MSK Session 4 Flashcards
What does a sclerotome give rise to?
Vertebrae and ribs
What are the ventral somites called?
Sclerotomes
Which somites are found dorsally?
Dermamyotomes
What do dermamyotomes give rise to?
Dermis and muscle
What does a dermamyotome develop in association with?
A specific neural level of the neural tube tissue
What does the neural tube eventually become?
Adult spinal cord
Why does the differentiated skin and muscle units from a common dermamyotome have a common source of nervous supply?
They take their neural supply with them irrespective of where they end up in the adult
What is the common source of nervous supply to the muscle and skin units of a dermamyotome?
Spinal segmental nerve
What are the parts of the spinal cord from head to tail end?
Medulla of brain ends Nerve cell bodies Neuronal axons Conus medullaris Film terminae
What makes up the grey matter of the spinal cord?
Nerve cell bodies
What makes up the white matter of the spinal cord?
Neuronal axons
How does the length of the spinal cord vary during growth?
In the baby it effectively extends its whole length
In the adult it is shorter than the vertebral column
What is a vertebral segment?
A single vertebra
How many vertebral segments are there in the spinal column?
33
What do the vertebral foramen form?
Spinal canal
What can be seen when looking at the spinal column from the side?
Inter-vertebral foramen
Describe the path of the spinal cord in the spinal column.
Runs through vertebral foramina
Gives off a pair of nerves at each vertebral level (L+R)
Where do the left and right spinal segmental nerves exit the vertebral column?
Intervertebral foramina
Where do spinal nerves emerge in the cervical cord?
Superior to their corresponding vertebral level
Which area of the body does the bulge in the cervical spinal cord provide innervation for?
UL
Why is there a bulge in the lumbar spinal cord?
To provide innervation to the LL
Along which axis does the distribution of sensory and motor neurones in the spinal cord vary?
Rostro-caudal
What can be seen in cross section of the spinal cord?
Specialisations that match the 4 vertebral regions
Where do spinal nerves emerge in the non-cervical spinal cord?
Inferior to their corresponding vertebral levels
What is a vertebral level?
Level of vertebra itself
How are the intervertebral foramina arranged in relation to the spinal cord?
Heavily offset
What is a fundamental feature of the design of the CNS?
Segmented throughout its extent
What does each segment of nervous tissue have?
Independence of connection to the periphery
What does each neural level have?
R + L sides
What are discrete territories of skin innervated by?
Sensory nerves
What do motor nerves innervate?
Myotomal territories
What is the function of the dorsal root of a segmented nerve?
Sensory/afferent
What is the function of a ventral root of a segmental nerve?
Motor and autonomic/efferent
Where can the spinal segmental nerves become strangulated?
Where they exit the vertebral column
What is a spinal segmental nerve?
One of the L or R branches given off at a vertebral level by the spinal cord
What is known as a mixed spinal nerve?
A vertebral level and a neuronal spinal level
What does a neurovascular bundle consist of?
Mixed spinal nerve
Equivalent segmental spinal nerves
Veins
What is a ramus?
A branch containing all functional modalities for that segmental level
What happens to the missed spinal nerve when it emerges from the vertebral column?
Branches into large and small
What does the large branch of a mixed spinal nerve do?
Supply posture muscles and some cutaneous supply
What can be said about the level of emergence in comparison to the site of innervation by the anterior/ventral ramus of a mixed spinal nerve?
Stay at approximately the same level
What happens to the small/posterior/dorsal ramus of a mixed spinal nerve?
Divides into medial and lateral branches to give one sensory and one non-sensory branch
Where does the nerve supply to the UL originate?
Mostly cervical spinal segments C5-T1
Rest from T2 roots
Which spinal nerves form the brachial plexus?
C5 C6 C7 C8 T1
What are the roots of the brachial plexus?
Neural level - anterior rami of C5-T1
What are the nerve roots of the three trunks in the brachial plexus?
Upper = C5 + C6 Middle = C7 Lower = C8 + T1
What are the divisions of the brachial plexus?
Anterior and posterior which supply respective compartments
What are the three cords of the brachial plexus?
Medial
Lateral
Posterior
Which nerves other than the brachial plexus supply the UL?
Lateral pectoral Upper and lower subscapular Dorsal scapular Suprascapular Long thoracic Axillary
Which spinal segments provide nerve supply to the lower limb?
L1-S4
Where does the nerve supply to the lower limb originate from?
Lumbar plexus: L1-L4
Sacral plexus: L4-S4
Where does the lumbar plexus form?
Behind psoas minor muscle
Which nerves does the medial emergence of the lumbar plexus give rise to?
Obturator
Lumbosacral trunk
Which nerves does the lateral emergence of the lumbar plexus give rise to?
Femoral
Iliohypogastric
Ilioinguinal
Lateral cutaneous nerve of thigh
Why does the sacral plexus have an anterior/posterior emergence?
Due to vertebral fusion
Where does the sacral plexus form?
W/in pelvic cavity
Where does the sacral plexus lie in relation to?
Piriformis
Which regions does the sacral plexus supply?
Pelvic
Gluteal
Perineal
LL
Via which nerve does the sacral plexus provide its innervation?
Sciatic
What spinal outflow gives rise to the sacral plexus?
1/2 L4
L5
Sacral spinal segmental
What division of the spinal cord gives innervation to dermatomes?
Sensory (inflow) division of the somatic branch
What allows the disruption of nervous supply to be accurately pinpointed?
Organised examination of the integrity and sensory function of the skin
What is a Dermatome?
Area of skin supplied by sensory nerve fibres from a single neural level
What does 1 spinal nerve root supply?
1 Dermatome
Why is there no C1 dermatome level?
There is no cutaneous innervation
Why are some sections of the skin served by 2 successive spinal nerves?
Due to overlap b/w adjacent dermatomes
What is the innervation to a typical dermatome sandwiched by 2 others?
Served by 3 successive sensory nerves
What does dermatomal overlap reduce the probability of?
Patches of skin being left w/out natural sensory neural supply
What can be said to mark the boundaries between the flexor and extensor compartments?
Anterior and posterior to pre and post axial borders
What is the axial line?
Line of junction between two of the dermatomes that appear to be missing from the trunk
Which dermatomes appear to be missing from the trunk?
C4-8
Why do C4-8 dermatomes appear to be missing from the trunk?
Skin enveloping UL is taken from the trunk and lies out along the limb
What marks the boundaries between the flexor and extensor compartments in the upper and lower limb?
UL = cephalic and basilic veins LL = great and small saphenous veins
Describe the dermatome locations on the UL.
C4 = shoulder tip C5 = radial side of upper arm C6 = radial side of forearm C7 = skin of the hand C8 = ulnar side of forearm T1 = ulnar side of upper arm T2 = skin of the axilla
Describe the sensory supply of the LL.
Front limb = lumbar segments
Back limb = sacral segments
Saddle area = sacral segments
Perineal area = sacral segments
What do sensory divisions of terminal nerves of the brachial plexus supply?
Skin in nerve territories
What supplies the skin in the LL in territorial domains?
Sensory divisions of terminal nerves of the lumbar plexus
What is the sensory innervation of the hand usually considered in?
Nerve territories
What three groups can the muscles of the posterior compartment of the forearm be organised into physiologically?
Muscles that extend and adduct/abduct hand at wrist joint
Muscles that extend medial 4 fingers
Muscles that extend/abduct the thumb
What are the muscles of the superficial layer of the posterior forearm?
Brachioradialis Extensor carpi radialis longus Extensor carpi radialis brevis Extensor digitorum Extensor digiti minimi Extensor carpi ulnaris
What is the general function of muscles in the posterior compartment of the forearm?
Extension
What is the main action of brachioradialis?
Weak flexion which is maximum when forearm is mid-pronator
What innervates all muscles in the posterior compartment of the forearm?
Radial nerve and its branches
What is the main action of ECRL?
Extend and abduct hand at wrist
What is the main action of ECRB?
Extend and abduct hand at wrist
What is the main action of extensor digitorum?
Extends medial 4 digits primarily at metacarpopharyngeal joints and secondarily at interphalangeal joints
What is the main action of EDM?
Extend 5th digit primarily at metacarpophalangeal joint and secondarily at interphalangeal joint
What is the main action of extensor carpi ulnaris?
Extend and adduct hand at wrist
Which are the muscles of the deep layer of the posterior forearm?
Supinator
Extensor indicis
What is the main action of supinator?
Supinates forearm - rotates radius to turn palm
What is the main action of extensor indicis?
Extend 2nd digit
Extend hand at wrist
Which are the outcropping muscles of the deep layer of the posterior forearm?
Abductor pollicis longus
Extensor pollicis longus
Extensor pollicis brevis
What is the main action of APL?
Abducts thumb
Extends thumb at carpometacarpal joint
What is the main action of EPL?
Extend distal phalanx of thumb at interphalangeal joint
Extend metacarpophalangeal and carpometacarpal joints
What is the main action of EPB?
Extend proximal phalanx of thumb at metacarpophalangeal joint
Extend carpometacarpal joint
