Cutaneous senses

Question 1

Why is it important to be able to feel physical stimuli?

Answer 1

Feedback from objects e.g. for grasping
Proprioception (body position)
Warning signals (protection)

Question 2

What are skin receptors sensitive to?

Answer 2

Mechanic deformation (pressure, stretching, vibration)

Question 3

What is the different between slow-adapting and rapid-adapting skin receptors?

Answer 3

SLOW= Activate when pressure applied and fire constantly until lessens with time
RAPDI= "detector for change", vigorous response when pressure first applied but then nothing, important for motor feedback

Question 4

What are the 2 types of slow-adapting receptors?

Answer 4

Ruffini cylinders - perception of stretching, deeper in skin so larger receptive field
Merkel receptors- sensing of fine spatial details, near epidermis so small receptive field, highest density in finger tips(tactile acuity)

Question 5

What are the 2 types of rapid-acting receptors?

Answer 5

Pacinian corpuscle - texture perception, deep in skin so large receptive field, responds well to high rates of vibration , layered like an onion with fluid between Meissner corpuscle - Perception of hand-grip control and light touch, near epidermis so small receptive field

Question 6

Define haptic perception

Answer 6

Perception achieved through the active exploration of surfaces and objects by a moving subject, as opposed to passive contact by a static subject during tactile perception.

Question 7

What is Katz’s DUPLEX THEORY of texture perception?

Answer 7

Katz (1925) proposed that perception of texture depends on two cues: –Spatial cues are determined by the size, shape, and distribution of surface elements –Temporal cues are determined by the rate of vibration as skin is moved across finely textured surfaces
Two receptors may be responsible for this process

Question 8

What exploratory procedures can be utilised for haptic perception?

Answer 8

Lateral motion
Pressure
Enclosure
Contour following

Question 9

How do receptors indicate the shape of an object?

Answer 9

An object will typically stimulate multiple receptors at once, but contact point will respond most and lessen with distance
e.g. merkel receptors - smaller ball has high activation at point of contact, but larger will have larger deformation region so wider activation and less as fibres less responsive

Question 10

How is shape perception conveyed to the brain?

Answer 10

Pattern of mechanoreceptor response sent to brain
Neurons in ventral posterior nucleus of thalamus have CENTRE-SURROUND receptive fields (neuron fires when excitatory centre stimulated)
Some neurons in the cortex have these same receptive fields and others that are even more specialised e.g. to a particular direction of motion (cortical neuron response is also increased by attention being paid to object)

Question 11

What is a key consequence of the high density of merkel receptors in the fingertips?

Answer 11

High tactile acuity
Areas of such acuity are represented by larger cortical area, meaning activity from two points less likely to overlap than two points on the forearm for example

Question 12

How do nerve fibres from receptors reach the brain?

Answer 12

Travel to dorsal root of spinal cord in peripheral nerve bundles, and then follow one of two pathways:

1) MEDIAL LEMNISCAL PATHWAY - signals of proprioception and touch, very rapid and important when it comes to controlling movement in response to tactile stimuli
2) SPINOTHALMIC PATHWAY - carries signals responding to pain and temperature

Question 13

What happens once in the brain?

Answer 13

Pathways cross over into contralateral hemisphere just before thalamus
Signals travel to somatosensory cortex in parietal lobe

Question 14

What is the structure of the somatosensory cortex?

Answer 14

Organised into map representing body locations - HOMUNCULUS
Larger areas dedicated to more sensitive body areas (and areas can increase with use via experience-dependent plasticity)

Question 15

What is a receptive field?

Answer 15

Area of skin which, when stimulated, influences the firing rate of a neuron
Smaller field = better acuity

Question 16

What are the 3 different types of pain?

Answer 16

NOCICEPTIVE - Activation of nociceptors in skin (different types respond to different stimuli)
INFLAMMATORY - Damage to tissues
NEUROPATHIC - Lesions to NS

Question 17

What does the gate-control pain model suggest?

Answer 17

Pain can be affected by factors additional to the biological cause, entering brain by separate additional spinal pathways:
MENTAL STATE - Perceived less severe if also has positive association to it
EXPECTATION - Placebo effect
PHANTOM LIMB - Suggests pain is a mental construct
ATTENTION - pain is less when distracted, especially where distraction technique confers positive emotion

Question 18

How has hypnosis been shown to be connected with pain?

Answer 18

The experience of pain induced hypnotically has been shown using fMRI to mirror the activation pattern of genuine physical pain

Question 19

What is meant by a pain matrix?

Answer 19

Pain is represented by the pattern of activation of a distributed range of brain areas
Certain areas are specifically responsible for specific elements of the pain experience though:
S1 - sensory experience (throbbing, dull) (influences the emotional experience too)
ANTERIOR CINGULATE CORTEX - emotional experience (torturing, annoying; altering the unpleasantness of pain does not alter its sensory experience)

Question 20

What role is played by opiate receptors in the brain?

Answer 20

Opiate drugs such as heroin and natural neurotransmitters such as endorphins bind and act to reduce pain
Placebos can trigger the release of endorphins

Question 21

What are pain thresholds?

Answer 21

Genetically determined and different for different people, these relate to how much opioid released in response to painful stimuli. If more opioids get released, the higher the pain threshold

Question 22

How can social situations influence pain?

Answer 22

Social pain e.g. through exclusion activates ACC which is the same area activated by the emotional experience of physical pain
The activation is greater when the distress is greater, and also when the observer can empathise with distress of someone else