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Chapter 13: The Spinal Cord and Spinal Nerves

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What are the superior and inferior boundaries of the spinal dura mater?
The superior boundary of the spinal dura mater is the foramen magnum of the occipital bone. The inferior boundary is the second sacral vertebra.
What portion of the spinal cord connects with nerves of the upper limbs?
The cervical enlargement connects with sensory and motor nerves of the upper limbs.
What is the difference between a horn and a column in the spinal cord?
A horn is an area of gray matter, and a column is a region of white matter in the spinal cord.
Lateral gray horns are found in which segments of the spinal cord?
Lateral gray horns are found in the thoracic and upper lumbar segments of the spinal cord.
Why are all spinal nerves classified as mixed nerves?
All spinal nerves are classified as mixed because their posterior roots contain sensory axons and their anterior roots contain motor axons.
Which spinal nerve branches serve the upper and lower limbs?
The anterior rami serve the upper and lower limbs.
Why does complete severing of the spinal cord at level C2 cause respiratory arrest?
Severing the spinal cord at level C2 causes respiratory arrest because it prevents descending nerve impulses from reaching the phrenic nerve, which stimulates contraction of the diaphragm, the main muscle needed for breathing.
What five important nerves arise from the brachial plexus?
The axillary, musculocutaneous, radial, median, and ulnar nerves are five important nerves that arise from the brachial plexus.
What are the signs of femoral nerve injury?
Signs of femoral nerve injury include inability to extend the leg and loss of sensation in the skin over the anterolateral aspect of the thigh.
What is the origin of the sacral plexus?
The origin of the sacral plexus is the anterior rami of spinal nerves L4-L5 and S1-S4.
Which is the only spinal nerve that does not have a corresponding dermatome?
The only spinal nerve without a corresponding dermatome is C1.
Based on its name, list the origin and destination of the spinothalamic tract. Is this a sensory or motor tract?
The spinothalamic tract originates in the spinal cord and ends in the thalamus (a region of the brain). Because "spinal" comes first in the name, you know it contains ascending axons and thus is a sensory tract.
What initiates a nerve impulse in a sensory neuron?
A sensory receptor produces a generator potential, which triggers a nerve impulse if the generator potential reaches threshold.
Which branch of the nervous system includes all integrating centers for reflexes?
Reflex integrating centers are in the CNS.
What makes the stretch reflex an ipsilateral reflex?
In an ipsilateral reflex, the sensory and motor neurons are on the same side of the spinal cord.
What is reciprocal innervation?
Reciprocal innervation is a type of arrangement of a neural circuit involving simultaneous contraction of one muscle and relaxation of its antagonist.
Why is the flexor reflex classified as an intersegmental reflex arc?
The flexor reflex is intersegmental because impulses go out over motor neurons located in several spinal nerves, each arising from a different segment of the the spinal cord.
Why is the crossed extensor reflex classified as a contralateral reflex arc?
The crossed extensor reflex is a contralateral reflex arc because the motor impulses leave the spinal cord on the side opposite the entry of sensory impulses.
Which of the three spinal meninges is the most superficial?
Dura Mater
Intercostal nerves
Do not enter into a plexus and directly connect to the structures they supply.
A man presents with median nerve palsy in his left hand. What is the most likely site of injury
Median Nerve
Name the direct motor pathways.
Lateral corticospinal, anterior corticospinal, and corticobulbar tracts.
Describe spinal nerves.
Parts of the PNS, connect the CNS to sensors and effectors in all parts of the body, and are named according to the region of the cord from which they emerge.
What is the sequence of events in a simple spinal reflex arc?
Receptor, afferent neuron, integration center, efferent neuron, effector
A reflex pathway having only one synapse in the CNS is called a
Monosynaptic Reflex Arc
After axonal injury, regeneration in peripheral nerves is guided by ________.
Schwann Cells
A reflex that causes muscle relaxation and lengthening in response to muscle tension is called a ________.
Golgi Tendon Reflex
The patellar "knee jerk" reflex is an example of a(n) ________.
Stretch Reflex
The area of the skin that provides sensory input to the CNS via one pair of spinal nerves is called
A Dermatome
Which nerves arise from the brachial plexus?
Dorsal scapular, long thoracic, nerve to subclavius, suprascapular, musculocutaneous, lateral pectoral, upper subscapular, thoracodorsal, lower subscapular, axillary, median, radial, medial pectoral, medial cutaneous nerve of arm, medial cutaneous nerve of forearm, and ulnar.
Which of the three spinal meninges is the most superficial?
Dura Mater
Which structures contain cerebrospinal fluid?
Subarachnoid Space and Ventricles
Denticulate ligaments are thickenings of
Pia Mater
What spinal cord feature is the area where the nerves that supply the lower limb emerge?
Lumbar Enlargement
Which structure contains only sensory axons that conduct nerve impulses from sensory receptors in the skin, muscles and internal organs to the CNS?
Posterior root of spinal nerves
Which layer of protective connective tissue is the outermost covering surrounding a spinal nerve?
Epineurium
What types of axons are wrapped in a protective endoneurium?
Myelinated and Unmyelinated
Describe spinal nerves
Are parts of PNS, connect the CNS to sensors and effectors in all parts of the body, and are named according to the region of the cord from which they emerge.
This division of a spinal nerve reenters the vertebral cavity through the intervertebral foramen and serves the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges.
Meningeal Branch
Describe intercostal nerves
Do not enter into a plexus and directly connect to the structures they supply.
A man presents with median nerve palsy in his left hand. What is the most likely site of injury?
Median Nerve
Which region of the spinal cord carries nerve impulses for proprioception?
Posterior White Column
These white matter tracts of the spinal cord carry sensory information.
Ascending Tracts
What type of information is carried in the descending tracts of the spinal cord?
Motor
Another term for the summing of EPSPs and IPSPs in the gray matter of spinal cord is
Integration
This type of descending motor pathway conveys nerve impulses that originate in the cerebral cortex and are destined to cause precise, voluntary movements of skeletal muscles.
Direct Pathway
This type of descending motor pathway originates in the brainstem and governs automatic movements that help regulate muscle tone, posture and balance.
Indirect Pathway
Which part of a reflex arc receives sensory information and decides how to respond to a change in the body's condition?
Integration Center
Which part of a nervous reflex arc is usually a muscle or gland?
Effector
Which part of a reflex arc would have a cell body in the posterior root ganglion?
Sensory Neuron
In response to a muscle being stretched, a muscle spindle initiates a somatic spinal reflex that causes
Contraction of the agonist muscle and relaxation of the antagonist muscle.
In response to a tendon being stretched excessively, a tendon organ initiates a somatic spinal reflex that causes
Contraction of the antagonist muscle and relaxation of the agonist muscle.
A typical spinal nerve has how many connections to the spinal cord?
2
This branch of a spinal nerve serves the deep muscles and skin of the posterior surface of the trunk.
Posterior Ramus
The thoracic nerves are also called the
Intercostals Nerves
Which regions of the spinal cord contains a conspicuous enlargement?
Cervical and Lumbar
The area of the skin that provides sensory input to the CNS via one pair of spinal nerve is called
A Dermatome
A severed obturator nerve will lead into paralysis of which region of the body?
Thigh
During childbirth, anesthesia is administered into the epidural space of the spinal column between which vertebrae?
L4 and L5
The cell bodies of the sensory neurons that carry information from the periphery to the spinal cord are located in the
Posterior Root Ganglion
List the connective tissue coverings of the axons, fascicles, and entire nerve in the correct order.
Endoneurium, Perineurium, Epineurium
What are some common characteristics of dermatomes?
Can be used clinically to determine area of spinal cord damage, complete anesthesia of a single dermatome often requires blocking three adjacent spinal nerves, dermatomes are designated based on the cranial or spinal nerve that serves that area of the skin, and the dermatome serving the face is supplied by the trigeminal cranial nerve.
What are some common characteristics of the spinothalamic tract?
Begins in the spinal cord, terminates in the thalamus, found in the white matter of the spinal cord, and is composed of multiple axons carrying information in the spinal cord.
Which nerve from the cervical plexus causes contraction of the diaphragm?
Phrenic
What is the largest nerve arising from the lumbar plexus?
Femoral
Injury of which nerve causes footdrop?
Common Fibular