NEURO: Somatosensation I Flashcards
What does the somatosensory system convey?
division of the nervous system that provides sensations from the body e.g.:
- touch
- proprioception
- heat, cold
- pain, itch
What nerves convey sensation?
peripheral nerves
-they connect the body to the CNS
How is the CNS connected to the rest of the body?
spinal nerves (31 pairs) cranial nerves (12 pairs)
Structure of a nerve
made of fascicles (bundle of axons) and connective tissue elements:
epineurium: outer connective tissue of nerve
perineurium: connective sheath surrounding each fascicle
endoneurium: connective tissue surrounding individual axons within fascicles
What is a spinal nerve
Spinal nerve divisions
the peripheral nerve which emerges from the spinal cord
Dorsal root
Ventral root
Dorsal root
sensory (afferent) branch of each spinal nerve;
enters spinal cord on the dorsal side
Dorsal root ganglion
a nodule on a dorsal root that contains cell bodies of afferent sensory spinal nerve neurones
The fate of afferent sensory neurones at the dorsal root
The central portion of the axon enters the spinal cord and either:
- synapses locally
- sends an axon up the white matter ascending towards the brain
Ventral root
motor (efferent) branch of each spinal nerve;
exits spinal cord on the ventral side
Where are motor neuron cell bodies located?
grey matter of the spinal cord
What are the different classes of sensory afferents?
Large fibres (myelinated, fast conduction)
- convey tactile sensation (touch) and proprioception
- A-β fibres and A-⍺ fibres
Small fibres (thinly/unmyelinated, medium/slow conduction)
- convey temperature, pain, itch, crude touch
- A-ẟ fibres and C-fibres
Cutaneous Receptors
nerve receptors in the skin that respond to pressure, temperature, or pain
What are the different cutaneous receptors?
- Meissner’s corpuscle (dermal papillae)
- Merkel’s disks (basal epidermis)
- Pacinian corpuscle (dermis)
- Ruffini’s corpuscle (dermis)
- Free nerve endings (dermis)
Cutaneous nociceptors
Free nerve endings:
- sensitive to noxious stimuli
- sensitive to low resolution tactile
- a sharp, localised type of pain
Afferents associated with cutaneous receptors
A-β tactile afferents
- large diameter
- myelinated
- 2nd fastest conducting (30-70 m/s)
- Meissner’s corpuscle (dermal papillae)
- Merkel’s disks (basal epidermis)
- Pacinian corpuscle (dermis)
- Ruffini’s corpuscle (dermis)