Sensory Receptors and Sensory Transduction Flashcards
What do mechanoreceptors detect?
Changes in pressure
What do thermoreceptors detect?
Changes in temperature
What do chemoreceptors detect?
Changes in chemical composition of blood
What do nociceptors detect?
Technically detects a harmful stimulus as pain is only detected in the brain
What do proprioceptors do?
Give information about position or limbs and other body parts
What do Meissner’s corpuscles detect?
Light touch
What do Merkle’s corpuscles detect?
Touch
What do Pacinian corpuscles detect?
Deep pressure
What do Ruffini corpuscles detect?
Warmth
What do free nerve endings detect?
Harmful stimuli
What is the role of sensory receptors?
To transduce their stimulus of interest into a depolarisation.
->this can be called a sensory receptor or a generator potential. Recommended we call them generator potential’s so we don’t get confused with pharmalogical receptors e.g. ligand binding etc.
What type of potential is a generator potential?
A graded potential
What is the job of a graded potential?
To get the cell to threshold so it can fire action potentials.
What does the size of the generator mean in terms of stimulus intensity?
Greater the stimulus, greater the generator potential.
What do action potentials do and what are they used for?
Travel down axons.
Used for long distance transmission.
How do sensory neurons enter the spinal cord?
Via dorsal root
Where in the spinal cord would the sensory neuron cell body be?
Dorsal root ganglion
Graded potentials don’t travel very far as they decay rapidly. Which term is given to this?
Decremental
Why does an action potential get fired?
As a result of opening of voltage-gated sodium channels causing depolarisation.
Depolarisation spreads and opens next voltage-gated sodium channel
Action potentials are able to travel long distances without decaying. Which term is given to this?
Self-propagating
Describe what would happen, in terms of action potentials, in response to a longer and stronger stimulus.
Bigger depolarisation which lasts for longer, cell is depolarised to threshold for longer meaning there is increased firing of action potentials.
Give an example of an area of skin which has a high density innervation of sensory receptors.
Skin on hands and face
What does the size of receptive fields determine?
Not sensitivity as most people think but acuity!!
Once action potentials are evoked, how are they transmitted into the CNS?
Via axons
Which types of primary afferent fibres mediate cutaneous sensation?
A beta fibres
A delta fibres
C fibres
Describe A beta fibres
Large myelinated fibres, fast
Describe A delta fibres.
Small, myelinated
Describe C fibres
Unmyelinated fibres
What do A beta fibres mediate?
Touch, pressure and vibration.
What do A delta fibres mediate?
Cold
‘Fast’ pain
Pressure
What do C fibres mediate?
Warmth
‘Slow’ pain
Which fibres mediate proprioception?
A alpha fibres
A beta fibres
Where do we have A alpha and beta fibres?
Muscle spindles
Golgi tendon organs
Where do the mechanoreceptive fibres synapse when transmitting sensory information up the dorsal column?
Cuneate and gracile nuceli in brainstem
Where do the thermoreceptive and nociceptive fibres synapse when transmitting sensory information up the anterolateral tract?
Synapse in dorsal horn as soon as they enter spinal cord
->this links into anatomy tract pathway lectures
What is Brown-Séquard syndrome?
A rare neurologival condition in which a lesion in the spinal cord causes weakness or paralysis in one side of the body and loss of sensation in the opposite side.
Therefore, in Brown-Séquard syndrome, what happens in the ipsilateral side of the site of injury?
Loss of vibration, motor function, deep touch and proprioception.
Therefore, in Brown-Séquard syndrome, what happens in the contralateral side of the site of injury?
Loss of pain and temperature
->due to fibres synapsing and crossing over as soon as they enter spinal cord, so they are affected on opposite side as have already crossed over…idk if that makes sense, sorry if not
Where is the ultimate destination for sensory information?
Somatosensory cortex (S1) of the postcentral gyrus
How would rapidly adapting sensory receptors respond to a stimulus e.g. touch on skin?
Respond by firing a burst of action potentials but then very quickly stop firing.
Typically, they fire again to signal that the stimulus has stopped.
How would slowly adapting sensory receptors respond to a stimulus e.g. touch on skin.
Initially fire burst of action potentials but then keep firing for duration of stimulus.
We have rapid and slow adapting receptors.
When putting on clothes, you soon forget they are on, otherwise you’d have sensory overload!
Which type of receptor is responsible for this adaption?
Rapidly adapting sensory receptors
What is lateral inhibition?
Activation of one sensory input causes synaptic inhibition of its neighbours.
What is phantom limb pain?
Patient’s who have had a limb amputated still feel sensation in the missing limb
There are some ways that nociceptors can detect potentially harmful stimuli.
This can be done via proteins, such as ASIC (acid sensing ion channel).
What does ASIC detect?
Low pH
What happens when ASIC detects low pH levels?
Opens integral ion channels and leads to depolarisation and firing of action potentials.
Which receptor detects noxious heat stimuli?
VR1 (vanilloid receptor 1)
What can activate VR1?
Capsaicin from chilli peppers which is why they can hurt your mouth
Another way that nociceptors detect potentially harmful stimuli is by releasing local chemical mediators, such as?
Bradykinin
What does bradykinin do?
Binds to G protein-coupled receptors and causes depolarisation and firing of action potentials.
What can sensitise bradykinin receptors to bradykinin?
Prostaglandins
What do opioid receptors do?
Hyperpolarise the cell making it less likely to fire action potentials
Give two common examples of NSAIDs.
Ibuprofen
Aspirin
Describe how prostaglandins can lead to increased pain felt.
Prostaglandin sensitise nociceptors to bradykinin via prostaglandin receptors.
This means when bradykinin binds to the receptor, it activates it more.
More action potentials will be fired meaning more pain.
Describe how NSAIDs can reduce pain felt.
NSAIDs inhibit the enzyme cyclo-oxygenase which converts the arachidonic acid into prostaglandins.
Therefore, if it’s inhibited, there will be less prostaglandins, fewer action potentials fired and less pain.
How do local anaesthetics work?
Blocking sodium action potentials and blocking transmission of axons.
What do trans cutaneous electric nerve stimulation (TENS) do?
Selectively activate large diameter fibres e.g. mechanoreceptive fibres to decrease neurotransmitter released.
How do opiates work to reduce pain?
Reduce the sensitivity of nociceptors.
Block transmitter release in dorsal horn.
Activate descending inhibitory pathways.
Give an example of an opiate.
Morphine
