Lecture 33 - Somatosensory Flashcards
Mechanoreceptors in the skin transmit sensations through nerves whose cell bodies are in the ______ _____ ganglia. These nerves travel through the _____ columns in the spinal cord.
Pain stimuli can be conveyed by Nociceptors or by free nerve endings. The nerves in this pathway synapse in the _____ horn of the spinal cord –> they decussate immediately and travel up via the _______ spinal tract.
Dorsal Root ganglia
Dorsal columns
Dorsal horn
Anterolateral spinal tract
Mechanosensation is transmitted via Free Nerve Endings and 4 types of Mechanoreceptors:
- Meissner corpuscles
- Merkel neurite complexes
- Ruffini endings
- Pacinian corpuscles
In which layer of the skin do each of these reside (including Free nerve endings)?
Free Nerve endings –> Epidermis
Meissner Corpuscles –> Papila of Dermis
Merkel neurite complexes –> Rete ridges of Epidermis
Ruffini endings –> Deep in the Dermis
Pacinian Corpuscles –> Subcutaneous
Pacinian Corpuscles respond to ______ pressure and _______. The dendrites of these neurons are encapsulated, and stretching of this capsule results in activation of cation channels.
Note: the degree of stretching is proportional to the degree of activation, resulting in _______ Potentials.
Deep pressure
Vibration
Receptor Potentials
Each of the mechanoreceptors in glabrous skin respond to diff stimuli.
Merkel (Rete ridges of Epidermis) –> _______
Meissner (Papilae of dermis) –> _______
Ruffini –> _______
Pacinian –> _______
Rank these receptors in order of the size of their respective receptor fields (think about being able to discriminate between stimuli types.)
Rank these receptor types in order of abundance in Glabrous skin.
Merkel –> Sharp corners, pin-point, curvatures
Meissner –> Skin motion (light touch and grip)
Ruffini –> Skin stretch and pressure
Pacinian –> deep pressure and vibration
Merkel < Meissner < Pacinian < Ruffini
Meissner > Merkel > Ruffini > Pacinian
What do Frequency coding and Population coding refer to?
Frequency coding –> size/intensity of the stimulus is proportional to the frequency of APs fired by the receptor neuron axon.
Population coding –> size of te stimulus in terms of the surface area of the skin that it covers is proportional to the number of receptors that will be activated.
Mechanoreceptors in glabrous skin are either Fast Adapting or Slow Adapting. Which is which?
Merkel –> Slow Adapting (sense the static nature of touch, so will continue to fire throughout duration of stimulus)
Meissner –> Fast Adapting (sense movement acoss skin, so will adapt/stop firing after initial response to stationary touch)
Pacinian –> Fast Adapting
Ruffini –> Slow Adapting (sustained response)
Sensory receptors respond to different stimuli, and these stimuli are coded differently. They MAINTAIN this different coding up to the Primary Somatosensory cortex; there is no integration of sensory info up to this point –> this is called “______ ______.”
Labeled Line
Mechanoreceptor axons from the Lower body travel up to the ______ nucleus (1 of the ______ ______ nuclei of the Medulla) via the ______ tract.
Mechanoreceptor axons from the Upper body travel up to the ______ nucleus (the other of the ______ ______ nuclei of the Medulla) via the ______ tract.
The Secondary neurons in this pathway decussate and travel from the Medulla to the Thalamus via the ______ ______ pathway.
Remember: sensory fibers from the body send info to the ______ _________ nucleus of the Thalamus, while info from the Face travels via the __________ tract to the _______ _________ nucleus of the Thalamus.
Gracilis nucleus
Dorsal Column nuclei
Gracile tract (more medial in the dorsal horn and Medulla BUT switched in the PONS)
Medial Lemniscal pathway
Cuneate nucleus
Dorsal Column nuclei
Cuneate tract (more lateral in the dorsal horn and Medulla BUT switched in the PONS)
Ventral Posteriolateral nucleus
Trigeminothalamic tract
Ventral Posteriomedial nucleus
Somatosensory info from the Concha patch behind the Ear travels via CN _____ (Facial nerve).
Somatosensory info from the Posterior 1/3 of the tongue, _____ Ear, and INTERNAL surface of the _______ membrane travels via CN ____ (Glossopharyngeal nerve)
Somatosensory info from the ______ ______ meatus, Parts of the ear, and _______ travel via CN _____ (Vagus nerve)
CN IIV
Posterior 1/3 of Tongue, External Ear, and INTERNAL surface of Tympanic Membrane
CN IX
External Auditory meatus, Parts of the ear, and Pharynx
CN X
Lateral inhibition referes to inhibition of _____ order sensory neurons in the Dorsal column of the Ascending spinal tracts.
What does Distal Inhibition refer to?
2nd order
What happens is 1st order neurons synapse with both 2nd order neurons AND Interneurons in the Dorsal horn. The interneurons INHIBIT adjacent 2nd order neurons, and this enhances the signal coming from the most activated 1st order neuron and its 2nd order neuron.
Distal inhibition refers to sensory afferents from the Primary somatosensory cortex Descending to the Medullary nuclei (Gracilis and Cuneate) and VPL of Thalamus via the Corticofugal or Centrifugal pathways. This regulates sensory info sent to higher centers, allowing for focussing/gating of info.
Remember that BOTH the ____ ____ Organ and _______ Spindles (around intrafusal muscle fibers) respond to muscle strething, but ONLY one of them responds to muscle contraction. Which one?
Golgi Tendon Organ
Muscle Spindles
ONLY Muscle Spindles respond to contraction.
Proprioceptive pathways are ______ (contralateral or ipsilateral?) and travel to the ______ via the ________ tract.
For the lower body, the 1st order neurons synapse in ______ Nuclei between ____ - ____ (which vertebrae?).
For the upper body, 1st order neurons synapse in either the External ______ nucleus or Accessory ______ nucleus.
Ipsilateral
Cerebellum
Spinocerebellar tract
Clarke’s Nuclei
L2-T1
External Cuneate or Accessory Cuneate Nucleus
Pain sensation travels to the Thalamus via the ________ (aka ________) tract.
Spinothalamic (aka Anterolateral)
Describe what type of Information is sent via each of the following white matter spinal cord tracts:
Drosal Column –>
Spinothalamic (aka Anterolateral) –>
Spinocerebellar –>
Dorsal Column –> Mechanical sensation
Spinothalamic (aka Anterolateral) –> Noxious (painful) stimuli
Spinocerebellar –> Proprioception
Adelta Nociceptor fibers are _______ (myelinated or unmyelinated) and convey _____ (sharp or dull?) pain, while C fibers are ________ (myelinated or unmyelinated) and convey ______ (sharp or dull?) pain.
Myelinated
Sharp
Unmyelinated
Dull
