Session 3 - Somatic Sensations and Sensory Pathways Flashcards Preview

Semester 5 - CNS > Session 3 - Somatic Sensations and Sensory Pathways > Flashcards

Flashcards in Session 3 - Somatic Sensations and Sensory Pathways Deck (21):

Give five general senses

o Somatic
 Tactile (touch, pressure, vibration)
 Thermal
 Pain
 Proprioception
o Visceral
 Internal organs)


Give five special senses

o Smell
o Taste
o Vision
o Hearing
o Balance


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

Joint receptors
Pain receptors


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.


What is a receptive field?

The receptive field of a sensory neurone is the area where stimulus will alter the firing of that neurone. Receptive fields vary in size and density, and overlap with neighbouring receptive fields.