muscular system. characteristics of muscles all muscles have four common characteristics: ...
TRANSCRIPT
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.
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.