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to accompany
Hole’s Human
Anatomy and Physiology
Eleventh Edition
Shier w Butler w Lewis
Chapter
9
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1
Chapter 9
Muscular System
Three Types of Muscle Tissues
Skeletal Muscle
• usually attached
to bones
• under conscious
control
• striated
Cardiac Muscle
• wall of heart
• not under
conscious control
• striated
Smooth Muscle
• walls of most viscera,
blood vessels, skin
• not under conscious
control
• not striated
2
Structure of a Skeletal Muscle
Skeletal Muscle
• organ of the muscular
system
- skeletal muscle tissue
- nervous tissue
- blood
- connective tissues
• fascia
• tendons
• aponeuroses
3
Connective Tissue Coverings
• epimysium
• perimysium
• fascicles
• endomysium
• muscle
• fascicles
• muscle fibers
• myofibrils
• thick and thin filaments
4
Skeletal Muscle Fibers
• sarcolemma
• sacroplasm
• sarcoplasmic reticulum
• transverse tubule
• triad
• cisternae of sarcoplasmic
reticulum
• transverse tubule
• myofibril
• actin filaments
• myosin filaments
• sarcomere
5
Sarcomere
• I bands
• A bands
• H zone
• Z lines
• M line
6
Myofilaments
Thick Filaments
• composed of myosin
• cross-bridges
Thin Filaments
• composed of actin
• associated with troponin
and tropomyosin
7
Neuromuscular Junction
• also known as
myoneural junction
• site where an axon and
muscle fiber meet
• motor neuron
• motor end plate
• synapse
• synaptic cleft
• synaptic vesicles
• neurotransmitters
8
Motor Unit
• single motor neuron
• all muscle fibers controlled by motor neuron
9
Stimulus for Contraction
• acetylcholine (ACh)
• nerve impulse causes release
of ACh from synaptic vesicles
• ACh binds to ACh receptors
on motor end plate
• generates a muscle impulse
• muscle impulse eventually
reaches sarcoplasmic reticulum
and the cisternae
10
Synaptic Transmission
Neurotransmitters are
released when impulse
reaches synaptic knob
11
Local Potential Changes
•if membrane potential becomes more negative, it has
hyperpolarized
• if membrane potential becomes less negative, it has
depolarized
• graded
• summation can lead to threshold stimulus that starts an
action potential
12
Resting Membrane Potential
• inside is negative
relative to the outside
• polarized membrane
• due to distribution of
ions
• Na+/K+ pump
13
Local Potential Changes
14
Action Potentials
• at rest membrane is
polarized
• threshold stimulus
reached
• sodium channels
open and membrane
depolarizes
• potassium leaves
cytoplasm and
membrane repolarizes
15
Action Potentials
16
Action Potentials
17
All-or-None Response
• if a neuron responds at all, it responds completely
• a nerve impulse is conducted whenever a stimulus of
threshold intensity or above is applied to an axon
• all impulses carried on an axon are the same strength
18
Impulse Conduction
19
Excitation Contraction
Coupling
• muscle impulses cause
sarcoplasmic reticulum to
release calcium ions into
cytosol
• calcium binds to troponin to
change its shape
• position of tropomyosin is
altered
• binding sites on actin are
exposed
• actin and myosin molecules
bind
20
Sliding Filament Model of Muscle
Contraction
• When sarcromeres
shorten, thick and thin
filaments slide past one
another
• H zones and I bands
narrow
• Z lines move closer
together
21
Cross-bridge Cycling
• myosin cross-bridge attaches
to actin binding site
• myosin cross-bridge pulls
thin filament
•ADP and phosphate
released from myosin
• new ATP binds to
myosin
• linkage between actin
and myosin cross-bridge
break
•ATP splits
•myosin cross-bridge goes back
to original position
22
Relaxation
• acetylcholinesterase – rapidly decomposes Ach
remaining in the synapse
• muscle impulse stops
• stimulus to sarcolemma and muscle fiber membrane
ceases
• calcium moves back into sarcoplasmic reticulum
• myosin and actin binding prevented
• muscle fiber relaxes
23
Major Events of Muscle
Contraction and Relaxation
24
Energy Sources for
Contraction
1) Creatine phosphate
2) Cellular respiration
• creatine phosphate – stores energy that quickly converts
ADP to ATP
25
Oxygen Supply and
Cellular Respiration
• Anaerobic Phase
• glycolysis
• occurs in cytoplasm
• produces little ATP
• Aerobic Phase
• citric acid cycle
• electron transport chain
• occurs in the mitochondria
• produces most ATP
• myoglobin stores extra
oxygen
26
Cellular Respiration
Occurs in three series of reactions
1. Glycolysis
2. Citric acid cycle
3. Electron transport chain
Produces
• carbon dioxide
• water
• ATP (chemical energy)
• heat
Includes
• anaerobic reactions (without O2) - produce little ATP
• aerobic reactions (requires O2) - produce most ATP 27
ATP Molecules
• each ATP molecule has three parts:
• an adenine molecule
• a ribose molecule
• three phosphate molecules in a chain
• third phosphate attached by high-energy bond
• when the bond is broken, energy is transferred
• when the bond is broken, ATP becomes ADP
• ADP becomes ATP through phosphorylation
• phosphorylation requires energy released from cellular respiration
28
Glycolysis
• series of ten reactions
• breaks down glucose into 2 pyruvic acid molecules
• occurs in cytosol
• anaerobic phase of cellular respiration
• yields two ATP molecules per glucose
Summarized by three main events
1. phosphorylation
2. splitting
3. production of NADH and ATP
29
Anaerobic Reactions
If oxygen is not available • electron transport
chain cannot accept new
electrons from NADH
• pyruvic acid is
converted to lactic acid
• glycolysis is inhibited
• ATP production less
than in aerobic reactions
30
Aerobic Reactions
If oxygen is available –
• pyruvic acid is used
to produce acetyl CoA
• citric acid cycle
begins
• electron transport
chain functions
• carbon dioxide and
water are formed
• 36 molecules of ATP
produced per glucose
molecule
31
Summary of Cellular
Respiration
32
Oxygen Debt
Oxygen debt – amount of oxygen needed by liver cells to
use the accumulated lactic acid to produce glucose
• oxygen not available
• glycolysis continues
• pyruvic acid
converted to lactic acid
• liver converts lactic
acid to glucose
33
Muscle Fatigue
• inability to contract
• commonly caused from
• decreased blood flow
• ion imbalances across the sarcolemma
• accumulation of lactic acid
• cramp – sustained, involuntary muscle contraction
34
Heat Production
• by-product of cellular respiration
• muscle cells are major source of body heat
• blood transports heat throughout body
35
Muscular Responses
Threshold Stimulus
• minimal strength required to cause contraction
Recording a Muscle
Contraction
• twitch
• latent period
• period of contraction
• period of relaxation
• refractory period
• all-or-none response
36
Length-Tension Relationship
37
Summation
• process by which individual twitches combine
• produces sustained contractions
• can lead to tetanic contractions
38
Recruitment of Motor Units
• recruitment - increase in the number of motor units
activated
• whole muscle composed of many motor units
• more precise movements are produced with fewer
muscle fibers within a motor unit
• as intensity of stimulation increases, recruitment of
motor units continues until all motor units are
activated
39
Sustained Contractions
• smaller motor units (smaller diameter axons)
- recruited first
• larger motor units (larger diameter axons)
- recruited later
• produce smooth movements
• muscle tone – continuous state of partial contraction
40
Types of Contractions
• isotonic – muscle contracts and
changes length
• eccentric – lengthening
contraction
• concentric – shortening contraction
• isometric – muscle contracts but
does not change length
41
Fast and Slow Twitch
Muscle Fibers
Slow-twitch fibers (type I)
• always oxidative
• resistant to fatigue
• red fibers
• most myoglobin
• good blood supply
Fast-twitch glycolytic fibers (type IIa)
• white fibers (less myoglobin)
• poorer blood supply
• susceptible to fatigue
Fast-twitch fatigueresistant fibers (type IIb)
• intermediate fibers
• oxidative
• intermediate
amount of
myoglobin
• pink to red in color
•resistant to fatigue
42
Smooth Muscle Fibers
Compared to skeletal muscle fibers
• shorter
• single, centrally located nucleus
• elongated with tapering ends
• myofilaments randomly organized
• lack striations
• lack transverse tubules
• sarcoplasmic reticula not well developed
43
Types of Smooth Muscle
Visceral Smooth Muscle
• single-unit smooth muscle
• sheets of muscle fibers
• fibers held together by gap
junctions
• exhibit rhythmicity
• exhibit peristalsis
• walls of most hollow organs
Multiunit Smooth Muscle
• less organized
• function as separate units
• fibers function separately
• irises of eye
• walls of blood vessels
44
Smooth Muscle Contraction
• Resembles skeletal muscle contraction
• interaction between actin and myosin
• both use calcium and ATP
• both are triggered by membrane impulses
• Different from skeletal muscle contraction
• smooth muscle lacks troponin
• smooth muscle uses calmodulin
• two neurotransmitters affect smooth muscle
• acetlycholine and norepinephrine
• hormones affect smooth muscle
• stretching can trigger smooth muscle contraction
• smooth muscle slower to contract and relax
• smooth muscle more resistant to fatigue
• smooth muscle can change length without changing
tautness
45
Cardiac Muscle
• located only in the heart
• muscle fibers joined together by intercalated discs
• fibers branch
• network of fibers contracts as a unit
• self-exciting and rhythmic
• longer refractory period than skeletal muscle
46
Characteristics of Muscle Tissue
47
Life-Span Changes
• myoglobin, ATP, and creatine phosphate
decline
• by age 80, half of muscle mass has
atrophied
• adipose cells and connective tissues replace
muscle tissue
• exercise helps to maintain muscle mass and
function
48
Clinical Application
Myasthenia Gravis
• autoimmune disorder
• receptors for ACh on muscle cells are attacked
• weak and easily fatigued muscles result
• difficulty swallowing and chewing
• ventilator needed if respiratory muscles are affected
• treatments include
• drugs that boost ACh
• removing thymus gland
• immunosuppressant drugs
• antibodies
49