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EDRA > 1. The Nerve > Flashcards

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
Q

B

fxn

diameter um

conduction vel

myelin

sens to LA

A

Preganglion autonomic

1-3

3-15

+

++

26
Q

C
fxn

diameter um

conduction vel

myelin

sens to LA

A

post ganglionic autonom/
pain / temp / mechanorec

.5-1

0.5-2

–

-
+ least

27
Q

K ion concentration intrcell vs excell

A

x10 intracell

28
Q

Na ion excell vs intracell

A

x 10 excell

29
Q

How is diff maintained

RMP is

A

Na/K atpase

resting nerve cell
selective permeabilty to K+
->
net efflux of small K+

=

RMP -60 to -70mV

30
Q

Action potential

A

Propagated impulse

Rise RMP to threshold potential -55mV

31
Q

Depolarising phase

how occur

A

Rise in NA perm
= influx of Na
RMP less negative

Then
Repolarisation phase

32
Q

Repolarisation phase

A

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
Q

refractory period

A

absolute refractory period - firing till 1/3
not stimulated

relative refractory period - 1/3 on to afterdepol
supranormal stimulus - cause excitation

34
Q

Subthreshold stimulus

A

No AP

follows all or none

35
Q

Margin of safety block

A

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
Q

Decremental impulse conduction

A

Slower rate depol / slower conduction velocity

When exceeds margin of safety = conduction failure
Underlies local anaes in RA

37
Q

How many nodes should be blocked for failure of conduction

A

3 successive nodes ranvier min

38
Q

Sensitivity of nerve fibres to LA

A

depends on fibre type and size

smaller beore larger
exception is B

39
Q

Sequence of blockade

A 
B 
Ad = C
Ay
Ab
Aa

sympatheitc before sensory before motor

40
Q

Sequence of block reversal

A 
Aa
Ab
Ay
Ad=C
B
41
Q

Na channel

how many subunits

How many domains in the subunit

A

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
Q

Na channel alpha subunit contains

A

The α subunit contains a

voltage sensor,

an ion selectivity filter,

gating structures

and

P segment,
which forms the pore.

43
Q

How many isoform of Na channel

A

9

7 in nerves

Nav 1.4 skeletal

Na 1.5 cardiac

44
Q

Where are the Na clustered

A

Around nodes of ranvier

essential high speed conduction

45
Q

What happens in MS

A

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
Q

The Na+ channel exists in three states

A

resting

Open

Inactivated

47
Q

Na channel

3 states transition

A

Resting state
->
open when stimulated

= Na influx

Triggers AP

Closed by going inactivated

48
Q

What does local have higher affinity for

A

Inactivated over resting

= More Na channel in inacivated state

Increase in refractory period
limits frequency firing

49
Q

What happens @ Higher frequency of impulse

A

Greater channels open as well as inactivated

Chance LA binding higher

= phase or use dependent block

50
Q

Phase (use) dependent block

A

@ 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
Q

Why are hydrophobic LA > toxic than hyphilic

A

rate dependent block of Cardiac Na channel

52
Q

What crosses Axon

A

Unionised base of LA

Ionises intracellularly

Cationic form acts within cell inactivate Na channel

53
Q

Cations

A

are positively-charged ions

54
Q

Anions are

A

negatively-charged

55
Q

Is blockade proportional to power functional loss

A

Impulse conduction is vital for

functioning of a peripheral nerve,

its blockade is not proportional
to functional loss produced

56
Q

define minimum blocking concentration of LA

A

The lowest concentration of LA
that blocks all impulse conduction

within a nerve within a
reasonable period of time

57
Q

Is 50% enough of a blockade of fibres

A

50% fibres may result in limb
movement and, more important,

pain, which would be unacceptable
clinically

58
Q

Differential block i

A

observation of motor preservation,

despite complete sensory loss.

This may be clinically employed in
‘walking epidurals’.

59
Q

pharmacokinetics of LA in nerve block includes the following

phases

A

1 delivery,

2 permeation of nerve sheath,

3 induction

4 recovery

60
Q

How does anaesthesia progress in a block

What direction

why

A

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
Q

How does recovery of a block occur

why

A

distal to proximal direction

vascularity of core fibres is higher, the
recovery occurs in

EDRA (26 decks)

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