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Flashcards in Spinal Nerves & Their Distribution Deck (25):

What are some reasons for needing to access the vertebral canal?

+ Sample CSF for blood or organisms
+ Measure CSF pressure
+ Injection of anaesthetics (subarachnoid and epidural)
+ Injection of antibiotics
+ Injection of chemotherapeutic agents


Why is it safest to access the vertebral canal in the lumbar region?

+ The spinal cord ends at L1/L2
+ Subarachnoid space extends to S2
+ Cauda equina unlikely to be damaged


When is one instance when a spinal tap should not be performed?

When patient has increased intracranial pressure


What are features of the lumbar cistern?

+ Area of subarachnoid space
+ Surrounds cauda equina
+ Extends from disc between L1 and L2 to the lower border of S2


Where is the optimum area for needle for lumbar puncture to pass through?

Between spinous processes of L3 and L4 or L4 and L5


What layers must the needle for a lumbar puncture pass through?

1. Skin
2. SC fascia and fat
3. Supraspinous ligament
4. Interspinous ligament
5. Ligamentum flavum
6. Epidural space and extradural fat
7. Dura mater
8. Arachnoid mater


What are somites?

+ Paired divisions of paraxial mesoderm
+ Give rise to musculoskeletal elements: somites will develop into individual muscles
+ Nerves always follow the muscle developing from the adjacent somite
+ Muscles will receive motor nerved from the adjacent segment of the spinal cord


What are myotomes?

The part of a somite that develops into the muscles:

E.g deltoid develops from C5 and C6 somite and is supplied by nerves arising from spinal segments C5 and C6.

Other muscles that bring about abduction will also be supplied by nerves arising from spinal segments C5 and C6 = MYOTOME


Where are motor neurons found during embryonic development?

Cell bodies lie anteriorly within the neural tube

Somatic motor efferents carry impulses that stimulate muscle contraction


Where are sensory neurons found during embryonic development?

Cell bodies lie in the dorsal root ganglia which develop from neural crest cells

Somatic sensory afferents carry sensation of temperature, pain, touch, proprioception


Give an example of dermatomes?

Skin that develops from ectoderm adjacent to a specific somite is innervated by sensory neurones arising from the adjacent specific spinal level

The lateral wall of each somite in a vertebrate embryo, giving rise to the connective tissue of the skin e.g:

Skin on the lateral side of the forearm develops adjacent to the C6 somite

The skin is therefore supplied by nerves that develop from spinal segment C6 = DERMATOME


What are the features/functions of dermatomes and myotomes?

+ Areas supplied by single spinal nerves/segments

+ Proves sensory and motor supply of an adjacent muscle mass (myotome) and the cutaneous supply of an area of skin (dermatome)


Dermatomes overlap - what does this mean in regards to damage to a single spinal nerve?

It would rarely result in the loss of sensation over the area illustrated by a dermatome map


What causes shingles?

Varicella zoster virus

After an infection with the virus (chicken pox) the virus lies dormant in a DRG. The virus can be reactivated in later life causing shingles.

The rash develops in the skin supplied by the spinal nerve affected i.e within a dermatome


Each segment of the spinal cord gives rise to a pair of spinal nerves. What do they consist of?

1. Axons of motor neurons that innervate a group of muscles arising from the same somite (they share a function) (myotome)

2. Axons of sensory neurons that innervate a defined area of skin (dermatome)

3. Axons of sympathetic neurons to structures in the body wall that control body temperature (blood vessels, sweat glands etc.)


Dorsal rami of thoracic spinal nerves are mixed nerves and will carry:

1. Motor neurons to erector spinae muscles (back muscles(

2. Sensory neurons from the skin of the back and from vertebral joints

3. Sympathetic neurons to blood vessels and sweat glands of the skin


Ventral rami of thoracic spinal nerves are mixed nerves and will carry:

1. Motor neurons to intercostal muscles

2. Sensory neurons from thoracic skin and pelura and vertebral joints

3. Sympathetic neurons to blood vessels and sweat glands of the skin

Ventral rami will form plexuses which give rise to peripheral nerves consisting of fibres from multiple spinal nerves


What are the branches of a thoracic spinal nerve?

+ Medial branch
+ Lateral branch
+ Posterior branch
+ Later cutaneous branch
+ Anterior branch
+ Lateral branch


Describe reflexes

+ Rapid
+ Involuntary motor response to a stimulus


Describe a reflex arc

+ Receptor
+ Sensory neuron
+ Integration centre
+ Motor neuron
+ Effector


Describe spinal reflexes

+ Somatic spinal reflexes provides information on integrity of the reflex pathway and degree of excitability of the SC


Where are cell bodies found?

Only in the thoracic region (T1-L2) but travel in all spinal nerves


What is altered sensation (e.g pins and needles) called?

Paraesthesia - caused by nerve irritation


What is the role of the L5 root in relation to motor function?

It provides motor innervation to the anterolateral muscles of the calf (dorsiflexors of the ankle)


What is the result of nerve compression?

Muscle weakness, loss of sensation and reflexes