252 exam 2

Functions of the Skeletal System

• protection: skeleton protects vital organs such as the brain

• mineral storage and acid base homeostasis: bone stores minerals such as calcium and phosphate which are necessary for electrolyte and acid base balance

• blood cell formation: red bone marrow site of blood cell formation

• fat storage: yellow bone marrow stores triglycerides

• movement: muscles produce body movement via their attachment to bones

• support

Which best describes why doctors recommend that women (XX genotyped individuals), who are prone to estrogen-dependent osteoporosis, take calcium supplements?

A. As women age, their ability to produce Ca2+ decreases and reduced Ca2+ causes the bone to shatter.

B. Women cannot make Ca2+, which is essential to maintaining the shape of bone

C. Estrogen prohibits Ca2+ production by the parathyroid gland, which causes bone to shatter

B. Women cannot make Ca2+, which is essential to maintaining the shape of bone

We can’t make Ca2+ we get it from our diets

Types of Specialized Connective Tissue: Bone

65%: hydroxyapatite crystals

35%: collagen and osteoid (ground substance)

Organic and Inorganic matrices work together to promote bone structure and function

If you remove the organic matrix

• collagen is brittle and the bone shatters easily

if you remove the inorganic matrix

• minerals cannot resist compression bone will bend/curve

Which of the following statements is/are true?

A. Osteoblasts secrete enzymes that break down the extracellular matrix.

B. Osteocytes are derived from osteoblasts.

C. Both of the above are true statements

D. Neither of the above are true statements

B. Osteocytes are derived from osteoblasts.

Bone Cells

Osteocyte

• maintains bone tissue

Osteoblast

• forms bone matrix

Osteogenic cell

• stem cell

Osteoclast

• resorbs bone

Osteoblasts and Osteocytes

1. osteogenic cells differentiate into osteoblasts

2. osteoblasts deposit bone until they are trapped and become osteocytes

3. osteocytes maintain the bone extracellular matrix (ECM)

Osteocyte

• mature bone cells that are amitotic; derived from osteoblasts

• thought to be mechanosensory cells that control activity of osteoblasts and osteoclasts

• communicate with other osteocytes via gap junctions

Osteoclasts

• sit on surface of bone

• enzymes and H+ degrade the bone ECM, Components of the bone ECM enter the osteoclast (bone resorption)

Chondrocyte

cells of cartilage that initiate bone formation. They differentiate into osteogenic cells → osteoblasts

epiphyseal plate

Diaphyseal side

• zone of ossification

  • osteoblasts and calcified cartilage

• zone of calcification

  • dead chondrocytes

• zone of hypertrophy and maturation

• zone of proliferation

  • chondrocytes in lacunae

• zone of reserve cartilage

epiphyseal plate

Which epiphyseal zone is closest to the diaphysis?

A. Zone of ossification

B. Zone of calcification

C. Zone of hypertrophy and maturation

D. Zone of proliferation

A. Zone of ossification

Longitudinal Bone Growth

Diaphysis

• newly formed bone

  • bone is resorbed by osteoclasts and replaced with bone

• zone of ossification

  • osteoblasts invade calcified cartilage and lay down bone

• zone of calcification

  • chondrocytes die (far from blood supply) and ECM calcifies

• zone of hypertrophy and maturation

  • chondrocytes enlarge, mature, and stop dividing

• zone of proliferation

  • chondrocytes divide in the zone of proliferation

epiphyseal plate

Growth hormone induces longitudinal bone growth

longitudinal bone growth = bone grows in length

Testosterone and Estrogen also promote bone growth

• appositional bone growth - growth in width (testosterone)

• increases rate of mitosis and epiphyseal plate

• can increase the closure of epiphyseal plates (estrogen is more potent than testosterone)

Testosterone and estrogen also prohibit the activity of osteoclasts

• Estrogen activates osteoclast apoptosis and inhibits osteoclast activity

• androgens like testosterone inhibit osteoclast activity and osteoblast apoptosis and activate osteoblast proliferation and differentiation

Bone terminology

• bone remodeling: continuous formation and loss of bone

• bone deposition: formation of new bone

• bone resorption: destruction of old bone

Bone deposition is caused by increased osteoblast activity due to:

1. compressional load/exercise

2. tension on bone

3. testosterone

4. vitamin consumption

Bone deposition is caused by decreased osteoclast activity due to:

1. estrogen

2. calcitonin

3. increased blood calcium ion concentration

Bone resorption is caused by decreased osteoblast activity due to

1. inadequate exercise

2. inadequate vitamin consumption

bone resorption is caused by increased osteoclast activity due to

1. continuous pressure placed on bone

2. parathyroid hormone

3. decrease in blood calcium ion concentration

If there is imbalance in bone deposition and resorption what disease(s) could occur?

rheumatoid arthritis

Below is a graph with age starting at adulthood on the x-axis and bone

mineral content on the Y-axis.

• Draw a solid line for what we’d expect for individuals who regularly

perform cardio exercises (e.g., walking, running, swimming).

• Draw a dotted line for what we’d expect for individuals who regularly

weight train.

Below is a graph of XY-individuals (same age; no homeostatic imbalances) who regularly engage in different physical activities. The star likely represents:

A. Someone who swims for an hour, 4 times per week.

B. Someone who walks for an hour, 4 times per week while wearing a 12 lb vest.

C. Someone who spends 45 minutes in the gym lifting free weights 3 times per week.

A. Someone who swims for an hour, 4 times per week.

Why is eating oranges (rich in vitamin C) important to bone health?

A. Promotes Ca2+ deposition in bone

B. Promotes the synthesis of collagen

C. Both of the above

D. Neither of the above

Promotes the synthesis of collagen

True or False: when you drink or consume collagen, the collagen immediately goes to your bones / tissues.

• FALSE

Factors Promoting bone remodeling

Hormones

• Testosterone – bone deposition

• Estrogen – inhibits osteoclast activity

Nutrition

• Calcium

  • Parathyroid hormone increases Ca2+ release into blood stream

  • Calcitonin hormone promotes deposition of Ca2+ into bone

• Vitamin D – promotes Ca2+ uptake in the intestines

  • Safe sun exposure or consumption of dairy products.

• Vitamin C – required for synthesis of collagen

• Vitamin K – glycoprotein production (bind Ca2+)

• Protein – collagen synthesis

Blood Ca2+ homeostasis

• Stimulus: blood calcium decreases below normal range

• receptor: parathyroid gland cells detect a low blood Ca2+ level

• control center: parathyroid gland cells release PTH int the blood

• effector/response: osteoclasts resorb bone, kidneys retain Ca2+, intestines absorb Ca2+

• in homeostatic range: as blood Ca2+ returns to normal, feedback stops effector responses

Properties of muscle cells

1. contractility - ability to contract (but not necessarily shorten)

2. excitability - responsive to stimuli

3. conductivity - electrical changes across the membrane

4. distensibility - stretch without damage

5. elasticity - stretch and retain shape

Which of the following are true (select all that apply)?

A. Striated cells are always multinucleated

B. Striated muscle tissue can be associated with voluntary and involuntary movements

C. Smooth muscle cells communicate with each other via gap junctions

D. Smooth muscle cells are only found in the heart

E. Striated muscle cells can have gap and tight junctions

B. Striated muscle tissue can be associated with voluntary and involuntary movements

C. Smooth muscle cells communicate with each other via gap junctions

E. Striated muscle cells can have gap and tight junctions

Skeletal Muscle Tissue

Structure

• long, cylindrical striated muscle fibers; cells are multinucleated.

Location

• mostly attached to skeleton

Voluntary

Function

• produced movement of the body

Cardiac Muscle Tissue

Structure

• Short, wide, branching striated cardiac muscle cells with intercalated discs; cells have a single nucleus or two nuclei.

Location

• heart

Involuntary

Function

• produces beating of the heart

Smooth Muscle Tissue

Structure

• thin, smooth muscle cells, generally joined by gap junctions; cells have a single nucleus

Location

• walls of hollow organs, as well as in the skin, and the eyes

Involuntary

Function

• changes diameter of hollow organs

• causes hairs to stand erect

• adjusts the shape of the lens and the size of the pupil of the eye

1. Extracellular matrix surrounding a single muscle fiber.

2. Connective tissue surrounding a cluster of many muscle fibers.

3. Connective tissue that connects muscle to bone

4. Connective tissue that surrounds numerous fascicles

A. Endomysium

B. Epimysium

C. Perimysium

D. Tendon

Function of Skeletal Muscles

• Muscle tension - contraction to generate force

  • action = production of body movement

• heat production

Muscle movement is a lever system

1. Lever

2. Load or object you are moving

3. Force (or effort) applied to the lever to move the object

4. Fulcrum – hinge point that allows lever to move

Features of skeletal muscle cells

• Long, thin cylinders

• Striated (striped)

• Multinucleated

Structure of Skeletal Muscle Fiber

• Sarcolemma: Plasma membrane of a muscle fiber

• Myofibril – proteins involved in cell contraction

• Sarcoplasmic reticulum – smooth endoplasmic reticulum that stores and releases Ca2+

• Transverse tubules (T-tubules) – inward extensions of sarcolemma that form a tunnel-like network and filled with extracellular fluid.

• Terminal cisternae – enlarged portions of the sarcoplasmic reticulum on either side of T- tubules

Which region within a sarcomere contains thick filaments only?

A. A band

B. H zone

C. I band

B. H zone

What are thick filaments?

MYOSIN!

Myofibril

Bundles of proteins (myofilaments)

Structural proteins within a myofibril ensure that the myofilaments themselves are in their proper place and promote the structural stability of the myofibril within a muscle fiber. Based on this definition, which of the following proteins would serve as a myofibril structural protein?

A. Myosin

B. Actin

C. Troponin

D. Titin

D. Titin

Stabilizes the thick filament

Thick Filaments

Myosin protein clusters – contractile

• Head – where thin filaments bind

• ATP dependent

Thin filaments

• Actin – subunits of contractile protein with an active site that binds myosin

• Tropomyosin – ropelike protein that spirals around actin and covers active site at rest

• Troponin – holds the tropomyosin in place

Elastic Filaments

Titin – thinnest filament shaped like a slinky

• Holds thick filaments in place

• Resist excessive stretching and provide elasticity

Myofilaments form sarcomeres

• I band contains only thin filaments (light)

• H zone contains only thick filaments

• outer edge of A band - the zone of overlap - contains thick and thin filaments (dark)

If a muscle fiber were excessively stretched to the extent that the thin and thick filaments did not overlap, the reaction of this fiber to a stimulus would be:

A. It will exert more tension than an unstretched muscle

B. It will exert less tension than an unstretched muscle

C. It will exert tension, but without changing the length of the muscle

D. It will not exert tension

D. It will not exert tension

For a muscle to exert tension, thick and thin filaments must overlap!

Actin has Myosin binding sites

Once bound, a change in the angle of the myosin head will pull the actin filaments

Sliding Filament Theory

• Upon stimulation, myosin heads bind to actin and sliding begins

• Thin filaments slide past the thick ones

when fully contraction shorter gap between z lines and reduction in H zone

According to the sliding filament theory, which region of a sarcomere changes in length during a muscle contraction?

A. I band only

B. H band only

C. A band only

D. I band and H band

E. I band and A band

F. I band, H band, and A band

D. I band and H band

Sarcomeres and myofibrils

- We have many sarcomeres in one myofibril

- When all sarcomeres shorten, so does the myofibril

- We have many myofibrils in one muscle fiber

- When all myofibrils shorten, so does the muscle cell

The graph below depicts the length of the sarcomere at rest (x-axis) vs. the tension generated (y-axis; percent of maximum). I

Optimal actin and myosin overlap will produce maximal contraction (tension)

How is myosin and actin interactions regulated?

In a resting state, tropomyosin prevents myosin from binding to actin

Acetylcholine causes muscle contractions when released at the neuromuscular junction. Muscle cells can also propagate action potentials. Therefore, which of the following are present in the membrane of a sarcolemma? (Select all that apply)

A. Voltage-gated K+ channels

B. Voltage-gated Na+ channels

C. K+ leak channels

D. Na+/K+ ATPase

A. Voltage-gated K+ channels

B. Voltage-gated Na+ channels

C. K+ leak channels

D. Na+/K+ ATPase

A and B: Action potentials!

C and D: RMP!

Skeletal muscle is innervated by motor neurons

• Acetylcholine (ACh) is the major neurotransmitter that signals to skeletal muscle cells. acetylcholinesterase (AChE) is found in the synaptic cleft.

• Motor end plate is region of sarcolemma that has “folded structure” that contains nicotinic cholinergic receptors (needed to induce skeletal muscle contraction)

Muscle contraction

1. an action potential arrives at the axon terminal and triggers Ca2+ channels in the axon terminal to open

2. Ca2+ entry triggers exocytosis of synaptic vesicles

3. synaptic vesicles release ACh into the synaptic cleft

4. ACh binds to ligand gated ion channels in the motor end plate

5. ion channels open and Na+ enter the muscle fiber

6. entry of Na+ depolarizes the sarcolemma locally, producing an end plate potential

Neural signals stimulate release of calcium from the SR to the sarcoplasm

ECM in t-tubules

1. the end plate potential stimulates an action potential

2. the action potential is propagated down the t-tubules

3. t tubule depolarization leads to the opening of the Ca2+ channels in the Sr and Ca2+ enter the cytosol

Calcium binds to troponin, leading to release of tropomyosin from the myosin-binding sites

crossbridge cycle starting ATP hydrolysis

1. ATP hydrolysis “cocks” the myosin head

2. the myosin binds to actin

3. the power stroke occurs when the phosphate detaches from the myosin head and myosin pulls actin toward the center of the sarcomere; ADP leaves the myosin head at the end of the power stroke

4. ATP breaks the attachment of myosin to actin (cycle restarts)

crossbridge cycle is repeated to contract the sarcomere

How many ATP molecules are required for a single

crossbridge cycle during the contraction phase?

A. 1

B. 2

C. 3

D. 4

1

Muscle relaxation

1. acetylcholinesterase degrades the remaining ACh, and the final repolarization begins

2. the sarcolemma returns to its resting membrane potential (-90 mV) and the Ca2+ channels in the SR close

3. Ca2+ are pumped back into the SR returning the Ca2+ concentration in the cytosol to its resting level

4. troponin and tropomyosin block the active sites of actin, and the muscle relaxes

ATP is required for cells to relax T or F

True

Ca2+ and AChE work continuously to allow for muscle contraction

• Muscle that is unable to relax = spasm

• Rigor mortis – when muscles cannot relax after death (Ca2+ remains in the cytosol and stimulate contraction)

Muscle cells need a lot of ATP

• Na+/K+ ATPase that maintains restingmembrane potential (-90 mV) of the sarcolemma

• Muscle contraction – crossbridge cycle and actin / myosin interactions

• Muscle relaxation – active transport of Ca2+ back into the sarcoplasmic reticulum

Muscle cells do not store high amounts of cytosolic ATP – they must have mechanisms to generate it quickly!

Creatine phosphate is the main immediate source of ATP in skeletal muscle cells during contraction.

True

False

True

Three mechanisms that skeletal muscles use to generate ATP

Immediate energy needs

• creatine kinase

• glycolytic catabolism

long-term energy needs

• oxidative catabolism

Glycolytic Catabolism

1 glucose = 2 (net) ATP

Glucose source

• Glucose from bloodstream

• Glycogen stores in muscle cells

Oxygen dependent and independent

• Aerobic – 2 pyruvate enter mitochondria and Citric Acid cycle

• Anaerobic – 2 pyruvate converted to 2 lactate (lactic acid)

Short-term energy

Equation for short term energy needs via creatine kinase

ADP + creatine phosphate ←-> creatine + ATP

The Cori cycle

converts lactate into glucose

Oxidative respiration

Oxygen-dependent mechanism that generates ~32-38 ATP per glucose

Three stages:

1. Glycolysis (2 net ATP) – cytosol

2. Pyruvate oxidation and Citric Acid cycle (2 net ATP) -- mitochondria (CAC has 2 rounds)

3. Oxidative phosphorylation (~28-34 net ATP) – mitochondria

Long-term ATP

Oxygen dependence

Oxygen (non-polar) diffuses into the muscle cell from the bloodstream

Myoglobin – oxygen-carrying protein found in the cytosol of muscle cells

• Releases O2 to be used in the mitochondria for oxidative catabolism

Contraction and Relaxation

Which type of wave summation would you expect to observe in a muscle fiber that is being used to lift something heavy for an extended period of time?

A. Unfused tetanus

B. Fused tetanus

B. Fused tetanus

Would need sustained to generate maximum tension in a muscle fiber to lift something heavy for an extended period of time – would therefore expect frequent action potentials.

Draw what the curve would look like for a fused and unfused tetanus.

Wave summation: the amount of tension produced depends on the frequency of stimulation

for an unfused tetanus we would expect more frequent stimuli for a fused tetanus we would expect less frequent stimuli

muscle fatigue is associated with a fused tetanus

Increasing stimuli frequency = increasing tension

- New stimulus starts before the Ca++ is returns to the SR

- Fused tetanus will lead to muscle fatigue

Again with lifting something heavy for an extended period of time. Which type of sarcomere would be LEAST effective at generating the required tension to lift the object?

A. Sarcomere that is overly short

B. Sarcomere that is overly stretched

Sarcomere that is overly short

Length-Tension Relationship

too much overlap = no room for movement

too little overlap = hard for myosin to grip actin

Myosin ATPase

Regulates how quickly a muscle fiber proceeds through a twitch contraction

Twitch Fibers

Fast twitch fibers: high myosin ATPase activity.

• Found in muscles that move body parts quickly (e.g., eyes).

Slow twitch fibers: low myosin ATPase activity.

• Found in muscles that require slow and sustained contractions (e.g., back muscles that maintain posture)

Availability of ATP regulates the speed of the twitch contractions

In which type of muscle fiber are you most

likely going to generate lactate?

A. Type I

B. Type IIa

C. Type IIx

C. Type IIx

Fast twitching fibers and primarily generate ATP via glycolysis (anaerobic)

Differentiating between Twitch fibers

Type I:slow oxidative

• small intermediate in diameter

• require high ATP levels and maintain extended contractions

• e.g. sitting in chair

Type II:

• large in diameter and contract rapidly but fatigue quickly

• rely on glycolytic energy and have reduced myoglobulin levels

  • IIa oxidative glycolytic: fast, precise e.g. handwriting notes

  • IIx glycolytic: fast anaerobic, buildup of lactic acid, greatest glycogen levels, e.g.sprinting to class

Dr. Ott is doing an endurance ride on her Peloton. Which type of skeletal muscle fibers helps her to be successful on her long distance, endurance ride?

A. Type I

B. Type IIa

C. Type IIx

B. Type IIa

The Motor Unit

• Average motor unit = approx. 150 muscle fibers

• Fine control = multiple small motor units

• Large and powerful muscles = 2000 – 3000 muscle fibers / motor unit

• Each motor unit consists of a single class of muscle fiber

Recruitment

The greater the force (tension) needed, the greater the motor units that are activated.

Slow motor units (type I fibers) are activated first, followed by fast motor units (type II fibers) if additional force is needed.

Muscle Tone

Involuntary activation of motor units to generate a small amount of tension of a muscle at rest

• Hypotonia – low skeletal muscle tone

• Hypertonia – abnormally high muscle tone

You are in the gym doing bicep curls. When you lower the dumbbell back to resting position, which type of muscle contraction are you performing?

A. Isotonic concentric

B. Isotonic eccentric

C. Isometric contraction

B. Isotonic eccentric

Isotonic Concentric Contraction

Muscle tissue shortens

Force generated by muscle is greater than the external load

Isotonic Eccentric Contraction

Muscle tissue lengthens

Force generated by muscle is less than the load

Elastic filaments (sarcomeres) stretch, although motor units are generating tension

Requires greatest amount of tension

• Muscle is elongating while under tension from opposing force that is greater than force generated by the muscle – control reposition of the load (no tension = flop).

Isometric Contractions

Length of muscle does not change

During isometric contractions:

A. Myosin filaments exert tension on the thin filaments, but sarcomeres do not shorten

B. Myosin heads do NOT bind to actin filaments

C. There is no overlap between thick and thin filaments to begin with

D. The sarcomere shortens, but the muscle organ does not

D. The sarcomere shortens, but the muscle organ does not

The graphs below depict time (x-axis) and tension (y-axis).

draw what the curves would look like for an isotonic concentric and isometric contraction.

The graphs below now depict time (x-axis) and length of muscle fiber (y-axis). draw what the curves would look like for an isotonic concentric and isometric contraction.

Elastic components of the muscle organ

(tendons, connective tissues between fibers, elastic molecules in the cytoplasm)

Principle of Myoplasticity

Muscle will alter its structure to support its function

Kenneth “Flex” Wheeler is a world-famous body builder who has won countless championships. Which best describes the anatomy of Flex’s muscle fibers?

A. Flex’s muscle fibers are enriched with blood vessels

B. Flex’s muscle fibers are enriched with mitochondria

C. Flex’s muscle fibers are enriched with myofibrils

C. Flex’s muscle fibers are enriched with myofibrils

Endurance Training

More repetitions, lighter load (swimming, jogging, cycling)

Resistance Training

Fewer repetitions, higher load (Strength or resistance training)

Hypertrophy = Enlargement of an organ, tissue, or cell.

Sedentary Lifestyle

Physical inactivity

Atrophy = A decrease in the size of a cell or organ

Muscle Fatigue

• The inability to maintain a level of intensity during exercise.

• Depletion of metabolites (creatine phosphate, glycogen, blood glucose)

• Reduced oxygen supply to muscle fibers (reduced O2 bound to myoglobin) and greater dependency on glycolysis

• Accumulation of Ca2+, ADP, PO4-

• Environment – high heat, high altitude

We continue to have elevated ventilation after our workouts to help us rid our muscle fibers of any lactic acid buildup.

A. True

B. False

False EPOC!!

Is homeostasis out of balance when we workout?

• Elevated body temperature – energy is lost during glycolysis and oxidative metabolism, raising our body temperature

• Ion concentrations are abnormal – abnormal [Na+] and [Ca2+] in the cytosol and [K+] in the extracellular fluid

• Correct blood pH – lactic acid and CO2 in the blood can reduce the blood pH

Excess Postexercise Oxygen Consumption (EPOC)

When the rate of ventilation remains high after our workout has concluded

EPOC restores homeostasis

• Elevated body temperature – sweating, an ATP-dependent process (active transport of Na+ out of cells), helps us to decrease our body temperature

• Ion concentrations are abnormal – Na+/K+ ATPase helps to restore ion gradients across a membrane (active transport – requires ATP)

• Correct blood pH – exhalation of CO2 helps to restore the slight alkalinity of blood (7.35-7.45)

Functions of blood

• Gas exchange – O2 in, CO2 out

• Distribute solutes – nutrients, ions, hormones, waste

• IMMUNE FUNCTION!!!!!!!!!

• Body temperature – distributes heat that is given off by metabolic reactions

• Clotting / wound healing

• Acid-base homeostasis (buffer)

• Blood pressure – volume of blood

Blood

• We have ~5 liters (8% of body weight)

• Connective tissue

  • Liquid (plasma) and formed elements (cells)