Dermatomes and myotomes Flashcards
With regards to segmentation what is a neural level?
A neural segment
What does the neural tube contain?
Precursor cells of the nervous system
How is the neural tube formed?
Under the influence of the notochord the 18 day old embryo starts to invaginate to form the neural groove.
The neural folds approach each other in the midline where they fuse - this forms the neural tube.
By 24 days the cephallic (head) and caudal (tail) ends of the neural tube have closed
What is a somite?
One of the longitudinal series of segments into which the body is divided
Describe the maturation of somites?
Day 30 - 34-35 pairs of somites
Differentiates into the sclerotome (ventral and gives rise to the vertebrae and ribs)
Dermatomyotome ( dorsal and forms the dermis via the dermatomes and muscle tissue via the myotomes)
Why does skin and muscle have a common spinal nerve supply?
Derived from a single dermatomyotome
What is a dermatome?
An area of skin that is supplied by a single spinal nerve
Label
What is a neuron?
What is a synapse?
A neuron (also called neurone or nerve cell) is an electrically excitable cell that receives, processes and transmits information through chemical and electrical signals.
Synapses - where signalling between neurons occurs
Describe the structure of a neuron
A typical neuron consists of a cell body, dendrites ( thin structures that arise from the cell body.) and an axon (specialised cellular extension that arises from the cell body at a site called the axon hillock and travels for a distance of up to 1 metre before synapsing)
What is an endoneurium?
A layer of connective tissue surrounding axons
Consists of an inner sleeve of material called the glycocalyx and a mesh of collagen
Describe the bundling together of nerve?
Why do nerves have blood vessels and what are they called?
The axons, surrounded by endoneurium, are bundled together into groups called fascicles and each fascicle is wrapped in a layer of connective tissue called perineurium. The fascicles are then grouped together and surrounded by epineurium.
Nerves have high metabolic requirements and hence contain their own blood vessels within the epineurium, called vasa nervorum.
What is a spinal nerve?
Mixed nerve that carries motor, sensory and autonomic signals between the body and the spinal cord
What is the dorsal root?
What is the dorsal root ganglion ?
Dorsal (posterior) roots contain afferent / sensory nerve fibres ONLY
Dorsal root ganglion - cell bodies of the sensory neurons from the periphery
What is the ventral (anterior) root?
An efferent root that carries the motor or autonomic fibres that are leaving the spinal cord.
Describe vertical segements?
Verticle segments differentiate from sclerotomes
1 vertebral segment refers to 1 vertebra
The spinal cold travels through the vertebral foramen
Multiple vertebral foramina make up the spinal canal
Spinal nerves leave the spinal canal via intervertebral foramina
Describe the location of the spinal cord?
Why doesn’t the spinal cord fill the length of the vertebral canal?
What is the name given to the area below the spinal cord?
Starts at inferior margin of medulla oblongata and ends as conus medullaris at L2
There is differential growth between the spinal cord and vertebral column.
Cauda equina - Here long roots from inferior segments (lumbar / sacral / coccygeal) descend to exit at their respective foramina
Describe the origins of spinal nerves?
Where does the first spinal nerves emerge from?
Where do the C1 - C7 nerves exit
Where does C8 exit?
Where do T1-L5 exit?
Where does S1 - S4 exit?
Where does S5 and Co1 exit?
First cervical pair of spinal nerves emerge between occipital bone and atlas (C1)
C1-C7 exit above corresponding vertebrae
Spinal nerve C8 exits between vertebrae C7 and T1
T1-L5 exit below corresponding vertebrae
S1-S4 exit via 4 pairs of sacral foramina
S5 and Co1 exit via sacral hiatus (posterior)
What is the posterior (dorsal) ramus ?
Supplies the deep muscles and skin of the dorsal trunk.
In humans, the dorsal rami are very small
What is the anterior (ventral) ramus?
Compare the size to dorsal rami?
Supplies the muscles and skin of the upper and lower limbs and also the lateral and ventral trunk.
The anterior rami are much larger than the dorsal rami.
What is a grey ramus communicans (pl. rami communicantes) ?
A branch that each spinal nerve recieves from adjacent paravertebral ganglion of the sympathetic trunk.
The grey rami communicantes contain post-ganglionic nerve fibres of the autonomic nervous system and are composed largely of unmyelinated neurons.
Describe how dorsal/posterior rami supply the skin of the back?
The posterior (dorsal) rami divide again into medial and lateral branches that supply the skin of the back in a ‘tidy’ segmental manner.
Each dorsal ramus supplies a narrow strip of muscle and skin in line with the intervertebral foramen
Describe the distribution of anterior (ventral) rami?
Follows a complicated distribution
Segmental for trunk
Enters brachial plexus to supply upper limb
Enters lumbo-sacral plexus to supply the lower limb
Describe the rotation of limb buds during development?
The upper limb rotates externally (laterally) through 90° on its longitudinal axis; thus, the future elbows point backwards (or posteriorly) and the extensor muscles come to lie on the lateral and posterior aspects of the limb
The lower limb rotates internally (medially) through almost 90°; thus, the future knees face forward (or anteriorly) and the extensor muscles come to lie on the anterior aspect of the lower limb.
How are the the boundaries of the dorsal (posterior) and ventral (anterior) compartments are marked?
By superficial veins
UL: Cephalic vein - marks pre-axial border
UL: Basilic vein marks the post-axial border
LL: Long (or great) saphenous vein marks the pre-axial border
LL: Short (or small) saphenous vein marks the postaxial border.
What are plexuses?
Complex networks of nerves that divide and merge with other bundles of nerve fibres multiple times.
Anterior (ventral) rami of the spinal nerves enter each plexus and, eventually, peripheral nerves emerge from the other end
What is the role of the C5 myotome?
Shoulder abduction and external rotation plus weak contribution to elbow flexion
What is the role of the C6 myotome?
Elbow flexion/wrist extension/supination /internal rotation of shoulder
What is the role of the C7 myotome?
Elbow extension/wrist flexion/pronation / weak contribution to finger flexion and extension
What is the role of the C8 myotome ?
Finger flexion / finger extension / thumb extension / wrist ulnar deviation
What is the role of the T1 myotome?
Finger abduction and adduction
What is the role of the L2 myotome?
Hip flexion
What is the role of the L3 myotome?
Knee extension and hip adduction
What is the role of the L4 myotome?
Ankle dorsiflexion
What is the role of the L5 myotome?
Great toe extension/ ankle inversion/ hip extension
