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Study Guide: Exam 3
Functions of the muscular system (4) |
Locomotion, facial expression, posture, regulation of body temperature |
Origin definition |
The place where the muscle strts on a bone- stays stationary (fixed end of muscle) |
Insertion |
The place where the muscle ends on bone- moves toward the origin (movable end of muscle) |
Lever |
Rigid bar --> bone |
Fulcrum |
Fixed point around which the right bar (bone) moves --> joint |
First class levers and Example |
(LFE) = Load, Fulcrum, Effort
Ex: Load=Head pulling down, Fulcrum=Temporal, Effort=Muscle pulling head back |
Second class levers and Example |
(FLE)= Fulcrum, Load, Effort
Ex: No examples found in the body |
Third class levers and Example |
(FEL)- Fulcrum, Effort, Load.
Ex: Most common type of lever in the body. Very inefficient energetically but yields controllable movements. F=Fulcrum, E= Bicep Brachii, L=Weight in hand |
Flexion/Extension |
Movement to reduce or increase the angle between articulating bones at a joint in the anterior/posterior plane |
Abduction/Adduction |
Movement away or toward the longitudinal axis (or midline) of the body in the frontal plane |
Circumduction |
Combination of adduction/abduction and flexion/extension such that the distal end of a limb moves in a circle |
Rotation: Medial (internal) rotation & Lateral (external) rotation |
Refers to the movement away from the long axis of the trunk |
Protraction/Retraction |
Movement of a part of the body anteriorly or posteriorly in the horizontal body plane. (Mandible, clavicles, scapula) |
Elevation/Depression |
Movement of a part of the body superiorly or inferiorly in the frontal body plane (Mandible, scapula, clavicle) |
Dorsiflexion/Plantar flexion |
Flexion and extension of the foot at the ankle.
Dorsiflexion=flexion of the dorsal surface of the foot
Plantar flexion=flexion of the plantar surface of the foot
-Plantar surface=sole of the foot |
Inversion/Eversion |
Inversion- movement of the foot such that the plantar surface is turned inward
Eversion- movement of the foot such that the plantar surface is turned outward |
Supination/Pronation |
Movement of the forearm such that the palms face anteriorly or posteriorly
The palm is supinated in standard anatomical position-palms face anteriorly
Pronation-palms face posteriorly |
Agonist and Example |
Muscle primarily responsible for the movement. Example: Biceps brachii. Ex2: Deltoid |
Antagonist and Example |
Muscle which opposes the action of the agonist. Example: Triceps brachii. Ex2: Latissimus dorsi |
Synergist and Example |
Assists the agonist in making the action more efficient. Example: Brachialis. Ex2: Supraspinatus |
Fixator and Example |
Special synergists which help to prevent movement at muscle origin. Example: Trapezius |
Skeletal Muscle Functions (5) |
1. Skeletal movement (locomotion) 2. Posture and body position (facial expression) 3. Support 'soft tissues' (gut) 4. Guard entrances and exits to the body 5. Maintain body temperature |
Cellular and Subcellular Skeletal Muscle Structure |
1. Muscle cells are FIBERS
2. Typically MULTINUCLEATE
-arise from fusion or MYOBLASTS |
Skeletal muscle fiber structure has three functional levels of organization. Structure ONE. |
1. Plasma membrane=SARCOLEMMA. Surrounds cytoplasm=SARCOPLASM. TRANSVERSE TUBULES (T-tubules) arise from sarcolemma. |
Skeletal muscle fiber structure has three functional levels of organization. Structure TWO. |
2. Sarcoplasmic Recticulum (SMOOTH ER). Close in location to T-tubules. Surrounds myofibrils. |
Skeletal muscle fiber structure has three functional levels of organization. Structure THREE. |
3. Myofibrils. Longitudinal bundles or protein filaments=ACTIN & MYOSIN. Highly organized into repeating units=SARCOMERES. |
Sarcomeres |
Functional Unit of Contraction Elements |
Thin Filament |
Unit of contraction in sarcomere. Attached to Z line (Z disc). Composed of two helically arranged strands of ACTIN. |
Thick Filament |
Unit of contraction in the sarcomere. Spans the distance between thin filaments. Composed of a highly organized array of MYOSIN molecules. Myosin head has ATPase activity when bound to actin. |
Titin |
The third myofilament of striated muscle. Largest known protein. Stores energy during shortening and then assists in returning the sarcomere to its resting length |
Sliding Filament Model of Muscle Contraction (3) |
1. Myosin "heads" bind to actin to form a CROSSBRIDGE. 2. Conformational change, energized by ATP hydrolysis, causes thin filaments to SLIDE along thick filaments. 3. Myosin head groups release, form new crossbridges, and the sliding cycle repeats |
End result of filament model of muscle contraction |
Z-Lines move toward one another. Sarcomere length decreases. Muscle fiber shortens. |
As Thick/thin filament overlap increases... |
-I band width gets narrower
-A band widths remains constant |
Crossbridge Cycling |
Cycle is entered following exposure of myosin binding sites on the actin thin filament. (Regulatory role for Ca2+) |
Crossbridge Cycling Step One |
1. MYOSIN HEAD BINDS TO ACTIN FORMING A CROSSBRIDGE
a. ATP has already bound to the myosin head
b. This ATP is hydrolyzed by the unbound head, and the released energy results in a "cocking" of the head group.(ADP and Pi remain bound to the cocked head).
c. Myosin head group binds to actin thin filament forming a crossbridge |
Crossbridge Cycling Step Two |
2. CROSSBRIDGE PIVOTS.
After binding, ADP and Pi are released and the head group 'pivots' back toward original orientation. When the ATP is hydrolyzed->release of energy trapped. The thin filament "slides" past the thick filament. |
Crossbridge Cycling Step Three |
3. CROSSBRIDGE DETACHES
ATP binds to the myosin head group -->breaking of crossbridge. The attaches head group-->RIGOR COMPLEX. The detached head group then hydrolyzes the ATP |
Sequence of Events of Excitation-Contraction Coupling |
1. Electrical signal transmitted from a motoneuron to a skeletal muscle fiber
2. Triggers a release of Ca2+ from SR
3. Ca2+ binds to a regulartory proteins of thin filament, thereby permitting crossbridges to form. (crossbridge cycling results in tension development) 4. Removal of Ca2+ results in relaxation |
The 'Electrical Signal' |
Neuromuscular Transmission!
1. Activation of SKELETAL muscle is VOLUNTARY. Requires a signal from the central nervous system (CNS). Signal results in an electrical impulse along a motoneuron that arrives at the NEUROMUSCULAR JUNCTION |
The Neuromuscular Junction Key Points (4) |
1. Synaptic vesicles of NMJ contain NEUROTRANSMITTER, ACETYLCHOLINE (ACh)
2. ACh released from synaptic terminal, diffuses across synaptic cleft & binds to ACh receptor. 3. The activated ACh receptor permits Na+ to enter muscle at motor endplate, producing an ACTION POTENTIAL along sarcolemma. 4. ACh broken down to acetate & choline |
Release of Ca2+ from the SR (5) |
1. AP runs along sarcolemma, continues into T-tubule
2. Triggers release of Ca2+ from SR
3. Ca 2+ binds to regulatory proteins on thin filament. MYOSIN BINDING SITE GETS EXPOSED.
5. Crossbridges form->tension generated |
Relaxation- Sequenstration of Ca2+ |
1. When APs stop arriving at the NMJ, the 'trigger' to release Ca2+ from the SR stops.
2. Active Ca2+ transporters in the SR membrane pump Ca2+ back into the SR. CYTOPLASMIC[CA2+] DECREASES. 3. As [Ca]cyto falls, Ca comes off regulatory proteins- the myosin binding sites covered. 4. Crossbridge cycling stops. TENSION DEVELOPMENT RELAXES |
The molecular/cellular basis of the length-tension relationship |
Tension is proportional to cross-bridge function |
How do we know that formation of crossbridges is responsible for the generation of tension in skeletal muscle? |
Observation(s)
a. actin plus myosin hydrolyzs ATP
b. 'Skinned' muscle fibers retain sarcomere structure and shorten in the presence of ATP and Ca2+ |
Hypothesis between tension by sarcomere and thick and thin filaments |
The level of tension generated by sarcomere is directly proportional to the overlap of thick and thin filaments.
Testing: Length-tension relationship |
Term: Neuromuscular Junction (NMJ) |
A synapse between the axon terminals of a motor neuron and the sarcolemma of a muscle fiber(cell) |
Term: Neurotransmitter |
One of a variety of molecules within axon terminals that are released into the synaptic cleft in response to a nerve impulse and that change the membrane potential of the postsynaptic neuron |
Term: Action potential (AP) |
An electrical signal that propagates along the membrane of a neuron or muscle fiber (cell); a rapid change in membrane potential that involves a depolarization followed by a repolarization |
Term: Acetylcholine (ACh) |
A neurotransmitter liberated by many peripheral nervous system neurons and some central nervous system neurons. It is excitatory at neuromuscular junctions |