Post on 01-Jan-2016
Chapter 6
The Muscular
System
O.K. Everybody
flex!
How many muscles are there?
• 656 (more or less)
• Comprise about half your body weight
• 3 main functions…
3 major functions
1. Body movement
2. Body form and shape, posture
3. Body heat: maintain body temperature
1. Skeletal muscle, a.k.a. voluntary or striated muscle
2. Smooth muscle, a.k.a. involuntary
3. Cardiac muscle (found only in the heart) also Involuntary.
3 types of muscle
• Skeletal muscle, a.k.a. voluntary or striated muscle– Attached to the
skeleton, moves the limbs
– Contracts quickly, tires easily, can’t stay contracted for long periods of time.
– Multinuclear– May be long: ex
thigh 12-16”
• Smooth muscle, a.k.a. involuntary– Unattached to
bone. – Walls of the
internal organs esp digestive tract, but uterus and blood vessels as well.
– Single nucleus, long spindle shape.
– Act slowly, do not tire easily, can stay contracted for long periods of time
• Cardiac muscle- found only in the heart. – Involuntary. – Membranes fused
together at intercalated discs to form a continuous network.
– No independent cell contraction
• Muscles are hundreds to thousands of muscle cells, called fibers. Each fiber is in turn made up of myofibrils
• Muscle cells are long cylinders- each cell may have 100 or more nuclei located just underneath membrane
Striated
Muscle
4 characteristics of muscle1. Contractibility.
-No other body tissue has this quality-Muscles only contract or relax - they do not push
2. Excitability-Both muscle and nerve cells respond to stimuli by producing electrical signals
called action potentials
3. Extendibility- The ability to be stretched
4. Elasticity- The ability to return to the original length when relaxed
These four qualities; contractibility, excitability, extendibility and elasticity create a mechanical mechanism capable of complex, intricate movement
• Muscles need to be attached to something to exert a pulling force
• Muscles only pull, never push. Attached to bones by non elastic cords of connective tissue called tendons.
• Muscles bridge the joints of bones
• Muscles are attached at both ends; bones, tendons, skin or other muscles.
• Muscles arranged in antagonistic pairs- one works in one direction while a second muscle works in the opposite direction.
Biceps/Triceps and movement of arm
One is prime mover, the other is antagonist
• Muscles are made up of muscle fibers (muscle cells), which in turn are made up of myofibrils.
• Myofibrils have two main components– Actin (thin)– Myosin (thick)
• We will discuss later how muscles move (sliding filament theory)
A review of terminology
• When discussing muscles and what they move, you use the terms origin and insertion
• The point of origin moves the least. The insertion is attached to a moveable part. Ex- flex your arm. Origin of biceps is the humerus; it’s insertion is the radius
• Atrophy- shrink from disuse• Hypertrophy- increase in size.
(Note: an increase in the size of a muscle is caused by an increase in cytoplasm, not by an increase in muscle fibers)