Muscle Physiology - Reflexes

Question 1

Alpha Motoneuron - Function and Location

Answer 1

innervate skeletal muscle that will cause muscle contraction. Release acetylcholine at the neuromuscular junction.
Clustered in spinal cord or brain stem.
Descending commands!

Question 2

Muscle Tone - Definition and Function

Answer 2

Skeletal muscle slightly contracted even when relaxed. Always ready to contract.
No production of active movement. Helps for joint stabilization and to maintain posture.

Question 3

Hypotonia - Definition and possible cause

Answer 3

Absence of low level contractions that lead to muscle tone. Weak reflexes.
Usually results from damage to parts of CNS (cerebellum) or loss of innervation to a skeletal muscle.

Question 4

Hypertonia - Definition and possible cause

Answer 4

Excessive muscle tone. Accompanied with hyperreflexia.
Often the result of damage to upper motor neuron in the CNS.
Can present with muscle rigidity or spasticity.

Question 5

Sensory Receptors - Mechanoreceptors

Answer 5

Ascending commands.

Question 6

Proprioception - Definition

Answer 6

Sense of the body’s position in space based on specialized receptors that reside in muscles and tendons.

Question 7

Reflexes - Definition and Division

Answer 7

Automatic reactions (or responses) to a stimulus, unconscious to changes, either inside or outside the body.
Involuntary.
Mono or poly-synaptic(inter-neurons) depending on the synapses needed.

Question 8

Spinal Reflexes (4) - Which receptors have an important role?

Answer 8

Stretch reflex
Golgi tendon reflex
Flexor and crossed-extensor reflex
Superficial reflexes
Muscle spindles and golgi tendon organs have an important role in spinal reflexes.

Question 9

Cutaneous Receptors (5)

Answer 9

Ruffini’s corpuscles
Pacinian corpuscles
Meissner corpuscles
Merkel discs
Free nerve endings

Ascending commands!

Question 10

Reciprocal Inhibition

Answer 10

Following the stretch reflex.
Stretch reflex: Muscle spindle activated by stretch, afferent impulses transmitted through sensory neurons and synapses with alpha motoneuron which activates the contractions of the agonist muscle.
Reciprocal inhibition: Also synapse with interneurons which inhibit motoneurons of the antagonist muscle. Efferent impulses of alpha motor neurons to antagonist muscles are reduced.

Question 11

Superficial Reflexes (2)

Answer 11

Plantar reflex: integrity of L4 to S2 + corticospinal tracts. Babinski sign.
Abdominal reflexes: integrity of spinal cord and ventral rami from T8 to T12 + absent when corticospinal lesion.

Question 12

How is sensory feedback controlled?

Answer 12

Afferent input flows constantly to the spinal cord from various sources including skin, muscles, tendons, and joints. Needs to be controlled through inhibition or dis-facilitation for motor task to be executed.
- Presynaptic inhibition
- Afferents III & IV
- Golgi tendon organ
- Reciprocal inhibition
- Recurrent inhibition
- Descending tracts, rubrospinal and corticospinal tracts.

Question 13

Synergist Activation

Answer 13

Stretch not limited to the muscle stretched.
Activation of alpha-MN from the agonist muscle and alpha-MN from synergist muscles acting on the joint. Reflex tap on tendon of biceps brachii will induce contraction of brachialis aswell.

Question 14

Afferents III and IV

Answer 14

Detect pain inside a muscle, connected to free nerve endings.

Question 15

Presynaptic Inhibition

Answer 15

Modulate influx of Ia before it’s transmitted to the MN. GABA synapses reduce the size of presynaptic potentials which lead to a decrease in the release of excitatory neurotransmitters. So that 1a afferents are not sending too much info to the motoneuron.

Question 16

Recurrent Inhibition

Answer 16

Renshaw cells.
Makes sure motoneurons are not sending too much info to the muscle.
Not only inhibiting alpha-MN but also gamma-MN and IA inhibitory interneurons.

Question 17

Hoffman Reflex

Answer 17

Electrical stimulation directly to the nerve of the muscle, activating alpha-MN, activating the muscle. Bypasses the muscle spindle.
Results in a monosynaptic excitation of alpha-MN. Provides info on the net excitatory input from group I afferent onto spinal MNs.

Question 18

H-Reflex Modulation

Answer 18

Changes in amplitude of H-reflex gives an indication on the efficacy of Ia afferents (from muscle spindles) to discharge spinal MNs.
Increase in H-reflex amplitude: increase efficacy between Ia afferents and MN.
Modulation happens through:
- presynaptic inhibition
- golgi tendon organ
- descending commands

Question 19

Reflex Practical - Biceps

Answer 19

Put thumb on tendon of biceps and hit the thumb. If you don’t get a reaction, check if muscle is contracting.

Question 20

Reflex Practical - Triceps

Answer 20

Place hand of patient on hip or hold around biceps and pull arm back a little and let forearm hand loose. Tap the tendon of the triceps just above the olecranon.

Question 21

Reflex Practical - Stylo radial

Answer 21

Just below the radial styloid process or if it doesn’t work, end of brachialis.

Question 22

Reflex Practical - Cubito Pronator

Answer 22

Have hand in anatomical position, put fingers over pronator teres, and hit the ulnar side. Arm should pronate slightly.

Question 23

Reflex Practical - Finger Flexor

Answer 23

Put fingers over the palmar surface of the fingers of the patient and hit them.

Question 24

Reflex Practical - Quadriceps

Answer 24

Patient sitting and hit the patellar tendon. Leg should lift up.

Question 25

Reflex Practical - Achilles

Answer 25

Patient sitting, hit Achilles tendon and ankle should plantar flex.