Physiological aspect of nerve and muscle for the Students of Physiotherapy, Medical and Paramedical students.

1. Dr. Shilpasree Saha (PT)
Lecturer, Sikkim Professional College of Physiotherapy,
Sikkim Professional University

2.  Neuron is the structural and functional unit of
the nervous system and consists of a nerve
cell body with all its process.

3. A neuron contains:
 A Nerve cell body (Soma, perikaryon)
 The processes
Dendrite
Axon

5.  Present in gray matter of brain and spinal
cord, in the nuclei of brain and ganglia of
CNS.
 It contains following structures:
1. Nucleus
2. Nissl bodies
3. Mitochondria
4. Golgi apparatus
5. Neurofibrils

7.  Central part of soma,
contains one
nucleolus.
 No centrosome,
neuron cannot
multiply.

8.  Also called “Tigroid
Substances”.
 Presents all over the
soma, except axon
hillock and extend
some extent in the
dendrites, but not
within the axon.
 Basophillic granules.

9.  Essentially small cavities, bounded by plasma
(cell) membrane.
 Containing ribosome (RNA & protein).
 RNA is of r-RNA variety.
 Synthesizes protein of neuron and these
protein travels down the axon by axonal flow.
 Chromatolysis : When the demand of protein
synthesis is great, there is excessive
overworking of the neuron or the neuron is
regenerated (following an injury), the nissl
granules disappear.

10.  Present in soma, as
well as in axon.
 Krebs cycle goes on,
ATP is produced.

11.  It is a network of
membranes that looks
much like a stack of fat
plates.This complex is
capable of producing
molecular products of
a neuron, such as
hormones

12.  Thread like structures traverse the whole
soma, also dendrites and axon.

13.  Two structures:
1. Axon
2. Dendrites

14.  Dendrite usually branches repeatedly .
 Axon may branch only at its terminal end-
terminal branch.

15.  An axon is a long projection of a
nerve cell, or neuron, that
conducts electrical
impulses away from the
neuron's cell body or soma.
 Axons are distinguished from
dendrites by several features,
including shape (dendrites often
taper while axons usually
maintain a constant radius),
length (dendrites are restricted
to a small region around the cell
body while axons can be much
longer), and function (dendrites
usually receive signals while
axons usually transmit them).

16.  Most nerve cells have several
dendrites.These increase the
receptive area of the neuron.
 Dendrites do not maintain a
constant diameter (unlike
axons) and transmit impulses
to the cell body.
 The regions of the dendrites
closest to the perikaryon are
usually larger, than those
farther away.
 Typically dendrites have
large numbers of thorny
spines, which are now known
to be areas of synaptic
contact.

18. AXON
 Only one axon is present in
neuron.
 Uniform thickened
&smooth surface.
 The branches of axon are
fewer.
 Contains neurofibrils , but
no nissl granules.
 Forms the efferent
component of impulse.
DENDRITES
 Usually multiple in a
neuron.
 Thickness diminishes as
they divided repeatedly.
 Dendrites branch
profusely.
 Contain both neurofibrils
and nissl granules.
 Forms the afferent
component of impulse.

19.  The function of a neuron is to communicate
information, which it does by two
methods. Electric signals process and conduct
information within a cell, while chemical
signals transmit information between cells.

20.  Sensory neurons have specialized receptors that
convert diverse types of stimuli from the
environment (e.g., light, touch, sound, odorants)
into electric signals. These electric signals are
then converted into chemical signals that are
passed on to other cells
called interneurons, which convert the
information back into electric signals. Ultimately
the information is transmitted to muscle-
stimulating motor neurons or to other neurons
that stimulate other types of cells, such as
glands.

21.  According to number of processes (neuritis) ,
they may be:
1. Unipolar: one process only, e.g-
mesencephalic nucleus
2. Pseudo-unipolar, e.g- sensory ganglia
3. Bipolar: one main dendrites and one axon,
e.g- spiral and vestibular ganglia
4. Multipolar: Several dendrites and one axon,
e.g- neurons in cerebrum and cerebellum

23. Structure of
medullated nerve fiber
•Axon emerges from the
region of axon hillock of
soma.
•Central core of the axon is
called axoplasm.
•Axoplasm is pasty (semi
fluid) in nature and
ensheathed by axolemma
membrane.

24.  Within the axoplasm following structures can
be seen:
1. Mitochondria
2. Axoplasmic vesicles
3. Neurotubules
 Nissl granules are absent.

25.  Axonal flow- axon
depends on soma for
protein synthesis .
 Myelin sheath: Outside
covering of axis cylinder
(axoplasm and
axolemma), composed
of lipid material
(sphingomyelin)
 Neurolemma: outer
most covering or,
outside cover of myelin
sheath.

26.  Node of Ranvier: Under
light microscope, axon
shows an apparently
constricted area at
regular interval – called
node of ranvier.
 No myelin sheath and
neurilemma.
 Internode: Portion
between two succesive
node, contains one
schwann cell (nucleus of
schwann)

27.  Propagation of action potential (wave of
excitation) is very fast in myelinated fiber but
slow in non-myelinated fiber.
 The nerves which for the sake of our survival ,
should conduct very fast are all myelinated.

28.  As there is no myelin sheath, the diameter of
nerves are small.
 No node of ranvier, neurilemma, axis cylinder.

29.  It is a contractile tissue which brings about
movements. Muscles are motors of the body
and nerves commanding them to contracts
are motor nerve.
 Skeletal muscle
 Cardiac muscle
 Smooth muscle

30.  Synonyms:
1. Striped muscles
2. Striated muscles
3. Somatic muscles
4.Voluntary muscles
 It has 2 ends- origin and insertion

32.  They are attached to the bone (skeleton) via
tendon or aponeurosis, hence called skeletal
muscle.
 Contractions lead to locomotion.
 They are supplied by somatic nerves.The
junction between somatic nerve and muscle ,
is called neuromuscular junction and the
neurotransmitter is acetyl choline.

33.  Contraction can be
voluntary and
involuntary.
 Cross straited.
 Multinucleated.
 No pace maker.

34.  Muscle belly consists of large numberof
muscle fasciculi.
 Each fasciculus consists of large number of
muscle fibers.
 Individual muscle cells are called fiber.

35.  Each Muscle Fiber is surrounded by a plasma
membrane called SARCOLEMMA.
 Individual MF is enveloped by layer of
connective tissue called ENDOMYSIUM ( which
lies outside Sarcolemma).
 Several MF are enveloped together by another
connective tissue called PERIMYSIUM.
 The entire Muscle is covered all round by
EPIMYSIUM.
 ( Sarcolemma—Endomysium– Perimysium–
Epimysium)

36.  Under light microscope,
skeletal muscle appear
to be cross straited.
 Every muscle fiber has
alternate dark and light
bands.
 Light does not pass
through dark band, so
appear dark. But can
pass through light
bands.

37.  Individual skeletal muscle fibers are
multinucleated.This is because, in the fetus-
a stage when muscle fibers develop,
individual muscle fibers develop by fusion of
several mononucleated cells-myoblast.
 But in post natal life, new muscle cells cannot
develop because muscle fibers or cell don’t
contain centrosomes, hence no daughter cell
can develop.

38.  Each myofibril is divided
into a number of
compartments by Z line.
 The portion between
two Z lines is called
Sarcomere.
 Within sarcomere two
types of thread like
structure can be seen –
filaments.
 Thin filament- made up
of actin protein.
 Thick filament- made up
of myosin protein.

39.  Myofibril contains I
band and A bands
alternately.
 In middle of A band,
comparatively lighter
zone, H zone is
present.

40.  Actin filament in periphery attached with Z
line, the other pole of actin forms boundary
of H zone.
 In the A band , the myosin and actin filament
overlap
 In the H zone, (develop in full relaxation state
of muscle) there is no actin.
 Because of presence of myosin and because
of overlapping , A bands are dark.
 H zone are lighter because of no overlapping.

41.  I bands have no myosin,
and no overlapping-
lighter.
 Myosin and actin can
become connected with
each other by structure
called cross bridges.
Looking like branches of
tree.
 The top of cross bridge has
site for attachment of ATP
and actin- myosin head .
 Each myosin is surrounded
by six actin filament.

42.  Sarcolemma- cell membrane of muscle fiber.
 Sarcolemmal membrane- cell membrane of
muscle fiber.

44.  Contractile protein-Thick + thin filament
Thin filament
 Contains 3 types of protein-
1. Actin
2. Tropomyosin
3. Troponin

45.  Actin in its monomer form (G actin) is
globular and has site for attachment with
myosin, troponin , various ion andATP
 In thin filament actin molecule remain in
state of polymer (F actin) and forms an
elongated thread like shape.
 2 F actin chains wind with each other to
constitute thin filament.

46.  Most of them made up of myosin (myosin-ii)
 Myosin-i is a member of non muscle
contractile protein
 Has head and tail.
 Myosin-ii has 2 head for attachment with
actin and ATP

47.  Muscle fibers are connected with connective
tissue.
 When muscle fiber shortens , the pull is
transmitted through the connective tissue to
the bone.
 The bone moves, and , thus , flexion-
extension occur.

48.  As the muscle begins to contract, thin
filament starts to move towards the H zone.
 H zone become obliterated.
 I band is narrowed.
 Sarcomere as a whole shortened.

49.  Mechanism originally proposed by A F
Huxley, and H E huxley in 1950.
 Sliding filament theory, or
 Cross bridge theory, or
 Ratchet theory.

50.  Myosin heads develop
contact with actin molecule-
cross bridge.
 Much cross bridges are
formed.
 The myosin head now rotate
(swivel)
Actin filament is pushed
towards H zone.
 Myosin heads are dettached
from the actin molecules and
reattach with another new
site in actin molecule-
swivels- the actin molecules
continues to move towards
H-zone.

51.  This attachment of myosin head-swievelling-
detachment- reattachment- i.e., the whole
cycle is called cross bridge.
 Repeated many times.
 All the myosin heads attach and swivel
simultaneously, therefore, their effects are
like the effect of “power stroke”.

52.  Isotonic- the muscle shortens during
contraction.
 Isometric- muscle contracts but does not
shorten.

54.  When the muscle is relaxed , tropomyosin is
placed in such a way that the sites of actin
which are meant for attachment with myosin
heads, are all covered.
 Myosin head don’t get a chance to bind with
actin.

55.  3 subunits of troponin- troponin- I, C, andT
 Troponin-I binds with actin.When Ca++ binds
with troponin C , the binding b/w troponin-
actin-tropomyosin become weak and
tropomyosin now shifts its position, so that
myosin head binds with actin.

56.  Neurons send messages electrochemically.
This means that chemicals cause an electrical
signal. Chemicals in the body are "electrically-
charged" -- when they have an electrical
charge, they are called ions.
 The important ions in the nervous system are
sodium and potassium (both have 1 positive
charge, +), calcium (has 2 positive charges,
++) and chloride (has a negative charge, -).

57.  There are also some negatively charged
protein molecules. It is also important to
remember that nerve cells are surrounded by
a membrane that allows some ions to pass
through and blocks the passage of other ions.
This type of membrane is called semi-
permeable.

58.  When a neuron is not sending a signal, it is "at
rest."When a neuron is at rest, the inside of the
neuron is negative relative to the outside.
 Although the concentrations of the different
ions attempt to balance out on both sides of the
membrane, they cannot because the cell
membrane allows only some ions to pass
through channels (ion channels).
 At rest, potassium ions (K+) can cross through
the membrane easily. Also at rest, chloride ions
(Cl-) and sodium ions (Na+) have a more difficult
time crossing.

59.  The negatively charged protein
molecules (A-) inside the neuron
cannot cross the membrane. In
addition to these selective ion
channels, there is a pump that
uses energy to move three
sodium ions out of the neuron
for every two potassium ions it
puts in.
 Finally, when all these forces
balance out, and the difference
in the voltage between the
inside and outside of the neuron
is measured, nerve has
the resting potential.

60.  The resting membrane
potential of a neuron is
about -70 mV
(mV=millivolt) - this
means that the inside of
the neuron is 70 mV less
than the outside. At
rest, there are relatively
more sodium ions
outside the neuron and
more potassium ions
inside that neuron.

61.  An action potential occurs when a neuron
sends information down an axon, away from
the cell body.
 Action potential is a rapid sequence of
changes in the voltage across a membrane.
The membrane voltage, or potential, is
determined at any time by the relative ratio
of ions, extracellular to intracellular, and the
permeability of each ion.

62.  In neurons, the rapid rise in
potential, depolarization, is
initiated by the opening of sodium
ion channels within the plasma
membrane.The subsequent
return to resting potential,
repolarization, is mediated by the
opening of potassium ion
channels.
 To reestablish the appropriate
balance of ions, an ATP-driven
pump (Na/K-ATPase) induces
movement of sodium ions out of
the cell and potassium ions into
the cell.

63.  The action potential is an
explosion of electrical activity
that is created by
a depolarizing current.This
means that some event (a
stimulus) causes the resting
potential to move toward 0
mV. When the depolarization
reaches about -55 mV a
neuron will fire an action
potential.This is
the threshold. If the neuron
does not reach this critical
threshold level, then no
action potential will fire.

65.  After death , the fresh supply of ATP become
impossible. Therefore the local supply of ATP
becomes impossible. Once the local store of
ATP molecules are exhausted, the
dettachment of actin from myosin cannot
take place (no return of Ca++ to cysterns),
results in permanent state of contraction
(stiffening ) of muscle.

66.  Fast muscles are pale looking.
 Greater speed of contraction.
 Intense activity
 Fatigue develops earlier.
 E.g.-extrinsic muscles of eye (causes
movement of eye ball )

67.  Slow muscle are red because of the presence
of myoglobins and capillary network.
 Less speed of contraction.
 Less intense activity.
 Fatigue develops slower.
 E.g.- postural muscles of body.

68.  The junctional region between the motor nerve
fiber and the corresponding skeletal muscle fiber
is called NMJ.
 Smooth muscle and cardiac muscle don’t have
NMJ.
 Junctional region is a region where 2 neurons or
1 neuron and its effector cell come exceedingly
close to each other without any protoplasmic
continuity and the impulse from the neuron is
transmitted to the effector cell through
neurotransmitter.

69.  AP develops in neuron
 Specific neurotransmitter is released at the
terminal end.
 NT crosses the synaptic cleft
 Binds with receptors present in post
junctional membrane
 End plate potential develops
 If the graded potential is of sufficient
magnitude , an AP develops in effector cells

73.  Motor nerve- nerve which transmits impulse
to muscle.
 Neuromuscular cleft- Space between the cell
membrane of the terminal bulb of the nerve
and sarcolemma, 50-100 nm wide.
 Within the terminal bulb of nerve fiber, large
number of vescicles present- synaptic
vescicles, contains Ach.

74.  Cell membrane of the bulbous terminal
(nerve) called pre junctional membrane.
 Cell membrane of muscle fibers called post
junctional membrane.
 Motor end plate-the part of sarcolemma
which forms the groove in which bulbous
expansion of neuron rests and on which Ach
receptors present.

75.  End plate potential- when Ach combines with
receptors the cause change in permiability of
the post junction membrane, as a result of
which the Na+ enter the post junctional
membrane is about -90 Mv. As the Na+ enter
the membrane, the potential drops , and
assume a value say, -60 Mv. This difference is
called EPP.

76.  Miniature EPP- even at rest, some vescicles
containing Ach burst occasionallygiving rise
to EPPs.

77.  Synthesis : Ach is a synthesized within the
neuron as follows –
 Acetyl CoA+ choline choline acetylase Acetyl choline
 Destruction: occurs in post synaptic
membrane.
 Acetyl choline acetyl choline esterase Acetyl CoA+
choline

78.  Contains one nucleus or uninucleated.
 Cardiac muscles are striated.
 Not under voluntary control.
 Supplied by ANS.
 Neurotransmmitter is either Ach or
Noradrinalin.
 Controlled by pacemaker.

79.  Involuntary
 Plain muscle. Don’t
show any cross
straiation.
 Supplied by ANS.
 Neurotransmmitter is
either Ach or
Noradrinalin.
 Contains one nucleus
or uninucleated.