Viva Neurophysiology

Question 1

What are the parts of brainstem?

Answer 1

• Midbrain
• Pons
• Medulla oblongata

Question 2

Classify the neurons

Answer 2

Neurons are classified by three different
methods:
• Depending upon number of poles:
– Unipolar neurons
– Bipolar neurons
– Multipolar neurons.
• Depending upon the function:
– Motor neurons
– Sensory neurons.
• Depending upon length of axon:
– Golgi type I neurons
– Golgi type II neurons

Question 3

Name the nerve fibers conducting the
impulse with maximum and minimum
velocity.

Answer 3

Type A alpha nerve fibers conduct the
impulse with maximum velocity (70 to 120
meters/second).
Type C fibers conduct the impulse with
minimum velocity (0.5 to 2 meters/second).

Question 4

What are the two types of potentials

noticed in nerve fibers?

Answer 4

• Action potential (nerve impulse) –
produced when the nerve is stimulated
with adequate strength of stimulus
(threshold or minimal stimulus). It is
propagated and nongraded.
• Electrotonic potential or local response –
is produced when the strength of
stimulus is not adequate (subthreshold
or subminimal stimulus). It is nonpropagated and graded.

Question 5

Differentiate between EPSP and AP

Answer 5

Question 6

What are the properties of generator

potential?

Answer 6

The properties of GP are:
• It is non-propagatory in nature
• It is monophasic
• It does not obey all or none law.

Question 7

What do you mean by spatial and

temporal summation?

Answer 7

• Simultaneous stimulation of two afferent
nerves by a stimulus of subthreshold
intensity can evoke action potential in
motor neuron. This property is known as
spatial summation.
• Whereas if subminimal stimuli are
repeated at short intervals in a single
nerve, reflex action can also be evoked
which is known as temporal summation

Question 8

What is the fractionation phenomenon?

Answer 8

Direct stimulation of motor nerve results in
more response than reflex response or in

other words the tension developed reflexly
is always a fraction of response that is
produced by direct motor nerve stimulation.
This is known as fractionation phenomenon.

Question 9

What is afterdischarge?

Answer 9

Continuation of discharge of impulses from
motor neuron even after withdrawal of
stimulation from sensory side is called
as afterdischarge.

Question 10

What do you mean by law of forward

conduction?

Answer 10

Synapse permits the conduction of impulse
from presynaptic to postsynaptic neuron
only, i.e. unidirectionally. This property is
known as law of forward conduction

Question 11

ame the receptors responsible for
following sensations—touch, pressure,
hot, cold and pain

Answer 11

• Touch—Markel’s disc or Meissner’s
corpuscle
• Pressure—Pacinian corpuscle
• Hot—Ruffini’s end organs
• Cold—Krause’s end bulb
• Pain—Free nerve endings.

Question 12

Name the properties of action

potential.

Answer 12

• Propagative
• Biphasic
• All or none law
• No summation
• Refractory period.

Question 13

What is saltatory conduction?

Answer 13

In a myelinated nerve fiber, the action
potential (nerve impulse) jumps from one
node of Ranvier to another node of Ranvier,
making the velocity of conduction faster.
This type of conduction in a myelinated
nerve fiber is called saltatory conduction.

Question 14

Explain the mechanism of saltatory

conduction briefly.

Answer 14

Myelin sheath is not permeable to ions. So
during the conduction of action potential,
the entry of sodium ions from extracellular
fluid into nerve fiber occurs only at the node
of Ranvier, where the myelin sheath is
absent. This causes depolarization only in
successive node and not in internode. So,
the action potential jumps from one node
to another. Hence, it is called saltatory
conduction (saltare = jumping).

Question 15

Why is the nerve fiber not fatigued

Answer 15

Nerve fiber is not fatigued because it can
conduct only one action potential at a time.
At that time it is completely refractory and
cannot conduct another action potential

Question 16

What are the changes, which take

place in nerve cell body during degeneration of nerve fiber?

Answer 16

• The Nissl granules disintegrate by
chromatolysis
• Golgi apparatus also disintegrates
• Cell body swells due to accumulation of
fluid and becomes round
• Neurofibrils disappear
• Nucleus is displaced towards the
periphery. In extreme conditions, nucleus
is extruded out of the cell.
Figure 17.2 illustrates the degeneration
and regeneration of a nerve fiber.

Question 17

What is Wallerian degeneration?

Answer 17

What is Wallerian degeneration?
Degenerative change in the distal cut end
of the nerve fiber is called Wallerian
degeneration.
Q.37 Explain the changes during Wallerian
degeneration briefly.
• Axis cylinder swells and breaks up into
small pieces. After few days, the debris is
seen in the space that was occupied by
the axis cylinder
• Myelin sheath disintegrates into fat
droplets
• Neurilemmal sheath is not affected but
the cells of Schwann multiply rapidly.
The macrophages invade from outside
and remove the debris of axis cylinder
and fat droplets. So neurilemmal tube
becomes empty and it is filled with
cytoplasm of Schwann cell.

Question 18

Degeneration of nerve fiber

Answer 18

What is retrograde degeneration?
The degenerative change that occurs at the
proximal cut end of the nerve fiber is called
retrograde degeneration.
Q.39 What is transneuronal degeneration?
If an afferent nerve fiber is cut, the
degeneration occurs in the neuron with
which the afferent nerve fiber synapses. This
is called transneuronal degeneration.

Question 19

Define and classify receptors

Answer 19

Define receptor.
Receptor is an afferent nerve terminal,
which receives the stimulus. It is defined as
the biological transducer that converts
various forms of energy, i.e. stimulus into
action potential in nerve fiber.
46.Classify receptors.
• Exteroceptors:
– Cutaneous receptors
– Chemoreceptors
• Interoceptors:
– Telereceptors.
– Visceroreceptors
– Proprioceptors.

Question 20

What are the cutaneous receptors or

mechanical receptors?

Answer 20

Receptors situated in the skin are called
cutaneous receptors. The different cutaneous
receptors (Fig. 17.4):
• Touch receptors – Meissner’s corpuscle
and Merkel’s disc
• Pressure receptors – Pacinian corpuscle
• Temperature or thermoreceptors –
Krause’s end organ for cold and Raffini’s
end organ for warm
• Pain receptors or nociceptors – free
(naked) nerve ending

Question 21

What are chemoreceptors, which

belong to the group of exteroceptors

Answer 21

Receptors giving response to chemical
stimuli are known as chemoreceptors. The
chemoreceptors, which belong to the group
of exteroceptors are taste receptors in taste
buds and olfactory receptors for smell in the
nose

Question 22

What are telereceptors?

Answer 22

The receptors, which give response to
stimuli arising away from the body are
called telereceptors. Telereceptors are:
• Hair cells of organ of Corti in the ear for
hearing
• Rods and cones of retina in the eye for
vision.