Muscle
1.
2.
3.
4.
5.
6.
7.
Structure
Motor unit
Types of contraction
Protein organization (actin/myosin)
Cellular mechanism of contraction
Muscle fatigue
Muscle stimulators
Muscle
• Comprises largest group of tissues in body
• Three types of muscle
– Skeletal muscle
• Make up muscular system
– Cardiac muscle
• Found only in the heart
– Smooth muscle
• Appears throughout the body systems as components
of hollow organs and tubes
• Classified in two different ways
– Striated or unstriated
– Voluntary or involuntary
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Categorization of Muscle
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Muscle
• Controlled muscle contraction allows
– Purposeful movement of the whole body or parts
of the body
– Manipulation of external objects
– Propulsion of contents through various hollow
internal organs
– Emptying of contents of certain organs to external
environment
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Motor Units in Skeletal Muscle
•Fine touch
•1:1 nerve to fiber
•Finger tips
•Big muscles
•1: 2000
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
•Leg muscles
Motor Unit Recruitment
• Motor unit
– One motor neuron and the muscle fibers it
innervates
• Number of muscle fibers varies among different
motor units
• Number of muscle fibers per motor unit and number
of motor units per muscle vary widely
– Muscles that produce precise, delicate
movements contain fewer fibers per motor unit
– Muscles performing powerful, coarsely controlled
movement have larger number of fibers per motor
unit
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Summation and Tetanus
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Muscle Tension
• Tension is produced internally within muscle
• Tension must be transmitted to bone by means of
connective tissue and tendons before bone can be
moved (series-elastic component)
• Muscle typically attached to at least two different
bones across a joint
– Origin
• End of muscle attached to more stationary part of
skeleton
– Insertion
• End of muscle attached to skeletal part that moves
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Lever Systems
• Bones, muscles, and joints interact to form lever
systems
• Tendons: muscle to bone
• Ligaments: bone to bone
• Muscles: contraction force
– Isotonic: movement
– Isometric: no movement
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Physics of Joint Movement:
• Muscle: origin near body, insertion distal
• Levers: bones, Fulcrum: joints
Figure 12-21a:Chapter
The arm
is a lever and fulcrum system
8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Muscle contraction
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Smooth Muscles: Contrasted to Skeletal
Muscle
• Homeostatic role
– Control fluid
– Sphincters
• Tonic contractions
– Support tubes
– Move products
• Slow contractions
– Little fatigue
– Low O2 use
Figure 12-24: Duration of muscle contraction in
three types of muscle
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Smooth muscle
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Cardiac Muscle
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
How does skeletal muscle contract?
Structure
Protein arrangements
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Structure of Skeletal Muscle
• Muscle consists a number of muscle fibers lying
parallel to one another and held together by
connective tissue
• Single skeletal muscle cell is known as a muscle
fiber
– Multinucleated
– Large, elongated, and cylindrically shaped
– Fibers usually extend entire length of muscle
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Structure of Skeletal Muscle
• Myofibrils
– Contractile elements of muscle fiber
– Regular arrangement of thick and thin filaments
• Thick filaments – myosin (protein)
• Thin filaments – actin (protein)
– Viewed microscopically myofibril displays
alternating dark (the A bands) and light bands
(the I bands) giving appearance of striations
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Muscle fiber
myofibril
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Structure of Skeletal Muscle
• Sarcomere
– Functional unit of skeletal muscle
– Found between two Z lines (connects thin filaments of two
adjoining sarcomeres)
– Regions of sarcomere
• A band
– Made up of thick filaments along with portions of thin filaments
that overlap on both ends of thick filaments
• I band
– Consists of remaining portion of thin filaments that do not
project into A band
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Structure of Skeletal Muscle
sarcomere
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Role of Calcium in Cross-Bridge Formation
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Changes in Banding Pattern During Shortening
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Muscle Fatigue
• Occurs when exercising muscle can no longer
respond to stimulation with same degree of
contractile activity
• Defense mechanism that protects muscle from
reaching point at which it can no longer produce
ATP
• Underlying causes of muscle fatigue are unclear
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Central Fatigue
• Occurs when CNS no longer adequately activates
motor neurons supplying working muscles
• Often psychologically based
• Mechanisms involved in central fatigue are poorly
understood
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Characteristics of
Skeletal Muscle
Fibers
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Muscle stimulators
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Reanimating Limbs After Disease
Richard B. Stein and Vivian Mushahwar
Review TRENDS in Neurosciences Vol.28 No.10 October 2005
Intact muscle not receiving input due to CNS
disease
Muscular dystrophy due to denervation
Chapter 8 Muscle Physiology
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning