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Lecture 4

Physiology 3120 Lecture 4: Neuro1

Course Code
Tom Stavraky

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Physiology 3120
Lecture 4
Somatosensory system 1
Capacity of the somatosensory system
- The hand is one of evolution’s greatest creations
- The hand helps in things like:
o Texture discrimination
o Braille (100 words/min)
We develop this when we lose another sense (Ex: sight) so that you can
maintain the capacity to read
Even though non blind people have the same machinery in the somatosensory
as a blind person, non blind people wont be able to read braille
o Recognize objects in hand
o Manipulate objects (fine dexterity) texting, tool-use, throwing etc.
How do we achieve fine sensory ability?
- Different populations of receptors with different modalities (provide diff info from skin and
- Different rates of adaptation (slowly/rapidly)
- Different neurons and receptors have different thresholds
- You are able to build up codes that relate to intensity and these populations codes that relate to
which particular neurons are firing
- Diff combinations of those associated with diff kinds of receptors give you all kinds of influx into
the CNS from the skin and tissues and so on
Lose tactile sensation = Lose manual dexterity
- Inject litacain and marcane (anesthetic into digital nerves)
o It removes the inputs of from the 1000s of receptors in the finger tips
- When they inject the anastehtic….
Receptors of the glabrous skin
- We attribute these diff types of neurons to diff actions
o They provide diff info to nervous system
o Ex: fast adapting type 1 and slow adapting type 1 allow for braille reading (give info
about really small details that you touch)
o Ex: fast adapting type 1 also give info about moving stimuli (things that are moving on
the hand)
o Ex: slow adapting type 1 is good for fine forms while giving info about contours of edges,
things that are static indentions
- So there are 4 classes which are broken up functionally:
o Fast adapting type 1
Innervate Meissner corpuscle
o Slow adapting type 1
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Small receptive fields
Innervate merkel endings
o Fast adapting type 2
Innervate pacini endings
o Slow adapting type 2
Innervate ruffini endings
- Glabrous skin = hairless skin (these 4 types of receptors are in this part of hand)
- Type 1 and type 2 refer to the size of the receptive field
o Look at green and red areas on the hand
- Type 2 responds even when don’t even touch the hand, through vibrations through the device
- Type 1 has very small punctative receptive fields
- Fast adapting type 1 give you info about moving stimuli these fast adapting events , changing
Full scope of somatosensory receptors
- There other types of receptors that provide information from somatosensory system ex:sense
of position of body in space, forces on muscle, pain, temperature etc
- This table summarizes the key features of what is going on in the somatosensory system
- Left Coolum is showing modality: the kind of info at a high level that these receptors provide
- 2nd column shows the specific receptor that is innervated by these neurons
o Free nerve endings means there is no specialized mechanoreceptors its just the nerve
ends and branches that diffuse into the tissue without any specialized outgrow
o Free nerve endings are the kinds of receptors that give us info about temperature and
pain the affective aspects of touch
- Adaptation state: either slow or rapidly adapting
- Axon column
o how fast info gets from receptor to CNS is determined by the axon diameter bc this
determines how fast an AP propagates
o Wider axon = the faster the AP can move along it = the faster it reaches CNS
o Ex: sharp and slow pain: when you hit a hammer on your thumb, you initially feel a
sharp pain, then you feel a dull aching pain
o This is bc the fast pain travels along the Adelta fibers (20m/s) while the slow pain goes
along the C fibers (1m/s)
- So the information comes in diff ways from the PNS to the CNS
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