Sensory Systems Flashcards
state 5 types of sensory receptors
mechanoreceptors, chemoreceptors, thermoreceptors, nociceptors, proprioceptors
what is the area where the sensory neuron will respond to a stimulus called?
receptive field
what does it mean when a sensory receptors transduces a stimulus ?
changes the stimulus into electrical energy
what is the stimulus called which is required to causes an AP to be produced and for the neuron to depolarise ?
an adequate stimulus
what is the potential called which is produced when the neuron depolarises?
receptor potential
what variable of the receptor potential conveys the intensity of the stimulus?
the size of the receptor potential
what variable of the action potential conveys the intensity of the stimulus?
the frequency of the AP
are APs all the same size?
yes
if a sensory neuron has a large receptive field then is the acuity small or large ?
acuity is small
are APs self propagating ?
yes
if there is a higher frequency of APs then will there be more neurotransmitters released ?
yes
what are the three types of afferent cutaneous sensation fibres?
A beta
A delta
C
what are the two types of primary afferent fibres fibres for proprioception?
A alpha
A beta
describe the appearance of A beta fibres?
Large myelinated
describe the appearance of A delta fibres?
small myelinated
what do A beta fibres detect?
touch, pressure, vibration
what do A delta fibres detect?
cold, “fast” pain, pressure
describe the appearance of C fibres
unmyelinated fibres
what do C fibres detect?
warmth, “slow” pain
what are the speeds of the three fibres used for cutaneous sensation?
A beta = 30-70m/s
A delta = 5-30 m/s
C = 0.5-2 m/s
where abouts for the A alpha and A beta fibres project up the spinal cord?
project straight up through ipsilateral dorsal columns
what does A alpha and A beta fibres detect?
mechanoreceptive
where do the A delta and C fibres project up the spinal cord ?
- the fibres synapse in the dorsal horn and cross over to the opposite side and then
- project up through the contralateral spinothalamic (anterolateral) tract to reticular formation, thalamus and cortex
where abouts do the A alpha and A beta fibres decussate ?
in the brain stem
where do the primary afferent fibres enter the spinal cord?
dorsal root ganglia
which afferent fibre type is used for detecting warmth
C fibres
which afferent fibre type is used for detecting cold
A delta fibres
which afferent fibre type is used for detecting proprioception
A alpha
A beta
which afferent fibre type is used for detecting touch?
A beta
which of the fibres is large and myelinated ?
A alpha
A beta
what sensory information would be lost if the dorsal column of the spinal cord was damaged ?
touch
vibration
proprioception
- these would be lost below the lesion on the ipsilateral side
what sensory information would be lost if the anterolateral column of the spinal cord was damaged ?
pain
temperature
- these would be lost below the lesion on the contralateral side
where abouts is the somatosensory cortex located?
post-central gyrus
what is adaptation of sensory pathways ?
- with a stimulus APs are fired
- with a rapidly adapting fibres the APs will decrease quickly after the stimulus has remained for a certain amount of time and it not harmful
give an example of the adaptation of sensory pathways
when you put on a hat you first feel it then you can’t tell its there anymore
what is convergence of neurons?
when several first neurons synapse with second neurons
what is the advantage of the convergence of neurons?
reduces the number of neurons required
what is the disadvantage of the convergence of neurons?
reduces acuity
convergence can be specific or non specific
- what are the differences ?
specific
- when the same type of fibres synapse together so increase the sensory field
non-specific
- when fibres of different types synapse together for example touch and temperature
what is lateral inhibition of sensory pathways ?
activation of one sensory input causes inhibition to the fibres near by
what is the advantage of inhibition of sensory pathways?
gives better definition to the boundaries of the stimulus
what is perception of sensory pathways?
different responses to stimuli in different people
e.g. picture of a scary dog and being in the same room as a scary dog
when a cell depolarises are the Na channels open or closed?
Na channels are open
what sensory fibres carry pain and temperature?
A delta and C fibres
what are the two ways that nociceptors and tempereceptors can be inhibited?
Segmental Control
Descending Control
Describe how segmental control of nociceptors work?
- Activity in Aα/β fibres activates inhibitory interneurones
- Inhibitory interneurones release opioid peptides (endorphins) that inhibit transmitter release from Aδ/C fibres, hence “closing the gate”
Describe how descending control of nociceptors work?
The same inhibitory interneurones used in segmental control are also activated by descending pathways from PAG via NRM, hence also “closing the gate”
How do NSAIDs work?
- They inhibit Cyclo-oxygenase enzyme
- COX converts arachidonic acid to prostaglandins
- Therefore, less prostaglandins are being produced
- This decreases the sensitivity of bradykinin
- This decreases the number of APs fired to the A delta and C fibres
- the perception of pain is less
what three properties do NSAIDS decrease?
- pain
- inflammation
- pyrexia
how do local anaesthetics work?
block Na+ action potential and therefore all axonal transmission (sensory transmission)
how does Trans cutaneous electric nerve stimulation (TENS) work?
stimulate PAG area and therefore stimulate the inhibitory interneuron which releases endorphins and inhibits the A delta and C fibres
how do opiates work?
- reduce the sensitivity of nociceptors
- block transmission release in dorsal horn
- activate descending inhibitory pathways
how does tissue damage result in pain?
- tissue damage results in an inflammation process where prostaglandin is released
- prostaglandins increase the sensitivity of nociceptors to bradykinin
- which causes depolarisation in the A delta and C fibres
how does referred pain occur?
- when there is a large sensory field
2. when neurons converge so a large area of skin will only stimulate one neuron
what is the gate control hypothesis of pain modulation?
when A alpha neurons are stimulated which stimulate an inhibitory interneuron which releases endorphins and causes inhibition in the nociceptor fibres
