2. Syllabus
• Mechanism of muscular contraction,
• summation of contractions and tetanus;
• dynamic units of muscle; role of action potential in the development
of muscular contractions;
Seminar:
• Heat generation during contraction process, energy of contraction;
muscular work and force; tiring of muscle; ergography;
• Muscle hypertrophy and hypotrophy
3. Motor Unit
• All the muscle fibres
innervated by a single nerve
fibre are called a motor
unit.
4. Motor unit
• All the muscle fibres innervated by a single nerve fibre are called a
motor unit.
• Small muscls, that react rapidly have more nerve fibres (laryngeal
muscles)
• Large muscles that do not require fine control have a several hundred
muscle fibres in a motor unit (soleus)
• On average a motor unit contains 80-100 muscle fibres.
5. • All the muscle fibres
innervated by a
single nerve fibre are
called a motor unit.
• Small muscls, that
react rapidly have
more nerve fibres
(laryngeal muscles)
6. • All the muscle fibres
innervated by a single
nerve fibre are called
a motor unit.
• Large muscles that do
not require fine
control have a several
hundred muscle fibres
in a motor unit
(soleus)
• On average a motor
unit contains 80-100
muscle fibres.
7.
8. Muscle contraction of different force
• Summation means the adding together of individual twitch
contractions to increase the intensity of overall muscle contraction.
• Summation occurs in two ways:
1. Multiple fibre summation – increasing the number of motor units
2. Frequency summation – increasing the frequency of summation,
that leads to tetanization
9. Multiple fibre summation
• CNS sends signals to contract a
muscle.
• A weak signal stimulates a small
motor unit, a strong signal stimulates
a larger motor unit. – Size Principle
• Larger units have 50 times the
contractile force of smaller motor
units.
• Size principle allows gradation of
contraction when greater and greater
amount of force is required.
10.
11. Frequency summation
• Individual twitch contractions
occurring one after another at low
frequency of stimulation are summed.
• As the frequency increases there is a
point where much contraction
happens, a new contraction happens
before the previous one is over. S a
resut the 2nd contraction added
partially to the 1st etc, total strength
of contraction rises progressively with
increasing frequency.
13. Maximum strength of contraction
• 1 cm squared – 3-4 kg
• 1 inch squared – 50 pounds
• 1 Inch = 2.54 cm
• 1 pound = 0.45 kg
• Quadriceps has 16 square inch muscle belly – on it may apply
800 pound of tension.
14.
15. Changing the muscle length
Starecase effect (Treppe)
• Contraction after the long length - its strength is little
• After 10-50 twitches later its strength can increase twice.
• Unknown process, suggestion – increase of Ca ions in the
cytsol, because of release of Ca from SR with each successive
AP
16. Skeletal muscle tone
Muscle Sensory Receptors
should send informations
about the following
parameters of the muscle:
• Its length
• Instantenous tension
• How rapidly does the
length or tension change
17. Muscle Sensory Receptors
should send informations
about the following
parameters of the muscle:
• Its length
• Instantenous tension
• How rapidly does the
length or tension change
19. Remodelling of Muscle to match the function
• Hypertrophy
• Atrophy
• Poliomyelitis: when some nerves are destroyed, the old ones branch
to create new axons and innervate paralyzed muscle fibres. Thus, the
motor unit increases – macromotor units are created. The finennes of
contraction decreases.
• Muscular dystrophy: genetic disorder – X linked recessive, weakness
and degradation of muscle fibres due to the abnormal protein
DYSTROPHIN that attaches actin to muscle cell membrane – thus
contractile apparatus does not work.
20. Role of action potential in the development
of muscular contractions;
• Motor end plate
• Synaptic trough
• Synaptic cleft
• Subneural cleft
26. Enhancement or block of transmission
• Curare –competes with acetylcholine for receptors, thus locks Aps
• Botulinium toxin – Decreses the release of acetycholin
• Nicotine, carbachol and metacholine – the same effects as
acetylcholine
