Reflexes

Question 1

Describe the reflex arc

Answer 1

Stimuli - detectable change in internal/external environment Receptor - detects the change Integrating centre - Signal received Effector Response - sometimes neg feedback

Question 2

List the compounants of a monosynaptic reflex

Answer 2

Sensory receptor, sensory nerve fibre, motoneuron and muscle

Question 3

Draw the motor reflex

Answer 3

Question 4

What are the principle differences between axons?

Answer 4

The diameter and myelination

Question 5

Describe some of the features of alpha motor neurons

Answer 5

They have a very large diameter with a very fast conduction velocity (70-120m/s).

They are classes as Aα type fibres and innervate skeletal muscle

Question 6

What is the entery root for sensory signals and what occurs after they have entered the grey matter

Answer 6

Entery point is the from the dorsal roots. Once enterd, the signal branches into two; one terminates immediatly in the grey matter and one signal is sent to higher levels in the NS

Question 7

Anterior motor neurons give rise to what fibres?

Answer 7

Alpha motor fibres and Gamma motor fibres

Question 8

Describe some of the features of alpha motor neurons

Answer 8

• Give rise to a large Type A alpha (Aα) motor neuron fibres which are very thick.
• These fibres innervate the large skeletal muscle fibres
• Stimulation of a single alpha nerve fiber innervates many fibres

Question 9

Describe some of the features of Gamma motor neurons

Answer 9

• Far fewer Gamma than Alpha motor neurons
• Transmit signals via much smaller Type A gamme motor nerve fibres
• Innervate special small skeletal muscle fibres called intrafusal fibres (help control muscle tone as they make up the middle part of muscle spindles)

Question 10

What are the other type of neurons in the spinal cord?

Answer 10

Interneurons

Question 11

Sensory information from muscles to the spinal cord is provided by what?

Answer 11

• Muscle spindles throughout the belly of a muscle (send info about muscle length or rate of change of length)
• Golgi tendon organs located in muscle tendons ( Sends info about tendon tension or rate of change of tension)

Question 12

Muscle spindal receptor excitation can be via?…

Answer 12

Lengthening of the whole muscle or contraction of end portions of the spindle’s intrafusal fibres (both streching the midportion of the spindle where sensory fibres originate from)

Question 13

What are the two types of sensory endings in the central muscle spindle receptor area?

Answer 13

Primary afferent (Type 1a) - big

Secondary afferent (Type 2) - small

Question 14

Name the different fibre types

Answer 14

Aα

Aβ

Aγ

Aδ (delta)

B

C

Question 15

For each fibre type (

Aα

Aβ

Aγ

Aδ (delta)

B

C) name their conduction velocity(m/s), diameter (µm) and function

Answer 15

Aα - 70-120m/s, 12-20µm and their function is proprioception and somatic motor

Aβ - 30/40m/s, 5-12µm and their function is for touch and pressure

Aγ - 15-30m/s, 3-9µm and their function is motor to muscle spindles

Aδ (delta) - 12-30m/s, 2-5µm and their function is pain and temperature

B - 3-15m/s, 1-3µm and their function is preganglionic autonomic

C - 0.5-2m/s, 0.1-2µm and their function is postganglionic sympathetic, pain, temp and pressure

Question 16

For each fibre (

Aα

Aβ

Aγ

Aδ (delta)

B

C) Name their other name

Answer 16

Aα - IA, IB (one A and B)

Aβ - II (two)

Aγ - II (two)

Aδ (delta) - III (three)

B - ?

C - IV (four)

Question 17

What are the two types of muscle spindle intrafusal fibres?

Answer 17

Nuclear bag and Nuclear chain intrafusal fibres

Question 18

What are some of the features of nuclear bag and nuclear chain fibres

Answer 18

Nuclear bag - 1-3 per muscle spindle and several nuclei gathered in ‘bags’

Nuclear chain - 3-9 per muscle spindle, 1/2 diameter and length of nuclear bags

Question 19

Primary sensory nerve endings are excited by what?

Answer 19

Both nuclear bag and nuclear chain intrafusal fibres

Question 20

Secondary sensory nerve endings are excited by what?

Answer 20

Only nuclear chain fibres

Question 21

Gamma Dynamic motor neurons excite what? and gives what response?

Answer 21

Gamma-d excite mainly the nuclear bag intrafusal fibres and so the dynamic response of the muscle spindles is enhances but static response is not.

Question 22

Gamma-static motor neurons excite what? and what response do they give?

Answer 22

Gamma-s excites mainly the nuclear chain intrafusal fibres and so enhanse static response but not on the dynamic response

Question 23

What are the static and dynamic responses?

Answer 23

Static Response - Its a response from both primary and seconday endings to a change in length or the deceptor

Dynamic Response - This is a response that arises from stimulation of the primary endngs to a rate of change of receptor

Question 24

Describe the basics of a muscle spindle strech reflex

Answer 24

Type 1a nerve fibre.

Branch of fibre goes directly to ventral horn of grey matter of spinal cord where it synapses with an anterior motor neuron and sends motor nerve fibres back to the same muscle where the muscle spindle fibre originated from.

Question 25

Explain what a dynamic response is elicted by and and what occurs after it is elicited.

Answer 25

Elicited from dynamic signals from primary sensory endings of the muscle spindle caused by rapid stretch/unstretch. It opposes sudden changes in muscle length.

This is a fast response and means if a muscle is stretch/unstreched then a signal is transmitted to the spinal cord and a strong reflex contraction/decrease in contraction occurs (preventing muscle from ripping)

Question 26

What is a static response elicited by and what does it involve?

Answer 26

It is elicited by continuous static receptor signals transmitted by primary and secondary endings.

It causes a degree of muscle contraction to remain constant and produces a slow gradual change.

Question 27

What does reciprocal innervation mean?

Answer 27

It is innervation of a mucle(s) that is accompanied by the simultaneus inhibition of antagonist muscle(s)

(for example if quads are innervated then hamstrings are inhibited)

Question 28

What is the function of a Golgi tendon organ receptor?

When is it stimulated?

Answer 28

It helps control muscle tension and is stimulated when the receptor is tensed by the contracting or stetching of the muscle

Question 29

How does the Golgi tendon organ reflex prevent excessive tension

Answer 29

GTO stimulated by increased tension in the muscle, the signals are transmitted to the spinal cord to cause an inhibitory reflex thus preventing the development of too much tension. If the tension becomes extreme the inhibitory effect of the GTO causes instantaneous relaxation of the muscle.

Question 30

Other than skeletal muscle, where else will you find reflexes?

Answer 30

In glands, heart, eyes, gut, vestibular system and capillary system

Question 31

Give examples of reflexes involving special senses?

Answer 31

Rotatory Nystagmus - Eye movement driven by movement of visual images

Post Rotatory Nystagmus - Eye movement driven by the movement of fluid in the semi-circular canals of the inner ear

Interpretation of movement within images on the retina - used to make postural adjustments to preserve balance.