Topic 4: PNS Road Maps Flashcards
In the lumbosacral region, the nerve roots descend almost vertically below the cord to form the
Cauda Equina
The area from which a pair of dorsal and ventral roots arise is defined as
A segment of the SC
How many roots does each segment of the spinal cord connect to
4 roots
Each root consists of bundled nerve fibers.
The anterior and posterior roots join together at the intervertebral foramen, to form a
Spinal nerve
The ventral (anterior) root contains axons that carry _________ signals from the spinal cord to muscles and viscera.
The cell bodies of these axons lie in the SC.
Efferent
The dorsal root contains ________ signals. A dorsal root ganglion contains cell bodies of 1st order neurons. Unipolar.
Afferent
On emerging from the intervertebral foramen, a spinal nerve divides immediately into anterior and posterior ramus with medial and lateral branches each containing what fibres
Motor and Sensory fibres
Supplies the posterior body trunk and back of the head
Dorsal Rami
Supplies the lateral and anterior trunk and upper and lower extremities
Ventral Rami
Both dorsal and ventral rami contain autonomic fibers. Both dorsal and ventral rami are mixed nerves because
They are branches of the spinal nerve, not the root.
Axons in the ventral rami that serve the upper and lower extremities mix and mingle with each other to form nerve networks called
Plexuses
Peripheral nerves
Peripheral nerves i.e. Those serving the upper and lower extremities, usually contain fibres from more than one spinal nerve. Why is this advantageous?
Because a muscle getting innervation from multiple spinal nerves can retain some function if one spinal nerve is damaged at the spinal cord location
True or False?
Only ventral rami form plexus’?
True
The level of SC injury is indicated by the highest level that remains intact.
Give an example:
A C3 lesion means that the dermatomes and myotomes associated with C1 to C3 are fully functioning. All those below C3 are affected.
The brachial plexus supplies the upper limb and supporting musculature of the scapula. The brachial plexus is formed by the ventral rami _________ (which spinal segments)
C5 - T1
The plexusbhas different regions. What are they?
Roots, Trunks, Divisions, Cords —> post plexus nerves ex. Radial Nerve
Innervates the muscles in the flexor compartment of the upper arm. (Biceps Brachii, brachilis, coracobrachialis)
Musculocutaneous
Innervates most intrinsic muscles of the hand - except the Thenar Eminence
Ulnar Nerve
Innervates most of the flexors muscles in the forearm and thenar muscles
Median Nerves
Innervation to the deltoid and Teres minor
Axillary Nerve
Innervates the extensor muscles of the elbow, wrist, and fingers & anotomical snuff box
Radial Nerve
Long Thoracic Nerve
Serratus Anterior
Thoracodorsal Nerve
Latissimus Dorsi
Area of skin supplied by sensory nerve fibres originating from a single dorsal nerve root of a single spinal nerve
Dermatome
What is a receptive field?
Responsibility of 1 unipolar neuron
Dermatomes are named according to the
Spinal nerve which supplies them
Lateral shoulder and arm
C5
Thumb, index finger (radial border of hand)
C6
Middle Finger
C7
Digiti minimi (ulnar border of hand)
C8
Medial elbow
T1
Intercostal nn. form segmental strips on thorax
T2-T12
Goes across the nipples
T4
Across the umbilicus
T10
Across upper edge of pubic bone
T12
