Sensory and Proprioception

Question 1

What are the three types of sensory receptors?

Answer 1

Mechanoreceptors, proprioceptors, nociceptors

Question 2

What is the role of mechanoreceptors?

Answer 2

Stimulated by mechanical stimuli on skin - e.g. touch and pressure

Question 3

What is the role of proprioceptors?

Answer 3

Stimulated by mechanical stimuli in joints and muscles

Question 4

What is the role of nociceptors?

Answer 4

Stimulated by painful stimuli - damage to tissue

Question 5

How are sensory receptors triggered by stimuli?

Answer 5

An adequate stimulus will cause local stretch ion channels to open, causing a graded potential/ flow of ions which will reach a node of ranvier and cause depolarisation, leading to an action potential.

Question 6

What determines if an Action potential will fire and how many

Answer 6

The level of stimulus. Low stimulus may not produce any action potentials, high stimulus may produce many.

Question 7

How can we figure out duration and strength of stimulus?

Answer 7

Looking at the pattern of action potentials produced

Question 8

What does ‘adaptation’ mean in relation to receptors?

Answer 8

Whether the receptor continues to produce action potentials in response to a stimulus, or adapts to a new ‘normal’ and stops producing action potentials. E.g. when we put socks on

Question 9

What are the 4 skin touch receptors?

Answer 9

Pacinian corpuscle (fast), Merkel receptors (f), Ruffini corpuscle (s) and Meissner corpuscle (s)

Question 10

Which type of receptor does not adjust?

Answer 10

Nociceptors - because it is important to feel painful stimuli

Question 11

What is the structure of the pacinian corpuscle?

Answer 11

A naked myelinated nerve ending encapsulated by a lamellae capsule with several layers, and liquid between each layer

Question 12

How does the pacinian corpuscle adapt to stimuli?

Answer 12

Mechanical stimulus deforms capsule and causes the nerve to stretch, so stretch ion channels open and cause Na+ to flow, which depolarises and causes AP at first node of ranvier. This tells brain about stimulus, and then the liquid redistributes in the lamellae to minimise deformation, so AP’s stop firing. When stimulus is removed, liquid flows and ions spread again, so AP’s occur again.

Question 13

What is the importance of capsules in sensory receptors?

Answer 13

Cause AP’s to stop firing. Without them they wouldn’t.

Question 14

What is a receptive field and what is its importance?

Answer 14

Its a area of skin which is associated with 1 sensory neuron, which synapses on 1 CNS neuron. Smaller receptive fields are found on more sensitive parts of the body, like lips and fingers, while large ones are found in less sensitive areas, like the back.

Question 15

What its the 2-point discrimination test?

Answer 15

Tests 2 adjacent points until we perceive 2 separate neurons rather than 1. Closer points = more sensitive

Question 16

What is convergence?

Answer 16

Neighbouring receptive fields may summate to 1 secondary neuron if they’re close together. High convergence = Less sensitive.

Question 17

How do convergence and acuity relate?

Answer 17

High convergence = low acuity and vice versa. Acuity is ability to differentiate between close points skinned locate a stimulus

Question 18

What is lateral inhibition?

Answer 18

When neuron closest to stimulus inhibits neighbouring neurons to allow us to identify exact point of stimuli

Question 19

What happens to sensory info from receptors?

Answer 19

Relays from skin, so primary sensory neuron, to secondary CNS neuron in spinal cord, to the thalamus and finally to the somatosensory area in the parietal lobe

Question 20

What are the main receptors involved in proprioception?

Answer 20

Muscle spindles, golgi tendon organs (GTO’s) and joint receptors

Question 21

What do muscle spindles do?

Answer 21

Measure muscle length and rate of change of length

Question 22

What do golgi tendon organs do?

Answer 22

Measure tension on tendons and muscles

Question 23

Extrafusal vs Intrafusal muscle fibres?

Answer 23

Extrafusal innervated by alpha-motor neurons, Intrafusal innervated by gamma-motor neurone. Most are extrafusal, intrafusal ones have their own sensory receptors and contained in capsule called muscle spindles. Extrafusal and Intrafusal are parallel

Question 24

What are the 2 types of intramural fibre?

Answer 24

Nuclear bag fibres (many nuclei collected together|) and nuclear chain fibres (many nuclei in chain).

Question 25

What must be present for a contraction to occur and how is it related to muscle spindles?

Answer 25

Sarcomeres. These aren’t found in the centre of muscle swindles so it centre doesn’t contract - it stretches instead.

Question 26

What are the 2 kinds of sensory nerve found in the centre of muscle spindles?

Answer 26

Ia - annulospiral and II - flower spray endings

Question 27

What happens when a muscle is stimulated

Answer 27

The ends of intramural fibres with sarcomeres are contracted by gamma motor neurons. This causes central section to stretch, which opens stretch-sensitive ion channels and creates a local generator potential, and nervous impulse leaves from Ia annulospiral sensory neuron.

Question 28

How do Golgi tendon organs communicate with the brain?

Answer 28

When muscle contracts, tendons are stretched, causing tension. This sends a message from II afferent fibres (flower spray endings) to the brain

Question 29

What is the importance of gamma motor neurons?

Answer 29

Without them, we wouldn’t be able to tell the brain about the length of our muscles, or tension. Muscle would be useless

Question 30

What is Frequency Coding?

Answer 30

The rate that action potentials is determined by the size of stimulus. Fast discharge of action potentials lead to more powerful muscle movement