Flashcards in L2 - Neural Coding in Somatosensory Systems Deck (68):
What are 4 features of perceptual experience?
Name 3 modalities of perceptual experience.
Touch, Taste, Vision
What are sub-modalities?
The individual aspects of each modality.
What are examples of sub-modalities of taste?
Bitterness, sweetness, saltiness, sourness
What do modalities often depend on?
Specific receptors that have receptor selectivity to certain stimuli.
What are 3 sensory 'qualities'?
- often depend on perceptual, relative coding, rather than absolute receptor differences.
- perception of distinct colour differences despite only having 3 photoreceptor types.
- no specific water receptor, but still a distinct quality/awareness of wetness
How is the modality of senses coded, if the only way of transmitting information is through identical action potentials?
'Labelled line' - action potentials are sent to specific areas of the brain to signal certain domains of sensory information (brain localisation). The receptor in this specific area knows how the incoming action potential is meant to be interpreted.
Rate coding does what?
Codes for intensity
What is the relationship between strength of stimulus and the rate of action potentials?
Non - linear. As the stimulus increases in strength, the increase in rate of firing decreases.
Sensory adaptation enables what?
Preservation of adequate sensitivity across a very wide range of input sensitivities, despite having a limited range due to the small variability in rate the lowest possible (0) and the maximum (refractory period)
What can the 2 point discrimination test show?
It can demonstrate differences in touch sensitivity, and therefore receptor density, between two different areas, such as the fingers and the back of the neck.
Those areas with less (or larger) receptive fields will respond as though two separate points on the skin is one.
What type of receptors do touch modalities have?
What type of receptors do temperature modalities have?
What type of receptors does proprioception have?
What type of receptors does nociception have?
What is proprioception?
The sense of one's own relative position, motion and equilibrium.
What is nociception?
The sensory nervous system's response to harmful, or potentially harmful stimuli.
Which tactile (touch) receptor is most responsive to vibration?
If you have hairy skin, where are the hair receptors found?
At the base of the hair follicle.
What are the main 5 types of touch/tactile receptors in the skin?
- Pacinian corpuscle
- Merkel's disc
- Meissner's corpuscle
- Ruffini ending
- Hair receptors
Where does the sensation of hair come from?
The bending of hair fibres causes twisting of receptors on the cell.
Where are free endings found and what are they important for?
Found in the skin, and important for the reception of pain
What are free endings?
An unspecialised nerve fibre ending of a sensory neuron which is more sensitive to chemical change than the other receptor types.
What are free endings also called?
Free nerve endings (FNE) or bare nerve endings
What are 3 types of shallow tactile receptors?
Hair receptors, Meissner's corpuscle and Merkel's disc.
What are 2 types of deep tactile receptors?
Pacinian corpuscle and Ruffini's ending.
What are 3 types of rapid adapting tactile receptors?
Hair receptors, Meissner's corpuscle and Pacinian corpuscle.
What are 2 types of slow adapting tactile receptors?
Merkel's disk and Ruffini's ending.
What are the properties of rapid adapting receptors?
- Short burst on stimulus application and removal (any large change)
- Rapidly adapt if stimulus is sustained
What are the properties of slow adapting receptors?
- Short burst on stimulus application and removal
- Takes longer to reduce firing rate if stimulus is sustained.
What are the features of the pacinian corpuscle?
- Many layers of protective sheath surrounding nerve ending
- Corpuscle is viscous - rapid forces are passed through
- Slow forces are absorbed at the capsule deforms
- Nerve ending is rapidly adapting
- Short train of action potentials during stimulus.
Why does the Pacinian corpuscle fire at the offset of a stimulus?
The removal of the stimulus that caused pressure to be applied to the receptor/surrounding sheath causes a 'twang' back into it's original shape. (rebound excitation)
What are the effects of thick skin on the force applied to it? Name an example of thick skin.
Soles of the feet. Forces applied are spread laterally
What are the effects of elastic skin on the force applied to it?
Absorbs energy from the stimulus
What are the effects of shearing forces on the skin?
They stretch the skin and have a directional component
Why do deep receptors have larger receptive fields?
They are more sensitive to larger areas of skin deformation
What is human microneurography?
The measurement of neurographic activity using microscopic pins.
Fast adapting cells/receptors allow what to occur?
A feedback system. Quick responses to changes in stimuli can aid feedback.
Why are population codes useful?
Synchronous activity of many neurons, potentially across different modalities, may be a more accurate signal than using single modalities or single neurons, which can fire randomly.
Why would population codes/a number of neurons be more useful in detecting the first spike, compared to using single neurons?
Individual neurons will have baseline levels of activity - it is more reliable to use groups of neurons as simultaneous spikes from these will more reliably signal a stimulus (/stimulus change).
What is the problem with using spike rates to gather information, and what is a better method?
It may take a lot of time for the second spike/many spikes to occur. First spikes are a better method.
What are first order afferents?
The original receptor cells that send information from the tips of fingers/toes to the spinal cord/brain stem.
What are second order afferents?
(spinal/brain stem) Cells that project from the synapse of the receptor cell to the contralateral thalamus.
What are third order cells?
Cells that take information from the thalamus to the sensory cortex - primary somatosensory areas.
What are 4 specific properties of neurons?
- They have receptive fields
- They adapt
- Responses depend on both neural (firing of cells) and non-neural (e.g. mechanical)
- Sensations signalled by changes in the membrane voltage of the sensory neuron.
What are mechanoreceptors?
Receptors that are sensitive to touch, and that change the shape of their membrane to allow action potentials.
'Labelled lines' allow coding for what?
Different modalities of sensory information
Firing frequency of neurons codes for what? (rate coding)
Intensity of stimuli
What is the second order afferent/nerve also called and what is it's specific capabilities?
'relay nuclei' recodes information through lateral inhibition, convergence and divergence.
What is glabrous skin?
More sensitive areas of skin will have higher concentrations of what?
More sensitive areas of skin will have smaller what?
Overlapping receptive fields allow what?
Population activity allows a more fine-grained resolution picture of skin than looking at single cells.
What allows for edge detection?
Relating to or denoting a sensation (such as pressure, pain, or warmth) which can occur anywhere in the body, in contrast to one localized at a sense organ (such as sight, balance, or taste).
What is microneurography?
Measuring neurographic activity using microscopic pins.
Describe shearing forces on the skin
Shearing forces stretch the skin and have a directional component.
Which type (and specific) skin receptors are suitable for light touch?
Surface level receptors - Merkel and Meissner.
Which type (and specific) skin receptors are suitable for vibration and indentation?
Deep skin receptors - Pacinian and Ruffini
What is central modulation?
Higher centres projecting back down to brain stem areas and actively gating information. Allows unimportant stimuli to be ignored.
What is an example of a neuro-modulator?
What are the 3 ways in which central modulation occurs?
- efferent projections from higher CNS areas to lower brain stem areas.
- changes in arousal and threshold
What are 2 ways in which peripheral modulation occurs?
- modulating receptor filtering properties (iris, muscles, cochlea) which enables usage of the motor system to probe the sensory environment.
- by modulating transmitter release
What is active touch?
The control of the sensory system by the CNS through action. Leads to combination of both systems to gain information and explore the environment.
What are afferent signals?
Inward signals that travel from the sensory system to the CNS.
What are efferent signals?
Outward signals that travel from the CNS to the periphery.
Which of the following brain areas is not involved in somatosensation?
S1, Primary sensory cortex, Brodmann's area BA1, 2 and 3, Anterior parietal cortex, Anterior cingulate cortex.
Anterior cingulate cortex is not involved.
S1, Primary sensory cortex and Brodmann's area BA1, 2 and 3 are all different names for the same area. This area is located in the anterior parietal cortex.