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Systems Neuroscience > Lec #3 > Flashcards

Lec #3 Flashcards

1
Q

3 functionally distinct systems in somatic sensory system ?

A 
1.  Cutaneous mechanoreceptors 
  Fine touch 
  Vibration 
  Pressure 
2.  Specialized receptors associated with muscles, 
tendons and joints 
  Proprioception 
3.  Free nerve endings 
  Pain 
  Temperature 
  Course touch
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2
Q

pseudounipolar neurons

A

Neurons found in peripheral nervous system
•  Attach to cell body in ganglia by a single process
•  Signal does not pass through cell body
•  Cell body maintains cellular machinery that mediates
transmission

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3
Q

Sensory transduction

A
  •   process of converting energy of a stimulus into an electrical signal
  •   Stimulus alters permeability of ion channels in the afferent nerve endings to generate a receptor potential; or action potential if reaches threshold
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4
Q

Types of sensory receptors ?

A

-Mechanoreceptors
• Afferent fibers can be encapsulate by specialized receptor cells to help tune to particular feature
-Free nerve endings
• Lack encapsulation by specialized receptors
• Sensation of pain
• Higher threshold for action potential

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5
Q

What are the different kind of afferents and what information do they convey in what pace ?

A

•  Ia afferents = largest and fastest, supply sensory receptors to muscles for proprioception
•  Aβafferents = smaller, convey touch
•  Aδand C afferents = small and slow, pain and temp
*Only C are unmyleinated

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6
Q

Receptive field

A

•  Receptive field = area of the skin surface over
which stimulation results in activation of a neuron
•  Highly variable per neuron; function of branching of afferent
•  Some overlap
•  More innervation by many neurons = smaller receptive fields (finger, lips vs back, forearm)

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7
Q

what is Two-point discrimination, and what stimuli activates what fibers ?

A

•  Two-point discrimination = apply 2 stimuli at same
time and measure distance required to receive stimuli as distinct

  •   Closely placed stimuli (green dots) = activate mostly the b fiber
  •   Move farther apart (red and blue) = activate mostly the a and c fibers
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8
Q

Afferents are adapting in two ways. what are they and what are they used for ?

A

-  Slowly adapting afferents
•  Generate sustained discharge during ongoing stimulus
•  Provide spatial info; size and shape of stimulus
-  Rapidly adapting afferents
•  Fire rapidly when a stimulus is first presented
•  Fall silent with continual stimulation
•  Convey changes in movement

  • Determined by receptor type
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9
Q

MECHANORECEPTORS SPECIALIZED
FOR TOUCH
Motion detection & grip; _____ adapting
Form & texture; _____ adapting
Cutaneous stretch during movement of fingers to
detect hand shape; _____ adapting
Vibrations (ie skilled usage of tools); _____ adapting

A

Motion detection & grip; rapidly adapting
Form & texture; slowly adapting
Cutaneous stretch during movement of fingers to
detect hand shape; slowly adapting
Vibrations (ie skilled usage of tools); rapidly adapting

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10
Q

Only ____ adapting Merkel cells provide highly accurate representation of Braille pattern

A

Only slowly adapting Merkel cells provide highly accurate representation of Braille pattern

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11
Q

MECHANORECEPTORS SPECIALIZED FOR PROPRIOCEPTION, what are they and what do they convey ?

A
  •   Muscle spindles = coil around muscle fiber bundles; stretch triggers action potentials
  •   Golgi tendons = distributed among tendons; inform on changes in muscle tension
  •   Joint receptors = in and around the joints; relay finger position for range of motion protection
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12
Q

Describe the Dorsal column medial-lemniscus pathway.

A

(serve touch from body)
-  First order neurons
•  Info ascends in columns ipsilaterally in spinal cord to the medulla
•  Topographic organization
••  Fasiculus gracilis to the gracile nucleus = lower limbs
••  Fasciculus cuneatus to cuneate nucleus = upper limbs, trunk and neck
-  Second order neurons
•  Internal arcuate fibers cross (decussation) the midline and form medial lemniscus; remains separated
•  Synapse at ventral posterior lateral nucleus (VPL) of the thalamus
-  Third order neurons
•  VPL neurons send axons to synapse in somatosensory cortex

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13
Q

Describe the Trigeminothalamic pathway.

A

(serve touch from face)
-  First order neurons
•  Cell bodies in trigeminal ganglia
•  Nerve has 3 subdivisions: opthalamic, maxillary, mandibular
•  Enter brainstem at pons to synapse on trigeminal brainstem complex; differ nuclei process differ stimuli submodalities
-  Second order neurons
•  Decussate and ascend as the trigeminothalamic tract
•  Synapse at ventral posterior lateral nucleus (VPL) of the thalamus
-  Third order neurons
•  VPL neurons send axons to synapse in somatosensory cortex

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14
Q

Describe the Spinocerebellar tract.

A

(serve proprioception)
-  First order neurons
•  Bifurcate into ascending and descending branches (dorsal and ventral horns)
•  Lower limbs innervate Clarke’s nucleus in the dorsal horn (blue), upper limbs (blue)
-  Second order neurons
•  Travel to medulla and into the cerebellum via the dorsal
spinocerebellar tract
•  Send collaterals to synapse in nucleus gracilus and travel with third order neurons in medial lemniscus

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15
Q
  •  More laterally located ventral posterior lateral nucleus (VPL) receives projections from ______ (and serve _____)
  •  Medially located ventral posterior medial nucleus (VPM) receives input from _______ (and serve _____)
A
  •  More laterally located ventral posterior lateral nucleus (VPL) receives projections from medial lemniscus (and serve body)
  •  Medially located ventral posterior medial nucleus (VPM) receives input from trigeminal lemniscus (and serve face)
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16
Q

What are the functions of area S1: 3b, 1, 3a, 2

A

Areas of SI :
•  3b and 1: respond to cutaneous stimuli
•  3a = proprioceptors
•  2 = tactile and proprioception

17
Q

what is the function of different areas in S1

A

=  3b: obligatory 1st step in cortical processing
  Lesions produce profound deficits
=  Area 1
  Lesions produce inability to discriminate texture of objects
= Area 2
  Lesions produce inability to discriminate shape of objects

18
Q

Vernon Mountcastle proposal

A

Vernon Mountcastle proposed that neurons with similar response properties might cluster in functionally-distinct columns

19
Q

Pain reception is poorly localized (as is temperature) (T/F)

A

True

20
Q

Nocireceptors

A

•  Free nerve endings network that respond to intense pressure = mechanical
•  Free nerve endings that respond to heat, acids, and capsaicin = thermal, chemical
•  Polymodal respond to all
•  Adapt slowly, if at all
Innervate:
•  Skin
•  Sheath around muscles, internal organs
•  Cornea of the eye
•  Pulp of the teeth

21
Q

Cutaneous somatosensory axons ______ at a greater rate when same stimuli becomes painful; instead nociceptors begin to ______

A

Cutaneous somatosensory axons do not discharge at a greater rate when same stimuli becomes painful; instead nociceptors begin to discharge. (which means pain is processed differently)

22
Q

Difference between fast and slow pain

A
  •   Fast pain
  •   Myelinated (A delta) fibers
  •   Sharp pricking sensation
  •   Well localized
  •  “First pain”
  •   Slow pain
  •   Unmyelinated C fibers
  •   Dull aching
  •   Poorly localized
  •  “Second pain”
23
Q

Generally, cold is processed by _ fibers while warm is processed by _ fibers.

A

Generally, cold is processed by A fibers while warm is processed by C fibers.

24
Q

Describe Anterolateral pathway (pain)

A
  •   First order: neurons synapse in dorsal horn
  •   Second order: neurons decussate and ascend to brainstem and thalamus in the spinothalamic tract

Trigeminothalamic tract = face/head/teeth pain

25
Q

Hyperalgesia

A

Hyperalgesia = heightened sensitivity to painful stimuli

26
Q

Allodynia

A

Allodynia = non-painful stimuli become painful

27
Q

Peripheral sensitization

A

“inflammatory soup” that augments nociceptors response:
•  Reduce firing thresholds
• Interact with metatropic receptors to increase singling.
•  Increase inflammatory mediator production

28
Q

Central sensitization

A

•  Central sensitization = activity-dependent increase in dorsal horn neuron excitability
Can become chronic

29
Q

GATE THEORY OF PAIN

A

= incoming pain signal in dorsal horn is modulated by

activation of large myelinated fibers associated with mechanoreceptors

30
Q

Difference between Endogenous and Exogenous ?

A
  •   Endogenous: endorphins, enkephalins, endocannabinoids

*   Exogenous: opioids

31
Q

REFERRED PAIN

A

When a person feels pain in a part of the body that is remote from the tissue causing pain.
Mechanism: branches of visceral pain fibers synapse in spinal cord on the same neurons from skin = overlap of signals

32
Q

PHANTOM PAIN

A

• Amputees have an illusion that missing limb still present and even painful

Systems Neuroscience (4 decks)

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