Chapter 1: Structure and Function of Body Systems Flashcards
Axial Skeleton
Skull
Vertebral Column (C1-Coccyx)
Ribs
Sternum
Appendicular Skeleton
Shoulder Girdle
Pelvic Girdle (L/R coxal or innominate bones)
Bones of Extremities
Joints
Types of Joints
Fibrous
Cartilaginous
Synovial
Fibrous Joints
visually no movement
e.g. sutures of skull
Cartilaginous Joints
allow limited movement
e.g. intervertebral disks
Synovial Joints
allow considerable movement
e.g. elbow and knee
Uniaxial Joints
virtually allows movement along one axis, like a hinge
e.g. elbow and knee
Biaxial Joints
allow movements about two perpendicular axes.
e.g. ankle and wrist
Multiaxial Joints
allow for movement about all three axes
e.g. hip and shoulder ball-and-socket joints
Spinal Vertebrae
7 cervical (neck) 12 thoracic (mid-upper back) 5 lumbar (low back) 5 sacral (coccygeal)
Connective Tissues
Epimysium (outer)
Perimysium (fascicles, or group of fibers)
Endomysium (individual fibers)
Limb muscle attachment distances
Proximal (closer to trunk)
Distal (further from trunk)
Neuromuscular Junction (motor end plate)
junction between motor neuron (nerve cell) and the muscle fiber it innervates
Motor Unit
motor neuron and the muscle fiber it innervates
Sarcoplasm
Cytoplasm of a muscle fiber, contains contractile components consisting of protein filaments, other proteins, stored glycogen and fat particles, enzymes, and specialized organelles such as mitochondria and the sarcoplasmic reticulum.
Myofibrils
~1mm in diameter.
Hundreds dominate sarcoplasm.
Contain contractile apparatuses (myofilament): Myosin and Actin
Myosin and Actin Filaments
Myosin (thick) and Actin (thin).
Organized longitudinally in sarcomeres.
Discharge of an AP from a…
motor nerve signals the release of Ca from the SR into the myofibril, causing tension development in the muscle.
Sliding Filament Theory
States that the Actin filaments on each end of the sarcomere slide inward on myosin filaments, pulling the Z-lines toward the center of the sarcomere, thus shortening the muscle fiber (aka muscle contraction).
Phases of a Muscle Contraction
Resting Excitation-Contraction Coupling Contraction Recharge Relaxation
Resting Phase of Muscle Contraction
Little Ca present in myofibril (most stored in SR) so very few myosin cross bridges are bond to actin.
Excitation-Contraction Coupling Phase
SR is stimulated to release Ca ions.
Ca bonds with troponin (protein situated along actin).
Shift occurs to tropomyosin (another protein along actin).
Myosin cross bridges now attach more rapidly to actin filament.
Contraction Phase
Power stroke (energy for pulling actin) comes from hydrolysis (breakdown due to reaction with water) of ATP to ADP + Phosphate (P).
Recharge Phase
Occurs as long as Ca in available in myofibril, ATP is available to assist uncoupling myosin from actin, and sufficient active myosin ATPase is available for catalyzing (accelerating) the breakdown of ATP.
Relaxation Phase
Occurs when stimulation of motor nerve stops.
Ca is pumped back into SR, which prevents link of myosin to actin filaments.
Contraction of a Myofibril
In stretched muscle I-band and H-zone is elongated, and there is low force potential due to reduced cross bridge actin alignment.
When muscle contracts, I-band and H-zone are shortened.
With completely contracted muscle, there is low force potential due to reduced cross-bridge actin alignment.
Step 1 of Muscle Contraction (5)
ATP splits (by myosin ATPase) causes myosin head to in energized state, allowing it to move into position to form bond with actin.
Step 2 of Muscle Contraction
Release of Phosphate from the ATP splitting process then causes myosin head to change shape and shift.
Step 3 of Muscle Contraction
Actin is pulled toward center of sarcomere and is referred to as Power Stroke; ADP is released.
Step 4 of Muscle Contraction
After Power Stroke has occurred, myosin head detaches from actin but only after another ATP binds to myosin head b/c the binding process facilitates detachment.
Step 5 of Muscle Contraction
The myosin head is now ready to bind to another actin (Step 1), and the cycle continues as long as ATP and ATPase are present and Ca is bound to the troponin.
Activation of Muscles
Arrival of AP as nerve terminal causes release of acetylcholine. Once sufficient amount if acetylcholine its released, and AP is generated across sarcolemma, and the fiber contracts.
Extent of muscle control depends on number of muscle fibers within each motor unit. Great and Less precision?
Greater precision: few as one muscle fiber per motor neuron.
Less precision: may have several hundred fibers served by one motor neuron.
All-or-none Principle
All of the muscle fibers in the motor unit contract and develop force at the same time. There is no such thing as a motor neuron stimulus that causes only some of the fibers to contact. Similarly, a stronger AP cannot produce a stronger contraction.
Twitch
Brief contraction caused by each AP traveling down motor neuron, causing a short period of muscle fiber activation within motor unit.
Second Twitch
If a second twitch is elicited from motor nerve before fibers completely relax, force from the two twitches summates, and the resulting force is greater than that produced by a single twitch.
Decreased time between twitches results in?
Greater summation of cross-bridge binding and force.
Tetanus
Maximal amount of force the motor unit can develop.
Muscle Fiber Types
Type I (slow-twitch) Type IIa (fast-twitch) Type Iix (fast-twitch)
Type I Muscle Fiber
Efficient and fatigue resistant, high capacity for aerobic energy supply, but have limited potential for rapid force development, as characterized by low myosin ATPase activity and low anaerobic power.
Type IIa Muscle Fibers
Inefficient and fatiguable and have low aerobic power, rapid force development, high myosin ATPase activity, and high anaerobic power.
Type IIx Muscle Fibers
Show less resistance to fatigue than Type IIa.
