Muscular System

  • Bones and ligaments do not produce movement
  • The body has more than 600 individual muscles
  • Muscles cause bones and supported structures to move by alternating between contractions and relaxation

Functions of the Muscles:

  • Muscle has the ability to contract, permitting muscle to perform various functions
  • Functions:
    • Movement
    • Stability
    • Control of body openings and passages
    • heat production

Movement:

  • Skeletal muscles:
    • Attach to bones by tendons
    • cross joints so when they contract, bones they attach to move
  • Smooth Muscles:
    • found on organ walls
    • contractions produce movement of organ contents
  • Cardiac Muscle:
    • produces atrial and ventricular contractions
    • pumps blood from the heart into the blood vessels

Stability:

  • Holds bones tightly together
    • stabilize joints
  • Small muscles hold vertebrae together
    • stabilize the spinal column

Control of body openings and passages:

  • Sphincters
    • Valve-like structures formed by muscles
    • Control movement of substances in and out of passages
    • Example: a urethral sphincter prevents or allows urinations

Heat:

  • Heat is released with muscle contractions
    • Helps the body maintain a normal temperature
    • moving the body can make you warmer if cold

Types of Muscle Tissue:

  • Skeletal Muscle
    • Attached to bone and skin of the face
    • produces body movement and facial expressions
    • Voluntary
  • Smooth Muscle:
    • walls of hollow organs, blood vessels, and iris of the eye
    • Moves contents through organs, vasoconstriction
    • Involuntary
  • Cardiac Muscle:
    • Walls of the heart
    • Pumps blood through heart
    • Involuntary

Skeletal Muscles:

  • Long, thin contractile fibers are striated
    • striations due to arrangement of thick and thin filaments
  • Under voluntary control
  • Attached to the bones of the skeleton by tendons
  • Allows for:
    • movement
    • facial expressions
    • breathing
    • swallowing
    • writing
    • talking
    • singing
    • posture
    • heat production
    • joint stability

Types of Muscle Tissue

  • Myocytes - muscle fibers
  • Sarcolemma - cell membrane
  • Sarcoplasm - cytoplasm of cell
  • Myofibrils - long structures in sarcoplasm
    • arrangement of filaments in myofibrils produce striations

Types of Muscle Tissue (Skeletal Muscles)

  • Muscle fibers respond to the neurotransmitter, acetylcholine
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    1. Motor impulse is initiated in the brain
  • \   
    1. Travels through the brain and spinal cord to nerve endings
  • \   
    1. Motor nerve endings (axons) depolarize
  • \   
    1. Calcium enters the axonal endings
  • \   
    1. Calcium causes the release of acetylcholine into the neuromuscular junctions and the muscle contractions
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    1. Following contractions, muscles release the enzyme acetylcholinesterase
    • Acetylcholinesterase breaks down acetylcholine
    • Acetylcholinesterase allows muscles to relax

Types of Muscle Tissue (Smooth Muscle)

  • Multiunit smooth muscles
    • In the iris of the eye and walls of Blood vessels
    • Responds to neurotransmitters and hormones
  • Visceral smooth muscles
    • In walls of hollow organs
    • spindle-shaped, non-striated, uninucleate fibers
    • responds to neurotransmitters
    • stimulate each other to contract so that muscle fibers contract and relax together in a rhythmic motion
    • peristalsis- rhythmic contraction that pushes substances through tubes of the body
    • neurotransmitters for smooth muscles contract involuntarily

Types of muscle tissue: cardiac muscle

  • Intercalated discs
    • striated, branched
    • connect groups of cardiac muscles
    • allow fibers in the group to contract and relax together
    • allows heart to work as a pump
  • Self-exciting
    • does not need nerve stimulation to contract
    • nerves speed up or slow down contractions

Neurotransmitters:

  • Acetylcholine - slows heart rate
  • Norepinephrine - speeds up heart rate

Production of Energy for Muscles:

  • ATP - adenosine triphosphate
    • a type of chemical energy
    • need for sustained or repeated muscle contractions
    • ATP = energy
    • More ATP = more energy
    • Less ATP = less energy
  • Muscle cells have three ways to store or make ATP

  

  1. Creatine Phosphate - rapid production of energy
  2. Aerobic Respiration ( with oxygen) - uses body’s store of glucose
  3. Lactic Acid production (anaerobic respiration without oxygen) = small amounts of ATP

Exercise and Contractions:

  • During intense strenuous activity, oxygen can be depleted. Why?
    • contraction of skeletal muscles decrease blood delivery to muscles
    • Nutrients and oxygen in contracted muscles decrease

Production of Energy: Oxygen Debt

  • Develops when skeletal muscles are used strenuously for several minutes and cells are low in oxygen

Production of Energy: Muscle Fatigue

  • Condition where muscles loose the ability to contract
  • Causes:
    • Accumulation of lactic acid
    • Interruption of blood supply to a muscle
    • A motor neuron looses its ability to release acetylcholine onto muscle fibers

Heat Production:

  • Cellular respiration is only about 40% effective
  • About 60% of energy found in glucose is lost as heat in cellular respiration
  • Muscle contractions generate heat because muscles use large amounts of nutrients to make ATP generating large amounts of heat
  • Heat is used to maintain body temperature

Structures of Skeletal muscles:

  • Skeletal muscles:
    • the major components of the muscular system
  • Composition
    • Connective tissue
    • skeletal muscle tissue
    • blood vessels
    • nerves
  • Structures: connective tissue coverings

  

  1. Fascia

      1. covers entire skeletal muscles 2. separates then from each other

  1. tendons

      1. a tough cord-like structure made of fibrous connective tissue 2. connects muscle to bone

  1. Aponeurosis

      1. a tough sheet-like structure made of fibrous connective tissue 2. attached muscle to other muscle

  1. epimysium

      1. a thin covering that is just below the fascia of the muscle and surrounds the entire muscle

  1. Perimysium

      1. connective tissue that divides muscles into sections called fascicles

  1. endomysium

      1. covering of connective tissue that surrounds individual muscle cells

  • Attachments and actions of the skeletal muscles
    • actions depend largely on what the muscles are attached to
    • Attachment sites:
    • Origin - an attachment site for a less moveable bone
    • Insertion - an attachment site for a more moveable bone
  • Movement usually produced by a group of muscles
    • Prime mover - muscle responsible for most of the movement
    • Synergist - muscles that help the prime mover by stabilizing joints
    • Antagonist (agonist) - produce movement opposite of the prime mover
    • relax when prime mover contracts