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27 Cards in this Set
- Front
- Back
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Compared to other sensory systems, what is unique about the somatosensory system with respect to distribution throughout the body?
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It's distributed throughout the body as opposed to concentrated in one are.
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Describe the basic pathway for all sensory stimuli to be perceived from stimulus to the end.
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Stimulus -->Sensory Receptors --> Spinal Cord --> Medulla/Brainstem --> Thalamus to Cortex
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What does the dorsal root ganglion house? What type of neurons are they?
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Cell bodies of sensory neurons. They are pseudounipolar cell bodies with peripheral and central processes (i.e. one going to CNS and one going to PNS)
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What are the three categories of sensory receptors?
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1. Exteroreceptive
2. Proprioceptive 3. Interoceptive |
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What are the three types of Exteroreceptive receptors and what does each one sense?
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1. Mechanoreceptors - touch (non-pain)
2. Thermoreceptors - warming and cooling (non-pain) 3. Nociceptors - sharp and burning pain (remember noncer = no harm) 3. Nociceptors |
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What are the two types of proprioceptive receptors and what does each one sense?
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1. Muscle afferent receptors called Golgi Tendon Organs and Muscle Spindles that code info for muscle length and muscle tension
2. Joint and tendon afferents - code info re joint angles |
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What do Interoceptive receptors sense and what is an example.
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They are visceral afferent receptors that code information about changes inside the body. Eg Baroreceptors are Interoceptive receptors - they localize sensation and pain poorly.
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What is "Receptive Field"?
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It is the area in the periphery where application of an adequate stimulus causes response.
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Pacinian corpuscle detects what sensation and is a modified...?
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Detects high frequency vibration and is a modified Schwaan Cell.
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How is a signal generated by a receptor? Use the Pacinian Corpuscle as an example. There are four steps/features
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1. Stimulus activates receptors and ion channels
2. This generates receptor potential 3. If R potential is strong enough, it generates an action potential 4. Signal (action potentials) are conveyed to spinal cord. |
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What are the two ways that the intensity of a stimulus is encoded? (there is a specific name for both)
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1. Rate Code = Frequency of action potential firing
2. Spatial Summation Code = Number of neurons firing |
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As you know, the speed of an action potential transmission depends on Axon Diameter and Thickness of Myelin. What are the three types of fibers that are classified according to how fast they transmit an action potential? And give examples of each.
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1. A-alpha and A-beta fibers are large myelinated fibers that conduct APs very fast (eg pain)
2. A-gamma fibers are thin myelinated fibers that conduct APs moderately fast (eg temp) 3. C fibers are unmyelinated fibers that conduct APs slowly (eg warming, non-pain stim) |
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Think/Describe how measuring action potential speed can be used diagnostically (see pg 82). What are some diseases that can slow an AP?
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An AP is generated at the elbow and detected at the hand. A-alpha fibers will be detected first, then A-gamma and then C fibers. If any of these are shifted to the left (i.e. takes longer to transmit) then there is a neuropathy. Eg diabetes, shingles, nerve entrapment, MS, nutritional deficiencies
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What are the four characteristics that set the sensitivity and function of different receptors?
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1. Location: Superficial vs deep
2. Type of ending: encapsulated or non-encapsulated 3. Slowly adapting vs rapidly adapting response determines sensitivity to constant vs changing stimuli 4. Spatial resolution for stimulus (i.e. two-point detection ability) |
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Describe Slowly Adapting vs Rapidly Adapting receptors.
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Slowly Adapting respond best to sustained, unchanging stimulus. They sense pressure and shape of objects. (many pulses)
Rapidly Adapting respond only when stimulus changes (on and offset). They sense impact and motion of objects on skin. (one pulse = off; another pulse = off) |
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Spatial resolution for a stimulus depends on two factors:
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1. Receptive field size
2. Innervation density |
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Do superficial receptors have a small or large receptive field?
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Small. It's the opposite for deep receptors.
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What are the 5 Mechanoreceptors discussed in class?
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1. Merkel Disks
2. Meissner's Corpuscles 3. Ruffini Endings 4. Pacinian Corpuscles 5. Hair Follicle Receptors |
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Describe mechanoreceptor axons with respect to their velocities and myelination. Do they require a lot of force to cause an AP?
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1. Myelinated
2. Very fast 3. They are very sensitive to force and have a low threshold |
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Review your Mechanoreceptor doc in M1 -> Neuro -> Block 2
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Review your Mechanoreceptor doc in M1 -> Neuro -> Block 2
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What are the two types of thermoreceptors?
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Cooling and Warming receptors
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In terms of firing rate, describe thermoreceptors.
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They are constantly firing at about 1Hz. For cooling receptors, firing rate is increased when skin is cooled. They stop firing when skin is warmed. Similar for warming receptors: when skin is warmed, the receptors increase their firing and stop when skin is cooled.
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What is the range of temperature changes that the warming receptors can detect?
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29C to 43C
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With respect to the axons of thermoreceptors, are they myelinated or unmyelinated? Do they have large or small receptive fields?
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1. Cooling: Free nerve endings with myelinated axons. Small receptive fields
2. Warming: Free nerve endings with unmyelinated axons (C-fiber) and very small receptive fields |
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What do nociceptors respond to? What are the two general types?
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They respond to stimuli that damage or threaten to damage tissue. A-Mechanonciceptors and C-Polymodal Nociceptors
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A-Mechanonociceptors:
1. Myelinated or Unmyl axons? 2. Respond to: 3. Receptive field size: 4. Adapting response: |
1. Myelinated (A-delta)
2. Responds to intense mechanical force, sometimes intense heat (greater than 52C). The mediate fast, initial pain; sharp pricking" quality; easy to localize 3. Small receptive field 4. Slow adapting response |
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C-Polymodal Nociceptors
1. Myelinated or Unmyl axons? 2. Respond to: 3. Receptive field size: 4. Adapting response: |
1. Axon is unmyelinated (c-fiber)
2. Responds to intense mechanical force, high heat (greater than 45C), noxious chemicals (eg bradykinin, histamine, acid; capsaicin). Mediate slow, aching, "burning" quality of pain; difficult to localize. 3. Small receptive fields 4. Slowly adapting response |
