What is gray matter
H-shaped region of cell bodies, dendrites, and proximal axons
What are the 2 main spatial divisions of gray matter
posterior (dorsal) horn and anterior (ventral) horn
What is white matter composed of
Axons that pass longitudinally along the spinal cord and myelin, which is what makes it white
What are rootlets
gray matter that extends out from the ventral and dorsal horns which then converges into roots
What do roots form
The dorsal and ventral roots exit the vertebral column and unite to form the spinal nerve
What does the spinal nerve split into
dorsal and ventral rami (s. is ramus)
What does the dorsal ramus innervate
Deep back muscles and overlying skin
What does the ventral ramus innervate
All of the stuff that the dorsal rami don’t innervate. Most of the nerves we deal with are ventral rami
What types of neurons are in rami
Motor, sensory, and autonomic
What do sensory neurons do
they convey information from the periphery to the CNS
Where is the cell body of a sensory neuron located
In the dorsal root ganglion
Where does a sensory neuron enter the CNS
sensory neurons enter the dorsal root and then dorsal horn
What do motor neurons do
Motor neurons convey information from the CNS to the periphery
Where are motor neuron cell bodies located
Motor neuron cell bodies are located in the ventral horn. Their axons exit via ventral root to innervate skeletal muscles
Where are sympathetic neurons located
Sympathetic neurons are found in essentially all nerves
Where are preganglionic sympathetic cell bodies located
in the intermediolateral column (IML). They project their axons to sympathetic ganglion`
Where are postganglionic sympathetic cell bodies located
Their cell bodies form the sympathetic ganglia; they project their axons to the periphery
Where are dorsal root ganglia located
C1-S5
What are chain ganglia
the vertical column of interconnected sympathetic ganglia
What does an interneuron do
It connects sensory and motor neurons to make a reflex arc
What is a myotactic reflex
Muscle stretch reflex: If a tendon gets contracted suddenly, the muscles extend to protect the joint. (the hammer test)
What is a withdrawal reflex
The pain reflex: neuronal pathway utilizes an interneuron pool to transmit from sensory to motor neurons
What is a crossed extension reflex
Almost immediately after a pain reflex causes flexion of a limb, the opposite limb begins to extend. (particularly with the legs so you don’t fall over after stepping on a nail)
What is reciprocal inhibition
When a muscle is excited, there is often a simultaneous inhibition of the antagonist muscle group. (This is clinically useful physical medicine)
What are all neurons surrounded by
Glia
What are Schwann cells?
Schwann cells are glial cells in the PNS
What is myelin
Myelin is a protein secreted by Schwann cells that serves as insulation for axons
Which type of nerve has the most myelin and what effect does this have on the nerve
Proprioception nerves have the largest amount of myelin, which makes their signal transduction the fastest.
Which type of nerve has the least amount of myelin and what effect does this have on the nerve
C5 nerves are tiny, essentially unmyelinated nerves that transmit pain. Unmyelinated nerves have the poorest signal transduction
How is myelin formed?
myelin is formed when a Schwann cell wraps itself repeatedly around the nerve fiber. This squeezes out the Schwann cell cytoplasm and organelles so that only the cell membrane is wrapped around the nerve fiber.
What is endoneurium
Connective tissue that wraps around individual axons
What is perineurium
Connective tissue that wraps around fascicles of nerve fibers (axons)
What is epineurium
Connective tissue that wraps around multiple fascicles (the entire nerve)
What are nervi nervorum
Literally translated: the nerves of the nerves. Local nerves to the CT of nerves
What are vasa nervorum
literally translated: vessels of the nerves. Local blood vessels to the nerves.
What is the main clinical significance of vasa nervorum
This microvasculature gets blocked up by the excess blood glucose in diabetes mellitus. This causes the peripheral numbness and eventual atrophy common in diabetes
What is proprioception
The sense of the relative position of one’s own body
What sorts of things gather proprioception information
Golgi tendon organs, muscle spindle fibers, cutaneous sensory nerves, the eyes, and the inner ear
Where is sensory information for proprioception processed
In the cerebellum and the cerebrum
What are 6 common causes of neuropathy
diabetes, kidney failure, chronic alcoholism, nutritional deficiency, autoimmune disease, and trauma
What are the symptoms of axonal degeneration
Often occurring after after injury to a axon, chemo, or inherited neurodegenerative disease, the symptoms eventually are numbness in the hands and/or feet that progresses proximally
What is demyelination
The unwrapping of myelin sheaths around axons (guillain-Barre and MS)
What happens if a nerve is temporarily compressed
After a period of compression there is local numbness. Once the compression is removed, painful tingling (pins and needles) starts because slow moving pain neurons are the first to recover from anoxia
What type of injury is a nerve most likely to regenerate after
A nerve has a better chance of recovering after a crushing or compressing injury, and much less chance after a complete severance.
What happens in the distal end of a damaged neuron
The axon and surrounding glial cells undergo degeneration and macrophagic absorption
What are the stages of nerve regeneration
After the initial damage, the distal axon undergoes degeneration. Then the proximal axon regenerates axons (sprouting) which are guided basal lamina tunnels to the distal end. If an axon successfully finds the distal portion, target structures use trophic factors to re-establish connections.
how fast can an axon regenerate
about 1 mm/day.
what type of nerves can regenerate
Only those in the PNS. In the CNS, regeneration is very localized to the brain since oligodendrocytes do not have basal lamina to form tunnels for axonal regrowth
What is the brachial plexus
Rearrangement of ventral rami C5-T1
In a single nerve to a limb structure, what kinds of axons are present and where do these axons originate
In a single nerve there are sensory, motor, and autonomic neurons. The axons originate from 2 or 3 contiguous levels of spinal cord
When does nerve arrangement form
It forms prenatally and independently of any influence from the spinal cord
What is the significance of remembering that Randy Travis drinks cold beer
Roots, trunks, divisions, cords, branches! This is the order of the stuff in the brachial plexus
Where does the brachial plexus originate
C5-C8, T1
What is nerve distribution
Area of skin innervated by one peripheral nerve, e.g. lateral cutaneous n. to forearm
What is a dermatome
Area of skin innervated by one spinal segment e.g. C5
What is a myotome
Area of muscle innervated by one spinal segment. There are normally 2-3 segments per muscle. Strength testing is a common way to evaluate myotomes
What is the posterior triangle and what passes through it
Space between the trap, clavicle, and sternocleidomastoid. The brachial plexus and axillary artery pass through it
What is the axilla
Pyramid shape between the pec major and latissmus, humerus, and ribcage
What is the spatial orientation of the Radius and Ulna
They are similar in shape but in reverse position
What are the 3 joints of the elbow
humeroulnar, humeroradial, proximal radio-ulnar
What composes the humeroulnar joint
the trochlea of the humerus and trochlear notch of the ulna
What composes the humeroradial joint
the capitulum of the humerus with with the head of the radius
What composes the proximal radio-ulnar joint
the head of the radius with radial notch on ulnar side
What type(s) of movement does the elbow have
Flexion and extension between humerus and ulna/radius, pronation and supination at the proximal rado-ulnar joint
What are the 3 main ligaments of the elbow joint
Ulnar collateral, radial collateral, annular
What is the interosseus membrane
It is CT that links the ulna and radius together
What is the function of the annular ligament
It permits rotation of the head of the radius around the ulna
What is the origin and insertion of the biceps brachii long head
Origin: supraglenoid tubercle
insertion: radial tuberosity
What is the origin and insertion of the biceps brachii short head
Origin: coracoid process
insertion: bicipital aponeurosis
What is the action of the biceps brachii
flex and supinate forearm
What is the origin and insertion of the brachialis
Origin: lower 1/2 of the humerus
insertion: coronoid process (ulna)
What is the action of the brachialis
flex forearm
What is the origin and insertion of the coracobrachialis
origin: corocoid process
insertion: middle 1/3 of humerus
What is the action of the coracobrachialis
flex and adduct arm
What does the musculocutaneous nerve innervate
biceps brachii, brachialis, and coracobrachialis
What is the origins and insertion of the triceps
origin: long head infraglenoid tubercle
lateral head posterior humerus (superior/lateral to radial groove)
medial head posterior humerus (inferior/medial to radial groove)
insertion: olecranon process of ulna
what is the action of the triceps
to extend the arm and forearm
What does the radial nerve innervate
the triceps and the brachialis
Where is the radial nerve located
it branches from the posterior cord of BP, passes between lateral and medial heads of the triceps along radial groove
