Ch. 36Structural Support and

MovementDaniel Batista

Pr.2 03/21/2012

SkeletonsA structure which muscles interact with to facilitate motion.

36.1 Invertebrate Skeletons

A skeleton can consist of fluid or external hard parts.

Fluid-filled closed chamber(s) that muscles act against.

Cnidarians (Jellyfish) & annelids (ringworms)

Hydrostatic Skeletons

In sea anemones, water fills and is trapped in a gastrovascular cavity, contractions by its muscles

redistribute water and alter body shape.

Sea Anemone

Possess a coelom divided into fluid-filled segments, muscles both longitudinal and circular contract

around them to lengthen or shorten the segments.

Earthworm

Stiff body covering to which muscles attach. Bivalve mollusks like clams have a hinged

two-part shell. Arthropods have hinged exoskeleton with

attached muscles. Some also use the movement of body fluid as well(spiders).

Exoskeletons

Same concept as our own skeleton, however the “bones” are on the inside and muscles contract from

within.

“Bones over Muscle”

Internal framework of hardened elements to which muscles attached.

Echinoderms and vertebrates have an endoskeleton.

Endoskeleton

Starfish Endoskeleton

36.2 Vertebrate Endoskeleton

All vertebrates have an endoskeleton.

Vertebrates refers to vertebral column. This along with the bones of the head and

rib cage = axial skeleton. Pectoral(shoulder) girdle, pelvic(hip) girdle,

and limbs(or bony fins) attached to the axial skeleton are the appendicular skeleton.

Features of the Vertebrate Endoskeleton

In humans: Brain and spinal chord connect through an

opening called the foramen magnum As upright walkers, vertebrae are parallel to

ground instead of perpendicular. Because of this we experience back pain as we age due to excess pressure on our intervertebral discs.

Features of the Vertebrate Endoskeleton Cont.

Human Skeletal System

36.3 Bone Structure and FunctionLiving cells in a secreted extracellular matrix.

Movement by interacting with skeletal muscle system

Support and anchor muscles Protection Mineral Storage Blood cell formation

Bone Function

There are Long bones such as femurs and flat bones such as the bones of the skull.

Bones are wrapped in dense connective tissue sheath with nerves and blood vessels.

The Extracellular matrix of bones is made up of collagen(protein) w/ calcium and phosphorus salts.

Bone Anatomy

3 types of Bone cells:◦ Osteoblasts: bone builders/ secrete matrix◦ Osteoclasts: secrete enzymes and acids to break

down bone◦ Osteocytes: former osteoblasts now surrounded

by the matrix they secreted.

Bone Anatomy cont.

Long Bones have two types of tissues:◦ Compact Bone: form the shaft and outer layer,

contain many functional units called osteons which have concentric rings of bone tissue w/ bone cells b/w rings. Nerves and blood vessels run through the center of osteons.

◦ Spongy Bone: Fills the shaft and ends of a long bone, strong and lightweight, matrix riddled with open spaces.

Bone Anatomy cont.

The cavities inside a bone contain bone marrow◦ Red marrow fills the spaces in spongy bone, major

site of blood cell formation.◦ Yellow marrow fills the central cavity of mature

long bones, mainly fat.

Bone Anatomy cont.

The first skeleton that forms in vertebrates consists of cartilage. In cartilaginous fishes it remains that way, and in other vertebrates it serves as a model for an adult skeleton of bone. Osteoblasts move in and replace cartilage.

Even once a bone stops growing in an adult, it is constantly changing: repairing microscopic cracks from normal movement and breaking down to release mineral ions.

Bone Formation & Remodeling

Bones store most of the body’s calcium, regulated by hormones(calcitonin).

Formation and remodeling influenced by hormones◦ Testosterone & estrogen encoarage bone

deposition.◦ Cortisol(stress) slows it.

Bone Formation & Remodeling cont.

After about 24 years of age, osteoblasts secrete less matrix that osteoclasts breakdown, gradually reducing bone mass.

Osteoporosis is when this reaches a point where the bones become weaker and more likely to break.

Most common in postmenopausal women b/c they no longer produce sex hormones that encourage deposition.

Osteoperosis

Skeletal JointsAllow no, little, or much range of motion

Joint: area of contact or near contact b/w bones

3 types:◦ Fibrous: Bones held securely in place by dense

connective tissue (teeth)◦ Cartilaginous: pads of cartilage allow a bit of

movement (vertebrae)◦ Synovial joints: Bones separated by a small cavity

and smooth cartilage covers ends. Ligaments hold bones in place, some forming a capsule enclosing the joint that secretes lubricating synovial fluid.

Skeletal Joints

Ball-and-socket joints: wide range of rotational motion(shoulders).

In the joints of the wrist and ankles, bones glide past one another.

Joints of the knee and elbows allow movement on one plane only.

Synovial Joints

36.5 Joint Injuries

Sprained ankle: a tearing of the ligaments in your ankle.

A tear of cruciate(cross, in this case they cross one another in the knee joint) ligaments in the knee can require surgery.

A torn meniscus, a c-shaped wedge of cartilage that cushions between the bones and reduces friction.

Dislocation of the bones of a joint.

Common Injuries

Arthritis is chronic inflammation of a joint◦ Osteoarthritis: occurs at worn down cartilage of

an often used joint at old age.◦ Rheumatoid arthritis: autoimmune disorder,

immune system attacks the fluid secreting lining of synovial joints.

◦ Gout: crystals of uric acid form at a joint, normally a byproduct of protein breakdown, increased levels can occur due to obesity and too much alcohol intake.

Arthritis

When a bursa (fluid filled sack acting as a cushion in many joints)becomes inflamed.

Caused by repeating a movement which puts pressure on a bursa.

Bursitis

36.6Skeletal-Muscular Systems

Bundles of muscle fibers sheathed in dense connective tissue

Muscle fiber: cylindrical cell, multiple nuclei(desdended from a group of cells that fused together in the developing embryo), contractile filaments.

Most muscle/bone interaction is like a lever. The bone is a rigid rod near a fixed

point(joint). Muscle contraction transmits force to move the bone.

Skeletal Muscles

Muscles can only pull on bone, not push Most muscles work in opposition Tendons connect muscle to bone. Have a role in respiration and circulation.

Cont.

36.7 Contraction of Skeletal Muscles

ATP fueled movements of protein filaments inside muscle fibers result in contraction.

Muscle fibers are packed with myofibrils, each a bundle of contractile filaments that run the length of the fiber.

Light-to-dark bands show up along the myofibrils stained for microscopy, giving it a striated appearance.

These bands are units of muscle contraction, sarcomeres.

Fine Structure of Skeletal Muscle

The contractile units of muscles Mesh of cytoskeletal elements called z

bands anchor adjacent sarcomeres. The sarcomere has parallel arrays of thin

and thick filaments. Thin filaments of two chains of

actin(globular protein) attached to z-bands extend inward.

Thick filaments of myosin(motor protein) are positioned in the center, ends a few nanometers from the thin filaments.

Sarcomeres

Filaments do not change length, the myosin bring actin filaments towards center, contracting the sarcomere.

Myosin has hundreds of “heads” that can attach to the actin.

When the muscle receives a signal from the nervous system, calcium levels around filaments rise.

Calcium allows myosin heads to bind to actin.

ATP binds to myosin heads.

Sliding Filament Model

The ATP is used and converted to ADP + Phosphate, causing the heads to tilt towards the center, moving the actin.

ADP+P is released and more ATP binding to the head releases the head.

This process continues as long as calcium and ATP is available.

Cont.

36.8 Closer Look at Contraction

Muscle cells are excitable, like neurons.

Neuromuscular junction: synapse b/w muscle and motor neuron.

For a muscle contract, an Action Potential must travel to the junction to release acetylcholine(ACh)

Binding ACh to the receptors on muscle fibers excites them (like neurons) causing an A.P. that travels along the muscle fiber membrane, through T-tubules, to the sarcoplasmic membrane( a special Smooth E.R. around myofibrils and contain Calcium.

Nervous Control of Contraction

Arrival of the A.P. opens voltage-gated channels allowing Calcium to flow down its concentration gradient.

When contraction ends, calcium pumps return it to the sarcoplasmic reticulum.

Cont.

Calcium affects these two proteins that regulate binding of myosin & actin filaments.

At rest, tropomyosin wraps around actin covering the binding sites. Troponin is bound to the tropomyosin and can reversibly bind calcium ions.

When calcium binds to the troponin, it changes shape and pulls the tropomyosin away from the binding sites.

Troponin & Tropomyosin

36.9 Energy for Contraction

ATP and creatine phosphate

The muscle first uses ATP, but little is stored within cells.

After ATP, muscles turn to creatine phosphate, which transfers a phosphate to ADP to make more ATP. This keeps the muscle going until ATP production from othe pathways catch up.

During prolonged moderate activity, most ATP is produced via cellular respiration.

ATP & Creatine Phosphate

36.10 Properties of Whole Muscle

Fibers respond as a unit.

Motor Unit: One motor neuron and all of the muscle fibers it synapses with.

Muscle twitch: When you briefly stimulate a motor neuron and its fibers contract for a few milliseconds.

If a new stimuli occurs before a response ends, the fibers twitch again.

Repeatedly stimulating a motor unit cause a sustained contraction, tetanus.

Motor Units & Muscle Tension

Muscle Fatigue: when unrelenting stimulation keeps a muscle in tetanus and decreases the muscle’s capacity to generate force; muscle relaxes despite continued stimulation.

In humans, we are born with all of our muscle fibers, we do not grow new ones.

Aerobic exercise promotes muscle endurance by increasing blood flow and mitocondria.

Brief, intense exercise promote synthesis of myosin and actin to exert more tension.

Fatigue, Exercise, & Aging

As we age, we lose muscle fibers. Tendons stiffen and are more likely to tear. Older people can exercise for long periods

but their muscles will no longer increase in mass as much.

They can perform moderate weight training to slow the loss however.

Cont.

36.11 Disruption of Muscular Contrations

A class of genetic disorders in which skeletal muscles progressively weaken.

Duchenne: occurs in children, mutation of a gene in the X chromosome. The gene codes for dystrophin, a protein found in plasma membrane of muscle fibers.

The mutant protein allows foreign material to enter fiber which breaks it down.

Myotonic: occurs in Adults.

Muscular Dystrophies

When neurons cannot escite muscle fibers, they wither away.

An example is poliovirus which infects and kills motor neurons.

Amyotrophic lateral sclerosis (ALS) als okills motor neurons. (Stephen Hawking)

Motor Neuron Disorders

Bacteria of the genus Clostridium produce toxins that disrupt the signal from nerves to muscles. C. botulinum can be found in canned foods and its spores release the toxin botulinum that keeps motor neurons from releasing ACh.

Bacteria C. tetani live in the gut of grazing animals, whose spores can live in the soil for years. If they get into a deep wound, they grow a toxin that is delivered to the brain and spinal cord. This toxin restricts the release of GABA neurotransmitter which control inhibition of motor neurons.

Botulism & Tetanus

W/o GABA, symptomes of tetanus begin. Over stimulated muscles stiffen and cannot

relax. The backbone is locked in an extreme curve and the jaw is locked.

Death occurs when the respiratory and heart muscles get locked in contraction.

Cont.