Session 3-Dermatomes, Myotomes And Segmental Innervation Of The Limbs Flashcards
What is each neural segment known as?
Neural level
Complete the sentence:
Neural tube contains ___________ cells of nervous system
Precursor
In which stage of gestation do paired somites appear in the neural tube?
4th week
What does the sclerotome give rise to?
Vertebrae
Ribs
What does the dermatomyotome give rise to?
Dermis (dermatome)
Muscle (myotome)
Complete the sentences:
Dermatomyotomes (DMT) develop in association with a specific ______ ________ of spinal cord. They take a nerve supply with them from neural tube as _______ (_________) nerve.
Neural level
Spinal (segmental)
True or false: skin and muscle derived from a single dermatomyotome have a common spinal nerve supply
TRUE
What do spinal nerve roots connect?
Each spinal nerve to a “segment” of cord
True or false: the spinal cord is discontinuous
FALSE - continuous
What do dorsal (posterior) roots contain?
Afferent/sensory nerve fibres only
What is the dorsal root ganglion?
Cell bodies of the sensory neurones from the periphery
What do ventral (anterior) roots contain?
Efferent/motor and autonomic nerve fibres only
What are spinal nerves?
Parallel bundles of axons encased in connective tissue
What are spinal nerves made up of?
Motor and sensory nerves
Complete the sentence:
The spinal nerves are very _____ and exist briefly as they pass through the ______________ _________, which marks the division between CNS and PNS
Short
Intervertebral foramen
How many pairs of spinal nerves are there?
31
How are the pairs of spinal nerves numbered?
According to the level of vertebral column from which they emerge
Where is the endoneurium?
Around each axon
Where is the perineurium?
Around each fascicle
Where is the epineurium?
Around the entire nerve
True or false: vertebral segments differentiate from sclerotomes
TRUE
What is equal to 1 vertebra?
1 vertebral segment or 1 segment of sclerotome
What is formed when multiple vertebral foramina are stacked on top of each other?
Spinal/vertebral canal
How do spinal nerves leave the spinal canal?
Via intervertebral foramina
Where does the spinal cord start?
At inferior margin of medulla oblongata
Where does the spinal cord end?
As conus medullaris at L2
True or false: most spinal cord segments are vertically aligned with the corresponding vertebrae
FALSE - not vertically aligned
What do long roots from inferior segments descend in?
Cauda equina (to exit at their respective foramina)
Where do the first cervical pair of spinal nerves emerge?
Between occipital bone and atlas (C1)
Where do C1-C7 exit?
Above corresponding vertebrae
Where does spinal nerve C8 exit?
Between vertebrae C7 and T1
Where to spinal nerves T1-L5 exit?
Below corresponding vertebrae
Where do S1-S4 exit?
Via four pairs of sacral foramina
Where do S5 and Co1 exit?
Via sacral hiatus (posterior)
What does the mixed spinal nerve divide into?
Rami
Where is the posterior/dorsal ramus?
Deep muscles and skin of dorsal trunk
Where is the anterior/dorsal ramus?
Muscles and skin of upper and lower limbs and lateral and ventral trunk
Which other branch do spinal nerves give off that re-enters the spinal canal through the intervertebral foramen?
Meningeal branch
What does the meningeal branch supply?
Vertebrae
Ligaments
Blood vessels
Meninges
What are the rami communicantes?
Contain components of autonomic nervous system (sympathetic)
What does the dorsal/posterior rami divide into?
Medial and lateral branches
What do the branches of the dorsal/posterior rami supply? (2)
1) Skin of back in ‘tidy’ segmental manner
2) Narrow strip of muscle/skin in line with intervertebral foramen
Where do the missing nerve roots in the ventral/anterior rami go?
Enter brachial plexus to supply upper limb
Define myotome
Group of muscles supplied by single spinal nerve (or spinal nerve root)
Define dermatome
Area of skin supplied by single spinal nerve (or spinal nerve root)
True or false: a myotome is a motor unit
FALSE - not a motor unit
What is a motor unit?
Motor neuron and the skeletal muscle fibres it innervates
Complete the sentences:
One spinal nerve contains neurons of _____ motor units. One spinal nerve supplies _____ myotome.
Many
One
True or false: there is functional overlap between adjacent dermatomes
TRUE
True or false: there is no functional overlap between adjacent dermatomes across an axial line
TRUE
What is an axial line?
Junction of two dermatomes supplied from discontinuous spinal levels
True or false: limbs only have an anterior axial line
FALSE - posterior too
What do axial lines mark?
Centre of either ventral or dorsal compartments of limb
What marks the pre-axial and post-axial boundaries of the ventral and dorsal compartments?
Veins
Which vein in the upper limb marks the pre-axial compartment?
Cephalic
Which vein in the upper limb marks the post-axial compartment?
Basilic
Which vein in the lower limb marks the pre-axial compartment?
Long saphenous
Which vein in the lower limb marks the post-axial compartment?
Short saphenous
True or false: peripheral nerve territories are not dermatomes
TRUE
What are peripheral nerve territories?
Areas of skin supplied by peripheral nerves eg branches of lumbar plexus
True or false: within each peripheral nerve, there may be fibres from more than one spinal nerve
TRUE
True or false: fibres from one spinal nerve enter only one peripheral nerve
FALSE - can enter more than one peripheral nerve
What causes shingles (herpes zoster)?
Reactivation of Varicella zoster virus (chickenpox)
True or false: shingles affects the skin of a single dermatome
TRUE (almost always)
What happens to the Varicella zoster virus after chickenpox?
Travels through a cutaneous nerve and remains dormant in a dorsal root ganglion. When host is immunosuppressed (eg old age), virus reactivates and travels through peripheral nerve to skin of single dermatome
What are the symptoms of shingles? (2)
Erythema (superficial reddening of skin)
Vesicle formation
