muscular system
what are the Muscle Functions:
1. Production of Movement
2. Maintenance of posture and body position
Muscle contraction is constantly allowing us to remain upright.
3. Guard entrances and exits
Encircle openings to digestive and urinary tracts. Control swallowing,
defecation and urination
4. Thermogenesis
Muscular contractions generate heat
Characteristics of Muscle Tissue
1. Excitability
2. Contractility
3. Extensibility
4. Elasticity
-The ability to receive and respond to a stimulus
In skeletal muscle, the stimulus is a neurotransmitter (chemical signal) release by a neuron (nerve cell).
~In smooth muscle, the stimulus could be a neurotransmitter, a hormone, stretch, pH, Pco2, or Po2. (the symbol means “a change in”)
~In cardiac muscle, the stimulus could be a neurotransmitter, a hormone, or stretch.
-The response is the generation of an electrical impulse that travels along the plasma membrane of the muscle cell.
1. Excitability
- The ability to shorten forcibly when adequately stimulated.
- This is the defining property of muscle tissue.
2. Contractility
- The ability to be stretched
3. Extensibility
- The ability to recoil and resume original length after being
stretched.
4. Elasticity
Types of Muscle Tissue
1. Skeletal muscle tissue
2. Cardiac muscle tissue
3.Smooth (visceral) muscle tissue
Associated with & attached to the skeleton
Under our conscious (voluntary) control
Microscopically the tissue appears striated
Cells are long, cylindrical & multinucleate
1. Skeletal muscle tissue
Makes up myocardium of heart
Unconsciously (involuntarily or autonomic) controlled
Microscopically appears striated
Cells are short, branching & have a single nucleus (uninucleated)
Cells connect to each other at intercalated discs
2. Cardiac muscle tissue
Makes up walls of organs (e.g the intestines) & blood vessels
Tissue is non-striated & involuntary (autonomic controlled)
Cells are short, spindle-shaped & have a single nucleus
(uninucleated)
Tissue is extremely extensible, while still retaining ability to contrac
3.Smooth (visceral) muscle tissue
The entire skeletal muscle is composed of _______
fascicles
• Each fascicle is a bundle of _________.
muscle fibers (muscle cells).
Each skeletal muscle cell is known as a ___________because
they are so long.
skeletal muscle fiber
part of muscle fiber
1. sarcolemma
2. sarcoplasmic reticulum
3. sarcosomes
4. sarcoplasm
_______ for plasma membrane . it has
invaginations that penetrate through the cell called transverse
tubules or T tubules.
sarcolemma
- ___________ for endoplasmic reticulum
- Surround each myofibril
- Stores calcium and releases it on demand for contraction
sarcoplasmic reticulum
____________ for mitochondria
sarcosomes
__________ for cytoplasm
sarcoplasm
• Each muscle fiber is composed of _____________
myofibrils
• Each myofibril is composed of bundles of __________
myofilament
Two types of myofilaments
1. Thin myofilament = actin filament
2. Thick myofilament = myosin filament
Connective Tissue Wrappings of Skeletal Muscle/ part of skeletal muscle
- Epimysium
- Perimysium
- Endomysium
– covers the entire skeletal muscle
Epimysium
– around a fascicle
Perimysium
– around single muscle fiber
Endomysium
•____________ are made the protein myosin
• IA single myosin protein molecule resembles 2 golf clubs whose shafts
have been twisted about one another- it has a “head” and a “tail”
• these myosin molecules are joined together to form a single thick filament
thick Myofilament
• Thick myofilaments are made the protein _______
• IA single _______ protein molecule resembles 2 golf clubs whose shafts have been twisted about one another- it has a “head” and a “tail”
• these ___________ molecules are joined together to form a single thick filament
myosin
The myosin head contains ____________ and it interacts with the binding
site at the thin (actin) filament during muscle contractio
ATP-binding site
• it is made up of 3 different types of protein: actin, tropomyosin, and troponin.
• it consists of a long helical double strand. This strand is a polymer that resembles a string of beads. Each “bead” is the globular protein
actin. On each actin subunit, there is a myosin binding site
• Loosely wrapped around the actin helix and covering the myosin binding site is the filamentous protein, tropomyosin (it covers the myosin binding site if muscle is not contracting).
• Bound to both the actin and the tropomyosin is a trio of proteins collectively known as troponin complex ( it contains binding site for Ca ions that will initiate conformational change in the tropomyosin molecule thus exposing the active site during contraction)
Thin Myofilaments
Each thin filament is made up of 3 different types of protein:
1. actin
2. tropomyosin
3. troponin
Myofibrils are aligned to give distrinct bands:
I band =
A band =
All the ends of the actin filaments are attached at the ____________
Z-line or Z-disc.
The portion of a myofibril that lies between two successive discs is called ___________ which is contractile unit of a muscle fiber
sarcomere
sarcolemma has invaginations that penetrate through the cell called ________.
transverse tubules or T tubules
• it consists of a long helical double strand. This strand is a polymer that resembles a string of beads. Each “bead” is the globular protein
_______.
actin
On each actin subunit, there is a _________
myosin binding site
• Loosely wrapped around the actin helix and covering the myosin binding site is the filamentous protein
• (it covers the myosin binding site if muscle is not contracting).
tropomyosin
• Bound to both the actin and the tropomyosin is a trio of proteins collectively known as _________( it contains binding site for Ca ions that will initiate conformational change in the tropomyosin molecule thus exposing the active site during contraction)
troponin complex
𝙙𝙖𝙧𝙠 𝙗𝙖𝙣𝙙. It contains the myosin filaments as well as the ends of the actin filaments.
A band
𝙡𝙞𝙜𝙝𝙩 𝙗𝙖𝙣𝙙. It contains only the actin filament
I band
- occurs when overlapping actin and myosin myofilaments
overlap further and shorten the muscle cell.
- Skeletal muscles require stimulation from the nervous system in order to
contract (Skeletal muscles must be stimulated by a nerve to contract
(motor neruron)
Muscle contraction
_______ are the nerve cells that cause muscle fibers to contract
Motor neurons
The point at which the motor neuron and the muscle sarcolemma
“meet” is referred to as the _______.
NEUROMUSCULAR JUNCTION
• All of the muscle fibers controlled by a single motor neuron constitute a
_______
motor unit
An action potential (AP), an electrical impulse (nerve signal), travels down to the ends of the axon of the motor neuron (axon terminals) resulting in the release of a chemical neurotransmitter, _______ into the synaptic cleft.
Acetylcholine (Ach)
•
gap between nerve and muscle
•
Nerve and muscle do not make contact
• Area between nerve and muscle is filled with interstitial fluid
Synaptic cleft
______diffuses across synaptic cleft & binds to
•receptors on muscle sarcolemma
Acetylcholine (Ach)
•This changes permeability to 𝙨𝙤𝙙𝙞𝙪𝙢 which result to sudden rush of sodium into sarcolemma that initiates the generation of ________
action potential within the muscle fiber
•The muscle action potential travels into the 𝙏𝙧𝙖𝙣𝙨𝙫𝙚𝙧𝙨𝙚 𝙩𝙪𝙗𝙪𝙡𝙚𝙨 (t-tubules) and causes the 𝙎𝙖𝙧𝙘𝙤𝙥𝙡𝙖𝙨𝙢𝙞𝙘 𝙍𝙚𝙩𝙞𝙘𝙪𝙡𝙪𝙢 to release stored 𝘾𝙖𝙡𝙘𝙞𝙪𝙢 𝙞𝙤𝙣𝙨 into the ______ .
•The increase in calcium triggers the contractile response.
Sarcoplasm
•The mechanics of muscle contraction follow the _______
SLIDING-FILAMENT THEORY
what are the step by step:
Step 1
The released calcium combines with Troponin complex which
pulls on the Tropomyosin and changes its orientation. This
exposes the myosin-binding sites on the actin myofilament
Step 2
Myosin head attaches to actin which needs ATP
Step 3
Once myosin is bound to actin, the myosin head will tilt toward
the center. This provides the “power stroke” for pulling the
actin filament. The results is sliding of the thin filament along
the thick filament
Step 4
Once the head is tilted the hydrolyzed ATP products (ADP + Pi)
are released which are previously attached from the head. A
new molecule of ATP binds to the head. This binding in turn
causes detachment of the head from the actin
Step 5
ATP is again hydrolyzed to form ADP + P which lead to the
reactivation of myosin head and a new power stroke cycle
continues.
•
Immediately after it binds to its receptors, Acetylcholine (Ach) will be broken
down by _________ – an enzyme present in the
synaptic cleft
•
If there are no longer Action Potentials generated on the motor neuron, no
more Acetylcholine (Ach) will be released
Acetylcholinesterase (AchE)
•
Acetylcholinesterase (AchE) will remove ______ from the motor
end plate, and transmission of Action Potentials on the muscle fiber will end
•
Calcium (Ca+) will be actively transported back into the Sarcolasmic
reticulum
•
With Ca removed from the sarcoplasm (& from troponin), tropomyosin will
re-cover the active sites of actin
•
No more cross-bridge interactions can form. Thin myofilaments slide back
to their resting state , thus causing muscle relaxation
Acetylcholine (Ach)
- an antoimmune disease (weakness and rapid fatigue of any of the muscle under voluntary control
Myathenia gravis