lecture 11 : the peripheral nervous system Flashcards
what does the peripheral nervous system consist of?
the peripheral nerves and the ganglia
what is a dorsal root ganglia?
this is a sensory ganglion
what is the structure of a dorsal root ganglion?
- the dorsal root ganglion is surrounded by a connective tissue capsule - inside the capsule is a mixture of neural cell bodies and axons
what is the structure of a single sensory neurone?
- there is a dark nucleus inside a pale nucleus - the small nuclei are the satellite cells which support the neurones - the sensory neurones are pseudo unipolar
where do the sensory neurone cell bodies lie?
they lie in the ganglia associated with the spinal dorsal roots or some cranial nerves
where do post ganglionic neuronal soma lie? how are they arranged?
they lie in the autonomic ganglia they are arranged in rows (sympathetic) or they are arranged closer to the internal organs ( parasympathetic)
what are the axon bundles called? what do these group to make?
the bundles are called fascicles they are grouped to make nerves
what are the three layers of connective tissue in nerves
- epineurium - connective tissue which surrounds the nerve 2. perineurium - this is the connective tissue that surrounds the fascicles 3. endoneurium - this is the connective tissue that surrounds the axons
what is the axon diameter of a myelinated cell?
1.5- 2 micrometers
what is the axon diameter of a non myelinated cell?
1 micrometer
what are the features of myelinated cells?
- they are clothed in succession of schwann cells - separated by the nodes of ranvier - the myelination allows the saltatory conduction to take place
what are the features of non myelinated cells?
each axon only has one single layer of membrane and there is no saltatory conduction
where are schwann cells present?
they are present on both non myelinated and myelinated cells
* show the structure of somatic, autonomic and sensory neurones:
* insert the pic - somatic neurones have their soma in the CNS - autonomic motor neurones have a preganglionic and postganglionic motor neurone - sensory neurones have a ganglion in the middle
* show a diagram of a spinal cord segment:
insert pic
what are the main 3 things that make up the spinal cord segment?
- the dorsal horn - the ventral horn - the spinal nerve
what are the four types of neurone?
- somatic neurone info from non internal organs 2. somatic motor controls the striated muscle 3. autonomic sensory sensory from internal organs 4. autonomic motor controls the internal organs
where are somatic sensory somatic motor and autonomic nerves found?
- somatic sensory and somatic motor are found in all spinal nerves - autonomic is found is most spinal nerves
what is the myotome?
this is the muscle area that the spinal nerve innervates
what is the dermatome?
this is the skin that the spinal nerve innervates
what is a plexus?
a plexus is when spinal nerves are combined to form peripheral nerves
what is ramus?
this is when as the spinal nerves leave the spinal cord some merge together and later divide into rami
what is the significance of rami?
- it gives rise to the mixing of spinal nerves so by the time one has 3 peripheral nerves emerging from the bottom of a plexus each of the nerves have axons that originate from more than one spinal nerve
where do we have spinal nerves and where do we have peripheral nerves?
spinal nerves - before the plexus peripheral nerves - after the plexus
whats the pattern of spinal and peripheral nerves?
spinal nerves - stripey pattern peripheral nerves- patchy pattern
what is the clinical relevance of the pattern of spinal and peripheral nerves?
if the area is a stripe - spinal nerve injury if the area is a path then it is a peripheral nerve injury
where does the dorsal rami innervate?
the muscle and the skin of the back
where does the ventral rami innervate?
the muscle and skin o the rest of the body
what is the significance of rami?
- they provide interconnections between some spinal nerves and the ganglia of the sympathetic chain
what do the ventral rami of spinal nerves C5-T1 innervate?
they innervate the upper limb through the brachial plexus
what do Ventral rami of spinal nerves L2-S2 innervate?
they innervate the lower limb through the lumbosacral plexus
* insert pic!! what is the timeline of what happens during compression injury healing of the nerve ?
- with a compression injury the axoplasm is completely separated (however the endoneurium remains intact) 2. after the compression has happened the part distal to the soma of the nerve degenerates 3. the macrophage influx then clears the debris 4. the schwann cells undergo mitosis and proliferate 5. the axonal sprouts grow from the proximal stump and there is competition as to which one synapses with the target organ first 6. once the axonal sprout synapses it grows and is myelinated (the other axonal sprouts stop growing) 7. the end product looks similar to the original but the internodal space (between the nodes of ranvier) has decreased so the conduction speed decreases
what happens if the injury is too close to the soma?
this might kill the whole cell
what the compression injury happens but it cuts the endometrial sheath?
- the axonal sprouts have no guidance cues and so you may have rein nervation of the wrong target
how can a cut of the endometrial sheath be fixed clean cut ? messy cut ?
- surgeon can fix using microsurgery - using a nerve graft from the back of the calf
what happens if the damage is very severe?
this means the axonal sprouts have no guidance at all and form a tangled bunch called a neuroma which is very painful which often has to be surgically removed
what is a peripheral neuropathy? where does it move towards?
this is the progressive degeneration of nerves moves towards the CNS
what are the common causes of peripheral neuropathy
- badly controlled diabetes - alcoholism - leprosy (infection)
what is the mechanism of peripheral neuropathy?
- happens either due to a direct problem with the axon - or a secondary effect of damage to the myelin sheath
what are the two types of peripheral neuropathy?
- segmental demyelination a. they is when the schwann cells sporadically die and fall away b. this will slow down the conduction due to lack of saltatory conduction AXON IS STILL PRESENT 2. axonal degeneration a. after the degeneration of the axon the myelin also degrades and you get a conduction block AXON IS NOT PRESENT
what are the main diagnostic techniques for peripheral nervous disorders
- conduction velocity measure the conduction velocity to see if it slows or if the shape of the wave changes - nerve biopsy biopsy a piece of nerve and the pathologist can see the different features
what are the factors that affect the conduction velocity of the peripheral axons?
- degree of myelination more insulation means faster conduction due to nodes of ranvier allowing saltatory conduction - diameter of the axon - thicker axons mean faster conduction speed as there are more receptors and free ions
