Muscle Tissue: Electrical excitability

Contractile proteins

- A thick filament and a myosin molecule - A string of actin molecules (Looks like strand of pearls) - During contraction, myosin heads connect with myosin binding sites on actin

The sarcomere structure

- An arrangement of thick and thin filaments in distinctive zones - A bands and I bands of a sarcomere give skeletal muscle fibers their striated (striped) appearance

Muscle proteins (sarcomeres are built from three groups of proteins)

- Contractile proteins (generate force during contraction) - Regulatory proteins (help switch the contraction process on and off) - Structural proteins (hold thick and thin filaments together; link myofibrils to sarcolemma)

Sarcomere

- Small compartment of a myofibril; functional units of muscle - Contain the thick filaments and thin filaments of contractile proteins

Parts of a sarcomere

- Z disc - A band (dark) - I band (light) - H zone - M line

know locations of

- motor end plate - synaptic terminal - synaptic cleft (space) - somatic motor neuron

What does it mean for a cell to be electrically excitable?

-A cell responds to an electrical stimulus -Changing electrical charge at the plasma membrane

Botulinum toxin (botox)

-Blocks exocytosis at synaptic bulb/terminal -Highly toxic; has medicinal uses

sub cellular structures to convert electrical excitation to contraction

1.Transverse tubules 2.Sarcoplasmic reticulum

Myofibrils

= Highly organized bundles of protein filaments -Several myofibrils are contained in a single muscle fiber

Transverse tubules

= Invaginations of the sarcolemma -Allow for electrical signal to quickly reach entire muscle fiber

Myasthenia Gravis

= Muscle weakness disease; autoimmune -Antibodies attack one's own ACh receptors

Curare

= Plant based poison blocks ACh receptors at motor end plate -Used by South American Indians in blowgun darts

Sarcoplasmic reticulum (SR)

= system of membranous sacs around each myofibril -When action potential reaches the SR, Ca2+ is released from SR

Motor unit

A somatic motor neuron and all the muscle fibers it innervates (controls).

EMG

Electromyography: Recording of the electrical activity of a muscle

Myosin

Major component of the thick filament

Actin

Major component of the thin filament

Neurotransmitter

a chemical released by a neuron to excite target cell

muscle action potential

an electrical signal that initiates muscle contraction

Regulatory muscle proteins (controlled by calcium ions)

bind to and change the shape of the regulatory proteins -> uncovers the myosin binding sites on actin

Acetylcholine (ACh)

initiates muscle contraction - this causes a muscle action potential

electrical change (action potential)

is a signal, It has to reach the myofibrils inside the cell and be converted to a chemical signal for muscle contraction.

During contraction

myosin slides actin toward M line to bring the Z discs together (shorten the sarcomere)

Synapse

region of communication between neuron and target cell

Motor end plate

sarcolemma at NMJ

The nervous system must

send a signal for the muscle fiber to contract, the signal gets converted to electrical change in the muscle fiber by having ions move in and out

Structural proteins contribute to

the alignment, stability, elasticity, and extensibility of myofibrils

Titin is

the third most plentiful protein in muscle (after actin and myosin). It connects the Z disc to the M line and accounts for much of the elasticity of myofibrils

Skeletal muscles are

voluntarily controlled

Neuromuscular junction (NMJ)

where the neuron and muscle fiber meet