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McKinley/O’Loughlin
Human Anatomy, 2nd Edition
CHAPTER 16
Answers to “What Did You Learn?”
1.
The cervical enlargement contains the motor neurons that innervate the upper
limbs. The lumbosacral enlargement contains the motor neurons that
innervate the lower limbs.
2.
There are 31 pairs of spinal nerves: 8 cervical C1-C8), 12 thoracic (T1-T12),
5 lumbar (L1-L5), 5 sacral (S1-S5), and 1 coccygeal (Co) nerve.
3.
The denticulate ligaments help suspend and anchor the spinal cord within the
middle of the vertebral canal, thus preventing potential lateral displacement of the
spinal cord.
4.
The gray matter in the spinal cord is centrally located and shaped like an H or
a butterfly. Bilaterally symmetrical right and left regions of gray matter are
connected in the midline by a thin, horizontal bar of gray matter, the gray
commissure, which surrounds a narrow central canal. Gray matter regions on
both sides are artificially separated into three projections, called horns. The
peripheral white matter is organized into funiculi. The anterior funiculi are
interconnected by the white commissure.
5.
The anterior horns primarily house the cell bodies of somatic motor neurons,
which innervate skeletal muscle. The axons of sensory neurons and the cell
bodies of interneurons.
6.
The: posterior, lateral and anterior funiculi are in the white matter of the
spinal cord.
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7.
Human Anatomy, 2nd Edition
The cell bodies of the sensory neurons in the posterior root are located in a
posterior root ganglion, which is attached to the posterior root. Each posterior
root ganglion is located medial to the pedicles of the adjacent vertebrae.
8.
From superior to inferior, the principal nerve plexuses are the cervical, brachial,
lumbar, and sacral.
9.
The brachial plexus is formed from the anterior rami of C5 through T1 spinal nerves.
10.
The main nerves of the lumbar plexus are the femoral nerve and the obturator
nerve. The main nerve of the sacral plexus is the sciatic nerve, which divides into
the tibial and common fibular nerves.
11.
The five steps in a reflex arc are: (1) activation of a receptor by a stimulus; (2)
nerve impulse travels through a sensory neuron to the spinal cord ; (3) the nerve
impulse is processed in the integration center by neurons; (4) a motor neuron
transmits a nerve impulse to an effector; and(5) the effector response to the nerve
impulse from the motor neuron.
12.
In a monosynaptic reflex, the sensory axons synapse directly on the motor
neurons, whose axons then project to the effector. Interneurons do not function in
this type of reflex. More complex neural pathways are observed in polysynaptic
reflexes, which have a number of synapses involving interneurons within the
reflex arc.
13.
Most components of the cranial and spinal nerves form from neural crest cells.
14.
The alar plates form the posterior horns of the gray matter and the posterior part
of the gray commissure.
McKinley/O’Loughlin
Human Anatomy, 2nd Edition
Answers to “Content Review”
1.
The major parts of the spinal cord are, from superior to inferior, the cervical part,
thoracic part, lumbar part, sacral part, and coccygeal part. Each part of the spinal
cord contains motor neurons and sensory axons whose axons contribute to spinal
nerves of the same name; for example, the cervical part contains the motor
neurons and sensory axons for the cervical spinal nerves.
The different parts of
the spinal cord do not match up exactly with the vertebrae of the same name,
because the spinal cord proper ends at the level of the L1 vertebra.
2.
The epidural space lies between the dura mater and the inner walls of the vertebrae.
This space houses areolar connective tissue, blood vessels, and adipose connective
tissue.
3.
Anterior horns house cell bodies of somatic motor neurons, which innervate
skeletal muscle. The anterior horns contain somatic motor nuclei. Lateral horns,
found only in the T1-L2 regions of the spinal cord, contain the cell bodies of
autonomic motor neurons, which innervate cardiac muscle, smooth muscle and
glands. The lateral horns contain autonomic motor nuclei. Posterior horns are
posterior masses of gray matter. The axons of sensory neurons and the cell bodies
of interneurons are located in the posterior horns. The posterior horns contain
somatic sensory and visceral sensory nuclei.
4. The cervical plexuses are located deep on each side of the neck immediately
lateral to cervical vertebra C1-C4. Branches of the cervical plexuses innervate
McKinley/O’Loughlin
Human Anatomy, 2nd Edition
the anterior neck muscles as well as the skin of the neck, portions of the head and
shoulders.
5. The five major terminal branches of the brachial plexus are the axillary nerve,
median nerve, musculocutaneous nerve, radial nerve and ulnar nerve. The axillary
nerve supplies the deltoid and teres minor muscles. The median nerve innervates
most anterior forearm muscles (except the medial ½ of the flexor digitorum
profundus and flexor carpi ulnaris), the lateral two lumbricals, and the muscles of
the thenar eminence. The radial nerve supplies the posterior arm and posterior
forearm muscles, as well as brachioradialis. The musculocutaneous nerve
supplies the anterior arm muscles (brachialis, coracobrachialis and biceps
brachii). The ulnar nerve innervates the medial ½ of the flexor digitorum
profundus, flexor carpi ulnaris, the hypothenar muscles, adductor pollicis, the
medial two lumbricals, and all of the interossei.
6. The lumbar plexus is formed from the anterior rami of L1-L4. The femoral and
obturator nerves are formed from this plexus.
7. The tibial nerve innervates most of the hamstring muscles (except the short head
of the biceps femoris), the posterior leg muscles, and the muscles on the plantar
side of the foot. The common fibular nerve innervates the short head of the
biceps femoris, the anterior leg muscles, lateral leg muscles, and the muscles on
the dorsum of the foot.
8. Reflexes are rapid, automatic, involuntary reactions of muscles or glands to a
stimulus. Usually a conscious movement is somewhat slower and not
predictable.
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9.
Human Anatomy, 2nd Edition
A stretch reflex is a simple, monosynaptic reflex that monitors and regulates
skeletal muscle length. When a muscle is stretched it reflexively contracts to
shorten. A withdrawal reflex is a polysynaptic reflex causing the movement
of a traumatize body part away for the source of harm. A Golgi tendon reflex
prevents skeletal muscles from tensing excessively.
10.
The basal plates lie anterior to the sulcus limitans. The basal plates will develop
into the anterior and lateral horns of the gray matter. Thus, the basal plates give
rise to motor structures in the gray matter. They also will form the anterior part of
the gray commissure.