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193 Cards in this Set
- Front
- Back
- 3rd side (hint)
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sensation begins with the activation of...
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primary receptors
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adequate stimulus
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stimulus to which each type of receptor is most responsive
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the conversion of stimulus energy into electrochemical energy is called...
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transduction
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electrochemical energy in the nervous system takes the form of...
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change in membrane potential
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receptor potential
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local change in membrane potential
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receptor potentials are converted into ______ for long distance communication with the CNS
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action potentials
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receptor potentials result from...
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opening or closing of membrane ion channels
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4 characteristics of stimulus that sensory systems convey
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quality
intensity location timing |
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most important mechanism for encoding stimulus quality
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receptor specificity
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DEFINITION of receptor specificity
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tuning of receptors to a narrow band of stimulus energy
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labeled line code
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the narrow band of stimulus energy
to which receptors tune in order to convey stimulus quality |
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modality, aka:
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stimulus quality
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2 ways stimulus intensity may be encoded
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frequency code
population code |
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frequency code
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receptor firing frequency is proportional to the stimulus intensity
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population code
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stimulus intensity is encoded by the number of activated receptors
as the stimulus increases it activates more receptors |
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recruitment
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process of activating more receptors as the stimulus increases
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stimulus location is signaled by the...
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spatial distribution of sensory neurons activated by a stimulus
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receptive field of a sensory neuron
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region that when stimulated, causes the cell to fire action potentials
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place code
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location and distribution of receptor endings that determine the
size and location of the receptive field |
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receptive field size varies [how?] with ______
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receptive field size varies INVERSELY with the DENSITY OF INNERVATION
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what determines how precisely the sensory system can resolve detail of stimuli in an area?
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the density of receptors in that area
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measurement used to define differences in spatial resolution on the skin
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two-point threshold
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DEFINITION of two-point threshold
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minimum distance between two detectable stimuli
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2 stimulus temporal properties
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duration
rate of change |
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how are stimulus temporal properties encoded?
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as changes in the frequency of sensory neuron activity
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adaptation
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receptors decrease their firing during constant stimulation
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Do all receptors decrease their firing during constant stimulation?
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YES
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2 types of adaption
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slow
rapid |
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describe SLOWLY ADAPTING RECEPTORS
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signal stimulus duration by persistent depolarization and generation of APs throughout the period of stimulation
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describe RAPIDLY ADAPTING RECEPTORS
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respond only at beginning and end of a stimulus,
signaling the rate at which a stimulus is applied or removed |
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which type of receptor encodes the MAGNITUDE of a hand-to-skin indentation?
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SLOW-ADAPTING receptors
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which type of receptor encodes the RATE OF CHANGE?
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RAPID-ADAPTING receptors
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which type of receptor encodes stimulus DURATION?
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both RAPID- and SLOW- ADAPTING receptors encode duration
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FEATURE EXTRACTION
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ability of the nervous system to represent different attributes of a complex sensory stimulus in the activity of different populations of sensory receptors
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3 broad categories of SENSORY NERVE ENDINGS
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exteroceptors
proprioceptors visceroceptors |
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EXTEROCEPTORS
location respond to... |
EXTEROCEPTORS
located in the skin respond to touch, pressure, pain, temperature |
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PROPRIOCEPTORS
location provide information about... |
PROPRIOCEPTORS
located in muscles, tendons, joints provide: afferent information for reflex adjustments of muscle tension awareness of position & movement |
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VISCEROCEPTORS
location involved in... |
VISCEROCEPTORS
located in mesentery and hollow organs involved in visceral reflexes mediate sensations of fullness & discomfort |
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Sensory endings are supplied by nerve fibers (axons) that differ in ____, _____, and ____
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Sensory endings are supplied by nerve fibers (axons) that differ in
SIZE, CONDUCTION VELOCITY, FUNCTION |
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What category of sensory receptor do CUTANEOUS SENSE ORGANS belong to?
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exteroreceptors
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6 sensory receptors in hairy and glabrous skin you should know
(superficial to deep) |
Meissner's corpuscle
Merkel's disk Free nerve ending Pacinian corpuscle Hair follicle receptor Ruffini's ending |
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Terminal branches of spinal & cranial nerves pass through subcutaneous CT into the ____, where they ______
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Terminal branches of spinal & cranial nerves pass through subcutaneous CT into the DERMIS, where they SPREAD OUT HORIZONTALLY
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Axons in the dermis spread out horizontally to form ____
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PLEXUSES
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Plexuses in the skin lie in what plane?
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skin surface
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Is density of cutaneous innervation fairly uniform all over the body?
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NO! Density of cutaneous innervation varies considerably between skin regions.
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Innervation density is directly proportional to the ability to ____
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localize stimuli
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What two general regions have the greatest innervation density?
the least? |
greatest = face & limbs
least = dorsal trunk |
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Cutaneous mechanoreceptors provide information about _____, ____, and _____
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Cutaneous mechanoreceptors provide information about:
LOCATION SPATIAL FORM TEMPORAL SEQUENCES OF SOMATIC STIMULI |
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Cutaneous mechanoreceptors are all served by what type of fibers?
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rapidly conducting, myelinated
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Sensation type encoded by MERKLE'S CELLS
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Merkle's cells =
PRESSURE |
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Sensation type encoded by HAIR FOLLICLES
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Hair follicles encode
MOTION or DIRECTION |
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Sensation type encoded by MEISSNER'S CORPUSCLES
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Meissner's corpuscles encode
TAP & FLUTTER |
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Sensation type encoded by
PACINIAN CORPUSCLES |
Pacinian corpuscles encode
VIBRATION |
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Sensation type encoded by
RUFFINI ENDING |
Ruffini endings encode
SKIN STRETCH or JOINT POSITION |
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Receptor types contribute differently to the perception of ____ & _____
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Receptor types contribute differently to the perception of
SPATIAL FORM and TEXTURE |
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Tactile information encoded by _____ & _____ are particularly important for the ability of blind people to recognize Braille characters with their fingertips.
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Tactile information encoded by
MERCKLE'S CELLS and MEISSNER'S CORPUSCLES are particularly important for the ability of blind people to recognize Braille with their fingertips |
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Proprioceptive sense organs
location information type signalled |
Proprioceptive sense organs
located in MUSCLES, TENDONS & JOINT CAPSULES signal information about LIMB MOVEMENT & POSITION IN SPACE |
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3 principal types of proprioceptive sense organs
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muscle spindles
Golgi tendon organs (GTOs) Ruffini endings |
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Muscle spindles are organized in parallel with _____
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Muscle spindles are organized in parallel with MUSCLE FIBERS
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What type of receptor are muscle spindles?
What do they signal? |
Muscle spindles are PROPRIOCEPTIVE SENSE ORGANS
that signal MUSCLE LENGTH & RATE OF CHANGE OF MUSCLE LENGTH |
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How many types of afferent endings supply muscle spindles?
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2
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Types of afferent endings that supply muscle spindles?
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Ia
II |
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do muscle spindles contract themselves during muscle activation?
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yes
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"special" motor neurons that sometimes innervate muscle spindles
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gamma motor neurons
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principal sense organ for proprioception
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muscle spindle
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GTOs
location organized how in relation to muscle fibers? signal ___ & ___ |
GTOs
located at junction of muscle & tendon organized in SERIES with muscle fibers signal muscle tension & amount of force generated by muscle contraction |
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Are GTOs located within the muscle?
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No. GTOs are located in the TENDON
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Ruffini endings
location respond to _____ & ______ sources of information about ___, ___ & _____ |
Ruffini endings are found in JOINT CAPSULES
respond to STATIC LIMB & JOINT POSITION or to LIMB MOVEMENTS important sources of information for BALANCE, POSTURE & LIMB MOVEMENT |
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2 types of end organs found in the viscera
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Pacinian corpuscles
free nerve endings |
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Many visceroceptors are supplied by ____ & ____ type fibers
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A-delta fibers
C fibers |
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Visceroceptors mediate ____ & _____
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Visceroceptors mediate
GI pain sensations of fullness in stomach, bladder & colon |
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central pathway for discriminative tactile and position sense for entire body (except head)
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Dorsal Column - Medial Lemniscal system
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What nerve provides discriminative tactile and position sense for the head?
Is it part of the DC-ML system? |
Trigeminal nerve.
Not part of DC-ML system. |
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5 main functions of DC-ML pathway
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Mechanical stimuli (location & intensity)
Two-point discrimination Flutter-vibration Kinesthesis Stereognosis Proprioception |
Make Two Flaky Kids Steer Properly
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stereognosis
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sensation of size, shape, texture by palpation
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kinesthesis
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awareness of limb movement
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First-order, CD-ML spinal afferents enter the spinal cord and ascend in the ______
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dorsal columns
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First-order, DC-ML sensory afferents enter the spinal cord and ascend in the dorsal columns to the ______
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cuneate and gracile nuclei located in the brainstem
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First order, DC-ML fibers from the lower limb and abdomen ascend adjacent to what structure?
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dorsal median septum
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Which fasciculus do first-order, DC-ML fibers from the lower limb form?
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gracile
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First order, DC-ML Fibers from the upper limb ascend ____ to the lower limb fibers and consitutute the ____ fasciculus.
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First order DC-ML fibers from the upper limb ascend LATERAL to the lower limb fibers and constitutde the CUNEATE fasciculus.
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Axons of second-order DC-ML sensory neurons cross to the _____
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contralateral medulla
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Axons of second-order DC-ML sensory neurons cross to the contralateral medulla via the ____ fibers
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internal arcuate fibers
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After crossing to the contralateral medulla, axons of second-order DC-ML fibers ascend in the ______ to the ventral posterolateral nucleus (VPL) of the thalamus
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medial lemniscus
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ventral posterolateral nucleus (VPL) of the thalamus is the location of synapse btw which two sets of DC-ML fibers
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second- and third- order DC-ML afferents
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thalmocortical fibers from third-order VPL neurons project through the ___ capsule
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internal
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thalamocortical fibers from third-order VPL neurons project through the internal capsule to the _____ of the ____ lobe
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postcentral gyrus of the parietal lobe
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primary somatosensory cortex is found where?
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postcentral gyrus of the parietal lobe
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how is the primary somatosensory cortex organized?
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somatotopic arrangement
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4 tracts that relay proprioceptive information to the cerebellum
collective name for these pathways |
spinocerebellar pathways:
dorsal spinocerebellar tract ventral spinocerebellar tract rostral spinocerebellar tract cuneocerebellar tract |
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two spinocerebellar tracts from the LOWER LIMBS
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dorsal spinocerebellar tract
ventral spinocerebellar tract |
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two spinocerebellar tracts from the UPPER LIMBS
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rostral spinocerebellar tract
cuneocerebellar tract |
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information in spinocerebellar pathways is
conscious/unconscious? originates from...? provides...? |
information from spinocerebellar pathways is UNCONSCIOUS
originates from MUSCLE SPINDLES, GTOs and JOINT CAPSULE RECEPTORS provides moment-to-moment information about muscle activity and joint position |
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information in spinocerebellar pathways is needed for...
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coordinated motor control
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lesions of the spinocerebellar pathways produce...
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ataxias
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symptoms of lesions in the spinocerebellar pathways may not be obvious if...
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damage is at the level of the spinal cord and involves the lateral corticospinal tract
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what does lateral corticospinal tract mediate?
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descending cortical control of voluntary movement
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unilateral compression or transection of the spinal cord is called ___
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Brown-Sequard Syndrome
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Brown-Sequard Syndrome produces...
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loss of position sense
impaired tactile discrimination imparied sterognosis on the side of injury |
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Tabes dorsalis results from...
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damage associated with CNS syphilis
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damage associated with Tabes dorsalis
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bilateral degeneration of the dorsal roots, particularly the large diameter fibers in the medial division that enter the dorsal columns
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Anterolateral system carries sensory information from the body related to ___, ___ & _____
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nociception
temperature nondiscriminative touch |
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anterolateral system is named after the...
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location of a major fiber bundle in the spinal cord
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is the ventral trigeminothalamic pathway part of the AL system
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no
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what does the ventral trigeminothalamic pathway carry?
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nociception, temperature, nondiscriminative touch from the face
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nociception
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reception in the CNS of signals evoked by specialized sensory endings that signal strong or tissue-damaging stimuli
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pain
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unpleasant sensation originating from a specific region of the body
does not always begin with nociception |
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pruritis
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itch
probably closely related to nociception |
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pain normally beings with activation of specialized sensory neurons called ...
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nociceptors
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Nociceptors have substantially _____ thresholds for all ordinary stimuli.
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ELEVATED thresholds
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many nociceptors are ONLY excited by stimuli that cause...
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overt damage to the tissue
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2 types of fibers comprising nociceptors
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A-delta fibers
C fibers |
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what is the consequence of nociceptors being A-delta or C fibers?
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conduct impulses much more slowly than receptors signaling innocuous stimuli
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2 major classes of nociceptors
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mechanical nociceptors (A-delta fibers)
polymodal nociceptors (C fibers) |
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mechanical nociceptors are activated by...
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sharp objects that pinch or penetrate the skin
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polymodal nociceptors respond to...
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high intensity mechanical, chemical or thermal stimuli
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Capsaicin activates which kind of nociceptor?
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C fiber (polymodal)
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what does capsaicin bind on nociceptor?
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ligand-gated membrane receptors
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sensitization
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When they are damaged by strong stimuli C fiber nociceptors demonstrate enhanced response to subsequent stimuli
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nociceptors found in visceral organs
respond to... are responsible for... |
nociceptors found in visceral organs
respond to strong mechanical stimuli & noxious chemical/thermal stimuli responsible for painful fisceral sensations associated with gall stones, kidney stones, angina and stomach ache |
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heat sensitive ion channel opened by noxcious heat and capsaicin
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TRPV1
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what type of current does TRPV1 activate in the receptor membrane?
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inward depolarizing membrane current
carried mostly by Ca2+ |
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TRPV1 knockout mice show...
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insensitivity to painful heat stimuli
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what two things work together to generate the sensation of pain?
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A-delta & C fiber nociceptors work together to generate the sensation of pain
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fast pain is mediated by ___ nociceptors
slow pain is mediated by ___ nociceptors |
fast pain is mediated by A-delta nociceptors
slow pain is mediated by C fiber nociceptors |
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children with congenital absence of C afferent fibers hae severe deficits in ____ & ____
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thermal and noxious stimuli sensitivity
autonomic functions, e.g.: sweating |
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Danger faced by individuals with congenital absence of C afferent fibers, related to autonomic function
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b/c these individuals cannot sense temperature and do not sweat, they can attain dangerously high body temperatures during exercise
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central pathways for pain, temperature and nondiscriminative touch sensation
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anterolateral system
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pathway of central AL fibers
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enter spina lcord through later part of dorsal root zone
divide into short ascending and descending branches branches run 2-3 segments rostrally & caudally in Lissauer's tract axons terminate on neurons in laminae I, II, V |
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2 neurotransmitters used by nociceptive primary afferent fibers
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glutamate
neuropeptides, e.g.: Substance P |
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Glutamate evokes ____ synaptic potentials in ____ neurons
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Glutamate evokes EXCITATORY synaptic potentials in DORSAL HORN neurons
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2 types of postsynaptic receptors activated by glutamate
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AMPA Receptors
NMDA Receptors |
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EPSP
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excitatory postsynaptic potentials
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when do nociceptive C fibers also release peptide NTs
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when undergoing high intensity stimulation
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what type of synaptic potentials do peptide NTs produce
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prolonged
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example of peptide NT
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Substance P
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path of second order AL neurons
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from dorsal horn, across midline to contralateral anterolateral funiculus
ascend to the brain in anterolateral funiculus |
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spinothalamic tract
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axons that project directly from the spinal cord to the thalamus
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what kind of sensation does the spinothalamic tract mediate?
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"fast" or "sharp" pain
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anterolateral system thalamic neurons relay information to the ____
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somatosensory cortex
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difference between AL and DC-ML system thalamic neurons
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AL system includes thalamic projections to other areas outside primary somatosensory cortex
e.g.: cingulate cortex & insula |
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AL pathways that take a less direct route to the brain, involving more synaptic connections area associated with a sensation of...
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"slow" or aching pain
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spinomesencephalic tract is associated with what type of sensation?
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slow/aching pain
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spinomesencephalic tract makes connections with neurons that are involved in..
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a descending system involved in central modulation of pain
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which system, AL or DC-ML, relays sensory information along multiple, intermingled fiber bundles that involve many indirect, polysynaptic connections
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AL
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Lesions of the anterolateral quadrant from spinal cord trauma can cause loss of ______
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anterolateral sensory function
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Brown-Sequard Syndrome
definition produces loss of... |
Brown Sequard syndrome
unilateral compression or transection of the spinal cord produces looss of pain and thermal sensation on the contralateral side & impairment of position and vibratory sense, and tactile discrimination associated with damage to the dorsal columns |
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syringomyelia
definition produce loss of.. |
syringomyelia
spinal cord cavitation (enlargement of the spinal canal at the cervical spinal segments) produce bilateral losses of pain and temperature sensibilities |
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infarct of the anterior spinal artery
interrupts... causes... spares.. |
infarct of the anterior spinal artery
interrupts the AL system causes loss of pain and temperature sensation spares dorsal columns and therefore spares touch & proprioception |
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endogenous pain control systems
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circuits in teh brain and spinal cord whose main function is to modulate the perception of pain
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stimulation of several brainstem areas can attenuate afferent signals from ____, but not ___ stimuli
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stimulation of several brainstem areas can attenuate afferent signals from PAINFUL, but not TACTILE stimuli
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analgesia
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selective suppression of nociceptive signals
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pain modulatory descending system involving seratonin
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connections from the periacqueductal gray matter
to neurons in the nucleus raphae magnus, which send axons via the dorsolateral funiculus to synapse with the dorsal horn cells and release seratonin |
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pain modulatory descending system involving NE
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axons from locus ceruleus in the brainstem project to the dorsal horn though the dorsolateral funiculus
releases NE |
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modulatory actions of both descending systems (seratonin & NE) are mediated through..
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inhibitory local circuit interneurons in the dorsal horn
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endogenous opioid peptides regulate _____
and contribute to ____ |
endogenous opioid peptides regulate NOCICEPTIVE TRANSMISSION
and contribulte to ANALGESIA |
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enkephalins
are a class of... |
endogenous opioid peptides
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presynaptic mechanism of enkephalins
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decrease Ca2+ entry into central terminals of nociceptors
thus, reducing release of excitatory NT onto spinothalamic projection neurons |
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postsynaptic mechanism of enkephalins
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activate K+ efflux from spinothalamic projection neurons
causes membrane hyperpolarization and decrease in their excitability to noxious sensory inputs |
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ability to localize stimuli depends on size of ____
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receptor field
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Large receptor fields produce ____ spatial resolution
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LOW
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Small receptor fields produce _____ spatial resolution
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HIGH
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stronger stimuli will be represented by more kinds of receptors. why?
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because stronger stimuli will activate receptors with low AND high thresholds.
so painful stimuli will activate nociceptors and more sensitive receptors. = POPULATION CODING (how many receptors activated = how large the stimulus intensity) |
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chemoreceptors are activated by which 3 things?
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smell
taste irritant chemicals on skin |
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mechanoreceptors are activated by which 5 things?
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touch, pressure, vibration
pinch, pinprick muscle/joint position distention of hollow organs hearing, balance |
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what's weird about photoreceptors?
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depolarize in the dark
light causes hyperpolarization |
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what two factors comprise the labeled line code that specifies stimulus modality?
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specificity of RECEPTOR
specificity of NEURAL PATHWAY |
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example that illustrates importance of labeled line code.
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what if you cut the olfactory nerve and grafted it on to the optic nerve afferent?
you could "see smells!" |
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when you apply a stimulus, slow-adapting receptors...
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keep on firing until you remove the stimulus
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when you apply a stimulus, rapid-adapting receptors...
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only discharge so long as there is change
(e.g.: if press on skin, discharge as long as indentation increases, but not if hold down at same depth over period of time. fire again when stimulus removed.) |
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the frequency at which a slow adapting receptor fires is proportional to what?
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the intensity of the stimulus
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the frequency at which a rapid adapting receptor fires is proportional to what?
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the rate of change of a stimulus
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Meissner's corpuscles
rapid/slow adapting? stimulus type |
Meissner's corpuscles
rapid adapting activated by TAP/FLUTTER |
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Merkel cells
rapid/slow adapting? stimulus type |
Merkel cells
slow adapting activated by TOUCH/PRESSURE |
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Pacinian corpuscle
slow/rapid adapting? stimulus type |
Pacinian corpuscle
rapid adapting activated by VIBRATION |
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tuning fork tests which sensory receptors?
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Pacinian corpuscles
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Ruffini endings
slow/rapid adapting? stimulus type |
Ruffini corpuscles
slow adapting activated by STRETCH |
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How are tap/flutter and touch/pressure different.
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Tap/flutter are carried by Meissner's corpuscles, which are RAPID-ADAPTING
Touch/pressure are carried by Merkel's cells, which are SLOW ADAPTING. Difference between slow and rapid adapting = difference btw tap & touch. |
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which type of cutaneous sense organs localize least well? why?
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Pacinian corpuscles have the largest receptor fields of the cutaneous sense organs and therefore localize least well.
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RECEPTOR / FUNCTION
____ / length ____ / tension _____/ joint angle |
RECEPTOR / FUNCTION
Muscle spindle / length GTO / tension Ruffini / joint angle |
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type of mechanoreceptor excited by passive stretch
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muscle spindle
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type of mechanoreceptor excited when muscle contracts
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GTO
(activated by tendon stretch, which occurs when muscle contracts) |
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where do spinocerebellar neurons from the lower limbs usually synapse?
spinal cord region nucleus lamina |
Spinocerebellar pathways from the lower limbs usually synapse in
thoracic, Clarke's nucleus, lamina 7 |
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does the dorsal spinocerebellar tract from the lower limb cross?
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no
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does the ventral spinocerebellar tract from the lower limb cross?
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yes - twice.
ergo, still ipsilateral, like dorsal. |
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do the spinocerebellar tracts from the upper limbs cross?
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no
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A alpha & beta fibers are in the ____ division
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medial division
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A alpha & beta fibers end in lamina ___ (nucleus?)
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A alpha & beta fibers end in lamina IV (nucleus proprius)
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A-delta and C fibers are in the ___ division
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lateral division
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A delta fibers end in which lamina and which nucleus?
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lamina I
posteromarginal nucleus |
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C fibers end in which laminae and which nuclei?
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C fibers end in laminae 2 and 5,
substantia gelatinosa and nucleus proprius, respectively |
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which laminae are associated with pain and temperature?
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lamina I & II
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Play the location game:
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if I lesion "here"
where are there losses? |
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