CNS - Lecture 3

Question 1

What is localization

Answer 1

determining the position of a stimulus on or within the body

Question 2

explain the location and transmission of modality-specific signals

Answer 2

travels along sensory axons in specific spinal cord tracts towards the brain

Question 3

The ability to locate a stimulus depends on:

Answer 3

the size and the density of the receptive fields of the receptors

Question 4

lateral inhibition

Answer 4

enhances spatial acuity within the CNS by refining sensory information in afferent neurons (like making an image sharper)

Question 5

Acuity is

Answer 5

the ability to differentiate between closely spaced stimuli

Question 6

How does spatial acuity work

Answer 6

ascending sensory signals are focused by lateral inhibition within the CNS

Question 7

process and outcome of ascending sensory axons that cross the midline in the brain

Answer 7

process: ascending sensory axons synapse on brainstem neurons that cross the midline

outcome: conveys sensory information from the right side of the body to the left side of the brain & vice versa

Question 8

what is two-point discrimination

Answer 8

the ability to distinguish between two closely spaced stimuli

Question 9

small receptive fields and high two-point discrimination/acuity are a result of

Answer 9

tightly packed receptors

Question 10

large receptive fields and low two-point discrimination/acuity are a result of

Answer 10

spaced receptors

Question 11

what is the relationship between receptive field size and acuity

Answer 11

receptive field size determines sensory acuity or two-point discrimination

Question 12

what are receptive fields

Answer 12

specific areas or regions of the body that, when stimulated, activate a particular sensory neuron or receptor

Question 13

overlapping stimulation between neighbouring receptive fields provides

Answer 13

general information about the location of a stimulus

Question 14

what is divergence

Answer 14

each sensory afferent sends branches to many neurons in the CNS
see document for diagram

Question 15

what is convergence

Answer 15

a given neuron in the CNS receives inputs from many sensory afferents
see document for diagram

Question 16

how does lateral inhibition allow the location of a stimulus to be perceived more accurately?

Answer 16

focuses the activation of the neurons on the centre of a stimulus

Question 17

describe firing rate profile in the presence of lateral inhibition

Answer 17

narrower firing rate profile due to lateral inhibition

Question 18

two-point discrimination is best and worst where?

Answer 18

best: hands and the face
worst: abdomen and parts of the limbs

Question 19

why is two-point discrimination best on hands and face

Answer 19

1. there is a higher density of receptors
2. more surface area of sensory cortex is devoted to sensory input from the face and hands

Question 20

sensation

Answer 20

the conscious awareness of a stimulus

Question 21

perception

Answer 21

when a sensation is combined with an understanding of it’s meaning

Question 22

sensation and perception result from processing in the

Answer 22

cerebral cortex

Question 23

what parts of the body is the somatosensory cortex largely devoted to receiving input from? which parts not as much?

Answer 23

• face and hands
• abdomen, legs and feet

Question 24

what does a sensory topographic map show

Answer 24

which areas of the skin are connected to specific regions in the brain.

Question 25

what is projection area

Answer 25

a specific region in the brain that receives and processes information from a particular sensory organ

Question 26

projection area of any given organ in the sensory cortex is related to

Answer 26

functional importance

Question 27

plasticity

Answer 27

topographic maps change according to usage

Question 28

dynamic plasticity means

Answer 28

the maps constantly change, sometimes within seconds

Question 29

what is descending inhibition

Answer 29

activity descending from higher centers in the brain and brainstem that can block out certain types of sensory information by inhibiting neurons in the afferent pathway

Question 30

how does presynaptic inhibition act

Answer 30

by reducing transmitter release at synapse between first and second order sensory neurons. inhibits specific sensations

Question 31

how does postsynaptic inhibition act

Answer 31

acts by hyperpolarizing second order membranes to move their potential further away from threshold

Question 32

how long does postsynaptic inhibition last?

Answer 32

very short, less than a ms

Question 33

what mediators are released when tissue is damaged, what do they do?

Answer 33

prostaglandins and histamine - activate the pain receptors

Question 34

pain receptors fire _______ _________ which travel to the _______ part of the spinal cord

Answer 34

action potentials dorsal

Question 35

what releases substance P and what does it do

Answer 35

- activated pain fibres in the spinal cord - activates interneurons called projection neurons

Question 36

what do projection neurons do

Answer 36

signal pain (pain sensation)

Question 37

what is analgesia

Answer 37

suppression of pain transmission

Question 38

how does aspirin work

Answer 38

blocks production of prostaglandins released by damaged tissue

Question 39

what does gabapentin do

Answer 39

blocks conduction of nociceptors

Question 40

how do opioids (morphine) work

Answer 40

block the release of substance P onto projection neurons in spinal cord

Question 41

What neurons release endogenous opiate neurotransmitters

Answer 41

Neurons in the brainstem and reticular formation

Question 42

What are the functions of endogenous opiate neurotransmitters

Answer 42

- reduce the release of substance P (reduce activity in the projection neurons that signal pain to the thalamus and the cortex) - gets released during fright, flight and flight reactions to reduce pain (nociceptive input)

Question 43

Why is pain from the viscera and internal organs interpreted by the brain as pain on the skin

Answer 43

Sensory afferents from the vicera enter the spinal cord and synapse onto the same interneurons as sensory afferents from the skin

Question 44

in the somatosensory system, pathways that mediate pain and temperature are different than those that mediate

Answer 44

touch pressure and muscle stretch (mechanoreceptive)

Question 45

What afferents are involved in the Anterolateral system

Answer 45

Pain and temperature

Question 46

What afferents are involved in the Dorsal column system

Answer 46

Touch, pressure and stretch

Question 47

** See document for the processes of neuron transmission in the somatosensory system