Kin & Bio: Skeletal Muscles

  • Attach to bone via tendons

  • Muscle origin: attached to the proximal bone of a joint or least moveable

  • Muscle insertion: attached to the distal bone of a joint or most moveable

Skeletal muscle Functions:

  • Movement

  • Protection

  • Joint support

  • Heat production

Muscle-

Motor Unit:

  • Motor nerve and all the muscle fibers it supplies

  • They vary in the number of muscle fibers innervated by one motor nerve

  • The strength of a muscle contraction depends on…

    1. The number of motor units recruited

    2. The frequency at which they are stimulated

Motor Unit Activation:

  • Muscle fiber contractions via excitation of the specific muscle fiber’s motor neuron

  • Size Principle: start with smaller motor units first then recruit larger motor units as needed

  • Recruitment strategy shaped by previous experience and exist to save energy

  • Muscle contraction- All or nothing theory, no such thing as a partial contraction of motor fibers

  • More stimuli= more moto units called into action and frequency of stimulation

  • Strength of contraction = number of impulse per second and number of motor units activated

  • Tetanus = continuous contraction (frequency of impulses not allowing muscle to relax)

Characteristics of Skeletal Muscles

  • Contractility- ability to shorten muscle fibers forcefully

  • Extensibility- ability to extend/stretch beyond resting length

  • Elasticity- ability to return to normal size after stretching

  • Excitability/irritability- ability to e stimulated by nerves or hormones

Specific adaptation to imposed demands (SAID) principle:

  • muscle can change in size and strength

Anatomy of the Muscle:

  • Muscle - Muscle Fiber- Myofibril -Myofilament - Sarcomere

Hyperplasia- Developing new growth (in this case muscle fibers)

Hypertrophy- Strengthening the muscle fibers that are already there

Muscle Actions:

  • Agonist- Prime mover

  • Synergists- assist the agonist in the movement

  • Antagonist- Opposite of agonist

  • Stabilizers- contraction of muscles in a region to stabilize thus making a movement more effective

  • Neutralizer- nullify other actions of muscles

Sarcomere:

  • functional unit of force generation

  • Organization of myofilaments

Muscle Strength:

  • Pennation- muscle fibers that attach obliquely

  • Angle of Pennation- created between fiber direction and one of pull

    • if the angle is 0 degrees, all of the force produced by the muscle is transmitted across he join and tendon

    • If the angle is greater than 0 degrees, you will have decreased force at the muscle joint

Muscle Spindle:

  • located in belly of muscle

    • sensitive to stretch of muscle that causes protective muscle contraction of the muscle fibers

  • Golgi Tendon Organ- located within muscle tendons

    • sensitive to tension (stretch of the tendon by muscle contraction) that leads to protective reflex of inhibition of agonist and excitation of agonistic muscles

Proprioception:

  • Knowing where your body is in space

Fascia Web:

  • connective tissue (collagen, elastin ground substance)

  • Support for entire body to function in an integrated manner

  • Connects body parts- cell to cel

  • Transmits forces throughout entire body- high tensile strength

  • Lubricated by hydration

  • Elastic (different than skeletal muscles): stores kinetic energy

  • Plasticity (permanent change)