Download Chapter 9 - Muscular System

Chapter 9 – The Muscular System
Copyright © McGraw-Hill Education. Permission required for reproduction or display.
1
Introduction
There are 3 types of muscle tissue
in the muscular system:
Skeletal muscle:
• Attached to bones of skeleton
• Voluntary (consciously controlled)
Cardiac muscle:
• Makes up most of the wall of the
heart
• Involuntary (non-consciouslycontrolled)
• Responsible for pumping action
of the heart
Smooth muscle:
• Found in walls of internal organs,
such as those of digestive tract
• Involuntary (non-consciouslycontrolled)
2
9.1: Structure of a Skeletal Muscle
Skeletal Muscles:
• Attach to bones, and skin of face
• Under conscious control (voluntary)
• A skeletal muscle is an organ of the muscular system
• Skeletal muscles are composed of:
• Skeletal muscle tissue
• Nervous tissue
• Blood
• Connective tissues
3
9.2: Skeletal Muscle Contraction
Contraction of a muscle fiber:
• Requires interaction from several chemical and cellular
components
• Results from a movement within the myofibrils, in which the
actin and myosin filaments slide past one another,
shortening the sarcomeres
• Muscle fiber shortens and pulls on attachment points
4
Neuromuscular Junction
Neuromuscular Junction:
• A type of synapse
• Also called a myoneural junction
• Site where an axon of motor neuron
and skeletal muscle fiber interact
• Skeletal muscle fibers contract
only when stimulated by a motor
neuron
• Parts of a NMJ:
• Motor neuron
• Motor end plate
• Synaptic cleft
• Synaptic vesicles
• Neurotransmitters
5
Oxygen Supply & Cellular Respiration
Cellular respiration:
Anaerobic Phase :
• In the absence of oxygen
• Glycolysis
• Occurs in cytoplasm
• Produces little ATP
Aerobic Phase:
• In the presence of oxygen
• Occurs in the mitochondria
• Produces the most ATP
6
Oxygen Debt
During rest or moderate exercise, respiratory & cardiovascular systems
supply enough O2 to support aerobic respiration
Anaerobic (Lactic Acid) Threshold:
Shift in metabolism from aerobic to anaerobic, during strenuous muscle
activity, when the above systems cannot supply the necessary O2. Lactic
acid is produced.
Oxygen debt:
Amount of oxygen needed by liver cells to convert the accumulated lactic
acid to glucose, and to restore muscle ATP and creatine phosphate
concentrations.
7
Muscle Fatigue
Muscle Fatigue:
Inability to contract muscle
Common causes of muscle fatigue:
• Decreased blood flow
• Ion imbalances across the sarcolemma
• Loss of desire to continue exercise
• Accumulation of lactic acid
Muscle Cramp:
• Sustained, involuntary muscle contraction
• May be caused by changes in electrolyte concentration in extracellular
fluids in the area
8
Heat Production
• Heat is a by-product of cellular respiration in active cells
• Muscle cells are major source of body heat
• More than half the energy released in cellular respiration becomes heat;
less than half is transferred to ATP
•
Blood transports heat throughout body core
9
9.3: Muscular Responses
• Muscle contraction can be observed by removing a single
skeletal muscle fiber and connecting it to a device that
senses and records changes in the overall length of the
muscle fiber.
• Electrical stimulator promotes the contractions
10
Threshold Stimulus
Threshold Stimulus:
Minimum strength of stimulation of a muscle fiber required to cause
contraction
• When strength of stimulus reaches threshold, an action potential is
generated
• Impulse spreads through muscle fiber, releasing Ca+2 which begins to
contraction process
• One action potential from a motor neuron releases enough Ach
(neurotransmitter) to produce threshold stimulus in muscle fiber, causing
a muscle impulse
11
Recruitment of Motor Units
Recruitment:
Increase in the number of motor units activated, to produce more force
• Certain motor units are activated first, and others are activated only when
the intensity of stimulus increases
• As intensity of stimulation increases, recruitment of motor units continues
until all motor units are activated
12
Sustained Contractions
• Smaller motor units (smaller diameter axons) - recruited first
•
Larger motor units (larger diameter axons) - recruited later
• Summation and recruitment can produce sustained
contractions of increasing strength
• Whole muscle contractions are smooth movements
•
Muscle tone (tonus): Continuous state of partial contraction
in resting muscles
13
Types of Contractions
Isotonic: muscle contracts and changes length; produces movement
– Walking
– Moving a body part
Isometric: muscle contracts but does not change length; produces no
movement
– Sitting up
– Standing
– Maintaining posture
14
9.4: Smooth Muscle
Compared to skeletal muscle fibers, smooth muscle fibers are:
•
•
•
•
•
Shorter
Single, centrally located nucleus
Elongated with tapering ends
Myofilaments randomly organized
Lack striations
15
Types of Smooth Muscle
2 types of smooth muscle:
• Multi-unit Smooth Muscle:
•
•
•
•
•
Cells are less organized
Function as separate units
Fibers function independently
Iris of eye, walls of blood vessels
Stimulated by neurons, hormones
• Visceral Smooth Muscle:
•
•
•
•
•
•
•
Single-unit smooth muscle; cells respond as a unit
Sheets of spindle-shaped muscle fibers
Fibers held together by gap junctions
Exhibit rhythmicity
Conduct peristalsis
Walls of most hollow organs
More common type of smooth muscle
16
Smooth Muscle Contraction
• Resembles skeletal muscle contraction in these ways:
• Interaction between actin and myosin (components of muscle fibers)
• Both use calcium and ATP
• Both are triggered by membrane impulses (motor neurons)
• Different from skeletal muscle contraction in these ways:
• Hormones can stimulate or inhibit smooth muscle
• Stretching can trigger smooth muscle contraction
• Smooth muscle slower to contract and relax
• Smooth muscle more resistant to fatigue
17
9.5: Cardiac Muscle
Cardiac Muscle:
•
•
•
•
•
•
•
Located only in the heart
Striated muscle cells
Muscle fibers joined together by intercalated discs
Fibers branch, contain a single nucleus
Network of fibers contracts as a unit (conduction system)
Rhythmic contractions
Longer refractory period (time where muscle is unresponsive) than
skeletal muscle
• No sustained contractions
18
Characteristics of Muscle Tissues
19
9.6: Skeletal Muscle Actions
• Skeletal muscles generate a great variety of body
movements
•
The action of each muscle mostly depends upon
- the type of joint it is associated with
- the way the muscle is attached on either side of the
joint
20
Body Movement
When bones or body parts move,
bones and muscles act as levers.
4 basic components of levers:
• Rigid bar or rod (bones)
• Fulcrum or pivot on which bar
moves (joint)
• Object moved against
resistance (weight)
• Force that supplies energy for
movement (muscles)
21
Origin and Insertion
One end of a skeletal muscle is
more fixed, and the other end is
more movable:
Origin: less movable end
Insertion: more movable end
When a muscle contracts,
insertion is pulled toward
origin
22
Interaction of Skeletal Muscles
Most skeletal muscle function in groups. Roles of muscles in performing
certain actions:
• Agonist: muscle that causes an action
• Prime mover: agonist primarily responsible for movement
(In some cases, the terms “agonist” and “prime mover” are used
interchangeably)
• Synergists: muscles that assist agonist / prime mover
• Antagonist: muscles whose contraction causes movement in the
opposite direction of the prime mover
23
9.7: Major Skeletal Muscles
Anterior View of the
Superficial Skeletal
Muscles:
24
Major Skeletal Muscles
Posterior View of the
Superficial Skeletal
Muscles:
25
9.8: Lifespan Changes
• Myoglobin, ATP, and creatine phosphate decline, starting in the 40s
• Connective tissue and adipose cells replace some muscle tissue
• By age 80, almost half of muscle mass has atrophied (wasted away)
• Muscle strength decreases, and reflexes become slower
• Exercise helps to maintain muscle mass and function
26