L21 Sensation And Motor Control

Question 1

What are the subdivisions of the somatosensory system?

Answer 1

1. Cutaneous sensations (skin)
2. Visceral ( internal organs and deep tissues)
3. Proprioception (positions of limbs and body in space)

Question 2

What are the functions of touch sense?

Answer 2

1. Recognition and properties of things
2. Communication - social and intimate
3. Control of movement

Question 3

Why do sensory system require receptors?

Answer 3

They convert stimulus energy into action potentials

Question 4

What is sensory transduction?

Answer 4

• the stimulus is converted into graded electrical signal (receptor potential)
• the receptor potential magnitude depends on stimulus strength

Question 5

What happens if the receptor potential exceeds threshold?

Answer 5

The nerve fibre fires action potentials

Question 6

What is stimulus strength coded by?

Answer 6

Coded by firing rate or pattern

Question 7

How can properties of receptors be recorded?

Answer 7

By recording action potential from single afferent nerves and mapping ‘receptive fields’

Question 8

Smaller set of nerves less myelin smaller diameter slower conduction

Answer 8

A beta
Type 2 axons
Cutaneous mechanoreceptors

Question 9

Large set of nerves, large diameter, lots of myelination, fast conduction

Answer 9

Type 1a/1b
A alpha
Proprioception

Question 10

What are the two main groups in Proprioception?

Answer 10

Muscle spindles - imbedded in the muscles
Golgi tendon organs

Question 11

Outline extrafusal muscle fibres

Answer 11

Innovated by alpha fibres - large fibres
Generate force

Question 12

Outline intrafusal muscle fibres

Answer 12

Gamma motor units - smaller than alpha motor units
Don’t really generate force
Set gain of spindle responses
They can detect whether the muscle has been stretched

Question 13

How are extrafusal and intrafusal muscle fibres divided?

Answer 13

Divided by a collagen/fibrobast sheath with a ‘fuse form shape’

Question 14

How are muscles activated?

Answer 14

Activated as a result of action potentials arising at the neuromuscular junction causing a release of Ach

Question 15

What makes up a motor unit?

Answer 15

A motoneuron and the muscle fibres it innervates

Question 16

Outline the Henneman Size Principle

Answer 16

Small motor units are recruited before large motor units
- these units produce low force but are more fatigue resistant

Question 17

Outline the monosynaptic stretch reflex

Answer 17

• add load to muscle
• muscle and muscle spindle stretch as arm drops
• reflex contraction initiated by muscle spindle restores arm position

Question 18

Where do spinal motoneurons receive input from?

Answer 18

• afferents
• spinal interneurons
• descending inputs from the brain

Question 19

What is the dorsal column pathway responsible for?

Answer 19

Fine touch / Proprioception

Question 20

What is the spinothalamic pathway responsible for?

Answer 20

Pain / Temperature

Question 21

What is the coritcospinal pathway responsible for?

Answer 21

Voluntary movement

Question 22

Which cutaneous receptors are located in the superficial area of the skin?

Answer 22

Meissner, merkel and free nerve endings

Question 23

What do A-delta nerve endings detect?

Answer 23

Detect cold temperatures via bare nerve endings
Detect a sharp, initial pain via nociceptors

Question 24

What do A-delta nerve endings detect?

Answer 24

Detect cold temperatures via bare nerve endings
Detect a sharp, initial pain via nociceptors

Question 25

What do C-fibres detect?

Answer 25

Detects warm temperatures via bare nerve endings
Detects the burning/nagging pain via nociceptors

Question 26

What do A-beta fibres transmit infomation about?

Answer 26

Info about pressure, vibration and flutter/stroking

Question 27

Outline the pathway for a neurone that senses fine touch

Answer 27

Dorsal column pathway
- neurones project into the medulla where they first synapse
- leads into the thalamus where the second synapse occurs
- leads to the somatosensory cortex

Question 28

Outline the pathway for a neurone that senses coarse touch

Answer 28

Spinothalamic tract pathway-also for nociception and temp
- the first synapse occurs in the spinal cord before crossing over
- continues through the medulla to the thalamus and somatosensory cortex