muscular system

• muscular system functions - 1. Movement

  2. Maintain posture

  3. Respiration

  4. Heat production

  5. Communication

  6. Organ and vessel constriction

  7. Heart contraction
• Contractility - the ability of muscle to shorten

  forcefully, or contract

  Excitability - the capacity of muscle to respond to a

  stimulus

  Extensibility - the ability to be stretched beyond its

  normal resting length and still be able to contract

  Elasticity - the ability of the muscle to recoil to its

  original resting length after it has been stretched
• resting membrane potential- The electrical charge difference across the cell membrane of an unstimulated cell
• Muscle fibers- have a resting membrane potential, but can

  also perform action potentials.
• resting membrane potential- is due to the inside of the

  membrane being negatively charged in comparison to the

  outside of the membrane being positively charged.
• Action potentials - are due to the membrane having gated

  channels.
• Depolarization- during the action potential is when

  the inside of the cell membrane becomes more

  positively charged than the outside of the cell

  membrane.
• Near the end of depolarization, the positive charge

  causes gated Na+ channels to close and gated K+ channels to open.
• repolarization- Opening of gated K+ channels of the cell membrane
• Repolarization- is due to the exit of K+ from the cell.
• In a muscle fiber, an action potential results in muscle contraction.
• Neurotransmitters- are chemicals that

  stimulate or inhibit postsynaptic cells.
• Acetylcholine- is the neurotransmitter that

  stimulates skeletal muscles.
• muscle twitch- is a single contraction of a muscle

  fiber in response to a stimulus.
• muscle twitch has three phases: latent phase,

  contraction phase, and relaxation phase.
• latent phase is the time between the application

  of a stimulus and the beginning of contraction.
• contraction phase is the time during which the

  muscle contracts
• relaxation phase is the time

  during which the muscle relaxes.
• In summation, individual muscles contract more

  forcefully.
• Tetanus- is a sustained contraction that occurs when

  the frequency of stimulation is so rapid that no

  relaxation occurs.
• Recruitment- is the stimulation of several motor

  units.
• Slow twitch fibers

  ◆ contract slowly

  ◆ fatigue slowly

  ◆ have a considerable amount of myoglobin

  ◆ use aerobic respiration

  ◆ are dark in color

  ◆ used by long distance runners
• Fast twitch fibers

  ◆ contract quickly

  ◆ fatigue quickly

  ◆ use anaerobic respiration

  ◆ energy from glycogen

  ◆ light color

  ◆ used by sprinters
• Muscle fibers- are very energy-demanding cells

  whether at rest or during any form of

  exercise.
• This energy comes from either aerobic (with

  O2) or anaerobic (without O2) ATP production
• Fatigue- is a temporary state of reduced work

  capacity.
• Without fatigue, muscle fibers would be

  worked to the point of structural damage to

  them and their supportive tissues.
• muscle tone- Constant tension produced by body muscles over long

  periods of time.
• muscle tone- Responsible for keeping the back and legs straight, the

  head in an upright position, and the abdomen from

  bulging.
• Smooth muscle- cells are non-striated small,

  spindle-shaped muscle cells, usually with one

  nucleus per cell.
• tendon- connects skeletal muscle to bone.
• Aponeuroses- are broad, sheetlike tendons.
• retinaculum- is a band of connective tissue that

  holds down the tendons at each wrist and ankle.
• Skeletal muscle attachments have an origin and an

  insertion
• origin- being the attachment at

  the least mobile location.
• insertion- is the end of the muscle attached to

  the bone undergoing the greatest movement.
• Muscles are named according to:

  1. Location – e.g. pectoralis muscle is located in the

  chest.

  2. Size – large or small, short or long.

  3. Shape - triangular, quadrate, rectangular, or round.

  4. Orientation of fascicles – run straight (rectus) or at

  an angle (oblique).
• Effects of Aging on Skeletal Muscle

  ❖ Loss of muscle fibers

  ❖ Decrease in surface area of neuromuscular

  junction

  ❖ Decrease in number of motor neurons

  ❖ Decrease in density of skeletal muscle cell

  capillaries