Muscles    

Major functions of Muscles                                Muscles Tutorial

  1. Movement - all 3 types of muscle
  2. Maintain posture - skeletal muscle
  3. Heat production - skeletal muscle

Characteristics of muscle tissue

  1. Excitability - ability to respond to stimuli
  2. Contractility - ability to shorten
  3. Extensibility - ability to stretch
  4. Elasticity - ability to return to original shape and length

Muscle tissue composes 40-50% of total body weight.  There are three types of muscle: smooth muscle found in the walls of the viscera, cardiac muscle found only in the heart, and skeletal muscle associated with bones.

3 types of muscles:

Non-striated muscle

1.    Smooth muscle - controlled by the autonomic nervous system; may either be generally inactive and then respond to neural stimulation or hormones or may be rhythmic.

 Occurs in small groups (ex. arrector pili) or sheets of overlapping cells tightly bound together (ex. digestive tube, uterus, bladder, respiratory tract, vessels), can regenerate.

Striated muscle

2.    Cardiac muscle - found in the heart, acts like rhythmic smooth muscle, modulated by neural activity and hormones

Branching network of cells forming layers that wind in overlapping spirals to form heart.  Cells connected by intercalated discs containing desmosomes and gap junctions.

3.    Skeletal muscle - move us around and responsible for most of our behavior; most attached to bones at each end via tendons

Bundles of cylindrical fibers (cells) run in parallel (fascicle); in various arrangements such as spindles, bands, or sheets; typically between 2 bones & across a joint

Motor unit - functional unit of muscle, consists of a motor neuron and all muscle fibers it innervates.  Degree of muscle contraction depends on number of active motor unit or recruitment

movement:

 

Motor Units

         Motor unit: all of the individual muscle fibers innervated by a single motor nerve fiber