Somatosensation 1 Flashcards
What sensations does the somatosensory system convey?
- Touch
- Propriception
- Heat,cold
- Pain,itch
What does the somatosensory system connect?
Connect the CNS to the body via peripheral nerves
How many nerves do we get from the spine?
From the spine we get 31 nerves from each segment
What is the CNS connected to the body via
The CNS is connected to the body via spinal nerves and cranial nerves
What are the connective tissue element in peripheral nerves?
Connective tissue elements:
- Epineurium
- Perineurium
- Endoneurium
What roots does the spinal cord give rise to?
Spinal cord gives rise to dorsal and ventral roots
What is the spinal cord roughly divided into?
The spinal cord is roughly divided into incoming sensory information in its dorsal half and outgoing ventral commands in its ventral half
What do dorsal roots contain?
Dorsal roots contain incoming sensory axons
What do ventral roots contain?
Ventral roots contain outgoing axons
Where do the dorsal and ventral roots unite into?
Dorsal and ventral root unite into the spinal nerve
What is white matter?
White matter is ascending and descending axon tracts
What is grey matter?
Grey matter is the cell bodies, dendrites and synapses
Where do the dorsal root ganglia occur?
They occur just as the dorsal and ventral roots fuse
What do dorsal root ganglia contain?
Contain the cell bodies of all the sensory neurons of the somatosensory system
What are the 2 systems in the dorsal root ganglia?
Two anatomically and functionally distinct systems:
- Large fibres
- Small fibres
Large fibres
- Myelinated
- Faster conduction
- Tactile and proproceptive
Small fibres
- Unmyelinated
- Temperature, pain, itch, crude touch
What does specificity of sensation depend on?
Specificity of sensation depends on afferent fiber type
What are the cutaneous classes in the skin of receptors of the somatosensory system?
- Meissner corpuscle (RA)
- Merkel disks (SA)
what are the deep classes in the skin of receptors of the somatosensory system?
- Pacinian corpuscle (RA)
- Ruffis Corpuscle (SA)
What do dorsal root ganglions contain and what is the action potential produced proportional to?
The axon terminals of the dorsal root ganglion contain ion channels which are mechanically sensitive
-Action potential produced is proportional to the strength of stimuli
What does rapidly adaptive fibers signal?
Rapidly adaptive fibers signal changing stimuli
What does slowly adaptive fibers signal?
Slowly adaptive fibers signal ongoing stimuli
What does the pacinian corpuscle detect?
Pacinian corpuscle are good at detecting vibration
What does the ruffini corpuscles detect?
Ruffini corpuscles detect stretch of skin
What is the meissner corpuscles responsible for?
Meissner corpuscles are responsible for sensitivity to light touch
What are the merkel disks responsible for?
Merkels disk are responsible for sensitivity to light touch
What do muscle spindles do?
Muscle spindles send information of changes to muscle length
What do golgi tendon organs sense?
Sense muscle tension and receptors of joints
What are the 2 types of free nerve ending fibres?
- A delta fibres
- C fibres
A delta fibres
- Thin
- Myelinated
C fibres
- Thin
- Unmyelinated
What does the ability to localize depend on?
Ability to localize depends on sensory receptive fields
What are the 2 major central pathways of the somatosensory sytem
- Dorsal column(Medial lemniscal system)
- Spinothalamic tract(STT, also known as anterolateral system)
What does the dorsal column mediate?
Dorsal column mediated discriminative touch, vibration, proprioception
What does the spinothalamic tract mediate?
Spinothalamic tract mediates coarse touch, temperature and pain
What is the pathway of the long fiber system in the somatosensory pathway?
- Primary afferent enters the spinal cord in the dorsal horns
- Then it ascends in white matter columns
- Then terminated in the medulla
- The medulla contains dorsal column nuclei
- Second order neurons then receive signals from the primary afferent and then cross and ascend up the medial lemniscus all the way to the thalamus
- Third order neurons then receive signals from the thalamus and send signals to the cortex
What is the pathway of the small fiber system in the somatosensory pathway?
- Small fiber system terminate in the dorsal horn and synapse with second order neurons and ascend up the anterior lateral margins
- Second order neurons go to the thalamus
- Then to the cortex by third order neurons
The regional variation in cortical cytoarchitecture?
Different areas of the cortex have the same basic cell types organised in layers with the same basic organisation
How can regional differences be identified in the cortex?
Regional differences can be identified on the basis of relative thickness of the different layers, cell size and density
