Nerves Flashcards
(83 cards)
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
How is the action potential propagated?
How does this occur in myelinated axons?
* 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
How do neurons communicate?
* 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
Name some examples of neurotransmitters?
* **Acetylcholine** ( preganglionic synpases, parasympathetic postganglionic synapses
* **adrenaline** ( sympathetic post ganglionic synapses)
* noradrenaline ( sympathetic postganglionic synapses
* **serotonin**
* **histamine**
28
When do the spinal nerve divide close to the spinal cord what do they form?
* **Sensory dorsal root**
* **motor ventral root**
29
What can superifical sensory receptors be divided into?
* **Mechanoreceptors**
* **Thermoreceptors**
* **Nociceptors**
30
What does a merkel cell respond to?
* _Sustained pressure_
* inervated by **fast myelinated Aß**
* Slowly adapting receptor status
31
What does a meissner corpsule respond to?
* **Changing stimuli**
* innervated by fast myelinated Aß
* rapidly adapting receptor
32
What does a ruffini's corpusle respond to?
* innervated by **fast myelinated Aß**
* **Slowly adapting** receptor status
33
What does a pacinian corspule inervated by
* fast myelinated Aß
* Rapidly adapting
34
what is a hair follicle innervated by?
* Fast myelinated Aß and Aσ
35
What are the different types of thermoreceptors?
* **Cooling receptors**
* **warming receptors**
* detect changes in environmental temperature
* Innervated by **Myelinated fast Aß** and **unmyelinated slow C fibres**
36
What do nociceptors respond to ?
* **Noxious stimuli**
* consist of
* **mechanical**
* **thermal**
* **mechanothermal**
* **polymodal receptors**
* **Myelinated fast Aß and unmyelinated slow C fibres** innervate these receptors
37
What do deep sensatio from muscles/ligaments /tendons adn joints occur via what?
* free nerve endings and receptors such as
* **Muscle spindles**
* intrafusal nuclear bag fibres
* nuclear chain fibres
* innevated by m**yelinated 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
In the motor system transmission of impulses to muscles is via what?
* **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
What can the autonomic nervous system be divided into?
* **Sympathetic**
* **parasympathetic**
* Central and Peripheral components
40
What does the sympathetic NS control?
* Sweating
* vasoconstriction
* erector pilae
* spincteric contraction
* bronchial dilation
* papillary dilation
* reduction of gut motility
* cardiac stimulation
41
What does the sympathetic ns consist of?
* **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
How do the post ganglionic neurons reach their target?
* 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
What do the parasympathetic nervous system consist of?
* **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
What do the peripheral ganglia of the parasympathetic system include?
* 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
What is the cause of nerve injury?
* Physical - trauma, injection, thermal,
* Inflammation
* infection
* ischaemia
* pharmacological
* tumour
* systemic disease
* iatrophic
46
What is the mechanism for nerve injury?
* open/closed injuries
* acute/chronic injuries
* single/continuing/repeated injuries
* whole/part of a nerve
* depth of lesion
* nerve state
47
Name one classification of nerve injury?
* **Seddon 1943**
* **Neurapraxia**
* **Axonotmesis**
* **Neuronotmesis**
48
What is neurapraxia?
* 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
What is axonotmesis?
* A degenerative lesion- manifests as a progressive loss of all peripheral funciton
* axon disrupted the endoneurium/perineurium and basal lamina intact
50
What is neuronotmesis?
* 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
Can you describe any other classificaiton system?
* **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
* **Degenerative unfavourable prognosis**
* neuronotmesis
* loss of continuity of nerve
52
What is wallerian degeneration?
* distal degeneration of the nerve axon occured with later regeneration of the neural tissue from the proximal stump
53
What happens when a neve is sectioned?
* 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
How can regeneration of a nerve be followed ?
* By advancing Tinel's sign
55
What factors determine the prognosis of the nerve injury?
* **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
What are the different type of neuropathic pain?
* **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
What is parathesia?
* spontaneous abnormal sensation
58
What is dysaethesia?
* unpleasant spontaneous normal sensation
59
What is allodynia?
* **pain from stimulation that does not normally cause pain**
60
what is hyperalgesia?
* **Increased response to a stimulus that is normally painful**
61
What is hypersensitivity?
* **Over reaction sensitivity of regeneration**
62
What is hyperpathia?
* **deep seated , poorly localised fiery pain radiating throughout the limb that is induced by palpation of the muscles**
63
How can the diagnosis of nerve injury be supplemented?
* **Nerve conduction studies (NCS)**
* **Elecromyography (EMG)**
64
How does the NCS work?
* 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
What is latency?
* **Measures the time between onset of the stimulus and the response **
* milliseconds (ms)
66
What is the amplitude?
* **Measure the size of the response in microvolts** (µV) or **millivolts** (mV)
67
What is velocity?
* **Distance between the stimulating and recording electrodes divided by the time, measured in metres per second (m/s)**
68
What does the amplitude indicate?
* The **Quantity** of the axons contributing to the action potential
69
What does the latency and velocity indicate ?
* The Quality of the action potential
70
What is the motor unit action potential?
* 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
How is the conduction velocity calculated?
* 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
How are sensory nerve action potentials measured?
* 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
How would you measure motor studies in carpal tunnel syndrome?
* 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 p**laced a few cm away
* a **ground electrode** place over an inactive muscle
74
What is the normal velocity of upper limb nerves?
* 50-70 m/s ( cf 40-50m/s in lower limb)
75
To measure the proximal nerve what is used?
* 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
What does the F response measure?
* 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
What is the H reflex?
* 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
What is seen on SNAP and EMG with conduction block neurapraxia?
_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
What is seen on SNAP and EMG with degenerative lesion. favourable prognosis axonomesis?
SNAP
* absent or reduced
* conduction velocity absent or normal if present
EMG
* **fibrillations**
* **reduced interference pattern**
* **increased firing rate o**f MUAP
80
What is seen on SNAP and EMG with degenerative lesion, unfavourable prognosis neuronomesis?
* SNAP
* **Absent**
* Conduction velocity
* **absent**
* EMG
* **fibrillations**
* **no voluntary MUAP**
81
What is the normal amplitude for emg testing of motor median and ulna nerves?
* \>5 mV
82
What is the normal amplitude for snap testing of sensory median and ulna nerves?
* \>5µV
83
What is the normal latency for motor median and ulna nerves?
* median \<4 ms
* ulna \<3ms
