Chapter 13- Spinal Cord and Somatic Reflexes

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Spinal Cord Functions

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58 Terms

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Spinal Cord Functions

conduction, neural integration, locomotion, reflexes

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Central Power Generators

Groups of neurons that coordinate repetitive muscle movements

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3

Where does the spinal cord begin?

superiorly at the brain stem (foramen magnum)

<p>superiorly at the brain stem (foramen magnum)</p>
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Where does the spinal cord end?

L1-L2

<p>L1-L2</p>
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5

The lower 1/3 of the spinal column is known as what?

cauda equina (L2-S5)

<p>cauda equina (L2-S5)</p>
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four regions of the spinal cord

cervical, thoracic, lumbar, sacral

<p>cervical, thoracic, lumbar, sacral</p>
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How many spinal nerves arise from the spinal cord?

31 pairs

<p>31 pairs</p>
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Cervical Enlargement of Spinal Cord

Responsible for supplying nerves to the upper limb

<p>Responsible for supplying nerves to the upper limb</p>
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Lumbar Enlargement of Spinal Cord

Responsible for supplying nerves to the lower limb

<p>Responsible for supplying nerves to the lower limb</p>
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Protective coverings of spinal cord (superficial to deep)

bone (vertebrae), epidural space, meninges

<p>bone (vertebrae), epidural space, meninges</p>
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epidural space

fatty space between the vertebrae and dura mater

<p>fatty space between the vertebrae and dura mater</p>
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Meninges layers

dura mater, arachnoid mater, pia mater

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dura mater (dural sheath)

most superficial of the three meninges

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arachnoid mater

weblike middle layer of the three meninges

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subarachnoid space

a space in the meninges beneath the arachnoid membrane and above the pia mater that contains the cerebrospinal fluid

<p>a space in the meninges beneath the arachnoid membrane and above the pia mater that contains the cerebrospinal fluid</p>
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pia mater

thin, delicate inner membrane of the meninges

<p>thin, delicate inner membrane of the meninges</p>
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In the spinal cord, gray matter is surrounded by

white matter

<p>white matter</p>
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gray matter of spinal cord

-composed of somas, dendrites, and trigger zones

-site of synapses (integraton) for local potentials

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white matter of spinal cord

-surrounds gray matter

-myelinated axons bundled together into tracts

-myelination gives white matter its pearly white color

<p>-surrounds gray matter</p><p>-myelinated axons bundled together into tracts</p><p>-myelination gives white matter its pearly white color</p>
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Decussation

The anatomical crossing over of neurons from left to right

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Ascending Spinal Tracts

carry sensory information toward the brain

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Ascending Tracts usually transverse 3 neurons:

1. First-order neuron

2. Second-order neuron

3. Third-order neuron

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First-Order Neuron

sensory neuron that detects stimulus and sends to spinal cord or brain stem

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Second-Order Neuron

Interneuron that carries signal to the thalamus

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Third-Order Neuron

Interneuron that carries signal from thalamus to the cerebral cortex

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What is the thalamus also called?

gateway to cerebral cortex or the "mailroom"

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descending tracts

carry motor information down the brainstem and spinal cord to effectors

<p>carry motor information down the brainstem and spinal cord to effectors</p>
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Descending Tracts transverse 2 neurons:

1. Upper Motor Neuron

2. Lower Motor Neuron

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Upper Motor Neuron

Soma is in the cerebral cortex (gray matter); its axon synapses with a lower motor neuron

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Lower Motor Neuron

carries signal from spinal cord to the effector

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Nerves are made up of

bundles of axons

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Spinal Nerve Anatomy

endoneurium, perineurium, epineurium

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Endoneurium

surrounds nerve fibers

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Perineurium

surrounds nerve fiber fascicles

<p>surrounds nerve fiber fascicles</p>
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Epineurium

surrounds the entire nerve

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The epineurium is important for

preventing the nerve from stretching

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Nerves can only be:

sensory, motor, or mixed

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nerve FIBERS can be:

afferent, efferent, somatic, visceral, general, or special

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Where do spinal nerves arise?

roots proximal to the spinal cord

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40

Spinal Nerve Anatomy:

-sensory input travels through the dorsal root

-motor output travels through the ventral root

-dorsal root ganglia house the soma of sensory neurons

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what type of fibers do spinal nerves contain?

afferent and efferent fibers

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4 traits of reflexes

1. require stimulation

2. must be quick

3. involuntary

4. stereotyped

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somatic reflexes

activate skeletal muscle

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visceral reflexes

involuntary muscles and glands

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Anatomy of Somatic Reflex

-utilizes a reflex arc

-somatic receptors in skin, muscles, or tendons

-afferent nerve fiber

-integration center

-efferent nerve fiber

-effectors

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example of a stretch reflex

patellar (knee-jerk) reflex

<p>patellar (knee-jerk) reflex</p>
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stretch reflex

-brain sets length for a muscle and stretch reflex maintains that length

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The stretch reflex is important for

-maintaining muscle tone and adjusting it without consciousness.

-large muscles involved in posture

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The Flexor (Withdraw) Reflex

-involves 2 reflex arcs simultaneously

-in response to a painful stimulus

-often accompanied by a crossed-extensor reflex

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A flexor reflex

withdrawals limb

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Crossed-extensor Reflex

stabilizes body during withdrawal

<p>stabilizes body during withdrawal</p>
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Testing reflexes demonstrates what?

health/integrity of the spinal cord

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Plantar Reflex (Babinski)

tests the integrity of the spinal cord from L4 to S2

<p>tests the integrity of the spinal cord from L4 to S2</p>
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An infant up until age 1 will exhibit the Babinski sign due to

incomplete myelination of their nervous system at birth

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The Babinski sign in older individuals indicates?

spinal cord or brain disease

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56

Polio

-Destroys motor neurons in brain stem and spinal cord

-Causes muscle pain, weakness, loss of reflexes, atrophy, and ultimately paralysis

-spread through contaminated water

<p>-Destroys motor neurons in brain stem and spinal cord</p><p>-Causes muscle pain, weakness, loss of reflexes, atrophy, and ultimately paralysis</p><p>-spread through contaminated water</p>
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57

Lou Gehrig's Disease (ALS)

-degeneration of motor neurons and muscle atrophy

-astrocytes fail to reabsorb glutamate (neurotransmitter) and it accumulates to toxic levels

-cause is unknown

<p>-degeneration of motor neurons and muscle atrophy</p><p>-astrocytes fail to reabsorb glutamate (neurotransmitter) and it accumulates to toxic levels</p><p>-cause is unknown</p>
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58

Rabies

-a viral infection from animal bites

-virus replicates in muscle tissue

-spreads via somatic nerve fibers to the CNS and then the autonomic nerve fibers

-causes seizures, coma, and death

-essential a 100% fatality rate if not treated before reaching the CNS

<p>-a viral infection from animal bites</p><p>-virus replicates in muscle tissue</p><p>-spreads via somatic nerve fibers to the CNS and then the autonomic nerve fibers</p><p>-causes seizures, coma, and death</p><p>-essential a 100% fatality rate if not treated before reaching the CNS</p>
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