21 MAY 2021
CASE STUDY
NEURO PHYSIOLOGY (FUNDENMENTAL)
YEAR ONE (MD)
APRIL 2021 BATCH
IMS MSU
PREPARED BY DR SHAHIDA@OML
21 MAY 2021
CASE 1Sue a healthy 27-year-old pregnant woman was going to deliver her first child. The
obstetrician chooses the mode of delivery as a cesarean section, since Sue became
increasingly fearful of the pain associated with a vaginal delivery.
The doctor explained that she would use the anaesthetic drug which prevent the labour pain
by blocking action potentials in the sensory nerve fibres that serve the pelvis and perineum.
(Hint; the anesthetic drug block action potentials in nerve fibres by binding to specific ion
channels)
1. Define membrane potential and describe the genesis of resting membrane potential.
- Membrane Potential is solely caused by diffusion of electrically charged
ions. a potential gradient that forces ions to passively move in one direction: positive ions
are attracted by the 'negative' side of the membrane and negative ions by the 'positive'
one. Rmp -potential differences btween inside and outside membrane at rest. The
concentration of both ions are maintain at both sides
2. What are the disturbances of the membrane potential?
1) the concentration of ions on the inside and outside of the cell;
2) the permeability of the cell membrane to those ions (i.e., ion conductance) through
specific ion channels; and
3) by the activity of electrogenic pumps (e.g., Na+/K+-ATPase and Ca++transport pumps)
that maintain the ion concentrations across the membran
3. Define an action potential of nerve and stages with involvement of ions channels.
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Action potential is a brief reversal of membrane potential in which the
membrane potential changes from -70mV to +30mV
The action potential has three main stages: depolarization, repolarization, and
hyperpolarization.
Depolarization is caused when positively charged sodium ions rush into a
neuron with the opening of voltage-gated sodium channels.
Repolarization is caused by the closing of sodium ion channels and the
opening of potassium ion channels.
Hyperpolarization occurs due to an excess of open potassium channels and
potassium efflux from the cell.
4. Based on your knowledge of how nerve action potentials are propagated, how would
you expect the anaesthetic drug to alter the conduction of the action potential along a
nerve fiber?
PREPARED BY DR SHAHIDA@OML
21 MAY 2021
Lidocaine and other local anesthetic agents block voltage-gated Mr' channels in the nerve membrane. At low
concentrations, this blockade results in a slower rate of rise (dV/dt) of the upstroke of the action potential. At
higher concentrations, the upstroke is prevented altogether, and no action potentials can occur.
Action potentials are propagated (e.g., along sensory nerve axons) by the spread of local cur- rents from active depolarized
regions (i.e., regions that are firing action potentials) to adjacent inactive regions. These local depolarizing currents are
caused by the inward Na+ current of the upstroke of the action potential. When lidocaine blocks voltage-gated Na+ channels,
the inward Na+current of the upstroke of the action potential does not occur. Thus, propagation of the action potential, which
depends on this depolarizing inward current, is also prevented.
5. State the types of nerve fibres occur in the body. what is the type of nerve that carry
the pain sensation?
Sensory & motor ( A,B,C) ERLANGER GASSER
Sensory only (l, II, III, IV) NUMERICAL
A Delta (fast) & C(small n slow) dorsal root
6. Discuss the properties of nerve types.
Myelinated both sensory & motor
A(largest) (somatic nerves/sciatic& saphenous)
-4 subgp -Aalfa (AFF & EFF)
-A beta (AFF & EFF)
-A gamma EFF
-A delta EFF
B (preganglionic autonomic nerve )
Unmyelinated both sensory & motor
C (smallest) (visceral/cutaneous nerve) (postganglionic nerve)
-high threshold (30 folds of A gp)
PREPARED BY DR SHAHIDA@OML
21 MAY 2021
CASE 2A-32-year-old woman has experience of blurred vision for 3 years and her symptoms
becomes worsen and she also feeling weakness in her legs. Her family doctor referred
her to a neurologist, and the investigation on magnetic resonance imaging (MRI) of
the brain showed lesions typical of multiple sclerosis (a disease of the central nervous
system, in which axons lose their myelin sheath).
The neurologist explained her that her vision abnormalities and muscle weakness is
due to decreased nerve conduction velocity results from the destruction of myelinated
nerve fibres.
1. Discuss the myelinated and non- myelinated nerves with their differences.
myelin is considered an electrical insulator. Its purpose is to speed the
transmission of nerve impulse. Myelin sheath is lipoproteinaceous
substance that envelopes the vertebrates axons whose size is bigger than
.5mcm in diameter.
2. What is the effect of myelination on conduction velocity, and why?
Unmyelinated- slower
3. What is the effect of nerve diameter on conduction velocity, and why?
PREPARED BY DR SHAHIDA@OML
21 MAY 2021
4. Apply your knowledge to this patient that how the loss of the myelin sheath alters
nerve conduction velocity?
Multiple sclerosis (MS) is the most common demyelinating disease of the central
nervous system. In this disorder, your immune system attacks the myelin sheath or
the cells that produce and maintain it.
This causes inflammation and injury to the sheath and ultimately to the nerve fibers
that it surrounds. The process can result in multiple areas of scarring (sclerosis).
PREPARED BY DR SHAHIDA@OML