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PowerPoint® Lecture Slides
prepared by
Janice Meeking,
Mount Royal College
CHAPTER
12
The Central
Nervous
System
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The Nervous System
Central Nervous System (CNS)
Brain
Peripheral Nervous System (PNS)
Spinal Cord
Motor Neurons
Somatic Nervous System
Sympathetic
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Sensory Neurons
Autonomic Nervous System
Parasympathetic
CNS protection
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CSF – cerebrospinal fluid
• Liquid cushion for brain and spinal cord
• Nourishes brain
• Removes waste
• Conducts chemical signals between parts of CNS
• Produced in Choroid Plexuses: group of capillaries
surrounded by ependymal cells
AP revealed – CSF flow
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Choroid Plexuses
http://cal.man.ac.uk/student_projects/2002/MNQJ9PP2/Webpages/structure&functionchoroid.htm
• Clusters of capillaries that
form tissue fluid filters,
which hang from the roof
of each ventricle
• Have ion pumps that allow
them
to
alter
ion
concentrations of the CSF
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CSF production
• CSF is formed by the choroid plexus present
within the four cerebral ventricles and a small
amount by the ependymal cells
• the choroid plexus of the lateral ventricles
producing the most.
• The rate of formation is approximately 0.35 ml/min or 500
ml/day; a rate which replaces the total volume of CSF
approximately 2-3 times over in 24 hours.
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Blood-Brain Barrier
• Helps maintain a stable environment for the brain
• Separates neurons from some bloodborne substances
• Composition
• Continuous endothelium of capillary walls
• Basal lamina
• Feet of astrocytes
• Provide signal to endothelium for the formation
of tight junctions
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Blood-Brain Barrier: Functions
• Selective barrier that allows nutrients to pass freely
• Is ineffective against substances that can diffuse through plasma
membranes (ex. Ethanol, caffeine)
• Absent in some areas:
• Ex. - hormones generally do not penetrate the brain from the
blood, so in order to control the rate of hormone secretion
effectively, there are specialized sites where neurons can
"sample" the composition of the circulating blood. At these sites,
the blood-brain barrier is 'leaky‘ (pituitary gland)
• Capillaries of the choroid plexus
• The BBB can break down under certain conditions:
• hypertension, radiation, infection and brain trauma
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The Brain
• 4 Parts
• Cerebrum
• Diencephalon
• Brain Stem
• Cerebellum
pg 348
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Cerebral Cortex
• The cortex – superficial gray matter; accounts for
40% of the mass of the brain
• It enables sensation, communication, memory,
understanding, and voluntary movements
• Each hemisphere acts contralaterally (controls the
opposite side of the body)
• Hemispheres are not equal in function
• No functional area acts alone; conscious behavior
involves the entire cortex
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Functional Areas of the Cerebral Cortex
• The three types of functional areas are:
• Motor areas – control voluntary movement
• Sensory areas – conscious awareness of sensation
• Association areas – integrate diverse information
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Cerebral Cortex: Motor Areas; Frontal Lobe Cortical
Regions
• Controls voluntary movement and found in the
posterior part of the frontal lobe
• Primary Motor cortex
• Conscious motor control
• Motor homonculus
• Premotor Cortex
• Learned motor skills
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Cerebral Cortex: Motor Areas; Frontal Lobe Cortical
Regions
• Broca’s area
• Motor for speech
• Frontal Eye Field
• Prefrontal Cortex
• Personality
• Intelligence
• Language comprehension
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Primary Motor Cortex
• Located in the precentral gyrus in the frontal lobe in each
hemisphere
• Pyramidal cells that have long axon project to the spinal cord and
form
a
voluntary
motor
tracts
called
pyramidal
tracts/corticospinal tracts
• A pyramidal cell (or pyramidal neuron, or projection neuron)
is a multipolar neuron found in the cerebral cortex.
• These cells have a triangularly shaped soma
• Pyramidal neurons compose approximately 80% of the
neurons of the cortex
• Release glutamate as their neurotransmitters, making them the
major excitatory component of the cortex
• Allows conscious
movements
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control
of
precise,
skilled,
voluntary
Primary Motor Cortex Homunculus
Posterior
• Somatotopy mapping
• Body is represented upside
down
• Although simplified in the
figure, one should remember
that:
Motor
Motor map in
precentral gyrus
Anterior
• A given muscle is
controlled by multiple spots
on the cortex
Toes
• Individual cortical neurons
send impulses to more than
one muscle
• Neurons that control related
movements will overlap
• Neurons that control unrelated
movements do not cooparate
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Jaw
Tongue
Swallowing
Primary motor
cortex
(precentral gyrus)
Figure 12.9.1
Premotor Cortex
• Located anterior to the precentral gyrus in the frontal lobe
• Controls learned, repetitious, or patterned motor skills
(playing a musical instrument)
• Coordinates the movements of muscle groups either for
simultaneous or sequential actions
• mainly by sending activating impulses to the primary
motor cortex
• also by controlling directly by supplying 15% of the
pyramidal tract fibers
• Involved in the planning of movements by receiving
sensory information and process them (moving arm
through maze to take hidden object)
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• Broca’s Area
• Located anterior to the inferior region of the
premotor area
• Present in one hemisphere (usually the left)
• A motor speech area that directs muscles of the
tongue
• Is active as one prepares to speak
• Frontal eye field
• Located anterior to the premotor cortex and
superior to Broca’s area
• Controls voluntary eye movement
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Prefrontal Cortex
• Located in the anterior portion of the frontal lobe
• Involved with intellect, cognition (complex
learning activities), recall and personality
• Necessary for judgment, reasoning, persistence,
and conscience
• Closely linked to the limbic system (emotional
part of the brain)
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Sensory Areas
• Areas that are associated with conscious awareness of
sensation
• Found in the parietal, temporal, occipital and insular
lobes
• Primary somatosensory cortex
• Somatosensory association cortex
• Visual and auditory areas
• Olfactory, gustatory, and vestibular cortices
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Primary Somatosensory Cortex
Posterior
• Located in the postcentral
gyrus, this area:
Sensory
Anterior
• Receives
information
from the skin and from
proprioceptors
(position) in the skeletal
muscles, joints and
tendons
• Identify the area of the
body from which the
signal was sent - spatial
discrimination
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Sensory map in
postcentral gyrus
Genitals
Primary somatosensory cortex
(postcentral gyrus)
Intraabdominal
Somatosensory Association Cortex
• Located posterior to the primary somatosensory cortex
and has connection with it
• Integrates sensory information like temperature and
pressure coming from the primary somatosensory
cortex.
• Forms understanding of the stimulus like size, texture,
and relationship of parts
• Ex.: putting the hand in the pocket and feeling
something. The center integrate previous information
to identify objects without seeing them
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Visual Areas
• Primary visual (striate) cortex
• Seen on the extreme posterior tip of the occipital lobe
• Most of it is buried in the calcarine sulcus (medial
aspect of the occipital lobe)
• Receives visual information from the retinas
• Visual association area
• Surrounds the primary visual cortex and covers much
of the occipital lobe.
• Interprets visual stimuli (e.g., color, form, and
movement) by processing previous experiences
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Auditory Areas
• Primary auditory cortex
• Located at the superior margin of the temporal lobe
• Receives information from mechanoreceptors in the
inner ear related to pitch, rhythm, and loudness
• Auditory association area
• Located posterior to the primary auditory cortex
• Stores memories of sounds and permits perception of
sounds (is it scream, speech, singing etc.)
• Wernicke’s area - on the left posterior section of the
superior temporal lobe, encircling the auditory cortex.
Function in language comprehension
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multimodal association areas
• Most of the cortex receives inputs from multiple senses and
sends outputs to multiple areas
• Theses areas are called – multimodal association areas
• In general the route is :
• Information accepted by sensory receptors
• Signal is transported to the appropriate primary sensory
cortex
• To sensory association cortex
• To multimodal association cortex
• Multimodal association allows to give a meaning to
received information, stores memory, connect signal to
previous experience, decide what action to take
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Language Areas as example of multimodal association
• Located in a large area surrounding the left (or languagedominant) lateral sulcus
• Major parts and functions:
• Wernicke’s area –sounding out unfamiliar words (sensory)
• Broca’s area – speech preparation and production (motor)
• Lateral prefrontal cortex – language comprehension and
word analysis
• Lateral and ventral temporal lobe – coordinate auditory and
visual aspects of language
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http://www.colorado.edu/kines/Class/IPHY3730/image/figure5-21.jpg
Lateralization of Cortical Function
• Lateralization – each hemisphere has abilities not shared with
its partner
• Cerebral dominance – designates the hemisphere dominant for
language. For most people:
• Left hemisphere – controls language, math, and logic
• Right hemisphere – controls visual skills, emotion, and artistic
skills
• For 10% of people the roles of the hemispheres are reversed or
the hemispheres share functions equally
• The hemispheres have communication with one another
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Cerebral White Matter
• Consists of deep myelinated fibers bundled into tracts
• The tracts are classified according to the direction in which
they run:
• Commissures –
• connect corresponding gray areas of the
hemispheres allowing them to work as one unit
two
• The largest is the corpus callosum
• Anterior and posterior commisures
• Association fibers – connect different parts of the same
hemisphere
• Projection fibers – enter the hemispheres from lower
brain or cord centers
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Basal Nuclei
• Masses of gray matter found deep within the cortical
white matter
• its major components include the caudate,
Putamen, globus pallidus
• The putamen and the globus pallidus form the
lentiform nucleus
• The lentiform and the caudata are called the corpus
striatum
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lentiform
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Basal Ganglia Function
• Organization
• Input from cortex
• Project motor to cortex
• Function
• coordinating the initiation
of movements
• Monitor movement
• Inhibit unnecessary
movement
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The picture
represents the
Somatotopy
mapping/
homunculi of the
cerebral cortex
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What white matter structure connects the two cerebral
hemispheres?
A. longitudinal fissure
B. lateral ventricles
C. corpus callosum
D. diencephalons
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Damage to the white matter of the brain would
prevent transmission of information between
nuclei.
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Diencephalon
• Consists of three paired
structures –
• thalamus
• Hypothalamus
• epithalamus
• Encloses the third
ventricle
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Thalamic Function
• The thalamus is the “gateway to the cerebral cortex”
• Major relay station for most sensory impulses that arrive to
the primary sensory areas in the cerebral cortex:
• taste, smell, hearing, equilibrium, vision, touch, pain,
pressure, temperature
• Contributes to motor functions by transmitting information
from the cerebellum and basal ganglia to the cerebral primary
motor area
• Connects areas of the cerebrum
• Impulses of similar function are sorted out, edited, and
relayed as a group
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Hypothalamus
• Located below the thalamus and forms the
inferolateral walls of the third ventricle
• Infundibulum – stalk of the hypothalamus;
connects to the pituitary gland
• Mammillary bodies
• Small, paired nuclei bulging anteriorly from the
hypothalamus
• Relay station for olfactory pathways
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Hypothalamic Function
• Function as the main visceral control in the body
• Regulates blood pressure, rate and force of heartbeat,
digestive tract motility, rate and depth of breathing, eye pupil
size etc.
• Perception of pleasure, fear, and rage
• Maintains normal body temperature (contains body’s
“thermostat”) by initiating cooling or heat-generating
processes
• Regulates food intake (hunger)
• Regulation of water intake
contain thirst center
and thirst – produce ADH,
• Regulates sleep and the sleep cycle
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Endocrine Functions of the Hypothalamus
• Releasing hormones control secretion of hormones
by the anterior pituitary
• The supraoptic and paraventricular nuclei produce
ADH and oxytocin
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Epithalamus
• Most dorsal portion of the diencephalon; forms roof of
the third ventricle
• Pineal gland – extends from the posterior border and
secretes melatonin
• Melatonin – a hormone involved with sleep
regulation, sleep-wake cycles, and mood
• Choroid plexus – a structure that secretes cerebral
spinal fluid (CSF)
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Brain Stem
• Consists of three regions –
• midbrain,
• Pons
• medulla oblongata
• Similar to spinal cord – deep gray matter surrounded by
white tracts but contains embedded nuclei in the white matter
• Controls automatic behaviors necessary for
(breathing, digestion, heart rate, blood pressure)
survival
• Provides the pathway for tracts between higher and lower
brain centers
• Associated with 10 of the 12 pairs of cranial nerves
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Midbrain
• Located between the diencephalon and the pons
• Midbrain structures include:
• Cerebral peduncles of the midbrain – two
structures that contain descending pyramidal motor
tracts (what areas do the pyramidal tracts
connect?)
• Cerebral aqueduct – hollow tube that connects the
third and fourth ventricles
• Various nuclei (what are nuclei)
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Midbrain Nuclei
• Nuclei that control cranial nerves III (oculomotor) and IV
(trochlear)
• Corpora quadrigemina
• 2 Superior colliculi – visual reflex centers; coordinate
head and eye movement when we follow a moving
object (does not have to be a conscious decision)
• 2 Inferior colliculi – auditory relay centers between
hearing receptors to sensory cortex.
• Reflexive responses to sound – turn head toward
sound
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Midbrain Nuclei
• Substantia nigra – functionally linked to basal nuclei,
contains melanin pigment (precursor of dopamine NT)
• Red nucleus – largest nucleus (rich blood supply) of
the reticular formation; relay nuclei for some
descending motor pathways
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Pons
• between the midbrain and the medulla oblongata
• Forms part of the anterior wall of the fourth ventricle
• Fibers of the pons:
• Connect higher brain centers and the spinal cord
• Relay impulses between the motor cortex and the
cerebellum
• Origin of cranial nerves V (trigeminal), VI (abducens),
and VII (facial)
• Contains nuclei of the reticular formation
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Medulla Oblongata
• Most inferior part of the brain stem
• Along with the pons, forms the ventral wall of the fourth ventricle
• Contains the choroid plexus of the fourth ventricle
• Pyramids – two longitudinal ridges formed by corticospinal tracts
descending from the motor cortex
• Before entering the spinal cord the corticospinal tracts crossover.
• The point in which the crossover occur is called decussation
of the pyramids
• Results in the controlling of each cerebral hemisphere in the
movements of the opposite side
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Medulla Nuclei
• Inferior olivary nuclei – gray matter that relays
sensory information regarding the stretch of muscle
and joints
• Cranial nerves IX (glosopharyngeal, X (vagus), XI
(accessory; neck muscle), and XII (hypoglossal;
tongue) are associated with the medulla
• Vestibular nuclear complex – synapses that mediate
and maintain equilibrium
• Ascending sensory tract nuclei, including nucleus
cuneatus and nucleus gracilis
• Serve as relay station for general somatic sensation
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Medulla Nuclei
• The medulla has an important role in the autonomic
reflex center that maintain homeostasis:
• Cardiovascular control center – adjusts force and
rate of heart contraction
• Respiratory centers – control rate and depth of
breathing
• Additional centers – regulate vomiting, hiccuping,
swallowing, coughing, and sneezing
• There is an overlap between medulla and
hypothalamus that uses medullary centers to carry out
instructions
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The Cerebellum
• Located dorsal to the pons and medulla; the activity is
subconscious
• Two bilaterally symmetrical hemispheres connected medially by
the vermis
• Folia – transversely oriented gyri
• Each hemisphere has three lobes – anterior, posterior, and
flocculonodular (deep to the vermis and posterior lobe; can not be
seen from the outside)
• Neural arrangement – gray matter cortex, internal white matter,
scattered nuclei
• Arbor vitae – distinctive treelike pattern of the cerebellar white
matter
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Cerebellar Function
• Adjust ongoing movements on the basis of comparison between
arriving sensation to one previously experienced
• Posture:
• Balance
• Equilibrium
• Fine Tune Movements
• Timing
• Rate
• Range
• Force
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Cerebellar Processing
• Cerebellum receives impulses of the intent to
initiate voluntary muscle contraction
• Proprioceptors and visual signals “inform” the
cerebellum of the body’s condition
• Cerebellar cortex calculates the best way to
perform a movement
• A “blueprint” of coordinated movement is sent to
the cerebral motor cortex
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Initiation of Skilled Movement
Frontal Association and Primary Motor Cortex
Frontal cortex can plan and initiate movement but cannot calculate the
complex, timed sequence of muscle contraction
Send information about intended movements to the cerebellum
Basal Ganglia
Somatosensory System
Information on current position
Lateral Zone of Cerebellum
When cerebellum receives information about initiated movement it
computes the contribution that various muscles will have to make
Sends results
Dentate Nucleus
In cerebellum
Via basal ganglia
Allows the cerebellum to
modify the ongoing
movement that was initiated
by the frontal cortex
Thalamus
The cerebellum can also control a skilled movement by timing the movement and by turning on the
antagonist muscle. This happens when the movement is rapid and cannot relay on feedback.
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Cerebellum White tracts
• Three paired fiber tracts that connect the cerebellum to the
brain stem
• All fibers in the cerebellum are ipsilateral (from and to
same side of the body)
• The superior cerebellar
cerebellum to the midbrain
peduncle
connects
the
• These are the axons that send feedback to the motor
cortex in the frontal lobe via the red nucleus in the
midbrain and thalamus.
• afferent fibers traveling in this peduncle bring
proprioceptive information to the cerebellum from the
lower body.
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Cerebellum White tracts
• The middle cerebellar peduncle is the largest of the
peduncles and carry one-way communication from the
pons to the cerebellum.
• Via this connection, the cerebellum receives “a copy”
of the information for voluntary muscle movement that
the pyramidal tract is carrying down from the motor
cortex to lower motor neurons.
• The inferior cerebellar peduncle connects the cerebellum
with the medulla
• Bring sensory information from the muscle
proprioceptors around the body and the vestibular
nuclei in the brain stem (equilibrium)
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Memory
• Memory is the storage and retrieval of information
• The three principles of memory are:
• Storage – occurs in stages and is continually
changing
• Processing – accomplished by the hippocampus
and surrounding structures
• Memory traces – chemical or structural changes
that encode memory
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Memory
• Storage and retrieval of information
• Two stages of storage
• Short-term memory (STM, or working memory)—
temporary holding of information; limited to seven
or eight pieces of information
• Long-term memory (LTM) has limitless capacity
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Transfer from STM to LTM
• Factors that affect transfer from STM to LTM
• Emotional state —best
surprised, and aroused
if
alert,
motivated,
• Rehearsal —repetition and practice
• Association —tying new information with old
memories
• Automatic memory — subconscious information
stored in LTM
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Categories of Memory
1. Declarative memory (factual knowledge)
•
Explicit information
•
Related to our conscious thoughts and our
language ability
•
Stored in LTM with context in which it was
learned
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Categories of Memory
2. Nondeclarative memory
•
Less conscious or unconscious
•
Acquired through experience and repetition
•
Best remembered by doing; hard to unlearn
•
Includes procedural (skills) memory, motor
memory, and emotional memory
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Brain Structures Involved in Nondeclarative Memory
• Procedural memory
• Basal nuclei relay sensory and motor inputs to the
thalamus and premotor cortex
• Dopamine from substantia nigra is necessary
• Motor memory—cerebellum
• Emotional memory—amygdala
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Spinal Cord
• CNS tissue is enclosed within the vertebral column from the foramen
magnum to L1
• Provides two-way communication to and from the brain
• Protected by bone, meninges, and CSF
• Conus medullaris – terminal portion of the spinal cord
• Filum terminale – fibrous extension of the pia mater; anchors the
spinal cord to the coccyx
• Denticulate ligaments – delicate shelves of pia mater; attach the
spinal cord to the vertebrae
• Spinal nerves – 31 pairs attach to the cord by paired roots (8 cervical,
12thoracic, 5 lumbar, 5 sacral 1 coccygeal)
• Cervical and lumbar enlargements – sites where nerves serving the
upper and lower limbs emerge
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Figure 12.29a
Spinal Cord
• Because the cord does
not reach the end of the
vertebral column, the
lumbar and sacral spinal
nerve roots angle
sharply downward and
travel inferiorly before
reaching their
intervertebral foramina
• This collection of nerve
roots at the inferior end
of the vertebral canal is
called the cauda equina
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White Matter in the Spinal Cord
• Composed of both myelinated and unmyelinated fibers that run
in three directions
• Ascending – to higher centers; sensory
• Descending – to lower levels from brain or higher places in
the cord; motor
• Transversely – from one side of the cord to the other
• Divided into three funiculi (columns) – posterior, lateral, and
anterior
• Each funiculus contains several fiber tracks with similar
destination and function
• Fiber tract names reveal their origin and destination
• Fiber tracts are composed of axons with similar functions
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