Nerves Flashcards
What is a neuron ?
A neuron is a functional unit of the nervous system
What is the basic structure of a neuron ?
A neuron has cell body, dendrites and axon, axon hillock
What are the three major types of neuron ?
bipolar, multipolar, and pseudounipolar
Draw the three main types of neuron
-
What is myelin ?
Myelin is lipid and protein substance. Secreted by Schwann cells (glial cell) around some axons in the PNS. Produced by Oligodendrocytes in the CNS. For neurons having an myelin sheath increase velocity of impulse conduction (insulation).
What are the membranes which wrap around a nerve cell ?
The first covering is the epineurium then the perineurium and finally the endoneurium
What is the blood supply to the nerves called?
The blood supply for the nerve is called the vase nervorum.
what is a dermatome ?
Area of skin supplied by a single spinal nerve
what is a myotome ?
Part of muscle supplied by a single spinal nerve. One muscle myotome may involve multiple spinal segments. Useful to test motor or sensory loss of one or more spinal nerves/segments by testing joint movement or an area of skin
what is a motor unit ?
muscles fibres supplied by one motor neuron
What are motor unit end plates ?
The neuromuscular junction. Where the axon meets the muscle.
How many pairs of cranial nerves are there ?
12
How many pairs of spinal nerves are there ?
31
Describe the path of a nerves signal through the spinal chord
Sensory information detected by the sensory neurons and passed along the rami.
Signal enters the dorsal root and moves into the spinal chord.
Moves through the CNS
Enters a motor neuron and moves out through the ventral root
Moves into the rami
Connects with a NMJ
What does the rami contain ?
Both sensory and motor neurons
What does the dorsal root contain ?
Sensory nerves
What does the ventral root contain ?
Motor nerves
Which part of the vertebrate does the rami run through ?
Runs through the intervertebral foramen
What two groups can our peripheral nerves system be divided into ?
Somatic (Voluntary)
Autonomic (Involuntary)
What is the somatic nervous system used for ?
Regulating voluntary control of body movements
What can the autonomic nervous system be divided into ?
Sympathetic
Parasympathetic
What is the sympathetic nervous system used for ?
‘fight or flight’ responses.
What is the parasympathetic nervous system used for ?
rest and digest responses
Which region does the sympathetic nerves flow out from?
T1-L2/3
Where are sympathetic neuron bodies found ?
Lateral horn of the spinal chord
What is contained in the dorsal root ganglion ?
cell bodies of sensory neurons
How does sympathetic nerves get to every level of the body ?
Although outflow of sympathetic nerves only occurs in the T1 – L2 region all regions of our body require sympathetic nerves. Therefore preganglionic fibres travel up or down the paravertebral sympathetic ganglia , only synapsing at the sympathetic ganglion levels higher of lower and enter the spinal nerve occurring at that vertebral level. Thus every spinal nerve therefore carries postganglionic sympathetic fibres plus their normal sensory and motor fibres.
Where is the outflow for the parasympathetic region ?
Craniosacral region.
S2-S4
Cranial nerve III, VII, IX, X
Describe the paravertebral sympathetic ganglia
The paravertebral sympathetic ganglia are paired meaning that there is one on each side of the vertebral bodies from C1 – S5. The ability to move superiorly and inferiorly along the chain that results in the mass response (mass distribution mechanism) of the sympathetic nervous system
Describe the basic pathway of sympathetic nerves. i.e. they can synapse in the chain at the same level
Sympathetic fibres originate in the lateral horn cells between spinal levels T1-L2(3).
They travel in the ventral root of the spinal nerve to the mixed spinal nerve (MSN).
They leave the MSN via a white (myelinated) ramus communicans as preganglionic fibres to enter the sympathetic ganglion of the same vertebral level.
After synapsing in the sympathetic chain ganglion, they re-enter the spinal nerve via the grey (unmyelinated) ramus communicans as postganlionic fibres and are distributed in both dorsal and ventral rami of the spinal nerve.
The rami then go to supply skin and body wall structures such as arrector pili muscles, blood vessels and glands at that vertebral level (dermatome) with sympathetic input.
Sometimes however this is not the path of the sympathetic nerves. Other ways include….
- they can run up or down the chain and synapse at a different level
- they can pass straight through the chain and synapse elsewhere, eg. in an autonomic nerve ganglion or plexus in the thorax or abdomen
- They can synapse in the sympathetic chain and then run as postganglionic fibres to thoracic organs (thoracic organ supplying splanchnic nerves T1-T4)
- They can run through without synapsing with the sympathetic chain and synapse with the preaortic ganglia before running as postganglionic fibres to abdominal organs (T5-L2/3)
Which region of the spinal chord supplies the face and head ?
Superior, middle and inferior cervical ganglion
Cranial nerves
What is Horners’ Syndrome ?
Damage to the cervical fibres supplying the face and head.
What are the symptoms of Horner’s syndrome?
Partial ptosis - Dropping of the upper eyelid
Miosis - Constriction of the pupil
Anhydrosis - Decreased sweating
