Download A View of Life

Chapter 11
Muscular System
1
•
•
•
•
Outline
Types and Functions of Muscles
– Smooth
– Cardiac
– Skeletal
Muscle Innervation
Whole Muscle Contraction
– Oxygen Deficit
– Athletics and Muscle Contraction
 Slow and Fast Twitch Fibers
Muscle Disorders
2
Types and Functions of Muscles
•
•
•
Smooth muscle is located in the walls of
hollow internal organs and contracts
involuntarily.
Cardiac muscle forms the heart wall and
contracts involuntarily.
Skeletal muscle runs the entire length of the
muscle and contracts voluntarily.
3
Types of Muscle
4
Functions of Skeletal Muscles
•
•
•
•
•
•
Body support.
Bone movement.
Maintenance of body temperature.
Assist movement in cardiovascular and
lymphatic vessels.
Protect internal organs.
Stabilize joints.
5
Skeletal Muscles of the Body
•
•
•
•
•
A whole muscle contains bundles of skeletal
muscle fibers, fascicles.
Muscles are covered with fascia that
becomes tendons.
Muscles originate on the stationary bone,
and insert on the bone that moves.
Cooperating muscle pairs have prime
movers and synergists.
Antagonistic pairs work opposite one
another to move in opposite directions.
6
Skeletal Muscles
7
8
Names and Actions of Skeletal Muscles
•
Skeletal muscles are
named based on
characteristics.
– Size.
– Shape.
– Direction of muscle
fibers.
– Number of
attachments.
– Action.
9
10
Skeletal Muscle Fiber Contraction
•
Overview of Muscular Contraction.
– Nerve impulses originate in the brain,
travel down motor neurons, and stimulate
muscle fibers at neuromuscular junctions.
 When muscle fibers are stimulated to
contract, myofilaments slide past one
another, causing sarcomeres to
shorten.
11
•
Muscle Innervation
Muscle fibers are innervated.
– Stimulated to contract by motor nerve
fibers.
 Signaled when nerve impulses bring
about release of neurotransmitter
molecules at a neuromuscular junction.
12
Neurotransmitter Junction
13
Muscle Innervation
•
Myosin filament heads break down ATP and
attach to an actin filament, forming crossbridges that pull the actin filament to the
center of the sarcomere.
– Contraction continues until nerve
impulses cease.
14
Whole Muscle Contraction
•
•
Muscle Twitch - Single muscle contraction.
– Divided into three stages.
 Stimulation.
 Contraction.
 Relaxation.
If a muscle is given a rapid series of
threshold stimuli, muscle contraction
summates in a sustained contraction,
tetanus.
15
Physiology of Skeletal Muscle Contraction
16
Whole Muscle Contraction
•
A motor neuron, together with all of the
muscle fibers that it innervates, is a motor
unit.
– As the intensity of nervous stimulation
increases, more motor units are activated.
17
Energy for Muscle Contraction
•
ATP produced previous to strenuous
exercise lasts a few seconds, and then
muscles acquire new ATP in three ways.
– Phosphate breakdown. (anaerobic)
– Fermentation. (anaerobic)
– Cellular respiration. (aerobic)
18
Oxygen Deficit
•
When a muscle uses the anaerobic means
of supplying energy, it incurs an oxygen
deficit.
– Repaying an oxygen deficit requires
replenishing creatine phosphate supplies
and disposing of lactic acid.
19
Athletics and Muscle Contraction
•
Muscles that are not used, or are used in
only weak contractions can atrophy.
– Can cause muscle fibers to progressively
shorten, leaving body parts contracted in
contorted positions.
 Hypertrophy occurs if the muscle
contracts to at least 75% of its
maximum tension.
20
Athletics and Muscle Contraction
•
•
Slow-twitch fibers produce most of their
energy aerobically and tire only when their
fuel supply is gone.
Fast-twitch fibers tend to be anaerobic and
seem to be designed for strength as their
motor units contain many fibers.
– Can develop greater, and more rapid,
maximum tension than slow-twitch fibers.
21
Slow-and-Fast Twitch Muscle Fibers
22
Muscle Disorders
•
•
•
Spasms are sudden, involuntary muscular
contractions most often accompanied by
pain.
– Multiple spasms of skeletal muscles are
called a seizure or convulsion.
A strain is an overstretching of a muscle near
a joint, while a sprain is a twisting of a joint
leading to swelling and injury.
Myalgia refers to inflammation of muscle
tissue.
23
Muscular Disorders
•
•
Muscular dystrophy is a broad term applied
to a group of disorders characterized by
progressive muscle degeneration and
weakening.
Myasthenia gravis is an autoimmune
disease characterized by weakness that
especially affects the muscles of the eyelids,
face, neck, and extremities.
24
Homeostasis
•
•
•
Cardiac muscle contraction accounts for the
heartbeat, delivering blood to the tissues.
Smooth muscle contraction accounts for
peristalsis and urination.
Skeletal muscle contraction returns blood to
the heart and moves bones, allowing for
body movement.
25
Review
•
•
•
•
Types and Functions of Muscles
– Smooth
– Cardiac
– Skeletal
Muscle Innervation
Whole Muscle Contraction
– Oxygen Deficit
– Athletics and Muscle Contraction
 Slow and Fast Twitch Fibers
Muscle Disorders
26
27