Peripheral Nerves and Dermatomes Flashcards
(30 cards)
What is the general structure of a neuron?
- Cell body
- Axon
- Axon terminal
Why are the shapes of different neuron types important?
-Their shapes relates to their function
What is the structure of peripheral nerves?
- Similar to an electric cable with an outer protective cover to help bundle together nerve cell axons.
- Peripheral nerves contain axons from two functionally distinct types of nerve cells: sensory and motor.
What types of axons may be in peripheral nerves?
- Myelinated
- Unmyelinated
What do myelinated axons have that unmyelinated don’t?
- Have a series of schwaan cells lined up along axon, each having a wrapped coating of myelin insulating the axon.
- Unmyelinated axons are encased by schwaan cells cytoplasm but no wrapped coating of myelin surrounding the axons.
What is the size difference between myelinated and unmyelinated axons in micrometres?
- Myelinated = large (5-20)
- Unmyelinated = small (0.2-1.5)
What is the difference in AP conduction rate between myelinated and unmyelinated axons in m/s?
- Myelinated = fast (5-120)
- Unmyelinated = slow (0.5-2)
What are the differences in function between myelinated and unmyelinated axons?
- Myelinated = touch, vibration, motor
- Unmyelinated = pain, thermal (hot or cold)
What can be seen at histological level if a peripheral nerve is sectioned?
- Separated into fasicles (bundles of axons from individual cells). Housed in tough connective tissue called epineurieum.
- Perineurium and blood vessels also visible
- If look at closer then myelinated sheaths of axons can be seen.
What are sensory afferents classed as?
-Pseudounipolar
Where are cell bodies of sensory neurons housed?
-In dorsal root ganglia
What sort of receptros may sensory neurons encounter?
- Mechanoreceptors = mechanical deflection, touch
- Thermoreceptors = hot/cold
- Nociceptors = noxious (pain)
- Special sensory (only in cranial nerves) = vision taste, olfaction
What matter composes the spinal cord?
- Grey matter (composed of lots of functionally distinct neurons)
- White matter (composed of axons that send info up to brain/down from brain)
Are dorsal and ventral horns found in grey or white matter?
-Grey matter
What are the spinal cord segments?
-C8
-T12
-L5
-S5
-C1
Total 31 pairs
What does the cervical section of SC innervate?
-Innervates skin and muscle around the neck, chest and most of upper limb.
What does the thoracic section of SC innervate?
-Mostly trunkal area, and distinct region of upper limb
What does lumbar section of SC innervate?
-Mostly lower limb
What does sacral and coccygeal section of SC innervate?
-Genitalia and skin around anus
What are some of the plexuses in the body and what spinal cord sections make them up?
- Cervical = C1-C5
- Brachial = C5-T1
- Lumbosacral = T12-S5
What is a dermatome?
-An area of skin innervated by a particular level/segment of spinal cord and its corresponding spinal nerve.
What is a myotome?
-Region of muscle supplied by a particular level/segment of the spinal cord and by its corresponding spinal nerves.
Why can dermatome and myotome maps be clinically significant?
- Allow docs to evaluate extent and level of spinal injury.
- Helps look at effects on voluntary, reflex movements and sensory responses. (important in ASIA scale)
What is the pathway for voluntary movement?
- Starts with activation of cells in motor cortex.
- Upper motor neuron travels down to lower motor neuron (SC) at most appropriate spinal segment to innervate the distinct muscle group.
