Ch 39.1 p.718

Ch 39.2 p.720

Ch 39.3 p.727

Skeleton UseProtectionSupportMovementStorage for ionsProduction of blood cells

Types of SkeletonsHydrostatic- “water standing”

can be fluid-filled gastrovascular cavityfound in Cnidaria and Platyhelminthes

analogy: stiff garden hose Organisms: worms, jellyfish, sea anemones, etc.

Earthworms-septa Muscle fibers at base of epidermal cells contract

body/tentacles shorten quickly=movement Muscular hydrostat-certain parts are helped to be

moved by “fluid contained within certain muscle fibers.” e.g. spider legs, elephant trunks

Exoskeleton- outerOrganisms: molluscs, arthropods, and

vertebrates Primarily for protection against outside predators

and environmentCalcium Carbonate shell in molluscs that can

grow with them. i.e. snails, clamsChitin, a “flexible nitrogenous polysaccharide”

in arthropods. i.e. insects allow for flexibility Arthropods must molt vulnerability (during the

waiting period while the new exoskeleton hardens and dries)

Endoskeleton- innerOrganisms: vertebrates and echinoderms e.g.

starfish Primarily for support and movement and protection

of vital organsSpicules and plates of calcium carbonateVertebrate endoskeleton=living tissueGrows with animal but molting is not neededCan support weight while leaving spaceJoints allow for complex movements

MovementMuscles = force by contractionTendons are what attach the muscles and

bonesBones = anchorage and levers change size

or direction of force by musclesLigaments are what connect bones and help

prevent dislocationNerves are what send messages from brain to

muscles to tell to contract and move at certain times and extents

JointsJunctions between bonesParts:

Cartilage-smooth tough tissue-bone friction reducer

Muscle-for bending, straighteningBones-lever, anchor, and forceSynovial fluid-joint lubricator Joint capsule-joint seal and holds in fluid

Like a bottle cap

Difference in MovementsHip joint

Movement in three planes Protraction/retraction, abduction/adduction, and

rotation

Knee JointHinge jointA lot of movement in one plane

Flexion/extension

What are Muscles? Muscles are bundles of tissue that are attached to bone

by tendons and are essential for movement Muscles provide the force for movement by working in

antagonistic pairs This means that when one muscle contracts, the other relaxes,

and vice versa Muscles are made of muscular tissue and involve three

types: Skeletal muscle, or striated voluntary muscle, is responsible

for posture, support, and movement. It also helps maintain homeostasis by keeping constant body temperature as well as releasing heat stored in the body by breaking ATP during contractions

Smooth muscle, or non-striated involuntary muscle, which contracts automatically. It is found in the digestive tract, respiratory tract, iris, and arrector pilli of the skin

Cardiac muscle, which is found specifically in the heart; it is responsible for heart contractions in order to pump blood to the rest of the body

Macroscopic Anatomy and Physiology There are about 700 different skeletal muscles in the body,

all of which make up about 40% of the body weight of an average human (point out some superficial muscles) Skeletal muscles attach to the skeleton by tendons Muscles shorten when the contract; they cannot lengthen

They can only push, not pull, and must therefore work in pairs (ask for volunteers)

Rapid stimuli can cause muscles to respond to subsequent stimuli without relaxing completely

(fishing pole analogy) Repeated stimulation causes increasing contraction until it

reaches the maximum sustained contraction, called tetanus

Even when they appear to be at rest, some muscles exhibit tone, which is when some of the fibers are still contracted

If all muscles went slack, people would just collapse

Microscopic Anatomy and Physiology Structure of skeletal muscles

Skeletal muscles are composed of bundles of muscle fiber, containing special components

The sarcolemma is a plasma membrane for muscle cells

The muscle fibers have modified endoplasmic reticulum, called sarcoplasmic reticulum, which serve as storage sites for calcium ions needed in contractions

The sarcoplasmic reticulum contains up to thousands of myofibrils, which are the part of the muscle fiber that contract

Myofibrils have light and dark bands (called striations) caused by the placement of protein filaments inside of contractile units called sarcomeres

Sarcomeres extend between two dark lines called “Z lines”

There are two types of filaments: thick, make of myosin, and thin, made of actin

The “I band” is light because it contains only actin

The darker “H zone” contains only myosin The “A band” contains overlapping actin and

myosin, so it is the darkest

Sliding Filament Model

Contracted muscle fibers show that sarcomeres within myofibrils are shortened When sarcomeres shortened, the actin slide

past the myosin and toward each other The “I band” then shortens and the “H zone”

basically disappears *NB: the sarcomere gets shorter, but the filaments

themselves remain the same length ATP supplies energy for the reaction; myosin

filaments are the ones that actually do the work and break down ATP to form cross-bridges that attach to and pull actin filaments to the center

ATP ATP provides the energy for muscle contraction

Although muscle cells contain myoglobin, an oxygen-storing molecule, cellular respiration does not necessarily supply all of the needed ATP

Therefore cells rely on phosphocreatine, a storage form of high-energy phosphate

Phosphocreatine does not directly participate in muscle contraction, but instead regenerates ATP in the following equation: creatine-P + ADP ---> ATP + creatine

*NB: Phosphocreatine and creatine phospate are the same After all of the phosphocreatine is used, the mitochondria will

then produce the required ATP for muscle contraction If not, then fermentation will occur, which causes the buildup of

lactate after a short period of time Hard breathing after exercise gathers the necessary oxygen to

complete the metabolism of lactate to restore cells to their original energy state (this is known as oxygen debt)

The lactate is transported to the liver, where about 20% of it is broken down into carbon dioxide and water to gain ATP in order to reconvert the remaining 80% of lactase into glucose

Muscle Innervation Muscle innervation refers to when muscles are stimulated to

contract by motor nerve fibers Nerve fibers have several branches that end in axon terminals that

lie very close to the sarcolemma; they are separated by a small gap called the synaptic cleft The entire region is called a neuromuscular junction

The terminals contain vesicles that hold the neurotransmitter ACh (acetylcholine), which is released when nerve impulses travel down the motor neuron and to the axon The ACh diffuses into receptors in the sarcolemma which

generates impulses that spread into the sarcoplasmic reticulum, causing the release of calcium ions

The calcium causes the sarcomere filaments to slide past one another, causing contraction of the sarcomere, resulting in myofibril contraction, then muscle fiber contraction, then contraction of the muscle itself

Once ACh is relased into the junction and created a response, it is removed

Acetylcholinesterase (AchE) breaks down ACh

Human Skeletal SystemCartilage included in most bones

Bibliography