Lecture 17: Reflexes

Question 1

what are the two main types of reflexes?

Answer 1

somatic reflexes - activate skeletal muscles
autonomic reflexes - activate visceral reflexes

Question 2

what are the five components of a reflex arc?

Answer 2

1. receptor - site of stimulus action
2. sensory neuron - transmits afferent impulses to CNS
3. integration centre - either monosynaptic or polysynaptic region within CNS
4. motor neuron - conducts efferent impulses from integration centre to effector organ
5. effector - muscle fibre or gland cell that responds to efferent impulses

Question 3

what are the two important receptors for somatic reflexes?

Answer 3

muscle spindle - long elongated structure aligned in parallel to skeletal muscle fibers
Golgi tendon organ - located within tendons near the muscle/tendon junction, aligned in series, respond to muscle tension

Question 4

at the integration centre, what two neurons do the sensory neurons activate?

Answer 4

the two different neurons activated can make direct connections with motor neurons and/or an intermediate neuron called an interneuron.

Question 5

what are the two types of motor neurons?

Answer 5

alpha motor neurons - receives input from sensory and interneurons
gamma motor neurons - innervate intrafusal muscle fibres within spindle

Question 6

explain the difference between monosynaptic and polysynaptic?

Answer 6

mono: sensory and motor neuron synapse directly
poly: sensory and motor neurons synapse with interneurons in the spinal cord (disynaptic and oligosynaptic).

Question 7

what is spinal reflex?

Answer 7

spinal reflexes are somatic reflexes mediated by the spinal cord.

Question 8

describe stretch reflex and ways to assess stretch reflex.

Answer 8

1. stretch reflex activates muscle spindles and transmits sensory neurons afferent impulses at high frequency to the spinal cord
2. sensory neurons synapse with alpha motor neurons to excite extrafusal fibers and interneurons to inhibit motor neurons of antagonist muscle.
   3a. efferent impulses of alpha motor neurons caused the stretched muscle to contract and resist the stretch
   3b. efferent impulses of alpha motor neurons to antagonist muscles are reduced

ways to assess stretch reflex:
- patellar/knee-jerk reflex
- h-reflex

Question 9

describe tendon reflexes and ways to assess tendon reflexes.

Answer 9

tendon reflexes prevent muscles from tearing due to excessive force.

1. the quads contract and tendon organs are activated
2. afferent fibres synapse with interneurons in the spinal cord
   3a. efferent impulses to muscle with stretched tendons are damped. the muscle relaxes and there is a reduced tension.
   3b. efferent impulses to antagonist muscle cause to contract

Question 10

what is flexor reflex?

Answer 10

this reflex was initiated by a painful stimulus and is the automatic withdrawal of a threatened body part that is protected and important for survival.

Question 11

what is a crossed extensor reflex?

Answer 11

this occurs with flexor reflexes in weight-bearing limbs to maintain balance. e.g. stepping on a nail, consisting of an ipsilateral withdrawal reflex and a contralateral extensor reflex.

Question 12

what are the two ocular reflexes and what do they do?

Answer 12

pupillary light reflex: controls the diameter of the pupil in response to light on the retina. helps with eye adjustment to different levels of light.

vesibulo-ocular reflex: controls eye movement when the head moves. involuntary eye movements equal and opposite to the head so that images can be continuously centred in the visual field. fastest human reflex.