles.
3.
The walls of the three vesicles become certain adult brain areas
See Fig 11.14 and Table 11.4, page 405.
a.
Forebrain = Cerebrum, basal nuclei, and diencephalon
b.
Midbrain = Midbrain
c.
Hindbrain = pons, medulla oblongata, and cerebellum
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UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.5
BRAIN
B.
Structure of the Cerebrum
1.
Cerebrum = the largest portion of the brain, which is divided into two
cerebral hemispheres.
a.
Hemispheres are connected by a deep bridge of nerve fibers called
the corpus callosum.
b.
Surface ridges are called convolutions (gyri).
c.
Each hemisphere is divided into lobes, which are named for the
bones that cover them including frontal, parietal,
temporal, and occipital lobes.
See Fig 11.16, page 407.
d.
Convolutions are separated by two types of grooves:
o
o
e.
sulci = shallow groove
1.
central sulcus (frontal/parietal)
2.
lateral sulcus (temporal/others)
fissure = deep groove
1.
longitudinal fissure separates the two cerebral
hemispheres.
2.
transverse fissure (cerebrum/cerebellum)
Composition:
o
Bulk of cerebrum is white matter.
*
bundles of myelinated nerve fibers carrying
impulses from cortex toward spinal cord (by
oligodendrocytes)
o
Cerebral cortex or the outer portion of cerebrum is
composed of gray matter.
*
bundles of interneuron cell bodies.
o
Sketch:
11
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.5
BRAIN
C.
Functions of the Cerebrum
1.
Functional Regions of the Cortex. See Fig 11.17, page 408.
The cerebral cortex is responsible for all conscious behavior by
containing three kinds of functional areas, which include sensory,
association areas, and motor areas.
a.
Sensory Areas are concerned with conscious awareness of
sensations and are located in the parietal, occipital, and temporal
cortex.
o
Primary somatosensory cortex
1.
receives information from general receptors (i.e.
temperature, touch, pressure, and pain).
2.
located in postcentral gyrus of parietal cortex
o
Visual (Cortex) Area
1.
receives incoming information from photoreceptors
(in retina of eye).
2.
located in occipital cortex
o
Auditory (Cortex) Area
1.
receives incoming information from hearing
receptors (in ear).
2.
located in temporal cortex
o
Gustatory cortex (Not Pictured on page 408)
1.
receives incoming information from taste receptors
in taste buds of tongue.
2.
located in parietal cortex just above the temporal
lobe
b.
Association Areas of cerebral cortex
o
General:
1.
include areas that are not directly involved in motor
or sensory function
2.
are involved in many traits
3.
are usually interconnected
4.
involve all four lobes
o
Association traits:
1.
include analyzing and interpreting sensory
experiences
2.
help provide memory, reasoning, verbalizing,
judgment, and emotions
See Table 11.5, page 410, Functions of Cerebral Lobes.
See box on page 407 re: “stroke” or cerebrovascular accident
(CVA).
See box on page 409 re: dyslexia.
*
*
*
12
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.5

BRAIN
C.
Functions of the Cerebrum
1.
Functional Regions of the Cortex. See Fig 11.17, page 408 and Fig
11.18, page 409.
c.
Motor Areas are located in the frontal cortex:
o
Primary motor cortex
1.
initiates all voluntary muscle movements




2.
located in the gyrus just anterior to the central
sulcus (precentral gyrus)
o
Broca's area
1.
motor speech area
2.
located in left frontal lobe, above temporal lobe
*
See box on page 410 re: apraxia.
d.
Hemisphere Dominance (Brain Lateralization)
o
Most basic functions (sensory & motor) are equally
controlled by both left & right hemispheres (remember
communication exists through corpus callosum).
o
However, for some association functions, one hemisphere
has greater control over language-related activities
including speech, writing, reading, mathematics and logic.
1.
This hemisphere is considered the "dominant
hemisphere".
a.
In most people, the left hemisphere is
dominant.
b.
The other hemisphere (non-dominant)
controls orientation in space, art, musical
appreciation, and emotions.
*
See box on page 410 re: R/L handedness.
e.
Memory
Memory is the consequence of learning. Whereas learning is the
acquisition of new knowledge; memory is the persistence of that
learning, with the ability to access it at a later time.
o
Two types of memory:
See page 410-411.
1.
Short Term
2.
Long Term
*
See box on page 411 re: hippocampus, amygdala and
memory.
2.
Basal Nuclei
See Fig 11.19, page 411.
a.
masses of gray matter located deep within the white matter of the
cerebral hemispheres.
b.
serve as relay stations for outgoing motor impulses from the
brain.
(i.e. from primary motor cortex in frontal cortex to basal ganglia
and then through brain stem, down spinal cord, etc.)
c.
Release dopamine, which inhibits excess movements
*
See Clinical Application 11.5, page 412: Parkinson Disease.
13
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.5
BRAIN
D.
Diencephalon:
1.
includes two important areas of gray matter:
a.
Thalamus
o




See Fig 11.15, page 406 and Fig 11.21, page 414.
b.
central relay station for incoming sensory impulses (except
smell); directs sensory impulse to the appropriate area of
the cerebral cortex for interpretation.
Hypothalamus
o
main visceral control center of the body (i.e. regulates
homeostasis).
1.
2.
3.
4.
5.
6.
7.
2.








heart rate and arterial blood pressure
body temperature
water and electrolyte balance
control of hunger & body weight
control of digestive movements and secretions
regulation of sleep-wake cycles
control of endocrine system function
Limbic System = involved in emotional response.
a.
also includes structures in the frontal and temporal cortex, basal
nuclei, and deep nuclei
b.
controls emotional experience and expression
c.
can modify the way a person acts
d.
produces feelings of fear, anger, pleasure, and sorrow
e.
recognizes life threatening upsets in a person's physical or
psychological condition and counters them
f.
involved in sense of smell
14
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.5
BRAIN
E.
Brain Stem: See Fig 11.20 and Fig 11.21, page 414, and Fig 11.15, page 406.
The brain stem is composed of three major parts that include the midbrain,
pons, and medulla oblongata. The brain stem serves as a pathway for fiber
tracts running to (sensory impulses) and from (motor impulses) the cerebrum and
is the sight where many cranial nerves (PNS) arise.
1.
2.
3.
Midbrain
a.
located between diencephalon and pons
b.
Corpora quadrigemina = 4 dome-like protrusions on the dorsal
midbrain surface (you will see these in the sheep brain dissection
lab when you separate the cerebrum from cerebellum)
c.
gray matter within white matter
d.
acts in reflex actions (visual and auditory)
e.
also contains areas associated with reticular formation
Pons
a.
bulging portion of brain stem
b.
"bridge" or pathway of conduction tracts
c.
location of Pontine Respiratory Group (formerly called the
pneumotaxic area), which regulates breathing rate; i.e. part of
respiratory center
d.
also contains areas associated with reticular formation
Medulla (Oblongata)
a.
inferior portion of brain stem, which blends into the spinal cord at
its base
b.
contains an autonomic reflex center involved in maintaining
homeostasis of important visceral organs
o
Cardiac center adjusts force and rate of heart contraction.
o
Vasomotor center regulates blood pressure (bp) by acting
on smooth muscle in the walls of peripheral arterioles (i.e.
vasoconstriction = bp increase vasodilation = bp decrease).
o
Respiratory center = controls the depth and rhythm of
breathing.
o
Additional centers regulate involuntary activities such as
vomiting, hiccupping, swallowing, coughing, and sneezing.
15
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.5
BRAIN
E.
Brain Stem:
4.
Reticular Formation
o
controls brain alertness
o
at its lowest activity while sleeping
o
inhibited by alcohol, tranquilizers, etc.
*
5.
See box on page 415 re: persistent vegetative state.
Types of Sleep
a.
During slow wave (90 min), overall decrease occurs in reticular
formation activity
b.
During rapid eye movement (REM) sleep, certain areas of brain
are active
o
o
o
c.
F.
Cerebellum
responsible for dreaming
lasts about 15 minutes
alternates with slow wave
See Table 11.6, page 416 re: Sleep Disorders.
See Fig 11.22, page 416, and Fig 11.15, page 406.
1.
large, cauliflower-like structure located dorsally to the pons and medulla
and inferiorly to the occipital lobe of the cerebrum (separated by
transverse fissure)
2.
note pattern of white matter (within gray matter) = "arbor vitae" (Tree of
Life, in Latin)
3.
coordinates all voluntary muscle movements (subconsciously), skilled
movements, posture, and equilibrium (i.e. balance).
*
See Clinical Application 11.4, page 412 re: Traumatic Brain Injury.
*
Clinical Application 11.5, page 418 re: Brain Waves.
16
UNIT 3 - CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.5
BRAIN
G.
Brain Function Summary Table: See Table 11.7, page 417.
Brain Part
Specific Portion
Cerebrum
Primary Motor Cortex
Location/ Characteristics
Functions
Broca’s Area
Primary Somatosensory
Cortex
Visual Cortex
Auditory Cortex
Gustatory Cortex
Association Areas
Basal Nuclei
Diencephalon
Thalamus
Hypothalamus
Brain Stem
Midbrain
Pons
Medulla (Oblongata)
Cerebellum
17
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.6
PERIPHERAL NERVOUS SYSTEM (PNS)
A.
PNS INTRODUCTION
The peripheral nervous system (PNS) consists of nerves that extend to and from
the CNS organs. In other words, the PNS includes the cranial nerves and spinal
nerves. The PNS connects all body parts to the brain and/or spinal cord.
The PNS is divided into a sensory and motor branches; the motor branch of the
PNS is further subdivided into a somatic nervous system (from CNS to skin and
skeletal muscles) and autonomic nervous system (from CNS to smooth muscle,
cardiac muscle, and endocrine glands).
B.
Structure of Peripheral Nerves
See Fig 11.23 and Fig 11.24, page 419.
1.
A nerve is a cord-like bundle of axons wrapped in CT.
2.
Structure of a Nerve:
a.
C.
Three types of CT wrappings (similar to muscle):
i.
endoneurium around each axon (and its myelin sheath)
ii.
perineurium around each fascicle (bundle) of axons
iii.
epineurium around each nerve.
Nerve and Nerve Fiber Classification
1.
Sensory (afferent) Nerves
a.
b.
c.
2.
Motor (efferent) Nerves
a.
b.
c.
3.
nerves that only carry sensory impulses toward the CNS
composed of only sensory axons
rare (only three pairs of cranial nerves)
nerves that only carry motor impulses away from CNS
composed of only motor axons
rare (only five pairs of cranial nerves)
Mixed Nerves
a.
b.
c.
d.
nerves that carry impulses both to and from the CNS
contain both sensory and motor axons
most common 2-way communication
all spinal nerves and four pairs of cranial nerves
18
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.6
PERIPHERAL NERVOUS SYSTEM
C.
Nerve and Nerve Fiber Classification
4.
5.
Four Groups of General Nerves
a.
General Somatic Efferent Fibers
o
Motor to skeletal muscle
b.
General Visceral Efferent Fibers
o
Motor to smooth and cardiac muscle, and glands
c.
General Somatic Afferent Fibers
o
Sensory from skin and skeletal muscle
a.
General Visceral Afferent Fibers
o
Sensory from blood vessels and internal organs
Three Groups of Special Nerves
a.
Special Somatic Efferent Fibers
o Motor to skeletal muscle for chewing, swallowing, speech, and
facial expression
b.
Special Visceral Afferent Fibers
o Sensory for smell and taste
c.
Special Somatic Afferent Fibers
o Sensory for sight, hearing, and equilibrium
19
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.6
PERIPHERAL NERVOUS SYSTEM
D.
Cranial Nerves
See Fig 11.25, page 420 and Table 11.9, page 423.
1.
12 pairs
a.
2 pairs to/from forebrain,
b.
10 pairs to/from brain stem
2.
designated by Roman numerals:
3.
I.
Olfactory = sense of smell; sensory only.
II.
Optic = sense of vision; sensory only.
III.
Oculomotor = innervates eye muscles; motor only.
IV.
Trochlear = innervates eye muscles; motor only.
V.
Trigeminal = largest sensory from face; motor to chewing muscles;
mixed. See Fig 11.26, page 421.
*
See box on page 421 concerning trigeminal neuralgia.
VI.
Abducens = innervates eye muscles; motor only.
VII.
Facial = innervates muscles of facial expression and sensory taste;
mixed. See Fig 11.27, page 422.
VIII.
Vestibulocochlear = sense of hearing and equilibrium; sensory only.
IX.
Glossopharyngeal = moves tongue and pharynx muscles and sensory
taste; mixed.
X.
Vagus = innervates visceral smooth muscle and sensations from those
organs; mixed. See Fig 11.28, page 422.
XI.
Accessory = innervates neck muscles; motor only.
XII.
Hypoglossal = moves tongue; motor only.
Memorize by using one of many mnemonic devices:
One example is: "Oh, Oh, Oh, To Touch And Feel Very Good Velvet AH!"
See www.medicalmnemonics.com for more.
20
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.6
PERIPHERAL NERVOUS SYSTEM
D.
Numeral
Cranial Nerves
4.
Summary Table: See Table 11.9, page 423 and key at the end of this
outline)
Name
Function
Sensory, Motor, or
Mixed Nerve
21
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.6
PERIPHERAL NERVOUS SYSTEM
E.
Spinal Nerves:
1.
2.
Introduction
a.
Recall that a spinal nerve is formed from the fusion of a dorsal and
ventral root. Then the spinal nerve passes through its intervertebral
foramen.
b.
Spinal nerves are associated with the spinal cord and are named for
the region of the spinal cord from which they arise.
General Characteristics:
a.
31 pairs:
i.
ii.
iii.
iv.
v.
b.
3.
See Figure 11.29, page 424.
C1 - C8
T1 - T12
L1 - L5
S1 - S5
Co
Composition = all mixed nerves.
Distribution of Spinal Nerves
A short distance after passing through its intervertebral foramen, a
spinal nerve branches into several branches:
See Fig 11.31, page 426.
a.
A posterior branch (dorsal ramus)
b.
A large anterior branch (ventral ramus)
c.
Branches to paravertebral
communicans
(autonomic)
ganglia
=
rami
22
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.6
PERIPHERAL NERVOUS SYSTEM
E.
Spinal Nerves:
4.
Nerve plexus
a.
Definition = a branching network (of the anterior branches or
ventral rami) of spinal nerves.
i.
b.
See Figure 11.32, page 427.
The nerves do not extend directly to the body part they
innervate; instead they form networks.
present in all spinal nerves except T2 - T12:
i.
Cervical Plexuses: neck muscles and diaphragm (breathing)
ii.
Brachial Plexuses: upper limbs
See Figure 11.33, page 428.
iii.
Lumbosacral Plexuses: anterior and medial thighs and
posterior lower limbs
See Figure 11.34, page 429.
c.
Each resulting branch of the plexus contains the fibers from several
spinal nerves.
d.
Fibers from each spinal nerve are carried to the body’s periphery
via several different routes or branches.
Therefore, damage to one spinal segment cannot completely
paralyze any limb muscle.
See Clinical Application 11.6, page 430, Spinal Nerve Injuries.
5.
Intercostal Nerves
a.
b.
Nerves T2-T11 run in intercostal spaces.
supply skin (sensory) and muscles (motor) in the surrounding area
23
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.7
AUTONOMIC NERVOUS SYSTEM (ANS)
A.
General Characteristics
The Autonomic Nervous System (ANS) regulates the action of smooth muscles,
cardiac muscle, and some glands. In other words, the ANS regulates involuntary
(automatic unconscious) actions. There are two major divisions of the ANS. The
parasympathetic division functions under normal conditions (to maintain
homeostasis), and the sympathetic division of the ANS functions under stress.
B.
Autonomic Nerve Fibers: See Figure 11.35, page 431.
1.
2.
Somatic (Fig 11.35b):
a.
one motor neuron
b.
no ganglia
c.
NT = acetylcholine (ACh); excitatory.
d.
Effectors = skeletal muscles.
ANS (Fig 11.35a):
a.
two motor neurons
b.
synapse between neurons occur within a ganglion
o
Definition: A ganglion is a collection of neuron cell bodies
outside the CNS.
c.
Effectors = smooth muscle, cardiac muscle, and glands.
d.
Two Divisions:
1.
2.
Sympathetic
Parasympathetic
24
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.7
AUTONOMIC NERVOUS SYSTEM
C.
Sympathetic Division: See Figs 11.36-11.38, pages 431-432.
1.
2.
3.
D.
functions in “fight or flight” response
a.
postganglionic fiber secretes norepinephrine.
Ganglia are located on either side of the spinal cord (chain ganglia;
sympathetic trunk), and are far from their effector.
Pre-ganglionic neuron is short.
a.
arise from the Thoracolumbar regions (T1 - L2) of spinal cord.
b.
General Pathway is complex!!!! See Fig 11.37, page 432.
i.
preganglionic neuron from spinal cord
ii.
out through white ramus communicans to enter an
adjoining
iii.
paravertebral (chain) ganglion forming part of the
sympathetic trunk (chain).
c.
Once a preganglionic axon reaches a paravertebral ganglion, one
of three things can happen:
i.
It can synapse with a postganglionic neuron within the
same ganglion = synapse in a paravertebral chain
ganglion at same level. The postganglionic neuron passes
through the gray ramus communicans and out the ventral
ramus leading to its effector (blood vessel, skin).
ii.
It can ascend or descend within the sympathetic chain to
synapse in another paravertebral ganglion = synapse in a
paravertebral chain ganglion at a different level. The
postganglionic neuron passes through gray ramus
communicans.
iii.
It can pass through the ganglion to prevertebral
(collateral) ganglion (via Splanchnic Nerve). Therefore
synapse occurs within the prevertebral ganglion and the
postsynaptic neuron extends to effector (abdominal organ).
Parasympathetic Division: See Fig 11.39, page 434.
1.
functions to maintain homeostasis
a.
postganglionic fiber secretes acetylcholine
2.
Ganglia are located at or near the effector.
3.
Preganglionic neuron is long
a.
arise from the Craniosacral regions of the brain & spinal cord.
b.
follow simple pathway
c.
Preganglionic fibers follow blood vessels to ganglia in or near wall
of effector.
25
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.7
AUTONOMIC NERVOUS SYSTEM
E.
F.
Autonomic Neurotransmitters
1.
ACh is released by cholinergic fibers (axons)
2.
Norepinephrine is released by adrenergic fibers (axons).
Actions of Autonomic Neurotransmitters
A receptor is present in the cell membrane of an effector and recognizes its NT,
allowing for a response to occur within the effector.
1.
Cholinergic receptors bind ACh two types:
o
Nicotinic is always stimulatory.
o
Muscarinic may be stimulatory or inhibitory.
See Fig 11.40, page 435.
2.
3.
Adrenergic receptors bind norepinephrine two types:
o
Alpha (α) is usually stimulatory.
o
Beta (β) is usually inhibitory.
Effects of Autonomic Stimulation on Various Effectors:
See Table 11.10, page 436.
G.
Terminating of Autonomic Neurotransmitter Actions
1.
Destruction of Neurotransmitter:
a.
Acetylcholinesterase destroys ACh in the neuromuscular junction,
so it only has a momentary effect (a fraction of a second).
2.
Reuptake of Neurotransmitter:
a.
Much of the norepinephrine is transported back into the
postsynaptic fiber through active transport.
b.
The enzyme monoamine oxidase (in mitochondria) inactivates
epinephrine and norepinephrine after reuptake; however this
process takes several seconds.
c.
Some norepinephrine escapes decomposition.
d.
Norepinephrine response may last as long as 30 seconds.
*
See box on page 437 re: drugs like ephedrine that influence the ANS.
26
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.7
AUTONOMIC NERVOUS SYSTEM
H.
Control of Autonomic Activity
1.
Overall CNS controls ANS
a.
medulla oblongata controls visceral activities
o
o
o
I.
cardiac
heart rate and rhythm
vasomotor
blood pressure
respiratory functions
depth of breathing
b.
hypothalamus regulates visceral control including renal and
digestive
c.
limbic system controls physiology of emotions
ANS Summary Table (Keyed at the end of this outline)
Branch of ANS
PARASYMPATHETIC
SYMPATHETIC
General
Function
Origin of Preganglionic
fiber
Length of
Preganglionic fiber
Location of Ganglia
NT secreted by postganglionic
Fiber
27
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
11.8
LIFE-SPAN CHANGES
As the nervous system ages, cells are lost, which over time, lead to slowed functioning.
A.
B.
C.
D.
E.
Apoptosis of brain neurons begins before birth.
Neuron loss among brain regions is not uniform.
In adults, the number of cerebral cortex dendrites has declined, leading to slower
neurotransmission.
Risk of falling increases as balance decreases.
Sleep problems are common in the elderly.
CHAPTER SUMMARY – see pages 438-440.
CHAPTER ASSESSMENTS - see pages 440-441.
INTEGRATIVE ASSESSMENTS/CRITICAL THINKING - see page 442.
Key to ANS Summary Table
Branch of ANS
PARASYMPATHETIC
SYMPATHETIC
General
Function
maintain homeostasis
to survive stressful or “fight
or flight” situations
Origin of Preganglionic
fiber
from cranial region of brain or
sacral region of spinal cord
from thoracic or lumbar
region of spinal cord
Length of
Preganglionic fiber
Long
short
Location of Ganglia
at or near effector
alongside spinal cord;
paravertebral
NT secreted by postganglionic
Fiber
acetylcholine
norepinephrine
28
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
Summary Table for Cranial Nerves
Numeral
Name
Function
Sensory, Motor, or
Mixed Nerve
I
OLFACTORY
OLFACTION/SMELL
SENSORY
II
OPTIC
VISION
SENSORY
III
OCULOMOTOR
MOVE EYE
MOTOR
IV
TROCHLEAR
MOVE EYE
MOTOR
V
TRIGEMINAL
CHEWING/MASTICATION
AND SENSORY FROM
FACE
MIXED
VI
ABDUCENS
MOVE EYE
MOTOR
VII
FACIAL
FACIAL EXPRESSION;
TASTE
MIXED
VIII
VESTIBULOCOCHLEAR
HEARING AND
EQUILIBRIUM
SENSORY
IX
GLOSSOPHARYNGEAL
MOVE MUSCLES OF
TONGUE AND PHARYNX;
TASTE
MIXED
X
VAGUS
INNERVATE VISCERAL
SMOOTH MUSCLE;
SENSATIONS FROM SAME
MIXED
XI
ACCESSORY
MOVE NECK MUSCLES
MOTOR
XII
HYPOGLOSSAL
MOVE TONGUE
MOTOR
29