Download Muscle Physio Notes Cox

Muscles
The Muscular System
• Muscles are responsible for all types of body
movement
• Function of a muscle is contraction (shortening)
• Three basic muscle types are found in the body
▫ Skeletal muscle
▫ Cardiac muscle
▫ Smooth muscle
Function of Muscles
• Produce Movement
▫ Allow us to escape danger, move, manipulate things,
express emotion
• Maintain Posture
▫ Muscles function constantly making tiny adjustments to
maintain erect or seated posture despite gravity
• Stabilize Joints
▫ Muscle tendons reinforce joints at their articulating
surface
• Generate Heat
▫ ATP is used to power muscle contractions 75% of this
energy escapes as heat
▫ It maintains our body temperature
Skeletal Muscle
• Muscle fibers are bundled
together by connective tissue
called endomysium
• Groups of muscle fiber are then
wrapped again by a coarser fiber
called perimysium which forms
bundles of fibers called a fascicle
• Many fascicles are wrapped
together by a connective tissue
called the epimysium which
covers the entire muscle.
• The epimysia blend in to make
the tendons which connect
muscle to bone
Microscopic Anatomy of Muscle
• Multinucleate
• Sarcolemma—Plasma
membrane of the muscle
cell
• In the muscle cell are long
ribbon like fiber called
myofibrils.
• Very little cytoplasm in a
muscle cell—filled with
myofibrils
Microscopic Anatomy
• Myofibrils are chains of contractile
units called sarcomeres aligned end
to end
• In a sarcomere there are
myofilaments
• There are 2 types of myofilaments
• Thick filaments which contain a
protein called myosin
▫ Myosin splits ATP which gives power for
muscle contraction
▫ End has projections which connect the
thick and thin fibers during contraction
• Thin filaments called actin
Nerve Stimulus
• Skeletal muscles are stimulated to move by nerve cells
• The nerve and the muscles it stimulates are called a
motor unit
• The axons of a nerve reaches the muscles at the
sarcolemma it is called a neuromuscular junction
• There is a gap called a synaptic cleft filled with
interstitial fluid
Nerve Stimulus--Physiology
• When the nerve impulse reaches the terminal a
neurotransmitter is released
• Neurotransmitter is a chemical called acetylcholine
(Ach) ( Later reabsorbed by : Acetylchoinestersae)
• It triigers the membrane to accept Na ions (called
depolarization of the membrane):
• Lots of sodium ions enter and some potassium ions
leave
• This causes an upset in the electrical conditions –this
upset is called an action potential
Mitochondria Role in Muscle Contraction
• At the NMJ Mitochondria produce energy:
ATP
• Energy used for muscle contraction
• ATP: made with ADP + P
• P=Creatine Phosphate
Nerve Stimulus--Physiology
• This action potential sends
electrical current from one end of
the cell to another
• This causes muscle contraction
• Myosin heads attach their tiny
“oars” and slide the actin
together= muscle contraction
• To relax myosin detach from Actin
filament and actin slides apart
• Then Ca+2 reabsorbed, Na+/K+
pump starts to reset muscle so it
can contract again