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How do sensory receptors transmit information?
In a series of action potentials
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What is the Labeled Line Principle?
Each type of sensation is projected to specific areas of the CNS
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The frequency of AP is dependent upon what?
Intensity of the stimulus
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Define somatosensory receptors
Specialized endings of primary afferent neurons
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What can somatosensory receptors be found?
skin, viscera, muscles, joints, connective tissue
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Name some somatic sensations
touch, pressure, vibration, body position, tickle, temperature, and pain (and itch)
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Recetors transform mechanical, chemical, and/or thermal energy into what?
electrical energy (action potential)
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Name the 5 classifications of receptors
- Mechanoreceptors
- Thermoreceptors
- Nociceptors
- Chemorecptors
- Electromagnetic receptors
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What are the two discriminatios of touch?
- Quality of touch (soft or coarse)
- Area being touched (2pt discrimination)
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What is Receptor Adaptation?
Diminishing rate of discharge of a somatosensory neuron occurs with continued stimulation of constant intensity (adaptation)
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What is the purpose of adaptation?
Allows the nervous system to focus on new or altered stimuli without the "distraction" of the constant stimulus
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What are rapidly adapting receptors called?
Phasic receptors
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What are slowly adapting receptors called?
Tonic receptors
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Describe Meissner's Corpuscle
- Encapsulated, located in the ridges of superficial glaborous skin
- Highly concentrated in the fingertips
- Sensitive to: Light, touch, and discriminative touch
- Rapidly adapting
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Describe Merkel's Disks
- Un-encapsulated; Located in the superficial skin (hairy and glaborous)
- Concentrated in the finger tips
- Sensitive to discriminative touch
- Slowly adapting
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Describe Pacinian Corpuscles
- Encapsulated
- located within: Dermis, subcutaneous fat, intramuscular connective tissue, and capsules of synovial joints
- Detects pressure, vibration, and acceleration
- Rapidly adapting
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Describe Ruffini's Endings
- Encapsulated, flower-spray neural endings
- Dermis, joints, glaborous, and hairy skin
- Detects light touch
- Slow adapting
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Describe the Hair Follicle
- Nerve endings embedded in hair follicle, surrounding hair shaft
- Deflection of hair deforms follicle, creating a stimulus for the receptor
- Consist of rapidly and slowly adapting types
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What are two types of Thermoreceptors?
- Krause's bulb - for cold
- Ruffini's ending - for warm
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What are Nociceptors?
Stimulatd by mechanical, termal, or chemical stimuli
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What are some chemical substances that stimulate nociceptors?
Bradykinin, serotonin, histamine, K+ and H+
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Prostaglandins and substance P increase sensitivity to what?
Pain (sensitize free nerve endings)
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What is hyperalgia?
Increased sensitivity to painful stimuli
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What are Free Nerve Endings?
Mechanical, Chemical, and Thermal stimuli
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Rate and extent of tissue damage is directly correlated with what?
Level of pain perceived
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What are some causes of tissue damage?
Bacterial infection, tissue ischemia, tissue contusion
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Describe fast pain
- Elicited by mechanical and thermal stimuli
- Transmitted on A-d (lower case greek delta) fibers
- Sharp, easily localized pain
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What is a receptor potential?
When a stimulus causes a change in the membrane electrical potential of a sensory receptor
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What does a receptor potential cause?
A change in ion permeability of the receptor membrane and results in depolarization of receptor
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A stronger stimulus results in what?
Increased action potential frequency
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A receptor will continue to send action potentials as long as...
a stimulus is present (continued depolarization)
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What is adaptation?
Diminishing rate of discharge of a somatosensory neuron that occurs with continued stimulation of constant intensity
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What does adaptation allow?
Allows the nervous system to focus on new or altered stimuli without the distraction of the constant stimulus
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What are some influenctial factors of adaptation rates?
- Properties of excitability of the membrane of the sensory neuron
- The non-neuronal accessory structure that surrounds the axon
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What is referred pain?
Pain felt in part of the body that is remote from the tissue causing the pain
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When does referred pain most frequently occur?
With injury to visceral organs (abdomen/thorax)
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Where do visceral and skin pain fibers terminate? Why is this important?
- Terminate at the same areas of spinal cord;
- The CNS perceives the pain as coming from the skin rather than abdominal/thoracic organs
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What is the modality and adaptation rate of Meissner's?
- Discriminate touch, light touch, vibration
- Rapidly adapting
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What is the modality and adaptation rate of Merkel's?
- Discriminate touch
- Slowly adapting
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What is the modality and adaptation rate of Pacinian?
- Pressure, vibration, acceleration
- Rapidly adapting
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What is the modality and adaptation rate of Ruffini's?
- Light touch, thermoreceptor
- slowly adapting
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What is the modality and adaptation rate of hair end organs?
- Light touch
- Rapid & slowly adapting
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What is the modality and adaptation rate of free nerve endings?
- Chemical, thermal, mechanical
- Slow or no adapting
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