1. Muscular System

2. Characteristics of Muscles  All muscles have four common characteristics:  Contractibility  Excitability ( irritability)  Extensibility  Elasticity Collectively, these 4 characteristics produce a veritable mechanical device capable of complex, intricate movements.

3. Contractibility  Quality possessed by NO other body tissue.  The muscle shortening or reducing the distance between the parts of its contents, or the space it surrounds.  Cardiac muscles contract; reduce the area in the heart chambers. Skeletal muscles contract; makes bones move.

4. Excitability/ Irritability  Characteristic of both muscle and nervous cells.  Ability to respond to certain stimuli by producing electrical signals: impulses or action potentials.

5. Extensibility  Ability to be stretched.  When we bend the forearm, the muscles on the back of it are extended or stretched.

6. Elasticity  Ability to return to original length when relaxing.

7. Heat and Energy  Muscles work= movement and heat  For muscles to work they need energy; the major source of energy is ATP ( adenosine triphosphate).  To make ATP you need O2, glucose, and other materials. Extra glucose is stored as glycogen.

8. Muscle stimulated ATP released Body heat produced, energy for muscle movement. Lactic acid build up begins.

9. Contraction of Skeletal Muscle  Movement occurs as a result of two events: Myoneural Stimulation and Contraction of muscle proteins.  Skeletal muscle MUST be stimulated by nerve impulses to contract.

10.  A motor neuron (nerve cell) stimulates all of the skeletal muscles within a motor unit.  A motor unit is a motor neuron plus all the fibers it stimulates.  The junction between the motor neuron’s fiber (axon), which transmits the impulses, and the muscle cell’s sarcolemma is the neuromuscular junction.  Acetylcholine is released when nerve impulses reach the end of the axon.

11. Muscle Fatigue  Caused by an accumulation of lactic acid in the muscles.  During vigorous exercise blood will not carry enough O2 and muscles will contract anaerobically. This can cause lactic acid build up, which can impede muscular contraction; causing muscle fatigue and cramps.  After exercising, need to rest to take in O2 so lactic acid can change back to glucose and other materials.  Amount of O2 needed is Oxygen Debt.

12. Muscle Tone  Muscle Tone = slightly contracted and ready to pull.  Two types of contractions are isotonic and isometric.  Isotonic = muscles contract and shorten  Isometric = muscle tension increases but muscle does not shorten.

13.  Atrophy – loss of muscle. Shrink from disuse. Not exercising or medical diseases.  Hypertrophy – Muscles become enlarged. Muscle fiber (cell) enlarges.

14. Naming of Skeletal Muscles  Use 7 criteria  Location  Size  Direction  Number of origins  Location of origins  Insertion  action

15. Principal Skeletal Muscles  Attached to and help move the skeleton.  They line the walls of the oral, abdominal, and pelvic cavities.  Also control the movement of the eyeballs, eyelids, lips, tongue, and skin.

16.  656 muscles in the human body  327 antagonistic muscle pairs and two unpaired muscles  Unpaired muscles – orbicularis oris and diaphraghm

17.  656 muscles can be divided and subdivided into:  Head Muscles  Neck Muscles  Trunk Muscles  Extremity Muscles

18. Head Muscles  Muscles of expression  Muscles of mastication  Muscles of the tongue  Muscles of the pharynx  Muscles of the soft palate

19. Neck Muscles  Muscles moving the head  Muscles moving the hyoid bone and the larynx  Muscles moving the upper ribs

20.  Muscles of the head and neck control human facial expressions.  Muscles of mastication control the mandible.  Muscles that move the head cause extension, flexion, and rotation.

22. Muscles of Facial Expression  Frontalis: located on either side of the forehead; raises eyebrows and wrinkles forehead  Depressor anguli oris: ring shaped muscle found around the mouth; compresses and closes the lips.  Platysma: broad, thin muscular sheet covering the side of the neck and lower jaw; draws corner of mouth down and back

23.  Zygomaticus major: extends diagonally upward from corner of mouth; raises corner of mouth.  Nasalis: found over the nasal bones; closes and opens the nasal openings  Orbicularis oculi: Surrounds the eye orbit underlying the eyebrows; closes the eyelid and tightens the skin on the forehead.

24. Muscles of Mastication  Masseter: covers the lateral surface of the ramus (angle) of the mandible; closes the jaw  Temporalis: Located on the temporal fossa of the skull; raises the jaw, closes the mouth, and draws the jaw backward

25. Muscles of the Neck  Sternocleidomastoid (two heads): large muscles extending diagonally down sides of the neck; flexes head, rotates the head toward opposite side from muscle.

26. Muscles of the Trunk  The trunk muscles control breathing and the movements of the abdomen and the pelvis.

29.  External intercostals: found between the ribs; raises the ribs to help in breathing.  Diaphragm: a dome-shaped muscle separating the thoracic and abdominal cavaties; helps to control breathing.  Rectus abdominus: extends from the ribs to the pelvis; compresses the abdomen.  External oblique: anterior inferior edge of the last eight ribs; depresses ribs, flexes the spinal column, and compresses the abdominal cavity.  Internal oblique: found directly beneath the external oblique with fibers running in the opposite direction; depresses ribs, flexes the spinal column, and compresses the abdominal cavity.