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Chapter 11
Nervous System II
PROTECTION OF THE CNS
The brain and spinal cord are
protected (surrounded) by bones,
membranes, and fluid.
Meningies
• membranes surrounding and protecting CNS
• three layers
– dura mater – outer, tough
• DM splits into two layers where it encloses the dural sinuses (that
collect venous blood from the brain)
– arachnoid mater – thin, weblike
• Beneath the arachnoid mater lies a wide space called the subarachnoid space
• This space is filled with cerebrospinal fluid (CSF) and serves as
a cushion for the brain
– pia mater – inner, very thin
• dips into grooves & contours
• The space between the dura mater and the bone is
called the epidural space and is filled with loose CT
and fat
• CSF fills the subarachnoid space and central canal
Ventricles of the Brian
• (interconnected cavities) within the cerebral
hemispheres and brain stem
• The Ventricles:
– are continuous with central canal of spinal cord
– are filled with cerebrospinal fluid (CSF)
– are lined by ependymal cells
• neuroglial cell in CNS
Cerebrospinal Fluid
• secreted by choroid plexus
• circulates in ventricles, central canal of
spinal cord, and subarachnoid space
• completely surrounds brain and spinal
cord
• clear liquid
• provides nutrition and protection
• helps maintain stable ion concentrations
in CNS
THE 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
Structure of the Spinal Cord
• Length = about 17 inches
– Start = foramen magnum
– End = tapers to point
(conus medullaris) and
terminates near the
intervertebral disc that
separates the 1st - 2nd
lumbar (L1-L2) vertebra
• Contains 31 segments
(and therefore gives rise
to 31 pairs of spinal
nerves)
• Note cervical and lumbar
enlargements
Structure of the Spinal Cord cont.
• 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)
• filum terminale that
represents distal portion
of the tail (pia mater)
– No actual nerve tissue
• A cross-section of the
spinal cord resembles a
butterfly with its wings
outspread (gray matter)
surrounded by white
matter
Functions of the Spinal Cord
• Nerve Pathway = the route traveled by a
nerve impulse through the nervous system
• Reflex arc = the simplest demonstration of a
nerve pathway (spinal reflexes)
– involves 2-3 neurons
– involuntary response
– often does not involve the brain
• Examples include:
– knee-jerk or patellar reflex
Spinal Nerves
• Spinal nerves extend to/from the spinal
cord and are part of the PNS
• Ganglion = a bundle of cell bodies outside
the CNS
• Dorsal Root Ganglion contains the cell
bodies of sensory (afferent) neurons
bringing impulses to the CNS
• The fusion of the dorsal and ventral roots
designates the beginning of the spinal
nerve which then passes through its
intervertebral foramen
Ascending and Descending Tracts
• The white matter of the
spinal cord represents the
location of our major nerve
pathways called "nerve
tracts"
• provide a 2-way system of
communication:
• ascending tracts conduct
sensory (afferent)
impulses from body parts
to brain
• descending tracts
conduct motor (efferent)
impulses from brain to
effectors
• All pathways are paired
(right and left)
BRAIN
The brain is the largest and most complex
portion of the nervous system.
Introduction
• 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 5 major portions
– cerebrum, cerebellum, diencephalon, basal
nuclei and brain stem
Structure of the Cerebrum
• Cerebrum = the largest portion of the brain,
which is divided into two cerebral
hemispheres.
– Hemispheres are connected by a deep bridge of
nerve fibers called the corpus callosum
– Surface ridges are called convolutions (gyri)
– Convolutions are separated by two types of
grooves. (Sulci and Fissures)
– Each hemisphere is divided into lobes, which are
named for the bones that cover them including
frontal, parietal, temporal, and occipital lobes
Structure/Function of the Cerebrum
• Composition:
– Bulk of cerebrum is white matter.
– bundles of myelinated nerve fibers (by
oligodendrocyte)
• Cerebral cortex or the outer portion of
cerebrum is composed of gray matter
– bundles of neuron cell bodies
– contains 75% of all neurons in nervous system
• Functional Regions of the Cerebral cortex
– Responsible for all conscious behavior by
containing three kinds of functional areas, which
include motor, sensory and association areas
Sensory Areas
• Sensory Areas are concerned with conscious
awareness of sensations and are located in
the parietal, occipital, and temporal cortex
• The include the
– Cutaneous Sensory Area
– Visual Area
– Auditory Area
– Sensory Area for Taste
– Sensory Area for Smell
Association Areas
• regions that are not primary motor or
primary sensory areas
• widespread throughout the cerebral
cortex
• Association traits include:
– analyzing & interpreting sensory experiences
– help provide memory, reasoning, verbalizing,
judgment and emotions
Hemisphere Dominance
• The left hemisphere is dominant is most
individuals
• Dominant hemisphere
controls
• speech
• writing
• reading
• verbal skills
• analytical skills
• computational skills
• Nondominant hemisphere
controls
• nonverbal tasks
• motor tasks
• understanding and
interpreting musical and
visual patterns
• provides emotional and
intuitive thought
processes
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
• Two types of memory:
– Short Term: working memory
– Long Term: changes structure or function of neurons
Motor Areas
Motor Areas are located in the frontal cortex:
• Primary motor cortex
– initiates all voluntary muscle movements
• Broca's area
– motor speech area
• Frontal Eye Field
– controls voluntary movements of eyes and
eyelids
Basal Nuclei
• masses of gray matter located deep within
the white matter of the cerebral hemispheres
• Release dopamine, which inhibits excess
movements
• control certain muscular activities
– primarily by inhibiting motor functions
• caudate nucleus, putamen, globus pallidus
Diencephalon
• includes two important areas of gray matter:
• Thalamus
– gateway for sensory impulses heading to cerebral
cortex
– receives all sensory impulses (except smell)
– channels impulses to appropriate part of cerebral
cortex for interpretation
• Hypothalamus
– maintains homeostasis by regulating visceral
activities
– links nervous and endocrine systems
Limbic System
• Limbic System = involved in Emotional
response
• interprets sensory impulses
• includes structures in the frontal and temporal
cortex, basal nuclei, thalamus, hypothalamus,
and deep nuclei
• controls emotional experience and expression
• produces feelings
• recognizes life threatening upsets in a person's
physical or psychological condition and counters
them
Brain Stem
• The brain stem is composed of three
major parts
– 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
Midbrain
• Corpora quadrigemina = 4 dome-like
protrusions on the dorsal midbrain surface
– centers for visual and auditory reflexes
• Cerebral peduncles – bundles of nerve fibers
• acts in reflex actions (visual and auditory)
• also contains areas associated with reticular
formation
• contains bundles of fibers that join lower parts of
brainstem and spinal cord with higher part of
brain
• cerebral aqueduct
Pons
• "bridge" or pathway of conduction tracts
• helps regulate rate and depth of breathing
• also contains areas associated with
reticular formation
• relays nerve impulses to and from
medulla oblongata and cerebellum
Medulla Oblongata
• conducts ascending and descending
impulses between brain and spinal cord
• contains an autonomic reflex center
involved in maintaining homeostasis of
important visceral organs
– contains cardiac, vasomotor, and respiratory
control centers
– contains various nonvital reflex control
centers (coughing, sneezing, swallowing,
vomiting)
Reticular Formation
• complex network of nerve
Types pf Sleep
fibers scattered throughout
• Slow wave (90min) overall
the brain stem
decrease in reticular
• controls brains alertness
formation activity
– inhibited = sleep, alcohol,
– person is tired
tranquilizers
– restful
• extends into the
– reduced blood pressure and
diencephalon
respiratory rate
• connects to centers of
• Rapid eye movement
hypothalamus, basal nuclei,
sleep (REM) certain areas
cerebellum, and cerebrum
of brain are active
• filters incoming sensory
– responsible for dreaming
information
– lasts 15 minutes
• arouses cerebral cortex into
– some areas of brain active
state of wakefulness
– heart and respiratory rates
irregular
Cerebellum
• note pattern of white matter (within gray matter)
= "arbor vitae"
• integrates sensory information concerning
position of body parts
• coordinates skeletal muscle activity
• maintains posture
PERIFERAL NERVOUS
SYSTEM
PSN Introduction
• The peripheral nervous system (PNS) consists of
nerves that extend to and from the CNS organs
• Cranial nerves arising from the brain
– Somatic fibers connecting to the skin and skeletal muscles
– Autonomic fibers connecting to viscera
• Spinal nerves arising from the spinal cord
– Somatic fibers connecting to the skin and skeletal muscles
– Autonomic fibers connecting to viscera
• The PNS is divided into a sensory and motor branch
• 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)
Structure Of Peripheral Nerves
• A nerve is a cord-like bundle of axons
wrapped in CT
• Structure of a Nerve:
• Three types of CT wrappings (similar to
muscle):
– endoneurium around each axon (and myelin)
– perineurium around each fascicle (bundle) of
axons
– epineurium around each nerve
Nerve Fiber Classification
• Mixed Nerves
– Nerves that carry impulses both to and from the CNS
– contain both sensory and motor axons
– most common; 2-way communication
• Sensory (afferent) Nerves
– Nerves that only carry sensory impulses toward the
CNS
– rare (only three pairs of cranial nerves)
• Motor (efferent) Nerves
– Nerves that only carry motor impulses away from
CNS
– rare (only five pairs of cranial nerves)
Nerve Fiber Classification cont.
• General somatic efferent
fibers
– carry motor impulses from CNS
to skeletal muscles
• General somatic afferent
fibers
– carry sensory impulses to CNS
from skin and skeletal muscles
• General visceral efferent
fibers
• Special somatic efferent
fibers
– carry motor impulses from
brain to muscles used in
chewing, swallowing, speaking,
and forming facial expressions
• Special visceral afferent
fibers
– carry sensory impulses to
brain from olfactory and taste
receptors
– carry motor impulses away from
• Special somatic afferent
CNS to smooth muscles and
glands
fibers
– carry sensory impulses to
• General visceral afferent
brain from receptors of sight,
fibers
hearing, and equilibrium
– carry sensory impulses to CNS
from blood vessels and internal
organs
Cranial Nerves
• 12 pairs
– 2 pairs to/from forebrain
– 10 pairs to/from brain stem
• 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.
Spinal Nerves
• Introduction
– 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
– Spinal nerves are associated with the spinal
cord and are named for the region of the
spinal cord from which they arise
Spinal Nerves cont.
• General
Characteristics:
• 31 pairs:
– 8 cervical nerves, 12
thoracic nerves, 5
lumbar nerves, 5
sacral nerves, 1
coccygeal nerve
• Composition = all
mixed nerves
Spinal Nerve cont.
• Dorsal root (posterior or sensory root)
– axons of sensory neurons in the dorsal root
ganglion
• Ventral root (anterior or motor root)
– axons of motor neurons whose cell bodies
are in spinal cord
• Spinal nerve
– union of ventral root and dorsal root
Dermatome
• an
area of
skin that the
sensory
nerve fibers
of a
particular
spinal nerve
innervate
Distribution of Spinal Nerves
• A short distance after
passing through its
intervertebral foramen,
a spinal nerve branches
into several branches:
– A posterior branch (dorsal
ramus)
– A large anterior branch
(i.e. ventral ramus)
– Branches to paravertebral
(autonomic) ganglia = rami
communicans
Nerve plexus
• Definition = a branching network (of the
anterior branches) of spinal nerves
– The nerves do not extend directly to the body
part they innervate, instead they form
networks.
• present in all spinal nerves except T2 T12:
– cervical plexus; neck muscles and diaphragm
(breathing)
– brachial plexus; upper limb
– lumbar plexus; anterior and medial thigh
– sacral plexus; posterior lower limb, leg
Nerve plexus cont.
• Each resulting branch of the plexus
contains the fibers from several spinal
nerves
• Fibers from each spinal nerve are carried
to the body periphery via several different
routes or branches.
• Therefore, damage to one spinal segment
cannot completely paralyze any limb
muscle
Intercostal Nerves
• Nerves T2-T11
run in intercostal
spaces
• Supply skin
(sensory) and
muscles (motor)
in the
surrounding
area
AUTONOMIC NERVOUS
SYSTEM (ANS)
Autonomic Nervous System
•functions without conscious effort
• controls visceral activities
• regulates smooth muscle, cardiac muscle, and
glands
• efferent fibers typically lead to ganglia outside
CNS
•Controlled largely by CNS
•Two Divisions
•sympathetic – prepares body for fight or flight
situations
•parasympathetic – prepares body for resting and
digesting activities
Sympathetic Division
• thoracolumbar
divison – location of
preganglionic neurons
•preganglionic fibers
leave spinal nerves
through white rami and
enter paravertebral
ganglia
•paraverterbral ganglia
and fibers that connect
them make up the
sympathetic trunk
Sympathetic Division cont.
• postganglionic
fibers extend from sympathetic
ganglia to visceral organs
• postganglionic fibers usually pass through gray
rami and return to a spinal nerve before
proceeding to an effector
Parasympathetic Division
division – location of
preganglionic neurons
•ganglia are near or within various organs
terminal ganglia
•short postganglionic fibers
• craniosacral
•continue to specific muscles or glands
•preganglionic fibers of the head are included in
nerves III, VII, and IX
•preganglionic fibers of thorax and abdomen are
parts of nerve X
Autonomic Neurotransmitters
•Cholinergic Fibers
• release acetylcholine
• preganglionic sympathetic and parasympathetic
fibers
• postganglionic parasympathetic fibers
•Adrenergic Fibers
•release norepinephrine
•most postganglionic sympathetic fibers