Muscular System

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.

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.

Excitability/ Irritability

Characteristic of both muscle and nervous cells.

Ability to respond to certain stimuli by producing electrical signals: impulses or action potentials.

Extensibility

Ability to be stretched.

When we bend the forearm, the muscles on the back of it are extended or stretched.

Elasticity

Ability to return to original length when relaxing.

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.

Muscle stimulated

ATP released

Body heat produced, energy for muscle movement. Lactic acid build up begins.

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.

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.

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.

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.

Atrophy – loss of muscle. Shrink from disuse. Not exercising or medical diseases.

Hypertrophy – Muscles become enlarged. Muscle fiber (cell) enlarges.

Naming of Skeletal Muscles Use 7 criteria

Location Size Direction Number of origins Location of origins Insertion action

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.

656 muscles in the human body

327 antagonistic muscle pairs and two unpaired muscles

Unpaired muscles – orbicularis oris and diaphraghm

656 muscles can be divided and subdivided into:

Head Muscles Neck Muscles Trunk Muscles Extremity Muscles

Head Muscles

Muscles of expression Muscles of mastication Muscles of the tongue Muscles of the pharynx Muscles of the soft palate

Neck Muscles

Muscles moving the head Muscles moving the hyoid bone and the

larynx Muscles moving the upper ribs

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.

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

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.

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

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.

Muscles of the Trunk

The trunk muscles control breathing and the movements of the abdomen and the pelvis.

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.