Download Unit 5 Muscle Tissue

Unit V: Movement
Muscle Tissue
Chapter 4 – pg 149-150
Chapter 9 – pg 281-285
Characteristics of All Muscle Tissue
• Excitibility (Responsiveness, irritability)
• Conductivity
– local electrical change triggered by stimulation
– results in contraction
• Contractility
• Extensibility
• Elasticity
Skeletal Muscle
General Properties
• Long, cylindrical, unbranched cells
• Multinucleated
• Striations
• Not capable of mitosis
• Voluntary
– movement, posture, breathing,
swallowing, facial expression,
speech, and excretion
Cardiac Muscle
General Properties
• Striations
• Short branched cells
– One nuclei
• Intercalated discs
• Not capable of mitosis
• Pumping of blood by cardiac (heart) muscle
Nucleus
Cardiac
muscle cells
Intercalated
discs
Striations
LM x 450
Smooth Muscle
General Properties
• Nonstriated
• Short fusiform cells
− One central nucleus
• Capable of mitosis
• Located in viscera
– digestive, respiratory, urinary
tracts, blood vessels, uterus
• Forms adjacent layers
– one encircling organ
– one longitudinal
The Muscle Fiber
Types of Myofilaments
• Thick filaments
– myosin
Types of Myofilaments
•Thin filaments
– F-actin (fibrous actin)
– G-actin (globular actin) binds to head of myosin molecule
– Tropomyosin
– Troponin
Active site
F-actin
Troponin
G-actin
Tropomyosin
Types of Myofilaments
•Elastic filaments
– Titin
– keeps filaments aligned
– resist over-stretching
– recoil of muscle cells
Nucleus
M line
Z disc
H band
A band
I band
1
I band
3
4
Individual myofibrils
5
Sarcomere
2
• A band
– dArk and darker areas
• I band
– lIght area
• Z disc
– sarcomere
Striations
(a)
Sarcomere
A band
H band
I band
(b)
Z disc
Thick filament
Thin filament
Elastic filament
M line
I band
Titin
Z disc
Nerve-Muscle Relationship
Spinal cord
Cell bodies of
motor neurons
Axons
of motor
neurons
Motor
nerve
• Single somatic motor neuron
– may branch 200 times
• Motor Unit
– somatic motor neuron + all the
muscle fibers it innervates
– muscle fibers of a motor unit are
NOT clustered together
– Result: weak contraction over a
wide area
KEY
Motor unit 1
Motor unit 2
Motor unit 3
• Fine control
– small motor units contain as few as
20 muscle fibers per nerve fiber
Neuromuscular Junction
Synapse between a neuron and muscle fiber
• Motor end plate
• Junctional Folds
• Acetylcholinesterase
Motor nerve
fibers
Neuromuscular
junction
Muscle fibers
(a)
100 m
Victor B. Eichler
Neuromuscular Toxins
• Pesticides and nerve agents
– cholinesterase inhibitors
– bind to acetylcholinesterase
– spastic paralysis
• Clostridium bacteria
– Tetanus or “lockjaw” (spastic paralysis)
• blocks glycine release from motor neurons
– botulism
• blocks release of ACh
• flaccid muscle paralysis (limp muscles)
• Arrow poison curare
– competes with ACh
– Flaccid paralysis