Flashcards in Session 3 - Somatic Sensations and Sensory Pathways Deck (21)
Give five general senses
Tactile (touch, pressure, vibration)
Give five special senses
Give four stimulus modalities
Light, touch, temperature and chemical change
What are stimulus qualities?
A subdivision of stimulus modalities
How specific are sensory receptors?
Specific to stimulus modalities
Outline the process of sensory transduction
1. Stimulus evokes change in permeability to ions of the receptor membrane
2. Movement of ions across membrane
3. Triggers action potential
4. Action potentials propagate into the CNS
What are tonic receptors?
Slowly adapting tonic receptors which may keep firing as long as the stimulus lasts
Give two places where tonic receptors found
What are phasic receptors?
Rapidly adapting phasic receptors respond maximally and briefly to a stimulus
Give an example of a phasic receptor
o Touch receptors
(E.g. you don’t feel your clothes touching you until they are moved)
What is signal strength determined by?
Signal strength is determined by rate of action potential firing (Frequency coding).
(Stronger stimuli also activate neighbouring cells, but to a lesser degree).
What is sensory acuity?
Sensory acuity is the precision by which a stimulus can be located,
Give three factors which determine sensory acuity
o Lateral Inhibition in the CNS
o Two Point Discrimination
o Synaptic Convergence and Divergence
What is lateral inhibition?
A stimulus causes a response in one receptor maximally and, to a lesser extent, in neighbouring receptors. If solely excitatory neurons link the inputs, the signal becomes blurred.
However, if inhibitory interneurons are introduced, then the cells that are not maximally stimulated will cease to fire. This sharpens sensory acuity.
What is two point discrimination?
Minimal interstimulus distances required to perceive two simultaneously applied skin indentations. E.g. bend a paperclip so it has two points about 1cm apart, close your eyes and touch it on your forearm. It only feels like there is one point.
What is two point discrimination of fingers
What is two point discrimination in the forearm?
Give two factors which determine two point discrimination?
o Density of sensory receptors (3-4x greater in fingertips than rest of hand)
o Size of neuronal receptive fields (1-2mm in fingertips, 5-10mm in palm)
What is synaptic convergence?
The convergence of several 1st order neurones onto a single 2nd order neurone. Convergence decreases acuity.
What is synaptic divergence?
The divergence of a single 1st order neurone onto several 2nd order neurones.
Divergence amplifies the signal.