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Terms in this set (135)

• Ball-and-socket joints
- Smooth, hemispherical head fits within a cuplike socket
- Shoulder joint: head of humerus into glenoid cavity of scapula
- Hip joint: head of femur into acetabulum of hip bone
• Only multiaxial joints in the body

• Condylar (ellipsoid) joints
- Oval convex surface on one bone fits into a complementary-shaped depression on the other
- Radiocarpal joint of the wrist
- Metacarpophalangeal joints at the bases of the fingers
• Biaxial joints—movement in two planes

• Saddle joints
- Both bones have an articular surface that is shaped like a saddle, concave in one direction and convex in the other
- Trapeziometacarpal joint at the base of the thumb
- Sternoclavicular joint: clavicle articulates with sternum

• Biaxial joint
- More movable than a condyloid or hinge joint forming
the primate opposable thumb
• Plane (gliding) joints
- Flat articular surfaces in which bones slide over each other with relatively limited movement
• Usually biaxial joint
- Carpal bones of wrist
- Tarsal bones of ankle
- Articular processes of vertebrae
• Although any one joint moves only slightly, the combined action of the many joints in wrist, ankle, and vertebral column allows for considerable movement

Classes of Synovial Joints
• Hinge joints
- One bone with convex surface that fits into a concave depression on other bone
- Elbow joint: ulna and humerus
- Knee joint: femur and tibia
- Finger and toe joints
• Monoaxial joint—move freely in one plane

• Pivot joints
- One bone has a projection that is held in place by a ringlike ligament
• Bone spins on its longitudinal axis
- Atlantoaxial joint (dens of axis and atlas)
• Transverse ligament
- Proximal radioulnar joint allows the radius to rotate
during pronation and supination
• Anular ligament
• Monoaxial joint
• Tibiofemoral (knee) joint—largest and most complex diarthrosis of the body
• Primarily a hinge joint
- Capable of slight rotation and lateral gliding when knee is flexed
- Patellofemoral joint—gliding joint
• Joint capsule encloses only the lateral and posterior aspects of the knee, not the anterior
- Anterior covered by patellar ligament and lateral and medial retinacula
• All are extensions of the tendon of quadriceps femoris muscle
• Knee stabilized
- Quadriceps tendon in front
- Tendon of semimembranosus muscle on rear of thigh
• Joint cavity contains two C-shaped cartilages
- Lateral meniscus and medial meniscus
- Joined by transverse ligament
• Absorbs shock on the knee
• Prevents femur from rocking side-to-side on the tibia
Popliteal region of knee
- Supported by a complex array of extracapsular ligaments external to joint capsule
• Prevent knee from rotating when joint is extended
• Fibular (lateral) collateral ligament
• Tibial (medial) collateral ligament
• Two intracapsular ligaments deep within joint capsule
- Synovial membrane folds around them, so they are excluded from the fluid- filled synovial cavity
- Ligaments cross each other to form an X
• Anterior cruciate ligament (ACL)
- Prevents hyperextension of knee when ACL is pulled tight
- Common site of knee injury
• Posterior cruciate ligament (PCL)
- Prevents femur from sliding off tibia
- Prevents tibia from being displaced backward
- Untwists the ligaments
• Ability to "lock" the knees
- Important aspect of human bipedalism
- When knee is extended to the fullest degree allowed by ACL
• Femur rotates medially on the tibia
• Locks knee, and all major knee ligaments are twisted and taut
• Popliteal region: popliteal bursa and semimembranosus bursa
• Seven more bursae on lateral and medial sides of knee joint
• Medial and lateral meniscus absorb shock and shape join
• Thick filaments—made of several hundred myosinmolecules
- Shaped like a golf club
• Two chains intertwined to form a shaftlike tail
• Double globular head
- Heads directed outward in a helical array around the bundle
• Heads on one half of the thick filament angle to the left
• Heads on the other half angle to the right
• Bare zone with no heads in the middle
• Thin filaments
- Fibrous (F) actin: two intertwined strands
• String of globular (G) actin subunits each with an active site
that can bind to head of myosin molecule
- Tropomyosin molecules
• Each blocking six or seven active sites on G actin subunits
- Troponin molecule: small, calcium-binding protein on
each tropomyosin molecule
• Elastic filaments
- Titin (connectin): huge, springy protein
- Flank each thick filament and anchor it to the Z disc
- Help stabilize the thick filament
- Center it between the thin filaments
- Prevent overstretching
• Contractile proteins—myosin and actin do the work
• Regulatory proteins—tropomyosin and troponin
- Like a switch that determines when the fiber can contract and when it cannot
- Contraction activated by release of calcium into sarcoplasmand its binding to troponin
- Troponin changes shape and moves tropomyosin off the active sites on actin
• At least seven other accessory proteins in or associated with thick or thin filaments
- Anchor the myofilaments, regulate length of myofilaments, keep alignment for optimal contractile effectiveness
• Dystrophin—most clinically important
- Links actin in outermost myofilaments to transmembrane proteins and eventually to fibrous endomysium surrounding the entire muscle cell
- Transfers forces of muscle contraction to connective tissue around muscle cell
- Genetic defects in dystrophin produce disabling disease muscular dystrophy
• Muscle fibers and neurons are electrically excitable cells
- Their plasma membrane exhibits voltage changes in response to stimulation
• Electrophysiology—the study of the electrical activity of cells
• Voltage (electrical potential)—a difference in electrical charge from one point to another
• Resting membrane potential—about −90 mV
- Maintained by sodium-potassium pump
• In an unstimulated (resting) cell
- There are more anions (negative ions) on the inside of the
plasma membrane than on the outside
- The plasma membrane is electrically polarized (charged)
- There are excess sodium ions (Na+) in the extracellular
fluid (ECF)
- There are excess potassium ions (K+) in the intracellular
fluid (ICF)
- Also in the ICF, there are anions such as proteins, nucleic
acids, and phosphates that cannot penetrate the plasma membrane
- These anions make the inside of the plasma membrane
negatively charged by comparison to its outer surface
• Stimulated (active) muscle fiber or nerve cell
- Ion gates open in the plasma membrane
- Na+ instantly diffuses down its concentration gradient into the
cell
- These cations override the negative charges in the ICF
- Depolarization: inside of the plasma membrane becomes
briefly positive
- Immediately, Na+ gates close and K+ gates open
- K+ rushes out of cell
- Repelled by the positive sodium charge and partly because of its concentration gradient
- Loss of positive potassium ions turns the membrane negative again (repolarization)
• Stimulated (active) muscle fiber or nerve cell (cont.)
- Action potential: quick up-and-down voltage shift from the
negative RMP to a positive value, and back to the negative value again
- RMP is a stable voltage seen in a waiting muscle or nerve
cell
- Action potential is a quickly fluctuating voltage seen in an
active stimulated cell
- An action potential at one point on a plasma membrane
causes another one to happen immediately in front of it, which triggers another one a little farther along and so forth
• At subthreshold stimulus—no contraction at all
• At threshold intensity and above—a twitch is produced
- Twitches caused by increased voltage are no stronger than those at threshold
• Not exactly true that muscle fiber obeys an all-or-none law—contracting to its maximum or not at all
- Electrical excitation of a muscle follows all-or-none law
- Not true that muscle fibers follow the all-or-none law
- Twitches vary in strength depending upon:
• Stimulus frequency—stimuli arriving closer together produce stronger twitches
• Concentration of Ca+2 in sarcoplasm can vary the frequency
• How stretched muscle was before it was stimulated
• Temperature of the muscles—warmed-up muscle contracts
more strongly; enzymes work more quickly
• Lower than normal pH of sarcoplasm weakens contraction—
fatigue
• State of hydration of muscle affects overlap of thick and thin filaments
• Muscles need to be able to contract with variable strengths for different task
• Stimulating the nerve with higher and higher voltages produces
stronger contractions
- Higher voltages excite more and more nerve fibers in the motor nerve which stimulates more and more motor units to contract
• Recruitment or multiple motor unit (MMU) summation—the
process of bringing more motor units into play
• When stimulus intensity (voltage) remains constant twitch strength can vary with the stimulus frequency
• Up to 10 stimuli per second
- Each stimulus produces identical twitches and full recovery between twitches
• 10-20 stimuli per second produces treppe (staircase)
phenomenon
- Muscle still recovers fully between twitches, but each twitch develops more tension than the one before
- Stimuli arrive so rapidly that the SR does not have time
between stimuli to completely reabsorb all of the Ca2+ it released
- Ca2+ concentration in the cytosol rises higher and higher
with each stimulus causing subsequent twitches to be stronger
- Heat released by each twitch causes muscle enzymes
such as myosin ATPase to work more efficiently and produce stronger twitches as muscle warms up
• 20-40 stimuli per second produces incomplete tetanus
- Each new stimulus arrives before the previous twitch is over
- New twitch "rides piggy-back" on the previous one generating
higher tension
- Temporal summation: results from two stimuli arriving close
together
- Wave summation: results from one wave of contraction added to another
- Each twitch reaches a higher level of tension than the one before
- Muscle relaxes only partially between stimuli
- Produces a state of sustained fluttering contraction called incomplete tetanus
• 40-50 stimuli per second produces complete tetanus
- Muscle has no time to relax between stimuli
- Twitches fuse to a smooth, prolonged contraction called complete tetanus
- A muscle in complete tetanus produces about four times the tension as a single twitch
- Rarely occurs in the body, which rarely exceeds 25 stimuli per second
- Smoothness of muscle contractions is because motor units function asynchronously
• When one motor unit relaxes, another contracts and takes over so the muscle does not lose tension
• Muscles can generate more tension than the bones and tendons can withstand
• Muscular strength depends on:
- Primarily muscle size
• A muscle can exert a tension of 3 or 4 kg/cm2 of cross-sectional area
- Fascicle arrangement
• Pennate are stronger than parallel, and parallel stronger than circular
- Size of motor units
• The larger the motor unit the stronger the contraction
- Multiple motor unit summation: recruitment
• When stronger contraction is required, the nervous system
activates more motor units
- Temporal summation
• Nerve impulses usually arrive at a muscle in a series of closely
spaced action potentials
• The greater the frequency of stimulation, the more strongly a
muscle contracts
- Length-tension relationship
• A muscle resting at optimal length is prepared to contract more
forcefully than a muscle that is excessively contracted or stretched
- Fatigue
• Fatigued muscles contract more weakly than rested muscles
• Resistance training (weightlifting)
- Contraction of a muscle against a load that resists movement
- A few minutes of resistance exercise a few times a week is enough to stimulate muscle growth
- Growth is from cellular enlargement
- Muscle fibers synthesize more myofilaments and myofibrils and grow thicker
• Endurance training (aerobic exercise)
- Improves fatigue-resistant muscles
- Slow twitch fibers produce more mitochondria, glycogen, and acquire a greater density of blood capillaries
- Improves skeletal strength
- Increases the red blood cell count and oxygen transport capacity of the blood
- Enhances the function of the cardiovascular, respiratory, and nervous systems
• Limited to the heart where it functions to pump blood
• Properties of cardiac muscle
- Contraction with regular rhythm
- Muscle cells of each chamber must contract in unison
- Contractions must last long enough to expel blood
- Must work in sleep or wakefulness, without fail, and without conscious attention
- Must be highly resistant to fatigue
• Characteristics of cardiac muscle cells
- Striated like skeletal muscle, but myocytes (cardiocytes) are shorter and thicker
- Each myocyte is joined to several others at the uneven, notched linkages—intercalated discs
• Appear as thick, dark lines in stained tissue sections
• Electrical gap junctions allow each myocyte to directly stimulate
its neighbors
• Mechanical junctions that keep the myocytes from pulling apart
• Sarcoplasmic reticulum less developed, but T tubules are larger and admit supplemental Ca2+ from the extracellular fluid
• Damaged cardiac muscle cells repair by fibrosis
- A little mitosis observed following heart attacks
- Not in significant amounts to regenerate functional muscle
• Can contract without need for nervous stimulation
- Contains a built-in pacemaker that rhythmically sets off a wave of electrical excitation
- Wave travels through the muscle and triggers contraction of heart chambers
- Autorhythmic: able to contract rhythmically and independently
- Autonomic nervous system does send nerve fibers to the heart
• Can increase or decrease heart rate and contraction strength
- Very slow twitches; does not exhibit quick twitches like skeletal muscle
• Maintains tension for about 200 to 250 ms
• Gives the heart time to expel blood
- Uses aerobic respiration almost exclusively
• Rich in myoglobin and glycogen • Has especially large mitochondria
- 25% of volume of cardiac muscle cell - 2% of skeletal muscle cell with smaller mitochondria
The pituitary gland is a tiny organ, the size of a pea, found at the base of the brain. As the "master gland" of the body, it produces many hormones that travel throughout the body, directing certain processes or stimulating (causing) other glands to produce other hormones.
Prolactin - Prolactin stimulates breast milk production after childbirth. It also affects sex hormone levels from ovaries in women and from testes (testicles) in men, as well as fertility.
Growth hormone (GH) - GH stimulates growth in childhood and is important for maintaining a healthy body composition and well-being in adults. In adults, GH is important for maintaining muscle mass and bone mass. It also affects fat distribution in the body. Read about growth hormone excess.
Adrenocorticotropin (ACTH) - ACTH stimulates the production of cortisol by the adrenal glands—small glands that sit on top of the kidneys. Cortisol, a "stress hormone," is vital to our survival. It helps maintain blood pressure and blood glucose (sugar) levels, and is produced in larger amounts when we're under stress—especially after illness or injury. Read about having too much ACTH.
Thyroid-stimulating hormone (TSH) - TSH stimulates the thyroid gland to produce thyroid hormones, which regulate the body's metabolism, energy balance, growth, and nervous system activity. Read about TSH-secreting tumors.
Luteinizing hormone (LH) - LH stimulates testosterone production in men and egg release (ovulation) in women.
Follicle-stimulating hormone (FSH) - FSH promotes sperm production in men and stimulates the ovaries to produce estrogen and develop eggs in women. LH and FSH work together to enable normal function of the ovaries and testes.