Physiology 3120 Lecture 4: Neuro1
9 May 2018
School
Department
Course
Professor
Physiology 3120
Dr.Pruszynski
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
tissues)
- 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
find more resources at oneclass.com
find more resources at oneclass.com
▪ 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
events
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
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The hand is one of evolution"s greatest creations. Different populations of receptors with different modalities (provide diff info from skin and tissues) 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. Inject litacain and marcane (anesthetic into digital nerves) It removes the inputs of from the 1000s of receptors in the finger tips. So there are 4 classes which are broken up functionally: fast adapting type 1. Innervate meissner corpuscle: slow adapting type 1, small receptive fields. Innervate merkel endings: fast adapting type 2. Innervate pacini endings: slow adapting type 2. Glabrous skin = hairless skin (these 4 types of receptors are in this part of hand)
