Somatic Sensation

Question 1

Outline somatic senses

Answer 1

Mechanoreceptors
Nociceptors
Thermoreceptors
Chemoreceptors

Question 2

List the stimuli for mechanoreceptors

Answer 2

Touch
Pressure
Vibration
Proprioception

Question 3

What is the stimuli for nociceptors

Answer 3

Pain

Question 4

Outline special senses

Answer 4

Vision
Hearing
Balance
Taste
Smell

Question 5

Why are special senses referred to as special

Answer 5

Have localises special organ structures associated with their reception

Question 6

What class of neurons are involved in sensory information

Answer 6

Unipolar - single process that branches

Question 7

How many neurons in dorsal/posterior column pathway

Answer 7

Three neurons between sensory receptor and post central gurus

Question 8

Outline neuron 1 of the dorsal/posterior column pathway

Answer 8

Cell body in dorsal rot ganglion (unipolar)
Peripheral fibre from sensory receptor in skin
Central fibre (output zone) ascends toward brain in dorsal columns white matter
Makes synapse on neuron 2 in medulla oblongata

Question 9

Outline neuron 2 in dorsal/posterior column pathway

Answer 9

Cell body in medulla oblongata
Axon crosses to opposite side and ascends
Makes synapse on neuron 3 in thalamus

Question 10

Outline neuron 3 in dorsal/posterior column pathway

Answer 10

Cell body in thalamus
Axon ascends to somatosensory cortex
Makes synapse on cell body of somatosensory cortex neuron
Hence perception of stimulus, e.g. touch

Question 11

What stimulates mechanoreceptors and what do nerve endings contain

Answer 11

Physical forces that distort the plasma membrane
Nerve endings contain mechanically gated ion channels

Question 12

What influences the sensitivity of compression sensing lamellar corpuscles

Answer 12

More superficial = more sensitive
More deep = less sensitivity

Question 13

What is glamorous skin

Answer 13

Hairless skin

Question 14

What stimulates nociceptors

Answer 14

Noxious stimuli - responding to signals generated by tissue damage - trigger perception of pain

Question 15

Where are nociceptors absent from

Answer 15

Absent from the brain

Question 16

Outline the nerve endings of nociceptors

Answer 16

Usually free nerve endings

Question 17

What are the 3 main stimuli that nociceptors respond to

Answer 17

Thermal
Mechanical
chemical

Question 18

What is the relation between a receptor potential and an action potential

Answer 18

Presence of stimulus opens ion channels, creating receptor potential
If receptor potential reaches threshold, and action potential is initiated at sensory receptor

Question 19

What is single transduction

Answer 19

Process of converting stimulus of one form (e.g. touch) into another (change in membrane potential) is called signal transduction

Question 20

What is a receptive field

Answer 20

Endings of any single receptor spread over a restricted area

Question 21

What dictates the receiving of a stimulus in terms of receptive field

Answer 21

Sensory neuron only stimulated when stimulus present within area receptors are located (receptive field)

Question 22

What is the relationship between receptive field size and perceived stimulus localisation

Answer 22

Large receptive field provides poor localisation of the stimulus, and small fields provide good localisation

Question 23

What is a tonic receptor

Answer 23

Continually active to reflect background level of stimulation. AP frequency is proportional to stimulus level (eg skeletal muscle position)
Slow adapting

Question 24

What is a physic receptor

Answer 24

Normally silent
Brief responce to change e.g. touch and temperature
Fast adapting

Question 25

What are the 4 types of information encoded in sensory stimuli

Answer 25

Modality - type of receptor activated
Intensity - stimulus strength, encoded by frequency of AP firing
Duration - time period over which stimulus exists/ AP are active
Location - place in body where receptors are activated

Question 26

Why do the regions of the tongue, lip, face etc occupy relatively larger areas of the somatosensory cortex

Answer 26

They have greater numbers of receptors with small receptor fields, in turn providing high reception fidelity, and having more physical synapses in the brain
Area of receptor fields proportional to area take up in brain