Exam 1/ Unit 1 Somatic Sensation Flashcards
(82 cards)
1
Q
What is transduction
A
Stimulus is changed into electrical signal
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)
3
Q
What are the 4 attributes all sensory systems mediate no matter what type of sensation
A
- Modality
- Location
- Intensity
- Timing (Duration)
4
Q
What are the two classifications of nerve fibers
A
- Erlanger’s (A, B, C)
- Lloyd’s (I, II, III, IV)
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)
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=)
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
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
9
Q
What are Lloyd’s fibers used for
A
Used for afferents from receptors in muscles and spinal joints
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
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
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
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
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)
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
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
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)
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
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
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
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
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
23
Q
What is tactile information
A
-The ability to recognize objects placed in the hand on the basis of touch alone
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
25
What is important about receptors in the skin
- 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
26
What is important about receptors in the skin (continued)
- 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
27
What are the categories and perceptions of sensory modalities
- Categories: pressure receptors, cold receptors, warmth receptors, nociceptors
- Perception: wet= + of pressure and temperature receptors, ticklishness= gentle + of pressure receptors, itching= gentle + of nociceptors
28
How are microtextures cool
- 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
29
How do Slow adapting(SA) and Rapidly adapting(RA) fibers differ in perception of tactile mechanoreceptors
- 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
30
What are the Rapidly adapting cutaneous mechanoreceptors
- 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
31
What are the Slowly adapting cutaneous mechanoreceptors
- 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
32
How are the receptors in the skin positioned
- Superficial(small receptive field): Meissner's corpuscles(RA), Merkel's discs(SA)
- Deep(large receptive field): Pacinian corpuscle(RA), Ruffini's end-organ(SA)
33
What is the somatosensory cortex
- 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
What is lateral inhibition
- 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
What are the 2 major pathways of somatosensory cortex
- 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
What is Protopathic from the somatosensory cortex
- Primitive feeling
- Old (phylogenetically)
- Synapse in cord
- Contralateral in cord
- Initiates actions
- Small fibers
- Pain, temp., tickle, itch, sexual sensations
37
What is Epicritic from the somatosensory cortex
- Precise objective information
- New (phylogenetically)
- Synapse in brain stem
- Ipsilateral in cord
- Modify actions
- Large fibers
- Encapsulated mechanoreceptors
38
What are the somatosensory pathways
- 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
What is a clinical significance of a spinal cord lesion
-Hemisection of the cord: Loss of vibration/ proprioception (Ipsilateral), Analgesia (contralateral)
40
How is the somatosensory cortex organized
- 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
Which brodman areas are associated with the somatosensory cortex
- 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
What are the 3 different types of neurons in Brodman area 1 and 2
- 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
What do the Brodman areas 5 and 7 do for the somatosensory cortex
- 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
What is the secondary somatosensory cortex
- 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
What are thermoreceptors
- 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
When are thermoreceptors inactive
-At extremes of skin temperatures 50C thermoreceptors are inactive but nociceptors activity quickly rises
47
When are nociceptors activated
- Mechanical stimuli
- Thermal stimuli
- Chemical stimuli
48
What are the sensations of pain
- Pricking
- Burning
- Aching
- Stinging
- Soreness
49
What is the difference from pain and nociception
- 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
What is the perception of pain
- 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
What does pain do for the body
-Conspicuous sensory experience that warns body of danger
52
Can nociceptors become desensitized
- 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
What is a A delta fiber nociceptive pathway
- Fast
- Glutamate
- Neospinothalmic
- Mechanical, thermal
- Good localization
- Sharp, pricking
- Most terminate in VB complex of thalamus
54
What is a C fiber nociceptive pathway
- 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
What does Substance P and Glutamate do
- 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
What are some nociceptive pathways
- Spinothalamic(major):neo=fast (Adelta), paleo=slow (C fibers)
- Spinoreticular
- Spinomesencephalic
- Spinocervial (mostly tactile)
- Dorsal columns (mostly tactile)
57
What are the cardinal signs of inflammation
- Rubor (redness)
- Calor (heat)
- Tumor (swelling)
- Dolar (pain)
58
What are some pain control mechanisms in the body
- 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
Where are endogenous opioids present
- Periaqueductal gray: encephalin projections to raphe
- Raphe nucleus: serotonin projections to the cord
- Inhibitory interneurons in cord: inhibit 2nd order projection neurons
60
What natural pain controls are found in the brain
- Cannabinoid receptors
| - Endogenous cannabinoids: anandamide, 2-AG, whch is why you get "runners high"
61
What are some reasons for headaches in the intracranial origins
- Meningitis: inflammation of meninges
- Migraine: vasocontraction/ vasodilation
- Irritation of meninges: ex. abuse of alcohol, constipation
62
What are some reasons for headaches in the extracranial origins
- 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
How can CN V cause headaches
- 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
What are the 2 types of muscle receptors
- 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
What are some parts of a muscle spindle
- Nuclear chain: most responsive to muscle shortening
| - Nuclear bag: most responsive to muscle lengthening, dynamic vs static bag
66
What are some sensory endings of a muscle spindle
- 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
Difference of muscle spindle to GTO
- 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
What is the gamma motor system
-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
Details about GTO
- 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
What happens when there is slow voluntary movements
-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
What are neuronal pools
-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
What are two ways of transmission signaling
- 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
What are two types of fibers in neuronal pools
- 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
What are divergence and convergence of neuronal pools
- Divergence: in the same tract, into multiple tracts
| - Convergence: to a single source, from multiple sources
75
What are some prolongation of signals in a neuronal pool
-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
What is a continuous signal output-self excitatory neuronal pool
- continuous intrinsic neuronal discharge: less negative membrane potential
- continuous reverberatory signals: IPS increased with excitation, IPS decreased with inhibition
77
What is a rhythmical signal output
- 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
Is every part of the brain connected to each other
-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
What are evoked potentials (EP)
- 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
What is somatosensory evoked potential
- 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
What are some clinical uses for an evoked potential
- 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
What are sensory nerve conduction studies
- 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
