lecture 11 : the peripheral nervous system

Question 1

what does the peripheral nervous system consist of?

Answer 1

the peripheral nerves and the ganglia

Question 2

what is a dorsal root ganglia?

Answer 2

this is a sensory ganglion

Question 3

what is the structure of a dorsal root ganglion?

Answer 3

• the dorsal root ganglion is surrounded by a connective tissue capsule - inside the capsule is a mixture of neural cell bodies and axons

Question 4

what is the structure of a single sensory neurone?

Answer 4

• 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

Question 5

where do the sensory neurone cell bodies lie?

Answer 5

they lie in the ganglia associated with the spinal dorsal roots or some cranial nerves

Question 6

where do post ganglionic neuronal soma lie? how are they arranged?

Answer 6

they lie in the autonomic ganglia they are arranged in rows (sympathetic) or they are arranged closer to the internal organs ( parasympathetic)

Question 7

what are the axon bundles called? what do these group to make?

Answer 7

the bundles are called fascicles they are grouped to make nerves

Question 8

what are the three layers of connective tissue in nerves

Answer 8

1. 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

Question 9

what is the axon diameter of a myelinated cell?

Answer 9

1.5- 2 micrometers

Question 10

what is the axon diameter of a non myelinated cell?

Answer 10

1 micrometer

Question 11

what are the features of myelinated cells?

Answer 11

• they are clothed in succession of schwann cells - separated by the nodes of ranvier - the myelination allows the saltatory conduction to take place

Question 12

what are the features of non myelinated cells?

Answer 12

each axon only has one single layer of membrane and there is no saltatory conduction

Question 13

where are schwann cells present?

Answer 13

they are present on both non myelinated and myelinated cells

Question 14

* show the structure of somatic, autonomic and sensory neurones:

Answer 14

* 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

Question 15

* show a diagram of a spinal cord segment:

Answer 15

insert pic

Question 16

what are the main 3 things that make up the spinal cord segment?

Answer 16

• the dorsal horn - the ventral horn - the spinal nerve

Question 17

what are the four types of neurone?

Answer 17

1. 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

Question 18

where are somatic sensory somatic motor and autonomic nerves found?

Answer 18

• somatic sensory and somatic motor are found in all spinal nerves - autonomic is found is most spinal nerves

Question 19

what is the myotome?

Answer 19

this is the muscle area that the spinal nerve innervates

Question 20

what is the dermatome?

Answer 20

this is the skin that the spinal nerve innervates

Question 21

what is a plexus?

Answer 21

a plexus is when spinal nerves are combined to form peripheral nerves

Question 22

what is ramus?

Answer 22

this is when as the spinal nerves leave the spinal cord some merge together and later divide into rami

Question 23

what is the significance of rami?

Answer 23

• 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

Question 24

where do we have spinal nerves and where do we have peripheral nerves?

Answer 24

spinal nerves - before the plexus peripheral nerves - after the plexus

Question 25

whats the pattern of spinal and peripheral nerves?

Answer 25

spinal nerves - stripey pattern peripheral nerves- patchy pattern

Question 26

what is the clinical relevance of the pattern of spinal and peripheral nerves?

Answer 26

if the area is a stripe - spinal nerve injury if the area is a path then it is a peripheral nerve injury

Question 27

where does the dorsal rami innervate?

Answer 27

the muscle and the skin of the back

Question 28

where does the ventral rami innervate?

Answer 28

the muscle and skin o the rest of the body

Question 29

what is the significance of rami?

Answer 29

• they provide interconnections between some spinal nerves and the ganglia of the sympathetic chain

Question 30

what do the ventral rami of spinal nerves C5-T1 innervate?

Answer 30

they innervate the upper limb through the brachial plexus

Question 31

what do Ventral rami of spinal nerves L2-S2 innervate?

Answer 31

they innervate the lower limb through the lumbosacral plexus

Question 32

* insert pic!! what is the timeline of what happens during compression injury healing of the nerve ?

Answer 32

1. 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

Question 33

what happens if the injury is too close to the soma?

Answer 33

this might kill the whole cell

Question 34

what the compression injury happens but it cuts the endometrial sheath?

Answer 34

• the axonal sprouts have no guidance cues and so you may have rein nervation of the wrong target

Question 35

how can a cut of the endometrial sheath be fixed clean cut ? messy cut ?

Answer 35

• surgeon can fix using microsurgery - using a nerve graft from the back of the calf

Question 36

what happens if the damage is very severe?

Answer 36

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

Question 37

what is a peripheral neuropathy? where does it move towards?

Answer 37

this is the progressive degeneration of nerves moves towards the CNS

Question 38

what are the common causes of peripheral neuropathy

Answer 38

• badly controlled diabetes - alcoholism - leprosy (infection)

Question 39

what is the mechanism of peripheral neuropathy?

Answer 39

• happens either due to a direct problem with the axon - or a secondary effect of damage to the myelin sheath

Question 40

what are the two types of peripheral neuropathy?

Answer 40

1. 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

Question 41

what are the main diagnostic techniques for peripheral nervous disorders

Answer 41

• 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

Question 42

what are the factors that affect the conduction velocity of the peripheral axons?

Answer 42

• 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