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Alex Backlund

Chapter 13 and 14 essays

1/19/13

1.  The four major plexuses of spinal nerves are Cervical, Brachial, Lumbar, and Sacral.

The Cervical Plexus is located alongside cervical vertebrae 1 through cervical vertebrae

4. The Brachial Plexus is located laterally and inferior to the cervical vertebrae 4 through

thoracic vertebrae 1. The Lumbar Plexus is located laterally to lumbar vertebrae 1

through lumbar vertebrae 4. The Sacral Plexus is located near lumbar 4 through sacral 3

and is anterior to the sacrum.

2.  There are six components of a spinal reflex arc. The first component is that a

sensory receptor responds to specific conditions of the body by producing a graded

potential. It responds to a specific stimulus. The second component is that a sensory

neuron conducts an impulse from the receptor to the integrating center in the gray matter

of the spinal cord. The third component is that an integrating center forms a synapse site

between a sensory and motor neuron. The fourth component is that the impulses that are

triggered by the integrating center propagate out of the Central Nervous System along a

motor neuron to the part of the body that will respond. The fifth component is that an

effector responds to the motor impulse, and its action produces a reflex.

3. 

A dermatome is an area of skin that provides sensory input to the Central Nervous

System via the posterior roots of one pair of spinal nerves or via the trigeminal (V) nerve.

Dermatomes are clinically significant in that they help localize neurologic levels.

Knowing which spinal cord segments supply each dermatome help to make it possible to

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locate damaged regions of the spinal cord. Information about the innervations patterns of 

spinal nerves also can be used therapeutically.

4.  I believe that this accident severely damaged the frontal lobe of Phineas Gage’s

brain, which is home to memory and intellect. It also specifically damaged the prefrontal

cortex on the left side of his brain, which would affect his judgment and conscious. As a

result, the right side of Gage’s brain couldn’t make up for the damage done to the the left

side of his brain. The epileptic seizures that preceded his death were most likely a result

from damage to his basil ganglia. The basil ganglia could no longer communicate with

the rest of the brain due to lost connections that came with his accident and as a result

from aging.

5.  The hypothalamus is responsible for releasing regulatory hormones into the capillary

networks in its median eminence to increase or decrease hormone production and also

secretion from the anterior pituitary gland. The posterior pituitary gland is formed from

axon cell bodies producing either oxytocin or antidiuretic hormone and then releasing it.