MUSCULAR SYSTEM Human Systems

Main Understanding Describe in general, the action of actin and myosin in muscle contraction and heat production.

Introductory video Watch up to 2:20 Up to 2:20 to introduce the types of muscles

THREE (3) TYPES OF MUSCLE TISSUE Smooth: Have 1 nucleus; Arranged in parallel lines; Contract involuntarily; Found in certain blood vessels, iris of the eye, digestive system (intestines); Does not fatigue easily Cardiac: Cells are tubular and striated (bands of light and dark); Contraction is involuntary; Does not fatigue Skeletal: Tubular and striated; Contraction is voluntary; Are very long; Have many nuclei because it needs a lot of energy and materials

Three Types of muscle Smooth: found in stomach, airways, blood vessels Helps with involuntary functions moving fluids and material by contracting and relaxing Not striated: not striped

Three types of muscle 2. Cardiac muscle: heart muscle Involuntary: pumps blood through your heart Striated: striped muscle

Three types of muscle 3. Skeletal Muscle: the muscles used for movement Mainly voluntary Usually attached to bones and create movement by relaxing and contracting Striated: has stripes

FUNCTIONS OF SKELETAL MUSCLES Support – allow us to stand and remain upright Move bones – allow us to move and have facial expression Help maintain body temp – release large amounts of heat Help protect organs and stabilize joints

COOPERATION OF SKELETAL MUSCLE When muscles contract they shorten They can ONLY pull Because of this muscles must work together to bend joints (work in pairs - antagonistic muscles ) Example: bicep and tricep Figure 10.2 pg 333

Skeletal muscle: Myofibrils made of tiny parallel threads called myofibrils

MyoFibrils: Made of Sarcomeres Myofibrils are made of repeating contractile units called sarcomeres

Muscle ↓ Muscle-fibre bundle Muscle fibre Myofibrils Myofilaments

Video Watch from 3:57- 4:36.

Sarcomeres Made of two myofilaments (strands of protein): actin and myosin Thin filaments: made of actin Thick filaments: made of myosin Sarcomeres separated by Z-lines

Video Watch from 4:36- 5:12

Muscle Contraction in a sarcomere Sliding filament theory: when muscle contraction occurs the myosin slides past the actin Two body guards that prevent myosin attaching to actin: troponin and tropomyosin. Step one: Brain stimulates the muscle, releasing calcium Calcium attaches to troponin which moves tropomyosin. Frees up a space where myosin can attach

MUSCLE CONTRACTIONS Involve the actions of two types of myofilaments Actin myofilament Thin Have two strands of actin molecules that wrap around each other

10X longer than actin and a different shape Myosin filament Thick Two strands of protein molecules wound around each other 10X longer than actin and a different shape

We will watch from 6:40- 9:15. 6:40- 9:15

Step Two: ATP binds to the myosin head, ATP breaks down into ADP + Pi. The myosin head is in an extended position like a stretched spring

Step Three: Myosin binds to actin and pulls, shrinking the sarcomere and contracting the muscle. This pulling is called a powerstroke ADP +Pi are released

Step Four: A new ATP binds to the myosin head attached to the actin The myosin is released from the actin

Cycle Repeats with Calcium Present The ATP then breaks down into ADP + Pi allowing the myosin head to again become extended. With calcium present, it can then reattach to actin and contract again

HOW MYOFILAMENTS CONTRACT heads of myosin move first are attached to actin myofilaments bends back and inward pulling the actin myofilament Requires ATP to work sliding filament model http://www.learnalberta.ca/content/seb20/html/interactiveLauncher.html?interactive=MyofilamentContraction.swf

ROLE OF CALCIUM at rest myosin heads are not bound to actin - blocked by tropomyosin calcium is needed to move the tropomyosin Calcium and troponin bind to make a complex which binds to tropomyosin, moving it out of the way http://www.learnalberta.ca/content/seb20/html/interactiveLauncher.html?interactive=Breakdown_ATP_CrossbridgeMovementDuringMuscleContraction.swf

MUSCLES AND HEALTH Atrophy occurs when muscles are not used reduction in size, tone and power can be permanent Hypertrophy increase in size of muscle fibers number of mitochondria increase through exercise improve strength endurance

Why do we shiver? Muscles involuntarily contract in response to a cold core body temperature Not very efficient Part of the ATP is released as heat