MUSCLE PHYSIOLOGY
INDIAN DENTAL ACADEMY

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TYPES OF MUSCLES
SKELETAL MUSCLE
SMOOTH MUSCLE
MUSCLE RECEPTORS
REFLEXES
NEUROTROPHISM
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Muscles are broadly classified into 3 types
– Skeletal muscle
– Smooth muscle
– Cardiac muscle

Muscle contains:
– 75% wat...
40 % of the body is skeletal muscle
10 % is smooth and cardiac muscle.
40% of adult body weight
50% of child’s body weight...
FASCIA
Connective tissue that encases the muscles
Functions of fascia –
– Protect muscle fibers
– Attach muscle to bone
– ...
Layers of fascia –
– Epimysium
• Surface of muscle
• Tapers at ends to form tendon

– Perimysium
• Divides muscle fibers i...
SKELETAL MUSCLE
All skeletal muscles are composed of numerous
fibers ranging from 10 to 80 micrometers in diameter.
In mos...
Sarcolemma- it is the cell membrane of the
muscle fiber.
consists of
• true cell membrane - plasma membrane,
• outer coat ...
Sarcoplasm- The spaces between the myofibrils
are filled with intracellular fluid called sarcoplasm,
containing large quan...
Sarcoplasmic Reticulum -

surrounding the
myofibrils of each muscle fiber is an extensive
reticulum called the sarcoplasmi...
Myofibrils –
Each muscle fiber contains several hundred to
several thousand myofibrils
Each myofibril is composed of about...
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The thick filaments are myosin and the thin filaments
are actin.
myosin and actin filaments partially interdigitate and
th...
I bands-

isotropic to
polarized light.
light bands
contain only actin filaments

A bands- anisotropic to
polarized light....
Z disc - composed of filamentous proteins, passes
cross wise across the myofibril and also crosswise
from myofibril to myo...
Sarcomere – The portion of the myofibril that lies
between two successive Z discs
When the muscle fiber is contracted, the...
Steps In Muscle Contraction
Excitation
– Action potential
– Neurotransmitter release
– Muscle fiber depolarization - Ca++ ...
Contraction
– Ca++ binding moves troponin-tropomyosin complex
– Myosin heads attach to actin
– Crossbridge cycling

Relaxa...
General Mechanism of Muscle
Contraction
Initiation and execution of muscle
contraction occur in the following
steps
1. An ...
3. The acetylcholine acts on a local area of the muscle
fiber membrane to open multiple acetylcholine gated
channels throu...
6. The action potential depolarizes the muscle
membrane, it causes the sarcoplasmic reticulum to
release large quantities ...
8. After a fraction of a second, the calcium ions are
pumped back into the sarcoplasmic reticulum by a
Ca++ membrane pump,...
Muscle Action Potential
Resting membrane potential: about -80 to -90 millivolts
Duration of action potential: 1 to 5 milli...
ACTION POTENTIAL –rapid changes in the
membrane potential that spread rapidly along the
fiber membrane.

Resting Stage- th...
Depolarization Stage – membrane becomes
very permeable to sodium ions, allowing diffusion of
the ions.

Repolarization Sta...
Voltage-Gated Sodium and Potassium
Channels

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At rest, virtually all of the voltage-gated channels are
closed, potassium and sodium can only slowly move
across the memb...
Two things happen next:
As the membrane depolarizes further and the cell
becomes positive inside and negative outside, the...
Next, the voltage gated K+ channels are activated at
the time the action potential reaches its peak. At this
time, both co...
The Neuromuscular Junction
Each nerve ending makes a junction, called the
neuromuscular junction, with the muscle fiber ne...
Motor end plate Branching Nerve Terminals - nerve fibers
invaginate into the surface of the muscle fiber but lie
outside t...
Subneural clefts – numerous small folds of the
muscle membrane which increase the surface area at
which the synaptic trans...
Acetylcholine is stored in synaptic vesicles (300,000)
which are in the terminals of a single end plate
When a nerve impul...
During the action potential the calcium channels open
and calcium ions to diffuse from the synaptic space to
the interior ...
Acetylcholine-gated ion channels, are located almost
entirely near the mouths of the subneural clefts. Has
5 subunit prote...
the principal effect of opening channels - allows
sodium ions to pour to the inside of the fiber, carrying
with them posit...
Destruction of the Released Acetylcholine
Most is destroyed by the enzyme acetylcholinesterase,
which is attached to the s...
Safety Factor of Transmission at the
Neuromuscular Junction
– Each impulse at the neuromuscular junction
causes about 3 ti...
A new action potential cannot occur in an excitable
fiber as long as the membrane is still depolarized
from the preceding ...
Absolute Refractory Period - period during which a
second action potential cannot be elicited, even with
a strong stimulus...
Cause of relative refractoriness :
1.

During this time, some of the sodium channels still
have not been reversed from the...
Excitation-Contraction Coupling
Skeletal muscle fibers are so large that action
potentials spreading along its surface mem...
T tubules
–
–
–
–
–

Very small
transverse to the myofibrils.
Penetrate muscle fibers from one side to the other
They bran...
Sarcoplasmic reticulum– Terminal cisternae
– Long longitudinal tubules
The vesicular tubules have calcium ions in high
con...
Molecular Mechanism of Muscle
Contraction
Sliding Filament Mechanism of
Muscle Contraction.

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Myosin Filament -The myosin filament is
composed of multiple myosin molecules, each having
a molecular weight of about 480...
heavy chains wrap spirally around each other to form
a double helix, called the tail of the myosin molecule.

One end of e...
Myosin Filament - Made up of 200 or more
individual myosin molecules. (Length -1.6
micrometers.)
Tails of the myosin molec...
Arm- part of the body of each myosin molecule
along with the head,

Cross bridges- protruding arms and heads
together. It ...
The hinged arms allow the heads either to be
extended far outward from the body of the
myosin filament or to be brought cl...
There are no cross-bridge heads in the center of the
myosin filament for a distance of 0.2 micrometer
because the hinged a...
ATPase Activity of the Myosin Head
-the myosin head functions as an ATPase enzyme.
This allows the head to cleave ATP and ...
Actin Filament- composed of 3 protein
components: actin, tropomyosin, and
troponin.

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Actin - double stranded F-actin protein molecule.
– The two strands are wound in a helix. Each strand
is composed of polym...
Actin filament - length -1 micrometer
The bases of the actin filaments are inserted strongly
into the Z discs; the ends of...
Tropomyosin Molecules-

molecular weight

70,000
length - 40 nanometers.
These molecules are wrapped spirally around the
s...
Activation of the Actin filament
The active sites on the normal actin filament of the
relaxed muscle are inhibited or phys...
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What Keeps the Myosin and Actin
Filaments in Place?
The side-by-side relationship between the myosin
and actin filaments i...
It is filamentous, and very springy. These molecules
act as a framework that hold the myosin and actin
filaments in place
...
The Walk-Along Theory of
Contraction

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When a head attaches to an active site, changes in
the intramolecular forces between the head and arm
of its cross-bridge ...
Chemical Events In the Motion of
the Myosin Head
1. Before contraction -the heads of the crossbridges
bind with ATP. The A...
2. When the troponin - tropomyosin complex binds with
calcium ions, active sites on the actin filament are
uncovered, and ...
4. Once the head of the cross-bridge tilts, it allows
release of the ADP and phosphate ion. At the site of
release of the ...
The process proceeds again and again until
the actin filaments pull the Z membrane up
against the ends of the myosin filam...
RELAXATION –muscle contraction continues as
long as the calcium ions remain in high concentration
and thus
A continually a...
Effect of Amount of Actin and Myosin
Filament Overlap on Tension Developed by
the Contracting Muscle

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Point D- no actin-myosin overlap. Tension
developed by the muscle - 0.

Point C- actin filament has overlapped all the

cr...
Effect of Muscle Length on Force of
Contraction in the Whole Intact Muscle.
Other factors to be
considered –
– connective ...
Relation of Velocity of Contraction to
Load
Against no load-skeletal muscle
contracts in about 0.1 second
When loads are a...
Work Output During Muscle Contraction
Sources of energy for muscle contraction
– Phosphocreatine
– Glycolysis of glycogen
...
Types Of Contraction
Isometric Contraction- when
the muscle does not shorten during
contraction

Isotonic Contraction- whe...
Fast And Slow Muscle Fibers.
Muscles that react rapidly are composed mainly of
fast fibers with small numbers of slow fibe...
Fast Fibers
Large fibers

Slow Fibers
Smaller fibers.

Less extensive blood supply

Extensive blood vessel
Supply

Fewer m...
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Motor neurons
Small muscles that react rapidly and whose control
must be exact have more nerve fibers for fewer
muscle fib...
Force Summation.
Summation - adding together of individual twitch
contractions to increase the intensity of overall
muscle...
Multiple Fiber Summation- When the CNS
sends a weak signal to contract a muscle, the smaller
motor units of the muscle are...
Frequency Summation and
Tetanization
As frequency increases, a new contraction occurs
before the preceding one is over. As...
Tetanization - When the frequency reaches a
critical level, the successive contractions fuse
together, and the whole muscl...
The Staircase Effect (Treppe)
When a muscle begins to contract after a long period
of rest, its initial strength of contra...
Skeletal Muscle Tone.
Muscle tone- Even when muscles are at rest, a
certain amount of tautness remains. It results entirel...
Muscle Fatigue.
Prolonged and strong contraction of a muscle leads
to the state of muscle fatigue. It results mainly from
...
Muscle Hypertrophy
– When the total mass of a muscle increases
– When muscles are stretched to greater than
normal length ...
When a muscle loses its nerve supply, it no longer
receives the contractile signals that are required to
maintain normal m...
Rigor Mortis
Several hours after death, the muscles contract and
become rigid, even without action potentials. This
rigidi...
SMOOTH MUSCLE
Smooth Muscle -1 to 5 micrometers – diameter
20 - 500 micrometers in length

Two major types– Multi-unit smo...
Multi-Unit Smooth Muscle– Composed of discrete, separate smooth muscle
fibers.
– Each fiber operates independently
– Inner...
Unitary Smooth Muscle– smooth muscle fibers that contract together as a
single unit.
– fibers are arranged in sheets or bu...
Smooth muscle have actin and myosin filaments
having chemical characteristics similar and interact
with each other in much...
Actin filaments are attached to dense
bodies.
Some dense bodies of adjacent cells are
bonded together by intercellular bri...
The rapidity of cycling of the myosin cross-bridges in
smooth muscle cycle is much, much slower than in
skeletal muscle (1...
Only 1/10 to 1/300 as much energy is required to
sustain the same tension of contraction in smooth
muscle as in skeletal m...
Visceral unitary type of smooth muscle of many
hollow organs, have the ability to return to nearly its
original force of c...
Regulation of Contraction by Calcium
Ions– the initiating stimulus for most smooth muscle
contraction is an increase in in...
Contraction1.

The calcium ions bind with calmodulin.

2.

The calmodulin-calcium combination joins with and
activates myo...
Cessation of ContractionWhen the calcium ion concentration falls below a
critical level, the contraction processes automat...
Latch Mechanism
Once smooth muscle has developed full contraction,
the amount of continuing excitation usually can be
redu...
When the myosin kinase and myosin phosphatase
enzymes are activated, the cycling frequency of the
myosin heads and the vel...
Therefore, the number of heads attached to the actin
filament at any given time remains large. Because
the number of heads...
Neuromuscular Junctions of Smooth
Muscle
The autonomic nerve fibers that innervate smooth
muscle generally branch diffusel...
The fine terminal axons have multiple varicosities
distributed along their axes. At these points the
schwann cells are int...
When acetylcholine excites a muscle fiber,
norepinephrine ordinarily inhibits it. Conversely, when
acetylcholine inhibits ...
Action Potentials in Smooth Muscle
The normal resting membrane potential is usually
about -50 to -60 millivolts

The actio...
Spike Potentials
similar to the skeletal muscles
occur in most types of unitary smooth muscle
duration -10 to 50 milliseco...
Action Potentials with PlateausThe repolarization is delayed for several hundred to
as much as 1000 milliseconds (1 second...
Smooth muscle cell membrane have more voltagegated calcium channels than does skeletal muscle
but few voltage gated sodium...
Slow Wave Potentials
Some smooth muscle are self-excitatory. ie: action
potential arises within the smooth muscle cell wit...
Cause
– The membrane potential becomes more negative
when sodium is pumped rapidly and less negative
when the sodium pump ...
Source of Calcium Ions
Almost all the calcium ions that cause contraction
enter the muscle cell from the extracellular flu...
When the extracellular fluid calcium ion concentration
falls to 1/3 to 1/10 normal, smooth muscle contraction
usually ceas...
Smooth Muscle Sarcoplasmic Reticulumcaveolae – analog of the transverse tubule system of
skeletal muscle. They excite calc...
MUSCLE RECEPTORS
Receptors provide information regarding:
– Chemical changes (i.e., O2, CO2, H+)
– Tension development: Go...
Muscle spindle –
– Detect dynamic and static changes in muscle
length– Stretch reflex
– Stretch on muscle causes reflex co...
Muscle spindles respond to muscle stretch Gamma motor neurons are co activated during
contraction
– Cause contraction of f...
Golgi Tendon Organ
Located in tendon
Monitor muscle tension
Activation causes inhibition of alphamotor neuron
Is a safety ...
MYOTACTIC / STRETCH REFLEX

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Causes contraction of stretched muscle

Receptor – proprioceptive nerve endings called
muscle spindles

Impulses are condu...
Functional significance – serves as a mechanism for
upright posture
In mandible it acts to maintain the postural rest
posi...
CLASP KNIFE REFLEX /AUTOGENIC INHIBITION

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Resistance is encountered as soon as the muscle is
stretched throughout the initial part of the bending.
This resistance i...
functional significance - to protect the overload by
preventing damaging contraction against strong
stretching forces.
The...
Receptors - Golgi tendon organs
impulses are conducted by the Group 1B sensory
nerve fiber
Impulses act on the motor neuro...
NEURO TROPHISM
Definition - interaction between nerves and other
cells which initiate or control molecular modifications
i...
Three types Neuro epithelial trophism
Neuro visceral trophism
Neuro muscular trophism

NEURO-MUSCULAR TROPHISM: Skeletal m...
Approximately
at
the
myoblast
stage
of
differentiation, neural innervation is established
without which further myogenesis...
Cross-innervation experiments show that many
significant morphologic, biochemical and functional
parameters of the re-inne...
Conformational features of myosin are determined by
the nature of the innervation and that the complex
chain of events lea...
Research shows that a qualitatively different myosin
that resembles that of the muscle, formerly
innervated by the nerve, ...
Implication of these data:
Since periosteal functional matrices regulate the size
and shape of specifically related skelet...
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Muscle physiology /certified fixed orthodontic courses by Indian dental academy

  1. 1. MUSCLE PHYSIOLOGY INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. TYPES OF MUSCLES SKELETAL MUSCLE SMOOTH MUSCLE MUSCLE RECEPTORS REFLEXES NEUROTROPHISM www.indiandentalacademy.com
  3. 3. Muscles are broadly classified into 3 types – Skeletal muscle – Smooth muscle – Cardiac muscle Muscle contains: – 75% water – 20% protein – 5% organic and inorganic compounds www.indiandentalacademy.com
  4. 4. 40 % of the body is skeletal muscle 10 % is smooth and cardiac muscle. 40% of adult body weight 50% of child’s body weight www.indiandentalacademy.com
  5. 5. FASCIA Connective tissue that encases the muscles Functions of fascia – – Protect muscle fibers – Attach muscle to bone – Provide structure for network of nerves and blood/lymph vessels www.indiandentalacademy.com
  6. 6. Layers of fascia – – Epimysium • Surface of muscle • Tapers at ends to form tendon – Perimysium • Divides muscle fibers into bundles or fascicles – Endomysium • Surrounds single muscle fibers www.indiandentalacademy.com
  7. 7. SKELETAL MUSCLE All skeletal muscles are composed of numerous fibers ranging from 10 to 80 micrometers in diameter. In most skeletal muscles, each fiber extends the entire length of the muscle. Each fiber is usually innervated by only one nerve ending, located near the middle of the fiber, except for about 2 % of the fibers www.indiandentalacademy.com
  8. 8. Sarcolemma- it is the cell membrane of the muscle fiber. consists of • true cell membrane - plasma membrane, • outer coat made up of a thin layer of polysaccharide material that contains numerous thin collagen fibrils – At the end of the muscle fiber sarcolemma fuses with a tendon fiber www.indiandentalacademy.com
  9. 9. Sarcoplasm- The spaces between the myofibrils are filled with intracellular fluid called sarcoplasm, containing large quantities of potassium, magnesium, phosphate, and multiple protein enzymes Large numbers of mitochondria that lie parallel to the myofibrils are present that provide ATP www.indiandentalacademy.com
  10. 10. Sarcoplasmic Reticulum - surrounding the myofibrils of each muscle fiber is an extensive reticulum called the sarcoplasmic reticulum. This reticulum has a special organization that is extremely important in controlling muscle contraction. www.indiandentalacademy.com
  11. 11. Myofibrils – Each muscle fiber contains several hundred to several thousand myofibrils Each myofibril is composed of about 1500 adjacent myosin filaments and 3000 actin filaments, which are large polymerized protein molecules that cause the actual muscle contraction. www.indiandentalacademy.com
  12. 12. www.indiandentalacademy.com
  13. 13. The thick filaments are myosin and the thin filaments are actin. myosin and actin filaments partially interdigitate and thus cause the myofibrils to have alternate light and dark bands. www.indiandentalacademy.com
  14. 14. I bands- isotropic to polarized light. light bands contain only actin filaments A bands- anisotropic to polarized light. dark bands contain myosin and ends of the actin filaments www.indiandentalacademy.com
  15. 15. Z disc - composed of filamentous proteins, passes cross wise across the myofibril and also crosswise from myofibril to myofibril, attaching the myofibrils to one another across the muscle fiber giving them a striated appearance. The ends of the actin filaments are attached to the Z disc. Filaments extend in both directions to interdigitate with the myosin filaments www.indiandentalacademy.com
  16. 16. Sarcomere – The portion of the myofibril that lies between two successive Z discs When the muscle fiber is contracted, the length of the sarcomere is about 2 micrometers. The actin filaments completely overlap the myosin filaments and the tips of the actin filaments begin to overlap www.indiandentalacademy.com
  17. 17. Steps In Muscle Contraction Excitation – Action potential – Neurotransmitter release – Muscle fiber depolarization - Ca++ release from sarcoplasmic reticulum Coupling – Ca++ binds to troponin-tropomyosin complex www.indiandentalacademy.com
  18. 18. Contraction – Ca++ binding moves troponin-tropomyosin complex – Myosin heads attach to actin – Crossbridge cycling Relaxation – Ca++ removed from troponin-tropomyosin complex – Cross bridge detachment – Ca++ pumped into SR – active transport www.indiandentalacademy.com
  19. 19. General Mechanism of Muscle Contraction Initiation and execution of muscle contraction occur in the following steps 1. An action potential travels along a motor nerve to its endings on muscle fibers. 2. At each ending, the nerve secretes a small amount of the neurotransmitter substance acetylcholine. www.indiandentalacademy.com
  20. 20. 3. The acetylcholine acts on a local area of the muscle fiber membrane to open multiple acetylcholine gated channels through protein molecules floating in the membrane. 4. This allows large quantities of sodium ions to diffuse to the interior of the muscle fiber membrane. This initiates an action potential at the membrane. 5. The action potential travels along the muscle fiber membrane www.indiandentalacademy.com
  21. 21. 6. The action potential depolarizes the muscle membrane, it causes the sarcoplasmic reticulum to release large quantities of calcium ions that have been stored within this reticulum. 7. The calcium ions initiate attractive forces between the actin and myosin filaments, causing them to slide alongside each other, which is the contractile process. www.indiandentalacademy.com
  22. 22. 8. After a fraction of a second, the calcium ions are pumped back into the sarcoplasmic reticulum by a Ca++ membrane pump, this removal of calcium ions from the myofibrils causes the muscle contraction to cease. www.indiandentalacademy.com
  23. 23. Muscle Action Potential Resting membrane potential: about -80 to -90 millivolts Duration of action potential: 1 to 5 milliseconds Velocity of conduction: 3 to 5 m/sec- www.indiandentalacademy.com
  24. 24. ACTION POTENTIAL –rapid changes in the membrane potential that spread rapidly along the fiber membrane. Resting Stage- the membrane potential before the action potential begins. The membrane is polarized during this stage because of the -90 millivolts negative membrane potential that is present. www.indiandentalacademy.com
  25. 25. Depolarization Stage – membrane becomes very permeable to sodium ions, allowing diffusion of the ions. Repolarization Stage.- after a few 10,000ths of a second the sodium channels begin to close and the potassium channels open more than normal. Rapid diffusion of potassium ions to the exterior reestablishes the normal negative resting membrane potential. www.indiandentalacademy.com
  26. 26. Voltage-Gated Sodium and Potassium Channels www.indiandentalacademy.com
  27. 27. At rest, virtually all of the voltage-gated channels are closed, potassium and sodium can only slowly move across the membrane, through the passive "leak" channels The first thing that occurs when a depolarizing graded potential reaches the threshold is that the voltage gated Na+ channels begin to open and Na+ influx into the cell exceeds K+ efflux out of the cell www.indiandentalacademy.com
  28. 28. Two things happen next: As the membrane depolarizes further and the cell becomes positive inside and negative outside, the flow of Na+ will decrease. 1. Even more importantly, the voltage- gated Na+ channels close When the inactivation gates close, Na+ influx stops and the repolarizing phase takes place. 2) www.indiandentalacademy.com
  29. 29. Next, the voltage gated K+ channels are activated at the time the action potential reaches its peak. At this time, both concentration and electrical gradients favour the movement of K+ out of the cell. These channels are also inactivated with time but not until after the efflux of K+ has returned the membrane potential to, or below the resting level (after hyperpolarization /positive afterpotential). www.indiandentalacademy.com
  30. 30. The Neuromuscular Junction Each nerve ending makes a junction, called the neuromuscular junction, with the muscle fiber near its midpoint The action potential initiated in the muscle fiber by the nerve signal travels in both direction toward the muscle fiber ends. With the exception of about 2 % of the muscle fibers, there is only one such junction per muscle fiber. www.indiandentalacademy.com
  31. 31. Motor end plate Branching Nerve Terminals - nerve fibers invaginate into the surface of the muscle fiber but lie outside the plasma membrane. Covered by Schwann cells that insulate it from the surrounding fluids. www.indiandentalacademy.com
  32. 32. Subneural clefts – numerous small folds of the muscle membrane which increase the surface area at which the synaptic transmitter can act. Synaptic trough - invaginated membrane Synaptic cleft - space between the terminal and the fiber membrane (20 to 30 nanometers wide.) www.indiandentalacademy.com
  33. 33. Acetylcholine is stored in synaptic vesicles (300,000) which are in the terminals of a single end plate When a nerve impulse reaches the neuromuscular junction, about 125 vesicles of acetylcholine are released from the terminals into the synaptic space www.indiandentalacademy.com
  34. 34. During the action potential the calcium channels open and calcium ions to diffuse from the synaptic space to the interior of the nerve terminal. The calcium ions attract the acetylcholine vesicles, drawing them to the neural membrane The vesicles fuse with the neural membrane and empty their acetylcholine into the synaptic space by exocytosis. www.indiandentalacademy.com
  35. 35. Acetylcholine-gated ion channels, are located almost entirely near the mouths of the subneural clefts. Has 5 subunit proteins, two alpha and one each of beta, delta, and gamma proteins. After the Ach attaches a conformational change occurs that opens the channel www.indiandentalacademy.com
  36. 36. the principal effect of opening channels - allows sodium ions to pour to the inside of the fiber, carrying with them positive charges creating a local positive potential change inside the muscle fiber membrane, called the end plate potential. this end plate potential initiates an action potential that spreads along the muscle membrane and thus causes muscle contraction. www.indiandentalacademy.com
  37. 37. Destruction of the Released Acetylcholine Most is destroyed by the enzyme acetylcholinesterase, which is attached to the spongy layer of the connective tissue that fills the synaptic space between the presynaptic nerve terminal and the postsynaptic muscle membrane. A small amount of acetylcholine diffuses out of the synaptic space and is then no longer available to act on the muscle fiber membrane. www.indiandentalacademy.com
  38. 38. Safety Factor of Transmission at the Neuromuscular Junction – Each impulse at the neuromuscular junction causes about 3 times as much end plate potential as that required to stimulate the muscle fiber. – Stimulation of the nerve fiber at rates greater than 100 times/sec for several minutes diminishes the number of acetylcholine vesicles so that impulse fail to pass into the muscle fiber- called fatigue www.indiandentalacademy.com
  39. 39. A new action potential cannot occur in an excitable fiber as long as the membrane is still depolarized from the preceding action potential. Shortly after the action potential the sodium channels (or calcium channels, or both) become inactivated, and any amount of excitatory signal applied to these channels at this point will not open the inactivation gates. www.indiandentalacademy.com
  40. 40. Absolute Refractory Period - period during which a second action potential cannot be elicited, even with a strong stimulus. Large myelinated nerve fibers 1/2500second. Relative Refractory Period - lasts about ¼ to ½ as long as the absolute period. During this time, stronger than normal stimuli can excite the fiber. www.indiandentalacademy.com
  41. 41. Cause of relative refractoriness : 1. During this time, some of the sodium channels still have not been reversed from their inactivation state 2. the potassium channels are usually wide open at this time, causing greatly excess flow of positive potassium ion charges to the outside of the fiber opposing the stimulating signal www.indiandentalacademy.com
  42. 42. Excitation-Contraction Coupling Skeletal muscle fibers are so large that action potentials spreading along its surface membrane cause almost no current flow deep within the fiber. This is achieved by transmission of action potentials along transverse tubules (T tubules) www.indiandentalacademy.com
  43. 43. T tubules – – – – – Very small transverse to the myofibrils. Penetrate muscle fibers from one side to the other They branch among themselves They are open to the exterior of the muscle fiber at their point of origination and so basically are internal extensions of the cell membrane. – The action potential spreads along the T tubules to the interior of the muscle fiber. www.indiandentalacademy.com
  44. 44. Sarcoplasmic reticulum– Terminal cisternae – Long longitudinal tubules The vesicular tubules have calcium ions in high concentration, and are released from each vesicle when an action potential occurs in the adjacent T tubule. www.indiandentalacademy.com
  45. 45. Molecular Mechanism of Muscle Contraction Sliding Filament Mechanism of Muscle Contraction. www.indiandentalacademy.com
  46. 46. Myosin Filament -The myosin filament is composed of multiple myosin molecules, each having a molecular weight of about 480,000. myosin molecule - 6 polypeptide chains– 2 heavy chains- molecular weight 200,000 – 4 light chains - molecular weights 20,000 each. www.indiandentalacademy.com
  47. 47. heavy chains wrap spirally around each other to form a double helix, called the tail of the myosin molecule. One end of each of these chains is folded bilaterally into a globular polypeptide structure called a myosin head. 4 light chains are also part of the myosin head. These light chains help control the function of the head during muscle contraction. www.indiandentalacademy.com
  48. 48. Myosin Filament - Made up of 200 or more individual myosin molecules. (Length -1.6 micrometers.) Tails of the myosin molecules bundle together to form the body of the filament, Heads of the molecules hang outward to the sides of the body. www.indiandentalacademy.com
  49. 49. Arm- part of the body of each myosin molecule along with the head, Cross bridges- protruding arms and heads together. It is flexible at the hinges– where the arm leaves the body of the myosin filament, – where the head attaches to the arm. www.indiandentalacademy.com
  50. 50. The hinged arms allow the heads either to be extended far outward from the body of the myosin filament or to be brought close to the body. The hinged heads participate in the actual contraction process www.indiandentalacademy.com
  51. 51. There are no cross-bridge heads in the center of the myosin filament for a distance of 0.2 micrometer because the hinged arms extend away from the center. The myosin filament itself is twisted so that each successive pair of crossbridges is axially displaced from the previous pair by 120 degrees. This ensures that the cross-bridges extend in all directions around the filament. www.indiandentalacademy.com
  52. 52. ATPase Activity of the Myosin Head -the myosin head functions as an ATPase enzyme. This allows the head to cleave ATP and to use the energy for the contraction process. www.indiandentalacademy.com
  53. 53. Actin Filament- composed of 3 protein components: actin, tropomyosin, and troponin. www.indiandentalacademy.com
  54. 54. Actin - double stranded F-actin protein molecule. – The two strands are wound in a helix. Each strand is composed of polymerized G-actin molecules, (molecular weight 42,000). – Attached to each one of the G-actin molecules is one molecule of ADP which are the active sites on the actin filaments with which the cross bridges of the myosin filaments interact to cause muscle contraction. www.indiandentalacademy.com
  55. 55. Actin filament - length -1 micrometer The bases of the actin filaments are inserted strongly into the Z discs; the ends of the filaments protrude in both directions Troponin- Attached intermittently along the sides of the tropomyosin molecules complexes of three loosely bound protein subunits – troponin I - affinity for actin, – troponin T - for tropomyosin, – troponin C - for calcium ions www.indiandentalacademy.com
  56. 56. Tropomyosin Molecules- molecular weight 70,000 length - 40 nanometers. These molecules are wrapped spirally around the sides of the F-actin helix In the resting state, the tropomyosin molecules lie on top of the active sites of the actin strands, so that attraction cannot occur between the actin and myosin filaments www.indiandentalacademy.com
  57. 57. Activation of the Actin filament The active sites on the normal actin filament of the relaxed muscle are inhibited or physically covered by the troponin tropomyosin complex. When calcium ions combine with troponin C, the troponin complex undergoes a conformational change that moves it deeper into the groove between the two actin strands. This uncovers the active sites of the actin www.indiandentalacademy.com
  58. 58. www.indiandentalacademy.com
  59. 59. What Keeps the Myosin and Actin Filaments in Place? The side-by-side relationship between the myosin and actin filaments is achieved by a large number of filamentous molecules of a protein called titin. (molecular weight- 3 million) www.indiandentalacademy.com
  60. 60. It is filamentous, and very springy. These molecules act as a framework that hold the myosin and actin filaments in place The titin molecule itself acts as template for initial formation of portions of the contractile filaments of the sarcomere, especially the myosin filaments. www.indiandentalacademy.com
  61. 61. The Walk-Along Theory of Contraction www.indiandentalacademy.com
  62. 62. When a head attaches to an active site, changes in the intramolecular forces between the head and arm of its cross-bridge occur. The head tilts toward the arm and drags the actin filament along with it (power stroke) Immediately after tilting, the head automatically breaks away from the active site. The head returns to its extended direction, it combines with a new active site farther down along the actin filament. www.indiandentalacademy.com
  63. 63. Chemical Events In the Motion of the Myosin Head 1. Before contraction -the heads of the crossbridges bind with ATP. The ATPase activity of the myosin head immediately cleaves the ATP but leaves the cleavage products, ADP plus phosphate ion, bound to the head. In this state, the head extends perpendicularly toward the actin filament but is not yet attached to the actin www.indiandentalacademy.com
  64. 64. 2. When the troponin - tropomyosin complex binds with calcium ions, active sites on the actin filament are uncovered, and the myosin heads then bind with these. 3.For the power stroke the energy that activates it already stored, like a "cocked" spring, by the conformational change that occurred in the head when the ATP molecule was cleaved earlier. www.indiandentalacademy.com
  65. 65. 4. Once the head of the cross-bridge tilts, it allows release of the ADP and phosphate ion. At the site of release of the ADP, a new molecule of ATP binds. This binding of new ATP causes detachment of the head from the actin. 5. After the head has detached from the actin, the new molecule of ATP is cleaved to begin the next cycle, leading to a new power stroke. www.indiandentalacademy.com
  66. 66. The process proceeds again and again until the actin filaments pull the Z membrane up against the ends of the myosin filaments or until the load on the muscle becomes too great for further pulling to occur. www.indiandentalacademy.com
  67. 67. RELAXATION –muscle contraction continues as long as the calcium ions remain in high concentration and thus A continually active calcium pump located in the walls of the sarcoplasmic reticulum pumps calcium ions away from the myofibrils back into the sarcoplasmic tubules. This pump can concentrate the calcium ions about 1O,OOO-fold inside the tubules. Inside the reticulum is a protein called calsequestrin that can bind up to 40 times more calcium. www.indiandentalacademy.com
  68. 68. Effect of Amount of Actin and Myosin Filament Overlap on Tension Developed by the Contracting Muscle www.indiandentalacademy.com
  69. 69. Point D- no actin-myosin overlap. Tension developed by the muscle - 0. Point C- actin filament has overlapped all the cross-bridges of the myosin filament but not reached the center. Length -2.2 micrometers. Point B- two actin filaments begin to overlap each other. Length -2 micrometers. Point A- the two Z discs of the sarcomere abut the ends of the myosin filaments. Length - 1.65 micrometers www.indiandentalacademy.com
  70. 70. Effect of Muscle Length on Force of Contraction in the Whole Intact Muscle. Other factors to be considered – – connective tissue – different parts of the muscle do not contract the same amount. Active tension decreases as the muscle is stretched beyond its normal length www.indiandentalacademy.com
  71. 71. Relation of Velocity of Contraction to Load Against no load-skeletal muscle contracts in about 0.1 second When loads are applied, the velocity of contraction becomes progressively less When load is equal to the maximum force of the muscle, the velocity of contraction is zero and no contraction results www.indiandentalacademy.com
  72. 72. Work Output During Muscle Contraction Sources of energy for muscle contraction – Phosphocreatine – Glycolysis of glycogen – Oxidative metabolism. The percentage of the input energy to muscle is less than 25 % with the remainder becoming heat. www.indiandentalacademy.com
  73. 73. Types Of Contraction Isometric Contraction- when the muscle does not shorten during contraction Isotonic Contraction- when muscle shortens but the tension on the muscle remains constant throughout the contraction. www.indiandentalacademy.com
  74. 74. Fast And Slow Muscle Fibers. Muscles that react rapidly are composed mainly of fast fibers with small numbers of slow fibers. Muscles that respond slowly but with prolonged contraction are composed mainly of slow fibers www.indiandentalacademy.com
  75. 75. Fast Fibers Large fibers Slow Fibers Smaller fibers. Less extensive blood supply Extensive blood vessel Supply Fewer mitochondria, Increased numbers of mitochondria, No myoglobin present in fibers Large amounts of myoglobin Large amounts of glycolytic enzymes Less amounts of glycolytic enzymes Extensive sarcoplasmic Less extensive sarcoplasmic www.indiandentalacademy.com reticulum reticulum
  76. 76. www.indiandentalacademy.com
  77. 77. Motor neurons Small muscles that react rapidly and whose control must be exact have more nerve fibers for fewer muscle fiber Large muscles that do not require fine control may have several hundred muscle fibers in a motor unit. www.indiandentalacademy.com
  78. 78. Force Summation. Summation - adding together of individual twitch contractions to increase the intensity of overall muscle contraction. – Types • Multiple fiber summation • Frequency summation www.indiandentalacademy.com
  79. 79. Multiple Fiber Summation- When the CNS sends a weak signal to contract a muscle, the smaller motor units of the muscle are stimulated in preference to the larger motor units. As the strength of the signal increases, larger motor units begin to be excited (size principle.) Cause -smaller motor units are driven by small motor nerve fibers, and are more excitable than the larger ones www.indiandentalacademy.com
  80. 80. Frequency Summation and Tetanization As frequency increases, a new contraction occurs before the preceding one is over. As a result, the 2nd contraction is added partially to the 1st , so that the total strength of contraction rises with increasing frequency. www.indiandentalacademy.com
  81. 81. Tetanization - When the frequency reaches a critical level, the successive contractions fuse together, and the whole muscle contraction appears to be smooth and continuous www.indiandentalacademy.com
  82. 82. The Staircase Effect (Treppe) When a muscle begins to contract after a long period of rest, its initial strength of contraction is as little as ½ its strength 10 to 50 muscle twitches later. Cause – increase in calcium ions in the cytosol because of the release of more and more ions from the sarcoplasmic reticulum with each successive muscle action potential and failure of the sarcoplasm to recapture the ions immediately. www.indiandentalacademy.com
  83. 83. Skeletal Muscle Tone. Muscle tone- Even when muscles are at rest, a certain amount of tautness remains. It results entirely from a low rate of nerve impulses coming from the spinal cord. www.indiandentalacademy.com
  84. 84. Muscle Fatigue. Prolonged and strong contraction of a muscle leads to the state of muscle fatigue. It results mainly from inability of the contractile and metabolic processes of the muscle fibers to continue supplying the same work output. www.indiandentalacademy.com
  85. 85. Muscle Hypertrophy – When the total mass of a muscle increases – When muscles are stretched to greater than normal length causing new sarcomeres to be added at the ends of the muscle fibers – Results from an increase in the number of actin and myosin filaments – Rate of synthesis of muscle contractile proteins is far greater www.indiandentalacademy.com
  86. 86. When a muscle loses its nerve supply, it no longer receives the contractile signals that are required to maintain normal muscle size and atrophy begins If the nerve supply grows back rapidly, return of function can occur in 3 months. Beyond that the capability of functional return becomes less, with no further return of function after 1 to 2 years. www.indiandentalacademy.com
  87. 87. Rigor Mortis Several hours after death, the muscles contract and become rigid, even without action potentials. This rigidity results from loss of all the ATP, which is required to cause separation of the crossbridges from the actin filaments during the relaxation process. www.indiandentalacademy.com
  88. 88. SMOOTH MUSCLE Smooth Muscle -1 to 5 micrometers – diameter 20 - 500 micrometers in length Two major types– Multi-unit smooth muscle – Unitary smooth muscle. www.indiandentalacademy.com
  89. 89. Multi-Unit Smooth Muscle– Composed of discrete, separate smooth muscle fibers. – Each fiber operates independently – Innervated by a single nerve ending – Outer surfaces are covered by a thin layer of basement membrane – Each fiber can contract independently of the others, and their control is exerted mainly by nerve signals. www.indiandentalacademy.com
  90. 90. Unitary Smooth Muscle– smooth muscle fibers that contract together as a single unit. – fibers are arranged in sheets or bundles, and their cell membranes are adherent to one another – cell membranes are joined by gap junctions through which ions can flow freely – Syncytial interconnections among fibers. www.indiandentalacademy.com
  91. 91. Smooth muscle have actin and myosin filaments having chemical characteristics similar and interact with each other in much the same way to those of the skeletal muscle They do not not contain the normal troponin complex www.indiandentalacademy.com
  92. 92. Actin filaments are attached to dense bodies. Some dense bodies of adjacent cells are bonded together by intercellular bridges which transmit the force of contraction from one cell to the next. Ends of actin filaments overlap a myosin filament located midway between the dense bodies. Myosin filaments have sidepolar crossbridges - bridges on both sides hinge in the opposite direction.www.indiandentalacademy.com
  93. 93. The rapidity of cycling of the myosin cross-bridges in smooth muscle cycle is much, much slower than in skeletal muscle (1/10 to 1/300) Reason- The cross-bridge heads have far less ATPase activity than in skeletal muscle. But the fraction of time that the cross-bridges remain attached to the actin filaments, which determines the force of contraction, is increased in smooth muscle - 4 to 6 kg/cm2 www.indiandentalacademy.com
  94. 94. Only 1/10 to 1/300 as much energy is required to sustain the same tension of contraction in smooth muscle as in skeletal muscle. smooth muscles – begin to contract 50 - 100 milliseconds after excitation – reach full contraction - 0.5 second later, – decline in contractile force -another 1 to 2 sec – total contraction time - 1 to 3 sec. www.indiandentalacademy.com
  95. 95. Visceral unitary type of smooth muscle of many hollow organs, have the ability to return to nearly its original force of contraction seconds or minutes after it has been elongated or shortened. www.indiandentalacademy.com
  96. 96. Regulation of Contraction by Calcium Ions– the initiating stimulus for most smooth muscle contraction is an increase in intracellular calcium ions. – Caused by – • nerve stimulation • hormonal stimulation, • stretch of the fiber • change in the chemical environment of the fiber. www.indiandentalacademy.com
  97. 97. Contraction1. The calcium ions bind with calmodulin. 2. The calmodulin-calcium combination joins with and activates myosin kinase, a phosphorylating enzyme. 3. In response the regulatory chain of the myosin head becomes phosphorylated and the head now binds with the actin filament and proceeds through the entire cycling process causing muscle contraction. www.indiandentalacademy.com
  98. 98. Cessation of ContractionWhen the calcium ion concentration falls below a critical level, the contraction processes automatically except for the phosphorylation of the myosin head. Reversal of this requires enzyme myosin phosphatase, which splits the phosphate from the regulatory light chain. Then the cycling stops and contraction ceases. www.indiandentalacademy.com
  99. 99. Latch Mechanism Once smooth muscle has developed full contraction, the amount of continuing excitation usually can be reduced to far less than the initial level, yet the muscle maintains its full force of contraction. Importance - can maintain prolonged tonic contraction in smooth muscle for hours with little use of energy. www.indiandentalacademy.com
  100. 100. When the myosin kinase and myosin phosphatase enzymes are activated, the cycling frequency of the myosin heads and the velocity of contraction are great. As the activation of the enzymes decreases, the cycling frequency decreases But the deactivation of these enzymes allows the myosin heads to remain attached to the actin filament for a longer proportion of the cycling period. www.indiandentalacademy.com
  101. 101. Therefore, the number of heads attached to the actin filament at any given time remains large. Because the number of heads attached to the actin determines the force of contraction, tension is maintained, yet little energy is used by the muscle, because ATP is not degraded to ADP. www.indiandentalacademy.com
  102. 102. Neuromuscular Junctions of Smooth Muscle The autonomic nerve fibers that innervate smooth muscle generally branch diffusely on top of a sheet of muscle fibers, These fibers do not make direct contact with the smooth muscle fiber cell membranes but instead form diffuse junctions that secrete their transmitter substance into the matrix a few nanometers to a few micrometers away www.indiandentalacademy.com
  103. 103. The fine terminal axons have multiple varicosities distributed along their axes. At these points the schwann cells are interrupted so that transmitter substance can be secreted through the walls of the varicosities. These are called as contact junctions In the varicosities are vesicles which contain acetylcholine and norepinephrine www.indiandentalacademy.com
  104. 104. When acetylcholine excites a muscle fiber, norepinephrine ordinarily inhibits it. Conversely, when acetylcholine inhibits a fiber, norepinephrine usually excites it Reason -the type of receptor determines whether the smooth muscle is inhibited or excited and also determines which of the two transmitters, acetylcholine or norepinephrine, is effective in causing the excitation or inhibition. www.indiandentalacademy.com
  105. 105. Action Potentials in Smooth Muscle The normal resting membrane potential is usually about -50 to -60 millivolts The action potentials of visceral smooth muscle occur in one of two forms: – Spike potentials – Action potentials with plateaus. www.indiandentalacademy.com
  106. 106. Spike Potentials similar to the skeletal muscles occur in most types of unitary smooth muscle duration -10 to 50 milliseconds www.indiandentalacademy.com
  107. 107. Action Potentials with PlateausThe repolarization is delayed for several hundred to as much as 1000 milliseconds (1 second). Importance - can account for the prolonged contraction that occurs in the ureter, the uterus etc www.indiandentalacademy.com
  108. 108. Smooth muscle cell membrane have more voltagegated calcium channels than does skeletal muscle but few voltage gated sodium channels. Thus calcium ions are mainly responsible for the action potential. They open more slowly than sodium channels, and remain open much longer accounting for the prolonged plateau action potentials Calcium ions act directly on the smooth muscle contractile mechanism to cause contraction. www.indiandentalacademy.com
  109. 109. Slow Wave Potentials Some smooth muscle are self-excitatory. ie: action potential arises within the smooth muscle cell without an extrinsic stimulus. Often associated with a basic slow wave rhythm of the membrane potential. It is not a self regenerative process that spreads progressively over the membranes of the muscle fibers www.indiandentalacademy.com
  110. 110. Cause – The membrane potential becomes more negative when sodium is pumped rapidly and less negative when the sodium pump becomes less active. – Or - the conductance of the ion channels increase and decrease rhythmically. When they are strong enough, they can initiate action potentials. www.indiandentalacademy.com
  111. 111. Source of Calcium Ions Almost all the calcium ions that cause contraction enter the muscle cell from the extracellular fluid at the time of the action potential. There is a rapid diffusion of the calcium ions into the cell from the extracellular fluid when the calcium pores open. Time required - 200 to 300 milliseconds and is called - latent period This latent period is about 50 times as great for smooth muscle as for skeletal muscle contraction. www.indiandentalacademy.com
  112. 112. When the extracellular fluid calcium ion concentration falls to 1/3 to 1/10 normal, smooth muscle contraction usually ceases. Calcium ions are removed by a calcium pump that pumps calcium ions out into the extracellular fluid, or into a sarcoplasmic reticulum www.indiandentalacademy.com
  113. 113. Smooth Muscle Sarcoplasmic Reticulumcaveolae – analog of the transverse tubule system of skeletal muscle. They excite calcium ion release from the abutting sarcoplasmic tubules www.indiandentalacademy.com
  114. 114. MUSCLE RECEPTORS Receptors provide information regarding: – Chemical changes (i.e., O2, CO2, H+) – Tension development: Golgi Tendon Organs – Muscle length: Muscle spindles Information from these receptors provides information about the energetic requirements of exercising muscle and about movement patterns www.indiandentalacademy.com
  115. 115. Muscle spindle – – Detect dynamic and static changes in muscle length– Stretch reflex – Stretch on muscle causes reflex contraction Golgi tendon organ (GTO) – – Monitor tension developed in muscle – Prevents damage during excessive force generation – Stimulation results in reflex relaxation of muscle www.indiandentalacademy.com
  116. 116. Muscle spindles respond to muscle stretch Gamma motor neurons are co activated during contraction – Cause contraction of fibers within muscle spindle – Deviations in consistency signal excessive stretch www.indiandentalacademy.com
  117. 117. Golgi Tendon Organ Located in tendon Monitor muscle tension Activation causes inhibition of alphamotor neuron Is a safety mechanism against excessive force during contraction www.indiandentalacademy.com
  118. 118. MYOTACTIC / STRETCH REFLEX www.indiandentalacademy.com
  119. 119. Causes contraction of stretched muscle Receptor – proprioceptive nerve endings called muscle spindles Impulses are conducted by group 1A sensory nerve endings Impulse carried by motoneurons / alpha efferent www.indiandentalacademy.com
  120. 120. Functional significance – serves as a mechanism for upright posture In mandible it acts to maintain the postural rest position in reln to the maxilla www.indiandentalacademy.com
  121. 121. CLASP KNIFE REFLEX /AUTOGENIC INHIBITION www.indiandentalacademy.com
  122. 122. Resistance is encountered as soon as the muscle is stretched throughout the initial part of the bending. This resistance is due to the hyperactive reflex contraction of the muscle in response to the myotactic reflex If flexion is forcibly carried further, a point is reached at which all resistance stops, and the previously rigid limb collapses readily "clasp-knife" reaction www.indiandentalacademy.com
  123. 123. functional significance - to protect the overload by preventing damaging contraction against strong stretching forces. The stimulus to elicit the clasp-knife reflex is excessive stretch and, when elicited, inhibits muscular contraction, thus causing the muscle to relax. www.indiandentalacademy.com
  124. 124. Receptors - Golgi tendon organs impulses are conducted by the Group 1B sensory nerve fiber Impulses act on the motor neuron, or alpha efferent. www.indiandentalacademy.com
  125. 125. NEURO TROPHISM Definition - interaction between nerves and other cells which initiate or control molecular modifications in other cells (Guth 1969) Or is a non impulse transmitting neural function that involves axoplasmic transport and provides from long term interactions between the nervous and innervated tissue that homeostatically regulate the morphological, compositional and functional integrity of those tissues. www.indiandentalacademy.com
  126. 126. Three types Neuro epithelial trophism Neuro visceral trophism Neuro muscular trophism NEURO-MUSCULAR TROPHISM: Skeletal muscle ontogenesis normally requires motor neuron innervation to proceed past the stage of myotubes Embryonic myogenesis is independent of neural innervation and trophic control. www.indiandentalacademy.com
  127. 127. Approximately at the myoblast stage of differentiation, neural innervation is established without which further myogenesis cannot continue. Neurotrophic influences are involved rather than conductive influences www.indiandentalacademy.com
  128. 128. Cross-innervation experiments show that many significant morphologic, biochemical and functional parameters of the re-innervated muscle come to resemble those of the muscle formerly innervated by the now ectopically implanted nerve. Therefore, these parameters of skeletal muscle are nervespecific, not muscle specific www.indiandentalacademy.com
  129. 129. Conformational features of myosin are determined by the nature of the innervation and that the complex chain of events leading to particular expression of the genetic – embryonic potential is not wholly within the cell, but also includes informational elements contributed by the nerve www.indiandentalacademy.com
  130. 130. Research shows that a qualitatively different myosin that resembles that of the muscle, formerly innervated by the nerve, is synthesized in crossinnvervated muscle, which indicates that a new species of protein has been synthesized, and it is therefore, suggested that the nerve influences gene expression in the cell. www.indiandentalacademy.com
  131. 131. Implication of these data: Since periosteal functional matrices regulate the size and shape of specifically related skeletal units, it is apparent that the genetic control of the structural, chemical and functional attributed of these same matrices cannot reside solely in the matrices themselves, but rather reflect constant neurotrophically regulated homeostatic control of genome. www.indiandentalacademy.com
  132. 132. Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com

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