L22 Sensory Systems

Question 1

describe the common plan of sensory systems

Answer 1

• designed to detect a physical stimulus (light, sounds etc.)
• stimulus is translated/signal transducted into cell activities into sensory receptor cells/neurons/transducers
• sensory receptor cells pass the signal onto second order neurons
• passes through thalamus (relay station)
• info reaches cerebral cortex - (sensory = parietal, occipital, temporal, insular)

Question 2

what are the components of the common plan of sensory systems?

Answer 2

stimulus – receptor – pathway – perception/behavior

Question 3

in what part of the brain does sensory info reach consciousness?

Answer 3

cerebral cortex - trigger behavior

Question 4

define perception

Answer 4

the process of interpretation of sensory input

Question 5

what are the 6 sensory systems?

Answer 5

• somatosensory
• visual
• vestibular
• auditory
• olfactory
• gustatory

*olfactory and gustatory are closely related = chemical senses

Question 6

what are the 4 basic sensory receptor classes?

Answer 6

mechanoreceptors - pressure on skin
thermoreceptors - sense temp changes
chemoreceptors - sense chemical changes
photoreceptors - sense light

Question 7

what sensory receptor classes does the somatosensory system need

Answer 7

• mechanoreceptors
• thermoreceptors
• chemoreceptors

Question 8

what sensory receptor classes does the visual system need

Answer 8

photoreceptors

Question 9

what sensory receptor classes does the vestibular system need

Answer 9

mechanoreceptors

Question 10

what sensory receptor classes does the auditory system need

Answer 10

mechanoreceptors

Question 11

what sensory receptor classes does the olfactory system need

Answer 11

chemoreceptors

Question 12

what sensory receptor classes does the gustatory system need

Answer 12

chemoreceptors

Question 13

what are the components of a sensory receptor

Answer 13

cell body - soma, perikaryon
t
ransduction site - stimulus is converted to nerve signal

axon
synaptic terminal

Question 14

what morphology (type) of neurons are somatosensory receptors?

Answer 14

pseudo-unipolar neurons

Question 15

what is a receptor potential

Answer 15

“graded potentials” = do not follow “all or none rule”

• variable durations and intensities
• variability lies in the number of AP per unit time

Question 16

where do receptor potentials take place

Answer 16

transduction site

Question 17

what is an action potential

Answer 17

stimulus conducted from distal to proximal axon to synaptic terminal

*note - in sensory receptor neuron, AP are NOT generated in axon hillock like seen in multipolar motor neurons

Question 18

where do action potentials take place

Answer 18

trigger zone

Question 19

what are transmitter release

Answer 19

transmitter is released into cleft and binds to receptors within the postsyn membrane of the postsym cells = second order neuron of the sensory pathway

Question 20

where does transmitter release take place

Answer 20

synaptic terminals of sensory receptor

Question 21

what are the morphological characteristics of sensory receptor cells?

Answer 21

• example - hair cell
• specialized epithelial cells (not neuronal origin)
• apical pole is transduction site
• lack an axon
• do NOT produce AP
• have graded potential that directly induces the release of signaling substances at the base of these cells
• form a synapse onto an afferent (sensory) fiber of the first neuron in the sensory pathway => neuron produces AP carried along its afferent fibers!

Question 22

what are the 4 attributes of stimulus

Answer 22

modality
intensity
duration
location

Question 23

define modality

Answer 23

the physical type (quality) of stimulus energy - may be light (visual system), sound (auditory system), touch (somatosensory system) etc.

Question 24

Define intensity

Answer 24

the amplitude (or quantity) of a stimulus

Question 25

define duration

Answer 25

the time between the start and the end of a stimulus

Question 26

define location

Answer 26

the place where the stimulus is located or originated - maybe some place in our 3D environment around us (light or sound) or a place on the surface of our body (touch)

Question 27

how is modality encoded?

Answer 27

labeled line code - pathways carrying sensory information centrally are therefore also specific, forming a "labelled line" regarding a particular stimulus

Question 28

how is intensity encoded?

Answer 28

- subthreshold stimuli may elicit a small receptor potential but may not induce an AP - frequency code - population code

Question 29

what is frequency code in wrt intensity encoding

Answer 29

assuming receptor potentials are above threshold, the higher the stimulus intensity is the more AP will be generated per unit time applies to individual neurons and their axons

Question 30

what is population code wrt intensity encoding

Answer 30

- high intensity stimuli can activate more individual axons than a low intensity stimulus - example -press harder and harder on your hand = stimulates a larger area thus more axon stimulation

Question 31

how is duration encoded?

Answer 31

-receptor adaptation - the disappearance of a sensation induced by a stimulus when the duration is too long example => disappearing feeling of wearing clothes all day even though you felt them when you put them on -slow adapting receptors -rapid adapting receptors

Question 32

what are slow adapting receptors wrt duration encoding

Answer 32

- used for constant monitoring - important for regulatory function of tight physiologic windows - they remain depolarized for the duration of the stimulus and maintain a constant output of APs

Question 33

what are rapid adapting receptors wrt duration encoding

Answer 33

- only signal at the onset of stimulus where the receptor potential quickly returns to baseline - no further APs are generated despite the persistence of the stimulus - much better equipped for sensitivity to changes and not constant stimulation

Question 34

what receptors are better in constantly monitoring levels of stimulation wrt duration

Answer 34

slowly adapting receptors

Question 35

what receptors are most sensitive to changes, not to constant stimulation?

Answer 35

rapidly adapting receptors

Question 36

define receptive field wrt location

Answer 36

the area monitored by a single neuron = the area where a stimulus would induce a response

Question 37

what happens if a stimulus is placed within the receptive field?

Answer 37

AP!

Question 38

what happens if a stimulus is placed outside of the receptive field

Answer 38

never be an AP on that neuron

Question 39

what are the 3 basic wiring mechanisms

Answer 39

- convergence - divergence - lateral inhibition

Question 40

what is convergence?

Answer 40

- when a second order neurons gets input from more than 1 first order receptor neuron - the inputs will summate and give a larger summation than the parts alone

Question 41

what is divergence

Answer 41

the signal from 1 first order neuron stimulates multiple second order neurons

Question 42

what is lateral inhibition

Answer 42

a situation where a first order neuron stimulates an interneuron which will relay that stimulus to an adjacent second order neuron only it is inhibiting that adjacent neuron