22. Spinal Cord and Postural Management

Question 1

What do pacinian corpuscles do? What do they look like?

Answer 1

Pacinian corpuscles sense pressure and vibration.

Have onion-skin appearance

Question 2

Muscle spindles are _____ receptors

Answer 2

Stretch

Question 3

Where are the extrafusal muscle cells and the intrafusal muscle cells?

Answer 3

Extrafusal - contractile muscle cells - surround muscle spindle
Intrafusal - contain the stretch-sensing portion of muscle spindles

Question 4

What are the nuclear bag fibers? What are the nuclear chain fibers? (as in what do they sense?

Answer 4

Nuclear bag fibers, DYNAMIC: Sense the rate of change of length
Nuclear bag fibers, STATIC: Sense the m. length
Nuclear chain fibers: Always static, so sense the m. length

Question 5

What are the differences between spindle Ia and Group II fibers?

Answer 5

Ia: Dynamic response, so sends information about the rate of change of m. length; monosynaptic connection to alpha motor neuron, indirect inhibition to antag MN
II: Static, sends info about m. length, make many connections to alpha motor neuron and others

Question 6

What is the similarity between short and long reflex pathways? What are the differences?

Answer 6

Short reflex pathway: Normal reflex arc w/o higher input
Long reflex pathway: Brain makes the decision about whether or not to contract the m.

Similarity is that they cause activation of alpha motor neuron

Question 7

What do gamma motor neurons do?

Answer 7

When muscle contracts, w/o any other input, the muscle spindle would go slack. Gamma motor neurons cause contraction of the muscle spindle fibers (both dynamic and statics)

Question 8

When does co-activation occur?

Answer 8

Co-activation occurs when an alpha motor neuron is excited, the gamma motor neuron is also excited to prevent the muscle spindle from going slack

Question 9

Does the gamma loop require signals from higher centers?

Answer 9

Yes

Question 10

What do golgi tendon organs sense, and where are they located?

Answer 10

Golgi tendon organs sense the force of muscle contraction or the load on a muscle
They are embedded in the tendon of a muscle, arranged in series with the m.

Question 11

What happens to a muscle when the GTO is stimulated?

Answer 11

The muscle is inhibited

Question 12

What is the cutaneous receptor reflex?

Answer 12

Protective reflex in response to a noxious stimuli (touch, pressure, PAIN)

Question 13

Say the reflex arc for the cutaneous receptor reflex

Answer 13

Pain stimulus under toe causes afferent signal to travel up to the spinal cord and synpase with the agonist alpha motor neuron (flexor hams m.). Also synapses with inhibitory interneuron that inhibits the antagonist m. (quads)

Question 14

Crossed extensor reflex

Answer 14

Pain receptor stimulated –> sensory info travels to SC –> ascending pathway to higher centers of brain, flex ipsilateral leg away from stimulus, crossed extensor reflex supports body (stimulate extensors and inhibit flexors)

WITHDRAWAL AND CROSSED REFLEX OCCUR TOGETHER

Question 15

Diff between center of mass and center of gravity

Answer 15

COM: point around which body matter is distributed equally
COG: point of which weight is distributed

Question 16

Where does the line of gravity pass through?

Answer 16

Forward of ankle, through knee, through hip, through thoracic spine, through acromium, through atlanto-occipital

Question 17

Which m. are the anti-gravity m?

Answer 17

Gastroc, quadriceps, paraspinal m., hip extensors, neck extensors
(Posterior kinetic chain + quads)

Question 18

What are the limits of stability?

Answer 18

Limits of stability = how far from midpoint you can lean w/o altering base of support
Anteriorly: 8 degrees
Posteriorly: 4 degrees

Question 19

What m. are activated with forward sway reflex? (What strategy is this a part of?)

Answer 19

Gastro-soleus, hams, paraspinal m

Ankle reflex strategy

Question 20

What m. are activated with backward sway reflex? (What strategy is this a part of?)

Answer 20

Anterior tibialis, quads, abdominals

Ankle reflex strategy

Question 21

Difference between hip strategy and anklestrategy

Answer 21

ankle strategy: Uses multitude of joints
Hip strategy: when ankle strategy cannot be used, involves flexion and extension of the hip joint to compensate for a lack of an ankle strategy

Question 22

Cenral pattern generators

Answer 22

Patterns of interconnected reflexes; produce rhythmic contractions and relaxation of groups of muscles (eg scratching, shaking, locomotion)