motor

• Motor system

  The motor system is often referred to as the muscular system or the skeletal-muscular system.

  Muscles work by contracting and relaxing.

  The role of the muscular system is to support the functioning of body systems such as:

  -locomotion

  -digestion

  -respiration

  -circulation

  -excretion
• 3 Types of Muscles

  There are over 600 muscles that can be sorted into 3 basic types:

  1. Smooth muscles
  2. Skeletal muscles
  3. Cardiac muscles
• Smooth Muscle

  Smooth muscle makes up the internal lining of many of the internal organs including the stomach, uterus, esophagus, and blood vessels.

  1. Smooth muscle contraction is involuntary and is often used to move things throughout the body.
  2. YES; spindle-shaped
  3. NO; striped
• Cardiac Muscle

  Cardiac muscle is the muscle found in the heart.

  It is the muscle that makes the heart beat.

  Cardiac muscle contracts and relaxes involuntarily and is under control of the automatic nervous system.

  YES; spindle-shaped

  YES; striped

  They appear to make connections between neighboring muscle cells.
• Skeletal Muscle

  Skeletal muscle are the muscles attached to the skeleton.

  1. They make the locomotion of the body possible and are responsible for much of the heat produced by the body.
  2. Skeletal muscles are under our voluntary control.
  3. We consciously control their movements.
  4. NO; spindle-shaped
  5. YES; striped
  6. Skeletal muscles are connected to the bones by connective tissue called tendons.
• Skeletal Muscles - Lengthening and Shortening

  When skeletal muscles contract, they shorten, pulling the body parts attached to it. When they relax, they lengthen.

  A body part only moves when a contracting muscle pulls on it.

  Relax → lengthen → loosening

  Contract → shorten → pulling
• Skeletal Muscles - Antagonistic Muscles

  7. Many skeletal muscles are arranged in pairs that work against each other to make a joint move. These are called ANTAGONISTIC muscles.

  8. A muscle that contracts to bend a joint is called a flexor.

  9. A muscle that contracts to straighten a joint is called an extensor.

  eg. Biceps and triceps

  biceps → flexor → "flex" arm

  triceps → extensor → "extend" arm
• Muscle Contraction - The Sliding Filament Theory

  Not all is known about muscle contraction, but the sliding filament theory provides a working model to help explain what is believed to be happening.

  1. Muscle cells are called fibers.
  2. Groups of these fibers/cells are packaged together and surrounded by a membrane called a sarcolemma.
  3. Muscle cells often have more than one nucleus.
• Muscle Contraction - The Sliding Filament Theory Part 2

  2. Inside each fiber (cell) are 2 types of protein filaments (collectively called myofilaments): ACTIN and MYOSIN.

  3. Myosin comes in different forms and is responsible for fast and slow twitch muscles.

  slow = marathon

  fast = sprint

  4. One sarcomere is the active basic unit (like a nephron) of a muscle and is made up of one set of myosin and two sets of actin.
• Muscle Contraction - The Sliding Filament Theory Part 2

  Myosin - (thick) acts like a ratchet

  Actin - (thin) slides over the myosin (from each side) causing the muscle cell, the sarcolemma and therefore the entire muscle to shorten.

  5. Heat can be generated by the flexing actions of the actin and myosin filaments rubbing and creating friction.
• Muscle Contraction - The Sliding Filament Theory Part 3

  1. The Z-lines are where actin filaments are connected.

  2. As actin slides over the myosin, the Z-lines move closer together.

  3. At the same time, the H-zone (space between the actin fibers) shrinks.

  4. ATP is needed for contraction and in its absence, muscles become rigid. You need energy for movement.
• Muscle Contraction - The Sliding Filament Theory Part 3

  5. Released calcium ions play a role in causing ATP to release its energy and when it is stored again, the muscles can relax.

  6. Creatine phosphate helps in the production of ATP in muscles through cellular respiration. It donates phosphate. High levels allow muscles to be active for longer without suffering fatigue.

  8. Oxygen is needed as well or else cellular respiration slows and lactic acid builds up. This is oxygen debt.
• Muscle Contraction - Nerve Impulse

  The contraction itself is caused by a nerve impulse.

  2. The impulse sets off a series of phases:

  -Latent (pause between impulse and action)

  -Contraction

  -Relaxation

  3. Impulses are sent very close together and can be summed (added together) in a process called summation.

  4. Summation → stronger contraction

  5. Too close together and the relaxation phase gets skipped leading to constant contraction → tetanus
• Injury and Atrophy

  1. cardiac and smooth are big problems.

  2. Skeletal muscle injuries include damage to the muscle cells themselves (cuts and bruises), tendon problems (connectors of muscle and bone), sprains & dislocations.

  3. As these heal, the muscles may not be used as much and can atrophy or waste away.

  4. Cells are not lost but the proteins inside can be.

  5. Fewer proteins → weaker muscle

  Working out does NOT add muscle cells, it just makes the cells stronger.

  Disuse returns them to their previous state.
• Different Types of Contraction

  Concentric contraction - muscle contracts and shortens

  Eccentric contraction - muscle contracts and lengthens

  Isometric contraction - when contraction perfectly matches load