Week 8: Motor- Spinal Region, Reflexions & SCI

What is a reflex

involuntary response to stimuli

For a reflex to occur, there must be: (5)

sensory receptor

primary afferent

connections between primary afferents and LMNs

efferent neuron (LMN)

muscle

What is the function of spinal reflexes

allow for protection from painful or damaging stimuli

adjust unforseen disturbance

provide for efficieint movement without conscious thought

Myotatic stretch reflex

muscular reflex created by excessive muscle spindle stimulation to prevent potential tissue damage

How many synapses in myotatic stretch reflex

one (monosynaptic)

What is the stimulus in the myotatic stretch reflex

brisk passive extension (stretching the quad by tapping its tendon)

What is the response in a myotatic stretch reflex

contraction of the agonist

afferent fibers fire:

- EXCITES alpha motor neurons of AGONIST (quad)

- INHIBITS alpha motor neurons of ANTAGONIST (hamstring)

What turns off the reflex in the myotatic stretch reflex

upper motor neurons

What is inverse myotatic reflex

The automatic response that causes a stretched muscle to relax when the Golgi tendon organ is stimulated.

How many synpases are in the inverse myotatic reflex

two (disynaptic)

What is the stimulus in an inverse myotatic reflex

contraction (i.e., bicep)

What is the response in an inverse myotatic reflex

contraction of the antagonist muscle (tricep)

afferent fibers fire:

- INHIBITS alpha motor neurons of AGONIST (bicep)

- EXCITES alpha motor neurons of ANTAGONIST (tricep)

What turns off the reflex in an inverse myotatic reflex

upper motor neurons

What is the receptor in an inverse myotatic reflex

golgi organ tendon

What is the receptor in a myotatic stretch reflex

muscle spindle

What are cutaneous reflexes

skin reflexes

helps protect the body from damaging stimuli (flexor withdrawal & crossed extension)

What is a dermatome

specific area of skin innervated by a single dorsal root

How is sensory function determined

by testing dermatomes for sensitivity to pink prick & light touch

What is a myotome

specific muscle or muscle group innervated by a single ventral root

On a myotome scale what does 3 mean

3= active, full ROM AGAINST gravity

On a myotome scale what does 5 mean

5= active, full ROM against gravity AND against full resistance

C5 injury affects what muscles

elbow flexors

C6 injury affects what muscles

wrist extensors

C7 injury affects what muscles

elbow extensors

C8-T1 injury affects what muscles

finger fexors & finger abductors

What happens immediately after an SCI

- bleeding into the injured area leads to swelling, which compresses and damages axons

- release of free radicals break up cell membranes

- macrophages invade the damaged site

- astrocytes form scar tissue

What happens in spinal shock phase

cord functions below lesion are lost

- reflexes: areflexia (at and below the level of injury)

- muscle tone: hypotonic (less muscle stiffness)

What happens weeks or months after SCI

- sensory, motor & autonomic impairment below the level of the lesion

- below the level of injury, muscle tone and reflexes become hyperactive

2 types of SCI:

Complete

Incomplete

What is a complete SCI

absense of sensory and motor function below the level of the lesion

What is an incomplete SCI

partial preservation of sensory and/or motor function below the lesion

SCI segmental function

interferes with function only AT the level of the lesion

SCI vertical tract function

results in the loss of function BELOW the level of the lesion

SCI vertical and segmental function means:

everything AT & BELOW the lesion is effected