NEURO: Somatosensation I Flashcards
What does the somatosensory system convey?
The somatosensory system conveys sensations from the body such as:
- touch
- proprioception
- heat, cold
- pain, itch
Describe the structure of a peripheral nerve.
A nerve is essentially a bundle of axons.
The nerve itself is covered in epineurium, a connective sheath covering. Inside it are several fascicles, each of which are covered in perineurium. Each fascicle contains multiple axons, each of which are covered in endoneurium.
Broadly, there are two anatomically and functionally distinct systems in the somatosensory system.
Explain.
One has large fibres (have a large diameter, myelinated, fast conduction): tactile and proprioceptive.
It’s called the dorsal column medial lemniscal system (DCML), and it mediates discriminative touch, vibration and proprioception.
The other has small fibres (small diameter, thinly-myelinated or non-myelinated, medium or slow conducting): temperature, pain, itch, crude touch.
It’s called the spinothalamic tract (STT, also known as anterolateral system), and it mediates touch, temperature and pain.
List the receptors of the somatosensory system.
PROPRIOCEPTION:
- Muscle spindles
TACTILE AFFERENTS (discriminative touch):
Cutaneous:
- Meissner’s corpuscles (rapidly adapting)
- Merkel’s discs (slowly adapting)
Deep:
- Ruffinni corpuscles (slowly adapting)
- Pacinian corpuscles (rapidly adapting)
FREE NERVE ENDINGS (low-resolution tactile, temperature, pain):
- A delta fibres
- C fibres
Describe the regional variation in the cortical cytoarchitecture.
Different areas of cortex have the same basic cell types organised in layers, with the same basic organisation.
Regional differences can be identified on the basis of relative thickness of the different layers, cell size and density.
Brodmann’s areas are cytoarchitectonic areas.
Describe the columnar organisation of the cortex.
Cells with similar receptive fields are organised in vertical columns.
