sensory receptors and pain

Question 1

what are the body parts that contribute to our sensory inputs that we are aware of

Answer 1

Sight
Smell
Sound
Touch
Taste (historical 5 senses)

Question 2

what are the body parts that contribute to our sensory inputs that we are unaware of

Answer 2

Body temperature
Blood pressure
Glucose levels
Muscle tension
etc.,

Question 3

what can the senses be classified into

Answer 3

general
special

Question 4

describe general senses

Answer 4

• Somatic (body & environment – tongue, eye)
• Visceral (internal organs – liver, kidney)

Question 5

describe special senses

Answer 5

• highly localised receptors (such as for tase then they would be found on the tongue)

Question 6

what does the brain do with the sensory input it receives

Answer 6

Translates input to perceive an effect

Question 7

name the 4 kinds of information that sensory receptors transmit

Answer 7

Modalities
Location (such as of the pain)
intensity
duration

Question 8

describe modalities in terms of sensory receptor information transmitted

Answer 8

Modalities of sensation refer to the form of sensation:

• Somatic
  Touch, pressure, temperature, pain, proprioception (= Ability to determine where body is located in space)
• Visceral
  Detect Pain (which is why we do feel pain from internal organs, except from the brain), changes in pressure pressure (such as blood pressure)
• Special
  Smell, taste, sight, sound, balance

Question 9

describe intensity in terms of sensory receptor information transmitted

Answer 9

Intensity can be encoded by:

• altering firing frequency
• recruit greater number of nerves
• nerve fibres of different thresholds (myelinated nerve fibre work slower than myelinated)

Question 10

describe duration in terms of sensory receptor information transmitted

Answer 10

phasic receptors
- stop even if stimulus continues

tonic receptors
- adapt slowly

Question 11

explain a 2-point Discrimination Test

Answer 11

Requires two people. Person one with closed eyes

Person two use 2 ‘points’ e.g., pulled-out paperclips or tweezers, and lightly touch areas of person one’s skin with the points apart but at the same time. Start fairly wide apart and then move closer together and record the smallest distance (in mm) apart of the 2 points that they could feel as 2 points (not 1)

One person (with eyes closed) to determine whether what they feel on their skin is 2 points or just 1 point.

Question 12

why is a 2 point discrimination test used

Answer 12

to find the position of sensory receptors

Question 13

how is the distance in a 2 point discrimination test measure

Answer 13

Can buy ready-made ‘pointers’ with known distance apart

Question 14

describe rough 2-point Discrimination Results

Answer 14

fingers, feet, lips , hand will all be able to detect the 2 points when they are much further together as these areas are far more sensitive compared to other areas like the arm and chest and thigh

Question 15

what is Somatosensory Cortex

Answer 15

when more sensitive parts of the body are shown as being larger

Question 16

the Ability to discriminate the 2 points in the 2 point discrimination test is due to what

Answer 16

different receptor fields

• narrow receptor field = Sense as 2 points (2 different receptor nerve endings in the skin)
• wide receptor field = sense as 1 point ( as 2 points only touch 1 nerve)

Question 17

explain sensory receptors structure

Answer 17

Structure specialised to detect a stimulus e.g., simple nerve endings, sense organs
- nerve endings + connective/epithelial/muscular tissues that enhance or moderate response

Macroscopic:
e.g., eyes & ears

Microscopic:
e.g., highly specialised structures within the skin, muscles, joints, viscera

Question 18

what are the 5 types of sensory receptors

Answer 18

Mechanoreceptors
- mechanical
eg. compression, bending, stretching of cells

Chemoreceptors
- chemicals become attached to membrane receptors

Photoreceptors
- light striking receptor cells (chemical change)

Thermoreceptors
- changes in temperature at site of receptor

Nociceptors
- pain
e.g. mechanical, chemical or thermal pain

Question 19

the type of sensory receptor activated depends upon what

Answer 19

the stimulus

Question 20

what are the 9 major types of sensory nerve endings involved in general sensation:

Answer 20

Unencapsulated (free and open):
- nerve endings
- merkels disc
- hair follicle endings

Encapsulated (within a defined region and protected by other cells):
- meissner corpuscle
- krause end bulb
- pacinian corpuscle
- ruffini endings
- muscle spindle
- golgi tendon organ

Question 21

what is pain

Answer 21

Conscious of tissue injuries/potential for injury

Question 22

what is leprosy

Answer 22

bacterium infects nerves, local loss of pain & other sensation (can be treated by medicine)

• minor injuries not noticed, which can cause:
• serious infections, leading to:
• lose fingers/toes

Question 23

Nociceptors are everywhere except where

Answer 23

the brain

brain surgery
- remain conscious, with only local scalp anaesthetised

Question 24

why are there 2 diff types of nociceptors

Answer 24

as they correspond to different pain sensations

Question 25

describe the 2 types of nociceptors

Answer 25

• Fast (1st) pain
• From myelinated pain fibres
• 12-30 m/sec
• Short, localised, stabbing
• Slow (2nd) pain
• From unmyelinated pain fibres
• 0.5-2 m/sec
• Longer-lasting, dull, diffuse

Question 26

what also classifies pain

Answer 26

point of origin

Question 27

what are the 2 points of origins that also classify pain

Answer 27

somatic
visceral

Question 28

explain somatic origin of pain

Answer 28

Pain arises from skin, muscles & joints

Superficial (wear off quickly but localised pain will feel sore at the time)
- sharp, stabbing, prickly

Deep
- less localised, longer-lasting, more aching, burning or nauseating, can cause bruising as well sometimes

Question 29

explain visceral origin of pain

Answer 29

Pain arises from viscera (hollow organs, smooth muscle)
- due to stretch, chemical irritants, deficient blood flow (ischaemia), inflammation

Often intense (such as appendicitis) & nausea
- but poorly localised pain as few nociceptors, and so tricky to tell where its coming from as well

Question 30

Injured tissues release several what

Answer 30

several chemicals that stimulate nociceptors

Question 31

what are the chemicals that stimulate nociceptors

Answer 31

Bradykinin
- Inflammatory mediator, vasodilator.
e.g. from blood protein, most potent

Serotonin
- Neurotransmitter
e.g. regulates pain sensation

Prostaglandins
- Hormone-like
e.g. inflammation, pain and fever as part of the healing process.

Histamine
- Chemical messenger
e.g. nociceptive pain, neurogenic inflammation

K+
- Determinants of neuronal excitability
- Nerve injury or inflammation alters K+channel activity in neurons of the pain pathway

(Therapies targeting K+channels may provide improved pain relief in these states.
Opening of these channels facilitates a hyperpolarizing K+efflux across the plasma membrane that counteracts inward ion conductance and therefore limits neuronal excitability)

Question 32

the release of several chemicals that stimulate nociceptors can render what and cause what

Answer 32

render neurons hyperexcitable and cause chronic pain.

Question 33

explain what referred pain means

Answer 33

Pain from viscera misinterpreted as coming from skin or other superficial structures

e.g., heart attack causes left arm pain
- this is due to shared spinal cord segments

Question 34

explain how the CNS modulates pain

Answer 34

by endogenous opioid peptides:

• endorphins
• enkephalins
• dynorphins