7.4

Question 1

describe muscle spindles

Answer 1

• composed of 3-10 short intrafusal muscle fibers in connective tissue capsule
• > intrafusal fibers are non contractile in central regions (lack myofilaments)

Question 2

what are intrafusal fibers

Question 3

what are the intrafusal fibers of muscle spinles wrapped with

Answer 3

• wrapped with 2 types of afferent ending

1. primary (Anulospiral) sensory endings of type Ia fibers

• > innervate spindle centre (wraps aorund the non contractile component in middle)
• > stimulated by rate and degree of stretch

2. secondary (flower spray) sensory endsings fo type II fibers

• > innervate spindle ends
• > stimulated by degree of stretch

Question 4

describe muscle spindle innervation

Answer 4

• contractile end regions are innervate by gamma effert fibers that maintain spindle sensitivity
• > gamma efferent (motor) fiber to muscle spindle
• > alpha efferent (motor) fiber to extrafusal muscle fibers (innervate muscles that cause movment)

*NOTE: extrafusal fibers (contractile muscle fibers are innerfacted by alpha effert fibers

Question 5

How are muscle spindles excited

Answer 5

1. External stretch of muscle & muscle spindle
2. Internal strecth of muscle spindle
   - > activating gamma motor neurons stimulates ends to contract, thereby stretching muscle spindle -> inc role in firing

*stretch causes INC RATE of impulses in Ia fibers

• in unstretched muscle; action potentials are generated at a constant rate in associated sensory (Ia) fiber
• in stretched muscle: stretching activates muscle spindle, INC rate of APs

Question 6

why is alpha-gamma coactivation of muscle spindles important?

Answer 6

• maintains tension and sensitivity of spindle during muscle contraction
• contracting muscle by acivating alpha motor neurons reduces tension on muscle spindle
• > if only motor neurons activates -> only extrafusal muscle finbers contract, spindles become slack and no AP fired

*unable to signal further length changes, have no contraction in middle

• in alpha-gamma coactivation, both extrafusal and intrafusal muscle fibers contract. muscle spinle tensions is maintains so it can signal changes in length

*sensitivity would be lost unless muscle spindle is shortened by impulses in gamma motor neurons

Question 7

what are the two types of reflexes

Answer 7

• Inborn (intrinsic) reflex: a rapid, involuntary, predictable motor response to a stimulus
• Learned (acquired) reflexes result from practice or repetition (driving_

Question 8

describe spinal reflexes

Answer 8

aka spinal somatic -> body reflexes

• integration center = spinal chord
• effectors = skeletal muscle

* testing of somatic relfexes is important clincially to evaluate sensorimotor function of body (how well brain and body communicate)

Question 9

components of sensorimotor arc

Answer 9

1. receptor: stim to skin receptor
2. Sensory neuron (comes in dorsally)
3. integration center (spinal chord)
4. Motor neuron
5. Effector (skeletal muscle)

Question 10

describe muscle tension at rest

Answer 10

1. extra fusal muscle fibers are at resting length
2. sensory neuron is tonically active
3. Spinal cord integrates function
4. alpha motor neurons to extrafusal fibers receive tonic input from muscle spindles
5. extrafusal fibers maintain a certain level of tension even at rest

Question 11

what is role of muscle spinldes and golgi tendon organs for reflexes

Answer 11

*for skeletal muscle activity to be smoothly coordinated, porprioceptor input is necessary

Muscle spindles: inform nervous system of length of muscle

• Golgi tendon organs inform brain as to amount of tension in muscle & tendons

Question 12

what do strecth reflexes have in common

Answer 12

all monosynaptic and ipsilateral (one side of body)

• maintain muscle tone in large postural muscles
• cause muscle contraction in repsonse to increased muscle length (stretch)

Question 13

describe the patellar reflex

Answer 13

1. Tapping patellar ligament excites muscle spindles in quadriceps femoris
2. Afferent impulses (Ia Primaru sensory endings) travel to spinal cord & synapse with alpha motor neurons and interneurons
   3a. alpha motor neurons send activating impulses to quadricepts femoris causing it to contract, extening knee
   3b. interneurons make inhibitory synpases with ventral horn neurons that prevent contraction of antagonist muscles (hamstrings) = reciprocal inhibtion

Question 14

what are golgi tendon reflexes

Answer 14

• polysynaptic relfexes
• help prevent damage from excessive stretch
• important for smooth onset & termination of muscle contraction

- produce muscle relaxation in response to tension

-> contraction/passive strecth acivates golgi tendon organs

• > afferent inpulses are transmitted to spinal chord
• > contracting muscles relaxes & antagonist contracts (reciprocal activation)

Question 15

give example of golgi tendon reflex in quadricpets

Answer 15

1. quadriceps strongly contract. Golgi tendon organs are activated
2. Afferent fibers synpase with interneurons in spinal chord

3a efferent impulses to muslce with stretched tendon are inhib -> muscle relaxes, tension dec

3b. Efferect impulses to antagonist muscle cause it to contract

Question 16

if put your arm out and threw on a very heavy load, why is it dropped

Answer 16

• golgi tendon reflex
• 1. neuron from golgi tendon organ fires
     
     2. motor neuron is inhibited
     3. muscle relaxes
     4. load is dropped

Question 17

describe the flexor withdrawal reflex

Answer 17

• painfil stimulus causes automatic withdrawal of threatened body part
• relfex is ipsilateral and polysynaptic

(only happens to body part that experiences the painul stimulus)

1. painsul stimulus detected by sensory neuron
2. distribution within grey horns to other segments of spinal chord
3. muscles undergo reciprocal inhibition: extensors are inhibited adn flexors are simulated to recoil arm

Question 18

describe the cross exntensor reflex

• where it occurs, and what it consists of

Answer 18

*occurs with flexor reflexes in weight bearing limbs to maintain balance

• consists of: ipsilateral flexor refelx + cntralateral extensor reflex
• > stimualted side is withdrawn (flexed)
• > contralateral side is extended

Question 19

describe superficial reflexes

Answer 19

• elicited by gentle cutaneous stimulation (scraping of skin)
• polysnaptic, they depend on upper motor pathways and cord-level reflex arcs
• ex: plantar reflex (postive = Babinski’s sign), abdominal refelx, cremaster reflex (testicles)