sensory receptors Flashcards
all sense require 3 common steps
They require a physical stimulus
They all must transform the stimulus into nerve impulses
This occurs in the peripheral nervous system
They all evoke a response to the signal in the form of perception or conscious experience of sensation
This occurs in the central nervous system
sensory receptors located
in the periphery
sensory transduction
conversation of energy in env to electrochemical signs
5 main senses
Photo receptors-sight
Chemicals- smell – olfactory transduce chemical into electrical
Taste- chemical- electrical
Touch- less specific, several receptors
Hearing- transduction – mechanical sound- electrical hair cells
Cochlea inner ear
thermal senses
interbal and external neon’s with specials nerve endings rather than specific receprotsr
pain- visercal
organ/internal pain
nociceptors afferent neurons
balance and proprioception
Balance: Hair cells (branch of hearing system?? Simialr strucutre using mechanical stimuli
Proprioception- body parts in relation to space
Muscle spindles
hearing
stimulus, receptor and location
mechanical
mechanorecprtor
cochlea
balance (stim, recp, loc)
mechanical
mechanoreceptor
vestibular sys
vision (stim, rep, loc)
light
photorecpeot
retina
touch (stimulus, receptor and location)
mechinal
mechanorecpetor
skin
temp ((stimulus, receptor and location)
mechinal
mechanoreceptor
skin
pain (stimulus, receptor and location)
mechanical, thermal, chemical
nociceptor
skin, internal organs
proprioception (stimulus, receptor and location)
mechanical
mechanorecpeot
muscles, tendons, joints
olfaction (stimulus, receptor and location)
chemical
chemoreceptor
nasal cavity
taste (stimulus, receptor and location)
chemical
chemoreceptor
tongue, pharynx, palate, epiglottis
cascade
1) stimulis
2) sensory receptor activated
3)membrane permeability altered in sensory cell
4) a receptor potneial developes
((5)) neurotransmitter is released onto afferent neuron terminals
6)an action potent is generated in afferent neurone terminal
7)AP propagates to CNS
8) info integrated by CNS
what is different about the cascade for touch receptors
misses out the neurotransmitter part because
receptor potential causes action potential in afferent nerve terminal directly because the sensory cell and th afferent nerve are the same thing
graded potentials in sensory receptors
Activation: g protein
Membrane – more permeable to cations –makes more positive
‘receptor potential’ = a graded potential
All sensory receptors always initially use a graded potential
Tends to be glutamate released to generate AP
difference between graded and action potentials
Graded receptor potentials increase in size in response to increases in stimulus amplitude
Action potentials are always the same size, but have a threshold for activation
graded:
The input is directly related to the size of the stimulus
Propagates slightly long the axon to the area where AP are generate
If the GP is big enough it will cause an AP
AP uses frequency to indicate stimulus size
example of cascade including synapse: taste receptors
stimulus is chemical (e.g. Na in salt)
membrane depolarises in a graded response
voltgage gated ca+ channaled open allowing calcium influx
synaptic vesical fusion triggers
releasing neurotransmitter
afferent nuron depolarised
example of cascade with direct activation= olfactory receptors
stimulis is chemical (odorant)
local changes in membrane permeability cause a graded receptor potential within a receptor cilium
large enough receptor potential cause depolarisation in the cell soma
triggering action potentials that travel along the olfactory nerve
if sensory receptor is a neuron itself
G protein coupled receptor
sensory receptors convey 4 types of info about stimulus
modality
location
intensity
timing
modality is determined by
the type of energy transmitted by the stimulus and the receptors that are specialised to detect that energy
labelled line code
- the receptor is selective for one type of stimulus energy
- the axons of the receptor/associated afferent neutron acts as a modality specific line of communication
- axons from these neurones make connections with specific areas in the CNS
synesthesia
the labelled line code is faulty
receptive fields in somatic system
region of skin innervated by the terminals of the receptor neuron
receptive fields int he visual system
the receptive field of a photoreceptor is the region of the visual field projected onto that receptor
not every single bit of light will activate all photoreceptors
depends which patches of photorecptors are activated in the retina
receptive field in the auditory system
arrangement of receptors enables frequency discrimination
can’t compute stimulus location just in the cochlea
different frequencies along cochlea length and location is actually registered downstream of the cochlea in the brainstem
overlapping receptive fields
bigger stimulus
activates multiple neurones stimulated
1 receptor=1 neuron
stimulus intensity
total amount of stimulus energy delivered to the receptor
sensory threshold
the lowest stimulus strength that can bed detected
intensity is determined by
resposne amplitude of the receptor and this the ring frequency of the afferent neurones
more intense stimulus also activates more receptors
Weak stimulus intensities activate low threshold fibres
Strong stimulus intensities activate high threshold fibres
onset timing determined
when the stimulus energy is received by the receptor and causes it to fire
stimulus duration is determined by
adaptation rates of receptors
Adaptation = In response to continuous stimuli, the firing rate of action potentials decreases
slowly adapting receptors
tonic receptors
respond to prolonged stimulation
rapidly adapting receptors
phasic receptors
response at the beginning and end of a stimulus
divergence
allows primary afferent neurones to signal to more than one relay neuron
convergence
ensures that relay neurons have larger receptive fields than primary afferent neurones
Convergence point is receiving information across both receptive fields
inhibitory neurons
ensures the single in the most active neutron is portage e.g this enables contrast enhancement in the eye
how is stimulus intensity encoded in sensory system1
the frequency of action potential firing
stimulus intensity
Stimulus intensity is the total amount of stimulus energy delivered to a receptor, e.g. a louder sound has a greater stimulus intensity than a quieter sound
what is special about the olfactory receptor cells?
they are the sensory cell and the afferent neurone
so the graded receptor potential will initiate action potential firing IF the graded receptor potential takes the membrane potential above the threshold for action potential firing
If the stimulus is larger, the graded receptor potential will be larger, this will keep the cell above the threshold for action potential firing for longer and will result in more action potentials being produced i.e. the frequency of action potential firing will increase
an increase in a graded receptor potential size will
NOT increase the amplitude of the action potential produced
sensory cell separate to primary afferent neuron
taste and hair cells e.g.
greater stimulus intuit would cause larger graded receptor potential in the sensory cell which would result in more neurotransmitter being released from the sensory cell onto the primary afferent neuron
More neurotransmitter would activate more receptors on the afferent neuron, creating a larger excitatory post-synaptic potential (EPSP) in the afferent neuron. The larger EPSP would have the same effect as a larger graded receptor potential and would keep the afferent neuron above the threshold for firing an action potential for longer, resulting in a greater frequency of action potential firing.
