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Neurophysiology > Exam 1/ Unit 1 Somatic Sensation > Flashcards

Exam 1/ Unit 1 Somatic Sensation Flashcards

1
Q

What is transduction

A

Stimulus is changed into electrical signal

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2
Q

Different types of transduction stimuli

A
  • Mechanical
  • Chemical
  • Change in temperature (warmth, cold, nociceptors also respond to extreme temps)
  • Electromagnetic (rods and cones in retina)
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3
Q

What are the 4 attributes all sensory systems mediate no matter what type of sensation

A
  • Modality
  • Location
  • Intensity
  • Timing (Duration)
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4
Q

What are the two classifications of nerve fibers

A
  • Erlanger’s (A, B, C)

- Lloyd’s (I, II, III, IV)

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5
Q

What does the speed of conduction depend on

A
  • Fiber diameter
  • Myelination
  • 1 micron = 1 m/s (unmyelinated)
  • Myelination increases conduction velocity 6 fold
    (ex. 2 microns = 12 m/s)
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6
Q

What is the diameter/velocity ratios of Erlanger’s fibers

A 
-A (alpha 8-20microns=50-120m/s, 
beta 5-12microns=30-70m/s,
delta 2-8microns=10-50m/s, gamma 1-5microns=3-30m/s)
-B (1-3microns=3-15m/s)
-C (1micron=)
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7
Q

What are Erlanger’s fibers used for

A
  • Motor nerves and skin afferents
  • Motor fibers mostly A(alpha), A(delta)
  • Skin afferents are mostly groups A(beta), A(gamma), and C
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8
Q

What are the diameter/velocity ratios of Lloyd’s fibers

A
  • I 12-20microns=70-120m/s
  • II 4-12microns=24-70m/s
  • III 1-4microns=3-24m/s
  • IV
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9
Q

What are Lloyd’s fibers used for

A

Used for afferents from receptors in muscles and spinal joints

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10
Q

How does a receptor potential work

A
  • Change in the receptor potential is associated with opening of ion (Na+) channels
  • Threshold as the receptor potential becomes less negative, the frequency of AP into the CNS increases
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11
Q

What is the labeled line principle

A

-Labeled line principle refers to the specificity of nerve fibers transmitting only one modality of sensation

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12
Q

What are some examples of the labeled line principle

A

-Type of sensation felt when a nerve fiber is stimulated(pain, touch, sight, sound) is determined by termination point in CNS

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13
Q

What happens when a neuron shows adaptation to a stimulus

A

In response to a sustained stimulus a neuron will show a decreased firing rate over time

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14
Q

Do tonic contractions adapt to continual stimulation

A
  • No
  • Examples: joint capsules, muscle spindles, Merkel’s discs(punctate receptive fields), Ruffini end organ’s “corpuscles” (activated by stretching the skin)
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15
Q

What on or in the body adapts quickly to stimulus

A
  • Hair receptors 30-40Hz
  • Pacinian corpuscles 250Hz
  • Meissner’s corpuscles 30-40Hz
  • (Hz represents optimum stimulus rate)
  • Reacts strongly when a change is taking place
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16
Q

What is the mechanism of adaptation

A
  • Membrane adaptation is thought to be due to entry of calcium ions during action potentials (AP)
  • Ca++ opens a K+ channel increasing permeability of the membrane for K+ taking membrane away from threshold
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17
Q

What is the most heavily sensory innervated section of the spinal cord

A
  • Cervical joints have a tremendous amount of innervation

- 4 types of sensory receptors (Type I, II, III, IV)

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18
Q

What are the type 1 mechanoreceptors of the spinal cord

A
  • Outer layer of joint capsule
  • Fire at a degree proportional to joint movement or traction
  • Low threshold
  • Dynamic- fire without movement
  • Slow adapting
  • Tonic effects on lower motor neuron pools
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19
Q

What are the type 2 mechanoreceptors of the spinal cord

A
  • Deep layers of joint capsule
  • Low threshold
  • Rapidly adapting
  • Completely inactive in immobilized joints
  • Functions in joint movement monitoring
  • Phasic effects on lower motor neuron pools
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20
Q

What are the type 3 mechanoreceptors of the spinal cord

A
  • Recently found in spinal joints
  • Very high threshold
  • Slow adaptation
  • Joint version of Golgi tendon organ
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21
Q

What are the type 4 mechanoreceptors of the spinal cord

A
  • Nociceptors
  • Very high threshold
  • Completely inactive in physiologic normal joint
  • Activation with joint narrowing, increased capsule pressure, chemical irritation
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22
Q

What do the mechanoreceptors in our fingers do

A
  • Firstly info is transmitted to our brain from mechanoreceptors in fingers
  • Feel shape and texture of objects
  • Play musical instruments
  • Type on computers
  • Palpate and preform adjustments
  • Preform tasks using our hands
  • Tactile info is fragmented by receptors and must be integrated by the brain
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23
Q

What is tactile information

A

-The ability to recognize objects placed in the hand on the basis of touch alone

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24
Q

What is stereognosis

A
  • The ability to perceive form through touch
  • Tests the ability of dorsal column-medial lemniscal system to transmit sensations from the hand
  • Also tests ability of cognitive processes in the brain where integration occurs
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25
Q

What is important about receptors in the skin

A
  • Most objects are larger than the receptive field of any one receptor in the hand
  • The object stimulates a large population of sensory nerve fibers (each of which scan a small portion of the object)
  • Deconstruction occurs at the periphery
  • By analyzing which fibers have been stimulated the brain reconstructs the pattern
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26
Q

What is important about receptors in the skin (continued)

A
  • No single sensory axon or class of sensory axons signals all relevant information
  • Spatial properties are processed by populations of receptors that form many parallel pathways
  • CNS constructs a coherent image of an object from fragmented information conveyed in multiple pathways
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27
Q

What are the categories and perceptions of sensory modalities

A
  • Categories: pressure receptors, cold receptors, warmth receptors, nociceptors
  • Perception: wet= + of pressure and temperature receptors, ticklishness= gentle + of pressure receptors, itching= gentle + of nociceptors
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28
Q

How are microtextures cool

A
  • Humans can detect extremely fine textures
  • When such fine textures are stroked on the fingerpad skin, the fingerprint ridges vibrate and cause Pacinian Corpuscles to respond enabling the detection of the microtexture
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29
Q

How do Slow adapting(SA) and Rapidly adapting(RA) fibers differ in perception of tactile mechanoreceptors

A
  • Depth of indentation and change in curvature of the skin surface are encoded by discharge rates of SAs
  • Velocity and rate of change in skin surface curvature are encoded by discharge rates of both SAs and RAs
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30
Q

What are the Rapidly adapting cutaneous mechanoreceptors

A
  • Meissner’s corpuscles in glabrous(non hairy) skin: concentrated in finger tips, signals edges, register sideways shearing of the skin
  • Hair follicle receptors in hairy skin
  • Pacinian corpuscles in subcutaneous tissue
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31
Q

What are the Slowly adapting cutaneous mechanoreceptors

A
  • Merkel’s discs have punctate receptive fields: senses curvature of an object’s surface
  • Ruffini end organs activated by stretching the skin: even at some distance away from receptor
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32
Q

How are the receptors in the skin positioned

A
  • Superficial(small receptive field): Meissner’s corpuscles(RA), Merkel’s discs(SA)
  • Deep(large receptive field): Pacinian corpuscle(RA), Ruffini’s end-organ(SA)
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33
Q

What is the somatosensory cortex

A
  • It receives projections from the thalamus
  • Somatotopic organization (homunculus which is that diagram with the parts of the body associated to the parts of the brain)
  • Each central neuron has a receptive field
  • Size of cortical representation varies in different areas of skin(based on density of receptors)
34
Q

What is lateral inhibition

A
  • Where 1st order neuron synapses it excites a 2nd order neuron as well as local interneurons that- neighbor the 2nd order neurons(surround inhibition)
  • A cell + more than average will have a larger effect on its neighbors than they will have on it
  • Found universally within the CNS
  • Enhances edges but does not improve acuity
35
Q

What are the 2 major pathways of somatosensory cortex

A
  • Dorsal column-medial lemniscal system (Epicritic): most aspects of touch and proprioception, 1st order neurons synapse in the brain stem
  • Anterolateral system (protopathic): Sensations of crude touch, nociception, temperature, tickle, itch, and sexual sensation. 1st order neurons synapse in the dorsal horn of the spinal cord
  • 2nd order neurons of both pathways cross to other side and ascend, synapsing in the thalamus
36
Q

What is Protopathic from the somatosensory cortex

A
  • Primitive feeling
  • Old (phylogenetically)
  • Synapse in cord
  • Contralateral in cord
  • Initiates actions
  • Small fibers
  • Pain, temp., tickle, itch, sexual sensations
37
Q

What is Epicritic from the somatosensory cortex

A
  • Precise objective information
  • New (phylogenetically)
  • Synapse in brain stem
  • Ipsilateral in cord
  • Modify actions
  • Large fibers
  • Encapsulated mechanoreceptors
38
Q

What are the somatosensory pathways

A
  • If 1st order neurons synapse in the spinal cord (anterolateral system), then 2nd order neurons cross over at the spinal cord level
  • If 1st order neurons synapse in the brain stem (dorsal column, medial lemniscal system), then 2nd order neurons cross over at the brain stem level
39
Q

What is a clinical significance of a spinal cord lesion

A

-Hemisection of the cord: Loss of vibration/ proprioception (Ipsilateral), Analgesia (contralateral)

40
Q

How is the somatosensory cortex organized

A
  • Into columns by submodality
  • Cortical neurons defined by receptive field and modality: some columns are activated by RA Messiner’s, others by SA Merkel’s, still others by Paccinian corpuscles
  • Most nerve cells are responsive to only one modality
41
Q

Which brodman areas are associated with the somatosensory cortex

A
  • Brodman area 3, 1, 2(dominate input)
  • 3a- from muscle stretch receptors(spindles)
  • 3b- from cutaneous receptors
  • 2- from deep pressure receptors
  • 1 RA cutaneous receptors
  • These 4 areas are extensively interconnected(series and parallel)
  • Each of the 4 regions contain a complete map of the body surface
42
Q

What are the 3 different types of neurons in Brodman area 1 and 2

A
  • They have complex detection capabilities
  • Motion sensitive neurons: respond well to movement in all directions but not to movement in any one direction
  • Direction-sensitive neurons: respond much better to movement in one direction than in another
  • Orientation-sensitive neurons: respond best to movement along a specific axis
43
Q

What do the Brodman areas 5 and 7 do for the somatosensory cortex

A
  • Brodman 5: integrates tactile info. from mechanoreceptors in skin with proprioceptive inputs from underlying muscles and joints
  • Brodman 7: receives visual, tactile, proprioceptive inputs(integrates stereognostic and visual info.)
  • They project to motor areas of frontal lobe
  • Sensory initiation and guidance of movement
44
Q

What is the secondary somatosensory cortex

A
  • Located in superior bank of the lateral fissure
  • Projections from 1st motor neurons required for function of the 2nd motor neuron
  • Projects to the insular cortex, which innervates regions of temporal lobe believed to be important in tactile memory
45
Q

What are thermoreceptors

A
  • Sensitive to temperature of the skin
  • Two types: cold(as skin is warmed, becomes inactive), warm(as skin is cooled, becomes inactive)
  • SA
  • Discharge spontaneously under normal conditions
  • Discharge phasically when skin temperature changes rapidly
46
Q

When are thermoreceptors inactive

A

-At extremes of skin temperatures 50C thermoreceptors are inactive but nociceptors activity quickly rises

47
Q

When are nociceptors activated

A
  • Mechanical stimuli
  • Thermal stimuli
  • Chemical stimuli
48
Q

What are the sensations of pain

A
  • Pricking
  • Burning
  • Aching
  • Stinging
  • Soreness
49
Q

What is the difference from pain and nociception

A
  • Nociception: reception of signals in CNS evoked by stimulation of specialized sensory receptors(nociceptors) that provide info. about tissue damage
  • Pain: perception of adversive or unpleasant sensation that originates from a specific region of the body
50
Q

What is the perception of pain

A
  • All perception involves an abstraction and elaboration of sensory inputs
  • Highly subjective nature of pain is one of the factors that make it difficult to define and treat clinically
51
Q

What does pain do for the body

A

-Conspicuous sensory experience that warns body of danger

52
Q

Can nociceptors become desensitized

A
  • Yes
  • Hyperalgesia: repeated heating, axon reflex may cause spread of hyperalgesia in periphery, sensitization of central nociceptors neurons as a result of sustained activation
53
Q

What is a A delta fiber nociceptive pathway

A
  • Fast
  • Glutamate
  • Neospinothalmic
  • Mechanical, thermal
  • Good localization
  • Sharp, pricking
  • Most terminate in VB complex of thalamus
54
Q

What is a C fiber nociceptive pathway

A
  • Slow
  • Substance P/ glutamate
  • 1st degree paleospinaothalamic
  • Polymodal/chemical
  • Poor localization
  • Dull, burning, aching
  • Diffuse termination(reticular formation, tectal area of mesencephalon, periaqueductal gray matter)
55
Q

What does Substance P and Glutamate do

A
  • Glutamate: effects are transient and short acting(the fast components of C-fiber)
  • Substance P: released more slowly and concentration builds over seconds/minutes, responsible for longer lagging predominant effect(slow pain)
56
Q

What are some nociceptive pathways

A
  • Spinothalamic(major):neo=fast (Adelta), paleo=slow (C fibers)
  • Spinoreticular
  • Spinomesencephalic
  • Spinocervial (mostly tactile)
  • Dorsal columns (mostly tactile)
57
Q

What are the cardinal signs of inflammation

A
  • Rubor (redness)
  • Calor (heat)
  • Tumor (swelling)
  • Dolar (pain)
58
Q

What are some pain control mechanisms in the body

A
  • Peripheral (Gating theory: involves inhibitory interneuron in cord impacting nociceptors, inhibited by C fibers, stimulated by A alpha and beta fibers, TENS)
  • Central (endogenous opioids, endogenous cannabinoids)
59
Q

Where are endogenous opioids present

A
  • Periaqueductal gray: encephalin projections to raphe
  • Raphe nucleus: serotonin projections to the cord
  • Inhibitory interneurons in cord: inhibit 2nd order projection neurons
60
Q

What natural pain controls are found in the brain

A
  • Cannabinoid receptors

- Endogenous cannabinoids: anandamide, 2-AG, whch is why you get “runners high”

61
Q

What are some reasons for headaches in the intracranial origins

A
  • Meningitis: inflammation of meninges
  • Migraine: vasocontraction/ vasodilation
  • Irritation of meninges: ex. abuse of alcohol, constipation
62
Q

What are some reasons for headaches in the extracranial origins

A
  • Muscle spasms: connective tissue bridges between muscle and dura in upper cervical spine
  • Irritation of nasal passages
  • Eye disorder
  • Cervical joint dysfunction
  • Traction of dura
63
Q

How can CN V cause headaches

A
  • CN V innervates most of the head and face
  • CN V nucleus of termination extends down to C2 level
  • Some cervical joint afferent synapse directly in CN V nuclei
  • Overlap between CN V and C2 can cause headache associated with cervical dysfunction
64
Q

What are the 2 types of muscle receptors

A
  • Muscle spindles: respond to stretch, located within belly of muscle in parallel with extrafusal fibers, innervated by 2 types of myelinated afferent fibers(group Ia large diameter) and (group II small diameter), also innervated by gamma motor neurons that regulate sensitivity of spindle
  • Golgi tendon organ: responds to tension, located at muscle and tendon junction, innervated by Ib afferent fibrer
65
Q

What are some parts of a muscle spindle

A
  • Nuclear chain: most responsive to muscle shortening

- Nuclear bag: most responsive to muscle lengthening, dynamic vs static bag

66
Q

What are some sensory endings of a muscle spindle

A
  • Primary: usually 1/ spindle and include all branches of Ia afferent axon (innervate all three types, much more sensitive to rate of change of length than secondary endings)
  • Secondary: usually 1/ spindle from group II afferent (innervate only chain and static bag, info. about static length of muscle)
67
Q

Difference of muscle spindle to GTO

A
  • Spindle: afferent innervation( Ia, II), efferent innervation (delta fiber), relationship to extrafussal fiber (parallel), stimulus (stretch), reflex response (contraction of extrafusal fibers)
  • GTO: afferent innervation( Ib), efferent innervation (none), relationship to extrafusal fiber (series), stimulus (contraction/ tension), reflex response (inhibition of extrafusal fibers)
68
Q

What is the gamma motor system

A

-Innervates intrafusal fibers
-Reticular formation (Mesencephalic area appears to regulate rhythmic gate)
-Vestibular system
(Lateral vestibulospinal tract facilitates gamma motor neuron antigravity control)
-Cutaneous sensory receptors (Over skeletal muscle, sensory afferent activating gamma motor neurons)

69
Q

Details about GTO

A
  • Sensitive to changes in tension
  • Stretching tendon organ straightens collagen bundles which compresses & elongates nerve endings causing them to fire which inhibits muscle contraction
  • Firing rate very sensitive to changes in tension
  • Greater response associated with contraction vs. stretch
70
Q

What happens when there is slow voluntary movements

A

-The Ia afferent firing rate from the spindle can: Increase spindle rate of shortening > extrafusal fiber, Decrease spindle rate of shortening < extrafusal fiber, stay the same spindle rate of shortening when the extrafusal fiber stays the same

71
Q

What are neuronal pools

A

-Number of neurons in these pools vary from a few to a vast number
-Each pool has its own special characteristics of organization which affects the way it processes signals
despite differences in function, pools share many similar principles

72
Q

What are two ways of transmission signaling

A
  • Spatial summation: increasing signal strength transmitted by progressively greater # of fibers
  • Temporal summation: increasing signal strength by increasing frequency of IPS (impulses per second)
73
Q

What are two types of fibers in neuronal pools

A
  • Input fibers: divide hundreds to thousands of times to synapse with arborized dendrites, stimulatory field
  • Output fibers: impacted by input fibers but not equally, excitation-supra-threshold stimulus, facilitation-sub-threshold stimulus
74
Q

What are divergence and convergence of neuronal pools

A
  • Divergence: in the same tract, into multiple tracts

- Convergence: to a single source, from multiple sources

75
Q

What are some prolongation of signals in a neuronal pool

A

-Synaptic Afterdischarge:
postsynaptic potential lasts for msec, can continue to excite neuron
-Reverberatory circuit:
positive feedback within circuit due to collateral fibers which restimulate itself or neighboring neuron in the same circuit, subject to facilitation or inhibition

76
Q

What is a continuous signal output-self excitatory neuronal pool

A
  • continuous intrinsic neuronal discharge: less negative membrane potential
  • continuous reverberatory signals: IPS increased with excitation, IPS decreased with inhibition
77
Q

What is a rhythmical signal output

A
  • Almost all result from reverberating circuits
  • Excitatory signals can increases amplitude and frequency of rhythmic output
  • Inhibitory signals can decrease amplitude and frequency of rhythmic output
78
Q

Is every part of the brain connected to each other

A

-Almost every part of the brain connects with every other part directly or indirectly
-Problem of over-excitation (epileptic seizure)
-Problem controlled by:
inhibitory circuits, fatigue of synapses, decreasing resting membrane potential, long-term changes by down regulation of receptors

79
Q

What are evoked potentials (EP)

A
  • Sensory EP is a change in EEG resulting from stimulation of a sensory pathway
  • Sensory EP is extracted from EEG using computer averaging techniques
  • EEG is recorded during repetitive natural stimulation (eg. tap on skin or flash of light)
  • Computers samples the EEG before and after stimulation and sample data are averaged
  • Clinically useful for assessing the function of sensory systems or evaluating demyelinating diseases
80
Q

What is somatosensory evoked potential

A
  • Repetitive electrical stimulation of a peripheral nerve is used to elicit the SSEP which are recorded over the scalp and spine
  • Configuration & latency of the responses depend on the nerve that is stimulated
81
Q

What are some clinical uses for an evoked potential

A
  • Detection of lesions in multiple sclerosis: functional status sometimes undetected with MRI
  • Detection of other CNS disorders: e.g. Spinocerebellar degeneration
  • Assessment and prognosis following CNS injury (trauma or hypoxia)
  • Intraoperative monitoring
82
Q

What are sensory nerve conduction studies

A
  • Stimulation of nerve to measure conduction velocity& amplitude of action potentials in sensory fibers when these fibers are stimulated at one point and response recorded at another point along course of the nerve
  • Provide a means of confirming the presence and extent of peripheral nerve damage

Neurophysiology (1 decks)

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