4,1 Tactile Flashcards
MechanoreceptorsProperties (3)<div><br></br></div><div>- What are they?</div><div>- Where are their cell bodies?</div>
<ul> <li>Receptors are not neurons, but nerve endings encapsulated in connective tissue</li> <li>Four types of mechanoreceptors that are innervated by large myelinate axons with cell bodies in the dorsal root ganglia.</li> <li>Transmission of this information to our brain generates our conscious experience of touch</li></ul>
Types of Mechanoreceptors (4)
Meissner Corpuscles<br></br>Merkel Complexex<br></br>Ruffini Organs<br></br>Pacinian Corpuscles<br></br>
Meissner CorpuscleLocation? (2)
<ul> <li>Epidermis Layer (Crest of dermal ridge)</li> <li>Close to the surface of the skin (border between dermis and epidermis)</li></ul>
Meissner Corpuscles Adaptation? (1)
<ul> <li>Rapid Adapting: Transient response to skin movement (dynamic response)</li></ul>
Meissner Corpuscles Receptive Field? (3)
<ul> <li>Very small receptor field</li> <li>Higher innervation density</li> <li>40%</li></ul>
Merkel ComplexesLocation? (2)
<ul> <li>Epidermis Layer (trough of dermal ridge/tips of epidermal ridge).</li> <li>Located close to the surface of the skin (border between dermis and epidermis)</li></ul>
Merkel ComplexesAdaptation? (1)
Slow adaptation: Sustained response to skin indentation (dynamic plus static response)
Merkel ComplexesReceptive Field? (3)
<ul> <li>Smallest receptor field</li> <li>Higher innervation density</li> <li>25%</li></ul>
Ruffini Organs Located? (1)
Upper dermis
Ruffini Organs Adaptation? (1)
Slow adaptation: Sustained response to skin movement (dynamic plus static response)
Ruffini OrgansReceptive Field? (4)
<ul> <li>Large Receptive Field</li> <li>Detects skin movement and stretch, hence provide proprioceptive information about hand positions</li> <li>Lower innervation density</li> <li>20%</li></ul>
Pacinian CorpusclesLocation(1)
<ul> <li>Location? (1) <ul> <li>Located deepest in the dermis</li> </ul> </li></ul>
Adaptation? (1)Pacinian Corpuscles
<ul> <li>Adaptation? (1) <ul> <li>Fast Adaptation: Transient response to skin vibration (Dynamic Response)</li> </ul> </li></ul>
Pacinian Corpuscles: Receptive Field? (2)
<ul> <li>Receptive Field? (2) <ul> <li>Large Receptive Field</li> <li>Lower innervation density</li> <li>15%</li> </ul> </li></ul>
Transduction (3)Mechanoreceptors
“<ul> <li> <div>Mechanoreceptor membranes contain stretch sensitive ion channels.</div> </li> <li> <div>Indentation of skin opens mechanically-gated Na+channels, depolarising the neuron a little (Does not give a sensation of touch)</div> </li><li><div>When threshold is reached, voltage-gated channels are open, and action potentials propagates along axon to spinal cord.<br></br><br></br><img></img><br></br></div></li><li><div><img></img><br></br></div></li></ul>”
Slow adaptation (2) vs Rapid Adaptation (2): Information provided and Neuronal Action
“<div><div>Slow adaptation (2):<br></br></div><ul><li>Information provided:Strength and duration of the stimulus</li><li>Neuronal Action: Initial excitement, followed by a regular proportional response</li></ul></div><div>Rapid adaptation (2)<ul><li>Information provided: Rate of change</li><li>Neuronal Action: Burst of activity, followed by no activity</li></ul></div><ul><li><img></img><br></br></li></ul><div></div>”
Dermatomes (1)
“Spinal cord representation is ordered (dermatomes).<ul> <li>Cervical</li> <li>Thoraic</li> <li>Lumbar</li> <li>Sacral<br></br><br></br><img></img><br></br></li></ul>”
Somatosensory afferents to central circuits:Properties of sensory afferent axons: Name, diameter, conduction velocity (3)
“<ul> <li>Alpha-Beta Fibres</li> <li>6-12um</li> <li>35-75m/s (Next fastest after motor)</li></ul><div><img></img><br></br></div>”
Somatosensory afferents to central circuits:Pathway Step 1 (2)
“Sensory neurons from the skin have their cell bodies in the DRG (or trigeminal ganglion from face).<div><br></br></div><div>They enter the spinal cord via the posterior horn<br></br><img></img><br></br></div>”
Somatosensory afferents to central circuits:Pathway Step 2 (1)
Posterior horn: Sensory neuron enters a tract on the ipsilateral side, and travels up to the brainstem
Somatosensory afferents to central circuits: Step 3 (1)
Brainstem: The sensory neuron SYNAPSES with another sensory neuron in the Dorsal Column Nuclei (Synapse #1: Sensory neuron). The axons from Dorsal Column Nuclei then crosses the midline (decussates) and projects to the thalamus on the contralateral side (Synapse #2: Thalamus)
Somatosensory afferents to central circuits: Step 4 (Thalamus)
Thalamic neurons make ipsilateral projections to primary somatosensory cortex (S1)
Somatosensory afferents to central circuits: Pathway run through
“<img></img>”
Primary somatosensory cortex (Location, alternative name. associated areas)?
“Location: Postcentral gyrus<br></br>Alternative names: Broadman areas 1,2,3a,3b<br></br>Associated areas: Secondary somatosensory cortex and posterior parietal cortex<br></br><img></img><br></br>”
Organisation (4) Primary somatosensory cortex
“Topographic (Ordered)<br></br><br></br><div>1.Body parts located close to each other are represented close to each other on the somatosensory cortex</div><div><img></img><br></br></div><div>2. Amount of cortical representation is related to the amount of sensory innervation of the structure (More cortex devoted to parts that requires higher spatial acuity - homunculus)<br></br></div><div><br></br></div><div>3. Neurons from the 4 types of mechanoreceptors, when considered by slowly or rapidly adapting properties, are represented in the cortex in a segregated but interspersed manner<br></br><br></br><img></img><br></br><br></br>4.All 4 Brodmann areas have the same mapping pattern<br></br><br></br><img></img><br></br></div>”
Plasticity (2) of S1
Mapping of the body onto the somatosensory cortex is plastic (this applies to all sensory cortices, not just the somatosensory cortex).<div><br></br></div><div>Hence, cortical representations adapt to changes, both in physiology (e.g., amputation) and stimulation (repetitive behavioural task)</div>
Plasticity S1: Rats (2)
“<img></img><div>Rats that are lactating have a greater proportion of their somatosensory cortex dedicated to their ventrum<br></br></div><div>After lactating, the cortical area dedicated to their ventrum reduces<br></br></div>”
Plasticity S1: Amputation and RBT (2)
“Digit amputation leads to expansion of representation of adjacent digits.<br></br><img></img><br></br><img></img><br></br><br></br>”
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