1.4 General Principles of Sensing Flashcards
What are sensory receptors
the receive stimuli from the environment
What are Neural pathways
that conduct information from receptors to CNS
How does sensory processing proceed
Transduction of stimulus energy into receptor potentials and then APs in afferent neurones
o The pattern of APs in particular neurones is a code that provides information about the stimulus
Intensity, location and specific type of energy
o Primary areas if CNS receive input and communicate with brain for processing
May involve reflex responses, perception, storage, etc…
what do sensory receptors do at peripheral ends of afferent neurones
they transduce information about the environment into graded potentials
- these potentials initiate APs that travel to CNS
what can receptor refer to
either sensory or receptor proteins on their membrane
what are different classes of receptors
o Mechanoreceptors o Thermoreceptors o Photoreceptors o Chemoreceptors o Nociceptors – pain
What does the transduction process involve
involves the opening and closing of ion channels
- causes a change in membrane potential and causes a graded potential called a receptor potential
what is not generated in the receptor region
AP
- local current flows to a trigger zone along the axon where there are channels
- if higher than the threshold then AP triggered
How long does the APs fire for
as long as the receptor potential is sufficient
- increase in receptor potential (RP) causes increase in firing freq of AP
- magnitude of AP is not affected
what controls the magnitude of RP
stimulus strength, rate of change of stimulus strength, temporal summation of RP and adaption
what is primary sensory coding
Coding is the conversion of stimulus energy into a signal that conveys relevant sensory information to the CNS
o Type of energy, intensity, and location of body it affects
single afferent neurone
with all its receptor endings makes up a sensory unit
o Generally the peripheral end divides into many fine branches each terminating with a receptor
Receptive field
Area of body that when stimulated leads to activity in a particular neurone
o Receptive fields of defend sensory units often overlap so single activation rarely occurs
what codes stimulus type (or modality)
coded by the type of sensory receptor that a stimulus activates
are receptors of a single afferent neurone sensitive to the same or different stimulus
the same type of stimulus
o Adjacent sensory units may be sensitive to different modalities
o As receptive fields overlap, a single stimulus source can give rise to multiple sensations (i.e. ice cube –> touch and temperature)
what does the frequency of APs convey
information about the magnitude of stimulus
larger stimulus is, larger receptor potential so a higher frequency of APs
what happens if strength of local stimulus increases
receptors pf adjacent branches on an afferent neurone are activated
the summation of their local currents so greater AP reference
whats recruitment
the process where stronger stimuli also affect a greater area so activate similar receptors on other afferent neurones
what are labelled lines
Stimulus location is coded by the site of a stimulated receptor as well as the specific neural pathway the information is received on and these pathways are labelled lines
whats acuity
the degree with which one stimulus can be located and differentiated from an adjacent one
o Depends upon the amount of convergence of the input in the ascending pathways
The greater the convergence, the lower the acuity
what does acuity depend on
depends on the size of the receptive field, the density of sensory units and the amount of overlap of receptive fields
what allows better simulus location
smaller receptive fields
Receptive field overlaps aid stimulus location
why do afferent neurones respond most vigorously to stimuli applied at the centre of its receptor field
This is due to greater receptor density
More receptors activated and more APs generated
w/ regards to stimulus location, and increase in AP rate
due to location or intensity
Overlap means many sensory units will trigger so neurones at periphery of stimuli fire at lower frequency than central ones
This provides better localisation and also intensity
what does lateral inhibition enable
greater localisation of a stimulus iste for some sensory systems
when does lateral information occur
at any stage, but usually at an early stage
Lateral inhibition used in pathways provides…
… the most accurate localisation
o In the retina to create sharp visual acuity
o Skin hair movements
what happens to information from afferent neurones whose receptors are at the edge of a stimulus
strongly inhibited compared to information from the stimulus centre
o Increases contrast between relevant and irrelevant information, thereby focussing on important messages
afferent sensory pathways are formed by…
chains of three of more neuronesconnected by synapses
o These chains travel in bundles of parallel pathways to the CNS
o Also called ascending pathways as they go up to the brain
where do central processes of afferent neurones enter
enter the brain or spinal cord and synapse upon many interneurons through divergence or convergence
sensory pathways can be specific ascending pathways that…
carry information about one stimulus modality o Go to different cortices: somatosensory, visual, auditory, olfactory
(there can also be non-specific pathways)
