2.  Excitability
 Conductivity
 Unfatigability
 Refractive period
 All or none response
 Summation
 Accommodation

3.  Excitability:
› nerve fibres are highly excitable tissue
› respond to various stimuli
› Capable of generating electrical impulse
 Conductivity:
› action potential is generated in the nerve fibre,
which is propagated along its entire length to the
axon terminal.

4.  Refractive period:
 during action potential the excitability of a
nerve become reduced
 i.e a new impulse cannot be generated
during a AP
 Types:
› a. Absolute refractory period (ARP)
› b. Relative refractory period( RRP)
 Note :- once initiated moving impulse wont
depolarize the area behind it

7.  Unfatiguability :
› Nerve fibres can not be fatigued even when they
are stimulated continuously.
 All or none response:
› Either all of the action potential is seen or none
at all
› If a stimulus of threshold strength is applied AP
will be generated
› Further increase in strength of stimulus or
duration has no effect on amplitude of AP
› But can affect frequency

8.  Summation:
› Application of a sub threshold stimulus does not
evoke an action potential. However if sub
threshold stimuli are applied in rapid succession
they are added and they produce an action
potential.
 Accommodation:
› Application of continuous stimuli may
decrease the excitability of nerve fibre.

9. 
Fiber
Type
Function
Fiber
Diameter
(μm)
Conduction
Velocity
(m/s)
Aα Proprioception; somatic
motor
12-20 70-120
Aβ Touch, pressure 5-12 30-70
Aγ Motor to muscle
spindles
3-6 15-30
Aδ Pain, cold, touch 2-5 12-30

10. Fiber Type
Function
Fiber
Diameter
(μm)
Conduction
Velocity
(m/s)
B Preganglionic
autonomic
<3 3-15
Dorsal root
(C)
Pain, temperature,
some Mechano-
reception, reflex
responses
0.4-1.2 0.5-2
Sympathetic Postganglionic 0.3-1.3 0.7-2.3

11.  Pressure – A> B > C
 Hypoxia – B > A > C
 Local Anesthesia – C > B > A

12.  It’s a protective insulator covering of the axon
 Formed by schwann cells
 Double layer membrane of a single schwann cell
wraps itself several times around axon
 1 mm in length , 8 -10 micrometer in thickness
 Layers stick to each other due to protein p0
 Schwann cell nucleus lies in the outermost layer

15.  Orthodromic
 Antidromic
 Axoplasmic Transport
› Fast antegrade – 400mm/day (kinesin)
› Fast retrograde – 200mm/day (dynein)
› Slow antegrade

16.  Distal fragment degenerates fully
 Proximal frag. Until previous node of Ranvier
 Swollen myelin sheath – (appear as beads )
 Schwan cells does not die
 Debris taken by macrophages
 Soma swells and become round
 Extrusion of nuclei
 Disintegration of Nissle granules – Chromolysis
 Disappearance of golgi apparatus
 Completed by 3 – 4 weeks

20.  Soma tries to repair by synthesizing new
protein (axonal reaction)
 Chromatolysis reversible
 Axonal sprouts may form
 Axonal cone (growth 1-4 mm/day)
 Schwan cells myelinate new axon
 Nucleus occupy center , RER , GA reappears
 Denervation hypersensitivity seen in target
organ