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Chapter 8
The Central Nervous System
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CNS
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Consists of:
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Brain.
Spinal cord.
Receives input from
sensory neurons.
Directs activity of motor
neurons.
Association neurons
maintain homeostasis in
the internal
environment.
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Embryonic Development
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Groove appears in ectoderm to fuse to form neural tube by
20th day after conception. Neural tube eventually forms the
CNS.
During 5th week, modified:
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Forebrain: telencephalon and diencephalon.
Midbrain: unchanged.
Hindbrain: metencephalon and myelencephalon.
Part of ectoderm where fusion occurs becomes neural crest.

Neural crest forms ganglia of PNS.
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Embryonic Development
(continued)
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Embryonic Development

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(continued)
Telencephalon grows disproportionately
forming 2 the hemispheres of the cerebrum.
Ventricles and central canal become filled with
cerebral spinal fluid (CSF).
CNS composed of gray and white matter.


Gray matter consists of neuron cell bodies and
dendrites.
White matter (myelin) consists of axon tracts.
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Cerebrum
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Only structure of the telencephalon.
Largest portion of brain (80% mass).
Responsible for higher mental functions.
Corpus callosum:

Major tract of axons that functionally interconnects
right and left cerebral hemispheres.
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Cerebrum
(continued)
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Cerebral Cortex
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Characterized by numerous convolutions.
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Elevated folds: gyri.
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Depressed groves: sulci.
Frontal lobe:
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Anterior portion of each cerebral hemisphere.
Precentral gyri:
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Contains upper motor neurons.
Involved in motor control.
Body regions with the greatest number of motor
innervation are represented by largest areas of
motor cortex.
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Cerebral Cortex
(continued)
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Cerebral Cortex

Parietal lobe:
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(continued)
Primary area responsible for perception of
somatesthetic sensation.
Body regions with highest densities of
receptors are represented by largest areas of
sensory cortex.
Temporal lobe:
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Contain auditory centers that receive sensory
fibers from cochlea.
Interpretation and association of auditory
and visual information.
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Cerebral Cortex
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Occipital Lobe:
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(continued)
Primary area responsible for vision and
coordination of eye movements.
Insula:
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Implicated in memory encoding.
Integration of sensory information with
visceral responses.
Coordinated cardiovascular response to
stress.
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Visualizing the Brain
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X-ray computed tomography (CT):
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Complex computer manipulations of data obtained from x-ray
absorption by tissues of different densities.
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Soft tissue.
Positron-emission tomography (PET):
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Radioisotopes that emit positrons are injected into blood stream.
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Collision of positron and electron result in emission of gamma rays.
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Pinpoint brain cells that are most active.
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Brain metabolism, drug distribution.
Magnetic resonance imaging (MRI):
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Protons (H+) respond to magnetic field, which align the protons.

Emit a radio-wave signal when stimulated.

Brain function.
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Electroencephalogram (EEG)
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Measures synaptic
potentials produced
at cell bodies and
dendrites.
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Create electrical
currents.
Used clinically do
diagnose epilepsy
and brain death.
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EEG Patterns
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Alpha:
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Recorded from parietal and occipital regions.
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Person is awake, relaxed, with eyes closed.
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Beta:
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Strongest from frontal lobes near precentral gyrus.
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Produced by visual stimuli and mental activity.
Evoked activity.
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13-25 cycles/sec.
Theta:
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Emitted from temporal and occipital lobes.
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Common in newborn.
Adult indicates severe emotional stress.
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10-12 cycles/sec.
5-8 cycles/sec.
Delta:
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Emitted in a general pattern.
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Common during sleep and awake infant.
In awake adult indicate brain damage.
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1-5 cycles/sec.
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EEG Sleep Patterns

2 types of EEG patterns during sleep:
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REM (rapid eye movement):
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Dreams occur.
Low-amplitude, high-frequency oscillations.
Similar to wakefulness (beta waves).
Non-Rem (resting):
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High-amplitude, low-frequency waves (delta
waves).
Superimposed on these are sleep spindles:
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Waxing and waning bursts of 7-14 cycles/sec.
Last for 1-3 sec.
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Basal Nuclei (basal ganglia)
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Masses of gray matter
composed of neuronal
cell bodies located deep
within white matter.
Contain:
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Corpus striatum:
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Caudate nucleus.
Lentiform nucleus:
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Putman and globus
pallidus.
Functions in the control
of voluntary movements.
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Cerebral Lateralization
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Cerebral dominance:
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Specialization of one
hemisphere.
Left hemisphere:
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More adept in language
and analytical abilities.
Damage:
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Severe speech
problems.
Right hemisphere:
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Most adept at
visuospatial tasks.
Damage:

Difficulty finding way
around house.
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Language
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Broca’s area:
 Involves articulation of speech.
 In damage, comprehension of speech in unimpaired.
Wernicke’s area:
 Involves language comprehension.
 In damage, language comprehension is destroyed, but
speech is rapid without any meaning.
Angular gyrus:
 Center of integration of auditory, visual, and somatesthetic
information.
 Damage produces aphasias.
Arcuate fasciculus:
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To speak intelligibly, words originating in Wernicke’s area
must be sent to Broca’s area.

Broca’s area sends fibers to the motor cortex which directly
controls the musculature of speech.
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Emotion and Motivation

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Important in the neural basis
of emotional states are
hypothalamus and limbic
system.
Limbic system:
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Group of forebrain nuclei
and fiber tracts that form a
ring around the brain stem.
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Center for basic emotional
drives.
Closed circuit (Papez circuit):
 Fornix connects
hippocampus to
hypothalamus, which
projects to the thalamus
which sends fibers back to
limbic system.
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Emotion and Motivation
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Areas or the hypothalamus and limbic system are
involved in feelings and behaviors.
Aggression:
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Hypothalamus (feeding and satiety centers).
Sexual drive and behavior:
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Amygdala and hypothalamus.
Feeding:
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Amygdala and hypothalamus.
Fear:
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(continued)
Hypothalamus and limbic system.
Goal directed behavior (reward and punishment):

Hypothalamus and frontal cortex.
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Memory
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Short-term:
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Medial temporal lobe:
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Memory of recent events.
Consolidates short term into long term
memory.
Hippocampus is critical component of
memory.
Acquisition of new information, facts
and events requires both the medial
temporal lobe and hippocampus.
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Long-Term Memory
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Consolidation of short-term memory into long-term
memory.
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Requires activation of genes, leading to protein synthesis and
formation of new synaptic connections.
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Cerebral cortex stores factual information:
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Altered postsynaptic growth of dendritic spines in area of
contact.
Visual memories lateralized to left hemisphere.
Visuospatial information lateralized to right hemisphere.
Prefrontal lobes:
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Involved in performing exact mathematical calculations.
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Complex, problem-solving and planning activities.
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Long-Term Potentiation
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Type of synaptic learning.
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Synapses that are 1st stimulated at high frequency will
subsequently exhibit increased excitability.
In hippocampus, glutamate is NT.
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Requires activation of the NMDA receptors for glutamate.
 Glutamate and glycine or D-serine binding and partial
depolarization are required for opening of channels for Ca2+
and Na+.
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May also involve presynaptic changes:
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Binding of glutamate to NMDA receptors and simultaneous
depolarization, open receptor channels for Ca2+.

Ca2+ causes long-term potentiation in postsynaptic neuron,
release of NO from postsynaptic neuron.

NO acts as a retrograde messenger, causing release of NT.
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Neuronal Stem Cells in Learning
and Memory
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Neural stem cells:
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Hippocampus has been shown to contain
stem cells (required for long-term memory).
Neurogenesis:
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Cells that both renew themselves through mitosis
and produce differentiated neurons and neuroglia.
Production of new neurons.
Indirect evidence that links neuogenesis in
hippocampus with learning and memory.
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Thalamus and Epithalamus
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Thalamus:
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Composes 4/5 of the diencephalon.
Forms most of the walls of the 3rd ventricle.
Acts as relay center through which all sensory information
(except olfactory) passes to the cerebrum.
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Lateral geniculate nuclei:
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Medial geniculate nuclei:
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Relay visual information.
Relay auditory information.
Intralaminar nuclei:
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Activated by many sensory modalities.
Projects to many areas.
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Promotes alertness and arousal from sleep.
Epithalamus contains:
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Choroid plexus where CSF is formed.
Pineal gland which secretes melatonin.
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Hypothalamus
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Contains neural centers for hunger, thirst, and
body temperature.
Contributes to the regulation of sleep,
wakefulness, emotions, sexual arousal, anger,
fear, pain, and pleasure.
Stimulates hormonal release from anterior
pituitary.
Produces ADH and oxytocin.
Coordinates sympathetic and parasympathetic
reflexes.
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Pituitary Gland
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Posterior pituitary:
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Hypothalamus produces releasing and
inhibiting hormones that are transported to
anterior pituitary.
Regulate secretions of anterior hormones.
Anterior pituitary:
 Regulates secretion of hormones of other endocrine
glands.

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Stores and releases ADH (vasopressin) and
oxytocin.
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Midbrain
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Contains:
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Corpora quadrigemina:
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Superior colliculi:
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Inferior colliculi:
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Composed of ascending and descending fiber tracts.
Substantia nigra:
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Relay centers for auditory information.
Cerebral peduncles:
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Involved in visual reflexes.
Required for motor coordination.
Red nucleus:
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Maintains connections with cerebrum and cerebellum.
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Involved in motor coordination.
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Hindbrain
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Metencephalon:
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Pons:
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Surface fibers connect to
cerebellum, and deeper fibers are
part of motor and sensory tracts.
Contains several nuclei associated
with cranial nerves V, VI, VII.
Contains the apneustic and
pneumotaxic respiratory centerss.
Cerebellum:
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Receives input from proprioceptors.
Participates in coordination of
movement.
Necessary for motor learning,
coordinating different joints during
movement, and limb movements.
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Hindbrain

(continued)
Myelencephalon (medulla oblongata):
 All descending and ascending fiber tracts between
spinal cord and brain must pass through the
medulla.
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Vasomotor center:
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Controls autonomic innervation of blood vessels.
Cardiac control center:
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Nuclei contained within the medulla include VIII, IX, X,
XI, XII.
Pyramids:
 Fiber tracts cross to contralateral side.
Regulates autonomic nerve control of heart.
Regulates respiration with the pons.
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Reticular Formation

Reticular Formation:
 Complex network of nuclei and nerve fibers within
medulla, pons, midbrain, thalamus and
hypothalamus.
 Functions as the reticular activating system (RAS).

Non specific arousal of cerebral cortex to incoming
sensory information.
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Ascending Spinal Tracts


Convey sensory
information from
cutaneous
receptors,
proprioceptors and
visceral receptors to
cerebral cortex.
Sensory fiber tract
decussation may
occur in medulla or
spinal cord.
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Descending Spinal Tracts

Pyramidal
(corticospinal) tracts
descend directly without
synaptic interruption
from cerebral cortex to
spinal cord.


Function in control of fine
movements that require
dexterity.
Reticulospinal tracts
(extrapyramidal):

Influence movement
indirectly.

Gross motor movement.
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Cranial and Spinal Nerves

Cranial nerves:
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2 pairs arise from neuron cell bodies in forebrain.
10 pairs arise from the midbrain and hindbrain.

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Roman numerals refer to the order in which the nerves are
positioned from front of the brain to the back.
Most are mixed nerves containing both sensory and motor
fibers.
Spinal nerves:
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
31 pairs grouped into 8 cervical, 12 thoracic, 5 lumbar, 5
sacral, and l coccygeal.
Mixed nerve that separates near the attachment of the nerve
to spinal cord.

Produces 2 roots to each nerve.


Dorsal root composed of sensory fibers.
Ventral root composed of motor fibers.
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Reflex Arc


Unconscious motor
response to a sensory
stimulus.
Stimulation of sensory
receptors evokes APs
that are conducted into
spinal cord.


Synapses with
association neuron,
which synapses with
somatic motor neuron.
Conducts impulses to
muscle and stimulates a
reflex contraction.

Brain is not directly
involved.