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Mia Alvarez Per:3 Muscular System - Coggle Diagram
Mia Alvarez Per:3 Muscular System
Major functions of the muscular system
An impulse travels down a motor neuron axon
The motor neuron releases the neurotransmitter
acetylcholine (ACh)
ACh binds to ACh receptors in the muscle fiber
membrane
The sarcolemma is stimulated. An implulse travels over
the surface of the muscle fiber and deep into the fiber
through the transverse tubules
Muscle coverings (connective tissue coverings)
Layers of dense connective tissue, called fascia, surround and separate each muscle.
Fascia blends with the epimysium, the layer of connective tissue around each skeletal muscle
The perimysium extends inward from the epimysium, it surrounds bundles of skeletal muscle fibers, call fascicles. within each muscle.
Each muscle cell (fibers) is covered by a connective tissue layer called endomyium.
This connective tissue extends beyond the ends of the muscle,and give rise to tendons that are fused to the periosteum of bones
Sometimes muscles are connected to each other by broad sheets of connective tissue called aponeuroses
Sliding filament theory of muscle contraction
According to the sliding filament model of muscle contraction, during muscle
contraction, a myosin head attaches to a binding site on the actin filament forming a cross-bridge
Sarcomere
Myofibrils are made up of many units called sarcomeres, joined end-to-end
A sarcomere extends from one Z line to the next
I bands (light bands) are made up of actin filaments, which are anchored to the Z lines
A bands (dark bands) are made up of overlapping thick and thin filaments
In the center of the A band is the H zone, which consists of myosin filaments only
The M line, in the center of the H zone, consists of proteins that hold the myosin filaments in place
3 types of muscles & their functions
Skeletal muscle – the specialised tissue that is attached to bones and allows movement.
Smooth muscle – located in various internal structures including the digestive tract, uterus and blood vessels such as arteries
Cardiac muscle – the muscle specific to the heart
Names of all the skeletal muscles (including the facial muscles)
each muscle fiber is single, long, cylindrical muscle cells
cell membrane of muscle fiber is the sarcolemma
Cytoplasm of a muscle cell is the sarcoplasm; it contains many mitochondria and nuclei
Sarcoplasm contains parallel myofibrils, which are active in muscle contraction
Thick filaments in myofibrils consist of the protein myosin
Thin filaments in myofibrils are mainly composed of the protein actin, but also contain troponin and tropomyosin
The organization of these filaments produces bands called striations
Neuromuscular junction
Skeletal muscle fibers contract only when stimulated by a motor
neuron
Each skeletal muscle fiber (cell) is functionally (not physically) connected to the axon of a motor neuron, creating a synapse
The neuron communicates with the muscle fiber by way of
chemicals called neurotransmitters,which are released at the synapse
Neuromuscular junction: a synapse between a motor neuron and a muscle fiber that it regulates
The cytoplasm of the distal end of the motor neuron contains numerous mitochondria and synaptic vesicles storing neurotransmitters
The muscle fiber membrane in this area contains a specialized region called the motor end plate, in which the sarcolemma is tightly folded
The motor end plate contains specific receptors for the neurotransmitter
When an electrical impulse reaches the end of the axon of a motor neuron, synaptic vesicles release neurotransmitter into the synaptic cleft, the gap between the membranes of the neuron and muscle fiber
The neurotransmitters diffuse across the cleft, bind to the motor end plate, and stimulate the muscle fiber to contract
Action potential in a muscle fiber
Myosin consists of two twisted strands, with globular heads
projected outward along the strands
A group of myosin molecules forms a thick filament
Actin is a globular protein arranged in twisted filaments,
containing myosin binding sites
Troponin and tropomyosin are 2 proteins associated with the
surface of the actin molecules; together, these 3 proteins form the thin filaments