Principles of Sensory Physiology Flashcards
What is a stimulus?
A change detectable by the body
What are the 5 modalities, or energy forms, of stimuli?
Heat Light Sound Pressure Chemical
Receptors are found at the _________ end of _______________.
Peripheral end
Afferent Neuron
Receptors convert the energy from a stimulus into _________________. This is called ___________________.
Electrical signals
Sensory Transduction
Stimuli bring about _________ potentials known as ________________ in the receptor.
Graded Potentials
Receptor Potentials
Receptors are specialised to respond to ____ stimulus, the ___________________.
One stimulus
Adequate stimulus
Some receptors can respond weakly to other stimuli, this gives rise to _______________________________.
The same sensation that the receptors adequate stimulus would cause
What are the 6 types of receptors and their adequate stimuli?
Photoreceptor = light Mechanoreceptor = mechanical energy Thermoreceptor = heat and cold Osmoreceptor = changes in osmotic activity Chemoreceptors = specific chemicals Nociceptors = Tissue damage
Receptors can either be:
Specialised endings of afferent neurons
OR
Separate receptor cells closely associated with the peripheral ending of a neuron
Stimulation of a receptor results in a change in ___________________. This usually occurs due to the opening of _______________. which causes an __________ and .’. ______________.
Membrane potential
Na Channels
Influx of Na
Depolarisation
What makes the receptor potential a graded potential?
The stronger the stimulus, the greater the permeability change and .’. the larger the receptor potential.
Because receptor potential have _____ refractory periods, summation in response to rapidly successive stimuli is ________.
No
Possible
How do specialised afferent endings transmit the signal to the afferent neuron?
If depolarised to threshold, voltage gated Na+ channels open and trigger an AP that is conducted along the afferent neuron
How do separate receptor cells transmit the signal to the afferent neuron?
- Receptor potential promotes opening of voltage gated Ca2+ channels
- Ca2+ entry causes exocytosis of neurotransmitters (nts)
- nts diffuse across the synapse and bind to receptors on the afferent
- Na+ channels open = AP
Where are APs initiated in the efferent and interneurons?
Axon Hillock: region at the start of the axon next to the cell body
Where are Aps initiated in afferent neurons?
The peripheral end of the fibre next to the receptor, a long distance from the cell body
The larger the receptor potential, the _________ the frequency of APs
Greater frequency of APs
The more rapidly an afferent fibre fires it will release _____ neurotransmitter.
More nt
What is adaptation?
The ability of a receptor to diminish the extent of it’s depolarisation despite a sustained stimulus strength
What are tonic receptors?
Receptors that do not adapt or adapt slowly, they are useful when it is important to maintain info about the stimulus i.e. muscle stretch receptor
What are phasic receptors?
Receptors that adapt rapidly to stimuli by no longer responding to a maintained stimuli. They are useful when it’s important to signal a change in stimulus intensity i.e. touch receptors
How do mechanoreceptors detect stimuli?
Mechanical forces distort non-specific cation channels in the membrane of these receptors which causes Na+ entry = receptor potential
What are some examples of tactile receptors?
Hair receptor - rapid adaptor, senses hair and gentle movement
Merkel’s Disc - slow adaptor, senses light sustained touch and texture
Pacinian Corpuscle - rapid adaptor, senses vibration and deep pressure
Ruffini endings - slow adaptor, sense deep, sustained pressure and skin stretch
Meissner’s Corpuscle - rapid adaptor, senses light, fluttering touch
How do receptors adapt?
Adaptation is a result of inactivation of channels that opened in response to the stimulus
What is an accessory structure?
Cellular or non-cellular structures that modify the stimulus before it reaches the receptor, can filter or amplify the stimulus
What are labelled lines?
Discrete chains of neurons synaptically connected in a particular sequence to accomplish progressively more sophisticated processing of sensory information.
1st order sensory (detects) –>2nd order sensory (relays)–> 3rd order sensory (in the thalamus, directs info to correct region in the brain)
What are somatosensory receptors?
Specialised neurons that usually don’t have a synaptic input
What are the features of a somatosensory receptor?
- Has 2 axons
- Have specialised ion channels at the end of 1 axon that open in response to the stimulus (Mechanical force, temp, pH, factors that signal tissue damage)
- Opening of these channels = generator potentials
What is a Nociceptor?
A receptor that respond to noxious/harmful stimuli, they have free nerve endings
What are the 2 categories of nociceptors?
Aδ fibres: respond to intense mechanical stimuli, fast conduction due to thick myelinated fibres
C fibres: respond to noxious chemical and thermal stimuli, slow conduction due to lack of myelin
Thermoreceptors result in 4 main types of sensation:
Cold
Cool
Warm
Hot
How do thermal receptors detect stimuli?
They detect the relative difference in temperature between the external and internal enviornment
What is a receptive field?
The area that a receptor is responsible for responding to stimulus
