sensory receptors and pain Flashcards
what are the body parts that contribute to our sensory inputs that we are aware of
Sight
Smell
Sound
Touch
Taste (historical 5 senses)
what are the body parts that contribute to our sensory inputs that we are unaware of
Body temperature
Blood pressure
Glucose levels
Muscle tension
etc.,
what can the senses be classified into
general
special
describe general senses
- Somatic (body & environment – tongue, eye)
- Visceral (internal organs – liver, kidney)
describe special senses
- highly localised receptors (such as for tase then they would be found on the tongue)
what does the brain do with the sensory input it receives
Translates input to perceive an effect
name the 4 kinds of information that sensory receptors transmit
Modalities
Location (such as of the pain)
intensity
duration
describe modalities in terms of sensory receptor information transmitted
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
describe intensity in terms of sensory receptor information transmitted
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)
describe duration in terms of sensory receptor information transmitted
phasic receptors
- stop even if stimulus continues
tonic receptors
- adapt slowly
explain a 2-point Discrimination Test
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.
why is a 2 point discrimination test used
to find the position of sensory receptors
how is the distance in a 2 point discrimination test measure
Can buy ready-made ‘pointers’ with known distance apart
describe rough 2-point Discrimination Results
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
what is Somatosensory Cortex
when more sensitive parts of the body are shown as being larger
the Ability to discriminate the 2 points in the 2 point discrimination test is due to what
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)
explain sensory receptors structure
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
what are the 5 types of sensory receptors
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
the type of sensory receptor activated depends upon what
the stimulus
what are the 9 major types of sensory nerve endings involved in general sensation:
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
what is pain
Conscious of tissue injuries/potential for injury
what is leprosy
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
Nociceptors are everywhere except where
the brain
brain surgery
- remain conscious, with only local scalp anaesthetised
why are there 2 diff types of nociceptors
as they correspond to different pain sensations
describe the 2 types of nociceptors
- 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
what also classifies pain
point of origin
what are the 2 points of origins that also classify pain
somatic
visceral
explain somatic origin of pain
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
explain visceral origin of pain
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
Injured tissues release several what
several chemicals that stimulate nociceptors
what are the chemicals that stimulate nociceptors
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)
the release of several chemicals that stimulate nociceptors can render what and cause what
render neurons hyperexcitable and cause chronic pain.
explain what referred pain means
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
explain how the CNS modulates pain
by endogenous opioid peptides:
- endorphins
- enkephalins
- dynorphins
