Week 9- Sensory Receptor Physiology

Question 1

Define a stimulus

Answer 1

Change detectable by the body that exists in a variety of energy forms

Question 2

What is a receptor?

Answer 2

Either a specialised ending of an afferent neuron or a cell body closely associated with the peripheral ending of the neuron that converts stimulus energy into action potentials

Question 3

What is transduction?

Answer 3

The process by which stimulus energy is converted into action potentials at a receptor

Question 4

What is meant by ‘perception’ of a stimulus?

Answer 4

what you receive as a stimulated being arises from multiple inputs from different senses

Question 5

What are the categories of receptors?

Answer 5

1. Photoreceptors
2. Mechanoreceptors
3. Thermoreceptors
4. Osmoreceptors
5. Chemoreceptors
6. Nociceptors (pain receptors)

Question 6

Define the term ‘compound sensations’

Answer 6

Perception that arises from integration of several simultaneously activated primary sensory inputs

Question 7

What is processing of sensory input by the brain stem critical for?

Answer 7

Cortical arousal and consciousness

Question 8

How does sensory stimuli have an effect on our emotions?

Answer 8

Afferent neurons send signals to limbic system, evoking responses that we don’t consciously notice, triggering emotional effects

Question 9

How does stimulation of a receptor alter its membrane permeability?

Answer 9

Causes a non-selective opening of small ion channels. Receptor potentials or graded potentials are generated. These are then converted into APs if required for long-distance transmission

Question 10

The intensity of a stimulus is reflected by what?

Answer 10

The magnitude of the receptor potential. The larger the receptor potential is, the greater the frequency of APs generated.

Also distinguished by the number or receptors activated within the area

Question 11

What is ‘adaption’?

Answer 11

Where stimuli of the same intensity not always bring about receptor potentials of the same magnitude from the same receptor

Question 12

What are the 2 types of receptors based on their speed of adaption?

Answer 12

Tonic receptors and phasic receptors

Question 13

What are tonic receptors and where are they important?

Answer 13

• no not adapt or adapt slowly
• Important in situations where it s valuable to maintain information about a stimulus e.g. muscle stretch receptors
• Continue to generate APs, however, to relay information to the CNS

Question 14

What are phasic receptors and where are they important?

Answer 14

• rapidly adapt
• adapts by no longer responding to a maintained stimulus
• When the stimulus is removed, the receptor has a slight hyperpolarisation “off response”
• Useful in situatons where it is important to signal a change in stimulus intensity

Question 15

What are the 2 possible scenarios when the afferent information reaches the spinal cord?

Answer 15

• Reflex arc; bringing about an appropriate effector response when integrated in the spinal cord
• May be relayed up to the brain for further processing & possible conscious awareness

Question 16

What are somatosensory pathways and what do they consist of?

Answer 16

Pathways conveying conscious somatic stimulation

consist of discrete chains of neurons, synaptically interconnected in a particular sequence to accomplish more sophisticated processing of the sensory information

Question 17

What is a first order sensory neuron?

Answer 17

The afferent neuron thats peripheral receptor first detects the stimulus

Question 18

What is a second order sensory neuron?

Answer 18

Located in either the spinal cord or the medulla, where the 1st order synapses onto

Question 19

What is the 3rd order sensory neuron?

Answer 19

In the thalamus, where the 2nd order synapses onto

Question 20

Where are particular sensory inputs usually projected?

Answer 20

defined areas of the somatosensory cortex

Question 21

What does labelled pathways allow?

Answer 21

Allows the brain to decode the type and location of the stimulus

Question 22

What is a receptive field?

Answer 22

The circumscribed region of skin in which each somatosensory neuron responds to stimulus. allows for differentiation of different stimuli on points of the skin

Question 23

What is the relation between the size of a receptive field and the density of the receptors in the region?

Answer 23

The size of a receptive field varies inversely with the density of receptors in the region. The closer the receptor spacing, the smaller the area of skin each monitors

Question 24

What factors influence acuity?

Answer 24

receptive field size and lateral inhibition

Question 25

The distorted cortical representation of various body parts in the sensory homunculus corresponds with what?

Answer 25

Corresponds precisely with the innervation density

Question 26

How is greater tactile discriminative ability allowed?

Answer 26

More cortical space is allotted for sensory reception from areas with smaller receptive fields

Question 27

What is the difference between the receptors under a point of contact and that of the surrounding skin?

Answer 27

Directly under= excited

surrounding= stimulated to a lesser extent due to being less distorted

Question 28

How does lateral inhibition occur?

Answer 28

The strongest activated signal pathway inhibits the lesser excited pathways. Inhibitory interneurons synapse laterally between ascending fibres of neighbouring afferent receptor neurons. Blockage of transmissions increases the contract between wanted and unwanted information

Question 29

Why does lateral inhibition occur?

Answer 29

To allow for accurate localisation of the point of contact