Download Brain and Spinal Cord

Chapter 10: Central Nervous
System, Spinal Nerves, and
Cranial Nerves
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Spinal Cord Protection and Coverings


Vertebrae
Spinal meninges

3 layers of connective tissue

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

Dura mater
Arachnoid mater
Pia mater
Continuous with cranial meninges
Cerebrospinal fluid (CSF)
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External Cord Anatomy


The spinal cord is located within the vertebral canal.
It is well protected. The vertebral ligaments,
meninges, and CSF
provide additional protection.
The meninges (e.g., dura,
arachnoid, pia) are three
layers of connective tissue
coverings that extend around
the spinal cord and brain.
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External Cord Anatomy


Spinal cord extends from the medulla
oblongata, to the upper border of L2
(ending with
the conus medullaris).
The roots of the
spinal nerves or
cauda equina, angle
down the vertebral
canal like wisps of
flowing hair.
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Internal Cord Anatomy



The gray matter of the spinal cord contains
neuronal cell bodies,
dendrites, unmyelinated axons, axon terminals,
and neuroglia.
On each side of the spinal cord, the gray matter is
subdivided
into regions called horns.
The white matter consists primarily of myelinated
axons of neurons and is organized into white
columns.
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Peripheral Nerves

Each spinal nerve (and cranial nerve) contains layers of
protective connective tissue coverings. Individual axons,
whether myelinated or unmyelinated, are wrapped in
endoneurium. Groups of axons with their endoneurium
are arranged in bundles,
called fascicles, each of
which is wrapped in
perineurium. The
superficial covering over
the entire nerve is
the epineurium.
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Reflexes

The pathway followed by nerve impulses that produce a
reflex is known as a reflex arc. Using the patellar reflex
(knee jerk reflex) as an example, the basic components of a
reflex
include:
1) sensory receptor,
2) sensory neuron,
3) integrating center,
4) motor neuron, and
5) effector.
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Animation:
• Reflexes
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The Human Brain
 The Human body uses only ~3 lbs. of tissue to process all
emotions, solve every equation, read every book, and take
every breath
 All these functions, and
many others, occur
within the 100 billion
neurons and 10 trillion
neuroglia that comprise
the human brain
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The Human Brain

The human brain, compared to all other animals’
brains, is marked by the highest ratio of brain to
body size － thought to directly correlate with our
higher level of intelligence.

Most of the expansion is manifest in man’s large cerebral
cortex. Especially expanded are the frontal lobes which are
associated with higher
(executive) functions such
as self-control, planning,
reasoning, and abstract thought.
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Parts of the Brain
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Parts of the Brain
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Production and Flow of CSF



CSF is a clear, colorless liquid that carries oxygen,
glucose, and other chemicals to neurons and
neuroglia and removes their wastes and toxic
substances.
CSF circulates through the subarachnoid space
around the brain and spinal cord, and through
cavities called ventricles.
The sites of CSF production are the choroid
plexuses.
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Production and Flow of CSF
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Production and Flow of CSF

Failure of CSF to form and drain normally results
in a buildup of pressure called hydrocephalus.
 Hydrocephalus occurs with congenital
abnormalities, head
injury, meningitis,
and episodes of
bleeding into
the brain.
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The Twelve Cranial Nerves
Cranial Nerves
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Cranial Nerves
 CN
I is the olfactory nerve (sense of smell).
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Cranial Nerves

CN II is the optic
nerve (sense of
sight).
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Cranial Nerves

CN III, IV, and VI innervate the extraocular
muscles that allow us to move our eyes.

CN III also supplies motor
input to our eyelid
muscles and
facilitates
pupillary
constriction.
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Cranial Nerves

CN V is the trigeminal nerve (the major
sensory nerve of the face).

It has three large
branches, each of
which supplies an
area of the face:
ophthalmic
maxillary
mandibular
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Cranial Nerves

CN VII is the facial nerve. It has 5 large
somatic branches which innervate the muscle
of facial expression. It also carries some taste
sensations (anterior 2/3 of tongue).

Paralysis of CN VII is called Bell’s Palsy
and leads to loss of ability to close the
eyes and impairment of taste and
salivation.
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Cranial Nerves
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Cranial Nerves

CN VIII is the vestibulocochlear nerve.
From the inner ear, the vestibular
component carries information on balance,
while the cochlear component enables
hearing.

Damage of CN VIII causes vertigo, ringing in
the ears, and/or deafness.
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Cranial Nerves
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Cranial Nerves

CN IX is the glossopharyngeal nerve. This
nerve carries some taste sensations as well
as ANS impulses to salivary glands and the
mechanoreceptors of the carotid body and
carotid sinus (senses changes in BP).
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Cranial Nerves
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Cranial Nerves

CN X is the vagus
nerve (“the
wanderer”), which
carries most of the
parasympathetic
motor efferents to
the organs of the
thorax and
abdomen.
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Cranial Nerves

CN XI is the spinal accessory nerve. This nerve
supplies somatic motor innervation to the
Trapezius and Sternocleidomastoid muscles.
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Cranial Nerves

CN XII is the glossopharyngeal nerve. This is a very
large nerve (a lot of resources) to be devoted solely
to the tongue—it takes a lot more coordination than
you might guess to chew, talk, and swallow without
injuring our tongue.
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Midbrain


The midbrain connects the pons to the diencephalon.
The anterior part consists of a pair of large tracts called
cerebral peduncles.
Midbrain contains nuclei (e.g., red nuclei, substantia
nigra).
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Midbrain


Red nuclei are reddish due to their rich blood supply and
iron. Axons from the cerebellum and cerebral cortex form
synapses here and help coordinate muscular movements.
Nuclei of the substantia nigra are large and darkly
pigmented. Loss of these neurons is associated with
Parkinson’s disease.
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Cerebrum


The cerebrum consists of the cerebral cortex (an outer rim
of gray), an internal region of cerebral white matter, and
gray matter nuclei.
The cerebrum provides us with the ability to read, write, and
speak; to make calculations and compose music; to
remember the past and plan for the future; and to create.
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Cerebrum


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The cerebral cortex rolls and folds upon itself so that it
can fit into the cranial cavity.
The folds are called gyri.
The deep grooves between folds are fissures. The
shallow grooves are sulci.
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Cerebrum



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The longitudinal fissure separates the cerebrum into right
and left halves called cerebral hemispheres.
The central sulcus separates the frontal and parietal lobes.
The precentral gyrus is located
immediately anterior to the
central sulcus.
The postcentral gyrus
is located immediately
posterior to the central
sulcus.
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Cerebrum
 Each cerebral hemisphere has four lobes that are
named after the bones that cover them: frontal lobe,
parietal lobe, temporal lobe, and occipital lobe.
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Limbic System


Encircling the upper part of the brain stem and the corpus
callosum is a ring of structures on the inner border of the
cerebrum and floor of the diencephalon that constitutes the
limbic system (limbic border).
The limbic system is
sometimes called the
“emotional brain”
because it plays a
primary role in a
range of emotions,
including pain, pleasure,
docility, affection, and anger.
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Cerebrum
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Somatic
Sensory
Pathways
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Somatic
Sensory
Pathways
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Animation:
• Somatic Sensory and Motor Pathways
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Lateralization

Brain controls opposite side of the body:
all sensory and motor pathways cross in
CNS



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Left side of the brain controls right side of body
Right side of brain controls left side of body
Left hemisphere important for spoken and
written language, numerical and scientific
skills, and reasoning
Right side more involved with spatial and
pattern recognition and emotional content
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Somatic
motor
pathways
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Memory




Process for storing and retrieving information
Involves structural and functional changes
Involves association areas, parts of limbic
system, and diencephalon
Skill memory also involves cerebellum and
basal ganglia
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Aging and the Brain

Rapid brain growth during first few years of
life



Due to increase in size of neurons and
proliferation of neuroglia
Increase in development of dendritic branches
and synaptic contacts
From early adulthood through
old age:



Decline in brain mass
Fewer synaptic contacts
Some decrease in brain function
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End of Chapter 10
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© 2013 John Wiley & Sons, Inc. All rights reserved.