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Features of Muscles
Functions of Muscular System
- Heat production
Connective Tissue of Muscle
Fascia: deep fascia vs superficial fascia
Deep Fascia divisons
- Epimysium = covers whole muscle
- Perimysium = covers bundles, or fascicles
- Endomysium = covers muscle cells, or fibers
Tendons and aperonosis
Dense regular connective tissue
Form attachments between muscle fascia and the periosteum of bone
Cell membrane =
scant; called sarcoplasm
sarcoplasmic reticulum (SR)
Tubule b/w sacs=
transverse tubule (TT)
Extends the length of the fiber, dominating the sarcoplasm.
Consist of two types of protein arrangements: thick filaments and thin filaments
Thick and Thin Filaments
- Composed of the very large protein myosin
- Appear like thick braids
- Composed of three proteins: actin, troponin, and
- The 3 proteins are bound together to form a complex that
- is thinner than the thick filaments
- Often called the functional subunit of the muscle fiber
- Consists of the region of a myofibril between Z lines
- Thus the myofibril is a linear sequence of sarcomeres
Resting Membrane Potential
A small electric charge exists on a living cell membrane
- Caused by a concentration gradient of mainly sodium and
- potassium ions; sodium on the outside and potassium on the inside
- The ions tend to leak across the cell membrane in an effort to restore equilibrium. To
- counter this, a transmembrane protein, the sodium-potassium pump, pumps sodium back out and potassium in, maintaining the gradient.
Muscle Cells are Excitable
That means their cell membranes maintain the resting membrane potential and are capable of responding to change resulting in an opening of the sodium and potassium gates, which allows the ions to flow readily: sodium in and potassium out.
The rapid phenomenon of ionic reversal along the membrane is called an action potential.
As excitable cells, muscle cells require an external stimulus to contract
The motor neuron originates from the brain or spinal cord.
The motor neuron terminates at many muscle fibers.
- One motor neuron and the muscle fibers it innervates is
- called the motor unit.
The microscopic area between a motor neuron terminal end and a muscle fiber is called the neuromuscular junction (NMJ).
- It consists of:
- Synaptic cleft
- Motor end plate
- Motor neuron terminal end
- the narrow space separating the motor neuron terminus and the muscle fiber.
- It is filled with interstitial fluid.
Motor end plate
- he highly folded sarcolemma that faces the synaptic cleft.
- It includes junctional folds that increase its surface area and number of receptors, and an enzyme that breaks down acetylcholine known as acetylcholinesterase.
Motor neuron terminal end
the enlarged terminus that contains vesicles containing the neurotransmitter acetycholine (ACh).
Function of Neuromuscular Junction
When the action potential arrives at the motor neuron terminus, calcium ions enter the motor neuron to stimulate the release of Ach from the synaptic vesicles.
ACh diffuses across the synaptic cleft to the motor end plate of the muscle fiber.
ACh binds to receptors on the motor end plate, triggering ion channels to open (by increasing membrane permeability).
Sodium ions flow through the open channels to enter the muscle cell, which initiates action potentials in the muscle cell.
Acetylcholinesterase breaks down the receptor-bound ACh.