Nerves Flashcards
1
Q
What does the CNS consist of?
A
-
Brain and spinal cord
- Terminates at L1
2
Q
What does the PNS consist of?
A
- ** Cranial ( 12 pairs)**
- Spinal ( 31 pairs)
- and peripheral nerves
3
Q
What does the autonomic nervous system consist of?
A
- Sympathetic and parasympathetic systems
4
Q
What does the CNS control?
A
- Somatic and visceral function
5
Q
What does the PNS do?
A
- relays information from the periphery to the brain and vice versa
6
Q
What do afferent ( sensory) nerve fibres transmit?
A
- Somatic and visceral information from the periphery to the brain
7
Q
What do the efferent ( motor) nerves transmit?
A
- Somatic and autonomic information from the brain to the periphery
8
Q
What is the basic functional unit of a nerve?
A
- Cell body
- Axon
- the axolemma ( cell membrane ) encloses the axoplasm ( cytoplasm)
- Dendrites- branch out from the cell body and conduct impulses to other cell bodies
9
Q
What is a nerve composed of?
A
- Fascicles or bundles ( groups of sheathed axons) of nerve fibres
-
Endoneurieum
- connective tissue covering the nerve fibres
- longitudinally arranged collagen fibres, fibroblasts and blood vessels
-
Perineurieum
- envelops the nerve fibre bundles -> a fascicle
- consists of alternating layers of collagen and cell processes acting as a diffusion barrier
-
Epineurium
- conists of collagen and fibroblasts acting as a supporting structure for nerve fasciles grouped into a nerve trunk
10
Q
Describe the blood supply to neves?
A
-
Intrinsic plexus
- distributed in longitudinal fashion in endoneurium, perineurium and epideneurium
-
Extrinsic plexus
- vessels are segmental
- found in the paraneurium ( layer external to the perineurium)
11
Q
What is the neuron supported by in the Extracellular matrix?
What are these cells in the CNS?
A
- Glial cells
- Ogliodendrocytes ( responsible for myelination)
- Astrocytes
- Microglia
12
Q
What is the myelin sheath made from?
A
- Cytoplasmic extension of oligodendrocytes in CNS
13
Q
What is different between myelin sheath of the PNS cf CNS?
A
- Myelin sheath of CNS has no neurilemma
14
Q
What is astrocytes role in CNS?
A
- **Regulate extracellular potassium concentration & Neurotransmitters **
- Storing and transfer metabolites from blood vessel to neurons
15
Q
What is microglia role in CNS?
A
- thought to play a phaogocytic role- defending the CNS from noxious stimuli
16
Q
What are responsible for myelination in the PNS?
Where do they arise?
A
- Schwann cells
- Neuroectoderm
17
Q
What determines myelination in the PNS?
A
- The size of the axon
- larger axons are invaginated into a series of schwann cells that lays down the myelin sheath in spiral layers => neurilemma
- Each schwann cell contributes myelin to one segment ( internode) of the axon
- At the end of each internode the axon has an increased diameter=> paranode
- here the axon and myelin sheath are crenated with myelin lamellae, ending in terminal loops of schwann cell cytoplasm
18
Q
What are the nodes of ranvier?
A
- Gaps between adjacent shwann cell internodes along the myelinated axon
- here the axon diameter is reduced slightly
- the axon diameter is inversely proptional to the length of the node of ranvier
- the concentration of Na channels is increased in this region to facilitate saltatory conduction
19
Q
What is axonal transport important?
What drives it?
A
- to maintain sturcture of nerve and supply neurotransmitters
- ATP ( adenosine triphosphate) driven
- can occur in an
- antegrade ( microtubule/microfilaments components) /
- retrograde fashion- neurotransmitter
20
Q
what is the membrane potential?
A
- -70 mV
- the voltage difference between intracellular and extracellular
21
Q
Why is there a membrane potential ?
A
- Due to high concentration of K+ ions and low conc of Na + and CL- ions in the cell
- In the extracellular space there is a low conc of K+ and high concn of NA+ and CL-
22
Q
How is the membrane potential maintained?
A
- Lipid membrane- prevents passage of water-soluble ions
- Selective permeable ion channels
- a metabolically active Na/K+ exhange pump
-
Donnan equilibrium
- irregular distribution of permant ions across an impermenant membrane when a large impermeable organic ion is present on one side
- Cl- ions diffuse out of cell thru the lipid membrane
- the Na/K+ xchange pump maintains a high concentration of K+ in the cell and high Na extracellularly
23
Q
What is the threshold stimulus?
A
- is the minimum stimulus intensity needed to produce an action potential
- A subthreshold stimulus will not produce a stimulus
- however summation of a subthreshold stimulus maybe enough to stimulate a response
24
Q
Describe an action potential?
A
- occurs when a neuron is stimulated
- -> opening of Na+ channels ( dependent on O2/ ATP)
- IN rush of Na+ into cell
- ->Depolaristion of membrane resting potential from -70 mV due to ionic conductance
- polarity across cell = positive
- This triggers the opening of more Na+ channels
- The channels stay open for 1ms before closing
- For a few milliseconds after closing they cannot reopen ( refractory period)- limiting the no of stimuli to which a nerve can respond
- Repolarisation then occurs= passage of K+ ions out of cell thru K= channels
- Electrical potential falls to below the orginal -70mV resting potential due to the delay in closure of the K+ channel & time taken for Na+ channels to convert from an inactive to a resting state.
25
Q
How is the action potential propagated?
How does this occur in myelinated axons?
A
- Local change in potential of an area of the nerve fibre membrane cf with an adjacent area at resting potential=> a current
- At the nodes of ravier the action potential jumps - ‘Saltatory conduction’
- this increases the efficiency of the cell=> fast conduction with minimal metabolic activity
26
Q
How do neurons communicate?
A
- Via synapses
- chemical or electrical
- in humans chemical predominate
- Synapse pccur between terminal branch of one axon and the cell body dendrites of another axon
- an action potential causes the release of neurotransmitters from synaptic vesicles
- the NT diffuses across the synaptic cleft to the postsynaptic membrane which it either excites ( excitatory postsynaptic membrane) or inhibits ( inhibitory postsynaptic potentials)
27
Q
Name some examples of neurotransmitters?
A
- Acetylcholine ( preganglionic synpases, parasympathetic postganglionic synapses
- adrenaline ( sympathetic post ganglionic synapses)
- noradrenaline ( sympathetic postganglionic synapses
- serotonin
- histamine
28
Q
When do the spinal nerve divide close to the spinal cord what do they form?
A
- Sensory dorsal root
- motor ventral root
29
Q
What can superifical sensory receptors be divided into?
A
- Mechanoreceptors
- Thermoreceptors
- Nociceptors
30
Q
What does a merkel cell respond to?
A
- Sustained pressure
- inervated by fast myelinated Aß
- Slowly adapting receptor status
31
Q
What does a meissner corpsule respond to?
A
- Changing stimuli
- innervated by fast myelinated Aß
- rapidly adapting receptor
32
Q
What does a ruffini’s corpusle respond to?
A
- innervated by fast myelinated Aß
- Slowly adapting receptor status
33
Q
What does a pacinian corspule inervated by
A
- fast myelinated Aß
- Rapidly adapting
34
Q
what is a hair follicle innervated by?
A
- Fast myelinated Aß and Aσ
35
Q
What are the different types of thermoreceptors?
A
- Cooling receptors
- warming receptors
- detect changes in environmental temperature
- Innervated by Myelinated fast Aß and unmyelinated slow C fibres
36
Q
What do nociceptors respond to ?
A
- Noxious stimuli
- consist of
- mechanical
- thermal
- mechanothermal
- polymodal receptors
- Myelinated fast Aß and unmyelinated slow C fibres innervate these receptors
37
Q
What do deep sensatio from muscles/ligaments /tendons adn joints occur via what?
A
- free nerve endings and receptors such as
-
Muscle spindles
- intrafusal nuclear bag fibres
- nuclear chain fibres
- innevated by myelinated afferent sensory A alpha fibres and efferent Ay fibres
-
Golgi tendon organs
- near neuromuscular junctions
- small bundles of tendon fibres enclosed in a capsule of concentric cytoplasmic sheets
- capsule peirced by A alpha nerve fibres that divide and wrap around tendon faciculi
- activated by passive stretch
- important in prioprioception
-
Paciniform receptors
- smaller than pacinain corpsules
- rapidly adapting low threshold mechanoreceptors found in joint capsule
- supplied by myelinated A alpha afferent fibres
38
Q
In the motor system transmission of impulses to muscles is via what?
A
- Motor end plate
- consists of neural endong and a muscle sole plate
- 2 type of neural ending
- extrafusal A alpha ( en plaque)
- intrafusal A gamma ( plate ) ending
- Muscle action potential is initated by acetylcholine release at nerve endings
39
Q
What can the autonomic nervous system be divided into?
A
- Sympathetic
- parasympathetic
- Central and Peripheral components
40
Q
What does the sympathetic NS control?
A
- Sweating
- vasoconstriction
- erector pilae
- spincteric contraction
- bronchial dilation
- papillary dilation
- reduction of gut motility
- cardiac stimulation
41
Q
What does the sympathetic ns consist of?
A
- preganglionic myelinated efferent axons from grey matter of the T1 to L2 of spinal cord
- the axons emerge from the spinal cord thru ventral spinal roots before passing via the white comminicantes to synapse in the paravertebral or axial ganglia
- the ganglia function as relay stations, where axons traverse or synapse with other axons, allowing amplication and dissemination of signals
42
Q
How do the post ganglionic neurons reach their target?
A
- Pass directly to viscera
- pass directly to adjacent blood vessels
- pass via grey rami commiucantes, the axons return to their orginating spinal nerve and on to blood vessels, erector pilae and sweat glands
- pass along sympathetic trunk to another level
43
Q
What do the parasympathetic nervous system consist of?
A
-
Efferent myelinated preganglionic fibres from the nuclei in the brain
- via the oculomotor, facial , glossopharyngeal, vagus and accessory nerves and 2-4th spinal nerves
44
Q
What do the peripheral ganglia of the parasympathetic system include?
A
- cranial ganglia
- ciliary
- pterygopalatine
- submandicular
- otic
- which are efferent
- afferent and postganglionic parasympathetic fibres also pass thru these ganglia but don’t synapse within them
45
Q
What is the cause of nerve injury?
A
- Physical - trauma, injection, thermal,
- Inflammation
- infection
- ischaemia
- pharmacological
- tumour
- systemic disease
- iatrophic
46
Q
What is the mechanism for nerve injury?
A
- open/closed injuries
- acute/chronic injuries
- single/continuing/repeated injuries
- whole/part of a nerve
- depth of lesion
- nerve state
47
Q
Name one classification of nerve injury?
A
- Seddon 1943
- Neurapraxia
- Axonotmesis
- Neuronotmesis
48
Q
What is neurapraxia?
A
- transient concussion/crushing of the nerve
- no wallerian degeneration
- local conduction block to flow of nerve impulses
- nerve and axons in continutity
- on histology segemental demyelination
- favourable outcome if source of injury removed
49
Q
What is axonotmesis?
A
- A degenerative lesion- manifests as a progressive loss of all peripheral funciton
- axon disrupted the endoneurium/perineurium and basal lamina intact
50
Q
What is neuronotmesis?
A
- Loss of continiuity of all elements of the nerve
- poor recovery if any
- only repair of the nerve gives any useful chance of recovery
51
Q
Can you describe any other classificaiton system?
A
- Birch and Bonney 1998
-
Transient conduction block ( non degenerative)
- neurapraxia
-
Prolonged conduction block ( non degenerative)
- neurapraxia
-
Degenerative favourable prognosis
- axonometesis
- axonal distruption; intact endo/perineurieum and basal lamina
-
Degenerative ( intemediate)
- axonomesis
- axonal disruption; basal lamina adn endoneurium damaged
-
degenerative unfavourable prognosis
- axonomesis
- axonal disruption, endoneurium and perineurium damaged, epi intact
- axonomesis
-
Degenerative unfavourable prognosis
- neuronotmesis
- loss of continuity of nerve
- neuronotmesis
52
Q
What is wallerian degeneration?
A
- distal degeneration of the nerve axon occured with later regeneration of the neural tissue from the proximal stump
53
Q
What happens when a neve is sectioned?
A
- the axon atrophies proximally
- cell body dendrites retract and the axon distal to the site of injury degenerates
- cell body role changes from neurotransmission to production of compoents for nerve regeneration
- cell nucleus migrates to the periphery of the cell and chromatolysis occurs
- the cell vol increases and production of RNA and regeneration enzymes increases
- distal to the site of injury the myelin sheath degenerates, a haematoma forms and the macrophages are stimulated to remove the axonal debris
- Schwann cells start to proliferate and migrate forming columns ( bands of Bunger)
- the mitotic activity of the Schwann cell increases, and the cell starts to produce growth factors as it phenotypically changes and becomes non myelinating
- axon proximal to site of injury=> mutliple axon sprouts with a growth cone situated at tip of each sprout
- Filopodia in the growth cone use contact guidance for fibronectin and laminin in the schwann cell basement lamina to facilitate regeneration at a rate of 1mm/day
54
Q
How can regeneration of a nerve be followed ?
A
- By advancing Tinel’s sign
55
Q
What factors determine the prognosis of the nerve injury?
A
-
Violence of injury
- high energy- worse prognosis
-
Delay between injury and repair
- due to time-dependent degeneration of the target organs
-
age
- better prognosis with younger patients
-
Gap between nerves
- larger the gap worse the prognosis
-
Level of injury
- repair better prognosis at distal level ( PIN ) cf proximal site ( radial nerve in axilla)
-
Condition of nerve ends:
- a tidy knife end better than untody crush
-
Assoc with arterial/bony injury
- nerve inj assoc w bone have worse prognosis
-
type of nerve
- those that innervate one/ 2 muscles better than those with mixed cutaneous and muscle innervation
56
Q
What are the different type of neuropathic pain?
A
-
Post-traumatic neuralgia
- pain after nerve injury with no sympathetic involvement
- pain expressed in territory of nerve
- tx is to repair the nerve
-
Neurostenalgia
- pain caused by perisistent neve compression/distortion/ischaemia
- pain usually confined to territory of the nerve
- tx of cause -> gd prognosis
-
Causalgia/chronic regional pain syndrome- type 2
- burning pain with allodynia, hyperpathia , distribance of skin colour, altered temp adn sweating.
- often seen with partial division of nerve
- pain intense extends beyond territory of damaged nerve
- sympathetic involvement is characteristic
-
Central pain
- caused by root avulsions
- constant crushing pain or burning pain felt within the anaesthetic part and a sharp shooting pain within the dermatone of the affected nerve
57
Q
What is parathesia?
A
- spontaneous abnormal sensation
58
Q
What is dysaethesia?
A
- unpleasant spontaneous normal sensation
59
Q
What is allodynia?
A
- pain from stimulation that does not normally cause pain
60
Q
what is hyperalgesia?
A
- Increased response to a stimulus that is normally painful
61
Q
What is hypersensitivity?
A
- Over reaction sensitivity of regeneration
62
Q
What is hyperpathia?
A
- deep seated , poorly localised fiery pain radiating throughout the limb that is induced by palpation of the muscles
63
Q
How can the diagnosis of nerve injury be supplemented?
A
- Nerve conduction studies (NCS)
- Elecromyography (EMG)
64
Q
How does the NCS work?
A
- utilises an electrode to stimulate large, fast myelinated conducting fibres and a recording electrode to measure the motor or sensory action potentials
- measurements of latency. ampitude and conduction velocity can then be made
65
Q
What is latency?
A
- **Measures the time between onset of the stimulus and the response **
- milliseconds (ms)
66
Q
What is the amplitude?
A
- Measure the size of the response in microvolts (µV) or millivolts (mV)
67
Q
What is velocity?
A
- Distance between the stimulating and recording electrodes divided by the time, measured in metres per second (m/s)
68
Q
What does the amplitude indicate?
A
- The Quantity of the axons contributing to the action potential
69
Q
What does the latency and velocity indicate ?
A
- The Quality of the action potential
70
Q
What is the motor unit action potential?
A
- The supramaximal stimulation of the motor nerve
- hence the amplitude mV of the MUAP = the number of functioning motor units
- the latency (ms) of the MUAP= the time taken from motor nerve stimulation to muscle response and includes synaptic transmission and muscle depolarisation
71
Q
How is the conduction velocity calculated?
A
- by stimulating the motor unit at 2 different sites
- the distance between the distal stimulation site and the recording electrode is substracted from the distance beween proximal stimulation site and the recording electrode
- the distance is then divided by the distal latency substracted from the proximal latency to give the velocity of the motor nerve
72
Q
How are sensory nerve action potentials measured?
A
- stimulating and recording at separate sites along the same sensory nerve
- the recording electrode is the more proximal of the 2 with the SNAP recorded for antidromic ( distal to proximal) conduction
- ampitude and latency can be measure directly
73
Q
How would you measure motor studies in carpal tunnel syndrome?
A
- A stimulating electrode placed over median nerve proximal to carpal tunnel
- a recording electrode placed over a muscle in the hand suplied by median nerve APB
- an indifference electrode placed a few cm away
- a ground electrode place over an inactive muscle
74
Q
What is the normal velocity of upper limb nerves?
A
- 50-70 m/s ( cf 40-50m/s in lower limb)
75
Q
To measure the proximal nerve what is used?
A
- Late responses such as the F response ( wave) or H reflex are measured
- these are low amplitude responses with long latencies including conduction in the proximal and distal sections of a nerve
76
Q
What does the F response measure?
A
- The antidromic conduction of an impulse from a peripheral nerve to the anterior horn cells along with reflex orthodromic conduction down the motor nerves to the muscles
- It does not cross any synapses so can be thought of as an echo.
- useful in dectection early proximal lesions
- a prolonged F response latency with normal peripheral motor nerve conduction would imply slowing over proximal motor fibres at the plexus / root level
- muscles are innervated by mutliple roots so an abnormal F response is present only with mutiple severe root compromise ( guillane barre) extensive proximal neuropathies ( plexopathies)
77
Q
What is the H reflex?
A
- A electophysiological equivalent of a deep tendon reflex
- elicited by a submaximal stimulation of A alpha afferent fibres from muscle stretch receptors that enter the dorsal horn and synapse with alpha motor neurons, resulting in a motor response on the completion of the monsynaptic reflex arc
78
Q
What is seen on SNAP and EMG with conduction block neurapraxia?
A
SNAP
- Reduced amplitude proximally
- normal distally
- conduction velocity- conduction block at site, preserved below
EMG
- No sparse fibrillations
- MUAP firing at rapid rates
- reduced interference pattern
79
Q
What is seen on SNAP and EMG with degenerative lesion. favourable prognosis axonomesis?
A
SNAP
- absent or reduced
- conduction velocity absent or normal if present
EMG
- fibrillations
- reduced interference pattern
- increased firing rate of MUAP
80
Q
What is seen on SNAP and EMG with degenerative lesion, unfavourable prognosis neuronomesis?
A
- SNAP
- Absent
- Conduction velocity
- absent
- EMG
- fibrillations
- no voluntary MUAP
81
Q
What is the normal amplitude for emg testing of motor median and ulna nerves?
A
- >5 mV
82
Q
What is the normal amplitude for snap testing of sensory median and ulna nerves?
A
- >5µV
83
Q
What is the normal latency for motor median and ulna nerves?
A
- median <4 ms
- ulna <3ms
