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79 Cards in this Set
- Front
- Back
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Common Features of Neurons |
- soma - axon - dendrite - synapses |
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Soma |
- cell body - where metabolic processes of the cell occur |
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Axon |
process that leaves the soma |
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Dendrite |
branches on which afferents (incoming fibers) make synapses |
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Functions of Neurons |
fundamental tasks of a neuron is to:
- receive signals - integrate signals - conduct signals - transmit signals |
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(2) Major Sub-Classes of Ion Channels |
- Voltage-gated channels (Na(+), Ca(2+), K(+), Cl(-)) - Ligand-gated channels (neurotransmitter, Ca(2+) activated K(+), cyclic nucleotide gated) |
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Identity of Information in Action Potential |
(eg. perception)
based on wiring of neurons |
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Intensity of Information in Action Potential |
based on frequency of impulses |
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Neuron Quantity vs. Synapse Quantity in Human Brain |
- ~90 Billion Neurons - ~ 100 Trillion Synapses |
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Levels of Analysis |
- Intrinsic Properties - Local Networks (integration of neurons) - Cortical Loops (integration of brain regions) - Subcortical Loops (integration of brain regions) |
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(5) Primary Functions of Sensory System |
Sensation: - transduction - transmission
Perception: - inference - deduction - followup |
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Success of Sensory System |
sometimes successful, sometimes not |
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Sensation |
recieving information |
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Perception |
interpretating of information |
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Transduction |
(sensation)
conversion of information into neural signals |
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Transmission |
(sensation)
passing of information onward |
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Inference |
(perception)
did something just happen? |
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Deduction |
(perception)
What was it? Where was it? |
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Follow-Up |
(perception)
Pay more/less attention? |
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(5) Qualities of Information to Encode |
- modality - intensity - duration - location - salience |
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(5) Factors Influencing Success/Failure |
- fatigue - adaption (eg. you don't notice shirt you wear) - sensitization (eg. itch gets worse when you think about it - overlap/redundancy - damage/overload (eg. long rock concerts frequently) |
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(4) Somatosensory Systems |
- Pain - Temperature - Touch (discriminative) - Proprioception |
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Proprioception |
feeling of inside of body (ie. feedback from tendons/joints)
- position (static forces: muscle length, muscle tension, joint pressure) - movement (dynamic forces: muscle length, muscle tension, joint pressure, joint angle) |
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Discriminative Touch |
- touch - pressure - flutter - vibration |
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Dermatome |
- cutaneous innervation related to a single spinal nerve - dermatomal maps vary between individuals - overlap more extensive for touch, pressure, and vibration than for pain -> clinical test for spinal injuries |
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Dorsal Root Ganglia |
- contains the sensory neurons of the somatosensory system - sends sensory information to the Dorsal Root - in Sacral portion of spinal cord |
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Spinal Cord |
- Dorsal Column - Ventral Column
|Cervical |Thoracic |Lumbar |Sacral (Dorsal Root Ganglia location) V |
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Dorsal Column of Spinal Cord |
sensory fibers |
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Ventral Root of Spinal Cord |
motor fibers |
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Dorsal Column-Medial Lemniscus System |
"touch" portion (tactile afferents) |
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Common Features of Neurons |
- soma - axon - dendrite - synapses |
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Receptive Fields of Neurons |
- differ in size among neurons - differ in responses to stimuli |
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Tactile Information |
mechanoreceptors in the skin |
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Deepness of Mechanoreceptors |
|(least deep) | Free Nerve Endings (epidermis) | Meissner Corpuscles (dermis) | Merkel Disks (dermis) | Ruffini Endings (dermis) | Pacinian Corpuscles (subcutaneous layer) V (deepest) |
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Speed of Sensory Functions (Axon Type) |
Proprioception > touch > pain/temperature > pain/temperature/itch |
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Tactile Information |
- detected by mechanoreceptors in the skin - body: uses medial lemniscal system - dorsal column of spinal cord - face: uses trigemino-thalmic system |
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Deepness of Mechanoreceptors in the Skin |
|(least deep) | free nerve endings (epidermis) | Meissner Corpuscle (dermis) | Merkel Disks (dermis) | Ruffini Endings (dermis) | Pacinian Corpuscle (subcutaneous layer) V (deepest) |
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Activation of Mechanoreceptors |
activation of the mechanosensitive nerve endings in the: - (body): dorsal root ganglia - (face): trigeminal ganglia transduces mechanical stimuli into action potentials to mediate the sense of touch |
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Diversity of Touch Receptors |
- show different pressure thresholds - show different adaption kinetics - (ie. decay of activity in response to continuous stimulation) |
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Mechanoreceptors Detect and Code: |
- gentle touch - shape - texture - vibration - a wide range of painful stimuli |
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Merkel's Disks |
- small receptive field - form and texture perception - stimuli = edges, points, corners, and curvature - slow adaption |
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Meissner's Corpuscles |
- small receptive field - motion detection, grip control - stimuli = skin motion - rapid adaption |
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Pacinian Corpuscles |
- large receptive field - perception of distant events through transmitted vibrations, and tool use (eg. grip adjustment) - stimuli = vibration - rapid adaption |
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Ruffini Endings |
- large receptive fields - tangential force, hand shape, motion direction - stimuli = skin stretch - slow adaption |
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Mechanoreceptor Best for Reading Braille |
Merkel's Disks |
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Sensory Afferent Degrees of Adaption |
(sensory afferents differ in their response to sustained stimulation)
- slow adaption - rapid adapting |
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Slow Adapting Afferents |
- convey information about spatial attributes of stimulus (ie. size and shape) - slow but last for a long period - Merkel Disks and Ruffini Corpuscles |
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Rapid Adapting Afferents |
- convey information about changes in ongoing stimulation (ie. stimulus movements) - the dynamic qualities of the stimulus - fire rapidly at first but slow eventually - Meissner Corpuscles and Pacinian Corpuscles |
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How Change is Encoded in Sensory Afferents |
(rapidly adapting afferents)
change is encoded in discreet bursts of action potentials |
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Mechano-Sensitive Channels |
(eg. proprioception) - use proprioceptors - "mechano" in that they "open" by stretch (ie. of muscles) - high threshold or low threshold |
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What can Lower the Threshold of a Mechano-Sensitive Channel? |
Deformation of the DRG (free or encapsulated) by a mechanical stimulus lowers the threshold needed to evoke an action potential |
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"Threshold" of a Mechano-Sensitive Channel |
the stretch (stimulus) needed for activation (action potential) |
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High-Threshold Mechano-Sensitive Channels |
- characterize nociceptors (receptors for pain) - found predominately in smaller DRG - activated by higher pressures |
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Proprioception |
- mechanoreceptors in the joints and muscles - "receptors for self": give information about the position of body and limbs in space - receptors include muscle spindles, Golgi tendon organs, and joint receptors |
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Muscle Spindles |
(proprioceptor) - 4-8 intrafusal muscle fibers in a capsule among extrafusal (force producing) fibers - activated by detected changes in muscle length on two types of afferent fibers (group Ia and group II) - more muscle spindles = more precise control |
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Y Motor Neurons |
- located in Dorsal Horn of spinal cord - controls tension of intrafusal fibers |
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Areas of the Body Requiring Precise Muscle Control |
(have more muscle spindles) - extraocular muscles (eye movements) - neck muscles - hand muscles |
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Group IA Afferent Fibers |
- large myelinated fibers - rapidly adapting - activated by stretching of the muscle (mechanoreceptors) |
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Group II |
- myelinated fibers - slowly adapting - activated by stretching of the muscle (mechanoreceptors) |
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Golgi Tendon Organs |
(proprioceptor) - signal changes in muscle tension - formed by branches of group Ib afferents |
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Medial Lemniscal System |
- dorsal column of spinal cord - tactile afferents from the body ("touch" portion) |
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Axons of Medial Lemniscus Synapse With: |
the thalamic neurons located in the Ventral Posterior Lateral Nucleus (VPL) |
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Somatosensory Cortex (SI) |
recieves information from 3rd order neuron axons |
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Second Order Neurons |
- destination of information is in the medulla (nucleus gracilis and nucleus cuneatus) - project to thalamus via the medial lemniscus |
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First Order Neurons of Medial Lemniscus System |
- project through dorsal column of spinal cord (fasciculus cuneatus and fasiculus gracilis) |
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Trigeminothalamic System |
- afferents from face - dorsal column of spinal cord |
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First Order Neurons of Trigeminothalamic System |
- project information through trigeminal nerve |
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Fibers of Proprioceptive Afferents from the Body |
- have ascending and descending branches (involved in reflexes) - important projection to the cerebellum (dorsal spinocerebellar tract) which controls timing of muscle contractions |
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Third Order Neurons From Within the Medullar... |
decussate and join cutaneous fibers in the medial lemniscus on the way to the VPL thalamus |
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All Sensory Information Goes Through: |
relay in the thalamus |
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Primary Somatosensory Cortex |
Brodmann's areas 3a, 3b, 1, and 2 |
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Brodmann's Area 3b |
- serves as obligatory first step in cortical processing of somatosensory information - lesions in this area have the largest impact |
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Columns |
functional modules of the cortex |
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Plasticity in Adult Cortex |
- reorganization of cortical maps in response to altered functional input (ie. blindness or amputation) - functional expansion of a cortical representation following repeated stimulation (repeated stimulation makes body part more relevant so sensation grows and vice-versa) |
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VP Complex |
for touch in the primary somatosensory cortex |
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Brodmann's Areas are Mapped.. |
by using only comparison of densities |
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Primary Somatosensory Cortex Mapped... |
according to function, not size |
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Different Layers of Cortex: |
- arrangements differ in different regions of the cortex - project to different parts of the brain |
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Columns in Somatosensory Cortex |
- functionally distinct columns from other area, but very similar to others in this area |
