Spinal Pathways

Question 1

What are the 4 types of mechanoreceptors in glabrous skin?

Answer 1

From superficial to deep:

Meissner corpuscles, Merkel complexes, Ruffini organs, Pacinian corpuscles

Question 2

Which mechanoreceptors are rapidly adapting?

Answer 2

Meissner corpuscles and Pacinian corpuscles

Question 3

Which mechanoreceptors are slowly adapting?

Answer 3

Merkel complexes and Ruffini organs

Question 4

What is the receptor field?

Answer 4

Over which region of space a specific receptor responds to

- size determines how fine the detail of information you can resolve is

Question 5

What does mechanical distortion do?

Answer 5

Opens sodium channels which are tethered to the membrane, allowing Na+ through and depolarising the axon

Question 6

Which mechanoreceptors have small receptor fields and which have large receptor fields?

Answer 6

Merkel and Meissner have small receptor fields

Ruffini and Pacinian have large receptor fields

Question 7

What do Meissner corpuscles encode?

Answer 7

Rate of force

Question 8

What do Merkel complexes encode?

Answer 8

Grip force (indentation)

Question 9

What do Ruffini endings encode?

Answer 9

Hand posture (proprioception)

Question 10

What do Pacinian corpuscles encode?

Answer 10

Vibrations

Question 11

What are the dorsal columns?

Answer 11

Gracile (lower limb, closer to midline) and cuneate (upper limb) tracts travel up the spinal cord (dorsal side). Carry information about fine touch and proprioception

Question 12

What is the 3 neuron sequence in the dorsal column-medial lemniscus pathway?

Answer 12

First synapse is in the medulla, then the tracts decussate (at the caudal medulla), form a band/ribbon (medial lemniscus) which travels along the midline. Projects to the thalamus where is synapses with the ventral posterior lateral nucleus of thalamus. These neurons then project up to the cerebral cortex

Question 13

What is the sensory mapping of the tissue?

Answer 13

The tissue is somatotopically organised

• neurons that are close to each other in the cortex represent areas that are close to each other in the periphery
• maps are of the contralateral side of the body

Question 14

What is the concept of plasticity?

Answer 14

The cerebral cortex can be reassigned to respond to different things - can happen with increased or decreased use. THE IDENTITIES DO NOT CHANGE

Question 15

What is different about nerve root C1?

Answer 15

It does NOT have a cutaneous distribution (no dermatome), as it only has motor branches

Question 16

What are segmental reflexes in the spinal cord?

Answer 16

When information comes in at one level, gets processed and goes out at the same level

Question 17

What are inter-segmental reflex in the spinal cord?

Answer 17

When multiple segments of the spinal cord are involved in a reflex

eg. bilateral (cross-extensor) if withdraw one of the limbs form a noxious stimulus then have to make sure that the remaining limb is functional for the whole body
- interneurons activate the flexors and inhibit the extensors of one leg, and at the same time on the contralateral leg excites the extensors and inhibits the flexors

Question 18

What is the general organisation of the spinal cord?

Answer 18

White matter on the outside, surrounding the nerve cells/bodies of the dorsal and ventral horns
- as you go down the cord see less white matter, because more information is coming up

Question 19

What is the arrangement of the spinal cord in terms of motor distribution?

Answer 19

Midline spinal cord –> proximal muscles

Lateral spinal cord –> distal muscles

Question 20

What is a motor pool?

Answer 20

All the motor neurons in the spinal cord that innervate a particular muscle
- one motoneuron innervates many fibres (motor unit) –> can control how many motor units are active at a time

Question 21

What are muscle spindles?

Answer 21

Intrafusal sensory structure, reports back about how much stretch the muscle is undergoing (length)

• fastest conducting fibre
• in parallel with the muscle
• low threshold

Question 22

What are golgi tendon organs?

Answer 22

The sensory nerve coming in interdigitates with the tendon

• reports back about how much force is being transmitted through the tendon
• in series with the muscle
• high threshold

Question 23

What is the monosynaptic stretch reflex?

Answer 23

Only one synapse involved
- tap the tendon –> activate the muscle spindles –> burst of neural activity back to the spinal cord –> muscle contraction

Question 24

How is the brain involved in the control of the spinal cord reflexes?

Answer 24

Brain sends inhibitory signals
- if see larger tendon reflexes then it means that the balance of power has changed and input isn’t coming from the brain