Skeletal Muscle Organ Reflex

Question 1

Receptor Organs

Answer 1

Receptor organs : encapsulated or non encapsulated
Mechanosensitive proprioceptors of skeletal muscle

CNS control body movement appropriately by
assessing the effect of gravity on many muscles of the body

(2) determining the initial position of the body parts to be moved

(3) detecting any discrepancy between the intended movement and the movement that actually occurs

Exteroreceptors

Proprioceptors

Interoceptors

Question 2

Exteroreceptors

Answer 2

Surface of the body and sensitive to external environment

Question 3

Proprioceptors

Answer 3

Muscle, tendons, joints and in the inner ears and sensitive to movement

Question 4

Interoceptors

Answer 4

Located in the viscera of the body and sensitive to changes in the internal environment

Question 5

Receptor System

Answer 5

Muscle spindle arranged in parallel to the contracting skeletal muscle fibers, detects muscle length

Golgi tendon organ arranged in series with the contracting skeletal muscle fibers, detects muscle tension

Question 6

Extrafusal fibers

Answer 6

Are input by alpha motor neurons.
These neurons are large and fast.

Extrafusal muscle fibers- surrounding muscle fibers supplied by alpha motor neurons.
2 types in muscle spindles:
- nuclear bag fibers - are larger, and their nuclei are accumulated in a central (“bag”) region
- nuclear chain fibers are smaller, and their nuclei are arranged in rows (“chains”).

Generally, both types of fibers are present in muscle spindle

Question 7

Intrafusal fibers

Answer 7

Are input by gamma motor neurons.
These neurons are relatively small and slow.
They are involved in the control of muscle tone.

Encapsulated group of ~ 3 to 12 small, slender, specialized skeletal muscle fibers. Capsule is spindle shaped or fusiform
They are short (about 4-10 mm)
They are attached to the extracellular matrix of extrafusal muscle fibers, and lie parallel to it

Question 8

Muscle Spindle

Answer 8

Interspersed among most skeletal muscle fibers and aligned parallel to them.
Measure muscle stretching.

Question 9

Muscle Spindle Innervations

Answer 9

Sensory Innervation

Motor Innervation

Question 10

Sensory Innervation

Answer 10

Ia afferent nerve, which innervates the central region of both the nuclear bag fibers. This synapses on alpha motor of extensor

group II afferent nerves, which innervate the nuclear chain fibers

Question 11

Motor Innervation

Answer 11

Contractile end regions are innervated by gamma (y) efferent fibers that maintain spindle sensitivity
They synapse on interneurons that are inhibitory to flexors

Question 12

Function of Muscle Spindles

Question 13

Alpha- Gamma Coactivation

Answer 13

1. Alpha motor neuron firesand gamma motor neuronfires.
2. Muscle Contracs
3. Stretch on centers ofintrafusal fibers unchanged.Firing rate of afferentneuron remains constant.

Question 14

Alpha activation without Gamma motor neurons

Answer 14

1. Alpha motor neuron fires.
2. Muscle contracts

3.Less stretch on centerof intrafusal fibers

4. Firing rate of spindlesensory neuron decreases.

Question 15

slide 11

Answer 15

1. Stretching lengthens intrafusal muscle fibers
2. Increases frequency of action potential of spindle sensory synapse
3. Increases action potential frequency in _ motor neurons on which they synapse
4. Contraction of extrafusal fibers and shortening of muscle

5.Shortening of the muscle spindle’s equatorial region

6. Reduces frequency of action potentials occurring on the spindle neurons to prestretch level, terminating the response
   (The cycle is a classic negative-feedback system)

Question 16

Golgi Tendon

Answer 16

located in the tendons of skeletal muscle. Sensory neuron branches of the organ are intertwined among braided collagen fibrils, which fold up and pinch the neural branches when tension develops in the tendon.

Question 17

Golgi Tendon Reflex

Question 18

Reflex arc

Answer 18

An involuntary, qualitatively unvarying response of the nervous system to a stimulus

fixed motor response to a sensory stimulus mediated through specific neuronal linkages

Question 19

5 components of reflex arc

Answer 19

1, receptor
2, sensory neuron
3, one or more synapses in CNS
4, motor neuron
5, target organ, usually a muscle

Question 20

Myostatic (stretch) reflex

Question 21

Withdrawal Reflex

Question 22

Flexor Withdrawal reflex

Answer 22

Reciprocal Innervation (also seen in knee jerk)
- Excite flexors
- Inhibit extensors

Question 23

Crossed-Extensor reflex

Answer 23

Part of the withdrawal reflex
- serves postural function
- extension of contralateral limb to support animal when an extremity is flexed
- polysnaptic
- double reciprocal innervation

Question 24

Innervation to the forelimb

Question 25

Biceps reflex test (tendon reflex)

Answer 25

Tests sensory and motor components

Musculocutaneous nerve, C6 and C7 spinal nerve

Question 26

Triceps reflex (tendon reflex)

Answer 26

Tests sensory and motor neurons: Radial nerve and spinal cord segments C7, C8, T1

Question 27

Cranial Tibial Reflex test

Answer 27

Tests integrity of spinal cord segments L6 to S2, and sciatic and peroneal nerves

Question 28

Perineal reflex

Answer 28

Light stimulation of perineum with forceps

Response: contraction of anal sphincter muscle and flexion of tail

Best test of function of sacral spinal cord segments and associated nerve roots