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98 Cards in this Set
- Front
- Back
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Somatosensory System refers to
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general sensation:
touch, proprioreception, pain and temperature |
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EXTERORECEPTION
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perception of external stimuli
receptors found near body surface (in skin and special sense organs) |
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INTEROCEPTION
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perception of internal stimuli
receptors found within the body (in viscera, blood vessels, glands, serous membranes, etc...) |
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PROPRIOCEPTION
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perception of body position and movement
within muscles, tendons, joints and the vestibular apparatus |
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various types of perceptions or sensations, (receptors are usually specific for a particular... )
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MODALITY
(hearing, seeing, tasting, etc..) |
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adequate stimulus
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type of stimulus, to which a particular receptor is responsive
generally- individual receptors respond to only one modality of stimuli |
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MODALITY: Vision
STIMULUS: RECEPTOR TYPE: |
STIMULUS: PHOTONS
RECEPTOR TYPE: PHOTORECEPTORS |
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MODALITY(ies):
STIMULUS: Specific Molecules RECEPTOR TYPE:Chemoreceptor |
TASTE and SMELL
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Modalities that involve perception of:
MECHANICAL FORCE (as stimulus) via (MECHANORECEPTORS) |
TOUCH, PROPRIOCEPTION, HEARING
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Receptor Type involved in Temperature perception
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Thermoreceptors
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Nociceptors are involved in what sensory modality?
therefore, receptive to what type of stimuli? |
PAIN
receptive to chemicals released by tissue damage |
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2 basic functions of sensory receptors
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1) detect energy of a physical stimulus
2) convert energy to transmissible form in nervous system (ACTION POTENTIAL) [SENSORY TRANSDUCTION] |
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How is a photoreceptor stimulated?
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alteration of membrane permeability by absorption of photons by rods and cones in the retina
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How is a chemoreceptor stimulated?
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alteration of receptor membrane permeability via opening of ion channels:
-due to specific ligand binding or -to a second messenger G-protein |
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How is a mechanoreceptor stimulated?
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ion channels are linked to the cytoskeleton and open when mechanical force is applied,
thereby altering membrane permeability |
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How is a thermoreceptor stimulated?
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not completely clear how temperature causes ion channels to open (in order to change thermoreceptor membrane permeability)
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How is a nocireceptor membrane permeability altered?
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chemicals released by damaged cells are though to bind to the ion channels directly or through a second messenger
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changes in the permeability of the receptor cell membrane results in what type of potential?
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a local graded potential called the RECEPTOR or GENERATOR POTENTIAL
(sim to an EPSP) |
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EPSP
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excitatory post-synaptic potential
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what must happen for a receptor to tranduce the signal (generate an action potential)
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RECEPTOR POTENTIAL must reach a certain threshold (can be accomplished by summation)
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Where is the ACTION POTENTIAL GENERATED in:
-Multipolar neurons -Pseudounipolar neurons |
-in multi-polar neurons: generated at AXON HILLOCK
-in pseudo-unipolar neurons: generated at the INITIAL SEGMENT (1st Node of Ranvier)of the DENDRITE (aka peripheral axon) (TYPICAL of 1st order sensory neurons) |
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Most 1st order sensory neurons are what type?
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PSEUDOUNIPOLAR (peripheral nerves)
-Receptor- -Io Segment (AP generated)of Dendrite (Peripheral Axon) -Cell Body -(Central) Axon |
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what is a labeled line?
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chain of neurons carrying one type of modality
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What information must a receptor and the generated AP convey about a given sensory stimuli?
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-MODALITY (touch, proprioception, etc..)
-INTENSITY -DURATION -LOCATION |
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INTENSITY of a stimulus is represented by what characteristic of the RECEPTOR POTENTIAL?
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represented by Amplitude of the receptor potential
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INTENSITY of a stimulus is encoded in ACTION POTENTIAL by its:
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FREQUENCY
(whereas intensity is encoded by amplitude in RECEPTOR POTENTIAL) |
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Increase in Intensity of stimulus results in:
?? in AMPLITUDE of RECEPTOR POTENTIAL ?? in FREQUENCY of AP |
results in
Increase in amplitude of Receptor Potential and Increase in frequency of Action Potential |
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SOFT TOUCH vs. HARD TOUCH
-degree of receptor membrane deformation -# of ion channels open -degree of depolarization (amplitude of receptor potential) -frequency of AP |
-slightly/significantly
-small#/large# -small/large -low/high |
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Basis for different "Pain Thresholds" in different individuals
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-receptors have different thresholds
-people have varying numbers of high and low threshold receptors |
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process by which receptors extract information about DURATION of a stimulus?
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ADAPTATION: when the response of a receptor to a constantly applied stimulus diminishes with time (receptor "adapts" and stops generating receptor potentials)
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receptors that respond maximally when the stimulus is first applied, but response quickly decreases if stimulus is maintained...are called:
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RAPIDLY ADAPTING (phasic) RECEPTORS
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receptors that generate receptor potentials as long as the stimulus is applied
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SLOWLY ADAPTING (tonic) RECEPTORS
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type of receptor that communicates information from DYNAMIC STIMULUS
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Rapidly adapting receptor
(communicates information when stimulus changes) |
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type of receptor that communicates information from STATIC stimulus
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Slowly adapting receptor
(communicates information the entire time the stimulus is applied) |
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RECEPTIVE FIELD
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region of the body within which a stimulus will cause a response in a particular receptor
smaller the receptive field, the more localized the sensation |
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Test used to measure receptive field size
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TWO-POINT Discrimination Test (measures the smallest distance required to perceive two poitns as separate and distinct)
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receptor density
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the density of receptor fields,
Fingers> Thumb > Face > Palm > Belly> Calf |
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Sensory Axons are classified by what feature?
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their conduction velocity
(fastest>slowest) Aa(Ia)>Aa(Ib)>Ab(II) >Ad(III)> C(IV) |
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the larger the nerve fiber the thicker the?
the faster the? |
thicker the myelin sheath
the faster the fiber conducts largest myelinated fibers v >100m/sec smallest unmyelinated fibers v <1 m/sec |
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what modalities are carried in the largest, myelinated fibers?
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proprioception(muscles)>
proprioception(tendons)> |
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what modalities are carried in medium sized myelinated fibers?
(6-12micrometers) |
proprioception (from joints)
touch, pressure, vibration >> |
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what modalities are carried in the smallest myelinated and unmyelinated fibers?
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myelinated: pain (sharp, well-localized) temperature, crude touch
smaller, unmyelinated: pain (dull, poorly localized) temperature |
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how/where are somatosensory axons segregated by modality?
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proximal to the cell body (in dorsal roots or within the spinal cord)
segregated by modality into PARALLEL PATHWAYS |
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clinical implications of parallel pathways in nerve compression and traumatic nerve injuries
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partial compression of a dorsal root could completely disable axons carrying touch sensation, but spare axons carrying pain sensations
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locations of cell body of:
1st, 2nd, 3rd order neurons |
1st: periphery (has specialized receptor end)
2nd: cell body in spinal cord or brainstem 3rd: cell body in the thalamus |
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pathways that carry unconscious information generally have how many neurons?
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two
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1st order neurons travel in what type of nerves?
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PERIPHERAL NERVES, either:
-Spinal Nerves (connect to spinal cord via dorsal and ventral roots) -Cranial Nerves (connect to brain, except CNXI) |
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cutaneous nerve domain
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area of skin that cutaneous nerves supply (cutaneous branches of spinal or cranial nerves)
eg: sensory loss to cutaneous nerve domain = likely damage to a peripheral nerve branch |
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dermatome
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innervation of the skin by a particular spinal nerve
eg: herpes zoster = dermatomal pattern |
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only area of skin that does not receive sensory innervation from spinal nerves
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anterior 2/3 of head (including anterior 1/2 scalp and face, not including angle of jaw)
area supplied by CNV |
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Major pathway that carries tactile and proprioceptive information:
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DORSAL COLUMN- MEDIAL LEMNISCUS
(DC-ML) SYSTEM |
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tactile and proprioceptive information from the anterior 2/3 of head travels via:
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TRIGEMINAL MECHANOSENSORY SYSTEM
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what travels on the Spinothalamic tract (STT)?
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small amount of tactile information ("crude-touch")
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dorsal spinocerebellar and cuneocerebellar tracts carry what type of information?
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carry unconscious sensory information
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what is the supposed function of the descending projections in the somatosensory system?
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modification of ascending information
MODULATORY PATHWAYS |
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Path of 1st order neuron in DC-ML System
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Peripheral Axon
-travels via spinal nerve to enter spinal cord through dorsal root -ascends dorsal column to caudal medulla (in gracile(<T6)or cuneate(>T6) tract) -synapses with 2nd order neuron in gracile or cuneate nuclei at spino-medullary jxn |
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where do first and second order sensory axons synapse?
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in CUNEATE NUCLEUS (if from area above T6) or GRACILE NUCLEUS (if from area below T6)
at spino-medullary junction |
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where are the cell bodies of second order neurons of DC-ML system?
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in the DORSAL COLUMN NUCLEI:
CUNEATE NUCLEUS and GRACILE NUCLEUS |
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path of 2nd order axons in DC-ML system
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-leave DORSAL COLUMN NUCLEI
-travel vetro-medially, to form INTERNAL ARCUATE TRACT -become MEDIAL LEMNISCUS as they DECUSSATE in the caudal medulla, then ascend through the medulla, pons and midbrain -terminate in VPL NUCLEUS of the thalamus (synapse w/ 3rd order) |
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sensory information from lower body follows what path in DC-ML system?
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-ascends GRACILE TRACT to caudal medulla
-caudally in most VENTRAL portion of MEDIAL LEMNISCUS -rostrally in most LATERAL portion of ML |
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sensory info from upper body is found in what regions of the brainstem as it ascends in DCML pathway?
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In dorsal column, ascends via CUNEATE TRACT
In caudal part of MEDIAL LEMNISCUS fibers located DORSALLY In rostral part of ML fibers located MEDIALLY |
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3rd Order Neurons of DC-ML System
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-Cell bodies located in VPL nucleus (of the ventral posterior complex of the thalamus)
-axons pass through posterior limb of the INTERNAL CAPSULE and project into the PRIMARY SOMOTOSENSORY CORTEX (SI) |
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PRIMARY SOMATOSENSORY CORTEX
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cortex of the POSTCENTRAL GYRUS and posterior part of the PARACENTRAL LOBULE
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sensory homounculus
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map illustrating the somatotropic organization represented by a caricature of a "little man"
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amount of sensory cortex devoted to a particular region is determined by:
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the sensitivity of the region (DENSITY of receptors)
NOT size of region |
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where does sensory information go after it reaches SI?
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transported to higher order cortical centers for further processing and integration.
these centers include the secondary somoatosensory cortex (SII) and the associated cortices |
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Phantom sensations perceived by amputees are a result of what process (also results from increased stimulation of specific pathways)
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constant remapping of the cortex. regions that are no longer receiving info (due to limb amputation) are remapped to be used by neighboring areas (violinists- left finger area of cortex, more extensive than right)
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1st Order Neurons of Trigeminal Mechanosensory System
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-peripheral axons travel in 3 divisions of CNV
-cell bodies located in TRIGEMINAL (semilunar) GANGLION -axons enter pons and terminate in PRINCIPLE (chief) SENSORY NUCLEUS of the TRIGEMINAL BRAINSTEM COMPLEX |
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3 divisions of TRIGEMINAL BRAINSTEM COMPLEX
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*PRINCIPLE NUCLEUS (mechanosensory info)
*SPINAL NUCLEUS (pain and temperature information) *MESENCEPHALIC NUCLEUS (proprioceptive info from the muscles of mastication) |
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2nd Order Neurons of Trigeminal Mechanosensory System
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-cell bodies in principal nucleus
-axons cross midline within the pons and then ascend in the ML (as the TRIGEMINAL LEMNISCUS/TRIGEMINOTHALAMIC TRACT) to the VPM nucleus of the thalamus |
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3rd order neurons of Trigeminal Mechanosensory System
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same as those in DC-ML system
project to the SOMATOSENSORY CORTEX (specifically the face area) |
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SPINOCEREBELLAR PATHWAYS
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pathways for proprioceptive information that travels directly to the cerebellum
Examples: DORSAL SPINOCEREBELLAR TRACT and the CUNEOCEREBELLAR DTRACT |
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1st Order neurons of SPINOCEREBELLAR PATHWAYS
from THORACIC, LUMBAR and SACRAL REGIONS |
-enter spinal cord via dorsal roots
-synapse w/ 2nd order neurons at the dorsal NUCLEUS OF CLARKE (column of nuclei bt C8-L3) |
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2nd Order neurons of SPINOCEREBELLAR PATHWAYS
from ALL REGIONS |
ascend to the cerebellum in the dorsolateral column as the DSCT (dorsal spinocerebellar tract)
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1st Order neurons of SPINOCEREBELLAR PATHWAYS
from below L3 |
ascend in the ipsilateral gracile tract, before synapsing (in Dorsal Nucleus of Clarke, doesn't begin until L3)
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1st Order neurons of SPINOCEREBELLAR PATHWAYS
from cervical region |
ascend to the medulla in the cuneate tract and synapse with 2nd order fibers in the LATERAL (accessory) CUNEATE NUCLEUS
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2nd Order neurons of SPINOCEREBELLAR PATHWAYS
from the cervical region |
travel with the DSCT to the cerebellum (forming the CUNEOCEREBELLAR TRACT, as opposed to
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disease or lesion affecting a peripheral nerve will demonstrate what pattern of sensory loss?
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cutaneous nerve domain
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disease or lesion affecting a dorsal root or spinal nerve will demonstrate what pattern of sensory loss?
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dermatomal pattern
(remember however, dermatomes overlap) |
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incomplete lesions or compression injuries might only effect
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certain modalities (due to PARALLEL PATHWAYS: grouping of axons by modality)
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TACTILE MECHANORECEPTORS
5 types |
Meissner's Corpuscles
Pacinian Corpuscles Merkel's Disks* Ruffini's corpuscles Hair follicle receptor* (NOT encapsulated, the others are) |
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mechanoreceptor located in glabrous skin between dermal papillae, abundant in lips, palms, fingertips, soles of feet
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MEISSNER'S CORPUSCLE
(fine touch pressure (dynamic)) RAPIDLY ADAPTING encapsulated mechanoreceptor |
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mechanoreceptor located in deep dermis, subcutaneous tissue, interosseous membranes, messenteries of viscera
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PACINIAN CORPUSCLE
(deep pressure, vibration) RAPIDLY ADAPTING encapsulated |
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mechanoreceptor located at the epidermal-dermal junction of skin
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MERKEL'S DISK
(fine touch pressure (static)) SLOW ADAPTING UN-ENCAPSULATED mechanoreceptor |
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mechanoreceptor located in the dermis of skin, ligaments, tendons
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RUFFINI'S CORPUSCLE
(stretch) SLOW ADAPTING ENCAPSULATED mechanoreceptor |
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mechanoreceptor found in hairy skin
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HAIR FOLLICLE RECEPTOR
(touch, hair movement) PRIMARILY RAPIDLY ADAPTING UN-Encapsulated MECHANORECEPTOR |
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Mechanoreceptors for Proprioception
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*MUSCLE SPINDLES
*GOLGI TENDON ORGANS *JOINT RECEPTORS |
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All mechanoreceptors for tactile information are associated with what type of axons?
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ABeta
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Muscle Spindles
-location -morphology -fxn -adaption rate -associated axons |
mechanoreceptors for proprioception
-in skeletal muscles -sense muscle length -SLOW AND RAPIDLY ADAPTING types -associated with Type Ia AND II axons |
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GOLGI TENDON ORGANS
-location -morphology -fxn -adaption rate -associated axons |
-located in tendons
-encapsulated -sense muscle tension -slow adapting -associated iwth Ib axons |
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JOINT RECEPTORS
-location -morphology -fxn -adaption rate |
proprioreceptive mechanoreceptors in joints
-both free and encapsulated -sense joint position -rapidly adapting |
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"Stocking-and-glove" pattern of sensory loss can be seen in what type of nerve damage?
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PERIPHERAL NEUROPATHY caused by toxins (alcohol, heavy metals), metabolic disturbances (DM), vit. deficiencies (B12)
affects longest, most metabolically active neurons first (those that travel from hands and feet!) |
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Damage to DC-ML system will impair what?
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TACTILE ABILITY
(with the exception of crude touch and proprioception) |
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what kind of deficit is associated with damage to dorsal columns of one side of spinal cord?
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SENSORY DEFICIT will be:
-IPSILATERAL (same side as damage) -at/inferior to level of lesion (BROWN-SEQUARD) |
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what kind of deficit is associated with damage to dorsal columns on both sides?
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POSTERIOR COLUMN SNYDROME
deficit will be bilateral at level of lesion and inferior |
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Lesions to what structures will cause contralateral sensory deficits?
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MEDIAL LEMNISCUS
THALAMUS or POSTcentral GYRUS |
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lesion of medial lemniscus on the right side within the rostral medulla will cause what type of deficit?
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mechanosensory loss to LEFT side of body
contralateral deficit |
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3 ways to test for descriminative touch sensations/abilities:
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-Two-point discrimination (compass)
-Stereognosis (id object by touch) -Graphesthesia (recognize writing on skin) |
