Energetics Of Muscle Contraction Flashcards
Muscle contraction depends on energy supplied by ATP. True or false?
True
In muscle contraction, ATP is used for
(1) Pumping calcium ions from the sarcoplasm into the sarcoplasmic reticulum after the contraction is over, and
(2) Pumping Na and K ions through the muscle fiber membrane to maintain appropriate ionic environment for propagation of muscle fiber action potentials
The concentration of ATP in the muscle fiber, is sufficient to maintain full contraction for how long?
1 to 2 seconds at most
Transfer of ATP for muscle contraction
ATP is split to form ADP, which transfers energy from the ATP molecule to the contracting machinery of the muscle fiber
ADP is rephosphorylated to form new ATP within another fraction of a second, which allows the muscle to continue its contraction.
There are __ major means by which ATP is rephosphorylated. They include:
- Using Phosphocreatinine, Glycogen (by glycolysis), Oxidative fat metabolism
How does phosphocreatinine supply energy?
The high-energy phosphate bond of phosphocreatine has a slightly higher amount of free energy than that of each ATP bond.
Therefore, phosphocreatine is instantly cleaved, and its released energy causes bonding of a new phosphate ion to ADP to reconstitute the ATP.
Total amount of phosphocreatine in the muscle fiber relative to ATP is
about five times as great as the ATP.
Therefore, the combined energy of both the stored ATP and the phosphocreatine in the muscle is capable of causing maximal muscle contraction for how long?
…only 5 to 8 seconds.
How glycolysis produces more energy
Rapid enzymatic breakdown of the glycogen to pyruvic acid and lactic acid liberates energy that is used to convert ADP to ATP.
The ATP can then be used directly to energize additional muscle contraction and also to re-form the stores of phosphocreatine.
The importance of glycolysis mechanism
First, the glycolytic reactions can occur even in the absence of oxygen.
Second, the rate of formation of ATP by the glycolytic process is about 2.5 times as rapid as ATP formation in response to cellular foodstuffs reacting with oxygen.
Downside of glycolysis for muscle contraction
So many end products of glycolysis accumulate in the muscle cells that glycolysis also loses its capability to sustain maximum muscle contraction after about 1 minute
What is oxidative metabolism?
Combining oxygen with the end products of glycolysis and with various other cellular foodstuffs to liberate ATP. More than 95 per cent of all energy used by the muscles for sustained, longterm contraction is derived from this source.
For extremely long-term maximal muscle activity—over a period of many hours—by far the greatest proportion of energy comes from ___
Fats
Myopathy is…
A muscular disorder in which the dysfunction of muscle fiber leads to muscular weakness.
Muscular dystrophy
This is a disease characterized by progressive degeneration and failure to regenerate of muscle fibers, without the involvement of nervous system.
Duchenne Muscular Dystrophy
Sex-linked recessive disorder due to the absence of a gene product called dystrophin in the X chromosome.
Dystrophin is necessary for…
the stability of sarcolemma.
Becker Muscular Dystrophy
- Sex-linked disorder
- Caused by the reduction in quantity or alteration of dystrophin
Common features of Becker Muscular Dystrophy
- Slow progressive weakness of legs and pelvis
- Pseudo-hypertrophy of calf muscles
- Difficulty in walking and fatigue.
Diseases involving muscle tone
Hypertonia
Hypotonia
Myotonia
Hypertonia
This is a muscular disease characterized by increased muscle tone and inability of the muscle to stretch
Hypertonia occurs in…
Upper motor neuron lesion
How hypertonia happens in UMN lesion
During upper motor neuron lesion, inhibition of lower motor neurons (gamma motor neurons in the spinal cord) is lost. This causes the exaggeration of lower motor neuron activity, resulting in hypertonia.
Spasticity is a motor disorder characterized by…
…stiffness of the certain muscles due to continuous contraction.
Hypertonicity is one of the major symptoms of
spasticity
Paralysis (complete loss of function) of the muscle due to hypertonicity is called
spastic paralysis.
Hypotonia is
…a muscular disease characterized by decreased muscle tone. The tone of the muscle is decreased or lost.
What happens to the muscle in hypotonia
- Muscle offers very little resistance to stretch
- Muscle becomes flaccid (lack of firmness) and the condition is called flaccidity.
The major cause for hypotonia is ___. Others are…
lower motor neuron lesion.
central nervous system dysfunction, genetic disorders or muscular disorders.
The paralysis of muscle with hypotonicity is called ___ and it results in ___.
flaccid paralysis, wastage of muscles
Clinical conditions associated with hypotonia are:
i. Down syndrome
ii. Myasthenia gravis
iii. Kernicterus (brain damage caused by jaundice in infants)
iv. Congenital cerebellar ataxia (incoordination)
v. Muscular dystrophy
vi. Congenital hypothyroidism
Myotonia is…
a congenital disease characterized by continuous contraction of muscle and slow relaxation even after the cessation of voluntary act.
Myotonia is caused by
mutation of genes of channel proteins in sarcolemma.
The main feature of Myotonia is…
…muscle stiffness, which is sometimes referred as cramps.
Types of myotonia
Becker-type myotonia
Thomsen-type myotonia
Becker-type myotonia or generalized myotonia
An autosomal (not sex-linked) recessive disorder produced by defective genes contributed by both the parents
Thomsen-type myotonia
Autosomal recessive disorder produced by defective gene contributed by one parent.
Muscles easily affected by myasthenia gravis are
muscles of the neck, limbs, eyeballs and eyelid movements
Symptoms of myasthenia Gravis
- Slow and weak muscular contraction
- Inability to maintain the prolonged contraction of skeletal muscle
- Fatigue an weakness
- Double vision and droopy eyelids
- Difficulty in swallowing due to weakness of throat muscles and difficulty in speech
Lamberteaton syndrome
A disorder of neuromuscular junction caused by development of antibodies against calcium channel in the nerve terminal, resulting in reduction in the release of quanta of acetylcholine.
Name one disease similar to Myasthenia Gravis
Lamberteaton syndrome
Why is Lamberteaton syndrome called carcinomatous myopathy?
It is commonly associated with carcinoma
Features of Lamberteaton syndrome not seen in Myasthenia Gravis
Blurred vision and dry mouth.
McArdle disease
A glycogen storage disease (accumulation of glycogen in muscles) due to the mutation of genes involving the muscle glycogen phosphorylase, necessary for the breakdown of glycogen in muscles.
Symptoms of McArdle disease
Muscular pain and stiffness
Mitochondrial myopathy
An inherited disease due to the defects in the mitochondria (which provide critical source of energy) of muscle fibers.
Mitochondrial myopathy is inherited. True or false?
True
Nemaline myopathy
A congenital myopathy characterized by microscopic changes and formation of small rod-like structures in the muscle fibers. It is also called nemaline-rod myopathy
Nemaline myopathy is non-congenital. True or false?
False. It is.
Features of nemaline myopathy
Delayed development of motor activities and weakness of muscles
