Lecture #14

Question 1

what are the two main parts of the sensory system?

Answer 1

thalamus and the somatosensory cortex

Question 2

what is the somatosensory cortex responsible for?

Answer 2

the elaboration of the sensory inputs

Question 3

describe pseudopolar unipolar neurons:

Answer 3

ex: in the finger there are the terminal regions of these cells whereas the cell bodies are in the dorsal route ganglia which are flanking the spinal cord → cytoplasmic bundles are directly connected to the axons allowing the electrical signal arising from the periphery to travel to the spinal cord

Question 4

what is one way you can activate some areas of the thalamus allowing the brain to discriminate the position of incoming stimuli?

Answer 4

some of the long axons cross the midline and some of them cannot

Question 5

what type of signal is created by mechanoreceptors?

Answer 5

located in the periphery and enter in contact with the stimulations - an analogical signal is transformed into an electrical signal formed by trains of action potentials

the signal then traces to pseudo-polar cells up to the dorsal nuclei of the spinal cord and to the thalamus

Question 6

what is the second relias important in?

Answer 6

contacts the somatosensory cortex and is involved in the elaboration of information

helps to build a representation of the external environment

Question 7

which of the two original philosophical theories about how the brain creates images is probably more correct?

Answer 7

Kant - the brain has an innate ability to elaborate images

Question 8

how to mechanoreceptors in the skin work?

Answer 8

specialized cells under the skin that can sense a variation in pressure and transform this input in trains of action potentials that propagate it to the dorsal root ganglia

Question 9

what do the specific mechanoreceptors in muscles, tendons, and joints sense?

Answer 9

proprioreception: to understand the position of a limb or allow you to move it in a specific way

Question 10

why are the cells n charge of perception called pseudo polar?

Answer 10

they are directly connected to a structure very similar to an axon → signals travel directly from the periphery to the spinal cord

Question 11

according to Webb, what does the difference between two stimuli depend on?

Answer 11

the intensity of the strength = there is a linear relationship

ΔS=k x S

Question 12

what formula is used today for the difference in two stimuli?

Answer 12

I=k x (S-S(0))^n

n depends on the sensory pathway involved (pressure = 1 for example)

Question 13

what is the sensory threshold?

Answer 13

under a certain intensity, a subject cannot sense a sound - if this threshold starts to drift to the right then there is an issue with the hearing system

Question 14

what is reaction time elicited by?

Answer 14

strong stimuli that are shorter than the ones elicited by weak stimuli

Question 15

describe a parallel analysis:

Answer 15

try to find a blue cross among red crosses → if you increase the number of items in a picture or if you reduce the number of items you need to look for, the reaction time does not change because in this case the brain is doing a parallel search

Question 16

describe a serial analysis:

Answer 16

if asked to find a blue cross among a bunch of blue dashes - objects need to be analyzed one by one to find the right one

Question 17

which is faster for our brains to perform, a parallel analysis or a serial analysis?

Answer 17

parallel analysis

Question 18

what happens when pressure is applied to your finger?

Answer 18

there is an alteration of the cell membrane of this specific receptor and sensors that are closed in resting conditions

these sensors can sense the membrane stretching, and when this stretch occurs ion channels start to open → these channels are specific for sodium so therefore you will have a sodium infiltration under the cell membrane

causes a depolarization of the cell membrane making the membrane potential drift from the resting potential

a strong stimulus will cross the critical threshold and you will generate an action potential

Question 19

what are the stretch receptors called?

Answer 19

Pacini cells

Question 20

what is the equation used to describer the firing rate of our sensory cells?

Answer 20

u= n(sp)T / T

Question 21

in essence, what are colors?

Answer 21

different frequencies of electromagnetic waves

Question 22

in essence, what is music?

Answer 22

vibrations

Question 23

in essence, what are scents?

Answer 23

different chemicals in the air

Question 24

what are mechanoreceptors?

Answer 24

located under the skin and in muscles and tendons → sense vibrations, light touch, and movement

Question 25

what are the function of chemoreceptors?

Answer 25

sense and manage inputs from olfaction, pain, and visceral sensations

Question 26

what are the function of thermoreceptors?

Answer 26

monitors blood temperature in the hypothalamus and are responsible for whether we feel hot or cold

Question 27

what is the tuning curve important for?

Answer 27

the visual sensation

Question 28

what are the four receptors we have the sense light?

Answer 28

rod, blue cone, green cone, and red cone

Question 29

what is the threshold of activation?

Answer 29

a certain wavelength in which the cones are activated at minimal energy

Question 30

describe how our brain can distinguish different colors:

Answer 30

if you activate the retina at 564 nm you can perfectly activate the red cone allowing you to see yellow

if you activate the retinal at 520 nm you are activating the red cone, but at the same time the green cone and only this combination will allow you to see that shade of green

Question 31

describe the process of events that occur if you stick your hand under hot water:

Answer 31

1. sensory receptors under the skin are activated
2. action potential runs through the dorsal route ganglionic neurons
3. enters the spinal cord where there is a specific second neuron that receives the synapsis and sends it along the very long axon
4. in this case the axon crosses the midline and travels to the thalamus
5. axon makes contact with the thalamic neurons that will send another signal to the somatosensory cortex and the activation of the first motor neuron
6. motor neurons have very long axons that cross the midline at the level of the cervical tract and enter the spinal cord to make contact with the second motor neuron connected to the muscles

Question 32

what is the average time for a sensory reaction like this?

Answer 32

100-200 ms

Question 33

describe how slowly adapting receptors work:

Answer 33

they start to fire in response to stimulation - the intensity of the firing is higher at the beginning, and the frequency is proportional to the intensity of stimulation

if stimulation is kept constant, there is a slight reduction in frequency, but the sensory cells are still firing

Question 34

describe rapidly adaptive receptors:

Answer 34

they start to fire at the beginning when there is a variation of stimuli, but then when the stimuli becomes constant, they stop firing and only result when the stimulation is removed

Question 35

what size of axons are the proprioreceptor cells of muscles and tendons characterized by?

Answer 35

big axons → their conduction is very fast

Question 36

what is the speed of conduction of the smaller receptors that sense vibrations, light tough, and pressure (smaller axon diameter and smaller conduction velocity)?

Answer 36

45-50 m/s

Question 37

what is the conduction speed of pain and temperature sensors (very small caliber fibers)

Answer 37

send action potentials with very slow speeds → 5-30 m/s