CHAPTER 3 - Book Review Questions

Question 1

The following statements concern nerves:

(a) The minor dense line of myelin is made up of
protein.
(b) lncisures of Schmidt-Lanterman are caused by
the mesaxons of the Schwann cells.
(c) Only five or six unmyelinated axons may share a single Schwann cell in the peripheral nervous
system (PNS).
(d) The node of Ranvier is the site of nerve activity. (e) Chromatolysis is the term used to describe the
changes in the arrangement of Nissl material within the axon following injury.

Answer 1

D is correct.

• The node of Ranvier is the site of nerve activity. A. The minor dense line of myelin is made up of lipid. B. lncisures of Schmidt-Lanterman represent where the dark major dense line is not fanned as a result of the localized persistence of Schwann cell cytoplasm (Fig. 3-7). C. As many as 15 or more unmyelinated axons may share a single Schwann cell in the PNS. E. Chromatolysis is the term used to describe the changes in the arrangement of Nissl material within the cytoplasm of the nerve cell body following injury (see p. 106).

Question 2

The following statements concern an oligodendrocyte:

(a) A single oligodendrocyte may be associated with one segment of myelin on a single axon.
(b) lncisures of Schmidt-Lanterman are not present in the myelinated fibers of the central nervous system (CNS).
(c) Myelination in the CNS occurs by the rotation of the axon within the oligodendrocytic process and the wrapping of it around the axon.
(d) A nonmyelinated axon in the CNS has a special relationship with the oligodendrocyte.
(e) A single oligodendrocyte may be associated with the myelin sheaths of as many as 60 axons.

Answer 2

E is correct.

• A single oligodendrocyte may be associated with the myelin sheaths of as many as 60 axons (see p. 72). A. A single oligodendrocyte may be associated with several segments of myelin on a single axon. B. lncisures of Schmidt-Lanterman are present In the myelinated fibers of the CNS. C. Myelination in the CNS occurs by the growth in length of the oligodendrocytic process and the wrapping of it around the axon. D. A nonmyelinated axon in the CNS has no special relationship with the oligodendrocyte (see p. 79).

Question 3

The following statements concern spinal nerves:

(a) There are 26 pairs.
(b) They are formed by the union of anterior and
posterior nerve roots.
(c) The posterior ramus contains only sensory
axons.
(d) The anterior root contains only sensory axons.
(e) The posterior root ganglion contains bipolar
neurons enveloped in capsular cells.

Answer 3

B is correct.

• Spinal nerves are formed by the union of anterior and posterior nerve roots (Fig. 3-1). A. There are 31 pairs of spinal nerves. C. The posterior ramus of a spinal nerve contains both motor and sensory axons. D. The anterior root of a spinal nerve contains only motor axons. E. The posterior root ganglion of a spinal nerve contains unipolar neurons enveloped in capsular cells.

Question 4

The following statements concern peripheral nerve
plexuses:

(a) They are formed by a network of connective
tissue fibers.
(b) Bundles of nerve fibers do not branch, and, in
most instances, the individual nerve fibers do
not branch.
(c) Plexuses at the roots of the limbs are formed
from posterior rami of spinal nerves.
(d) The plexuses of the autonomic nervous system possess a network of efferent nerve fibers and
no nerve cells.
(e) A plexus situated at the root of a limb permits
nerve fibers from different segments of the spinal cord to become rearranged so that they more easily travel to different parts of the limb.

Answer 4

E is correct.

• A peripheral nerve plexus situated at the root of a limb permits nerve fibers from different segments of the spinal cord to become rearranged so that they more easily travel to different parts of the limb (seep. 81). A. Peripheral nerve plexuses are formed by a network of nerve fibers. B. In peripheral nerve plexuses, bundles of nerve fibers branch, but in most instances, the individual nerve fibers do not branch. C. The peripheral nerve plexuses at the roots of the limbs are formed from the anterior rami of the spinal nerves. D. The nerve plexuses of the autonomic nervous system possess a network of nerve fibers and nerve cells.

Question 5

The following statements concern nerve conduction:

(a) Adequate stimulus decreases the permeability of the axolemma to Na+ ions at the point of stimulation.
(b) During the absolute refractory period, a very strong stimulus will excite the nerve fiber.
(c) As the action potential moves along the axon, the entry of Na+ ions into the axon increases and the permeability to K+ ions decreases.
(d) A typical action potential is about +40 mV.
(e) In the resting unstimulated nerve fiber, the interior of the axolemma is positive to the
exterior.

Answer 5

D is correct.

• In nerve conduction, a typical action potential is about +40 mV (see pp. 44-45). A. In nerve conduction, an adequate stimulus increases the permeability of the axolemma to Na+ ions at the point of stimulation. B. During the absolute refractory period of nerve conduction, no stimulus, no matter how strong, will excite the nerve fiber. C. During nerve conduction, the action potential moves along the axon; the entry of Na+ ions into the axon ceases, and the permeability of the plasma membrane of the axon to K+ ions increases (see p. 44). E. In the resting unstimulated nerve fiber, the interior of the plasma membrane (axolemma) is negative to the exterior.

Question 6

The following statements concern the propagation
of a nerve impulse:

(a) Conduction velocity is smallest in nerve fibers
having a large cross-sectional diameter.
(b) In nonmyelinated nerve fibers, the action potential occurs along the length of the fiber.
(c) A myelinated nerve fiber can be stimulated only between the nodes of Ranvier.
(d) Saltatory conduction occurs only in the central nervous system.
(e) At the node of Ranvier, the action potential has no effect on the surrounding tissue fluid.

Answer 6

B is correct.

• In nonmyelinated nerve fibers, the action potential occurs along the length of the fiber. A. Conduction velocity is greatest in nerve fibers having a large cross-sectional diameter. C. A myelinated nerve fiber can be stimulated only at the nodes of Ranvier. D. Saltatory conduction occurs in both the peripheral and central nervous systems. E. At the node of Ranvier, the action potential sets up an electrical current in the surrounding tissue fluid (see p. 72).

Question 7

The following statements concern Wallerlan degeneration:

(a) Myelin breaks down into droplets that are phagocytosed by the Schwann cells.
(b) The axon rapidly disappears.
(c) Schwann cells round off and do not multiply.
(d) In the central nervous system (CNS), debris is
removed by the astrocyte cells.
(e) In the peripheral nervous system (PNS), tissue
macrophages play no part in the digestion of
the nerve fragments.

Answer 7

A is correct.

• In Wallerian degeneration, the myelin breaks down into droplets that are phagocytosed by the Schwann cells. B. In Wallerian degeneration, the axon first breaks up into fragments before it is phagocytosed by the surrounding Schwann cells (see p.105). C. In Wallerian degeneration, the Schwann cells proliferate rapidly and become arranged in parallel cords within the persistent basement membrane. D. In Wallerian degeneration in the CNS, the debris is removed by the microglial cells. E. In Wallerian degeneration in the PNS, the tissue macrophages are very active in removing the nerve fragments.

Question 8

The following statements concern the failure of regeneration of nerve fibers In the central nervous system (CNS):

(a) Endoneurial tubes are present.
(b) Oligodendrocytes have a basement membrane.
(c) Oligodendrocytes fail to multiply and form a
band fiber, as do Schwann cells in the peripheral nervous system (PNS).
(d) Blood supply is not usually adequate.
(e) Nerve growth factors are not present.

Answer 8

C is correct.

• Following injury to the CNS, the oligodendrocytes fail to multiply and form a band fiber as do Schwann cells in the damaged PNS (see p. 106). A. The absence of endoneurial tubes may be important in the failure in the regeneration of injured CNS tissue (see p. 106). B. Ollgodendrocytes have no basement membrane. D. Blood supply to the central nervous tissue is usually adequate. E. In the CNS, no nerve growth factors are present.

Question 9

The following factor may explain the partial return of function following injury to the spinal cord:

(a) Edema fluid persists at the site of injury.
(b) Nonfunctional neurons never take over the
function of damaged neurons.
(c) Reduction in the number of receptor sites may
occur on the postsynaptic membranes.
(d) Some of the axons completely regenerate.
(e) With training, the patient may use other muscles
to compensate for the loss of paralyzed muscles.

Answer 9

E is correct.

• The partial return of function seen in spinal cord injuries may be due in part to the patient using other muscles to compensate for the loss of the paralyzed muscles. A. Following injury to the central nervous system, the edema fluid usually subsides at the site of injury and will result in some clinical improvement (see p. 107). B. Nonfunctional neurons may take over the function of damaged neurons. C. The receptor sites on the postsynaptic membrane may increase in number and be responsible for some posttraumatic improvement. D. Evdence does not show that destroyed axons in the central nervous system completely regenerate after injury.

Question 10

The following statements concern receptor endings:

(a) Rods and cones of the eyes are chemoreceptors.
(b) Taste and smell endings are electromagnetic
receptors.
(c) Free nerve endings have no Schwann cells covering their tips.
(d) Merkel discs are fast-adapting touch receptors. (e) Meissner corpuscles are absent from the skin of
the palm of the hand and the sole of the foot.

Answer 10

C is correct.

• Free nerve endings have no Schwann cells covering their tips (seep. 84). A. The rods and cones of the eyes are examples of electromagnetic receptors. B. Taste and smell receptors are chemoreceptors. D. Merkel discs are slow-adapting touch receptors. E. Meissner corpuscles are present in the skin of the palm of the hand and the sole of the foot.

Question 11

The following statements concern receptor endings:

(a) Pacinian corpuscles are slowly adapting mechanoreceptors.
(b) Ruffini corpuscles are fast-adapting stretch
receptors found in the dermis of hairy skin.
(c) Each Pacinian corpuscle has no capsule but has a central core containing the nerve ending.
(d) Annulospiral endings in skeletal muscle do not
possess intrafusal muscle fibers.
(e) The number of Meissner corpuscles considerably diminishes between birth and old age.

Answer 11

E is correct.

• The number of Meissner corpuscles is considerably reduced between birth and old age. A. Pacinian corpuscles are fast-adapting mechanoreceptors. B. Ruffini corpuscles are slow-adapting stretch receptors found in the dermis of hairy skin. C. Each Pacinlan corpuscle has a Iamellated capsule and a central core containing the nerve ending (Figs. 3-23 and 3-24). D. Annulospiral endings in skeletal muscle do possess intrafusal muscle fibers.

Question 12

The following statements concern cutaneous receptors:

(a) Different histologic types of receptors transmit different types of nerve impulses.
(b) The type of sensation felt is determined by the specific area of the central nervous system (CNS) to which the sensory nerve fiber passes.
(c) Transduction at the receptor is the process by which the stimulus is changed into the mechanical energy of the nerve impulse.
(d) When applied to the receptor, the stimulus brings about a change in the potential of the plasma membranes of the capsule cells and not the nerve ending.
(e) If small enough, the receptor potential will generate an action potential in the afferent sensory nerve fiber.

Answer 12

B is correct.

• The type of sensation felt is determined by the specific area of the CNS to which the sensory nerve fiber passes (see p. 89). A. Although a variety of histologic types of receptors exist, their nerves only transmit the same nerve impulses. C. Transduction at the receptor is the process by which the energy of the stimulus is changed into electrochemical energy of the nerve impulse. D. When applied to the receptor, the stimulus brings about a change in the potential of the plasma membrane of the nerve ending (seep. 89). E. If large enough, the receptor potential will generate an action potential in the afferent sensory nerve fiber.

Question 13

The following statements concern the function of a neuromuscular spindle:

(a) It gives rise to intermittent afferent nerve
impulses.
(b) Only active muscle movement causes an
increase in the rate of passage of nerve impulses
in the afferent nerve fiber.
(c) The neuromuscular spindle keeps the central
nervous system (CNS) informed about muscle
activity.
(d) The neuromuscular spindle directly influences
the control of voluntary movement.
(e) Flower-spray endings are situated mainly on the nuclear bag fibers close to the equatorial
region.

Answer 13

C is correct.

• The neuromuscular spindle keeps the CNS informed about muscle activity (see p. 89). A. The neuromuscular spindle gives rise to afferent nerve impulses all the time. B. When active or passive muscle movement occurs, the rate of passage of nerve impulses in the afferent nerve fibers of the neuromuscular spindles increases. D. The neuromuscular spindle indirectly influences the control of voluntary movement (see p. 90). E. Flower-spray endings are situated mainly on the nuclear chain fibers some distance from the equatorial region (Fig. 3-25).

Question 14

The following statements concern the neurotendinous spindles:

(a) They are situated in tendons some distance
away from the musculotendinous junction.
(b) The nerve terminates in a single club-shaped
ending.
(c) Each has a fibrous capsule, loosely arranged
collagen fibers, and tendon cells.
(d) Neurotendinous spindles are found only in
slow-acting muscles.
(e) The neurotendinous spindle is activated by
changes in muscle tension and stimulates muscle contraction.

Answer 14

C is correct.

• Each neurotendinous spindle has a fibrous capsule, loosely arranged collagen fibers, and tendon cells (see p. 92). A. Neurotendinous spindles are situated in tendons close to the musculotendinous junction. B. The nerve ends within the spindle by branching and terminating in club-shaped endings. D. Neurotendinous spindles are found in fast- and slow-acting muscles. E. The neurotendinous spindle is activated by changes in muscle tension and inhibits muscle contraction.

Question 15

The following statements concern the neuromuscular junctions in skeletal muscle:

(a) Each terminal branch of the motor nerve ends
as an axon covered with fine connective tissue.
(b) Each axon lies in a groove on the surface of
the muscle fiber formed by the infolding of the
muscle plasma membrane (sarcolemma).
(c) Having caused depolarization of the postsynaptic membrane, acetylcholine (ACh) is reabsorbed into the axon terminal.
(d) ACh is released from the axon terminal when
the nerve impulse leaves the initial segment of
the axon.
(e) Schwann cells form the floor for the groove on
the surface of the muscle fiber.

Answer 15

B is correct.

• At a neuromuscular junction, each axon lies in a groove on the surface of the muscle fiber formed by the infolding of the muscle plasma membrane (sarcolemma) (Fig. 3-30). A. At a neuromuscular junction, each terminal branch of the motor nerve ends as a naked axon. C. Having caused depolarization of the postsynaptic membrane, ACh is immediately hydrolyzed in the synaptic cleft by acetylcholinesterase (see p. 96). D. ACh is released from the axon terminal when the nerve impulse reaches the neuromuscular junction. E. At the neuromuscular junction, the Schwann cells form a cap or roof for the groove on the surface of the muscle fiber.

Question 16

The following statements concern the neuromuscular junctions on smooth and cardiac muscle:

(a) In smooth muscle, the autonomic nerve fiber exerts control over a single muscle fiber.
(b) In smooth muscle, the wave of contraction does not pass from one muscle fiber to another.
(c) In cardiac muscle, the wave of contraction spreads slowly from one muscle fiber to another by way of desmosomes and gap junctions.
(d) Autonomic nerve fibers terminate on smooth muscle as unmyelinated fibers.
(e) At the site of the neuromuscular junction, the axon is completely surrounded by Schwann cells.

Answer 16

D is correct.

• Autonomic nerve fibers terminate on smooth muscle fibers as unmyelinated fibers (see p.98). A. In neuromuscular junctions of smooth muscle, the autonomic nerve fiber exerts control over several muscle fibers (see p. 98). B. In smooth muscle, the wave of contraction passes from one muscle fiber to another by means of gap junctions. C. In cardiac muscle, the wave of contraction spreads rapidly from one muscle fiber to another by way of desmosomes and gap junctions. E. At the site of a neuromuscular junction involving smooth muscle, the axon lies in a shallow groove on the muscle surface, and the Schwann cell is retracted to expose the axolemma (Fig. 3-34).

Question 17

The following statements concern skin sensations
and dermatomes:

(a) To produce a region of complete anesthesia on
the trunk, at least three segments of the spinal
cord have to be damaged.
(b) When contiguous spinal nerves are sectioned,
the area of tactile loss is always smaller than the area of loss of painful and thermal sensations.
(c) The dermatome present on the medial side of the wrist is C5.
(d) The dermatome present on the point of the shoulder is C2.
(e) The dermatomes for the limbs run almost horizontally.

Answer 17

A is correct.

• To produce a region of complete anesthesia on the trunk, at least three segments of the spinal cord have to be damaged (see p. 9 8). B. When contiguous spinal nerves are sectioned, the area of tactile loss is always greater than the area of loss of painful and thermal sensations. C. The dermatome present on the medial side of the wrist is C8. D. The dermatomes present on the point of the shoulder are C3-C4. E. Limb dermatomes run almost vertically (see Figs. 3-36 and 3-37).

Question 18

The following statements concern muscle reflexes:

(a) The biceps brachii tendon reflex involves the
C5-C6 segments of the spinal cord.
(b) The triceps tendon reflex involves the T1 segment of the spinal cord.
(c) The patellar tendon reflex (knee jerk) involves
L5-S1 segments of the spinal cord.
(d) A tumor pressing on the second, third, and fourth lumbar segments of the spinal cord is
likely to interfere with the ankle jerk.
(e) The abdominal superficial reflexes involve T3-T5 segments of the spinal cord.

Answer 18

A is correct.

• The biceps brachii tendon reflex involves C5-C6 segments of the spinal cord (see p. 100). B. The triceps tendon reflex involves the C6-C7 and C8 segments of the spinal cord. C. The patellar tendon reflex (knee jerk) involves the L2-L4 segments of the spinal cord. D. A tumor pressing on the S1-S2 segments of the spinal cord is likely to interfere with the ankle jerk. E. The abdominal superficial reflexes involve T6-T12 segments of the spinal cord.

Question 19

The following statements concern the dermatomes
of the trunk and lower limbs:

(a) The T8 dermatome includes the skin of the
umbilicus.
(b) The L5 dermatome lies over the lateral side of
the knee joint.
(c) The L2 dermatome lies over the medial side of
the knee joint.
(d) The S2 dermatome runs along the lateral side of
the foot.
(e) The L1 dermatome lies over the inguinal ligament.

Answer 19

E is correct.

• The L1 dermatome lies over the inguinal ligament (see Fig. 3-36). A. The T10 dermatome Includes the skin of the umbilicus; the T8 dermatome involves the skin between the xiphoid process and the umbilicus. B. The L5 dermatome lies over the anterior and lateral surfaces of the leg below the knee. C. The L2 dermatome lies over the anterior and lateral surfaces of the thigh. D. The S2 dermatome extends down the middle of the posterior surface of the thigh and leg (see Fig. 3-37).

Question 20

The following statements concern muscle innervation:

(a) A motor unit consists of the posterior root
ganglion and all the neuromuscular spindles to
which it is connected.
(b) In the small muscles of the hand, one nerve
fiber supplies large numbers of muscle fibers.
(c) Neurotendinous spindles are innervated by
nonmyelinated nerve fibers.
(d) Muscle tone is dependent on the integrity of a
simple monosynaptic reflex arc.
(e) They motor efferent fibers innervate the extrafusal fibers of a muscle spindle.

Answer 20

D is correct.

• Muscle tone is dependent on the integrity of a simple reflex arc (see p. 101). A. A motor unit consists of a motor neuron in the anterior gray column (horn) of the spinal cord and all the muscle fibers it supplies (Fig. 3-39). B. In the small muscles of the hand, one nerve fiber supplies only a few muscle fibers. C. Neurotendinous spindles are innervated by myelinated nerve fibers. E. The y motor efferent fibers innervate the intrafusal fibers of a muscle spindle.

Question 21

The following statements concern skeletal muscle action:

(a) When a muscle begins to contract, the larger motor units are stimulated first.
(b) Muscle fatigue is caused by an exhaustion of the presynaptlc vesicles at the neuromuscular junction.
(c) When a prime mover contracts, the antagonistic muscles are inhibited.
(d) When a muscle is paralyzed, it does not immediately lose its normal tone.
(e) To paralyze a muscle completely, destroying several adjacent segments of the spinal cord or their nerve roots is not necessary.

Answer 21

C is correct.

• In voluntary muscle movement, when a prime mover contracts, the antagonistic muscles are inhibited (see p. 92). A. When a muscle begins to contract, the smaller motor units are stimulated first. B. Muscle fatigue ls caused by reduced adenosine triphosphate within the muscle fibers. D. When a muscle is paralyzed, it immediately loses its normal tone (see p. 101). E. To paralyze a muscle completely, destroying several adjacent segments of the spinal cord or their nerve roots is usually necessary.

Question 22

The following statements concern posture:

(a) In the standing position, the line of gravity passes through the odontoid process of the axis, behind the centers of the hip joints, and in
front of the knee and ankle joints.
(b) Posture depends on the strength of the joint ligaments and not on the degree and distribution of muscle tone.
(c) A particular posture can often be maintained for long periods by groups of muscle fibers in a muscle contracting together continuously.
(d) The cerebral cortex has no role in the maintenance of normal posture.
(e) Nerve impulses arising in the eyes and ears cannot influence posture.

Answer 22

A is correct.

• In the standing position, the line of gravity passes through the odontoid process of the axis, behind the centers of the hip joints, and in front of the knee and ankle joints (see p. 102). B. Posture depends on the degree and distribution of muscle tone. C. A particular posture can often be maintained for long periods by different groups of muscle fibers in a muscle contracting in relays. D. The cerebral cortex makes an important contribution to the maintenance of normal posture (see p. 102). E. Nerve impulses arising in the eyes and the ears can greatly influence posture.

Question 23

The following clinical observation on muscle activity can be made:

(a) Muscle contracture is a condition in which the muscle contracts for a long period of time.
(b) Muscle fasciculation is seen with chronic disease that affects sensory nerves supplying
muscles.
(c) Muscle atrophy does not take place when a
limb is immobilized in a splint.
(d) Muscle wasting can occur if only the efferent
motor nerve fibers to a muscle are sectioned.
(e) Wasting does not occur in the muscles acting on the shoulder joint in patients with painful
perlcapsulltis involving that joint.

Answer 23

D is correct.

• Muscle wasting can occur if only the efferent motor nerve fibers to a muscle are sectioned (see p. 109). A. Muscle contracture is a condition In which the muscle contracts and undergoes permanent shortening; it occurs frequently in muscles that normally oppose paralyzed muscles. B. Muscle fasciculation is seen with chronic disease that affects anterior horn cells or the motor nuclei of cranial nerves. C. Muscle atrophy takes place when a limb is immobilized in a splint. E. Wasting occurs in the muscles acting on the shoulder joint in patients with painful pericapsulitis involving that joint.

Question 24

The following statements concern nerves:

(a) Nerve tract is the name given to a nerve fiber in the peripheral and central nervous systems
(PNS and CNS).
(b) The supporting cell of a myelinated nerve fiber
in the CNS is called an oligodendrocyte.
(c) A node of Ranvier in peripheral nerves is where two Schwann cells come together and cover the exposed part of the plasma membrane of the axon.
(d) Nodes of Ranvier are absent from myelinated
nerve fibers in the CNS.
(e) The major dense line of myelin consists of two inner lipid layers of the plasma membrane that are fused together.

Answer 24

B is correct.

• The supporting cell of a myelinated nerve fiber In the CNS is called an oligodendrocyte. A. Nerve tract Is the name given to a nerve fiber In the CNS. C. A node of Ranvier in peripheral nerves is where two Schwann cells terminate and the plasma membrane of the axon is exposed (see p. 72). D. Nodes of Ranvier are present in myelinated nerve fibers in the CNS. E. The major dense line of myelin consists of two inner protein layers of the plasma membrane that are fused together.