Neuroscience Chapter 13: Spinal Region

1. What is a spinal nerve?

1. 1. A spinal nerve is the brief union of the dorsal and ventral roots of a single spinal segment within the intervertebral foramen. The spinal nerve divides into the anterior and posterior rami.

Case 1 P.E. is a 17-year-old woman. She fractured the C7 vertebra in a diving accident 2 months ago. The fracture is stable. Current findings are as follows: •Sensation is intact (pinprick, temperature, conscious proprioception, and discriminative touch) in her head, neck, and lateral upper limbs. •She has no sensation in the medial upper limbs, the trunk below the sternal angle, and the lower limbs. •All head and shoulder movements are normal strength except shoulder extension. •Elbow flexion and radial wrist extensors are normal strength. •The remaining upper limb, trunk, and lower limb muscles have no trace of voluntary movement. •Babinski's sign is present bilaterally. Without adaptive equipment, P.E. is unable to care for herself. Using adaptive equipment, she is able to eat, dress, and groom independently. She uses a wheelchair. She cannot voluntarily control her bladder or bowels. Questions 1. Is the lesion in the dorsal or ventral root or in the spinal cord? 2. What neurologic level is the lesion? Note: The neurologic level in a spinal cord injury is the most caudal level with normal sensory and motor function bilaterally. Refer to Table 13-4 to determine the neurologic level. Is the lesion complete or incomplete?

1. The lesion is in the spinal cord and not in a root, because the loss of sensation and motor control throughout the medial upper limb and the entire trunk and lower limb indicates that vertical tracts are interrupted. 2. The signs include loss of sensation below the C6 dermatome and complete loss of motor control below C6. These signs indicate a complete lesion of the spinal cord at the C6 level.

Dorsal root

Afferent (sensory) root of a spinal nerve.

Match the structure with it's function Spinal Nerve

Contains all of the motor, sensory, and autonomic axons of a single spinal segment.

Rexed's lamina

Histologic division of the spinal cord gray matter.

Paraplegia

Paresis or paralysis of both lower limbs; may also involve part of the trunk.

Cauda equina syndrome

Sensory impairment and flaccid paralysis of the lower limbs, bladder, and bowels

Dorsal root ganglion

The collection of primary sensory neuron cell bodies located in the dorsal root.

4. What is the function of the dorsal horn?

The dorsal horn processes sensory information.

2. What is the difference between a ventral root and a ventral primary ramus?

1. 2. A ventral root is a collection of motor and autonomic efferent axons from one segment of the spinal cord. The ventral primary ramus is a branch of the spinal nerve and provides innervation to the anterior and lateral trunk and the limbs.

Case 2 B.D. is a 16-year-old adolescent. He sustained a spinal cord injury 2 months ago in a fall from a bicycle. Current findings are as follows: •Pinprick and temperature sensation are impaired, as indicated in Figure 13-26. All other sensations are fully intact. •Manual muscle test scores are also indicated in Figure 13-26. •Babinski's sign is present bilaterally. •He is independent in all activities. He is able to walk 30 meters using an ankle-foot orthosis on his left leg and a cane. Questions 1. What level is the cord lesion? Is the lesion complete, or does the pattern indicate a spinal cord syndrome? 2. Why is this patient independent, while the patient in Case 1 requires adaptive equipment, a wheelchair, and maximal assistance on stairs?

1. BD has anterior cord syndrome at C6. Anterior cord syndrome interrupts upper motor pathways, lower motor neurons, and the spinothalamic tracts. The dorsal columns and dorsal horns are intact. Because some neurons in the spinothalamic tract are intact, pain and temperature sensation is partially preserved. In this case, the incomplete injury slightly damaged anteriorly located tracts on the right side and moderately damaged the same tracts on the left side, leaving parts of the vertical tracts intact. 2. This patient's outcome is very different from the complete lesion of the cord in Case 1, because many axons in vertical tracts were spared.

3. What is a spinal segment?

A spinal segment is a section of the spinal cord that is connected with a specific dermatome, myotome, and sclerotome by a spinal nerve, its roots, and its rootlets.

Complete spinal cord lesions above which one of the following level results in long-term ventilator dependence? A. C4 B. C5 C. C6 D. C7 E. All of the above

ANS: A Rationale: Lesions above C4 interrupt most fibers of the phrenic nerve (C3 and C5 make small contributions to the phrenic nerve), so the diaphagm does not receive adequate signals for breathing. If C4 is intact, the diaphragm receives adequate signals for breathing.

Spinothalamic tract

ANS: The origin of the spinothalamic tract is sensory neurons in the dorsal horn of spinal cord.

When the bladder is empty, what efferent control inhibits contraction of the bladder wall and maintains closure of the external sphincter?

ANS: The sympathetic efferents from T11 to L2 inhibit contraction of the bladder wall and maintain closure of the internal sphincter.

14. What is an incomplete spinal cord injury? Give two examples of syndromes that may result from incomplete spinal cord injury.

An incomplete spinal cord injury is damage to the spinal cord in which sensory and/or motor function is preserved in the lowest sacral segment. Anterior cord, Brown-Séquard, or central cord syndrome can produce incomplete spinal cord injury. Cauda equina syndrome is damage to the cauda equina, not the cord, so cauda equina damage does not produce incomplete spinal cord injury.

Ventral horn

Anterior section of gray matter in the spinal cord; contains endings of upper motor neurons, interneurons, dendrites, and cell bodies of lower motor neurons.

15. List the three conditions that arise when the spinal cord below the T6 level is deprived of descending sympathetic innervation.

Autonomic dysreflexia, poor thermoregulation, and orthostatic hypotension arise when the spinal cord below the T6 level is deprived of descending sympathetic innervation.

Complete T10 spinal cord lesion

Babinski's sign; paralysis; hyperreflexia; muscle hypertonia; complete loss of all sensation below the level of the umbilicus

Dorsal primary ramus

Branch of a spinal nerve that innervates the paravertebral muscles, posterior parts of the vertebrae, and overlying cutaneous areas.

Ventral primary ramus

Branch of a spinal nerve that innervates the skeletal, muscular, and cutaneous areas of the limbs and/or of the anterior and lateral trunk.

Case 3 V.K. is a 30-year-old man. He plays recreational sports 4 days a week and is a highly competitive soccer player. Two years ago, he experienced temporary weakness in his left lower leg, which gradually resolved without consultation or treatment. His primary complaint now is inability to control his right foot. He first noticed poor kicking skills 3 weeks ago. Sensation and motor control are normal except in the right lower limb. The following deficits are observed in the right lower limb: •Discriminative touch, vibration sense, and position sense are impaired throughout. •Pain and temperature sensations are intact. •Movement is ataxic. Gait deficits: dragging of toes on the ground during the swing phase of walking (foot drop), poor placement of the foot on the ground, weight bearing on the right lower limb only half the time spent weight bearing on the left lower limb •Gluteals, hamstrings, and all muscles originating below the knee are weak, less than half the strength of the homologous muscles on the left. The same muscles are hypertonic. Reflex testing reveals gastrocnemius hyperreflexia and Babinski's sign on the left. Questions 1. Why are pain and temperature sensations intact bilaterally? 2. Where is the lesion? 3. What is the probable etiology? Thank

CASE 3 1. 1. Vertical tracts conveying pain and temperature information are not impaired, because the spinothalamic tracts are anterior to the lesion. 1. 2. The dorsal column signs (impaired proprioception, discriminative touch, and vibration sense plus somatosensory ataxia) and upper motor neuron signs (weakness, hyperreflexia, hypertonia) indicate a lesion in the right posterolateral cord at the L2 spinal segment. Although the lesion does interfere with transmission of pain information from the dermatome that projects to the right L2 segment, no deficit is evident clinically, because of the overlap of adjacent sensory fields in the periphery. 1. 3. The earlier incident of weakness in the left leg, with full resolution, plus the current signs, indicate multiple sclerosis as a possible diagnosis.

Match the structure with it's function Dorsal root ganglion

Contains cell bodies of primary sensory neurons.

Match the structure with it's function Ventral Root

Contains efferent axons, including axons that innervate skeletal muscle.

Match the structure with it's function Dorsal Root

Contains sensory axons that connect with a single segment of the spinal cord.

Orthostatic hypotension

Decrease of 20 mm Hg or more in systolic blood pressure when moving from prone or supine to sitting or standing.

Reciprocal inhibition

Decreased activity in an antagonist when an agonist is active.

Right C5 spinal nerve lesion

Decreased strength in right deltoid and biceps; decreased sensation in anterolateral right upper arm; sensation and motor function intact for the remainder of the body

Cervical spondylosis

Degeneration of the cervical vertebrae and disks that produce narrowing of the vertebral canal and intervertebral foramina.

Neurologic level

Describing spinal cord injury, neurologic level is the most caudal level with normal sensory and motor function bilaterally.

Meningomyelocele

Developmental defect; inferior part of the neural tube remains open.

Multiple sclerosis

Disease that is characterized by random, multifocal demyelination limited to the central nervous system. Signs and symptoms include numbness, paresthesia, Lhermitte's sign, asymmetric weakness, and/or ataxia.

Autonomic dysreflexia

Excessive activity of the sympathetic nervous system; is usually elicited by noxious stimuli below the level of a spinal cord lesion.

Crossed extension reflex

Extension of the opposite lower limb when one lower limb is moved away from a stimulus.

Match the part of the gray matter with it's function Rexed lamina

Histologic and functionally specific regions in the spinal cord gray matter

Tetraplegia

Impairment of arm, trunk, lower limb, and pelvic organ function, usually from damage involving the cervical spinal cord.

Recurrent inhibition

Inhibition of agonists and synergists, combined with disinhibition of antagonists.

Match the structure with it's function Dorsal ramus

Innervates paravertebral muscles, posterior vertebral structures, and overlying cutaneous areas.

Renshaw cells

Interneurons that produce recurrent inhibition in the spinal cord; act to focus motor activity.

Withdrawal reflex

Is a movement of a limb away from a stimulus.

Ventral root

Is an efferent (motor) root of a spinal nerve.

Right radial nerve lesion

Lack of posterolateral sensation in digits four and five of the right hand; intact sensation of all fingertips; paralysis of long extensors for right wrist and finger; paralysis of the right supinator; sensation and motor function intact for remainder of the body

Complete spinal cord injury

Lack of sensory and motor function in the lowest sacral segment.

5. Which of Rexed's laminae is also known as the substantia gelatinosa?

Lamina II is also known as the substantia gelatinosa.

Lateral horn

Lateral section of gray matter in the spinal cord; contains cell bodies of preganglionic sympathetic neurons.

Radiculopathy

Lesion of a dorsal or ventral nerve root; clinical use of the term may refer to a spinal nerve lesion.

Match the part of the gray matter with it's function Dorsal horn

Location of neurons that convey sensory information from peripheral mechanoreceptors

Spastic cerebral palsy

Motor disorder that develops in utero or during infancy; is characterized by neuromuscular overactivity.

Spinal nerve

Nerve located in the intervertebral foramen, formed by the dorsal and ventral roots that contains both afferent and efferent axons; spinal nerves branch to form dorsal and ventral rami.

Match the structure with it's function Propriospinal neuron

Neuron that begins and ends within the spinal cord.

Match the structure with it's function Tract cell

Neuron with a long axon that conveys information from the spinal cord to the brain.

Tract: Spinothalamic

Origin: Dorsal horn of spinal cord Function: Conveys discriminative information about pain and temperature

Tract: Spinolimbic, spinomesencephalic, spinoreticular

Origin: Dorsal horn of spinal cord Function: Nonlocalized perception of pain; arousal, reflexive, motivational, and analgesic responses to nociception

Tract: Dorsal column/medial lemniscus

Origin: Peripheral receptors; first-order neuron synapses in medulla Function: Conveys information about discriminative touch and conscious proprioception

Right hemi-lesion of spinal cord, L1 segment

Paralysis of the right iliopsoas and all muscles in the right lower limb; loss of discriminative touch and conscious proprioception in the right lower limb; loss of discriminative pain and temperature sensation in the left lower limb and left buttock region

Substantia gelatinosa

Part of the dorsal gray matter in the spinal cord; is involved in processing nociceptive information. Synonym: lamina II

Nucleus proprius

Part of the dorsal gray matter in the spinal cord; processes proprioceptive and two-point discrimination information. Synonyms: lamina III and IV

Dorsal horn

Posterior section of gray matter in the spinal cord. Primarily sensory in function, the dorsal horn contains endings and collaterals of first-order sensory neurons, interneurons, and dendrites and somas of tract cells.

Incomplete spinal cord injury

Preservation of sensory and/or motor function in the lowest sacral segment (American Spinal Cord Injury Association definition).

Lhermitte's sign

Radiation of a sensation similar to an electrical shock down the back or limbs elicited by neck flexion.

Syringomyelia

Rare, progressive disorder; a syrinx (fluid-filled cavity) develops in the spinal cord, almost always in the cervical region; segmental signs occur in the upper limbs, including loss of sensitivity to pain and temperature stimuli; upper motor neuron signs in lower limbs include paresis, muscle hypertonia, and spasticity; loss of bowel and bladder control often occurs.

Brown-Séquard syndrome

Segmental loss of all sensation and paresis of muscles innervated by the involved spinal segment(s); ipsilateral loss of voluntary motor control, conscious proprioception, and discriminative touch below level of lesion, contralateral loss of pain and temperature sensations below level of lesion

Brown-Séquard syndrome

Signs and symptoms produced by a hemisection of the spinal cord; segmental losses are ipsilateral and include loss of lower motor neurons and all sensations. Below the level of the lesion, voluntary motor control, conscious proprioception, and discriminative touch are lost ipsilaterally, and temperature and nociceptive information are lost contralaterally.

Cauda equina syndrome

Signs and symptoms produced by damage to the lumbar and/or sacral nerve roots, causing sensory impairment and flaccid paralysis of lower limb muscles, bladder, and bowels.

Anterior cord syndrome

Signs and symptoms produced by interruption of ascending spinothalamic tracts, descending motor tracts, and damage to the somas of lower motor neurons; this spinal cord syndrome interferes with pain and temperature sensation and with motor control.

13. Why do some people with spinal cord injuries have exaggerated withdrawal reflexes?

Some people with spinal cord injuries have exaggerated withdrawal reflexes because the normal descending reticulospinal inhibition on the neurons within the withdrawal reflex circuit has been removed.

12. Why are cord functions below the lesion depressed or lost immediately after a spinal cord injury?

Spinal cord functions are depressed or lost immediately below the lesion after a spinal cord injury, because descending tracts that supply tonic facilitation to the spinal cord neurons are interrupted by the lesion.

10. What are the differences in signs between segmental and vertical tract lesions?

The differences between segmental and vertical tract signs are as follows: Segmental signs are limited to a dermatomal and/or myotomal distribution. The sensory signs include lost or abnormal sensation, and the motor signs include lower motor neuron signs: flaccid weakness, atrophy, fibrillations, and fasciculations. Vertical tract signs occur at all levels below the lesion and include decreased or lost sensation, decreased or lost voluntary control of pelvic organs, and upper motor neuron signs: increased muscle resistance to stretch, paresis, phasic stretch hyperreflexia, and Babinski's sign. Signs of interruption of the sympathetic tracts above the T6 level include autonomic dysreflexia, poor thermoregulation, and orthostatic hypotension.

11. List the four adult-onset spinal region syndromes, and draw spinal cord cross-sections that illustrate the location of the lesion in each syndrome.

The four adult-onset spinal region syndromes are anterior cord syndrome, central cord syndrome, Brown-Séquard syndrome, and cauda equina syndrome. See Figure 13-19 for illustrations of the location of the lesion in each syndrome.

9. How is voluntary voiding of urine controlled?

Voluntary voiding of urine requires that information regarding fullness of the bladder be conveyed to the sacral spinal cord by afferents, then to the cerebral cortex, where a decision is made. Then the brain initiates voiding by corticospinal inhibition of lower motor neurons that innervate the external sphincter and by brainstem pathways to the autonomic efferents that stimulate contraction of the bladder wall.

Right L3 ventral root lesion

Weakness of the quadriceps on the right side; no other motor or sensory loss

Propriospinal

Within the spinal cord; usually refers to neurons that are located entirely in the spinal cord.

Central cord syndrome S

igns and symptoms produced by interruption of spinothalamic fibers crossing the midline, producing loss of pain and temperature sensation at the involved segments. Larger lesions also impair upper limb motor function because the lateral corticospinal tracts to the upper limb are located in the medial part of the white matter and because the lesion typically occurs in the cervical region.

Case 5 A 48-year-old woman has a 5 year history of intermittent low back pain. She is otherwise healthy. Yesterday she had abrupt onset of severe pain in the perineal and sacral region and intermittent shooting pain down the back of her right lower limb, exacerbated by sitting and by coughing. Two hours later, she developed increased urinary frequency and a sensation of being unable to fully empty her bladder. Defecation frequency also increased. •Somatosensation: decreased light touch and pinprick in perineal and sacral region. Somatosensation intact throughout rest of body. With the patient in the supine position, shooting pain is elicited in the posterior right leg when the therapist lifts the patient's leg to 30 degrees of hip flexion with the knee straight. The same maneuver flexing the left hip to 70 degrees does not elicit pain. Normally, this test, the straight leg raise, does not elicit pain with hip flexion to 70 degrees. •Autonomic: increased frequency of urination and defecation; abnormal sensation of inability to completely empty bladder •Motor: weak contraction of anal sphincter. MMT (manual muscle test) grade is 5 throughout both lower limbs. Questions 1. Where is the lesion? 2. What is the probable etiology? 3. After the examination, what is the next step with this patient?

1. The pain radiating down the posterior right leg indicates impingement of the S1 and S2 sensory nerve roots, and the impaired sensation in the saddle region indicates impingement of the S2-S5 sensory nerve roots. No dermatomal or myotomal signs of lumbar root involvement are present. The bowel and bladder signs indicate involvement of the S2-S4 nerve roots. Because skeletal muscle power in the lower limbs is preserved, the lesion does not involve most anterior nerve roots. However, the weak contraction of the anal sphincter indicates that the lower motor neurons to the anus are affected by the lesion. This case appears to be a cauda equina lesion, primarily affecting sacral sensory nerve roots. Recall that the entire sacral spinal cord is located at the L1 vertebral level. The lesion is most likely at the L5-S1 vertebral level, because the spinal cord ends at L1-L2 vertebral level, no signs of lumbar spinal nerve impingement are present, L5-S1 vertebral level is often the site of disk herniations, and only the sacral roots are present at L5-S1. 2. Because cauda equina syndrome is usually caused by a herniated nucleus pulposis, that is the most likely etiology. 3. The next step is emergency medical referral, because without treatment cauda equina syndrome can cause paraplegia and/or permanent problems with sensory loss and with bowel and bladder control.

Which one of the following is NOT a sign of an upper motor neuron lesion? A. Muscle paresis B. Hyperreflexia C. Dystonia D. Positive Babinski's sign E. Spasticity

ANS: C Rationale: Muscle paresis, hyperreflexia, positive Babinski's sign, and spasticity are all signs of an upper motor neuron (UMN) lesion. Dystonia is a basal ganglia sign and does not occur in UMN lesions.

Vertebral canal stenosis is associated with which one of the following? A. Narrowing of the vertebral canal caused by bone growth or tissue hypertrophy B. Compression of neural and vascular structures of the spinal cord C. Radiating pain with numbness and loss of proprioception D. All of the above E. None of the above

ANS: D Rationale: Vertebral canal stenosis causes narrowing of the vertebral canal (by bone growth or tissue hypertrophy), compression of neural and vascular structures of the spinal cord, and radiating pain with numbness and loss of proprioception. Clumsiness occurs secondary to lack of proprioception. Upper motor neuron signs may occur with cervical stenosis.

What is the function of Renshaw cells?

ANS: Renshaw cells are interneurons that regulate recurrent inhibition of the motor neuron to the agonist.

Match the part of the gray matter with it's function Lateral horn (T1-L2)

Location of neurons that integrate and transmit signals for sympathetic regulation

Match the part of the gray matter with it's function Ventral horn

Location of neurons that integrate sensory and motor signals and innervate skeletal muscles

Anterior cord syndrome

Loss of discriminative pain and temperature sensation and paralysis of muscles below the level of the lesion; conscious proprioception and discriminative touch remain intact

Central cord syndrome

Loss of pain and temperature information at several cervical segments; all sensations and motor and autonomic functions intact throughout remainder of body

Tethered cord syndrome

Low back and lower limb pain, difficulty in walking, excessive lordosis and scoliosis, bowel and bladder control problems, foot deformities

Case 4 E.V. is a 62-year-old woman. She reports constant burning pain radiating down the back of her left leg into her foot. When she coughs or sneezes, sharp, stabbing pains become excruciating. The pain began as a backache 3 months ago. Pain intensity has been consistently increasing. Following are the results of testing: •Sensation is intact in the right lower limb. •Sensory testing results for the left lower limb are shown in Table 13-5. •Strength in all limbs is within normal limits. •Ankle deep tendon reflex is absent on the left side. Questions 1. Where is the lesion? 2. What is the probable etiology? 3. Why is discriminative touch more affected than pain and temperature sensations?

1. Complete loss of sensation is limited to the S1 dermatome on the left. Because the L5 level contributes to ankle kinesthesia, ankle position sense is partially retained. Preserved sensation at the left S4 and S5 levels and intact sensation in the right lower limb indicate that vertical tracts are not damaged. Thus the lesion is likely to be outside the spinal cord. 2. Given the S1-S3 dermatomal distribution of symptoms, a lesion compressing the dorsal roots can be suspected. In this case, the lesion is a small tumor compressing the left S1-S3 dorsal roots. 3. Touch and proprioceptive sensations are more affected than pain and temperature sensations, because compression affects large axons more than small axons. A lesion in the dorsolateral cord would have interfered with ascending dorsal column information from the left lower limb and descending lateral corticospinal information to the left lower limb.

Autonomic dysreflexia is characterized by which one of the following? A. Abrupt decrease in blood pressure because of sympathetic vasoconstriction B. Abrupt increase in blood pressure and pounding headache C. Profuse sweating below the level of the lesion D. Excessive activation of the parasympathetic nervous system E. Excessive shivering associated with hyperthermia

ANS: B Rationale: Autonomic dysreflexia occurs when a complete spinal cord lesions above the T6 level prevents most of the spinal cord from receiving signals from the brain that inhibit sympathetic activity. Autonomic dysreflexia is an excessive sympathetic response, usually to stretch of the bladder or bowel, characterized by an abrupt increase in blood pressure, a pounding headache. In addition, flushing of the skin and profuse sweating occur above the level of the lesion. The sudden spike in blood pressure may be life threatening.

After a complete spinal cord injury affecting S2-4, a bladder that cannot be emptied is which of the following? A. Hypertonic and hyperreflexive B. Flaccid and paralyzed C. Spastic D. Autoreflexive E. None of the above

ANS: B Rationale: Complete lesions that damage any part of the reflexive bladder emptying circuit, that is, levels S2-S4—or afferents or parasympathetic efferents—produce a flaccid, paralyzed bladder. With an S2-4 lesion, the sympathetic efferents are intact and their signals inhibit contraction of the bladder wall and facilitate closure of the internal spincter. Complete lesions above the sacral cord interrupt descending axons that normally control bladder function but do not interrupt sacral level reflexive control of the bladder. This results in a hypertonic, hyperreflexive bladder with reduced bladder capacity. Hyperreflexive bladder and spastic bladder are synonymous. Autoreflexive is not a neuroscience term.

Reciprocal activation of a stepping pattern generator (SPG) is thought to be coordinated by signals conveyed in the: A. DCML B. Golgi tendon organs (GTOs) C. Posterior commissure of spinal cord D. Anterior commissure of spinal cord E. Ventral horn gamma motor neurons

ANS: B Rationale: Reciprocal activation of stepping pattern generators is essential for swing phase of one lower limb to occur simultaneously with the stance phase of the other lower limb. The signals to coordinate the right and left stepping pattern generators are conveyed in the anterior commissure of the spinal cord.

Dorsal rhizotomy is the selective surgical ablation of which of the following? A. Dorsal horn neurons B. Posterior commissural axons C. Dorsal roots D. Dorsal columns E. Nucleus dorsalis

ANS: C Rationale: Dorsal rhizotomy is selective surgical ablation of the dorsal roots. The purpose of the surgery is to decrease or eliminate hyperreflexia by interrupting the afferent limb of the stretch reflex. The procedure is selective because individual dorsal rootlets are stimulated electrically before ablation to determine whether activity in that specific dorsal rootlet contributes to hyperreflexia. If stimulating the rootlet does not contribute to hyperreflexia, the rootlet is left intact to provide somatosensation.

Loss of pain and temperature sensation in a capelike distribution over the shoulders, lower limb paresis, hyper-reflexia, and loss of bowel and bladder function are characteristic of which of the following? A. Multiple sclerosis B. Cervical spondylosis C. Meningomyelocele D. Syringomyelia E. Erb's paralysis

ANS: D Rationale: The loss of pain and temperature sensation in a cape-like distribution over the shoulders, lower limb paresis, hyperreflexia, and loss of bowel and bladder function are characteristic of syringomyelia. In syringomyelia, a syrinx, or a fluid-filled cavity, develops in the spinal cord, almost always in the cervical region. Syringomyelia usually is congenital but may occur secondary to trauma or tumor. Accumulation of cerebrospinal fluid in the syrinx causes increased pressure inside the spinal cord, expanding the cavity and compressing adjacent nerve fibers. The loss of sensitivity to pain and temperature stimuli is due to interruption of spinothalamic axons crossing the midline in the anterior white commissure.

Loss of descending sympathetic control as a result of complete spinal cord lesions above T6 result in which of the following? A. Orthostatic hypotension B. Autonomic dysreflexia C. Poor thermoregulation D. Both A and B E. A, B, and, C

ANS: E Rationale: Complete spinal cord lesions above T6 cause serious abnormalities of autonomic regulation because many segments of the cord below the lesion are free from descending sympathetic control. The loss of descending sympathetic control results in orthostatic hypotension, autonomic dysreflexia, and poor thermoregulation.

Klumpke's paralysis is the result of which of the following? A. Avulsion of the C5 to C6 ventral roots B. Mechanical irritation of the C7 to C8 dorsal roots C. Traction force applied to the cervico-occipital region D. Lesion of the dorsal root ganglion because of a herniated disk E. Avulsion of the C8 through T1 motor nerve roots

ANS: E Rationale: Traction on the abducted arm can cause avulsion of the motor roots of C8 and T1, resulting in Klumpke's paralysis. Loss of lower motor neuron output from the C8 and T1 spinal levels results in paralysis and atrophy of the hand intrinsic muscles and the long flexors and extensors of the fingers.

What type of neural circuit ensures that antagonists are inhibited during contraction of the agonist?

ANS: Reciprocal inhibition of motor neurons in the spinal cord inhibit alpha motor neurons that elicit antagonist contraction.

What anatomic division marks the end of the spinal region and beginning of the peripheral nervous system?

ANS: The anatomic division is marked at the point where the spinal nerve is exterior to the intervertebral foramen and branches into dorsal and ventral primary rami.

Dorsal column-medial lemniscus tract (DCML)

ANS: The origin of the DCML is the peripheral somatosensory receptors.

Ceruleospinal tract

ANS: The origin of the ceruleospinal tract is motor neurons of the locus coeruleus.

Lateral corticospinal tract

ANS: The origin of the lateral corticospinal tract is motor neurons in the supplemental motor, premotor, and primary motor areas of the cerebral cortex.

Reticulospinal tract

ANS: The origin of the reticulospinal tract is motor nuclei of the pontomedullary reticular formation (see Table 13-2).

7. What is the function of reciprocal inhibition?

Reciprocal inhibition prevents or decreases activation of an antagonist when an agonist is firing. This prevents opposing muscle forces from being activated when an agonist contracts.

6. Are reflexes and voluntary motor control entirely separate systems?

Reflexes and voluntary motor control are not separate, because afferent and descending voluntary information converges on the same spinal interneurons. This convergence allows descending voluntary signals to modify reflexive actions and allows afferent input to adjust movements elicited by descending commands.

Nucleus dorsalis

Site of synapse between first- and second-order neurons that convey unconscious proprioceptive information to the cerebellum; second-order axon is in the posterior spinocerebellar tract. The nucleus dorsalis is located in the medial dorsal horn of the spinal cord, from T1 to L2 spinal segments. Synonym: Clarke's nucleus

8. What aspects of walking are controlled by stepping pattern generators in the spinal cord? Why are stepping pattern generators by themselves inadequate to control walking?

Stepping pattern generators in the spinal cord elicit repetitive, rhythmic, alternating flexion and extension movements of the hips and knees. Stepping pattern generators alone are inadequate to control walking, because postural control, cortical control of dorsiflexion, and afferent information to adapt movements to the environment and task are also essential for normal human walking.