REFLEXES

Question 1

What are reflexes?

Answer 1

Reflexes are involuntary movements/actions to a stimulus

Question 2

Why are reflexes tested?

Answer 2

Health care providers test reflexes to determine the healthy function of the central nervous system
i.e. neonatal reflexes, planar and Babinski reflexes. Also assess conditions of N.S

Question 3

What are reflexes ext.

Answer 3

Reflex actions are immediate and involuntary actions, they are shorter pathways (nerve message sped up)
and learned response (condition reflex)

Question 4

What do reflexes do?

Answer 4

Reflexes help maintain posture, control visceral activities and safety mechanisms, they can also be modified by learning a conscious effort ( learned =aquired) –> reflexes result from practice/repetition

Question 5

What are the two different types of reflexes?

Answer 5

Somatic reflexes (activate skeletal muscle) and autonomic (visceral) reflexes (activate visceral effectors - smooth/cardiac muscle/glands)

Question 6

What are the 5 components of a reflex?

Answer 6

1) Receptor: site of stimulus action
2) sensory neuron transmits afferent impulses to the CNS
3) Integration center: either monosynaptic/polysynaptic region with CNS
4) Motor neuron: conducts efferent impulses from the integration center to effect organ
5) effector: the muscle fiber or gland cell that responds to different impulses

Question 7

What are monosynaptic reflexes?

Answer 7

Monosynaptic: sensory and motor neuron synapse directly

Question 8

What are polysynaptic reflexes?

Answer 8

Sensory/motor neuron synapse with interneurons in the spinal cord (FIG)

Question 9

What are spinal reflexes mediated by?

Answer 9

Spinal reflexes are somatic reflexes mediated by the spinal cord: spinal reflexes occur without the direct involvement of higher brain centres

Question 10

Note

Answer 10

The brain is still advised of spinal reflex acitivty/have an effect on reflex

Question 11

What are some ways reflexes are tested?

Answer 11

Stretch & tendon
flexor/crossed exten. ref
superficial ref and ocular ref

Question 12

What is the point of stretch & tendon reflexes?

Answer 12

function to smoothly coordinate the activity of skeletal muscle. It provides the NS with important proprioceptive information to regulate joint position and movement (know where muscles are in the dark)

Question 13

How do stretch and tendon reflexes tell us where our muscles are?

Answer 13

1) length of the muscle (sent from muscle spindles) monosynaptic
2) amount of tension (fore in the muscle sent from Golgi to tendon organs (polysynaptic)

Question 14

What do muscle spindles do?

Answer 14

Functional anatomy of muscle spindles (3-10 modified skeletal muscle fibers intrafusal muscle fibers within a capsule)
they run parallel to the extrafusal muscle fibers and act as receptors that provide information on muscle length and the rate of change in muscle length. The spindles are stretched when the muscle lengthens.

Question 15

What are the 2 different types of afferent endings in muscle spindles which send sensory inputs to CNS

Answer 15

1) Anulospiral end: wrap around the spindle and stimulate by the rate and the degree of stretch
2) Flower spray endings: small axons at spindle ends and stimulated by the degree of the stretch only

Question 16

What are contractile ends regions innervated by? And how does this help it?

Answer 16

contractile ends regions of the spindle are innervated by gamma and efferent fibers. This helps maintain sensitivity - always sense muscle lengths

Question 17

What are extrafusal fibres innervated by?

Answer 17

extrafusal fibres are innervated by alpha motor neurons (FIG)

Question 18

What is the co-activation of alpha and gamma motor neurons?

Answer 18

It allows the muscle spindle to be sensitive (and not go slack) when the muscle shortens (contracts). It is important to continuously send the input of the nervous system about muscle length (FIG)

Question 19

What is the patella/knee jerk reflex?

Answer 19

it is a reflex that keeps the knee from buckling when standing upright. It asses the nervous tissue between the L2 and L4 segments of spinal cord (FIG)

Question 20

What are tendon reflexes?

Answer 20

• prevents muscles from tearing due to excessive forces
• initiated by Golgi tendon organs
• involves polysynaptic reflexes
• produces muscle relaxation (lengthening) in response to tension
• contraction/passive stretch-activated tendon reflex
• afferent impulses transmitted to the spinal cord
• contracting muscles relaxes (antagonist contractor (reciprocal activation)

Question 21

What is the flexor and crossed-extensor reflexes

Answer 21

• Flexor (withdrawal) reflex is initiated by a painful stimulus
• automatic withdrawal of threatened body part (ipsilateral and polysynaptic)
• Crossed extensor reflex occurs with the flexor reflexes in weight-bearing limbs to maintain balance
• consists of ipsilateral withdrawal reflex and contralateral extensor reflex
  stimulated side withdrawn flexed and contralaterally extended (FIG)

Question 22

What are the two ocular reflexes?

Answer 22

Pupillary light reflex and vesibulo-ocular reflex

Question 23

What is pupillary light reflex

Answer 23

Controls the diameter of the pupil in response to light on the retina, it is important for adjusting eyes to different levels of light as it regulates it

Question 24

What is the vesibulo-ocular reflex?

Answer 24

controls the eye movement when the head moves
- involuntary eye movements equal or opposite to the head so that images can be continuously centered in visual field (FASTEST REFLEX 5ms)

Question 25

What is the plantar refelex

Answer 25

Test the integrity from L4 to L2
Stimulus: stroke later aspect of sole of the foot
response: downward flexion of toes
Damage to the motor cortex and corticospinal nerves causes abnormal response known as Babinski’s sign (for babies because myelination is incomplete)

Question 26

Difference between temporal summation and spatial summation

Answer 26

Temporal summation refers to several EPSPs from the same synapse, one after the other. Alternatively, spatial summation refers to 2+ EPSPs from different synapses. Temporal summation and spatial summation both have the potential to initiate an action potential, whereas most singular postsynaptic potentials decline before they reach the axon hillock.

Question 27

What would happen is a-y coactivation in muscle spindles did not occur?

Answer 27

Extrafusal (contractile) muscle fibres are innervated by alpha motor neurons. Intrafusal muscle fibres are innervated by gamma motor neurons.

If a-y coactivation did not occur and only alpha motor neurons were activated, only extrafusal muscle fibres would contract. The muscle spindle would subsequently become slack and unable to detect changes in length.

With a-y coactivation both extrafusal and intrafusal fibres contract so that tension is maintained the muscle spindle can detect changes in length.