Anatomy and Physiology I Chapter 9 - Muscles and Muscle Tissue

Functions of the Muscular System

• Produce Movement

• Maintain Posture

• Stabilize Joints

• Generate Heat

Skeletal Tissue

Voluntary , Striated

Smooth Muscle Tisssue

Visceral, Nonstriated, Involuntary

Cardiac Muscle Tissue

Striated , Involuntary

Structure of a Muscle

Muscle → Fascicle → Fiber → Fibril → Sarcomere

Myofibril

Composed of sarcomeres

Fiber

Have a striated appearance, one part of fascicle

Sarcomere

Smallest unit of function

A bands

Middle Horizontally

H zone

Middle vertically, multiple lines

M line

Ends of sarcomeres

Z disk

Runs in a Z-shape in middle of I bands

Epimysium

Surrounds the whole muscle

Perimysium

Surrounds the fascicles

Endomysium

Surrounds fibers

Skeletal Muscle Contraction 1st Step

Neuromuscular Junction

Skeletal Muscle Contraction 2nd Step

Muscle Fiber Excitation

Skeletal Muscle Contraction 3rd Step

Excitation-Contraction Coupling

Skeletal Muscle Contraction 4th Step

Cross Bridge Cycle

What happens at the Neuromuscular Junction

1. Action potential goes down the axon

2. Neuron releases Ach

3. Ach binds to Sarcolemma

4. Ach causes end plate potential

What happens at muscle fiber excitation

1. Depolarization triggers action potential in Sarcolemma

What happens at Excitation-Contraction Coupling?

1. Action potential travels down the T tubules

2. SR releases Calcium Ions

3. Myosin Binds to Actin

What happens during the Cross Bridge Cycle

1. Myosin binds to Actin

2. ADP & P are released

3. ATP breaks down Actin & Myosin

4. Myosin returns to its original position

What are the steps of Smooth Muscle contraction

1. Calcium enters by either voltage or non-voltage gated channels

2. Ca binds to Calmodulin

3. Myosin is activated

4. Sliding Filament Theory

   • Remain the same length

   • Only slide

   • Actin = Thin

   • Myosin = Thick

ATP Generation Pathway #1

Direct Phosphorylation

• Creatine

• Net of 1 ATP

ATP Generation Pathway #2

Anaerobic

• 30 sec-2mins

• Lactic Acid & Alcohol

• Net of 2 ATP

ATP Generation Pathway #3

Aerobic

• Needs oxygen

• Produces 95% of ATP

• Slower

• 32 Net ATP gain

EPOC

• Oxygen Must be replenished

• Lactic Acid gets converted to pyruvic

• ATP is resythesized

  • Requires extra oxygen

  • Takes a while to cool down - car engine

  • Greatest effect after HIIT

Motor Unit

Nerve Muscle functional unit

• Consists of 1 Motor neuron and all fibers

Muscle Twitch

Response of a muscle to a single stimulation

3 Steps of Muscle Twitch

1. Latent

2. Contraction

3. Relaxation

Latent Period

ECC is occuring, not yet measurable

Contraction

Cross bridges are active

Relaxation

Pumping calcium back into the Sarcoplasmic Reticulum

Increase in frequency causes

Temporal summation

Increase in strength causes

Recruitment

Isotonic

Muscle changes in length, Actin Slides

Concentric

Muscle shortens

Eccentric

Muscle lengthens

Isometric

Muscle does not change length, Actin does not slide

Slow Oxidative Fibers

• Endurance

• Red

• Aerobic

• Slow Speed

Fast Oxidative Fibers

• Fast

• Red-pink

• Aerobic

• Sprinting Walking

Fast Glycolytic Fibers

• Fast

• Anaerobic

• White

• Short-term

Skeletal Site of Calcium

Troponin/Actin

Smooth Site of Calcium

Calodulim/Cytosol