Transcript Nerve activates contraction

6
PART A
The Muscular System:
Structure and
Physiology
PowerPoint® Lecture Slide Presentation by Jerry L. Cook, Sam Houston University
ESSENTIALS
OF HUMAN
ANATOMY
& PHYSIOLOGY
EIGHTH EDITION
ELAINE N. MARIEB
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Function of Muscles
 Produce movement
 Maintain posture
 Stabilize joints
 Generate heat
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Characteristics of Muscles
 Muscle cells are elongated
 muscle cell = muscle fiber
 Contraction of muscles is due to the movement of
microfilaments
 All muscles share some terminology
 Prefix myo refers to muscle
 Prefix mys refers to muscle
 Prefix sarco refers to flesh
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Characteristics of Muscle Tissue
 Excitability
 Muscle tissue (and nervous cells) receive and respond to
stimuli by producing electrical signals
 Contractability
 Ability to shorten and thicken when stimulated
 Extensibility
 Ability to stretch without damaged
 Elasticity
 Ability to return to its original shape
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Types of Muscle Tissue
 Cardiac muscle
 Skeletal muscle
 Smooth muscle
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Cardiac Muscle
 Has striations
 Usually has a single
nucleus
 Joined to another
muscle cell at an
intercalated disc
 Involuntary
 Found only in the
heart
Figure 6.2b
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Smooth Muscle
 No striations
 Spindle-shaped cells
 Single nucleus
 Involuntary – no
conscious control
 Found mainly in the
walls of hollow
organs
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Skeletal Muscle
 Most are attached by tendons to bones
 Cells are multinucleate
 Striated – have visible banding
 Voluntary – subject to conscious control
 Cells are surrounded and bundled by
connective tissue
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Connective Tissue Wrappings of
Skeletal Muscle
 Tendon – cord-like
structure, attaches muscle
to bone
 Endomysium – around
single muscle fiber
 Perimysium – around a
fascicle (bundle) of fibers
 Epimysium – covers the
entire skeletal muscle
Figure 6.1
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Connective Tissue Wrappings of
Skeletal Muscle
 Fascia – on the outside of the
epimysium
 Superficial: subcutaneous
tissue; made of areolar
connective tissue and
adipose
 Deep: holds muscles
together and separates them
into functional groups;
made of dense irregular
connective tissue
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 6.1
Skeletal Muscle Tissue
Each skeletal muscle is a
separate organ composed of
hundred to thousands of
skeletal muscle cells called
muscle fibers because of
their elongated shapes.
Connective tissue surround
muscle fibers and whole
muscles, blood vessels, and
nerves penetrate muscle.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Microscopic Anatomy of
Skeletal Muscle
 Muscle fibers(cells) are arranged parallel to one another.
 Sarcomeres are the basic functional unit of striated muscle fibers;
occurs at the overlap of filaments.
 Sarcolemma is the plasma membrane that covers each muscle fiber
 Sarcoplasm is the muscle fiber’s cytoplasm.
 Tranverse (T) tubules are tunnel-like extensions of the sarcolemma
that pass through muscle fiber from side to side
 Sarcoplasmic reticulum is a network of membrane –enclosed
tubules that stores Ca2+ ions required for muscle contractions.
 Myoglobin is found in the sarcoplasm; reddish pigment; stores
oxygen until needed by mitochondria for ATP production.
 Myofibrils extend along the entire length of the muscle fiber; are
cylindrical; consists of two types of protein filaments: light & dark
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Microscopic Anatomy of
Skeletal Muscle
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Organization of the Scarcomere
 Z-discs (lines) are zigzagging
zones that separates sarcomeres
 A bands (dark bands) extend
the entire length of thick
filaments; at end thick & thin
filaments overlap
 I bands (light bands) are
composed of thin filaments
only
 H zone is found at the center of
each A band; contains only
thick filaments
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Organization of the Sarcomere
 Thick filaments are
composed of the protein
myosin. Shaped like 2 golf
clubs twisted together
 Thin filaments are
composed of the protein
actin. Twisted into helix.
 Thin filaments also
contains the proteins
tropomyosin &
troponin
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Sliding Filament Theory of
Muscle Contraction
 Overall summary of what happens in a sarcomere when a
muscle contracts:
 Myosin heads of thick filaments pull on thin filaments
 Thin filaments slide toward center of sarcomere
 I bands and H zone becomes narrower
 I band and H zone disappears @ maximum contraction
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Sliding Filament Theory of
Muscle Contraction
Figure 6.7
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Contraction Terminology
 Neuromuscular Junction (NMJ)- area of contact between
axon terminal & portion of sarcolemma
 Axon terminal-branches of motor neuron that approaches,
but not touch the sarcolemma
 Acetylcholine (Ach)- neurotransmitter
 Synaptic cleft- narrow gap that separates axon terminal of
one neuron from muscle fiber
 Motor end plate- part of sarcolemma that receives the
neurotransmitter
 Acetylcholinesterase (AChE)- enzyme that breaks down
acetylcholine
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Muscle Contraction
 Nerve impulse arrives at axon terminal of motor neuron
and triggers release of acetylcholine (ACh)…
 ACh binds to its receptors and is activated, this causes
Na/K ions to flow across membrane...
 Inflow of Na ions generates a muscle action potential,
which travels down sarcolemma & through T-tubules…
 As the impulse moves down SR, Ca2+ is released from the
SR to the thick and thin myofilaments…
 Ca2+ binds to troponin molecules in thin filaments,
causing the troponin-tropomyosin complex to change
shape….
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Muscle Contraction
 This change in shape of the troponin/tropomysosin complex
causes movement of the attached tropomyosin molecule….
 Allowing the myosin head to contact/bind actin, causing the
myosin head to swivel (this requires ATP!)
 During the swivel, the myosin head is firmly attached to the
actin, so when the head moves, it pulls the actin filament
forward.
 This is called the ”power stroke” of contraction
 Many myosin heads are swiveling simultaneously and their
collective efforts are enough to pull the entire actin filament
past the myosin filament into the H zone and causes
shortening (contraction) of the muscle fiber
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Muscle Relaxation
 Neurotransmitter Ach (acetylcholine) is broken down by
AChE.
 Muscle action potentials stop
 Ca2+ release channels in the SR close
 As levels of calcium in sarcoplasm falls, troponin releases
calcium and slides back into original position where it
covers the myosin binding sites
 Thin filaments slips back into their relaxed positions.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings