Sensory Systems Flashcards by Lisa McCulloch

state 5 types of sensory receptors

mechanoreceptors, chemoreceptors, thermoreceptors, nociceptors, proprioceptors

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what is the area where the sensory neuron will respond to a stimulus called?

receptive field

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what does it mean when a sensory receptors transduces a stimulus ?

changes the stimulus into electrical energy

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what is the stimulus called which is required to causes an AP to be produced and for the neuron to depolarise ?

an adequate stimulus

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what is the potential called which is produced when the neuron depolarises?

receptor potential

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what variable of the receptor potential conveys the intensity of the stimulus?

the size of the receptor potential

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what variable of the action potential conveys the intensity of the stimulus?

the frequency of the AP

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are APs all the same size?

yes

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if a sensory neuron has a large receptive field then is the acuity small or large ?

acuity is small

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are APs self propagating ?

yes

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if there is a higher frequency of APs then will there be more neurotransmitters released ?

yes

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what are the three types of afferent cutaneous sensation fibres?

A beta
A delta
C

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what are the two types of primary afferent fibres fibres for proprioception?

A alpha

A beta

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describe the appearance of A beta fibres?

Large myelinated

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describe the appearance of A delta fibres?

small myelinated

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what do A beta fibres detect?

touch, pressure, vibration

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what do A delta fibres detect?

cold, “fast” pain, pressure

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describe the appearance of C fibres

unmyelinated fibres

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what do C fibres detect?

warmth, “slow” pain

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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

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where abouts for the A alpha and A beta fibres project up the spinal cord?

project straight up through ipsilateral dorsal columns

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what does A alpha and A beta fibres detect?

mechanoreceptive

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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 ?

1. with a stimulus APs are fired 2. 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?

1. Activity in Aα/β fibres activates inhibitory interneurones 2. 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?

1. They inhibit Cyclo-oxygenase enzyme 2. COX converts arachidonic acid to prostaglandins 3. Therefore, less prostaglandins are being produced 4. This decreases the sensitivity of bradykinin 5. This decreases the number of APs fired to the A delta and C fibres 6. 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?

1. reduce the sensitivity of nociceptors 2. block transmission release in dorsal horn 3. activate descending inhibitory pathways

how does tissue damage result in pain?

1. tissue damage results in an inflammation process where prostaglandin is released 2. prostaglandins increase the sensitivity of nociceptors to bradykinin 3. which causes depolarisation in the A delta and C fibres

how does referred pain occur?

1. 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