This is about body sensation
it often turns up later due to not knowing what you dont feel. it isnt just feeling but propriuoception and temperature etc
Sensory system
the sensory system acquires informaiton about the environment, internal and external. it converts information into action potentials and communicates this around the body
then it processes the informaiton and gives it meaning, stimulating responses
subsystems
there are 3 subsystems
- somatic senstion (concious from bodt)
- visceral senstion
- special senses
Somatic sensation
this is discriminitave sensation which tell you about the world
and affective sensation which compels you to act
Discriminative sensation (TVP) this includes Touch Vibration (useful for lots of things that are subtle and often the first to go) and Proproception + muscle length and tension. (also haptic) so all of this is really telling you about the world around you.
Affective senstion (compels to act) potentially damaging stimuli
- pain (free nerve ending)
- warm/cold
- erotic touch
this is because we need to act to this.
components of the sensory system
we need some sensors and wires and computers
(he brings out chart)
The pathways are
Sensory receptors
varienty of types these are mechano chemo thermo photo and nociceptors
each type is sensitive to a specific stimulus, and coding depend on which receptors activated
they transduce the physical stimulus to molecular level (you know this from bioly jasper) This can be a specialised ending of a sensory neuron or a specific cell associated with the sensory axon
intensity of senstion is coded forby increasing frequenct or more receptors, this is like muscle activation in reverse
distinguish wide range of intensities vega fecner law
this turns the stimulus and intensity is a logatithmic relationship eg 10X stimulus turns to 2X sensation.
just noticable difference
the exception is pain sensation it is all light
Receptive fields one sensory neuron is associated with more htan one receptor (as you know)
smaler receptive field lead to more localisation and discrimination
surround inhibition thisis when the receptive field of a neuron inhibits surrounding fields to increase contrast.
sensory adaption
often signalling falls off in intensity over time with the same stimulus
not all of them like baroreceptors but it will with like touch.
Half 2
axons can be big or small, myelinated or unmyelinated and fast or slow
nerves go into the dorsal horn where there is processing. local processing does stuff like reflexes.
there are spinal cords which have pathways to the thalamus and the thalamus goes to the coretex. pathways cross over as well
3 neurons ususally one is dorsal root, one in spinal cord, one in thalamus to end somatic
Acending tracts
dorsal column (aka medial lemniscus)
this does touch vibration and joint position it is fast and crosses at the medulla they ascend ipsilaterally and fo dorsal horn to dorsal column to cuneate and gracile nuclai and to arcutate faciculus and VPL of thalamus and then to post central gyrus
unconcious proprioception is different as it goes to cerebellum
after postcentral gyrus
then the secondary sensation
anterolateral/spinothalamic
this does pain and temp it is slow and crosses at antry to spinal cord
affective sensation acends contralaterally and crosses at level on entry
dorsal root → Dh → cross in anterior commissure → anterolateral tract → vpl - Post sencort synrus
also activates cingulate gyrus and stuff
it spreads widely bc pain need to activate stuff
cortical processing
primary somatosensory cortex in parietal lobe
generally there is thinking in the front and feeling in the back
somatotopy body map which corresponds a body part to a part of the brain.
complex sensations are produced by integration of inputs association cortex xombines sensory modalities and allows complex interpretaion links with emotion memory and other areas of CNS
pathway
thalamus to s1 then s2 then posterior parietal cortex
s1 has 4 areas 3a +3b and 1 + 2
cortical structure layers are inputs and outputs columns area modality
computation matrix
we also have selective attention,