Parasympathetic System

Parasympathetic = Craniosacral outflow (Figure 111-1-9)



Chapter Summary

The vertebral column is composed of a series of cervical, thoracic, lumbar, sacral, and coccygeal vertebrae connected by intervertebral disks and ligaments. The disks consist of an outer core erf fibrocartilage, the annulus fibrosus, and an inner part—the nucleus pulposus, which developed from the notochord, Herniation of the nucleus pulposus is usually posterolateral where it can compress a spinal nerve at the intervertebral foramen.

The spinal nerve exits the vertebral column at the intervertebral foramen. The foramen is bound superiorly and interiorly by the pedicles of the vertebrae, anteriorly by the vertebral bodies and intervertebral disks, and posteriorly by the zygapophyseal joint.

The spinal cord is covered by three protective layers of meninges: dura mater, arachnoid, and pia mater. The dura and dural sac terminate interiorly at the second sacral vertebra, and the spinal cord terminates at the second lumbar vertebra. The cauda equina fills the lower part of the dural sac and contains the filum terminale and the ventral and dorsal roots of the lumbar and sacral spinal nerves. Between the arachnoid and pia is the subarachnoid space that contains cerebrospinal fluid, and between the dura mater and the vertebrae is the epidural space, which contains fat and a plexus of veins. Spinal taps are performed at the level of the L4 vertebra (located at the horizontal level of the iliac crest) to avoid puncturing the spinal cord.

Autonomic Nervous System

The autonomic nervous system (ANS) provides visceral motor innervation to smooth muscle, cardiac muscle, and glands. The ANS is divided into two divisions: sympathetic (thoracolumbar) and parasympathetic (craniosacral). The peripheral distribution of these two divisions consists of two neurons: (?) the preganglionic neuron (ceil bodies in the CMS) and (2) the postganglionic neuron (cell bodies in motor ganglia in PNS).

Sympathetic preganglionic cell bodies are found in the lateral horn of the gray matter of spinal cord segments Tl -L2. These synapse with postganglionic cell bodies located in either chain (paravertebral) ganglia or collateral (prevertebral) ganglia. Sympathetic to the body wall, head, and thoracic viscera synapse in the chain ganglia. Sympathetics to the foregut and midgut (thoracic splanchnic nerves: T5-T12) and to the hindgutand pelvic viscera (lumbar splanchnic nerves: LI-L2) synapse in collateral ganglia. Interruption of sympathetic innervation to the head results in ipsilateral Homer syndrome.

Parasympathetic preganglionic neuron cell bodies are located in the brain stem nuclei of cranial nerves III, VII, IX and X, or in the gray matter of the spinal cord segments S2-S4 (pelvic splanchnics). The preganglionic neurons synapse with postganglionic neurons in terminal ganglia scattered throughout the body. Parasympathetics to the head originate in cranial nerves III, VII, and IX; those to the thorax, foregut and midgut originate in cranial nerve X; and those to the hindgut and pelvic viscera originate in the S2-S4 cord segments.

Review Questions

1. Which of the following procedures is correctly matched to the last layer that a needle will traverse in the proper performance of that procedure?

(A) Lumbar puncture/arachnoid mater

(B) Pericardiocentesis/fibrous pericardium

(C) Thoracocentesis/visceral pleura

(D) Culdoscopy/posterior fornix

(E) Pudendal block/dura mater

2. You are performing a spinal tap slightly off the midline between the L3 and L4 vertebrae. What structure will the needle pass through during proper performance of this procedure?

(A) Posterior longitudinal ligament

(B) Ligamentum flavum

(C) Anterior longitudinal ligament

(D) Denticulate ligament

(E) Filum terminale

3. Which nerves accompany branches of the superior mesenteric artery that increase peristalsis and glandular secretion in the GI tract?

(A) Greater splanchnic nerves

(B) Lesser splanchnic nerves

(C) Pelvic splanchnic nerves

(D) Vagus nerves

(E) Lumbar splanchnic nerves

4. Your patient has a dry eye and reduced nasal secretions. The location of a lesion might be in the

(A) otic ganglion

(B) pterygopalatine ganglion

(C) ciliary ganglion

(D) superior cervical ganglion

(E) submandibular ganglion

5. Your patient has a herniated nucleus pulposus of the intervertebral disc between the L4 and L5 vertebrae. Which is the most likely condition that your patient would present with?

(A) Altered sensation in the L3 dermatome

(B) Weakness of muscles innervated by the L5 spinal cord segment

(C) Inability to contract the bladder

(D) Fecal incontinence

(E) Weakness in the ability to extend the leg at the knee

6. During a pregnancy, amniocentesis reveals elevated levels of alpha-fetoprotein, and ultrasound imaging indicates the presence of a cyst in the dorsal midline in the lower lumbar region. Corrective postnatal surgery reveals that the cyst contains cerebrospinal fluid but no neural tissue. What is your evaluation of the cyst?

(A) It is seen in infants with spina bifida occulta.

(B) It was a meningomyelocele.

(C) It was an Arnold Chiari formation.

(D) It results from the rostral neuropore failing to close.

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