Chapter 50 (Motor Mechanism) Flashcards
skeletal muscle
moves bones and the body and is characterized by a hierarchy of smaller and smaller units. consists of a bundle of long fibers, each a single cell, running along the length of the muscle
Myofibrils
Each muscle fiber (cell) is itself a bundle of smaller myofibrils arranged
longitudinally
Muscle cell contraction relies on what interaction
interaction between thin filaments, composed mainly of actin, and thick filaments, staggered arrays of
Myoblast
Mononucleated, undifferentiated muscle precursor cell. A skeletal muscle cell is formed by the fusion of multiple myoblasts.
sliding-filament model
thin and thick filaments ratchet past each other longitudinally, powered by the myosin molecules
The regulatory protein tropomyosin and the troponin complex
a set of additional proteins, bind to actin strands on thin filaments when a muscle fiber is at rest. This prevents actin and myosin from interacting
what has to happen for a muscle fiber to contract
myosin-binding sites must be exposed. This occurs when calcium ions (Ca2+) bind to the troponin complex and expose the myosin-binding sites
What does Ca2+ have to do with the contraction of muscle fiber
Contraction occurs when the concentration of Ca2+is high; muscle fiber contraction stops when the concentration of Ca2+is low
What is the stimulus leading to contraction of a muscle fiber
an action potential in a motor neuron that makes a synapse with the muscle fiber. The synaptic terminal of the motor neuron releases the neurotransmitter acetylcholine
How does the neurotransmitter Acetylcholine affect our muscles
depolarizes the muscle, causing it to produce an
action potential. The action potential causes the sarcoplasmic reticulum (SR) to release Ca2+
Sarcoplasmic reticulum
is a specialized endoplasmic reticulum that regulates the Ca2+ concentration in the cytosol of muscle cell.
Actin Filaments
Slide past mycosin, causing contraction
Myosin Filaments
pull actin filaments by means of cross-bridges; are enzymatic and split ATP
Ca2+
Needed for mycosin to bind to actin
motor unit
consists of a single motor neuron and all the muscle fibers it controls
Myasthenia gravis
is an autoimmune disease that attacks acetylcholine
receptors on muscle fibers
Amyotrophic lateral sclerosis (ALS)
formerly called Lou Gehrig’s disease, is a fatal degenerative disease characterized by the death of
neurons which signal muscle contraction.
Botulinum toxin
inhibits presynaptic release of acetylcholine. Untreated botulism is typically fatal because muscles required for breathing fail to contract when acetylcholine release is blocked.
Tetnus
is an infection caused by bacteria called Clostridium tetani. Tetanus neurotoxin binds to the presynaptic membrane of the neuromuscular
junction and blocks release of GABA, inhibitory neurotransmitter inducing paralysis.
Ligaments
Connect bone to bone
Tendon
Connects muscle to bone
paired muscles work cooperatively
Can only pull, cannot push. When one muscle contracts, it stretches its antagonistic partner
Three Types of Joints
1) Ball and Socket Joint
2) Hinge Joint
3) Pivot Joint
Osteoblasts
bone-forming cells, Synthesize new matrix
Osteoclasts
Break down bone, remove worn cells, deposit calcium in
the blood
Osteocytes
mature bone cells, become caught in the matrix
OSTEOPOROSIS
silent disease: it does not produce symptoms until fracture occurs. Is a bone disease that leads to an increased risk of fracture. The form of osteoporosis most common in women after menopause
