sensory systems

Question 1

what are sense organs?

Answer 1

structures containing receptors and interneurons that are specialised for detecting and processing particular types of stimuli

Question 2

what are the 5 types of sensory system?

Answer 2

2. mechanical
3. visual
4. thermal
5. chemical
6. electrical

Question 3

describe receptor neurons?

Answer 3

specialised to detect internal and external stimuli of a particular sensory modality

act as filter for stimulus info, transforming stimulus energy in neural signals that are transmitted to sensory interneurons

Question 4

what is meant by sensory labelled lines as a solution to knowing which receptor received the stimulus?

Answer 4

sensory receptors and interneurons from each sensory modality project to segregated areas or layers within the brain

send signals to CNS which interprets signal based on which axon conveyed it

Question 5

what is the difference between sensory receptors cells for touch and smell compared to those for sound and taste?

Answer 5

touch and smell have receptors cells which are neurons with axons and enter CNS

sound and taste have no axons so synaptically excite sensory neurons

Question 6

how do animals have other senses?

Answer 6

adaptations at level of receptor neurons and/or processing sensory pathways and brain areas

Question 7

what do sensory systems demonstrate?

Answer 7

some of the known fundamental principles of brain organisation and neural network

as show serial processing

Question 8

what is the serial processing order of sensory systems (not exclusively this)?

Answer 8

receptors
thalamic nuclei
primary the secondary sensory cortex
association cortex

Question 9

what are several different examples of touch mechanoreceptors?

and why do they each have a distinct pathway to the brain?

Answer 9

1. touch
2. pain
3. stretch
4. vibration

distinct pathways to the brain so different qualities of skin stimulation ca be communicated to different areas in the brain

Question 10

what are mechanoreceptors?

Answer 10

A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortions

Question 11

what are the main receptors found in the human skin?

Answer 11

Pacinian corpuscles,
Meissner’s corpuscles,
Merkel’s discs, Ruffini’s endings,
and free nerve endings

Question 12

what is a neuron’s receptive field?

Answer 12

region in space in which stimuli affect that neuron’s firing rate

Question 13

which receptors have small or large receptive fields?

what does this mean?

Answer 13

small: Merkel’s disc and Meissner’s corpuscle and free nerve endings
- sensitive to stimuli in small areas of skin

large: Pacinian corpuscles and Ruffini’s endings
- sensitive over a larger area of skin and in deeper layers

Question 14

what does it mean to have a large/small receptive field?

Answer 14

small - sensitive to stimuli in small areas of the skin

large - sensitive to stimuli over larger areas of skin

Question 15

what is a Pacinian corpuscle?

what is the structure?

how does it work?

Answer 15

unipolar cell
exetends one branch of axon to skin and other to spinal cord (transmit signal from skin to spinal cord)

cell bodies part of dorsal root ganglion
afferent projections form the dorsal root nerve

vibration/pressure on skin deforms corpuscle and stretches tip of axon opening mechanically-gated ion channels and creates graded potential

Question 16

what do spiking receptor neurons do?

Answer 16

convert the receptor potential into spikes

Question 17

what is meant by the response threshold of a receptor neuron?

Answer 17

only certain intensities will stimulate the neuron to respond

high threshold = lower sensitivity

Question 18

can receptors adjust their response thresholds over time and why would they do this?

Answer 18

yes

if range of stimulus intensities change then response threshold needs to adapt to optimise coding of the stimulus

Question 19

what are phasic receptors?

Answer 19

receptors that show fast loss of response shortly after onset of stimulation

rapid adaptation so fires a few times then stops

Question 20

what are tonic receptors?

Answer 20

slow loss of response after onset of stimulation

slow adaptation

Question 21

which tonic receptors have small or large receptive fields?

and when are they activated?

Answer 21

small- Merkel’s disc (texture)
large - Ruffini’s ending (sustained contact)

segregated in cortex

Question 22

which phasic receptors have small or large receptive fields?

and when are they activated?

Answer 22

small - Meissner’s corpuscle (vibration)

large - Pacinian corpuscle (initial contact)

Question 23

what are the structure and order of sensory pathways?

what info is preserved about the stimuli and how?

Answer 23

segregated projections to different areas of brainstem (CNS) to thalamus then cortex

spatial location of stimulus is preserved by separating projections coming form different locations

Question 24

where is the primary somatosensory cortex located?

what is the coding of it related to the body?

Answer 24

in the postcentral gyrus in the parietal lobe

Brdoman areas 1,2 and 3a&b

adjacent regions in cortex encode for the adjacent regions of body (somatosensory map which has different areas for different skin receptors)

Question 25

can cortical maps be changed?

Answer 25

yes, experience dependent so can change with over/under use
plastic

e.g loss of hand leads to reorganisation and taking over of region by skin receptors of other body parts

Question 26

how are receptors suppressed?

2 ways

Answer 26

involves accessory organs which reduce intensity or alter stimulus before reaching stimulus e.g eyelid

or top-down processes e.g brain stem sending message to receptor cells in ear to dampen sounds

Question 27

what is meant by sensory segregation?

Answer 27

fast adapting (phasic) and slow adapting (tonic) signals remain segregated in cortex