Sensory systems

Question 1

What encodes stimulus type

Answer 1

Line labelling

Question 2

What encodes the position of a stimulus

Answer 2

Mapping

Question 3

What response to touch receptors have to touch?

Answer 3

• Depolarise with touch

- Even weak/unpercieved stimulus generates a receptor potential

Question 4

Name two types of pain receptors, how fast do they travel?

Answer 4

First pain (A6 fibres) travel at 15-30ms
Second pain (C fibres) travel at 0.5-2ms

Question 5

What is adaptation?

Answer 5

When generator potentials ‘fade away’ with a constant maintained stimulus causing a drop in spike frequency

Question 6

What are the characteristics of a pacinian (lamellar) corpuscle?

Answer 6

• Responds to deformation of skin surface due to sudden touch/vibration
• Large (1mm) and surrounded by a multi-layered capsule
• Can activate more than one neuron at a time

Question 7

Why are pacinian corpuscles so fast adapting?

Answer 7

As for both ‘on’ and ‘off’ stimulus, layers of the capsule slide past each other to relieve deformation at the centre

Question 8

How do touch stimuli travel to the CNS?

Answer 8

• Most proprioceptive input enters the dorsal root
• Travels up spine to brain stem/medulla
• Interneurons are activated crossing over to the thalamus
• further neurons relay input to the primary somatosensory cortex

Question 9

What are the two types of light receptor?

Answer 9

Rods - respond in low light levels to shades of grey

Cones - respond in bright light to colour

Question 10

What is the state of rod cells in the dark?

Answer 10

High cGMP levels keep Na+ channels open, depolarising the cell with a resting potential of -30mV

Question 11

How do cone cells react to light?

Answer 11

• Light interacts with rhodopsin which activates transducin which goes on to activate phosphodiesterase enzyme (PDE)
• Na+ channels then close, making the cell hyperpolarised

Question 12

How do rod cells adapt to light levels?

Answer 12

Ca2+ interacts with a negative feedback loop keeping cGMP within range needed to detect a range of light intensities

Question 13

What are the 3 layers of the retina?

Answer 13

receptor, bipolar cell, ON/OFF ganglion

Question 14

What are ON/OFF ganglions?

Answer 14

ON ganglions depolarise in response to light, OFF in response to dark.
rods/cones make exitatory inputs to OFF bipolar cells and inhibitory inputs to ON bipolar cells

Question 15

How does the visual pathway project to the brain?

Answer 15

• Ganglion cell axons project to a region of the thalamus after passing the optic chiasm (note: only part of the retina crosses over to the other side)
• Relay then projects to the visual cortex at the back of the brain