This week…

• The functions of the Muscular System• The types of Muscle, where they are found

and what they do• Muscle cells • How muscles contract on the microscopic

level• How muscles use energy

THE MUSCULAR SYSTEM

Why do we have muscles?

Functions• Movement– Jump, run, walk–Move eyeballs, swallow, blink, smile– Blood pressure, moving food, releasing

urine, having a baby–Moving blood through the body

• Support– Posture and stabilizing joints

• Generate Heat

3Types of Muscle • 1. Skeletal Muscle tissue– Attach to and cover the skeletal system– STRIATED and VOLUNTARY muscle– Can contract fast, but gets tired– Adaptable for light touch or strong

• 2. Cardiac Muscle– Only found in the heart– STRIATED but INVOLUNTARY– Contracts at a steady rate

• 3. Smooth Muscle– Found in the walls of your organs– NOT STRIATED and INVOLUNTARY– Contracts slow and the contractions can last a while

Why is each muscle tissue good for where it is found?

- Skeletal- contracts fast, at variable amounts a lot or a little. We can control it for movements. Needs to rest though.- Cardiac- steady contractions. Can’t ever rest. We don’t want to have to think about beating our heart.- Smooth-slow and sustained contractions. Don’t want to have to think about moving our food along. Good for forcing things through our systems

Characteristics of Muscle• EXCITABILITY/ IRRITABILITY– Can receive and respond to a stimulus

• CONTRACTILITY– Can shorten when stimulated

• EXTENSIBILITY– Can be stretched or extended when relaxed

• ELASTICITY– Can resume length after being stretched

Microscopic Anatomy of a Muscle Cell

• Cell= Muscle Fiber– Very long- can run the length of the muscle

• Cell Membrane = Sarcolema• Many Nuclei• Glycosomes store large amounts of glycogen (for making

energy) and Myoglobin (stores Oxygen)• Cytoplasm = Sarcoplasm– Hundreds of Mitochondria here making ATP

• ER = Sarcoplasmic Reticulum– Stores Calcium for muscle contractions

Muscle cell made of MyofibrilsMyofibrils are cords of protein

2 types that alternateThick – made of MYOSINThin – made of ACTIN

A band = where thick and thin overlap (looks like DARK stripe)I band = only thin (looks like LIGHT stripe)SARCOMERE = from z disc to z disc

Myofibrils make up Muscle Cells

Muscle cells all held together with connective tissue into a muscle.

Muscles and Nerves

• Neuromuscular junction = where nerve meets muscle for stimulus

• Motor neurons = the nerve cells that stimulate the muscle fibers

• Motor End Plate/ Synaptic Cleft = the part of the muscle cell that interacts with the motor neurons

Muscles and Nerves

• Cell membranes have more positive ions on the outside than on the inside= RESTING MEMBRANE POTENTIAL

• Nerve stimulus causes positive ions to rush into cells= ACTION POTENTIAL

• NEUROTRANSMITTER = a chemical that carries the signal from a nerve to a muscle- Acetylcholine

How Info gets from Nerve to Muscle

• An action potential arrives at the end of the motor neuron – Releases Acetylcholine- Goes across Synaptic Cleft to Motor End Plate.

• Acetylcholine binds to muscle cell membrane causing positive (sodium) ions to rush into cell = Action potential in muscle cell

• Action potential causes muscle to contract

Neuromuscular Junction

How Muscles Contract

• Action potential allows CALCIUM into the muscle cells

• Calcium binds to troponin molecules in the thin filaments causing a shape change– it is like the key opening a lock

• Cross bridges form between Actin and Myosin while Calcium causes the breakdown of ATP– produces energy to move cross bridges and heat

The Sliding Filament Theory

• YouTube - Sarcomere Contraction - Process Of Muscle Contraction With Myosin & Actin.mp4

• Actin ratchets down the length of Myosin by forming and reforming cross-bridges

• Sarcomeres get shorter causing muscle to become shorter = Muscle contraction