Proptrioception

Question 1

What two things does muscle control require?

Answer 1

Excitation of alpha motor neurons

Continuous feedback from each muscle to the nervous system

Question 2

Where does information on muscle length come from?

Answer 2

The muscle spindle

Question 3

What is a golgi tendon organ?

Answer 3

It is a proprioceptive sensory receptor that senses changes in muscle tension of skeletal muscle fibres
It provides the sensory information of the golgi tendon reflex
The information is relayed to the spinal cord and cerebellum

Question 4

What is proprioception?

Answer 4

Sense of knowing your orientation

Question 5

Describe the structure of type 1a afferent fibres

Answer 5

They are anulospiral

They wrap around the equator of both bag and nuclear chain intrafusal muscle fibres

Question 6

Describe the structure of group ii afferent fibre endings

Answer 6

They have a ‘flower spray’ terminal ending embedded in the equatorial regions of the nag fibres

Question 7

Anulospiral afferent endings are confined to which nerve endings?

Answer 7

Nuclear chain fibres

Question 8

What information do group 1a and group 2 sensory fibres relay?

Answer 8

1a = the dynamic phase of muscle stretch ie as the stretch is occuring
2 = information on the static phase of the stretch eg the muscles final length

Question 9

When do muscle spindles not send action potentials?

Answer 9

When they are slack they stop sending action potentials so they lose proprioception

Question 10

What happens when a muscle contracts?

Answer 10

Gamma motor neurons are co-activated with alpha motor neurons
The spindle shortens in register with the extrafusal fibres
Gamma motor neurons gather up the slack causing tension in the intrafusal spindle

Question 11

What analagy can be used to decribe how gamma motor neurons work?

Answer 11

The fisherman - the line is slack until the fish swims towards the fisherman
This means he no longer can locate the fish due to the loss of tension
The tension has to be increased again to relocate the fish

Question 12

What can increase gamma motor neuron activity?

Answer 12

Serotonin

Question 13

What can decrease gamma motor neuron activity?

Answer 13

Noradrenaline (Na)

Question 14

What is the effect of serotonin on the gamma motor neurons?

Answer 14

The intrafusal fibres become slightly stiffer in the presence of serotonin
The stiffer materials transmit stretches with greater fidelity

Question 15

What is the effect of noradrenaline on gamma motor neurons?

Answer 15

Causes the intrafusal fibres to become elastic and floppy

Elastic materials do not transmit stretches well

Question 16

What is the tendon jerk reflex?

Answer 16

It is the only monosynaptic reflex in the body
The muscle is stretched by a hammer blow to its tendon
This causes the primary sensory endings (group 1a) to be activated and they send action potentials along the limb to the spinal cord
The muscle contracts in opposition to the stretch and the limb jerks as a consequence

Question 17

What is jendrassik’s manoevre?

Answer 17

The patient clenches the teeth , flexes both fingers and interlocks the fingers
The tendon below the patients knee is then hit to elicit the patellar reflex

Question 18

What is the effect on the jerk reflex in the jendrassik’s manoevre?

Answer 18

The position of the hands causes excitation in the upper segments of the spinal cord
This excitation spins over to the rest of the spinal cortex so the alpha motorneurons which supply the quadriceps are bought more to threshold
The reflex response is therefore bigger

Question 19

Describe the tonic vibration reflex

Answer 19

Group 2 afferents vibrate at around 50Hz when the arm is straight
Group 2 afferents fire about 20Hz when the arm is fully stretched
If a vibrator is applied to the tendon it drives the Group 2 afferents in muscle so they discharge at 100Hz

Question 20

What did Sherrington show?

Answer 20

Showed that a reflex required sensory input from the muscle and a return pathway to the muscle
He used a the decerebrate cat to show this

Question 21

Spindle 1a neurons make connections on what two types of muscles?

Answer 21

A homonymous muscle (a muscle that the spindle is in) 
Syngergistic muscles (those that help maintain contraction)

Question 22

When a muscle stretches what happens to 1a firing rates?

Answer 22

They increase

Question 23

How do 1a motor neurons cause the relaxation of the antagonists muscles?

Answer 23

They act through inhibitory interneurones that innervate antagonistic muscles

Question 24

What is the central pathway called for the somatosensory system?

Answer 24

The Dorsal-Column-Medial Lemniscal system

Question 25

What is the The Dorsal-Column-Medial Lemniscal system?

Answer 25

An ascending spinal tract carrying sensory information to the brain, mediatinf conscious proprioception

Question 26

What are the three relays in the The Dorsal-Column-Medial Lemniscal system?

Answer 26

1) The central process of DRG cells synapse on to neurons in the gracile and cuneate nuclie in the lower medulla
2) These then ascend in to the medial lemniscus and synapse on neurons in the ventral posterior lateral nucleus of the thalamus
3) These send axons to the primary somatosensory cortex

Question 27

Where are the primary and secondary somatosensory cortices located?

Answer 27

The anterior parietal lobe and the posterior parietal cortex
S2 is deep within the lateral sulcus

Question 28

Lesioning in the primary somatosensory cortex causes what?

Answer 28

Produces proprioceptive deficits eg lost ability to discriminate size, texture and shape of objects

Question 29

How many regions are there in the primary somatosensory cortex?

Answer 29

Four