CHAPTER SIXTEEN
Content Review
1. The cervical enlargement of the spinal cord controls the upper limbs, and the lumbar
enlargement controls the lower limbs. These regions are larger because they contain
more neuron cell bodies.
2. The epidural space lies between the dura mater and the vertebrae. This space houses
areolar connective tissue, blood vessels, and adipose connective tissue.
3. Anterior horns are masses of gray matter that house the cell bodies of somatic motor
neurons, which innervate skeletal muscle. 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. Posterior horns are masses of
gray matter that house the axons of sensory neurons and the cell bodies of
interneurons.
4. The cervical plexuses are located deep on each side of the neck immediately lateral to
cervical vertebrae C1–C4. Branches of the cervical plexuses innervate the anterior
neck muscles as well as the skin of the neck and 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. The median nerve supplies most anterior forearm
muscles (except the medial half of the flexor digitorum longus and flexor carpi
ulnaris), the lateral two lumbricals, and the thenar muscles. The radial nerve
innervates the posterior arm and forearm muscles as well as the brachioradialis. The
musculocutaneous nerve supplies the coracobrachialis, brachialis, and biceps brachii.
The ulnar nerve innervates the medial half of the flexor digitorum profundus, flexor
carpi ulnaris, the hypothenar muscles, medial two lumbricals, and the interossei.
6. The tibial nerve innervates the posterior leg muscles and muscles on the sole of the
foot. The common fibular nerve branches into a deep fibular nerve (supplies anterior
leg and dorsal foot muscles) and a superficial fibular nerve (supplies lateral leg
muscles).
7. The anterior rami of L1–L4 make up the lumbar phexus. The femoral and obturator
nerves form from this plexus.
8. Reflexes are rapid, automatic, involuntary reactions of muscles or glands to a
stimulus. Conscious movements are usually somewhat slower and not as predictable
as reflexes.
9. A stretch reflex is a 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 that causes a traumatized body part to move away from
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 develop into the
anterior and lateral horns of the gray matter, and thus they give rise to motor
structures in the gray matter. They also form the anterior part of the gray commissure.