Muscoskeletal system

Read Chapter 49 Pages 1075-1086

3 types of skeletons

1. hydrostatic p. 1077
2. exoskeleton p. 1077
3. endoskeleton p. 1078

 

Hydrostatic; consists of fluid held under pressure in a closed body compartment

·        Allows movement by peristalsis

·        Ex. Flatworms, worms, annelids and nematodes and hydra

 

Exoskeleton; outside covering or shell

·        Composed of cuticle or chitin ( a polysaccharide of cellulose)

·        Ex. Insects

 

Endoskeleton; inner skeleton

 

Human Skeletal System

p. 1079

 

Skeleton made of

·        Bone; connective tissue that contains blood and nerve vessels

·        Cartilage; found in the embryonic stages of vertebrates

§         Later replaced by bone except in external ear or tip of nose

§         Lack nerves and blood vessels

 

Bones

·        Comprised of 2 substances

§         Collagen; fibrous structural protein

§         Calcium salts

·        Joints hold bones together.  you need review the different joints Figure 49.28 p. 1079

§         Ball-and-socket

§         Hinge

§         Pivot

·        Ligaments attach bone to bone

·        Tendons attach muscle to bone

 

3 Kinds of Muscles

1. skeletal
2. smooth
3. cardiac

Skeletal aka striated

p. 1080

·        Attached to bone; responsible for movement Figure 49.30 p. 1080

·        Control voluntary movements

 

·        Figure 49.31 AND 49.32 p. 1081

 

·        Consists of a bundle of long fibers running the length of the muscle

·        Each fiber is a single cell with multiple nucleus (multinucleated)

§         A result of many cells fusing together during embryonic development

·        Striation (stripes) appearance

§         Each fiber is itself a bundle of smaller Myofibrils

·        SARCOMERE is the functional unit   

Within sacromere

·        Actin (a protein); thin filaments

·        Myosin (a protein) thick filaments

§         During a muscle contraction filaments slide by each other and contract

·        Sarcoplasmic reticulum; p. 1083 Figure 49.35 Special structure that releases calcium ions causing the muscle to contract. (Similar to the endoplasmic reticulum)

·        Contractions of skeletal muscles are rapid and powerful

 

 

 

Smooth muscles

p. 1086

·        Found throughout the body

·        Found in walls of blood vessels, digestive tract and internal organs

·        Long tapered, single nucleus

·        Responsible for involuntary movements

·        Smooth muscles are slow

 

Cardiac muscles

p. 1086

·        Located in the heart

·        Have characteristics of both smooth and skeletal muscles

·        Striated (like skeletal)

·        Involuntary (like smooth)

·        Intercalated discs; special junctions that hold together cardiac muscles

§         Cardiac muscles are branched and the ends are joined by intercalated discs which relay signals from cell to cell during a heartbeat

·        Contractions in cardiac muscles

§         Spontaneous and automatic (beats on its own)

·        Both smooth muscle and cardiac muscles get their nerve supply from the autonomic nervous system

 

 

Muscle Contractions

When muscles contract Figure 49.32 p.1081

SARCOMERE

 

·        Sliding filaments

§         The length of each sarcomere is reduced (distance from Z line to Z line)

§         Actually I bands shorten

·        H zone disappears

§         Zone of overlapping increases (band does not get shorter)

§         Myosin consists of a tail and head

·        Head can bind with ATP (hydrolyzed to ADP)

·        Some of the energy is absorbed by myosin

·        Which in turn the “energized” myosin binds to a specific site on actin forming cross-bridges

§         Myosin relaxes…shifting angles pulling thin filaments to the center of the sarcomere

·        A skeletal muscle contracts only when stimulated by a motor neuron

At rest

·        Myosin binding sites on the actin molecules are blocked by regulatory protein; Tropomysin (controlled troponin)

§         Must be uncovered for a muscle to contract

§         Calcium ions cause tropomysin to change shape exposing myosin binding sites on actin (contraction now can occur)

§         When calcium levels drop contraction stops

§         Sarcoplamic reticulum regulates calcium concentrations

·        Nerve impulse is sent to a skeletal muscle

§         Motor neuron receives the impulse releases a neurotransmitter

§         Muscle depolarizes

§         Depolarization causes sarcoplasmic reticulum to release calcium ions

§         Calcium ions cause the actin and myosin filaments to side past each other

o       Muscle contractions are energy dependent; require ATP in order for actin and myosin to slide

 

Types of muscle tissue
	Skeletal	Smooth	Cardiac
Location	Attached to skeleton	Wall of digestive tract; inside the blood vessels	Wall of heart
Type of control	Voluntary	Involuntary	Involuntary
Striations	Yes	No	No
Multinucleated	Yes	No	No
Speed of contraction	Rapid	Slowest	Intermediate