Support and Locomotion

Muscles

Muscles work by contracting: getting smaller in size

Three types of muscles–Skeletal (Striated, voluntary)–Cardiac (Heart)–Smooth (Involuntary)

Skeletal Muscle

Called striated because of how it looks

Responsible for voluntary actionsHuman body has over 700 different

skeletal muscles (this makes up ~35% to 45% of the total body weight!)

SkM contracts by having two proteins, actin and myosin, slide past each other

Skeletal Muscle

The sarcomere is the functional unit of muscle contraction

Thin filaments consist of two strands of actin and one tropomyosin coiled about each other

Thick filaments consist of myosin molecules

Actin (thin filament) and myosin (thick) slide past each other

Myosin has little “feet” called cross-bridges

Skeletal Muscle

At rest, tropomyosin blocks the myosin binding sites on actin

Skeletal Muscle

When Ca2+ binds to the troponin complex, a conformational change results in the movement of the tropomyosin- tropinin complex and exposure of actin’s myosin binding sites

Skeletal Muscle

Using ATP, cross-bridges from myosin “grab” binding sites on actin and pull the filaments closer

This action occurs over and over until the muscle fiber is completely contracted

Muscles are controlled by the Nervous System

Action potentials run along a neuron until they reach a synapse, where they release neurotransmitters (ACh)

Once at the muscle cells, the action potential releases Ca2+ from the sarcoplasmic reticulum

The Ca ions allow the proteins on the actin and myosin to bind, forming the cross-bridges

Cardiac Muscles

Cardiac muscles are those that power the heart

Very similar to SkM, except CM is controlled by the SA node, not a motor neuron

Smooth Muscles

SmM surround blood vessels and most hollow organs: uterus, bladders, GI tract

Most SmM contraction is slow and sustained, sometimes rhythmic (peristalsis)

Smooth Muscles

SmM contraction can be initiated by stretching, hormones, or the nervous system

Most are involuntary, but some can be controlled (urinary bladder)

ATP

Large amounts of ATP are required for muscle contraction AND relaxation–Breaks/reforms connections

between actin and myosin–Powers pumps that return Ca2+

to the sarcoplasmic reticulum

Rigor mortis

Stiffening of muscles after deathMuscles run out of ATP after death

–Connection between actin and myosin cannot be broken – muscle remains contracted

–After ~72 hours, relaxation occurs because of decomposition

Skeletons

What do skeletons do?–Provide the framework for

support of the bodyThree basic types:

–Hydrostatic Skeleton–Exoskeleton–Endoskeleton

Hydrostatic Skeletons– fluid pressure provides support

(Cnidarians, Annelids)

Exoskeleton

Encase the bodies of Arthropods (insects, crustaceans, and arachnids)

Made of proteins, chitin, or are calcareous

Thin exoskeleton where the animal needs to bend or move

Crustacea, Molluska, and Insecta

Endoskeleton

Found in Echinoderms, Chordates, and Sponges

Serve several functions for vertebrates:

1. Supports body and protects internal organs

2. Used as muscle attachment sites to allow locomotion

3. Produce blood parts (RBC’s, WBC’s, and platelets

4. Serve as storage sites for Calcium and Phosphorus

5. Some even aid in sensory transduction (hammer, anvil, and stirrup of the middle ear)

Cartilage

Consists of chondrocytes embedded in a collagen/elastin matrix

Located at ends of long bones and between vertebrae

Functions as shock absorber

Bones

Compact bone provides strength and rigidity as well as attachment sites for muscles

Spongy bone is very porous; site where blood cells are produced (bone marrow)

How does the body move?

Muscles work in antagonistic pairs–One always

extends (bends out) while the other always

flexes (bends in)

How does the body move?

A muscle attaching two bones is attached to one fairly immovable bone (origin) and one that moves (insertion)

Tendons connect muscle to bone

Ligaments connect bone to bone

Joints are where two bones meet

Three basic types of joints:–Fixed: Skull–Hinge: Elbows and

knees–Ball-and-Socket:

Shoulders and hips

Arthritis (joint inflammation)

Osteoarthritis (“wear-and-tear” arthritis)– Cartilage covering the ends of bones

slowly wears away, causing stiffness and soreness

Rheumatoid arthritis– Autoimmune disease

in which the body’s immune system attacks the synovial membranes