Functional anatomy

• Structure of skeletal muscle

  • Epimysium
  • Endomysium
  • Muscle belly
  • Fascicle
  • Perimysium
  • Muscle fiber
  • Myofibril
• Structure of skeletal muscle

  1. Skeletal muscle is surrounded by an epimysium

  2. Skeletal muscle/ muscle belly is made up of bundles of muscle fibers (fascicles) surrounded by a perimysium

  3. Each fascicle contains individual muscle fibers, surrounded by an endomysium

  4. Each fiber is arranged into myofibrils

  5. Myofibrils contain a chain of sarcomeres, which are composed of acting and myosin filaments
• Concentric contraction


  Muscle shorts, opposite gravitational pull
• Eccentric contraction


  Muscle lengthens, in the same direction as gravitational pull
• Actin filaments attached to z line and pull the z line towards the midline of the sarcomere in a concentric contraction
• Myosin filaments are thick proteins filaments which contains cross bridges. The myosin cross bridges attach to the actin when stimulated in the presence of calcium
• Sliding Filament Theory


  1. Neurochemical stimulation results in calcium being released by the sarcoplasmic reticulum

  2. Causes the binding to troponin and moving the tropomyosin to reveal a binding site for myosin heads to attach

  3. Myosin heads bind to actin filaments creating a cross bridge to reveal a binding site for the myosin head to connect this is due to calcium binding to the actin filaments creating a cross bridge

  4. Breakdown of ATP released energy to stimulated the myosin cross bridges to pull the actin filaments towards the midline of the sarcomere

  5. This results in shortening of the sarcomeres as the actin and myosin filaments 'slide over' each other, causing x line to come closer together the h zone to shorten, the A band remain the same and the I band to shorten as well

  6. Shortening each sarcomere shortens the myofibril resulting in the shortening of the muscle fiber and movement occurs

  7. Cross bridges attach and reattach at different times to create movement and maintain tension

  8. Excess ATP disconnects the myosin head from the actin filament as the myosin and actin filaments returns to a relaxed position
• Slow twitch fibers (Type I)

  • Increased capillary density to allow increased delivery of oxygen to working muscles
  • Increased mitochondria for improved production of ATP
  • Increased myoglobin for improved storage of ATP
  • Increased aerobic enzymes for increased ATP production
• Slow twitch fibers (Type I)

  • Marathon runner
• Fast twitch Type IIA


  • Intermediate speed of contraction
  • Moderate levels of myoglobin
  • Moderate levels of mitochondria
  • Moderate levels of blood capillaries
• Fast twitch Type IIA

  • 400 M, 800m run
• Fast twitch IIB


  • High force of contraction
  • Low resistance to fatigue
  • Rapid contraction speed (used for speed, strength and power activities)
  • Large cross sectional area which allows for greater muscle force and power to be generated
• Fast twitch IIB


  • 100, 200 sprint, throw/ jumps
• The greater the diameter of the fibers

  The larger the neuron needed to activate the muscle fibers
• Muscle Fiber types recruitment

  1. During low intensity Type I are recruited because low stimulus threshold, low intensity for motor unit to fire

  2. At high level intensity- type IIA are predominantly recruited, fibers larger in diameter, a higher stimulus threshold, intensity required for the motor unit to fire is higher than Type I but lower than type IIB

  3. At very high intensity- type IIB are recruited fibers very large in diameter, higher stimulus threshold means the stimulus intensity required for the motor unit to fire is very high
• Comparison of Muscle Fiber types

  • Slow twitch Type I
  • Fast twitch Type IIA
  • Fast twitch type IIB
• Force-Velocity


  Describes the relationship between force production and the velocity of movement
• Concentric contraction


  The greater the force required, the slower the speed of contraction
• Eccentric contraction


  The greater the force required the faster the velocity of contraction
• Force-Length


  Relates to the amount of muscle force that can be produced at varying muscle lengths
• The joint angle at which the muscle can generate its greatest force varies for different body parts but is normally near the middle of the joints range of motion as this allows the greatest number of cross bridges to be attached
• Parts of the nervous system

  • Central nervous system
  • Peripheral nervous system
• Motor Neuron


  A cell within the nervous system that transmits impulse to other nerve cells or muscles
• Parts of a motor neuron

  • Dendrites
  • Cell body
  • Axon
• Motor unit


  The motor neuron and the fibers it activates
• The motor neuron is just one cell, however a motor unit, is the neuron and the fibers it activates
• Nervous control of the muscular system

  1. Brain sends messages in the form of an action potential to the spinal cord

  2. Spinal cord is responsible for the transmission of the message between the brain and the muscle and from the muscle / body to the brain

  3. Motor neurons receive the messages/ action potential from the spinal cord and delivers it to the targeted muscle and movement occurs

  4. Sensory neurons sends messages back to the brain via the spinal cord

  5. Brain analyzes the information delivery by the spinal cord to determine next action- process repeats
• Smaller motor unit


  Activates a small number of muscle fibers, more precise action of the muscle
• Larger motor unit


  Activates a larger number of muscle fibers, requires a larger action potential and results in the creation of gross motor skills
• All or none principle

  When a motor unit receives action potential to threshold, all the muscle fibers associated with that motor units will contract to their maximum potential
• Recruiting more motor units

  Motor units are recruited in order depending on exercise intensity. Increasing the number of motor units fired increases amount of force that can be generated
• Motor unit recruitment


  Motor unit is the neuron and the fibers it activate however muscle fiber recruitment is when it is activated, in order of Type I then type IIA and lastly Type IIB
• Increasing force produced by a muscle

  1. Increasing the number of motor units recruited by increase the size of the stimulus. Increase in the number of motor units used in generating force will increase the size of the force generated

  2. Increasing the rate at which impulses are sent to the motor unit resulting in the motor unit firing repeatedly to increase the force generated