Nerve muscle physiology 1

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

1. Dr. ShilpasreeSaha(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:
ANervecellbody(Soma,perikaryon)
Theprocesses
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.Nisslbodies
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.
Basophillicgranules.

9. Essentiallysmallcavities,boundedbyplasma
(cell)membrane.
Containingribosome(RNA&protein).
RNAisofr-RNAvariety.
Synthesizesproteinofneuronandthese
proteintravelsdowntheaxonbyaxonalflow.
Chromatolysis:Whenthedemandofprotein
synthesisisgreat,thereisexcessive
overworkingoftheneuronortheneuronis
regenerated(followinganinjury),thenissl
granulesdisappear.

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. Thiscomplexis
capable of producing
molecular products of
aneuron, 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. Anaxonis a long projection of a
nerve cell, orneuron, that
conductselectrical
impulsesaway from the
neuron'scell bodyor 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 perikaryonare
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 nisslgranules.
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 nisslgranules.
Forms the afferent
component of impulse.

19. Thefunctionofaneuronistocommunicate
information,whichitdoesbytwo
methods.Electricsignalsprocessandconduct
informationwithinacell,whilechemical
signalstransmitinformationbetweencells.

20. Sensoryneuronshavespecializedreceptorsthat
convertdiversetypesofstimulifromthe
environment(e.g.,light,touch,sound,odorants)
intoelectricsignals.Theseelectricsignalsare
thenconvertedintochemicalsignalsthatare
passed on to other cells
calledinterneurons,whichconvertthe
informationbackintoelectricsignals.Ultimately
theinformationistransmittedtomuscle-
stimulatingmotorneuronsortootherneurons
thatstimulateothertypesofcells,suchas
glands.

21. According to number of processes (neuritis) ,
they may be:
1.Unipolar: one process only, e.g-
mesencephalicnucleus
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
medullatednerve fiber
•Axon emerges from the
region of axon hillock of
soma.
•Central core of the axon is
called axoplasm.
•Axoplasmis pasty (semi
fluid) in nature and
ensheathedby axolemma
membrane.

24. Within the axoplasmfollowing structures can
be seen:
1.Mitochondria
2.Axoplasmicvesicles
3.Neurotubules
Nisslgranules are absent.

25. Axonal flow-axon
depends on soma for
protein synthesis .
Myelin sheath: Outside
covering of axis cylinder
(axoplasmand
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
schwanncell (nucleus of
schwann)

27. Propagation of action potential (wave of
excitation) is very fast in myelinatedfiber but
slow in non-myelinatedfiber.
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 mononucleatedcells-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 sarcomeretwo
types of thread like
structure can be seen –
filaments.
Thin filament-made up
of actinprotein.
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. Actinfilament in periphery attached with Z
line, the other pole of actinforms boundary
of H zone.
In the A band , the myosin and actinfilament
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 actincan
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 actinfilament.

42. Sarcolemma-cell membrane of muscle fiber.
Sarcolemmalmembrane-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. Actinin its monomer form (G actin) is
globular and has site for attachment with
myosin, troponin, various ion and ATP
In thin filament actinmolecule remain in
state of polymer (F actin) and forms an
elongated thread like shape.
2 F actinchains wind with each other to
constitute thin filament.

46. Most of them made up of myosin (myosin-ii)
Myosin-iis a member of non muscle
contractile protein
Has head and tail.
Myosin-ii has 2 head for attachment with
actinand 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.
Sarcomereas a whole shortened.

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

50. Myosin heads develop
contact with actinmolecule-
cross bridge.
Much cross bridges are
formed.
The myosin head now rotate
(swivel)
Actinfilament is pushed
towards H zone.
Myosin heads are dettached
from the actinmolecules and
reattach with another new
site in actinmolecule-
swivels-the actinmolecules
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 , tropomyosinis
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, and T
Troponin-I binds with actin. When Ca++ binds
with troponinC , the binding b/w troponin-
actin-tropomyosinbecome weak and
tropomyosinnow shifts its position, so that
myosin head binds with actin.

56. Neurons send messageselectrochemically.
This means that chemicals cause an electrical
signal. Chemicals in the body are "electrically-
charged" --when they have an electrical
charge, they are calledions.
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 calledsemi-
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 apumpthat
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
theresting 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. Anaction potentialoccurs 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
adepolarizing 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
thethreshold. 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
dettachmentof actinfrom 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 myoglobinsand capillary network.
Less speed of contraction.
Less intense activity.
Fatigue develops slower.
E.g.-postural muscles of body.

68. The junctionalregion between the motor nerve
fiber and the corresponding skeletal muscle fiber
is called NMJ.
Smooth muscle and cardiac muscle don’t have
NMJ.
Junctionalregion is a region where 2 neurons or
1 neuron and its effectorcell come exceedingly
close to each other without any protoplasmic
continuity and the impulse from the neuron is
transmitted to the effectorcell 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
junctionalmembrane
End plate potential develops
If the graded potential is of sufficient
magnitude , an AP develops in effectorcells

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 vesciclespresent-synaptic
vescicles, contains Ach.

74. Cell membrane of the bulbous terminal
(nerve) called pre junctionalmembrane.
Cell membrane of muscle fibers called post
junctionalmembrane.
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 permiabilityof
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 occasionallygivingrise
to EPPs.

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

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

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