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Definition
| Most diverse, mediates touch, pressure, vibration, limb position, heat, cold and pain. |
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Definition
| Sensations are transduced by receptors in skin/muscles and sent to CNS targets. |
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Definition
| Different sets of peripheral receptors and central pathways w/ different functions. |
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| Subsystem from cutaneous mechanoreceptors |
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Definition
| Mediates fine touch, vibration, pressure. |
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| Subsystem from receptors in muscles, tendons, and joints |
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Definition
| Responsible for proprioception |
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Definition
| Ability to sense position of body in space |
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| Subsystem from receptors w/ info of painful stimuli & changes in temp |
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Definition
| Also gives info of coarse touch. |
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| Where somatic sensation comes from |
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Definition
| Activity of afferent nerve fibers w/ peripheral processes in skin/muscle. |
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Term
| Cell bodies of somato afferent nerves |
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Definition
| In series of ganglia along spinal cord & brainstem. |
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Definition
| For info from body. Cell bodies reside here. |
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Definition
| For info from head. Cell bodies reside here. |
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Term
| How AP's propagate in afferent fibers from skin/muscle stimulation |
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Definition
| Propagate along fiber until past the location of ganglia, where synapse. |
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Definition
| Peripheral & central components of afferent fibers continuous. Attached to cell body in ganglia by one process. |
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| Electrical conduction through cell body membrane |
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Definition
| Unnecessary to convey sensory info to central targets. Cell bodies still help maintain cellular machinery that mediates transduction, conduction, and transmission. |
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Definition
| Converting energy of stimulus into electrical signal. Similar in all somatosensory afferents. |
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| How sensory transduction works |
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Definition
| Stimulus alters permeability of cation channels in afferent nerve ending, makes depolarizing current (receptor or generator potential). If gets to threshold, have AP. AP rate proportional to magnitude of depolarization. |
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Term
| Receptor/generator potential |
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Definition
| Depolarizing current of afferent nerve ending from sensory transduction. |
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Definition
| Tune fiber to particular types of somatic stimulation. Encapsulate fibers. Lower thresholds for AP and more sensitive to stimulation than w/o mechanoreceptors. |
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Definition
| Afferent fibers w/o mechanoreceptors. Important for sensation of pain. |
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Term
| Differentiating factors of classes of somatosensory afferents |
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Definition
| Axon diameter, receptive field. |
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Term
| Axon diameters of different fibers |
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Definition
Largest: Ia, supply sensory receptors in muscles.
Slightly smaller: Abeta, info from touch
Smallest: Adelta and C, convey info about pain & temp. |
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Definition
| Area of skin surface where stimulation results in significant change in rate of AP's. Fields of dense innervation (fingers, lips, etc.) much smaller than receptive fields of less innervation (back, leg, etc.) |
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Term
| Limiting factors of accuracy of tactile stimuli reception |
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Definition
| Regional differences in receptive field size, innervation density. |
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Definition
| Measure minimum interstimulus distance (distance between stimulus A and B) required to perceive two simultaneously applied stimuli as distinct. Fingertip only 2mm, forearm at least 40mm! |
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Term
| Rapidly adapting afferents |
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Definition
| Silent in face of continued stimulation. Good for conveying info about changes in ongoing stimulation, like stimulus movement. Pacinian corpuscles. |
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| Slowly adapting afferents |
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Definition
| Better to give info about spatial characteristics, like size & shape. |
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Term
| When sensory afferent can give rise to mulitple peripheral branches... |
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Definition
| Transduction properties of all branches are identical. |
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Definition
| Differ in conduction velocity, receptive field size, dynamics and effective stimulus features. Segregated through several stages of central processing. |
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| Understanding of cutaneous sensation |
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Definition
| Palm and fingertips, b/c don't have hair which alters senses. Specialized for high-def neural image of felt objects. |
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Definition
| Ability to identify an object by manipulating it with the hand |
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Definition
| Slowly adapting. 25% of mechanosensory afferents in hand. Especially in fingertips. Get info from receptor cells in epidermis. Merkel cell complexes in tips of primary epidermal ridges (underlying of fingerprints); excitable w/ voltage-sensitive Ca2+ channels and molecules used for synaptic vesicle release. Highest spatial resolution of all. Highly sensitive to points, edges, curvature. |
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| AP's from Merkel cell afferents |
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Definition
| Come from mechanosensitive ion channels in membrane of afferents. Merkel cells may modulate activity of afferents instead of being site of transduction. |
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Definition
| Rapidly adapting. 40% of mechanosensory innervation in hand. More densely innervate skin than Merkel. Corpuscles in tips of dermal papillae, adject to primary ridges & closest to skin surface; formed by connective tissue capsule of several lamellae of Schwann cells. Center of capsule has 2-6 afferent nerve fibers that derminate as disks between Schwann cell lamellae (see a pic). More than 4x sensitive to skin deformation than Merkel, b/c so close to surface. Receptive fields larger than Merkel, transmit signals with less spatial resolution. Best at transducing info at low-frequency vibrations like when textured objects move across skin & grip. |
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Definition
| Rapidly adpating. 10-15% of hand. Deep in dermis (subcutaneous) tissue. Like small onions w/ layers of membrane surrounding one afferent fiber. Capsule acts as filter, only lets high-frequency stimulation activate nerve endings. Adapt more rapidly than Meissner, lower threshold. Very sensitive, receptive fields often large & boundaries hard to define. Good for detecting vibrations through objects that contact the hand or are being grasped, like tools (cutting bread). |
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Definition
| Slowly adapting. 20% of hand. Receptors elongated, spindle-shaped. Deep in skin and in ligaments & tendons. Parallel to stretch lines of skin. Very sensitive to stretching of skin (like movement). Help w/ movement of fingers and hand and knowing finger position and conformation. |
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Term
| Responses from Braille reading |
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Definition
| Merkel recognizes details of Braille pattern, Meissner have coarser version of pattern but still show it, Ruffini & Pacinian both lose pattern b/c having nothing to do with that kind of stimulus. |
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Definition
| Means receptors for self. Focus about info from body itself, especially from musculoskeletal system. Get info from muscle spindles, Golgi tendon organs, and joint receptors. |
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Definition
| In almost all striated skeletal muscles. 4-8 intrafusal muscle fibers surround. Innervated by Ia and II afferents. |
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Definition
| In parallel arrangement with extrafusal fibers. Keep muscle spindle always at around same length. Sensory afferents are coiled around in central part of intrafusal spindle. When muscle swtretched, tension on intrafusal fibers activates mechanically-gated ion channels in nerve endings and makes AP's. Contractile, too. Controlled by gamma motor neurons. |
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Definition
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| Primary endings are largest myelinated sensory axons. Rapidly adapting responses to changes in muscle length. Transmit info about velocity & direction of movement of limbs. |
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Definition
| Secondary endings make sustained responses to constant muscle lengths. Gives info about static position of limbs. |
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Definition
| In ventral horn of spinal cord. Keep intrafusal fibers around same length at all times so spindle afferents can still be sensitive to change in muscle length. |
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Definition
| In large muscles for coarse movements, have few spindles. Muscles in hand & neck have many spindles (neck b/c of continuous demand for position of head). No spindles in middle of ear, which don't need feedback from these receptors. |
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Definition
| Made by branches of group Ib afferents among collagen fibers which form tendons. Each has 10-20 muscle fibers. Population of them for given muscle tells average tension in muscle. [image] |
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Definition
Look like Ruffini endings and Pacinian corpuscles. Get cutaneous signals from Ruffini afferents and inputs from muscle spindles in joints.
[image] |
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Term
| Dorsal Column-Medial Lemniscal System (DCMLS) |
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Definition
| Tract of cutaneous mechanosensory afferents. |
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Definition
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Term
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Definition
| Enter spinal cord through dorsal roots. Most on same side of body through dorsal columns. |
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Term
| DCMLS: from dorsal columns |
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Definition
| From dorsal columns to lower medulla, synapse on neurons in dorsal column nuclei (gracile for lower-body, cuneate for upper-body). |
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Term
| DCMLS: first-order tract of lower & upper body |
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Definition
Lower: travel in fasciculus gracilis, end in nucleus gracilis. More medial.
Upper: travel in fasciculus cuneatus. End in nucleus cuneatus. |
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Term
| DCMLS: second-order tracts |
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Definition
Axons leaving dorsal column nuclei: internal arcuate fibers.
Internal arcuate fibers cross midline and makes dorsoventrally elongated tract called medial lemniscus (cuneatus and gracilis meet up, gracilis ventral & cuneatus dorsal). Ascends through pons & midbrain, rotates 90 degrees laterally (upper & lower-body axons switch positions).
Axons synapse with thalamic neurons in ventral posterior lateral nucleus (VPL). |
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Term
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Definition
| Send axons through internal capsule to terminate in postcentral gyrus (primary somatosensory cortex, SI; lower-body) or secondary somatosensory cortex (SII; upper body). |
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Definition
| Central pathway to convey tactile info from face |
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Term
| Overall pathway of trigeminothalamic system |
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Definition
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Term
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Definition
| Info from mechanoreceptors of face by first-order neurons in trigeminal (cranial nerve V) ganglion. Peripheral processes split into subdivisions of trigeminal nerve: ophthalmic (vision), maxillary (nasal, sinuses, palate), mandibular (mouth, teeth, jaws, etc.) made of central processes of trigeminal ganglion. The nerve enters brainstem at pons, terminates on neurons in trigeminal brainstem complex - principal nucleus (info from low-threshold receptors, like dorsal column nuclei from body) and spinal nucleus (neurons sensitive to pain, temp and coarse touch). |
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Term
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Definition
| Second-order neurons of trigeminal brainstem nuclei give axons that cross midline and ascend to ventral posterior medial nucleus (VPM) of thealamus through trigmeinothalamic tract. |
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Term
| Proprioceptive Pathway: first-order |
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Definition
LOOK AT LECTURE PIC!
Enter spinal cord through dorsal roots, travel with axons w/ cutaneous info. Many separate into ascending & descending branches, some pentrate dorsal horn & synapse there and in ventral horn. Reaches higher cortical areas than tactile info. Ones that enter between mid lumbar & thoracic levels synapse on neurons in Clark's nucleus (medial aspect of dorsal horn). Ones below synapse with Clark's nucleus, too.
From upper: enter and travel through fascilus cuneatus up to medulla where synapse on proprioceptive neurons in dorsal column nuclei. |
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Term
| Proprio: second-order of upper body |
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Definition
| Send axons across midline and join medial lemniscus to go to VPL of thalamus. |
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Term
| Proprio: second-order of lower body |
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Definition
| From Clark's nucleus send axons into ipsilateral posterior lateral column of spinal cord, travel to level of medulla in dorsal spinocerebellar tract. Axons continue into cerebellum. Give off collaterals that synapse with neurons just outside of nucleus gracilus. |
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Term
| Proprio: third-order lower body |
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Definition
| Axons from outside nucleus gracilus cross over and join medial lemniscus to VPL of thalamus. |
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Term
| Proprioceptive Pathway from Face |
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Definition
| Through trigeminal nerve, too. Proprioceptive info from face. |
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Term
| Proprio face: first-order |
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Definition
First-order neurons in CNS in mesencephalic trigeminal nucleus, a cluster of neurons at lateral extent of central gray midbrain - peripheral processes innervate muscle spindles & Golgi tendon organs for facial musculature, central processes project to brainstem nuclei for reflex control of facial muscles.
Info must reach thalamus, represented in somatic sensory cortex. |
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Term
| Somatosensory part of thalamus |
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Definition
All pathways onto part of ventral posterior complex of thalamus.
Info gets supplied by different pathways. VPL gets info from medial lemniscus (somatosens from body & posterior head), VPM gets info from trigeminal lemniscous w/ somatosens from face.
[image] |
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Term
| Projections from ventral posterior complex of thalamus |
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Definition
| Most project to cortical neurons in layer 4 of primary somatic sensory cortex, near midline. |
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Term
| Primary somatosensory cortex |
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Definition
SI. Postcentral gyrus of parietal lobe, with 4 regions: Brodmann's areas 3a, 3b, 1 and 2.
[image]
Homunculus, little person, mapped out onto it.
[image] |
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Term
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Definition
3b (bulk input from ventral posterior complex, gives dense projections to areas 1 and 2) and 1 respond mostly to cutaneous stimuli. 3a responds mostly to stimulation of proprioceptors. 2 responds to both tactile & proprioceptive.
3b necessary first step in processing. |
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Term
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Definition
Info goes from SI to higher order cortical fields. One SII, upper bank of lateral sulcus, gets convergent projections from all areas of SI.
[image]
Amygdala and hippocampus get projections from SII (tactile learning & memory).
[image]
SI neurons project to parietal areas behind area 2, espeically 5a and 7b (direct projections from area 2, give inputs to motor & premotor of frontal lobe) - integration of sensory & motor info!
[image] |
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Term
| If finger cut off, what happens? |
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Definition
| Regions around cut-off area start to stimulate nerves that cut off digit were attached to after a while. Functional remapping happens in thalamus and brainstem. Requires plasticity. |
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Term
| If use finger more often over a period of time, what happens? |
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Definition
| Functional electrical area will be enlarged for finger used and others will be smaller. |
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Term
| Effects of local anesthesia on receptive field |
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Definition
| Neurons in anesthetized region take on new receptive fields that respond to stimulation of skin around anesthetized area. When anesthesia fades, goes back to normal. Why cheek feels puffy after novacaine. |
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Term
| Plasticity here permanent? |
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Definition
| No, seem mostly temporary. |
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Term
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Definition
| 9.10, 9.11, 9.12, 9.13, powerpoint |
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