CNS Lecture 3 Flashcards Preview

Vanders Human Physiology (PHYSL 210) > CNS Lecture 3 > Flashcards

Flashcards in CNS Lecture 3 Deck (39)
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1
Q

The ability to locate a stimulus depends on what two factors?

A

The Size and Density of receptive fields of the receptors

2
Q

What is the difference between sensation and perception?

A

Sensation: conscious awareness of a stimulus

Perception: Sensation combined with an understanding of its meaning

Both result from processing in the cerebral cortex

3
Q

What process focuses ascending sensory signals to enhance spatial acuity?

A

Lateral Inhibition focuses ascending sensory signals, enhancing spatial acuity

Acuity: ability to distinguish between things that are near eachother

4
Q

Ascending sensory axons synapse on neurons in the ______ that then Cross-Over conveying sensory information from the right side of the body to the left side of the brain and vice versa

A

Ascending sensory axons synapse on neurons in the brainstem that then Cross-Over conveying sensory information from the right side of the body to the left side of the brain and vice versa

5
Q

What is two point discrimination?

A

Clinical test used to evaluate sensory discrimination

6
Q

What is the relationship between spatial acuity and receptive field size?

A

Smaller receptive fields will provide greater spatial acuity

ie: in areas where receptors are tightly packed, receptive fields will be smaller and sensory acuity (two point discrimination) is high

7
Q

What would you assume the sensory acuity would be in areas where the receptors are NOT tightly packed?

A

When receptors are loosely packed, the receptive fields are larger = decrease in sensory acuity (low two-point discrimination)

8
Q

What kind of information is provided by overlapping stimulation between neighbouring receptive fields?

A

General information about the location of the stimulus

9
Q

What is divergence?

A

Each sensory afferent sends branches to many neurons in the CNS

10
Q

What is convergence?

A

A given neuron in the CNS receives inputs from many sensory afferents

11
Q

What is Lateral Inhibition?

A

Method of refining sensory information in afferent neurons and ascending pathways whereby fibres inhibit each other; the most active causing the greatest inhibition of adjacent fibres

ie: Sharpens contrast by focusing activation of CNS neurons

12
Q

What type of neuron functions in lateral inhibition?

A

Interneurons within the CNS

13
Q

As shown in the image, lateral inhibition focuses __________ firing to the centre of the stimulus location

Thus increasing:

A

As shown in the image, lateral inhibition focuses second-order sensory afferent firing to the centre of the stimulus location

Thus increasing: sensory perception

14
Q

Where is Two-Point discrimination the best and the worst?

A

Best on hands and face

Worst on abdomen and proximal parts of limbs

15
Q

Why is Two point discrimination best on hands and face and worst on abdomen and proximal parts of the limbs?

A
  1. Density of receptors = highest in skin areas with best 2-pt discrimination
  2. Surface are of sensory cortex = largest in regions to which receptors from skin areas with the best 2-pt discrimination project
    • more surface are of the somatosensory cortex devoted to sensory inputs from the fingers, thumb, forehead, cheek, nose and upper lip
16
Q

The projection area (topographic maps) is related to _______

A

The projection area (topographic maps) is related to Functional importance

17
Q

What is it called when topographic maps (neurological maps) change in response to use?

A

Plasticity

18
Q

What is dynamic plasticity?

A

The idea that topographic maps are constantly changing, sometimes within seconds

19
Q

What is descending inhibition?

A

The processes through which activity descending from higher centers of the brain and brainstem can “screen out” certain types of sensory information via inhibiting neurons in the afferent pathway

20
Q

What are the two types of descending inhibition?

A

Presynaptic inhibition

Postsynaptic inhibition

21
Q

What is presynaptic inhibition?

Where does it occur?

A
  • results from inhibition of the sensory axon close to the synaptic terminal;
  • occurs close to the synapse between the sensory afferents and the neurons that convey information to the brain
22
Q

How does presynaptic inhibition act?

A
  • Reduces transmitter release at the synapse btwn 1st order and 2nd-order neurons
  • inhibits specific sensations (eg pain)
  • lasts several milliseconds
23
Q

What is Postsynaptic inhibition?

How long does it last?

A

Hyperpolarization of the membrane of the second-order sensory neurons to move their membrane potential further away from the AP threshold

  • Non-selective: reduces effect of all synaptic inputs
  • lasts less than 1 millisecond
24
Q

Describe the pathway of pain transmission

A
  • Painful stimulus causes tissue damage
  • Damaged tissue releases prostaglandins and histamine which activate the pain receptors
  • pain receptors fire AP’s which travel to the dorsal part of the spinal cord
  • in the spinal cord, activity in the pain fibres causes release of Substance P
  • Substance P activates interneurons called projection neurons
  • Signal pain and excite neurons in the thalamus and the cortex
  • Results in sensation of pain
25
Q

What is analgesia?

A

Suppression of pain transmission

26
Q

How does aspirin work as an analgesic?

A

Aspirin blocks the productions of prostaglandins that are released by damaged tissue

Reduces the firing rate of the nociceptive afferents

27
Q

How does Gabapentin act as an anelgesic?

A

Gabapentin blocks conduction in nociceptive axons

  • nociceptive afferents are very thin with low conduction velocity = C-Fibre
28
Q

How do opioids act as anelgesics?

A

Block the release of Substance P onto the projection neurons in the spinal cord

29
Q

What two regions of the brainstem have neurons that project down the spinal cord and release endogenous opiate neurotransmitters?

A

Periaqueductal gray matter and Reticular formation

30
Q

What do endogenous opiate neurotransmitters do?

A

Reduce the release of Substance P and reduce activity in the projection neurons that mediate pain sensation and signal pain to the thalamus and cortex

31
Q

Why are endogenous opiate neurotransmitters released during fight or flight?

A

To reduce nociceptive input

32
Q

Projection neurons can be inhibited by sensory input from ________ (those signalling touch, pressure, muscle stretch)

A

Projection neurons can be inhibited by sensory input from large sensory afferents (those signalling touch, pressure, muscle stretch; have most rapid velocities)

33
Q

What is referred pain?

A

The sensation of pain is experienced at a site other than the injured or damaged tissue

34
Q

How does referred pain occur?

A

Convergence of visceral and somatic afferents on ascending projection neurons in the spinal cord

  • ie sensory afferents from the viscera and internal organs enter the spinal cord and synapse onto the same interneurons as sensory afferents from the skin
  • Brain interprets pain from the viscera as pain in those areas of the skin that converge onto the same interneurons
35
Q

What information is carried in the Anterolateral system?

A

Temperature and Pain

36
Q

Where do temperature and pain afferents synapse in the anterolateral system?

A

Pain and temperature afferents synapse onto second-order interneurons in the spinal cord

  • these interneurons send axons that cross to the opposite side of the spinal cord (within two segments of the spinal cord generally)
  • After crossing, the axons ascend to the brain in the spinothalamic or anterolateral tracts
37
Q

What type of information is carried in the Dorsal Column system,?

A

Touch, pressure and stretch afferents

38
Q

Describe the Dorsal Column system

A
  • Touch, pressure and stretch afferents enter the spinal cord and form the dorsal columns (DO NOT immediately contact interneurons)
  • The dorsal columns ascend to the brainstem where the afferents then synapse onto second order neurons in the brainstem
  • the second order neurons send axons that CROSS OVER to the contralateral side of the NS
39
Q

When does cross-over occur in the anterolateral system vs the Dorsal Column system?

A
  • Anterolateral:
    • pathway crosses over within one or two vertebral segments upon entering the spinal cord
  • Dorsal Column:
    • In the brainstem, second order neurons send axons that cross over