Chapter 13 Review Questions

Ascending tracts...

Carry sensory information to the brain.

Proceeding deep from the most superficial layer, number the following in the correct sequence: (a) Walls of Vertebral Canal (b) Pia Mater (c) Dura Mater (d) Arachnoid Membrane (e) Subdural Space (f) Subarachnoid Space (g) Epidural Space (h) Spinal Cord

(a) 1 (b) 7 (c) 3 (d) 5 (e) 4 (f) 6 (g) 2 (h) 8

List, in sequence, the five steps involved in a neural reflex.

1. Arrival of stimulus and activation of receptor 2. Activation of sensory neurons 3. Information processing 4. Activation of a motor neuron 5. Response by an effector (muscle, gland, or adipose tissue)

The ventral roots of each spinal segment...

1. Control peripheral effectors; OR 2. Contain the axons of somatic motor and visceral motor neurons

What five characteristics are common to all polysynaptic reflexes?

1. Involvement of pools of interneurons 2. Intersegmental distribution 3. Involvement of reciprocal innervation 4. Motor response prolonged by reverberating circuits 5. Cooperation of reflexes to produce a coordinated, controlled response

The following are the steps involved in a reflex arc. 1. Activation of a sensory neuron 2. Activation of a motor neuron 3. Response by an effector 4. Arrival of a stimulus and activation of a receptor 5. Informing processing The proper sequence of these steps is...

4, 1, 5, 2, 3

A sensory region monitored by the dorsal rami of a single spinal segment is...

A fascicle

The subarachnoid space contains...

Cerebrospinal Fluid.

Spinal nerves are called mixed nerves because they...

Contain sensory and motor fibers

The synapsing of several neurons on the same postsynaptic neuron is called...

Convergence

Side-to-side movements of the spinal cord are prevented by the...

Denticulate Ligaments.

Reflex arcs in which the sensory stimulus and the motor response occur on the same side of the body are...

Ipsilateral

Which of the following statements is false concerning the gray matter of the spinal cord?

It is primarily involved in relaying information to the brain.

The genitofermoral, femoral, and lateral femoral cutaneous nerves are major nerves of the...

Lumbar plexus

The reflexes that control the most rapid, stereotyped motor responses to stimuli are...

Monosynaptic reflexes

The major nerve of the cervical plexus that innervates the diaphragm is the...

Phrenic nerve

An example of a stretch reflex triggered by passive muscle movement is the...

Patellar reflex

The contraction of flexor muscles and the relaxation of extensor muscles illustrate the principle of...

Reciprocal inhibition

What effect does the stimulation of a security neuron that innervates an intrafusal muscle fiber have on muscle tone?

Stimulation of the sensory neuron will increase muscle tone.

Karen falls down a flight of stairs and suffers spinal cord damage due to hyperextension of the cord during the fall. The injury results in edema of the central cord with resulting compression of the anterior horn cells of the lumbar region. What signs would you expect to observe as a result of this injury?

The anterior horn in the lumbar region of the spinal cord contains somatic motor neurons that direct the activity of skeletal muscles of the hip, lower limb, and foot. As a result of the injury, Karen would be expected to have poor control of most muscles of the lower limbs, causing difficulty walking (if she could walk at all) and problems maintaining balance (if she could stand).

If the anterior gray horns of the spinal cord were damaged, what type of control would be affected?

The cell bodies of spinal motor neurons are located in the anterior gray horns, so damage to these horns would result in a loss of motor control.

Why do cervical nerves outnumber cervical vertebrae?

The first cervical nerve exits superior to vertebra C_1 (between the skull and vertebra); the last cervical nerve exits inferior to vertebra C_7 (between the last cervical vertebra and the first thoracic vertebra). There are thus 8 cervical nerves but only 7 cervical vertebrae.

The adult spinal cord extends only to...

The first or second lumbar vertebra

Bowel and urinary bladder control involve spinal reflex arcs that are located in the sacral region of the spinal cord. In both instances, two sphincter muscles - an inner sphincter of smooth muscle and an outer sphincter of skeletal muscle - control the passage of wastes (feces and urine) out of the body. How would a transection of the spinal cord at the L_1 level affect an individual's bowel and bladder control?

The individual would still exhibit a defecation (Bowel) and urination (Urinary Bladder) reflex because these spinal reflexes are processed at the level of the spinal cord. Efferent impulses from the organs would stimulate specific interneurons in the sacral region that synapse with the motor neuron controlling the sphincters, thus bringing about emptying then the organs began to fill. (this is the same situation that exists in a newborn infant who has not yet fully developed the descending tracts required for conscious control.) However, an individual with the spinal cord transection at L_1 would lose voluntary control of the bowel and bladder because these functions rely on impulses carried by motor neurons in the brain that must travel down the cord and synapse with the interneurons and motor neurons involved in the reflex.

Polysynaptic reflexes can produce far more complicated responses than can monosynaptic reflexes because...

The interneurons involved can control several muscle groups.

Mary complains that when she wakes up in the morning, her thumb and forefinger are always "asleep." She mentions this condition to her physician, who asks Mary whether she sleeps with her wrist flexed. She replies that she does. The physician tells Mary that sleeping in that position may compress a portion of one of her peripheral nerves, producing her symptoms. Which nerve is involved?

The median nerve

The improper use of crutches can produce a condition known as "crutch paralysis," characterized by a lack of response by the extensor muscles of the arm, and a condition known as "wrist drop," consisting of an inability to extend the fingers and wrist. Which nerve is involved?

The radial nerve

Explain the anatomical significance of the fact that spinal cord growth ceases at 4.

The vertebral column continues to grow, expanding beyond the spinal cord. The end of the spinal cord is visible as the conus medullaris near L_1, and the cauda equina extends the remainder of the vertebral column.

Predict the effects on the body of a spinal cord transection at C_7. How would these effect differ from those of a spinal cord transection at T_10?

Transection of spinal cord at C_7 would most likely result in paralysis from the neck down. Transection at T_10 would produce paralysis and eliminate sensory input in the lower half of the body only.

List all of the CNS sites where cerebrospinal fluid (CSF) is located. What are the functions of CSF?

Within the CNS, cerebrospinal fluid fills the central canal, the ventricles, and the subarachnoid space. CSF acts as a shock absorber and a diffusion medium for dissolved gases, nutrients, chemical messengers, and waste products.