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1. The Nerve Flashcards

1
Q

The nervous system (central and peripheral) is derived from

A

ectoderm

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2
Q

Vertebral column is derived

A

mesodermal

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3
Q

During their development, the limbs rotate in what direction

A

opposite directions;

upper limbs rotate laterally.
- extensors posterolaterally

lower limbs rotate medially
- extensors anteromedially)

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4
Q

What is preaxial

A

anterior to the bone or fascial plane or axis of the limb

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5
Q

postaxial

A

structures posterior to bone or fascial plane or axis of the limb
postaxial

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6
Q

How many sheaths for tibial and peroneal nerve

A

In the lower limb,
tibial nerve (preaxial) and common peroneal nerve
(postaxial) lie enclosed within a single sheath.

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7
Q

a typical neuron possesses a

how many axons / dendrites

A

cell body (often called the soma),
dendrites
and an axon

Each neuron has only one axon,
although it may have many dendrites

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8
Q

Neurons may be classified according to

A 
polarity
functionality
direction
myelination
characteristics of peripheral nerve fibres

neurotransmitters produced

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9
Q

Nerve polarity and examples of each

A

unipolar (primary sensory neurons),
bipolar (bipolar cell of the retina)
or multipolar (cortical neurons, motor neurons,
interneurons)

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10
Q

neurotransmitters produced by nerves

A

cholinergic, adrenergic, glutamatergic,

GABAergic, dopaminergic, serotonergic and so forth.

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11
Q

Myelin

A

Myelin is a dielectric (electrically insulating) material that forms a layer,
the myelin sheath

usually around only the axon of a neuron.

It is essential for the proper functioning of the nervous system

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12
Q

dielectric

A

electrically insulating

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13
Q

Schwann cells

A

(a type of glial cell)

supply the myelin
for peripheral neurons,

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14
Q

oligodendrocytes

A

myelinate the axons

of the

central nervous system.

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15
Q

A and B fibres possess

layers of

Also have

A

several layers of myelin.

They have nodes of Ranvier
resulting in a continuous
but non-homogenous
saltatory conduction.

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16
Q

C fibres

Myelin?

A

C fibres are the
only unmyelinated fibres
(Schwann cells do not form myelin)

Their impulse conduction is uniform and homogenous

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17
Q

endoneurium

A

Within a nerve,
each axon is surrounded by a
layer of connective tissue

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18
Q

fascicles

A

axons are bundled together

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19
Q

perineurium

A

fascicle wrapped in a layer of connective tissue

blood–nerve barrier and acts as a
diffusion barrier to local anaesthetics.

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20
Q

epineurium

A

entire nerve is wrapped in a layer of connective tissue

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21
Q

Aa
fxn

diameter um

conduction vel

myelin

sens to LA

A

Motor

12-20

70-120 ms

+++

++

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22
Q

Ab
fxn

diameter um

conduction vel

myelin

sens to LA

A

Touch / pressure

5-12

30-70

+++

++

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23
Q

Ay
fxn

diameter um

conduction vel

myelin

sens to LA

A

Proprioception / muscle tone

1-4

15-30

++

+++

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24
Q

Ad

fxn

diameter um

conduction vel

myelin

sens to LA

A

pain / temp

1-4

12-30

++

+++

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25
B fxn diameter um conduction vel myelin sens to LA
Preganglion autonomic 1-3 3-15 + ++
26
C fxn diameter um conduction vel myelin sens to LA
post ganglionic autonom/ pain / temp / mechanorec .5-1 0.5-2 -- - + least
27
K ion concentration intrcell vs excell
x10 intracell
28
Na ion excell vs intracell
x 10 excell
29
How is diff maintained RMP is
Na/K atpase resting nerve cell selective permeabilty to K+ -> net efflux of small K+ = RMP -60 to -70mV
30
Action potential
Propagated impulse Rise RMP to threshold potential -55mV
31
Depolarising phase how occur
Rise in NA perm = influx of Na RMP less negative Then Repolarisation phase
32
Repolarisation phase
Slowing of Na influx opening voltage depend K channel Large outward K rapidly restoring to RMP (or beyond - Hyperpolarisation Na/K atpase restores gradient
33
refractory period
absolute refractory period - firing till 1/3 not stimulated relative refractory period - 1/3 on to afterdepol supranormal stimulus - cause excitation
34
Subthreshold stimulus
No AP follows all or none
35
Margin of safety block
The current flowing through the nerve is 5–10 times that needed to depolarise it; this is called ‘the margin of safety’ for impulse conduction. Because of this, 80% of Na+ channels must be blocked before conduction failure occurs
36
Decremental impulse conduction
Disease / drug reduce membrane excitability - Slower rate depol / slower conduction velocity When exceeds margin of safety = conduction failure Underlies local anaes in RA
37
How many nodes should be blocked for failure of conduction
3 successive nodes ranvier min
38
Sensitivity of nerve fibres to LA
depends on fibre type and size | smaller beore larger exception is B
39
Sequence of blockade
``` B Ad = C Ay Ab Aa ``` sympatheitc before sensory before motor
40
Sequence of block reversal
``` Aa Ab Ay Ad=C B ```
41
Na channel how many subunits How many domains in the subunit
The Na+ channel is made up of two types of subunit: α (one) and β (one or two). The α subunit has four domains, each having six helical membrane-spanning segments.
42
Na channel alpha subunit contains
The α subunit contains a voltage sensor, an ion selectivity filter, gating structures and P segment, which forms the pore.
43
How many isoform of Na channel
9 7 in nerves Nav 1.4 skeletal Na 1.5 cardiac
44
Where are the Na clustered
Around nodes of ranvier | essential high speed conduction
45
What happens in MS
involves only central nervous system (brain and spinal cord) and not the PNS. ``` It is associated with demyelination in brain and spinal cord. ``` the loss of clustering underlies the electrophysiological consequences (decreased conduction velocity) and resultant manifestations.
46
The Na+ channel exists in three states
resting Open Inactivated
47
Na channel 3 states transition
Resting state -> open when stimulated = Na influx Triggers AP Closed by going inactivated
48
What does local have higher affinity for
Inactivated over resting = More Na channel in inacivated state Increase in refractory period limits frequency firing
49
What happens @ Higher frequency of impulse
Greater channels open as well as inactivated Chance LA binding higher = phase or use dependent block
50
Phase (use) dependent block
@ higher frequencies of impulse firing, a greater number of channels are in open as well as inactivated state; hence, the chance for LA binding is greater.
51
Why are hydrophobic LA > toxic than hyphilic
rate dependent block of Cardiac Na channel
52
What crosses Axon
Unionised base of LA Ionises intracellularly Cationic form acts within cell inactivate Na channel
53
Cations
are positively-charged ions
54
Anions are
negatively-charged
55
Is blockade proportional to power functional loss
Impulse conduction is vital for functioning of a peripheral nerve, its blockade is not proportional to functional loss produced
56
define minimum blocking concentration of LA
The lowest concentration of LA that blocks all impulse conduction within a nerve within a reasonable period of time
57
Is 50% enough of a blockade of fibres
50% fibres may result in limb movement and, more important, pain, which would be unacceptable clinically
58
Differential block i
observation of motor preservation, despite complete sensory loss. This may be clinically employed in ‘walking epidurals’.
59
pharmacokinetics of LA in nerve block includes the following | phases
1 delivery, 2 permeation of nerve sheath, 3 induction 4 recovery
60
How does anaesthesia progress in a block What direction why
proximal to distal direction ``` outer fibres (mantle bundle) innervate the proximal structures ``` while the inner fibres (core bundle) innervate the distal structures. LA diffuses down the mantle to the core gradient,
61
How does recovery of a block occur why
distal to proximal direction vascularity of core fibres is higher, the recovery occurs in

EDRA (26 decks)

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