spinal cord and sematosensation Flashcards
Basic spinal cord function:
Receives sensory afferent inputs
Motor efferent
Cross regulation within for movement
describe shape of grey and white matter within spinal chord
Central H or algebra x shaped grey matter surrounded by white matter rich in myelination.
what role do morphogens play in development state two prominent ones
Dictate development of nervous system
Dorsal, sensory BMP dictator factor
Ventral motor- sonic hedge hog
Dermatomes dictate destination of somite-induced outgrowing of spinal sensory afferents
how can spinal chord segments can be identified
Spinal cord segments can be identified by the ratio of grey to white matter
White matter volume increases while ascending as more sensory afferents and motor efferents are added to the spinal cord
state some experimental evidence of mitogens actions on motor neuron fate
transplant segments of the floor plate in the embryonic notocord causes different innovation by motor neurons
Sensory afferents termination in the spinal cord:
AAlpha-
ABeta-
AQ-
Sensory afferents termination in the spinal cord:
AAlpha- proprioceptors innovate muscle spindles large diameter for speed thicker myelination than Abeta
ABeta- mechanoreceptors also quite large
Both enter midialy
AQ- enter laterally fine diameter axons- Lissuer’s tract (LT)
state structure, location, receptive field and adaption speed of different touch receptors
pacinian courpuicles- Ab wrapped in viscous fluid shwann cell membranes very large - found deep in tissue - very large receptive fields - rapidly adapting - pressure changes in skin and high frequency vibrations 10-500Hz
meisners courpusles - structural similar to pacinain smaller with less membrane wrapping - found at dermis/epidermis interface - small receptive field - rapidly adapting - light flutter on skin and vibration 3-40Hz
merkel cells - modified epithelial cells that synapse onto Ab DRG neuron. - shallow in skin in epidermis - small receptive field - slowly adapting - sustained pressure, light touch
rufini endings - a single, branching sensory fiber in a thin capsule surrounded by collagen fibers. - in dermis - large receptive field slowly adapting - skin strech
explain the layout of a typical touch DRG neuron
classified as bipolar or pseudo unipolar;
transduction site for all touch receptors bar merkel’s disks.
Dorsal root ganglion cells somas are in ganglion adjacent to the spinal cord.
receptor potentials are encoded into pre somatic action potentials close to the receptor site.
Action potentials then propagate into the ipsilateral (same side) brain stem where they synapse.
explain the layout of a typical touch DRG neuron
classified as bipolar or pseudo unipolar;
transduction site for all touch receptors bar merkel’s disks. Dorsal root ganglion cells somas are in ganglion adjacent to the spinal cord.
receptor potentials are encoded into pre somatic action potentials close to the receptor site.
action potentials propagate into the ipsilateral (same side) brain stem where they synapse.
classification and function of nossiceptive afferents
A-Delta fibers (type 3) = thin mylenated fibers 1-2um diameter 5-30 m/s transmission responsible for temperature and pain
C- fibers (type 4) = small diamiter 0.2-1.5um and slow transmission 0.5-2 m/s responsible for pain ache and temp
explain how the membranous wrapping of coupucels enables fast adaptation times
As the membranous surrounding adjusts to touch, deforming to relive pressure on nerve after brief pressure period, it enables the nerve to be more selectively attentive to the onset and offset of the signal. Altering the properties of the action potential produced.
Properties encoded by touch
Spatial dimensions, size weight
Surface compliance hard/soft
Motion
Object recognition
why does spatial acuity decline with age
Spatial acuity declines with age number of mesners and merkels goes down
what do rappidly adapting vs slow adapting cells encode
rappid =change in stimulus, rate indicates speed of indentation
slow= absolute level of indentation/ intensity demonstrate object size
how can the affect sensation produced be demonstrated for each receptor type
stimulate with a micro electrode
explain what happens in shingles
Shingles: varicella-zoster virus reactivation along a dermatome leaves people with rashes localised to one dermatome as the virus lies dormant in the DRG
Perceptual touch reaches the cortex in a three neuron relay with two synapses in the Dorsal coulomb medial leminiscal pathway
1st order neuron: DRG
periphery–up ipsilateral spinal chord–>dorsal column nuclei
2nd order neuron:
dorsal column nuclei–decusation to contra-lateral side—>VPL(venteral posterolateral) thalmus
3rd order neuron:
VPL—->primary sematosensory cortex
what is lateral inhibition used for in touch processing on they way to the brain
Lateral inhibition is used to discriminate touch, decrease receptive field sizes. It occurs at both synapses in relay to the brain.
how did we first understand the structure of the homunculus
The montreal procedure wilder penfield open brain surgery and stimulation of the brain used to outline homunculus
how dos touch processing differ as it is moved from S-1 to the posterior parietal cortex?
S-1
4 homunculus’ 3a, 3b, 1, 2,
Six layered cortical structure
Receptor types are still processed
Posterior parietal cortex
Touch types converge to generate perception of an object/ recognition of a stimulus.
what is alerdinia
alerdinia- pain on normal touch inter-neurons enable us to perceive touch as pain in damaged tissues
explain mutations that can result in a lack of pain sensation in a person
NaV1.7 mutation- no transduction in nociceptors
NRTK1 mutation- no maintenance nociceptive afferents don’t survive
can also be caused in some form by over expression of opoids
three main types of nociceptors:
A-delta mechanosentitive nociceptors (glutamtergic)
A-delta mechanothermal nociceptors
C fiber poly modal receptor (glutamatergic also release substance P)
3 ascending nociceptive pathways:
spinothalamic
spinoreticular
spino mesenphalic
