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91 Cards in this Set
- Front
- Back
What type of receptor mediates cutaneous sensation?
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Exteroreceptors
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Primary cutaneous sensory experiences include:
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Touch, pressure, heat, cold and pain
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How are secondary cutaneous sensory experiences produced?
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They are a combination of several receptor types being stimulated simultaneously
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Are nociceptors free or encapsulated?
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Free nerve endings
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What do high-threshold mechanoreceptors respond to?
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Intense mechanical stimulation such as cutting, pinching and stretching
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What to polymodal nociceptors respond to?
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Intense mechanical stimuli, temperatures over 40 degrees Celsius and chemical substances that are present when tissue damage occurs
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What is hyperalgesia?
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When nociceptors become sensitized due to long-standing stimulation
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Does hyperalgesia raise or lower the threshold for evoking pain?
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Lowers the threshold
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Can the same thermoreceptor mediate both hot and cold sensations?
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Yes
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Where are low threshold mechanoreceptors located in the skin?
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Close to hair roots on hairy skin
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Are low threshold mechanoreceptors in the skin rapidly or slow adapting?
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Rapidly adapting
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What do low threshold mechanoreceptors mediate?
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A crude sense of touch
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Are low threshold mechanoreceptors in the skin free or encapsulated?
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Free
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Where are Meissner's corpuscles found in the skin?
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In the dermis of glabrous skin of the hand and foot, just below the epidermis
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Are Meissner's corpuscles free or encasulated?
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Encapsulated
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Are Meissner's corpuscles rapidly or slowly adapting?
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Rapidly adapting
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What constitutes adequate stimulus for Meissner's corpuscles?
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Low threshold stimuli-depression of the skin just a few microns
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Where are Ruffini corpuscles found in the skin?
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In the dermis of glabrous skin
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What are Ruffini corpscles made of?
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A bundle of collagen fibrils that are connected with collagen fibrils in the dermis
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What constitutes adequate stimulus for Ruffini corpuscles?
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Stretching of the skin
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Are Ruffini corpuscles rapidly or slowly adapting?
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Slowly adapting
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What type of information do Ruffini corpuscles provide?
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They provide information about the direction and magnitude of skin stretch
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Where are Merkel's discs found in the skin?
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At the junction of the dermis and epidermis in the distal extremities, external genitalia and lips. Found in hairy and glabrous skin.
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Are Merkel's discs rapidly or slowly adapting?
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Slowly adapting
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What constitutes adequate stimulus for Merkel's discs?
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Pressure
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Where are Pacinian corpuscles found in the skin?
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At the junction between dermis and subcutaneous tissue
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What constitutes adequate stimulus for Pacinian corpuscles?
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Very rapid indentation of the skin (100-400 Hz)
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What do Pacinian corpuscles consist of?
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Large ovoid bodies, axon surrounded by connective tissue and fluid-filled spaces
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Skin indentation of frequency below 100 Hz are signaled by what receptors?
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Meissner's corpuscles
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The size of a receptive field depends on what?
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The density of receptors and the number of receptors sending axons to one neuron
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What are three tests of cutaneous sensation?
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Light brushing, two-point discrimination and discriminative sensation (able to recognize letters/numbers drawn on body part)
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What are the four functions of cutaneous mechanoreceptors?
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Awareness of objects touching the skin, recognize objects without vision (stereognosis), judge the speed and direction of an object moving on the skin and to determine friction on the skin
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Sensory information from proprioceptors comes from what parts of the body?
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Muscles, tendons, joint capsules and ligaments
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Where are muscle spindles located?
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Within striated (extrafusal) muscle fibers
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How large are the connective tissue capsules that encase muscle spindles?
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About .2 mm in diameter and about 1-5 mm long.
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How many intrafusal muscle fibers are contained in each connective tissue capsule?
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2 to 12
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Are intrafusal or extrafusal fibers bigger?
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Extrafusal fibers
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Do intrafusal fibers generate force?
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No
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What are the two types of intrafusal fibers?
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Nuclear bag fibers and nuclear chain fibers
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Do muscles involved in fine, precise movements have a high or low density of muscle spindles?
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High density
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Ia afferent fibers spiral around the center of what fibers?
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Nuclear bag fibers and nuclear chain fibers
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II afferent fibers spiral around what fibers?
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The distal segment of nuclear chain fibers
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What constitutes adequate stimulus of a muscle spindle?
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Stretch of the intrafusal fibers and excitatory input to alpha motor neurons of the same muscle and synergistic muscles
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Muscle spindle density varies with what?
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Function of muscle
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How are muscle spindles arranged with extrafusal fibers?
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Parallel
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What happens to muscle spindles when extrafusal muscle is stretched?
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The muscle spindles are also stretched
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What happens to muscle spindles when extrafusal muscle contracts?
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The spindles are passively shortened
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Static sensitivity of muscle spindles is mediated by what type of fiber?
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Nuclear chain fibers
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Nuclear chain fibers gather what type of information for the CNS?
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Information about the length of muscle at any and all times
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What happens to nuclear chain fibers when extrafusal muscle is stretched?
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The nuclear chain fiber is stretched and generates increased frequency of action potentials in Ia and II afferents
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Are nuclear chain fibers rapidly or slowly adapting?
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Slowly adapting
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What happens to nuclear chain fibers when extrafusal muscle is shortened?
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Nuclear chain fibers are put on slack and the action potential firing rate will decrease
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Dynamic sensitivity of muscle spindles is mediated by what fibers?
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Nuclear bag fibers
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Are nuclear bag fibers rapidly or slowly adapting?
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Rapidly adapting
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Nuclear bag fibers provide what type of information to the CNS?
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Information about rate of muscle length change
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Nuclear bag fibers send information to the CNS via what fibers?
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Ia fibers only
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Nuclear chain fibers send information to the CNS via what fibers?
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Ia and II afferent fibers
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What neurons provide efferent innervation to muscle spindles?
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Gamma motor neurons
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Where are gamma motor neurons located in the spinal cord?
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In the ventral horn
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Where do gamma motor neurons terminate in the muscle spindle fiber?
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On the contractile portion of the fiber on either side of the centrally located sensory portion of the fiber
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What happens to intrafusal fibers when gamma motor neurons contract?
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The distal ends of the intrafusal fibers contract
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What is the function of gamma static motor neurons?
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They increase the sensitivity of nuclear chain fibers to muscle length (static sensitivity)
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What occurs when gamma static motor neurons are active?
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Ia and II afferent fibers discharge at a greater rate at all muscle lengths
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What is the function of gamma dynamic motor neurons?
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They increase sensitivity of the nuclear bag fiber to rate of change in muscle length (dynamic sensitivity)
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What occurs when gamma dynamic motor neurons are active?
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Ia afferent fibers discharge at a greater rate during change in length. Discharge rate returns to normal after new length is reached.
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Gamma dynamic motor neurons allow the nervous system to do what?
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React more quickly and forcefully to unexpected changes in muscle length
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Gamma static motor neurons allow the nervous system to do what?
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Have precise information about muscle length during movements requiring fine control
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Alpha-gamma co-activation allows the nervous system to do what?
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Maintain spindle sensitivity during shortening contractions
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Alpha-gamma co-activation prevents muscle spindles from doing what?
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Going on slack
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Where are golgi tendon organs (GTO's) located?
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Close to the musculotendinous junction, they follow collagen fibrils along a tendon
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How many GTO's are in a muscle compared to muscle spindles?
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About the same number of GTO's and muscle spindles
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Do GTO's have efferent innervation?
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No, only afferent innervation
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What afferent fibers come from GTO's?
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Ib afferent fibers
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What constitutes adequate stimulus of a GTO?
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Stretch of the part of the tendon in which the GTO lies
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Is a GTO rapidly or slowly adapting?
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Slowly adapting
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How many GTO's are in a muscle compared to muscle spindles?
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About the same number of GTO's and muscle spindles
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Do GTO's have efferent innervation?
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No, only afferent innervation
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What afferent fibers come from GTO's?
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Ib afferent fibers
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What constitutes adequate stimulus of a GTO?
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Stretch of the part of the tendon in which the GTO lies
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Is a GTO rapidly or slowly adapting?
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Slowly adapting
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Do golgi tendon organs have efferent innervation?
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No, the sensitivity cannot be controlled like a muscle spindle
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Are golgi tendon organs located in series or parallel to extrafusal muscle fibers?
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In series
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Why are golgi tendon organs located in series with extrafusal muscle fibers rather than parallel?
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They provide info to the CNS about muscle tension rather than muscle length
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Is a golgi tendon organ more sensitive to tension created by active contraction or by passive stretch?
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Active contraction
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What is the function of golgi tendon organs?
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They provide inhibitory feedback to alpha motor neurons that innervate extrafusal muscle, which allows for fine control of muscle activation
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Do golgi tendon organs play a protective role in muscle function?
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No
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What is kinesthesia?
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The perception of joint position and direction and velocity of joint movement
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What is the static component of kinesthesia?
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The ability to know where a joint is in space or in relation to the body when it's not moving
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What type of receptors detect the static component of kinesthesia?
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Slowly adapting receptors
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What type of receptors detect the dynamic component of kinesthesia?
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Rapidly adapting receptors
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What is the dynamic component of kinesthesia?
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Direction and velocity of movement
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