Muscle Tissue
• Muscle tissue functions
– Movement
– Maintain Posture
– Joint stabilization
– Heat generation
(11.5a)
Muscle tissue properties
•
•
•
•
Contractility
Excitability
Extensibility
Elasticity
(11.5a)
Muscle tissue types
• Skeletal
– Striated,
voluntary
• Cardiac
– Heart, striated,
involuntary
• Smooth
– Nonstriated,
involuntary
Table 10.2
Muscle tissue terminology
• Myofiber – A skeletal, cardiac or smooth
muscle cell
• Myofilaments Protein “threads” within a
myofiber 1.Actin – thin filaments
2. Myosin – thick filaments
• Sarcolemma – plasma membrane
• Sarcoplasm – cytoplasm
Skeletal Muscle C.T.
• Epimysium –
surrounds entire
muscle/organ
• Perimysium –
surrounds muscle
fascicle
• Endomysium –
surrounds individual
muscle fiber
(10.1a)
THE CONNECTIVE TISSUE WRAPPINGS
– A VIEW
Skeletal Myofiber (muscle fiber)
• Cylindrical
– 10-100 m diameter
– Varied length – up to entire muscle
• Formed by cell fusion
• Multinucleated
– Peripheral nucleus
• Striated
• LM Demonstration
Table 10.2
Sliding filament theory
• Muscle contracts by actin and myosin sliding
past each other
• Myosin forms cross-bridges that attach to actin
• Cross bridges all swing in same direction and
pull actin along
• Increased overlap of
filaments results in
contraction of muscle
(10.6)
Sliding filament
theory
• Actin and myosin do
not shorten
• A band does not
change
• I band shortens
• Sarcomere shortens
(10.7)
The Neuromuscular junction
• Neuromuscular
Junction
• Axon terminal
– Mitochondria
– Synaptic vesicles – ACh
• Synaptic cleft
• Motor end plate
– AChR
– AP to muscle fiber
(14.5ab)
Sarcoplasmic reticulum
• SR surrounds each
myofibril
• Stores Ca++
– Release Ca++ for
contraction
– Ca++ uptake for
relaxation
(10.8)
Muscle contraction
•
•
•
•
•
•
•
•
Signal to axon terminal
ACh released
AChR activated
Muscle excited
Excitation travels down t-tubule
SR releases Ca++
Ca++ activates sliding filament process
Muscle contracts
(14.5b)
http://www.blackwellpublishing.com/matthews/myosin.html
VIEW OF MYOFILAMENT
STRUCTURES
Motor Unit
• Definition: a motor neuron
and all the muscle fibers it
innervates.
• When a motor neuron fires, all
muscle fibers in the motor
unit contract.
– All or none principle
• A motor unit may contain
hundreds to four muscle fibers
(average ~ 150)
• Each muscle fibers receives
one NMJ
(14.6)
Summary: skeletal muscle fibers
muscle
myofibril
fascicle
fiber
Table 10.1
Myofilaments :actin & myosin
Cardiac muscle
•
•
•
•
Only in heart
Sliding filament theory
Striated
No NMJ
18.4
Cardiac muscle cells
• 15 m wide X 100 m long
• Branched
• Intercalated discs
– Desmosomes
• adhesion
– Gap junctions
• transmit electrical impulses
• Forms two networks – atrial
and ventricular
(10.10a)
Cardiac muscle cells
•
•
•
•
•
•
Central 1-2 nuclei
Mitochondria – numerous
Less SR
Fewer T tubules
Myofibrils
Sarcomeres
–
–
–
–
–
A band
I band
Z disc
H zone
Striated
(10.10cd)
Smooth muscle
• Six major locations
–
–
–
–
–
–
Blood vessels
Respiratory system
Digestive system
Urinary system
Reproductive system
Eye (lens and iris)
• Siding filament theory applies
– Actin & myosin
– No myofibrils – no striations
Smooth muscle fibers
• Spindle shaped
– 2-10 m diameter
– 20-200 m long
• Nonstriated
• Central nucleus
• Arranged in sheets
– Usually in layers around a
tube
– Peristalsis - waves of
contraction to propel
contents along tube
(10.12b)
Smooth muscle properties
•
•
•
•
•
Slower to contract vs. skeletal muscle
Slower to relax vs. skeletal muscle
Can maintain contraction longer
Resistant to fatigue
Unconscious control
– ANS – autonomic nervous system
– Stretch
– Hormones
Smooth muscle organization
• Single unit innervation
– Smooth muscle fibers connected by gap
junctions
– Network receives single innervation
– Coordinated contraction
• Multiunit innervation
– Each fiber innervated
– Locations
• Iris of eye
• Arrector pili muscle of skin