This chapter presents the following content: Gross anatomy of a skeletal muscle, microscopic anatomy of a skeletal muscle fiber, sliding filament model of contraction, physiology of skeletal muscle fibers, contraction of a skeletal muscle, muscle metabolism, force of muscle contraction, velocity and duration of contraction, adaptations to exercise.
Trang 1PowerPoint ® Lecture Slides
prepared by Janice Meeking, Mount Royal College
C H A P T E R
Copyright © 2010 Pearson Education, Inc.
9
Muscles and Muscle
Tissue: Part B
Trang 2Copyright © 2010 Pearson Education, Inc.
Review Principles of Muscle Mechanics
single fiber and a whole muscle
exerted on the load or object to be moved
Trang 3Copyright © 2010 Pearson Education, Inc.
Review Principles of Muscle Mechanics
muscle:
muscle tension increases but does not exceed the load
length and moves the load
Trang 4Copyright © 2010 Pearson Education, Inc.
Isotonic Contractions
eccentric:
shortens and does work
as it contracts and does work
Trang 5Copyright © 2010 Pearson Education, Inc.
Review Principles of Muscle Mechanics
response to stimuli of different frequencies and intensities
Trang 6Copyright © 2010 Pearson Education, Inc.
Motor Unit: The Nerve-Muscle Functional Unit
several hundred) muscle fibers it supplies
Trang 7Copyright © 2010 Pearson Education, Inc. Figure 9.13a
Spinal cord
Motor neuron cell body
Muscle
Nerve
Motor unit 1
Motor unit 2
Muscle fibers
Motor neuron axon
Axon terminals at neuromuscular junctions
Axons of motor neurons extend from the spinal cord to the muscle There each axon divides into a number of axon terminals that form neuromuscular junctions with muscle fibers scattered throughout the muscle.
Trang 8Copyright © 2010 Pearson Education, Inc.
Motor Unit
movements (fingers, eyes)
muscles (thighs, hips)
Trang 9Copyright © 2010 Pearson Education, Inc.
Motor Unit
throughout the muscle so that a single motor unit causes weak contraction of entire muscle
asynchronously; helps prevent fatigue
Trang 10Copyright © 2010 Pearson Education, Inc.
Trang 11Copyright © 2010 Pearson Education, Inc.
Muscle Twitch
• Latent period: events of excitation-contraction coupling
• Period of contraction: cross bridge formation; tension increases
• Period of relaxation: Ca 2+ reentry into the SR; tension declines to zero
Trang 12Copyright © 2010 Pearson Education, Inc. Figure 9.14a
Period of relaxation
(a) Myogram showing the three phases of an isometric twitch
Trang 13Copyright © 2010 Pearson Education, Inc.
Muscle Twitch Comparisons
Different strength and duration of twitches are due to variations in metabolic properties and enzymes between muscles
Trang 14Copyright © 2010 Pearson Education, Inc. Figure 9.14b
Latent period Extraocular muscle (lateral rectus)
Trang 15Copyright © 2010 Pearson Education, Inc.
Graded Muscle Responses
movement
Responses are graded by:
1 Changing the frequency of stimulation
2 Changing the strength of the stimulus
Trang 16Copyright © 2010 Pearson Education, Inc.
Response to Change in Stimulus Frequency
response—a muscle twitch
Trang 17Copyright © 2010 Pearson Education, Inc. Figure 9.15a
Contraction
Relaxation
Stimulus
Single stimulus single twitch
A single stimulus is delivered The muscle
contracts and relaxes
Trang 18Copyright © 2010 Pearson Education, Inc.
Response to Change in Stimulus Frequency
not have time to completely relax between
stimuli)
temporal (wave) summation
unfused (incomplete) tetanus
Trang 19Copyright © 2010 Pearson Education, Inc. Figure 9.15b
Stimuli Partial relaxation
Low stimulation frequency
unfused (incomplete) tetanus
(b) If another stimulus is applied before the muscle relaxes completely, then more tension results.
This is temporal (or wave) summation and results
in unfused (or incomplete) tetanus.
Trang 20Copyright © 2010 Pearson Education, Inc.
Response to Change in Stimulus Frequency
(complete) tetany results
Trang 21Copyright © 2010 Pearson Education, Inc. Figure 9.15c
Stimuli
High stimulation frequency
fused (complete) tetanus
(c) At higher stimulus frequencies, there is no relaxation
at all between stimuli This is fused (complete) tetanus.
Trang 22Copyright © 2010 Pearson Education, Inc.
Response to Change in Stimulus Strength
the first observable muscle contraction occurs
strength is increased above threshold
recruitment (multiple motor unit summation), which brings more and more muscle fibers
into action
Trang 23Copyright © 2010 Pearson Education, Inc. Figure 9.16
Stimulus strength
Proportion of motor units excited
Strength of muscle contraction
Maximal contraction
Maximal stimulus Threshold
stimulus
Trang 24Copyright © 2010 Pearson Education, Inc.
Response to Change in Stimulus Strength
larger fibers are recruited as stimulus intensity increases
Trang 25Copyright © 2010 Pearson Education, Inc. Figure 9.17
Motor unit 1 Recruited (small
fibers)
Motor unit 2 recruited (medium fibers)
Motor unit 3 recruited (large fibers)
Trang 26Copyright © 2010 Pearson Education, Inc.
Muscle Tone
muscles
motor units alternately in response to input from stretch receptors in muscles
respond
Trang 27Copyright © 2010 Pearson Education, Inc.
Isotonic Contractions
eccentric:
shortens and does work
as it lengthens
Trang 28Copyright © 2010 Pearson Education, Inc. Figure 9.18a
Trang 29Copyright © 2010 Pearson Education, Inc.
Isometric Contractions
muscle is able to develop
but the muscle neither shortens nor lengthens
Trang 30Copyright © 2010 Pearson Education, Inc. Figure 9.18b
Trang 31Copyright © 2010 Pearson Education, Inc.
Muscle Metabolism: Energy for Contraction
contractile activities
seconds
Trang 32Copyright © 2010 Pearson Education, Inc.
Muscle Metabolism: Energy for Contraction
• Direct phosphorylation of ADP by creatine
phosphate (CP)
• Aerobic respiration
• Anaerobic pathway (glycolysis)
Trang 33Copyright © 2010 Pearson Education, Inc. Figure 9.19a
Coupled reaction of creatine phosphate (CP) and ADP
Energy source: CP
(a) Direct phosphorylation
Oxygen use: None Products: 1 ATP per CP, creatine
Duration of energy provision:
15 seconds
Creatine kinase
ADP CP
Trang 34Copyright © 2010 Pearson Education, Inc.
Aerobic Pathway
moderate exercise
glucose, pyruvic acid from glycolysis, and free fatty acids
Trang 35Copyright © 2010 Pearson Education, Inc.
Energy source: glucose; pyruvic acid;
free fatty acids from adipose tissue;
amino acids from protein catabolism
(c) Aerobic pathway
Aerobic cellular respiration
Oxygen use: Required Products: 32 ATP per glucose, CO 2 , H 2 O
Duration of energy provision: Hours
Glucose (from glycogen breakdown or delivered from blood)
acids
Amino acids
Trang 36Copyright © 2010 Pearson Education, Inc.
Anaerobic Pathway
• Bulging muscles compress blood vessels
• Oxygen delivery is impaired
• Pyruvic acid is converted into lactic acid
Trang 37Copyright © 2010 Pearson Education, Inc.
Anaerobic Pathway
• Diffuses into the bloodstream
• Used as fuel by the liver, kidneys, and heart
• Converted back into pyruvic acid by the liver
Trang 38Copyright © 2010 Pearson Education, Inc.
Energy source: glucose
Glycolysis and lactic acid formation
(b) Anaerobic pathway
Oxygen use: None Products: 2 ATP per glucose, lactic acid
Duration of energy provision:
60 seconds, or slightly more
Glucose (from glycogen breakdown or delivered from blood)
Lactic acid
O 2
O 2 ATP
Trang 39Copyright © 2010 Pearson Education, Inc. Figure 9.20
ATP stored in
muscles is
used first.
ATP is formed from creatine Phosphate and ADP.
Glycogen stored in muscles is broken down to glucose, which is oxidized to generate ATP.
ATP is generated by breakdown of several nutrient energy fuels by aerobic pathway This pathway uses oxygen released from myoglobin
or delivered in the blood
by hemoglobin When it ends, the oxygen deficit is paid back.
Trang 40Copyright © 2010 Pearson Education, Inc.
• Prolonged exercise damages the SR and
interferes with Ca 2+ regulation and release
of continuous contraction, and causes
contractures (continuous contractions)
Trang 41Copyright © 2010 Pearson Education, Inc.
• ATP and CP reserves
glucose, and glycogen
Trang 42Copyright © 2010 Pearson Education, Inc.
Heat Production During Muscle Activity
activity is useful as work
radiation of heat from the skin and sweating