Sensory Systems

Question 1

how many senses to humans have

Answer 1

• 5 classic senses
• but we detect many other things

Question 2

what is a receptive field

Answer 2

• What and where a sensory neuron responds to
• “sensory space” in which a stimulus can drive an electrical response in a sensory neuron

Question 3

describe the correlation of the five senses to different receptors

Answer 3

• hearing and touch respond to mechanoreceptors
• sight responds to photoreceptors
• taste and olfaction respond to chemo receptors

Question 4

what are two examples of sensory detectors present in non-human animals

Answer 4

• magnetoreceptors - orient north and south in animals, common in species that migrate
• electroreceptors - common in animals that hunt in dark or turbid waters

Question 5

modality

Answer 5

• the types of sensory information being processed by the brain such as vision, hearing, touch, or smell
• must be appropriate to the type of sensory receptor

Question 6

describe the pathway of a stimulus from the environment to the brain

Answer 6

1. peripheral sensory neurons
2. spinal chord
3. thalamus
4. primary sensory cortex
5. Further cortical areas

Question 7

describe the function of the thalamus

Answer 7

• takes info and sends it to the rest of the brain
• major site of initial processing of sensory information

Question 8

how do sensory areas in the brain vary between species

Answer 8

• they are larger or smaller depending on the needs of the specific animal
• chimps and humans have relatively small primary sensory areas - larger brain, more space for secondary processing

Question 9

sulci

Answer 9

• the folds of the brain

Question 10

gyri

Answer 10

• the smooth regions of the brain

Question 11

gray matter

Answer 11

• neuronal cell bodies

Question 12

white matter

Answer 12

• bundles of myelinated axons

Question 13

describe the 6 layers of the cortex

Answer 13

1. almost no neuron cell bodies
   - lots of dendrites from lower layers and axons synapsing on those dendrites
2. small densely-packed pyramidal neurons receiving inputs from other layers
3. pyramidal neurons with outputs to other cortical areas
4. many spiny stellate (excitatory) interneurons
   - receives input from the thalamus
   - thicket layer in the sensory cortex
   - nearly absent in motor cortex
5. largest pyramidal neurons
   - outputs to brain stem and spinal cord (
   - must be large so it can send signals far away
6. outputs leading back to the thalamus

Question 14

in what ways is the cortex divided

Answer 14

• layers and columns

Question 15

describe touch receptor responses

Answer 15

• response reduces over time with exposure to the same stimulus
• ex: When you put on shoes, you feel it but after a bit you don’t notice it as much. But when you get a stone in your shoe, you notice it because its a change

Question 16

acuity

Answer 16

• the ability to extract detail from something
• touch acuity varies a lot throughout the body
• small 2pd means high acuity

Question 17

describe the route to the brain for touch information

Answer 17

• touch afferents enter spinal cord via dorsal root ganglion (DRG)
• the area of the skin sending input into each DRG is called a dermatome
• afferents enter brain via Ventero-posterior lateral/medial nuclei of the thalamus

Question 18

describe cortical columns

Answer 18

• within a column, all the cells are concerned with the same part of the body
• adjacent columns are for the same body, but a different kind of touch

Question 19

describe the star-nosed mole’s adaptations for foraging

Answer 19

• its nose has 11 pairs of appendages to sweep tunnel walls
• large scale cortical magnification
• improved ability of the nose to take in tactile information
• nose moves very fast
• can smell underwater

Question 20

what is large-scale cortical magnification

Answer 20

• a cognitive neuroscience concept that describes how the number of neurons in the brain relate to the size of visual angles

Question 21

foveation

Answer 21

• the idea that the center of the visual field has a higher density of photoreceptors than the peripheral

Question 22

describe the somatosensory case of whiskers in rats and mice

Answer 22

• they have poor eyesight, so the whiskers help them gather information

Question 23

what are the characteristics of pathway 1 from whiskers to cortex

Answer 23

• similar to the way we detect touch
• receptive fields of neurons at each stage are mainly focused on a single whisker

Question 24

what are the characteristics of pathway 2 from whiskers to cortex

Answer 24

• broad receptive fields
• thalamus (POm) neurons target septal regions
• Septal regions form wide connections including to contralateral barrel field via corpus callosum
• parallel processing - whisker specific, broad context dependent information

Question 25

active sensing

Answer 25

- the process of directing sensors to gather task-relevant information through a combination of perception and action - ex: rodents move their whiskers in varying ways to actively sense the environment - active whisking can help determine position, shape, and texture of objects

Question 26

describe bat echolocation in the context of active sensing

Answer 26

- Search phase, bats scan the environment with narrowband, long-duration sonar calls - Approach pase, increase in bandwidth, locking beam onto target and increasing rate of calls - Capture, further decreasing the inter-pulse interval, until it intercepts the target - Beam gets narrower and more frequent as you get closer