Sensory receptors Flashcards
what are sensory receptors
are nerve endings that inform your brain about the internal and external environment. convert different stimuli into frequency of action potentials so are transducers
3 types of sensory receptors
proprioceptors, mechanoreceptors, nociceptors
sensory modality
stimulus type that activates a particular receptor eg touch, pressure, joint angle, pain
adequate stimulus
form of energy to which a receptor normally responds
what is a mechanoreceptor
stimulated by mechanical stimuli, pressure, strength, deformation, give us skin sensations of touch and pressure
what are proprioceptors
mechanoreceptors in joints and muscles. they signal information about body or limb position
what are nociceptors
respond to painful stimuli
how are sensory receptors specific
highly sensitive to one specific energy form but they can be activated by other intense stimuli
what is a receptor potential
adequate stimulus causing a graded membrane potential change
what is the adequate stimulus in cutaneous mechanoreceptors and proprioceptors
membrane deformation- activates stretch sensitive ion channels. ions flow across the membrane and change the membrane potential locally
how is receptor potential graded
by stimulus intensity. stimulus triggers ions to flow through membrane locally and when depolarisation reaches the area with voltage gated ion channels (first node of Ranvier), action potentials start firing
what electrodes measure change in membrane potential
those at receptor membrane and first node of ranvier
why is it important that some mechanoreceptors experience a drop off in APs if stimulus persists
the brain can process new or changing events eg taking off or putting on clothes. some receptors only signal the onset of a stimulus
which receptors do not adapt
nocireceptors
pacinian corpuscle
senses pressure and vibration. mechanoreceptor comprised of a myelinated nerve and a naked nerve ending. mechanical stimulus deforms the capsule and nerve ending, stretches and opens ion channels, sodium influx causes depolarisation, APs generated and myelination begins.
how can pacinian corpuscle adapt
depends on capsule surrounding. can rapidly adapt by fluid between lamellae distributes, spreading stimulus impact out, minimising deformation which causes the stop of nerve endings stretching so APs stop firing. if stimulus withdrawn, the capsule lamellae spring back like suction force and Ap fire again
receptive field
a specific area where a somatic sensory neurone is activated by stimuli
ability to tell 2 points apart on the skin is measured by
two points discrimination test- the receptive field size and neuronal convergence
neuronal convergence
if there is a single path to the brain or more than one that merge
simultaneous sub threshold stimuli effect
can merge together and sum together at the secondary neuron, forming a larger secondary receptive field and initiating APs (two pencils test)
acuity
ability to locate a stimulus on the skin and differentiate it from another close. low acuity means one signal goes to brain instead of two when there is two stimuli- caused by high convergence
lateral inhibition
enhances perception of stimulus and means you can localise the central point of a stimulus precisely by receptors at edge of stimulus being more strongly inhibited than receptors near centre
where does sensory information go
to the brain, relayed via the spinal cord to the thalamus and on to the somatosensory cortex
proprioceptors include
muscle spindles, Golgi tendon organs, joint receptors
3 things that proprioceptors do
control our voluntary movements, generate spinal reflex movements, perceive limb and body position and movement in space= kinaesthesia
muscle spindles
intrafusal muscle fibres that have their own sensory and motor innervation. contained within a capsule. lie in parallel with muscle fibres
two types of intrafusal fibre
nuclear bag fibres, nuclear chain fibres
what part of intrafusal fibres contain contractile sarcomeres
ends not central area so when they fire the two ends contract and shorten but the central area does not so it therefore gets stretched out
what motoneurones cause contraction of intrafusal fibres
gamma
annulospiral endings
formed by primary endings of 1a afferent nerves wrapped around centre of intrafusal fibres
how is the brain informed by joint position
spindle and joint receptors. muscle stretch stimulates spindle stretch receptors. stretch sensitive ion channels open, create a local generator potential which causes regenerative action potentials in the 1a afferent fibres
what does Golgi tendon organ do
lie in series with extrafusal muscle fibres. monitors muscles tension by using stretch receptors and monitoring stretch of tendon. muscles have to develop tension by contracting to stretch the tendons. if contraction, the nerve endings of GTO stretch and initiate APs in group 1b afferent fibres from the GTO
what happens if an alpha motor neurone fires without gamma
extrafusal muscle contracts and shortened but intrafusal muscle stays the same length so spindles go slack so 1a spindle sensory firing would decrease
alpha-gamma coactivation
alpha motoneurons are activated causing contraction, gamma motoneurons are activated in parallel to maintain spindle sensitivity. makes sure brain is informed on movements and position of our body in space
