1.3 - Sensory Systems

Question 1

pathway of sensory info from environment to brain (5)

Answer 1

1. peripheral sensory neurons
2. spinal cord
3. thalamus
4. primary sensory cortex
5. further cortical areas

Question 2

how does sensory information enter the spinal cord

Answer 2

in via the dorsal rood sensory neuron cell bodies in dorsal root ganglia

Question 3

benefit of having lots of sensory neurons at periphery

Answer 3

can categorise where/what of sensory signals (neurons receptive field)

Question 4

primary and association sensory areas of the brain?

Answer 4

see diagram in one note

Question 5

folds in the cortex

Answer 5

sulci (sing, sulcus)

Question 6

smooth regions in the cortex

Answer 6

gyri (sing,gyrus)

Question 7

gray matter

Answer 7

neuronal cell bodies

Question 8

white matter

Answer 8

bundles of myelinated axons

Question 9

cortex (2)

Answer 9

1. sheet of even depth/thickness
2. folding increases surface area in large brained animals

Question 10

cortical layers: layer I (2)

Answer 10

1. almost no neuron cell bodies
2. lots of dendrites from lower layers and axons synapsing those dendrites

Question 11

cortical layers: layer II

Answer 11

small densely-packed pyramidal neurons receiving inputs from other layers

Question 12

coritcal layers: layer III

Answer 12

pyramidal neurons with outputs to other cortical areas

Question 13

cortical layers: layer IV (3)

Answer 13

1. many spiny stellate (excitatory) interneurons
2. receives input from thalamus
3. thickest layer in sensory cortex, nearly absent in motor cortex

Question 14

cortical layers: layer V (2)

Answer 14

1. largest pyramidal neurons
2. outputs to brain stem and spinal cord

Question 15

cortical layers: layer VI

Answer 15

outputs leading back to thalamus

Question 16

how are cortical neurons in sensory areas organised

Answer 16

roughly organised into columns perpendicular to cortical surface (perhaps the physiological units of computation)

Question 17

pathway of sensory info in cortical layers (4)

Answer 17

1. sensory inputs first activate neurons in layer 4
2. layer 4 neurons propagate activity to layer 2 and 3
3. from there down to layers 5 and 6
4. recurrent pathways will send excitation back from layer 6 to layer 4

4 -> 2+3 -> 5+6 -> 4

Question 18

receptive field

Answer 18

part of “sensory space” in which a stimulus can drive a electrical response in a sensory neuron

Question 19

how do receptors adapt

Answer 19

response reduces over time to same stimulus

Question 20

acuity

Answer 20

ability to discern detail in sensory stimulus (small 2PD means high acuity)

Question 21

route to brain for touch information (2)

Answer 21

1. touch afferents enter spinal cord via DRG
2. afferents enter brain via ventero-posterior lateral/medial (VPL/M) nuclei of the thalamus

Question 22

area of skin sending input to each DRG

Answer 22

dermatome

Question 23

how is the cortex not isomorphic with sensory surfaces? (2)

Answer 23

1. area of cortex isn’t proportional to the area of sensory space it represents
2. adjacent areas of cortex might not deal with adjacent areas of sensory space

Question 24

cell response conditions within a cortical column (3)

Answer 24

1. respond to stimuli from same modality
2. respond to inputs origination from same type of sensory receptor
3. respond to stimuli from same area

Question 25

cell response in adjacent cortical columns

Answer 25

can respond to different stimuli from same region

Question 26

star-nosed mole nose adaptation (4)

Answer 26

1. nose is tactile appendage with 25,000 mechanoreceptors 2. 100,000 neurons from nose to brain 3. large-scale cortical magnification 4. foveation (centre of visual field - high resolution)

Question 27

how is the star-nosed mole's nose similar to an eye?

Answer 27

eyes have peripheral and foveal vision, the nose is a similar arrangement

Question 28

very specific touch patterns of star-nosed mole's nose (3)

Answer 28

1. touch 2. foveate 3. eat

Question 29

how fast does a star-nosed mole's nose touch

Answer 29

12 touches/second = 25ms to decide if something is food (600ms to press brake-pedal)

Question 30

how does the star-nosed mole reduce handling time of food?

Answer 30

proximity of nose to teeth

Question 31

barrel cortex specialisation

Answer 31

specialisation within primary somatosensory cortex (S1) - almost 70% mouse somatosensory cortex (surface area) devoted to processing info from whiskers

Question 32

how are whiskers represented in the somatosensory cortex of rodents

Answer 32

same pattern on whisker follicle arrangement as in layer IV of S1 cortex

Question 33

difference in thalamic afferents between barrel cortex and normal S1 (2)

Answer 33

1. normal - thalamic afferents forma a relatively continuous distribution of connections in S1 2. barrel cortex - thalamic afferents form discrete clumps

Question 34

how are barrels separated

Answer 34

gaps called septae

Question 35

whisker to cortex (3)

Answer 35

1. deflection of a whisker 2. mechanically gated ion channels 3. sensory neurons

Question 36

whisker to cortex sensory neurons: pathway 1 (4)

Answer 36

1. trigeminal ganglion 2. brainstem nuclei (PrV) 3. thalamus (VPM) - same area of thalamus as for human touch 4. cortex (barrels)

Question 37

barrels

Answer 37

same as S1 but in animals with whiskers

Question 38

receptive fields of sensory neurons in pathway 1

Answer 38

at each stage mainly focused on single whisker

Question 39

whisker to cortex sensory neurons: pathway 2 (4)

Answer 39

1. trigeminal ganglion 2. brainstem nuclei (SpV) 3. thalamus (Pom) 4. cortex (barrels and septae)

Question 40

receptive fields of sensory neurons in pathway 2

Answer 40

broad

Question 41

main difference in whisker to cortex sensory neuron pathway 2 (3)

Answer 41

1. axons of PoM neurons target septal regions 2. septal regions form wide connections including to contralateral barrel field via corpus callosum 3. therefore parallel processing (whisker specific, broad context dependant information)

Question 42

phases of bat echolocation (3)

Answer 42

1. search phase 2. approach phase 3. capture

Question 43

bat echolocation search phase (phase 1)

Answer 43

bats scan environment with narrowband, long-duration sonar calls

Question 44

bat echolocation approach phase (phase 2)

Answer 44

increase in bandwidth, locking beam onto target and increasing rate of calls

Question 45

bat echolocation capture (phase 3)

Answer 45

further decreasing inter-pulse interval until it intercepts target

Question 46

saccadic (eyes)

Answer 46

moving fovea over image discontinuously

Question 47

saccades (eyes) (2)

Answer 47

1. 20ms-100ms 2. during saccades (10% of time) we are blind. blur or 'saccadic suppression'

Question 48

fixations (eyes) (2)

Answer 48

1. 200ms-300ms 2. conscious or unconscious control