Reflex Centers

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Reflex Centers

 

The central nervous system is comprised of the brain and spinal cord.

The peripheral nervous system consists of cranial nerves, which

branch out of the brain, and spinal nerves, which branch out of the

spinal cord. A total of 31 sets of nerves branch out of the spinal

cord. The point at which the nerve branches out from the cord is

known as the nerve root.

 

Each nerve travels a short distance (about ½ inch) from the cord and

then divides into small posterior divisions (dorsal rami) and larger

anterior divisions (ventral rami). The dorsal rami innervate the

posterior muscles and skin of the trunk; the ventral rami, from, T1

to T12, innervate the anterior and lateral muscles and skin of the

trunk. The remaining anterior divisions form networks called

plexuses, which then distribute nerves to the body. The nerves from

each plexus innervate specific muscles and areas of skin in the body

and are numbered according to the location in the spine from which

they exit. Following are the four main plexuses:

 

cervical plexus, C1 - C4, innervates the diaphragm, shoulder and neck

brachial plexus, C5 - T1, innervates the upper limbs

lumbar plexus, T12/L1 - L4, innervates the thigh

sacral plexus, L4 - S4, innervates the leg and foot.

 

 

The latter two plexuses, which innervate the lower limbs, are often

considered together as the lumbosacral plexus. This text will focus

on the brachial plexus and lumbosacral plexus from level T12/L1 to S1.

 

 

Brachial Plexus - Neurologic levels C5 - T1

 

Neurologic Level C5: The muscles found within this myotomal pattern

are the deltoid and the biceps brachii. Because the latter is also

innervated by C6, the deltoid is the most " pure " C5 muscle. The

deltoid's most powerful motion is abduction. One of the most commonly

used tests for shoulder abduction is to instruct the patient to flex

the elbow at 90 degrees, then offer gradual resistance to abduction

until determining the extent of resistance h/she can overcome. Below

are illustrations of neurologic level C5 and of the test for shoulder

abduction.

 

Neurologic Level C6: As mentioned above, the biceps brachii is

innervated by C5 and C6. C6 also innervates the most powerful wrist

extensors, carpi radialis longus and brevis, which do radial

extension. The ulnar extensor, extensor carpi ulnaris, is innervated

by C7. To test for wrist extension, stabilize the patient's forearm

with the palm of your hand on the anterior aspect of the wrist. With

the patient's wrist in full extension, place the palm of your free

hand over the posterior aspect of the patient's hand and try to force

it out of extension. If no damage is present, the patient will be

able to resist movement. If C6 is damaged, ulnar deviation will

occur. If C7 is injured, radial deviation will occur. Below are

illustrations of neurologic level C6 and of the test for wrist

extension

 

Neurologic Level C7: The muscles found within this myotomal pattern

are the triceps, wrist flexors and finger extensors. The triceps

muscle primarily does elbow extension. A common test for this action

is to ask the patient to fully flex the arm. Stabilize the patient's

arm just above the elbow and ask h/her to slowly extend it. Before

the arm reaches a 90 degree angle, begin to offer firm, constant

resistance until discerning the maximum resistance h/she can

overcome. Below are tests of neurologic level C7 and of the test for

elbow extension.

 

Neurologic Level C8: The muscles found within this myotomal pattern

are finger flexors—flexor digitorum superficialis, flexor digitorum

profundis, and the lumbricals. To test for finger flexion, the

patient fully flexes h/her fingers at all joints while you curl your

fingers into them. Ask the patient to resist your attempt to pull

h/her fingers out of flexion. A normal response is for all joints to

remain flexed. Below are illustrations of neurologic level C8 and of

the test for finger flexion.

 

Neurologic level T1: The muscles found within this myotomal pattern

are those involved in finger abduction—dorsal interossei and abductor

digiti quinti (5th finger)—and adduction—palmar interossei. To test

for abduction, instruct the patient to abduct h/her fingers. Then

pinch each set of fingers to try to force them together (index to the

middle, ring, and little finger, the middle to the ring and little

finger, and the ring to the little finger.) Note any significant

weaknesses between pairs. Test both hand in order to compare the

strength of each, and evaluate them according to the standardized

grading scale for muscle strength. To test for finger adduction, ask

the patient to extend h/her fingers and hold a piece of paper (or a

dollar bill) between two of h/her fingers. Then you pull it out. Test

the other hand in the same manner and compare the strength of each.

Following are illustrations of neurologic level T1 and of the tests

for finger abduction and adduction.

 

 

Lumbosacral plexus - Neurologic levels t12 to s1

 

Neurologic Levels T12 to L3: The muscles found within this myotomal

pattern are the iliopsoas (T12-L3—main hip flexor), quadriceps (L2-L4—

hip flexion, knee extension), and adductors (L2-L4—hip adduction).

Because this myotomal pattern includes multiple muscle groups (and,

therefore, does not have individual muscles which can be tested) an

injury to this nerve root level can be more easily evaluated by

sensory testing of the dermatomal patterns. However, motor testing

may be performed if desired. An example of a test for knee extension,

for instance, would be to have the patient sit on the treatment

table. Place one hand above the knee to stabilize the thigh, and the

other hand on the patient's anterior leg above the ankle. Offer

resistance to knee extension, and note the amount of resistance the

patient can overcome. Test both limbs in order to compare the

strength of each, and evaluate them according to the standardized

grading scale for muscle strength. Following is a detailed

illustration of the dermatomes of the lower extremities and of the

above- mentioned test for knee extension.

 

Neurologic Level L4: The muscle predominantly innervated at this root

nerve level is the tibialis anterior, which does dorsiflexion with

inversion. To test this muscle, ask the patient to sit on the

treatment table. With one hand, stabilize the patient's leg by

holding it just above the ankle. Instruct the patient to dorsiflex

and invert h/her foot. With your free hand, hold the patient's foot

and ask h/her to resist your attempt to move the foot into

plantarflexion and eversion. Test both feet in the same manner in

order to compare the strength of each, and evaluate them according to

the standardized grading scale for muscle strength. Following is an

illustration of neurologic level L4 and of the above-mentioned muscle

test for dorsiflexion with inversion:

 

Neurologic Level L5: The muscles found within this myotome are the

extensor hallucis longus (big toe extensor), extensor digitorum (heel

walk) and the gluteus medius (the most powerful abductor of the hip.)

A common test for hip abduction is to ask the patient to lie on h/her

side with both legs extended, careful not to flex at the hip. Place

one hand on h/her pelvis to stabilize it and ask h/her to fully

abduct it. Place your free hand on the lateral knee at the joint and

ask the patient to resist your attempt to push the leg into

adduction. Test both sides in the same manner in order to compare the

strength of each, and evaluate them according to the standardized

grading scale for muscle strength. Following is an illustration of

neurologic level L5 and of the above-mentioned test for hip

abduction.

 

Neurologic Level S1: The muscles found within this myotome are the

peroneus longus (plantarflexion with eversion) peroneus brevis (toe

walk) and gluteus maximus (hip extension.) To test for hip extension,

ask the patient to lie face down on the treatment table and bend the

leg at the knee (this relaxes the hamstrings.) Stabilize the hip by

placing your forearm over the iliac crest, and ask the patient to

hyperextend h/her hip. Place your other hand on the thigh below the

gluts and ask the patient to resist your attempt to push the thigh

back down on the table. Test both sides in the same manner in order

to compare the strength of each, and evaluate them according to the

standardized grading scale for muscle strength.

 

 

Andrew Pacholyk, LMT, MT-BC, CA

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