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S2 Neuroscience > PNS and Sensory Receptors > Flashcards

PNS and Sensory Receptors Flashcards

1
Q

what is sensation

A

the process where sensory receptors receive information from both the internal and external environment and encode the information for transmission to various areas of the nervous system

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2
Q

sensation includes what processes?

A

sensory transduction
receptor potential summation
action potential generation
neural processes that integrate signals centrally by either facilitation (polarization) or inhibition (hyperpolarization)

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3
Q

what is perception

A

the process where the CNS receives and interprets the sensation based on

  • present experiences
  • present state of the internal and external environment
  • memory of similar situations
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4
Q

where does perception and its refinement occur?

A

thalamus
basal ganglia
cerebellum
cortex

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5
Q

perception at the cortical level is usually considered…

A

conscious perception

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6
Q

perception at the level of the cerebellum is considered…

A

unconscious perception

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7
Q

how may the basal ganglia be involved in perception

A

unconscious representations of movement experiences

perception of inter- and intrapersonal space

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8
Q

without the cortex, perceptions are…

A

incomplete or skewed from the normal which may include lack of localization, anesthesia, or hyperesthesia, paresthesia

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9
Q

what is sensory transduction

A

changing the energy of a stimulus into a neural energy

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10
Q

sensory transduction

  • what type of energy can it be
  • how does it produce a change
A

energy may be mechanical, chemical, light
how
-produces a change in the receptor membrane such that a local potential difference occurs
-i.e. Na+, K+, and Cl- channels open to allow ion movement
this potential change is local and spreads only a few millimeters as it decays

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11
Q

what is the “threshold for stimulation”

A

amount of stimulus energy it takes to cause a local receptor potential
threshold depends on receptor

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12
Q

what is the “threshold for perception”

A

lowest stimulus intensity necessary for perception of stimulus
usually the same as receptor threshold, but may be modified by context and experience

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13
Q

what is adaptation

A

the duration for which the receptor potential is generated to the stimulus

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14
Q

adaptation is determined by…

-examples

A

morphology of the receptor
eg. Pacinian corpuscle receptor potential is RAPIDLY adapting and thus a generator potential is only generated when the stimulus comes on or off
-APs will only be generated at onset and offset of stimulus
Ruffini corpuscles are slowly adapting and continue to signal throughout the duration of the stimulus

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15
Q

quality - specificity coding

-how does our nervous system discern different types of sensation via the receptors?

A

receptors are specialized by their morphology to respond to only one type of stimulus

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16
Q

stimulus intensity

  • directly related to…
  • what happens once the stimulus intensity is determined
A

size of the receptor potential
number of receptors activated
after stimulus is coded, it is transferred to the generation of an AP and coded by the frequency of AP and the number of discharge fibers

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17
Q

as a stimulus intensity increases, what happens to the

  • AP frequency
  • AP amplitude
  • AP speed
A

only frequency changes (increases)

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18
Q

what is a receptive field

A

area surrounding the receptor that when stimulated excited or inhibits the firing of a particular cell

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19
Q

where is the concentration of receptive fields the greatest

A

tips of fingers and tongue
-smallest receptor fields
-most sensitive parts of the body
as you move proximally, receptive field size increases and density of receptors decreases

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20
Q

what is a dermatome

A

area of the body surface contributing sensory input to one dorsal root

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21
Q

two concepts related to somatotopic organization of the CNS

A

lateral inhibition

orderal mapping of sensations from body surface onto CNS areas

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22
Q

what is lateral inhibition

-function

A

excitatory discharge is greatest at center of receptive field, and is inhibitory at the periphery
serves to sharpen peak of activity within the brain

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23
Q

where does lateral inhibition occur

A

first in the dorsal column nuclei
then at subsequent synapses in the CNS
also present in visual system

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24
Q

lateral inhibition function in the visual system

A

serves to enhance distinction between two stimuli and aids in recognition of pattern and contour

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25
Q

what areas are responsible for orderly mapping of sensation from body surface onto CNS areas

A

dorsal column nuclei
thalamus
somatosensory cortex
(termed the sensory homunculus)

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26
Q

the areas with the largest receptor density will have the largest…

A

cortical receptive field

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27
Q

some cells in the sensory cortex respond to specific…

A

orientation, movement, and shape of stimulus

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28
Q

what are different ways of classifying sensory receptors

A

according to stimulus location
according to sensory system
according to stimulus energy

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29
Q

sensory receptor classificiation based on stimulus location

A

exteroceptors
-stimuli from the external environment
proprioceptors
-position of body segments relative to each other and position of body and head in space
interoceptors
-signal body events such as blood glucose level and blood pressure

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30
Q

sensory receptor classificiation based on sensory system

A 
somatic
-tactile, joint, muscle, tendon, thermal, pain
visual
vestibular
auditory
olfactory
gustatory
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31
Q

sensory receptor classification according to stimulus energy

A 
mechanoreceptors
-touch/pressure, proprioception, air waves
chemoreceptors
-taste, smell, blood gas level
nocipeptors
-damaging stimuli
thermoreceptors
-heat and cold
photoreceptors
-light
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32
Q

sensory fiber types

A 
Ia (A-alpha)
Ib (A-alpha)
II (A-beta)
III (Adelta)
IV (C)
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33
Q

Ia sensory fibers

  • diameter (um)
  • conduction velocity m/s
  • receptors innervated
A

12-20 um
70-120 m/s
receptors
-primary afferents of muscle spindle

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34
Q

Ib sensory fibers

  • diameter (um)
  • conduction velocity m/s
  • receptors innervated
A

12-20
70-120
receptors
-golgi tendon organ

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35
Q

type II sensory fibers

  • diameter (um)
  • conduction velocity m/s
  • receptors innervated
A 
5-14 um
30-70
receptors
-secondary afferents of muscle spindle
-touch
-pressure
-vibration
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36
Q

type III sensory fibers

  • diameter (um)
  • conduction velocity m/s
  • receptors innervated
A 
2-7
12-30
receptors
-touch and pressure
-pain and temperature (cold)
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37
Q

type IV sensory fibers

  • diameter (um)
  • conduction velocity m/s
  • receptors innervated
A

0.5-1
0.5-2
receptors
-pain and temperature (warm)
-unmyelinated fibers

38
Q

conduction velocity

-effect of size

A

small diameter fibers are slower because they provide more resistance to flow of current and have less insulation from myelin

39
Q

which fibers are small diameter?

-large diameter

A

small
-free nerve endings (Ad, C)
large
-encapsulated nerve endings (Ia, Ib, II)

40
Q

AP amplitude

-effect of size

A

small diameter fibers have lower amplitude because potential change across the membrane is smaller
can distinguish size by size of EMG amplitude

41
Q

threshold for stimulus

-effect of size

A

small diameter have a higher threshold for stimulation because they offer more resistance to current
-C will require higher intensity

42
Q

motor fiber types

A

alpha (A-a)
gamma (A-y)
preganglionic ANS fibers (B)
postganglionic ANS fibers (C)

43
Q

alpha motor fibers

  • diameter (um)
  • conduction velocity (m/s)
  • role
A

12-20
15-120
role
-motor neuron innervating extrafusal muscle fiber

44
Q

gamma motor fibers

  • diameter (um)
  • conduction velocity (m/s)
  • role
A

2-10
10-45
role
-motor neuron innervating intrafusal muscle fiber

45
Q

preganglionic ANS fibers (B)

  • diameter (um)
  • conduction velocity (m/s)
  • role
A

> 3
3-15
role
-lightly myelinated

46
Q

postganglionic ANS fibers (C)

  • diameter (um)
  • conduction velocity (m/s)
  • role
A

1
2
unmyelinated

47
Q

type I joint mechanoreceptors

-structure

A

structure

-encapsulated “Ruffini-like”

48
Q

type I joint mechanoreceptors

-location

A

ligaments
joint capsule
proximal joints

49
Q

type I joint mechanoreceptors

-response

A

mechanoreceptors, slow adapting, low threshold

active during movement and at rest

50
Q

type I joint mechanoreceptors

-function

A

contributes to regulation of postural muscle tone
kinesthesia
regulation of muscle tone during movement

51
Q

type II joint mechanoreceptors

-structure

A

encapsulated “paciniform”

52
Q

type II joint mechanoreceptors

-location

A

synovial junction of joint capsule
fat pads of joint
distal joints

53
Q

type II joint mechanoreceptors

-response

A

mechanoreceptors, rapidly adapting, low threshold

active at beginning and end of movement

54
Q

type II joint mechanoreceptors

-function

A

provides information about beginning and end of joint movement
may help “boost” muscle tone at beginning of movement to overcome inertia

55
Q

type III joint mechanoreceptors

-structure

A

encapsulated “GTO-like”

56
Q

type III joint mechanoreceptors

-location

A

ligaments

all joint of the body

57
Q

type III joint mechanoreceptors

-response

A

mechanoreceptors, slow adapting, high threshold

active at extremes of range and with longitudinal traction

58
Q

type III joint mechanoreceptors

-function

A

response to sudden joint movements and may cause reflex muscle contraction to limit further movement

59
Q

type IV joint mechanoreceptors

-structure

A

free nerve endings

60
Q

type IV joint mechanoreceptors

-location

A 
joint capsule
ligaments
periosteum
synovial lining
fat pads
61
Q

type IV joint mechanoreceptors

-response

A

pain receptor, slow adapting, high threshold

active with extreme mechanical force or chemical irritation

62
Q

type IV joint mechanoreceptors

-function

A

may contribute to a flexion reflex, or to a co-contraction pattern around a joint to prevent further movement

63
Q

thermal afferents

  • function
  • primary receptor
A

encode temperature changes sensed by skin (normal skin temperature is 34 C)
primary receptor is the free nerve ending located in the dermal layer of the skin

64
Q

thermal afferent primary receptors

  • continuous with
  • location of highest concentration
A

continuous with A delta and C fibers

highest concentration located near midline

65
Q

how are thermal afferent receptors classified

A

response to cold or heat

66
Q

cold afferents respond to temperature changes in what range

A

10-33 C

67
Q

cold travels over what fiber types

A

A delta and C

68
Q

heat afferents respond to temperature changes in what range

A

32-45 C

some respond to 45+

69
Q

heat afferents travel over what fiber types

A

C fibers

70
Q

nociceptors

  • location
  • free or encapsulated primary receptor nerve ending
A

location
-dermal layers of the skin
-many deep tissues including muscles and joints
free nerve ending

71
Q

primary stimulus for nociceptors

A

mechanical damage to tissue, either by temerature extremes or destruction fo tissue (mechanical, chemical)`

72
Q

cutaneous nociceptive afferents

-fiber type classification

A

a delta mechanoreceptive nociceptor
a delta mechanothermal nociceptors
C-polymodal nociceptors

73
Q

A-delta mechanoreceptive receptors

  • characteristic
  • primary stimulus
  • sensitized by…
A

high threshold for stimulation with small receptive areas, 20% that lie within fascial planes
primary stimulus
-sharp pain allowing for discrimination between sharp and dull
sensitized by
-intense heat that results in burn hyperalgesia

74
Q

A-delta mechanothermal nociceptors

  • maximally responsive to…
  • responsible for…
A 
maximally responsive to temperature between 45-53 C
-also respond to temperatures <20 C
receptors are responsible for
-first pain from intense thermal stimuli
-intense mechanical stimuli
75
Q

C-polymodal nociceptors

  • majority of _____
  • what type of nerve ending
  • activated buy…
A 
majority of cutaneous receptors (>90%)
free nerve endings
activated by
-thermal (<10 C and >45 C)
-mechanical (crush)
-chemical (histamine release from tissue damage)
76
Q

muscle and joint nociceptive afferents

  • have what fiber components
  • how are these fibers activated
A

have both A delta and C fiber components
A-delta
-activated by muscle stretch or contraction - ergoceptive
C fibers
-activated by intense mechanical or chemical stimuli - ischemic muscle pain

77
Q

joint nociceptive afferent receptors (both A-delta and C) are activated by…

  • sensitized by
  • this develops into a high background firing in the presence of…
A

activated by intense pressure and movement
sensitized by inflammation
develops into a high background firing in the presence of inflammation

78
Q

visceral nociceptive afferents

  • fiber type
  • similar fiber to…
  • relay what type of information
  • stimulated by…
A

C fibers similar to C polymodal nociceptors
relay poorly localized and referred information
stimulated by
-twisting
-distention
-inflammation

79
Q

types of vestibular (and auditory) receptors

A

hair cells

stereocilia and kinocilia

80
Q

hair cells

  • location
  • types
  • how are they activated
A

vestibular apparatus
two types
activated by acceleration of the head by a mechanism knows as mechanoelectrical transduction
-basically a mechanical deflection of stereocilia and kinocilia

81
Q

stereocilia and kinocilia

  • what is the model?
  • cliia anchored together by…
A

gated spring model
cilia are anchored together by a protein link that is attached to (or near) leaky K+ and Ca++ channels, not Na+ as other excitable membranes

82
Q

stereocilia and kinocilia

  • upon deflection
  • results in…
A

upon deflection, channels are modified (opened or closed) to increase or decrease the influx of ions
this mechanical deflection results in an increase or decrease in the release of neurotransmitter (glutamate?) onto the 1st order neuron

83
Q

structure of receptor apparatus

A 
ampulla of the semicircular canals and macula of the saccule and utricle
receptor apparatus (ampulla or macula) is bathed in endolymph, a fluid high in K+
inertial movement of the endolymph results in a corresponding movement of the stereocilia in relation to the kinocilia resulting in an opening or closing of the leaky channels
84
Q

visual receptor types

-function and location of each

A 
rods and cones
rods
-more active at times of low light
-located at the periphery of the retina
cones
-most active in bright light
-located in the foveal (central) region of the retina
85
Q

visual receptor are leaky

  • similar to…
  • result
A

similar to hair cells of the vestibular system

results in a continual release of neurotransmitter

86
Q

when visual receptor is activated by light, what happens

A

it becomes hyperpolarized and results in a decrease in neurotransmitter release

87
Q

the output of the retina is the…

A

ganglion cell

88
Q

prior to the gangion cell of the retina being activated, what happens

A

a great deal of integration by multiple synapses through bipolar cells, horizontal cells, and maacrine cells

89
Q

end result of ganglion cell activation

A

receptive fields are defined for ganglion cells

  • large RFs representing peripheral vision
  • smaller more precise RFs representing central vision
90
Q

receptor fields distribution corresponds with the distribution of…

A

rods and cones respectively

  • large RFs correspond with rods
  • small RFs correspond with cones
91
Q

what types of inhibiton are demonstrated using central vision and the activation of cones

A

surround inhibition

lateral inhibition

S2 Neuroscience (25 decks)

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