Lab 4 Flashcards
Types of muscle cells in an organism
Smooth, striated and skeletal cells
What are the functions of the muscles
Enable motion
Maintain posture
Stability of joints
Participate in vital functions
What are the vital functions of the organism
Respiration
Blood circulation
Digestion
Micturition
Parturition
Prehension and swallowing
Generate heat
Cover skeleton and internal organs
How much of the body mass is made up of skeletal muscle
40 percent
What is skeletal muscle attached to the muscle by
Connective Tissue
What is skeletal muscle made up of
Fascicles (bundles of muscle fibers)
made up of muscle fibers
These are made up of myofibril
These have sarcomeres at the end of them
Inside sarcomeres theres myosin and actin filaments
What is each cell innervated by
Somatic motor neurons (neuromuscular junctions)
How do somatic motor neurons innervate the cell
voluntary contractions
What are somatic motor neurons capable of
tectonic contractions
What kind of metabolism do they have during exercise
aerobic and anaerobic
What kind of contractions and energy expenditure do they have
fast contractions and high energy expenditure
What is the difference between isotropic bands and anisotropic bands and what are they
They are parrallely arranged structural elements forming alternating strips ( at the same height in adjacent muscle fibers). A (anisotropic) bands are dark and more refractive in polarised light. I (isotropic) bands are bright and less refractive in polarised light
What are skeletal muscles made up of and describe what they are made up of
They are composed of many thousands of cells called myocytes. These cells are 10-100um thick and several dozen cm long (depending on the length of the muscle and arrangement of the fibers). Myocytes are cylindrical in shape, with many nuclei (peripherally) and fibrils arranged in parrallel - myofibrils (centrally). The fibers are in bunches and surrounded by connective tissue
What is the arrangement of myofibrils
The contractile fibrils (myofibrils, approx 1 um in diamater) consist of identical sections, the sarcomeres. The sarcomere is the
basic structural and functional unit of skeletal muscles. Length of the
sarcomere at rest: 2 -2.2 µm
What do sarcomeres consist of
The sarcomere
consists of:
- ½ band I,
- band A
- ½ of next band I
What are sarcomeres separated from each other by
Sarcomeres are separated from each other by Z lines (at the same heights in
adjacent myofibrils)
What filaments do sarcomeres consist of
thin - actin (form I bands) and thick -
myosin (form A bands)
How do the filaments work
The filaments do not shorten, but they they slide between each other when
the muscle contracts
In the cross-section, they form a hexagonal system (1m/6a), maintained by
stabilizing proteins.
What do thick filaments consist of and what do these substances contain
Thick filaments
consist of myosin
particles.
The myosin head
contains:
center for ATPase
activity
surface for
interaction with
actin
What do thin filaments consist of
Thin filaments
consist of
actin (contractile
protein) as
well as
troponin and
tropomyosin
(regulatory
proteins).
What is the contraction cross bridging cycle
The contraction of
myofilaments is the
result of the interaction
of actin and myosin,
which results in the
sliding of actin filaments
between the myosin and
shortening of the
sarcomeres.
What happens to actin at rest vs when released
At rest, actin is protected against interaction with
myosin by a regulatory protein - tropomyosin,
which covers the myosin binding site on the actin
filaments.
Once released from the sarcoplasmic reticulum,
calcium ions bind to the regulatory protein -
troponin.
What is troponin
Troponin is closely related to tropomyosin, which undergoes conformational changes after the addition of calcium ions, leading to the exposure of the myosin binding site on the actin filament
What do calcium and magnesium deficiencies lead to
Calcium and magnesium deficiencies
can lead to disturbances in the
contractile activity of skeletal muscles
called tetany. These are states of
increased neuromuscular excitability,
often with bouts of tonic cramps, e.g.
grass tetany in cattle (magnesium
deficiency) or postpartum tetany in
bitches (calcium deficiency).
What is the sarcoplasmatic reticulum
The sarcoplasmic reticulum is a
specialized membrane system
that entraps Ca2+ ions when
the muscles are at rest and
releases them when a nerve
impulse arrives.
What is the transverse tuburcle
On the border of A-band and
I-band there is an indwelling of
the cell membrane called the T
transverse tubule, on both
sides symmetrically there are
reservoirs of the smooth
sarcoplasmic reticulum
(marginal cisterns). This
arrangement is called a triad.
1st half of the biochemical mechanisms of contraction
The action potentials arriving at the
neuromuscular junction release
acetylcholine (Ach) from the motor
neurons.
The Ach receptor, located in the cell
membrane of the muscle fiber, is an
ion channel that opens after Ach
attaching to it.
It triggers an inward Na+ current,
responsible for depolarization of the
cell membrane and the creation of an
action potential.
The action potential spreads along the
muscle fiber to special cavities in the
cell membrane called T-tubules.
2nd half of the biochemical mechanisms of contraction
The T channel is located adjacent to
the marginal sarcoplasmic reticulum
(SR) cistern.
#
The spreading wave
of depolarization
along the T tubule
causes the release of
calcium ions from
the SR.
The other SR
fragments
containing Ca2+
-ATPase are
responsible for the
re-accumulation of
Ca2+ ions in the
marginal cisterns of
the SR, thus allowing
the contraction to
end.
What is a motor unit
Motor unit
- it is a group of
vertebrate
skeletal muscle
cells (muscle
fibers) innervated
by the same
nerve cell, thus
being jointly
stimulated and
simultaneously
working
(contracting).
#
The motor units of the same
muscle may show
different excitability
What does the threshold stimulus only activate
The threshold stimulus only
activates the motor units
with the lowest
excitability threshold.
What can stronger stimulus stimulate
Stronger stimuli stimulate
the contraction of units
with a higher excitability
threshold.
What can the maximum stimulus stimulate
The maximum stimulus
stimulates contraction of
all motor units in the
muscle.
Can the subthreshold stimuli cause a contraction
The subtreshold stimuli are
too weak to cause a
contraction so no
What can a single nervous stimulus cause
A single nervous stimulus
(α-motoneuron) causes the
maximum contraction of all
fibers of the motor unit
innervated by it according to the
“all or nothing” principle.
What does the strength of contraction depend on
The strength of contraction,
however, depends on the
frequency of stimulation of a
single motoneuron and the
number of recruited motor
units.
What does unit recruitment depend on
Unit recruitment depends on their
excitability. S units (lowest
excitable threshold) are
recruited first, followed by FR
units, finally FF.
Where are smooth muscles present
They are present in:
the wall of blood vessels
the wall of the organs of
the digestive and
respiratory systems
the urinary and genital
organs
the secretory/excretory
ducts
the in the eyeball
the skin
What are features of smooth muscles
They contract independently (you cannot consciously
make them contract)
They are innervated by the autonomic nervous system
They constrict slowly with low energy consumption
Contractions can be caused by different types of stimuli:
nerve, mechanical, chemical, hormonal, or pacemaker
cell stimuli
What is the structure of smooth muscle
Fusiform
mononuclear
cells;
2x more actin and
4x less myosin
than in skeletal
muscle;
No visible stripes.
How does smooth muscle compare to skeletal muscle
There are dense bodies
instead of the Z line
of skeletal muscles.
The contractile units are
pseudosarcomers.
Transverse bridges
between actin and
myosin are formed
and the filaments
slide one on another.
How does the contraction of smooth muscle work
The maximum contractile tension
developed by smooth muscles in terms of
the cross-sectional area does not differ
from that produced by striated muscles, but
with from 100 to 1000 times less energy
used.
Smooth muscle contraction is very slow,
the price paid for high energetic efficiency.
Energy for smooth muscle contraction
Give an example of pacemaker cells
Intestinal cels of
Cajal are an
example of
pacemaker cells
in smooth
muscle.
What is the function of gap junctions
Gap junctions - thanks to them, the
electrical potential spreads to neighboring
myocytes.
Show how pacemaker cells work
When does a single muscle contraction occur
A single contraction occurs when a muscle is subjected to a
single stimulus or when the frequency of stimuli is so low that
the next stimuli act after the muscle relaxes.
When does an incomplete tetanus contraction occur
Incomplete tetanus contraction arises when a muscle is
subjected to a series of stimuli of such frequency that
subsequent stimuli act on the muscle after the contraction
phase is over, during muscle relaxation.
When does a complete tetanus contraction occur
Complete tetanus contraction arises when a muscle is subjected
to a series of stimuli of such frequency that each successive
stimulus acts in the contraction phase, even before its end.
When does the strength of the contraction increase
The strength
of the
contraction
increases as
the
frequency of
the stimuli
increases,
because the
contractions
add up then.
What is the duration of the contraction of a single frog calf muscle
The duration of the
individual phases of
contraction of a single
frog calf muscle:
period of latent
excitation (A) = 0.01 s,
contraction period (B) =
0.04 s,
diastolic period (C) =
0.05 s
What happens during the incomplete tetanus contraction of a frog calf muscle
This type of contraction
can be achieved by
applying stimuli with a
frequency of 10 to 25·s-1
on the frog calf muscle
(for mammalian muscles
the frequency will be
higher).
The phase of latent
excitation occurs after
the activation of the first
stimulus and is the same
as in a single contraction.
What happens during the complete tetanus contraction of a frog muscle
This type of contraction
can be obtained using
stimuli with a frequency
of more than 25 · s-1 on
the frog calf muscle (for
mammalian muscles the
frequency will be higher).
The phase of latent
excitation occurs after
the activation of the first
stimulus and is the same
as in a single contraction.
What happens during a single frog smooth muscle contraction
The entire contraction of the smooth muscle from the frog’s
stomach may take about 100 seconds.
The latent excitation period (A) is significantly extended and
may last from 0.1 to 2 seconds.
The contraction phase (B) is also longer in duration than in
skeletal muscle.
The duration of the diastolic phase (C) is usually many times
longer than the systole phase.
Smooth muscles do not undergo tetanic contractions.
What is an isometric contraction
An isometric contraction is a contraction in which the developed forces
are unable to overcome the resistance, the muscle changes the
tension, not the length.
What is an isotonic contraction
Isotonic contraction is a contraction that in physiological conditions does
not occur at all (it occurs when one attachment is free), the muscle
changes length, while the tension does not change.
What is an auxotonic contraction
An auxotonic contraction is a typical contraction characteristic of muscle
activity. In phase I, there is a contraction with no change in length, but
with a change in tension - this is the isometric contraction phase. The
muscle tenses to a degree that balances the load. Phase II is the
shortening of the muscle while the tension remains unchanged - the
isotonic phase.
Give an example of an isotonic contraction and give an example of an isometric contraction
Isotonic contraction - e.g. lifting a weight at a
constant speed (constant tension)
Isometric contraction - e.g. an attempt to lift a
weight without taking it off the floor (the muscle
does not shorten)
Talk about the difference between isometric and isotonic contractions
In isometric
contraction,
the tension
produced by
the muscle is
less than the
load, in the
isotonic (and
second
auxotonic
phase) the
tension
exceeds the
load.
.
Force developed by a contracting muscle is directly proportional to
Number of transverse bridges (formed per unit time between the filaments of actin and myosin.)
Force generated by muscle is greatest when length of sacromere
Ensures the use of all actin-myosin bridges.
At optimal degree of streching what is the length of the sacromere? What is this calles
2.2 µm. The muscle resting length
Muscle resting length
1.Length of the muscle that is neither shortened nor stretched
2.Initially streched in living body- passive force created shortens length by 20% (Also shortened by 20% when muscle is isolated)
- Muscle develops gretest strength at rest
4.When the sarcomere is stretched above 3.5 µm, there is no contact between the actin and myosin filaments, which prevents the formation of a contraction force.
5.If the stretching exceeded by approx. 3 times the resting length, the continuity of the muscle structure is broken and the muscle breaks.
Absolute muscle strangth depends on
Physiological cross-section of the
muscle, i.e. perpendicular to the course of the fibers (spindleshaped vs, feathered)
Why does training increase muscle mass?
Increase in the synthesis of contractile proteins, manifested by the thickening of individual cells.
Factors that affect the growth of muscle mass excluding training
1.Exercise
2.Hormones(T)
3.Growth factors
4.Sex
5.Age
