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Question 1

Define Sensation

Answer 1

Is a conscious or sub-conscious awareness of an external or internal stimulus

Question 2

Define sensory modalities

Answer 2

The different types of senses that cause a response in receptors

Question 3

What are the different types of senses?

Answer 3

General somatic- tactile, thermal, pain, proprioceptionGeneral visceral Special senses

Question 4

Describe sensory receptors

Answer 4

Receptors which are specialised to detect stimuli, usually found throughout the layers of skin. There are many different types of sensory receptors and are often specific to a modality.

Question 5

What components make up a sensory receptor?

Answer 5

Free nerve endingEncapsulated nerve endingSpecialised cell

Question 6

What is a sensory quality?

Answer 6

A subdivision of modalitye.g. sweet and sour are qualities of the taste modality

Question 7

Describe proprioceptors

Answer 7

These are sensory receptors found in muscles and joints which provide an awareness of where our body is in space.

Question 8

Describe the receptors involved in proprioception

Answer 8

Muscle spindles - info about length of the muscleGolgi tendon organ - measures the tension in the tendons

Question 9

What is sensory transduction?

Answer 9

The ability of a stimulus to be converted into an action potential and for to travel along to the brain control centres.

Question 10

Describe the process of signal transduction.

Answer 10

1. Stimulus stimulates a receptor and evokes a change in the permeability of the ions in the receptor membrane at the peripheral axon, in proportion to the size of the stimulus. 2. A receptor potential is generated due to ion movement across the membrane3. If the stimulus is great enough, the combination of receptor potentials will reach threshold level and generate an action potential which can propagate along the nerve.

Question 11

What things determine the strength of an action potential stimulus?

Answer 11

Frequency coding - the rate of action potential stimulus. There will be a greater rate of firing with a greater stimulus. Activation of neighbouring cells can occur with a stronger stimulus.

Question 12

What are the two different adaptations that receptors have?

Answer 12

Tonic receptorsPhasic receptors

Question 13

Describe tonic receptors

Answer 13

Slowly adapting receptors which keep firing as long as they are being stimulated by a stimulus

Question 14

Where do you find tonic receptors?

Answer 14

They are joint receptors and pain receptors

Question 15

Describe phasic receptors

Answer 15

These rapidly adapting receptos respond maximally and briefly to a stimulus

Question 16

What kind of receptors are phasic receptors?

Answer 16

Touch receptors

Question 17

Define sensory acuity

Answer 17

The precision by which a stimulus can be located.

Question 18

What things determine sensory acuity?

Answer 18

Lateral inhibitionTwo point discriminationSynaptic convergence and divergence

Question 19

Describe lateral inhibition

Answer 19

Inhibitory neurones will prevent the transmission of action potentials which do not have a maximum stimulus. This means that only maximally stimulated neurones will fire, leading to a sharpening of sensory acuity.

Question 20

How does lateral inhibition work?

Answer 20

Inhibitory interneurons act on the neurones which have not been stimulated to inhibit the transmission of their action potentials.

Question 21

Describe two point discrimination

Answer 21

There is a minimum distance that needs to be between two points so that you are able to distinguish between them.

Question 22

How does two point discrimination vary?

Answer 22

In areas which have a high density of sensory receptors and a small neuronal field (fingers) you are able to distinguish between two points which are closer together compared to an area such as the forearm which has a lower sensory receptor density and larger neuronal field.

Question 23

Describe synaptic convergence

Answer 23

Several 1st order neurones converge onto a single 2nd order neurone.

Question 24

What effect does synaptic convergence have?

Answer 24

It decrease sensory acuity

Question 25

Describe synaptic divergence

Answer 25

A single 1st order neurone divergse to several 2nd order neurones

Question 26

What effect dose synaptic divergence have?

Answer 26

It amplifies the signal

Question 27

What is a receptive field?

Answer 27

This is an area where a stimulus will alter the firing of that neurone- the smaller the receptive field, the higher the receptor density

Question 28

Describe the structure of a receptive field

Answer 28

Found at the end of an axonDetermines where an axon can sense stimuli. Vary on size and densityCan overlap with neighbouring fields

Question 29

Where do you feel sensation?

Answer 29

In the thalamus- have crude localisation and discrimination of a stimulus- have highly organised projections to the cortex

Question 30

Describe the somatosensory cortax

Answer 30

Is located at the post central gyrusHave somatotrophic representation - each area of the body is mapped to a specific part of the cortex.

Question 31

What does the somatosensory cortex do?

Answer 31

It allows for the sharp localisation and recognitions of the different qualities of modalities. Relays information to other cortical and subcortical areas. The choice to respond to a stimulus is taken but the cortical areas.

Question 32

Define the sensory homunculus

Answer 32

This is a contralateral representation of specific body areas. Each area of the cortex is mapped to a body areas and the relative size of the area depends on the degree of sensory acuity associated with it.

Question 33

Define perception

Answer 33

The awareness of stimuli and our ability to discriminate between different types of stimuli.

Question 34

Describe synesthesia

Answer 34

A neurological disorder whereby the stimulation of one sense gives rise to an automatic response from a second sense.

Question 35

Describe the pathology of shingles

Answer 35

Caused by the varicellar zoster virusPrimary infection causes chicken pox but the virus stays in the dorsal root ganglia and is reactivated to cause shingles

Question 36

How does shingles cause pain?

Answer 36

Increases the sensitivity of the dorsal root neurones, triggering burning and tingling sensation. The skin of the affected dermatome becomes red and blisters and it is extremely painful.

Question 37

Why does shingles only affect one or two dermatomes?

Answer 37

The infection is restricted to one or two dorsal root ganglia.