A&P 2.4 stretch reflex, CNS anatomy

Question 0

Stretch reflex

Defined

Answer 0

Myotatic reflex - causes the contraction of a skeletal muscle (the effector) in response to stretching the muscle.

Example: knee jerk reflex

7 steps

Question 1

Reflex arc

Answer 1

Fast and involuntary action in response to a stimulus
Simplest form of integration
Shortest pathway from a stimulus to a response

7 steps

Question 2

Myotatic

Answer 2

Of the muscle

Question 3

Stretch reflex

Knee jerk example

Stimulus

Answer 3

Stretch the muscle belly via tap on tendon or muscle

Question 4

Sensory receptor

Answer 4

Dendrite or specialized structure that stimulates a dendrite = muscle spindle

Question 5

Sensory neuron

Answer 5

Afferent - conducts a nerve impulse from receptor to the CNS

Question 6

Integrating center

Answer 6

Sensory neurons synapse (directly with motor neurons therefore are MONOSYNAPTIC)

NO INTERNEURON OR ASSOCIATION NEURON

Question 7

Motor neuron

Answer 7

Efferent - conducts a nerve impulse from the CNS to an effector

Question 8

Effector

Answer 8

The muscle that was stretched

Question 9

Response

Answer 9

Muscle contraction

Question 10

Muscle spindle

Three bullets

Answer 10

Specialized structure that stimulates a dendrite

• PNS subtype: proprioceptors- found in muscles, fascia and tendons
• cellular characteristics: free nerve ending, simple, encapsulated
• stimulus: mechanoreceptor- main function is to measure muscle length and respond to sudden or prolonged stretching of muscle spindle fibers

Question 11

MONOSYNAPTIC

Answer 11

Only one synapse in the CNS

Question 12

Knee jerk example

Three steps

Answer 12

• Quads are stretched by tapping on the tendon
• quads are the agonist/prime mover and contract
• hamstring are the antagonist are inhibited by reciprocal innervation

Ipsilateral reflex- entire reflex from stimulus to response happens on 1 side or the same side of the body

Question 13

Argonist

Answer 13

Prime mover

Muscle that’s contracting

Question 14

Antagonist

Answer 14

Muscles opposing the contraction/ muscles that do the opposite action at the SAME JOINT

Prime stopper

Question 15

Ipsilateral

Answer 15

One side or same side

Question 16

Reciprocal innervation

Answer 16

When a stretched muscle contracts during a stretch reflex, antagonist muscles oppose the contraction relax. Reciprocal innervation prevents conflict between opposing muscles and is vital in coordinating body movements. These are motor pathways that excite a muscle and simultaneously inhibit its’ antagonist.

Question 17

Reflexes categorized according to

2 things

Answer 17

Effector: Somatic versus visceral

Location of integration: spinal versus cranial

Question 18

Effector

Answer 18

Somatic- body(skeletal, muscles, bones, fascia)

Visceral- organs in the abdomen, often G.I tract (example: defication after eating)

Question 19

Location of integration

Answer 19

Spinal reflexes - integration in the grey matter of the spinal cord; includes most proprioceptive and pain reflexes are spinal (including stretch reflex)

Cranial reflexes - integration takes place in the brain stem; eye reflex, startled reflex, propriocepative/pain reflex

Question 20

Propriocepative/pain reflex

Answer 20

Mostly spinal reflexes unless arising muscles are innervated by cranial nerves

Examples: muscles of the head, face, jaw, SCM, trapezius

Question 21

Startled reflex

Answer 21

Looking in the direction of the stimulus

Question 22

Teres minor

A, I, O

Answer 22

A - laterally rotate the shoulder, stabilize the head of the humerus in the glenoid cavity

O - upper 2/3 of lateral/axillary border

I - greater tuberercle of the humerus

Question 23

Subscapularis

A, I, O

Answer 23

A - medially rotate the shoulder, stabilize the head of the humerus in the glenoid cavity

O - subscapular fossa of the scapula (costal surface of the scapula)

I - lesser tubercle of the humerus