SENSORY CODING

Question 1

What four things make up sensory coding?

Answer 1

Modality
Intensity
Location
Duration

Question 2

Describe modality

Answer 2

Class of stimulus defined by the type of energy that the stimulus transmits (touch vs temperature)

Question 3

What two things determine intensity?

Answer 3

• the frequency of action potentials in each axon

- the number of axons activated

Question 4

Describe how intensity is encoded

stronger stimuli will result in larger ________ potentials - in the case of a mechanoreceptor, increased ________ on the receptor _________ will open greater numbers of mechanically gated ______ channels, resulting in a larger _________ current. This larger current will be more effective at bringing the membrane at the first ________ of Ranvier to ________ (the membrane may remain above threshold for longer, or reach threshold more ________ after a preceding AP, resulting in a higher _________ of action potential generation). The larger the ____________, the more effective it is in overcoming the ____________ current (through ______ channels) underlying the ________ refractory period that influences the intervals between APs.

Answer 4

stronger stimuli will result in larger action potentials - in the case of a mechanoreceptor, increased pressure on the receptor membrane will open greater numbers of mechanically gated ion channels, resulting in a larger depolarising current. This larger current will be more effective at bringing the membrane at the first Node of Ranvier to threshold (the membrane may remain above threshold for longer, or reach threshold more quickly after a preceding AP, resulting in a higher frequency of action potential generation). The larger depolarisation, the more effective it is in overcoming the hyperpolarising current (through K+ channels) underlying the relative refractory period that influences the intervals between APs.

Question 5

How is location coded?

Answer 5

Mapping of receptive fields of individual primary afferents to specific cortical locations (somatotopic representation in the somatosensory cortex)

Question 6

How is duration encoded?

Answer 6

“Rapidly adapting” receptors respond briefly, even if the stimulus is sustained. This allows them to detect movement and changing pressure.
“Slowly adapting” receptors can signal true duration of the stimulus

Question 7

Which ending allows us to determine which way the skin is being pulled?

Answer 7

Ruffini corpuscles