Transcript Muscular System

Honors Biology
• From the Latin mus meaning little mouse (Flexing
muscles looked like mice scurrying under the skin)
• Have ability to transform ATP into mechanical energy
• Muscles can only pull, never push, which allows them to
exert a force
ATP --> ADP + P + Energy
ADP + P + Energy ---> ATP
Myosin
Actin
• Skeletal - Slow to Fast twitch
• Cardiac - Fast twitch
• Smooth - Slow twitch
• Twitch = contraction
• Skeletal & smooth muscle cells are elongated &
called fibers
• All have contractile myofilaments actin & myosin
-Produce movement
• Skeletal – locomotion & manipulation in response to
the environment
• Cardiac – moves blood
• Smooth – propels (squeezes) stuff through the
digestive, urinary, circulatory, and reproductive
systems
-Maintaining posture
-Stabilizing joints
-Generating heat (40% of your body heat)
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Striated
Multinucleate
Voluntary muscles
Can generate great power but fatigue quickly
Non-rhythmic contraction
Sarcoplasmic Reticulum
Sarcoplasm = (Cytoplasm with
lots of glycogen stored)
Sarcolemma
(Plasma membrane)
Sarcomere – Contractile Unit of
Muscle
Nerve & Blood Supply
Each muscle is served by:
• 1 nerve
• 1 artery
• 1 or more veins
Skeletal Muscle Attachment
Skeletal muscles attach to bones in at least 2 places
• When the muscle contracts, the moveable bone (Insertion),
moves toward the immovable or less-moveable bone (Origin)
Sliding Filament Theory
•
Hugh Huxley 1954 proposed that during contraction
actin will slide past myosin which result in overlapping
filaments
1.
Cross bridge attachment
2.
Power stroke (Myosin head pivots pulling actin)
3.
Cross bridge detachment (ATP binds to myosin head
loosening the bond to actin)
4.
“Cocking” the myosin head – ATPase hydrolyzes ATP to
ADP & Pi returning the myosin head to it’s cocked
position
• Muscle contraction is stimulated
by an action potential from a nerve
• The neuromuscular junction in
skeletal muscle is regulated by
acetylcholine (ACh)
• Ach needs to be broken down as
soon as it is used; the enzyme
acetlycholinesterase serves this
function.
a.
b.
c.
Generating an Action Potential
• Depolarization (Na channels open)
• Repolarization (Na channels close K channels open)
• Refractory Period (K channels close)
• Na/K pump
Homeostatic Imbalance
• Myasthenia gravis – autoimmune disease where ACh receptors
are broken down by ACh antibodies resulting in drooping
eyelids and general muscle fatigue
• Curare – arrowhead poison used in South America which
blocks ACh receptors resulting in respiratory arrest & death
• Cobra venom – same as curare
• Botulinum toxin prevents ACh release
• Black widow spider venom releases all Ach
• Nerve gasses inhibit AChase which keeps cleft flooded with
ACh
ACh destruction
• After ACh initiates the action potential the ACh
is broken down by acetylcholinesterase
• This prevents continued muscle contraction in
the absence of additional nerve stimuli
Mysostatins control muscle growth
Absence of results in enlarged muscle development