4,1 Tactile

Question 1

MechanoreceptorsProperties (3)<div><br></br></div><div>- What are they?</div><div>- Where are their cell bodies?</div>

Answer 1

<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>

Question 2

Types of Mechanoreceptors (4)

Answer 2

Meissner Corpuscles<br></br>Merkel Complexex<br></br>Ruffini Organs<br></br>Pacinian Corpuscles<br></br>

Question 3

Meissner CorpuscleLocation? (2)

Answer 3

<ul> <li>Epidermis Layer (Crest of dermal ridge)</li> <li>Close to the surface of the skin (border between dermis and epidermis)</li></ul>

Question 4

Meissner Corpuscles Adaptation? (1)

Answer 4

<ul> <li>Rapid Adapting: Transient response to skin movement (dynamic response)</li></ul>

Question 5

Meissner Corpuscles Receptive Field? (3)

Answer 5

<ul> <li>Very small receptor field</li> <li>Higher innervation density</li> <li>40%</li></ul>

Question 6

Merkel ComplexesLocation? (2)

Answer 6

<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>

Question 7

Merkel ComplexesAdaptation? (1)

Answer 7

Slow adaptation: Sustained response to skin indentation (dynamic plus static response)

Question 8

Merkel ComplexesReceptive Field? (3)

Answer 8

<ul> <li>Smallest receptor field</li> <li>Higher innervation density</li> <li>25%</li></ul>

Question 9

Ruffini Organs Located? (1)

Answer 9

Upper dermis

Question 10

Ruffini Organs Adaptation? (1)

Answer 10

Slow adaptation: Sustained response to skin movement (dynamic plus static response)

Question 11

Ruffini OrgansReceptive Field? (4)

Answer 11

<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>

Question 12

Pacinian CorpusclesLocation(1)

Answer 12

<ul> <li>Location? (1) <ul> <li>Located deepest in the dermis</li> </ul> </li></ul>

Question 13

Adaptation? (1)Pacinian Corpuscles

Answer 13

<ul> <li>Adaptation? (1) <ul> <li>Fast Adaptation: Transient response to skin vibration (Dynamic Response)</li> </ul> </li></ul>

Question 14

Pacinian Corpuscles: Receptive Field? (2)

Answer 14

<ul> <li>Receptive Field? (2) <ul> <li>Large Receptive Field</li> <li>Lower innervation density</li> <li>15%</li> </ul> </li></ul>

Question 15

Transduction (3)Mechanoreceptors

Answer 15

“<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>”

Question 16

Slow adaptation (2) vs Rapid Adaptation (2): Information provided and Neuronal Action

Answer 16

“<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>”

Question 17

Dermatomes (1)

Answer 17

“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>”

Question 18

Somatosensory afferents to central circuits:Properties of sensory afferent axons: Name, diameter, conduction velocity (3)

Answer 18

“<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>”

Question 19

Somatosensory afferents to central circuits:Pathway Step 1 (2)

Answer 19

“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>”

Question 20

Somatosensory afferents to central circuits:Pathway Step 2 (1)

Answer 20

Posterior horn: Sensory neuron enters a tract on the ipsilateral side, and travels up to the brainstem

Question 21

Somatosensory afferents to central circuits: Step 3 (1)

Answer 21

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)

Question 22

Somatosensory afferents to central circuits: Step 4 (Thalamus)

Answer 22

Thalamic neurons make ipsilateral projections to primary somatosensory cortex (S1)

Question 23

Somatosensory afferents to central circuits: Pathway run through

Answer 23

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Question 24

Primary somatosensory cortex (Location, alternative name. associated areas)?

Answer 24

“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>”

Question 25

Organisation (4) Primary somatosensory cortex

Answer 25

“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>”

Question 26

Plasticity (2) of S1

Answer 26

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>

Question 27

Plasticity S1: Rats (2)

Answer 27

“<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>”

Question 28

Plasticity S1: Amputation and RBT (2)

Answer 28

“Digit amputation leads to expansion of representation of adjacent digits.<br></br><img></img><br></br><img></img><br></br><br></br>”

Question 29

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Answer 29

%<br></br>RF<br></br>Density <br></br>Sensitvity<br></br>Location

Question 30

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Answer 30

%<br></br>RF<br></br>Density <br></br>Sensitvity<br></br>Location

Question 31

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Answer 31

%<br></br>RF<br></br>Density <br></br>Sensitvity<br></br>Location

Question 32

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Answer 32

%<br></br>RF<br></br>Density <br></br>Sensitvity<br></br>Location

Question 33

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Answer 33

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