BMS11004 WEEK 10 - THURSDAY Flashcards
sensory receptors, dorsal column, medial lemniscal projection, thalamus, cortex
name 2 major input components in somatic sensory system
mechanical stimuli (light touch, vibration, pressure, cutaneous tension)
painful stimuli and temperature
what does the somatic sensory system allow us to do
identify shape, object textures
monitor internal/external forces
detect harmful situation
sense of self within environment and planning actions
name 3 sensory receptors with encapsulated nerve endings
Meissner (tactile) corpuscles
Pacinian (lamellated) corpuscles
Ruffini corpuscles
what are Meissner (tactile) corpuscles - encapsulated nerve endings of SNS
including location, modality, Hz, adaptations
in dermal papillae of skin, light touch modality (texture, movement), sensitive to 30-50H, rapidly adapting
what are Pacinian (lamellated) corpuscles - encapsulated nerve endings of SNS
including location, modality, Hz, adaptations
in dermis, joint capsules, viscera
deep pressure modality (stretch, tickle, vibration)
sensitive to 250-350Hz
rapidly adapting
what are Ruffini corpuscles - encapsulated nerve endings in SNS
including location, modality, Hz, adaptations
dermis, joint capsules, subcutaneous tissue
heavy touch, pressure, skin stretch, joint movements (proprioceptor
slowly adapting
name 2 unencapsulated nerve endings in SNS
Merkel (tactile) discs
Free-nerve endings
what are merkel (tactile) discs in unencapsulated nerve endings of SNS
including location, modality, Hz, adaptations
superficial skin (epidermis)
light touch, texture, edges, shapes
slowly adapting
what are free-nerve endings - uncapsulated nerve endings of SNS
including location, modality, Hz, adaptations
widespread in epithelia, connective tissue
heat and cold
what are cellular receptors made up of, with example
made up of multiple cells (merkel’s disc, free nerve endings, meissners corpuscle)
what are molecular receptors made up of with an example
made up of multiple components (stretch receptors)
name 2 types of mechanoreceptors (based on response)
rapidly adapting/phasic receptors
slowly adapting/tonic receptors
describe rapidly adapting (phasic) mechanoreceptors
when stimulated, neuron fires rapidly over time then stop= transient response, giving into about change to stimulus
give an example of a rapidly adapting (phasic) mechanoreceptor
pacinian corpuscle
describe slowly adapting (tonic) mechanoreceptors
continue to respond as long as stimuli present
giving into on persistence of stimulus
give example of slowly adapting (tonic) mechanoreceptor
ruffini corpuscle
how are primary afferent axons classified
by conduction velocity, reflecting diameter of axon
faster = wider diameter
primary afferent axon subtypes - what are axons coming from skin classified as
designated by letters (A, B, C) from fastest to smallest
A group further broken down to alpha, beta
primary afferent axon subtypes - what are axons coming from muscles classified as
designated by Roman numeral (I, II, III from largest - smallest)
I group broken into Ia…
why are pain fibres slower than proprioceptors
need info from proprioceptors (regarding balance) quicker so we dont collapse but pain can be slower
name 2 main routes (tracts) that somatosensory projection get to brain via
medial lemniscal tracts
spinothalamic tracts
what does medial lemniscal tract carry to brain (somatosensory projection)
carry mechanoreceptive and proprioceptive signals to thalamus
what does spinothalamic tract carry to brain (somatosensory projection)
carry pain and temperature signals to thalamus
what 3 type of neurons does somatosensory projections (medial leminiscal and spinothalamic tracts) travel by
first/second/third order neurons
what does first-order neurons in medial leminscal and spinothalamic tracts do
detect stimulus, transmits to spinal cord
what does second-order neurons in medial leminscal and spinothalamic tracts do
relay signal to thalamus “gateway” to cortex
what does third-order neurons in medial leminscal and spinothalamic tracts do
carry signal from thalamus, to cortex
explain topological arrangement of axons (regarding 1st order) for upper body
1st order axon from upper body follows lateral pathway, synapses onto 2nd order in cuneate nucleus
explain topological arrangement of axons (regarding 1st order) for lower body
1st order axons from lower body follow medial pathway, synapses onto gracile nucleus neurons
together, what is topological organisation of 1st order axons from upper/lower body known as
dorsal column nuclei
describe topological arrangement of 2nd order axons in medial-leminiscal system
crosses midline and ascend in medial lemniscus
reverses topology so lower body axons are more lateral on reaching thalamus
describe topological arrangement of 3rd order axons in medial lemniscus system
reverse topology - lower body axon synapses onto medial cortical neurons, but upper body axons map to lateral cortex
what does topological mean
mapping body and physiological distributions in cortex
what are dermatomes
specific patch of skin innervated by sensory ganglion, with dermis from specific somite in embryo
what does somatosensory homonculus mean?
map along the cerebral cortex of where each part of the body is processed, representations not proportional
what does receptive fields mean, and how is it measured
size depends on where it is located, measured by assessing ability to discriminate 2 sharp points set apart at different distances
when measuring receptive field, what does it mean when subject can feel 2 pin point
distance between points is larger than receptive field
what does large receptive field mean (in terms of discrimination)
low discrimination= arms and legs
what does small receptive field mean, in terms of discrimination
high discrimination
cortex more dedicated to regions for smaller receptive field
whereabouts in brain is somatotopic map preserved
coronal plane, postcentral gyrus with different sensory modalities being localised along our sagittal axis
what does loss of stimulation of specific body area lead to in the cortex
disappearance of area devoted to area and increase in neighbouring patch
