Sensory Receptors 1 Flashcards
what are sensory receptor?
- nerve endings often with specialised non-neural structures (sinorpuscles)
- transducers which convert different forms of energy
- inform CNS aout internal and external environment
what is sensory modality?
type of stimulus activating a particular receptor (e.g. touch, pressure, pain ,temperature, light)
what is adequate stimulus?
type of energy a receptor usually responds to
what do mechanoreceptors detect?
stimulated by mechanical stimuli (pressure, stretch, deformation) Detect: -hearing -balance -blood pressure - skin sensation like touch and pressure
what do proprioceptors detect?
mechanoreceptors in joints and muscles.
Signal information related to body or limb position
what do nociceptors detect?
respond to painful stimuli (e.g. tissue damage or heat)
what do thermoreceptors detect?
detect cold or warmth
what do chemorecetors detect?
chemical change (pH, pO2, pCO2)
what do photoreceptors detect/respond to?
respond to particular wavelengths of light
what activates the stretch-sensitive ion channels causing ion flow across the membrane?
membrane deformation as a result of adequate stimulus
- causes voltage-gated channels to open that generate APs
what does receptor potential depend on?
stimulus intensity (higher frequency of APs)
what does low stimulus intensity produce?
no APs
what does high stimulus intensity produce?
lots of APs
what is the frequency coding of the stimulus intensity?
the larger the stimulus, the larger the receptor potential, more APs produced with higher frequencies
what do Merkel receptors on skin sense?
steady pressure and texture
what does Meissner’s corpuscle on skin sense?
responds to flutter and stroking movements
what do sensory nerves sense?
carry signals to spinal cord
what does Ruffini corpuscle on skin do?
responds to skin stretch
what does Pacinian corpuscle on skin sense?
senses vibration
what do free nerve endings on nociceptors sense?
responds to noxious stimuli (painful, tissue damaging)
what do free nerve endings on hair roots sense?
senses hair movement
what is the generator potential?
sensory potential (initial graded potential sensed by sensory nerves)
what are examples of rapidly adapting receptors?
- pacinian corpuscle (vibration)
-meissner’s corpuscle (flutter/stroking)
adapt very quickly; shut down for some time and then fire again when stimulated
what are examples of slowly adapting receptors?
-merkel’s disc (pressure and texture)
- ruffini endings (skin stretch)
receptors take longer to adapt but they do eventually
do nociceptors adapt?
No, not at all; otherwise pain would not be detected which is a vital protective mechanism
why do both fast and slow adapting receptors exist?
as when they integrate, they allow brain to constantly adapt to new stimuli (flexible to a range of stimuli)
what is the best understood mechanoreceptor?
pacinian corpuscle
vibration spreads throughout it
what does a pacinian corpuscle look like?
like an “onion”
- myelinated nerve with naked nerve ending enclosed by a connective tissue capsule of layered membrane lamellae separated by fluid
how does a pacinian corpuscle respond? what are the steps?
- mechanical stimulus deforms capsule and nerve ending
- nerve ending is stretched and opens ion channels
- Na influx causes local depolarisation (generator potential)
- APs generated and fire at myelinated nerve
- stimulus is turned ON
what happens after signal is gone in a pacinian corpuscle? (steps)
- fluid redistribution in the capsule occurs
- this rapidly dissipates/ dissolves stimulus and removes mechanical stretch of nerve ending
- APs stop firing
what would happen if the lamallae (capsule) is removed from a pacinian corpuscle?
-adaptation would be lost: the non-neural accessory structure is vital as it enhances sensory function
what does an intact capsule indicate?
- receptor is rapidly adapting ON/OFF response
- membrane potential continously produced
what does a removed capsule indicate?
- bare nerve ending looses much of adaptation
- generator/receptor potential is still produce but it’s reduced
what is the receptive field?
- somatic sensory neurone is activated there by active stimuli
- it’s a spatial area on the body
how can we tell 2 points on the skin apart?
- receptive field size
2. neural convergence determined by a 2 point discrimination test
what is convergence?
- multiple presynaptic neurons input on a smaller number of post-synaptic neuornes (or one neurone)
- forms a LARGE receptive field for initiating APs
what does a large secondary receptive field indicate about sensitivity?
the area is insensitive
what is 2 point discrimination?
distance between points;
e.g. fingers and lips are very sensitive so its 2 point treshold is smaller than back and limbs threshold which is less sensitive.
the closer the 2 point discrimination test…the..
the more sensitive the area
define acuity
ability to locate a stimulus on the skin and differentiate it from another close by
what is divergence?
one neurone joining onto multiple neurones passing the signal along
Properties of convergence in terms of discrimination test and acuity
- small 2 point discrimination test
- high acuity
Properties of divergence in terms of discrimination test and acuity
- big 2 point discrimination test
- low acuity
why is pain/response to stimuli so precise?
due to inhibition
why is stimulus from afferent neurones strongly inhibited?
receptors at the edge of the effected area are inhibited by the CENTRAL receptors which focuses the body on the relevant information.
describe what happens in terms of inhibition if a pin is stuck into the skin
(lateral inhibition)
- there is no smearing of information but a focused, precise and localisation of pain
- focal area is stimulated
- stimulus strength is highest where the pin is and surrounding skin is slightly deformed
- secondary neurones from central receptors send neurotransmitters to inhibit other neurones on the skin
- this means only one neurone transfers AP instead of having a spread response to the small localised deformed area
- activation is right in the centre whereas surrounding receptors are less stimulated
what does cortical map detect?
different sensory information from around the body
the most sensitive areas in the body, occupy small or big cortical space?
big space; as more sensory info is processed there
