Dermatomes, myotomes and segmental innervation Flashcards
what is a neural level anatomically?
Each neural segment is a neural level
when are pairs of somites formed?
4th week gestation
What does the neural tube contain?
Precursor cells of nervous system
What does the sclerotome form?
Vertebrae and ribs
What does the dermatomyotome form?
Dermis and muscle
Two parts of somite
sclerotome (ventral underneath myotome)
Dermatomyotome (dorsal)
How do dermatomyotomes develop?
From somites (dorsal part)
In association with a specific neural level
Take their nerve supply with them from neural tube
What is the nerve associated with dermatomyotome known as?
Spinal nerve
What occurs if skin and muscle are derived from a single dermatomyotome?
They have a common spinal nerve supply
Nerve structure
Endoneurium (around axons)
Perineurium (around fasicle of axons)
Epineurium (around entire nerve)
(have blood vessels within to supply them)
What do roots do?
Connect each spinal nerve to a segment of spinal cord
What do dorsal roots contain?
Afferent (towards CNS)
sensory nerve fibres ONLY
Where are dorsal roots located?
Posterior of spinal cord
What do ventral roots contain?
efferent (away from CNS)
motor and autonomic nerve fibres ONLY
Where are ventral roots located?
Anterior of spinal cord
What does dorsal root ganglion contain?
Cluster of cell bodies of sensory neurons from periphery
What do spinal nerves contain?
Mixed motor and sensory nerves
Where are spinal nerves found?
Only briefly as they pass through intervertabral foramen
when dorsal root and ventral root come together
What does the interbvertabral foramen mark?
The division between CNS and PNS
How many spinal nerves are there and how are they named?
31
named according to the level of vertabrae that they emerge from
What are vertebral segments derived from?
Differentiate from sclerotomes
Each one derived from pair of adjacent somites (overlap)
Where does the spinal cord run?
Through vertebrae foramen
known as spinal canal when they are stacked
How do the spinal nerves leave the spinal canal?
Via intervertebral foramina
where does spinal cord begin and end?
inferior margin Medulla oblongata Conus medullaris (L2)
are spinal cord segments in line with their vertebrae?
NO (vertabra is longer than cord)
What is cauda equina?
Lower part of spinal canal
contains spinal nerves but not cord
How do the roots from inferior spine exit vertebrae if they are not in line with their segment?
Long roots from inferior spinal cord often have to descend down into cauda equina and exit at their intervertabral foramina
Where does the first spinal nerve emerge?
Cervical nerves
C1 (between occipital bone and atlas)
where do C1 - C7 spinal nerves emerge?
Above their corresponding vertebrae
Where does C8 spinal nerve emerge?
Between C7 and T1
Where do T1 and L5 spinal nerves exit?
Below their corresponding verterbrae
where do s1-s4 nerves exit?
Sacral bones are fused together
Exit via 4 pairs of sacral foramina
Where do S5 and Co1 exit?
Sacral hiatus
What are rami?
Mixed spinal nerves divide into them
Branches of spinal nerve
Dorsal rami
Ventral rami
Rami communicantes
Meningeal branch
Dorsal ramus
Posterior and small
Supplies deep muscles of skin and dorsal trunk
Ventral ramus
Anterior and larger
Supplies muscles and the skin of upper and lower limbs and lateral and ventral trunk
Meningeal branch
Re-enters spinal canal through intervertebral foramina
Supplies vertebrae, ligaments, blood vessels and meninges
Rami communicantes
Part of the autonomic nervous system
Grey rami communicantes
Contains unmyelinated post ganglionic nerve fibres
Travels from a sympathetic ganglion to adjacent spinal nerve
Supply the periphery
ALL SPINAL NERVES RECIEVE
White rami communicantes
Myelinated
Come off between T1 and L2
Preganglionic nerve fibres of sympathetic system
Connects spinal cord to sympathetic chain
What do the dorsal/posterior rami do?
Divide into medial and lateral branches
Supply the skin of the back
What is a dermatome?
Area of skin supplied by a single spinal nerve
What do the ventral/anterior rami do?
Complicated
Enter plexuses to supply limbs
Junction on anterior chest dermatome
C4 and T2 (T1 supplies upper limbs instead)
Learn dermatome map ella
LEARN ITTT (Foerester map)
Key sections dermatome map:
T4/T5 - nipples
T10 - umbilicus
L1 - Groin
