Spinal Nerves and their Distribution Flashcards
Describe the embryonic development of the nervous system
- The notochord sends signals/growth factors, causing the neural folds to fold closer together
- A neural tube is formed and the neural crest cells are released from the neural crests to form the dorsal root ganglion and sympathetic ganglion
- The notochord develops into the nucleus pulposus
- The somites (paried divisions of paraxial mesoderms) give rise to musculoskeletal systems
- — Mesoderm develops into mesenchyme, which then develops into connective tissue
- — Cell bodies of the motor neurons lie anteriorly to the neural tube; they follow the muscles, developing the dorsal and ventral roots of the motor neuron in the spinal nerve; they supply the back and anterior part of the body + lower limbs respectively; remember myotomes
- — Cell bodies of the sensory neurons lie in the dorsal root ganglia which develop from the neural crest cells; they too follow the muscles and divide into dorsal root and ventral root of sensory neurons; somatic sensory afferents carry sensation of temperature, pain, touch; remember dermatome
What does myotome mean?
A muscle or group of muscles with a similar function that are supplied by motor nerves of a single spinal segment
e.g.: nerves always follow the muscle developing from the adjacent somite, and muscles will receive motor nerves from the adjacent segment of the spinal cord
What does dermatome mean?
An area of skin which is innervated by sensory neurons of a single spinal segment
What virus is Shingles caused by?
How does it arise?
Varicella zaster/chickenpox
After infection with the virus, the virus lies dormant in a dorsal root ganglia; the virus can be reactivated in later life causing Shingles; the rash develops in the skin supplied by the spinal nerve affected within a dermatome
Each segment of the spinal cord gives rise to a pair of spinal nerves that consist of what?
- Axons of motor neurons (to innervate a group of muscles arising from the same somite)
- Axons of sensory neurons (to innervate a defined area in the skin)
- Axons of sympathetic neurons (to structures in the body wall to control body temperature - blood vessels and sweat glands)
Describe the difference between multipolar, unipolar, pseudounipolar neurons
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Describe the difference between the dorsal and ventral roots
Dorsal root
- has sensory/pseudounipolar neurons
- the cell body of the neurons is in the dorsal root ganglion/outside of CNS
- has general somatic afferents (GSA) - carries info about general sensation e.g.: pain and temperature
- has general visceral afferents (GVA) - information coming back to the CNS about internal environment
Ventral root
- has motor/multipolar neurons
- the cell body of the neurons is in the ventral horn
- has general somatic efferent (GSE) - towards the effectors e.g.: voluntary/skeletal muscle
- has general visceral efferent (GVE) - towards smooth muscle and ganglial tissue
How is the nervous system divided up?
NS can be CNS or PNS
CNS:
- Brain
- Spinal cord
PNS:
- somatic (voluntary)
- autonomic/visceral (involuntary):
- —- sympathetic (fight or flight)
- —- parasympathetic (rest and digest)
The dorsal and ventral rami of thoracic spinal nerves are mixed and they carry what?
Dorsal rami:
- Motor neurons - to erector spinae muscles/back muscles
- Sensory neurons - from the skin of the back and from vertebral joints
- Sympathetic neurons - to blood vessels and sweat glands of the skin
Ventral rami:
- Motor neurons - to intercostal muscles
- Sensory neurons - from thoracic skin and pleura and vertebral joints
- Sympathetic neurons - to blood vessels and sweat glands of the skin
What is a reflex?
Rapid, involuntary motor response to a stimulus
What is a reflex arc?
Receptor, sensory neuron, integration centre, motor neuron and effector
What is a spinal reflex?
Somatic spinal reflexes provide information on integrity of the reflex pathway and degree of excitability of the spinal cord
