MSK dermatomes Flashcards
What does sclerotome form (ventral)?
What does dermatomyotome (dorsal) form?
Vertebrae and ribs
Dermis (dermatome) and muscle (myotome)
During what week of gestation are somites paired?
4th week
How do the dermatomyotomes have a nerve supply?
They take their nerve supply with them from neural tube as spinal (segmental) nerve
How many nerves does the skin and muscle supplied from a single dermatomyotome have?
They have a common single nerve supply
What do the spinal nerve roots connect?
What do the dorsal (posterior) roots contain?
What do the ventral (anterior) roots contain?
Each spinal nerve to a ‘segment’ of cord
Dorsal (posterior) - afferent/sensory nerve fibres ONLY
Ventral (anterior) - efferent/ motor and autonomic nerve fibres ONLY
What is a spinal nerve?
What does each spinal nerve contain?
How many pairs of spinal nerves are there?
How are they numbered?
Parallel bundles of axons encased in connective tissue
Dorsal and ventral root - mixed nerves (motor and sensory)
31 pairs - numbered according to the level of vertebral column from which they emerge
What marks the division between the CNS and PNS?
Intervertebral foramen
What surrounds each axon?
What surrounds each fasicle?
What surrounds each nerve?
Endoneurium
Perineurium
Epineurium
What runs through the vertebral foramen?
Where do the spinal nerves leave the spinal canal?
Spinal cord
Intervertebral foramina
Where do dermatomyotome so develop?
In association with a specific neural level of spinal cord
What are the layers of the meninges from outside in?
Dura mater
Arachnoid
Pia meter
DAP
Where does the spinal cord start and end?
Starts - Inferior margin of medulla oblongata
Ends - conus medullaris at L2
Why are most spinal nerve segments not vertically aligned with corresponding vertebrae?
Spinal nerves are shorter than corresponding column
What happens in the cauda equina?
Where is it?
Long roots from inferior segments descend into it to exit at respective foramina
Located below spinal cord
Where does the first pair of cervical spinal nerves emerge?
Where do C1-C7 exit?
What exists between vertebrae C7 and T1?
Where do T1-L5 exit?
Where do S1-S4 exit?
What exits via sacral hiatus?
Occipital bone and atlas (C1)
Above corresponding vertebrae
Spinal nerve C8
Below corresponding verebrae
Exit via 4 pairs of sacral foramina
S5 and Co1
What does a mixed spinal nerve divide into?
What does the posterior/dorsal Ramus innervate?
What does the anterior/ventral ramus innervate?
Rami
Deep muscles and skin of dorsal trunk
Muscles and skin of upper and lower limbs and lateral and ventral trunk
What other branch do spinal nerves give off?
Where does it re-enter spinal canal?
What does it supply?
Meningeal branch
Re enters spinal canal through intervertebral foramen
Supplies vertebrae, ligaments, blood vessels and meninges
What are rami communicantes?
Components of autonomic nervous system
What does the dorsal ramus innervate?
What does it split into?
What does it supply?
What is the narrow strip of muscle in line with?
Deep muscles and skin of dorsal trunk
Medial and lateral branches
Skin of back in tidy segmental manner
Intervertebral foramen
Which nerve originates from the lateral cord of the brachial plexus?
What muscle does it supply?
Lateral pectoral
Pectoralis major
What is the level of injury defined as?
The lowest level of full sensation and function
What two plexuses does the anterior rami form?
What are they connected by?
Lumbar plexus (L1-L4)
Sacral plexus (L4-S4)
Lumbosacral trunk (lumbosacral plexus)
What muscles does the lumbar plexus innervate?
Where does the lumbar plexus form?
Psoas major
Psoas minor
Forms behind psoas muscles, emerges medial and lateral to psoas major
What are the origins and insertions of psoas major and minor?
Lumbar plexus innervates them
Psoas major
Origin: T12, L1-L4 and intervertebral discs
Insertion: Lesser trochanter of femur
Psoas minor
Origin: T12, L1
Insertion: Innominate line and iliopectineal eminence (pelvis)
Often absent
What are the major branches of lumbar plexus?
Medial and lateral.
Medial - obturator (L2, 3, 4) Lumbosacral trunk (L4 and 5)
Lateral Femoral (L2, 3, 4) Iliohypogastric (L1) Illioinguinal (L1) Lateral cutaneous nerve of thigh (L2, 3)
Where does the sacral plexus form?
What does it supply?
Within the pelvic cavity
Anterior to piriformis
Pelvic region
Gluteal region
Perineal regio
Lower limb via sciatica nerve
Define Myotome
Define dermatome
A group of muscles supplied by a single nerve
Area of skin supplied by a single spinal nerve
What is a motor unit?
What does one spinal nerve contain in terms of neurones?
A motor neuron and the skeletal muscle fibres it innervates
1 spinal nerve contains the neurone of many motor units
What is an axial line?
What do these lines mark?
Do dermatomes cross them?
Junction of two dermatomes supplied from discontinuous spinal levels
The centre of either pre-axial or post axial compartments of the limb e.g. Anterior and posterior compartments of forearm.
No but there is functional overlap between adjacent dermatomes
What marks the boundaries of the pre axial and post axial compartments?
Veins
Cephalic and basilic
Long (great) saphenous and short (small) saphenous
What are the peripheral nerve territories?
NOT dermatomes
Areas of the skin supplied by peripheral nerves e.g. Branches of lumbar plexus
What is shingles?
What happens after chickenpox?
How does it manifest?
Viral infections - affecting the skin of a single dermatome
Reactivation of chickenpox
Virus travels through a cutaneous nerve and remains dormant in dorsal root ganglion after chicken pox.
When host is immunosupressed, varicella zoster virus) reactivated and travels through peripheral nerve to skin of single dermatome.
Why does transection of a single spinal dorsal nerve not lead to anaesthesia of entire dermatomal area?
What is the exception?
As there is considerable overlap between dermatomes
Skin areas that abut onto an axial line
What spinal nerves is the upper limb innervated by?
Anterior primary rami originating from neural levels C5 to T1
These rami form brachial plexus and it is from various parts of this plexus of nerves that the entire neuronal innervation of upper limb is derived
Where does the lower limb receive its motor innervation?
What are they formed from?
From branches of either lumbar or sacral plexus
Formed from anterior primary rami of L2,3,4,5 and S1,2 and 3
What is the difference between myotome and motor unit?
Myotome - muscles innervated by single spinal nerve root
Motor unit - Within a muscle each axon innervates a variable number of muscle fibres. Muscle fibres innervated by a single motor nerve fibre
What spinal nerves stimulate flexion at the elbow?
Which ones stimulate extension?
Flexion = C5 and C6
Extension = C7 and C8
What will a lesion of a spinal nerve root cause?
What will a lesion in a peripheral nerve cause?
Loss of sensation in relevant dermatome and loss of function in relevant myotome
Loss of sensation and muscle weakness in the distribution of the peripheral nerve
Which myotome causes movement of intrinsic muscles of hand?
Fingers?
Shoulder?
Elbow?
Pronation/supination?
Wrist
1
Flexion = 7,8 Extension = 7,8
Flexion = 5 Extension = 6, 7, 8
Flexion = 5,6 Extension = 7,8
Pronation = 6 Supination = 7,8
Flexion = 6,7 Extension = 6,7
What is the area of skin a peripheral nerve innervates called?
Cutaneous distribution of a peripheral nerve
What is each neural segment known as?
Neural level
