Sensory System Flashcards
What do thermoreceptors detect?
Temperature
What do chemoreceptors detect?
Chemical changes
What do nociceptors detect?
Damaging stimuli/pain
What do proprioceptros detect?
Position and movement
What is the receptive field?
The specific area to which a receptor will respond to stimulus
What do sensory receptors transduce an adequate stimuli to?
Depolarisation to generate a receptor generator potential
What does the intensity of the stimuli encode?
The size of the receptor potential
What does the frequency of AP encode?
The intensity of the stimulus
What do receptor potential then generate?
Evoke firing of AP for long distance transmission
Does the amplitude tell us anything about the stimulus?
no
What does the receptive field encode?
The location of the stimulus
What is the duration of a series of AP proportionate to?
The duration of the stimulus
How are AP transmitted to the CNS?
By axons
What 3 types of primary afferent fibres mediate cutaneous sensation?
Aβ
Aδ
C
What are Aβ fibres?
Large myelinated fibres that detect touch, pressure and vibration
What are Aδ fibres?
Small myelinated fibres, detect pain and pressure
What are C fibres?
Unmyelinated fibres that detect pain
What 2 types of primary afferent fibres mediate proprioception?
Aα & Aβ
Where do all afferent fibres enter the spinal cord?
Via the dorsal root ganglion
What are chemoreceptive fibres?
(Aα & Aβ)
Where do chemoreceptive fibres project up?
Straight up through the ipsilateral dorsal columns
Where do chemoreceptive fibres synapse?
In the cuneate and gracile nuclei
Where do chemoreceptive 2nd order fibres cross over?
In the medulla
Remember touch and pressure does not cross over at spinal cord entry
Where do chemoreceptive fibres project from the medulla?
To the thalamus and cortex
What types of fibres carry thermoreceptive and nociceptive information?
Aδ & C
Where do thermo and nociceptive fibres synapse?
In the dorsal horn
At the level of the spinal cord
Where do thermo and nociceptive 2nd order order fibres decussate?
Over the midline at the level of spinal cord entry
Where is always the origin of the 3rd order neuron?
Thalamus
Why are the tracts called spinothalmic?
As they travel from the spinal cord to the thalamus
What happens to touch and vibration proprioception below a lesion on the dorsal column?
It is lost on the ipsilateral side
What happens to pain an temperature below a lesion on the doral column?
Causes loss on the contralateral side
Where does the sensory pathway end?
At the sensory cortex
Sensory homunuculus
What does convergence save on?
Neurons
What does convergence reduce?
Acuity
What is lateral inhibition?
When activation of one sensory input causes synaptic inhibition of its neighbours
What is the benefit of lateral inhibition?
Gives better definition of boundaries
What does lateral inhibition clean up?
Sensory information
What is perception?
How important things are in your mind
How you perceive them
Is pain subjective?
Yes very
What is pains main function?
To protect
What acitvates signal transduction in nociceptors?
Low pH
Low chemical mediators
What is released when tissues are crushed?
Bradykinin
What is gate control theory?
stop information coming in at the first synapse then it cannot make its way up to the thalamus and up the spinal cord.
What is segmental control?
activate inhibitory interneurons release opioid peptide which inhibit transmitter release from fibres hence closing the gate.
What sensitises nociceptors to bradykinin?
Prostaglandin
Hows to NSAID’s have an analgesic effect?
because they inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins
And prostaglandins sensitises nociceptors to bradykinin
How do local anaesthetics work?
The block Na+ AP and all axonal transmission
They inhibit synaptic transmission between the primary afferent fibres and the 2nd order projection fibres
How do optiates work?
Ð reduce sensitivity of nociceptors
Ð block transmitter release in dorsal horn (hence epidural administration)
Ð activate descending inhibitory pathways
Ð gate control theory
What is morphine a class of?
Opiate
