Session 5 MSK Flashcards
The neural tube contains the
Precursor cells of the nervous system
What happens in an 18 day embryo
- Influence of notochord
- Neural tube invaginate to form neural groove
- Neural folds fuse at midline
- Neural tube formed
What has happened by 24 day stage
Cephalon head and caudal tail ends of neural tube have closed
What happens from day 20 onwards-
paired Somites (primitive segments) appear
What happens by day 30
Embryo has approx 34-35 pairs of Somites that begin to differentiate as soon as they are formed
What happens during the 4th week after fertilisation
Each Somite differentiates into the sclerotome, (ventral- gives rise to vertebrae and ribs), dermatomyotome (dorsal and forms dermis via dermatomes) and muscle tissue via the myotomes
Dermatomyotomes develop in association with
A specific neural level of spinal cord and take nerve supply with them from neural tube as spinal nerve
Skin and muscle derived from a single dermatomyotome have a
Common spinal nerve supply
What is a dermatome
An area of skin supplied by a single spinal nerve
Landmarks of Foerster dermatome map
T4/T5- nipped
T10- umbilicus
L1- groin
What is a neuron
An electrically excitable cell that receives, processes and transmits information through chemical and electrical signals
Within the nerve, each axon is surrounded by a layer of connective tissue called
Endometrium
Structure within endoneurium
- Endonurial fliud
- Axons are bundled into fascicles and surrounded by perineurium connective tissue
- Fascicles grouped together and surrounded by epineurium
- Vasa nervorum
What is a spinal nerve
A mixed nerve that carries motor, sensory and autonomic signals between body and spinal cord
What does dorsal nerve root do
Transmits sensory fibres from the sensory receptors to the spinal cord, afferent
What does ventral nerve root do
Carried motor and autonomic fibres leaving spinal cord, efferent
Spinal nerves key points
31 pairs, numbered according to level of vertebral column they emerge from. Short and exist briefly as they pass through intervertebral foramen
Each vertebra is derived from
Parts of 2 adjacent Somites
Spinal cord runs through
Vertebral foramen, multiple vertebra foramina form spinal canal
Spinal nerves leave spinal canal through
Gaps between vertebrae knows as intervertebral foramina
Spinal cord commences at
Inferior margin of medulla oblongata, base of brain stem
Spinal cord ends at
Conus medullaris at L2
Spinal cord is shorter than
Vertebral canal
What is below conus medullaris
Cauda equina
How many pairs of cervical spine roots and cervical vertebrae
8 and 7
Significance of difference in cervical spine roots and vertebrae number
Cervical spinal roots emerge above the corresponding vertebral body with the exception of the 8th, C8, which emerges between C7 and T1 (above T1)
Exit of nerve roots in thoracic vertebra
From T1, each corresponding nerve root exits inferior to vertebral body
Sacral nerve roots exit through the
Sacral foramina and the S5 and first coccygeal nerve roots exit via the sacral hiatus
What happens to spinal nerves after emerging through intervertebral foramen
Divides into rami.
Posterior ramus supplies deep muscles and skin of the dorsal trunk.
Anterior ramus supplies muscles and skin of upper and lower limbs and lateral and ventral trunk. Larger.
What is meningeal branch
Each spinal nerve gives one off that re-enters spinal canal through intervertebral foramen (to supply ligaments, vertebra, blood vessels and meninges)
Spinal nerves from T1-L2 all give off
White ramus communicans (pre ganglionic sympathetic nerve) which enters the sympathetic trunk via adjacent paravertebral ganglion
All spinal nerves receive
Grey ramus communicans from adjacent paravertebral ganglion (unmyelinated)
What is a dermatome
An area of skin in which sensory nerves derive from a signal spinal nerve root (anterior rami from upper and lower limbs)
Posterior rami divide again into
Medial and lateral branches that supply back (in line with intervertebral Foramen)
What does functional overlap between adjacent dermatomes mean
If a single spinal nerve is damaged, the area of anaesthesia will be smaller than you think
Functional overlap does not extend across
An axial line
What is an axial line
Junction of two dermatomes supplied from discontinuous spinal levels
The developing upper and lower limbs…
Rotate in opposite directions and to different degrees
What marks pre-axial and post-axial border in upper limb
Pre - cephalic vein
Post- basillic vein
What marks the pre-axial and post-axial border in lower limb
Great saphenous vein - pre
Small saphenous vein- post
Anterior rami of C5-T1 enter the
Brachial plexus to supply muscles and skin of upper limb
Anterior rami of L1-S5 enter the
Lumbosacral plexus to supply the muscles and skin of lower limb
Peripheral nerves generally contain fibres from
More than 1 spinal nerve (hence skin supplied by a single peripheral nerve does not correspond to the dermatome map)
A dermatome may be supplied by
Multiple peripheral nerves as fibres may enter multiple different peripheral nerves
What is a myotome
group of muscle fibres supplied by a single spinal nerve
What is a motor unit
Single motor neuron and the skeletal muscle fibres it innervates
Myotomes of lower limb
L2- hip flexion L3- hip extension L4- ankle dorsiflexion L5- great toe extension S1- ankle plantar flexion S2- great toe flexion
What is Hilton’s law
The nerves supplying the muscles moving the joint also supply the joint capsule and the skin overlying insertions of the muscles
What is the neural level
Lowest level of fully intact sensation and motor function
L2 dermatome includes territory from
- Obturator nerve
- Femoral nerve
- Lateral cutaneous nerve of thigh
(And Genitofemoral nerve L1-2)
What are peripheral nerve territories
Areas of skin supplied by the peripheral nerves
branches of brachial plexus in upper lumb and lumbosacral plexus in lower limb
Often overlap sections of multiple dermatomes
