L5.1 Nerve Endings & Sensations

Question 1

Perception is our conscious interpretation of the external world created by pattern of nerve impulses delivered to it by the brain. Is the world as we perceive it in reality?

Answer 1

• No because of limited receptor types for existing energy forms (modalities) (i.e. x rays, radio-waves)
• range of existing receptor types (i.e. hearing)
• precortical and cerebral cortex manipulation of information (‘completing the picture’)

Question 2

what are the different receptor types?

Answer 2

photoreceptors, mechanoreceptors, thermoreceptors, osmoreceptors, chemoreceptors

Question 3

what are the 2 basic receptor types?

Answer 3

1 cell or 2 cell

Question 4

describe the 1 cell receptor

Answer 4

• peripheral nerve, sensory nerve running towards the CNS which actually synapses within the spinal cord
• these free nerve endings are mostly pain receptors
• when you injure or stimulate the nerve, it opens up sodium channels
• action potential goes to homunculus

Question 5

describe the labelled line theory

Answer 5

hypothesis holds that the CNS determines the type of stimulus based receiving input from all sensory cells activated by that stimulus `

Question 6

describe the 2 cell receptor

Answer 6

• the receptor in itself is just a single cell
• stimuli would create a local potential by opening some form of ion channel
• you get a greater potential within the receptor membrane which then allows voltage gated calcium channel to open - calcium enters the cell and in the cell we have neurotransmitters - get released - crosses the cleft and binds onto receptors on the sensory nerve itself which are unspecific ion channels which create another graded potential now in the nerve membrane and if that graded potential is enough for voltage gated sodium channel to open by the membrane reaching thresholds then we get an action potential

Question 7

sensory systems convey four types of information, what are these?

Answer 7

• modality (touch, pressure, pain, light, sound, chemical changes- modality is nerve specific, not receptor specific)
• location
• intensity (larger receptor potentials = more action potentials; normally higher frequency of AP increases intensity; also larger stimulus leads to activation of more receptor)
• timing (when a response, firing of AP, begins ands ends, therefore also encoded by frequency of firing)

Question 8

in relation to adaption, what are the two type of receptors?

Answer 8

tonic receptors: receptors that keep firing as long as the stimulus is there = they are really slowing adapting

phasic receptors: e.g. when you are being touched you will feel it because they are firing off but as long as you are being touched, they stop firing and you don’t feel it anymore –> but if then someone releases the touched you then feel it again = firing off response

Question 9

see notes for thermal receptors

Answer 9

see notes for thermal receptors

Question 10

how do we perceive being wet?

Answer 10

while we don’t have receptors for ‘wetness’ we use a combination of multiple inputs (touch, pressure, thermal receptors)

Question 11

describe the differences of receptors fields in highly sensitive and not as sensitive areas

Answer 11

• in areas where you are highly sensitive (e.g. finger tips), you have very small receptor fields in high densities (can discriminate against touches)
• in areas where we are not as sensitive we have larger receptor fields in low densities (can’t discriminate against touches)

Question 12

see notes for lateral inhibition

Answer 12

see notes for lateral inhibition