A Case of Spinal Cord Injury Essay

Custom Student Mr. Teacher ENG 1001-04 20 August 2016

A Case of Spinal Cord Injury

1. Describe the functional anatomy of the spinal cord using the following terms: white matter, gray matter, tracts, roots, and spinal nerves.

The spinal cord is a cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull. (p. 481) The spinal cord, like the brain consists of two kinds of nervous tissue called gray and white matter. (p. 482) Gray matter is located deep to the white matter and forms an “H” pattern. White matter is on the periphery of the spinal cord. The gray matter is dull because it contains little myelin. It contains the somas, dendrites, and proximal parts of the axons and neurons. It is the site of synaptic contact between neurons, and therefore the site of all neural integration in the spinal cord. The white matter has an abundance of myelin which gives it it’s pearly white appearance. It is composed of bundles of axons, called tracts, that carry signals and allow communication between different levels of the spinal cord.

5. Define the terms dermatome and myotome and explain how each relates to SCI.

Dermatomes show the relationship between a spinal nerve and the skin and myotomes show the relationship between a spinal nerve and muscle. Each spinal nerve (except C1) receives sensory input from a specific area of skin called a dermatome. A dermatome is an area of skin in which sensory nerves derive from a single spinal nerve root. There are 31 segments of the spinal cord, each with a pair (right and left) of ventral (anterior) and dorsal (posterior) nerve roots that innervate motor and sensory function, respectively. (http://emedicine.medscape.com/article/1878388-overview) A dermatome map is used to show how each zone of the skin is innervated by sensory branches of the spinal nerves. Viruses that lie dormant in nerve ganglia (for example the varicella zoster virus, which causes both chickenpox and herpes zoster commonly shingles) often cause either pain, rash or both in a pattern defined by a dermatome.(http://en.wikipedia.org/wiki/Dermatome_(anatomy)).

Dermatomes are clinically important and necessary for assessing and diagnosing the level of spinal cord injury in the American Spinal Injury Association (ASIA) Impairment scale. Spinal nerve fibers and the corresponding muscle make up a myotome. Myotomes are necessary for proper motor functioning; making it possible to bend the knee, straighten the elbow, flex fingers, and manipulate other muscle groups. Myotome charts and motor exams are useful for determining if myotome functioning is impaired. According to the American Spinal Injury Association (ASIA) standard neurological classification guide the last dermatome or region of skin with healthy intact sensation displaying normal spinal cord function is considered the neurological level of injury.

This does not necessarily correspond with the vertebral (spinal column bone or disc) level of injury. Therefore both neurological and vertebral diagnoses are recorded. Additionally while the following muscles grades are not included in determining the ASIA motor score and level they should still be assessed and noted. By examining the dermatomes and myotomes, a motor score, level and completeness of a spinal cord injury can be determined. http://www.streetsie.com/neurological-examination-assessment/
6. Define the term stretch reflex and describe how such reflexes are used to anatomically localize SCI.

Stretch reflex (also termed: Myotatic Reflex, Deep Tendon Reflex)

1. Stimulus – fast stretch of muscle; clinically this is produced by a brief sharp tap to a muscle tendon (this results in sudden small lengthening of muscle, not in stimulation of tendon receptors).

2. Sense organ excited – this strongly excites muscle spindle Primary (Group Ia) afferents; can also produce much weaker discharges of muscle spindle Secondary (Group II) afferents.

3. Primary response – muscle that is stretched contracts rapidly

Stretch reflexes are abnormal reflexes that work to increase muscle resistance to passive motion. They are frequent complications of spinal cord injury and contribute to muscle spasticity or continuous spasm. It is believed that the damaged nerves send messages via neurotransmitters that are carried by serotonin and norepinephrine. Following spinal cord injury, there is a change in the balance of neurotransmitters that may cause the increased stretch reflex intensity. Reflexes below a SCI become exaggerated, as there is no suppresion from the uppper motor neurons. While reflexes above the SCI are normal. (http://www.livestrong.com/article/320023-stretch-reflex-spinal-cord-injury/)

The monosynaptic refex arc is referred to as the “stretch”, “deep tendon”, or “myotatic reflex” and it is the basis of the knee, ankle, jaw, biceps, or triceps responses tested in a routine neurological examination. The stretch reflex arc is a negative feedback loop used to maintain muscle length at a desired value. (http://www.ncbi.nlm.nih.gov/books/NBK10809/)

Muscle stretch reflexes are elicited by the hammer tap of a selected tendon, which causes a brief or single contraction of its muscle. The tendon tap causes passive stretching of its muscle and the muscle spindles, which activates sensory nerve fibers (afferent reflex arc) with subsequent depolarization of the alpha motor neurons at the anterior horn of the spinal cord. The depolarization of motor nerves leads to the contraction of muscle fibers and a visible “twitch”.

(http://www.stritch.luc.edu/lumen/MedEd/neurology/Neurologic%20Examination%20of%20Sensation%20Reflexes%20and%20Motor%20Function.pdf)

When a stretch reflex is absent it is indicative of a missing component in the negative feedback loop at a certain location or level on the spinal cord. For example the patellar reflex assesses the nervous tissue between and including the L2 and L4 segments of the spinal cord.(http://en.wikipedia.org/wiki/Patellar_reflex)

Stretch reflexes are abnormal reflexes that work to increase muscle resistance to passive motion. They are frequent complications of spinal cord injury and contribute to muscle spasticity or continuous spasm. It is believed that the damaged nerves send messages via neurotransmitters that are carried by serotonin and norepinephrine. Following spinal cord injury, there is a change in the balance of neurotransmitters that may cause the increased stretch reflex intensity. Reflexes below a SCI become exaggerated, as there is no suppresion from the uppper motor neurons. While reflexes above the SCI are normal. (http://www.livestrong.com/article/320023-stretch-reflex-spinal-cord-injury/)

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