Skeletal and Muscular Systems PDF

10/29/20 Chapter 21 Skeletal and Muscular Systems The Skeletal System • Skeleton: an internal framework of bones and cartilage Axial skeleton Cartilage Appendicular skeleton Skull Clavicle Scapula Sternum - Axial skeleton forms the central axis of the body - skull, ribs, vertebra - Appendicula...

10/29/20 Chapter 21 Skeletal and Muscular Systems The Skeletal System • Skeleton: an internal framework of bones and cartilage Axial skeleton Cartilage Appendicular skeleton Skull Clavicle Scapula Sternum - Axial skeleton forms the central axis of the body - skull, ribs, vertebra - Appendicular skeleton attaches to the axis - limbs, pelvis, shoulder girdle Figure 19.5 Ribs Humerus Vertebra Radius Ulna Pelvis Carpals Metacarpals Phalanges Femur Patella Tibia Fibula Tarsals Metatarsals Phalanges 1 10/29/20 • Human skeleton is composed of 206 bones: 80 bones in the axial skeleton - 126 bones in the appendicular skeleton - Stapes (in the middle ear) – the smallest bone in the body Femur (thigh bone) – the longest and biggest bone in the body • Functions of the skeleton: - Support the body (a) Ball and socket joint (hip) (b) Hinge joint (knee) Femur Pelvic bone - Aid movement (joints) - Store minerals (calcium) Tibia Fibula Femur (c) Pivot joint (neck) Atlas - Protect internal organs - Blood cell production Axis Figure 19.6 2 10/29/20 Bone Structure • Compact bone: densely packed; form the hard, outer shell of bones • Spongy bone: loosely packed; porous; form the interior of bones • Marrow: in the cavity of bone; produce blood cells • Blood vessel: inside and along their surface Cartilage Spongy bone Compact bone Marrow Blood vessel Figure 19.7 Bone Remodeling • Bones are made of cells - Osteoclast – break down bone tissue by bone reabsorption - Osteoblast – regenerate bone tissue by bone deposition • Bones are remodeled continuously - Regulate the body’s calcium levels Bones are broken down to release calcium into the bloodstream Bones are regenerated to remove calcium from the bloodstream 3 10/29/20 Sex Differences in Bone Structure • Arise in part due to the timing and length of puberty – Later and longer in boys A larger proportion of growth occurs in the arms and legs than in the torso. Men generally have longer legs and arms than women (a) Skeletal differences Women have smaller: • Frontal bones (forehead) • Temporal bones (a pair of) • Mandible (jawbone) Women also have: • Lower center of gravity • Flatter, broader pelvis (two ossa coxae) • Greater spinal curvature Childbirth • Larger, rounder pelvic inlet • Shorter long bones (b) Q angle Women have: • Increased Q angle Figure 19.9 4 10/29/20 • The differences in skeleton affects success of men and women in certain physical activities - Men are 15 cm (5.9 inches) taller than women on average - Longer limbs for men = more power - faster runner - stronger slap shots - Lower center of gravity for women = better balance - gymnastics (balance beam) - ballet - Increased Q angle = higher risk factor for knee injury Athletics World Records - 4x100 m relay 5 10/29/20 Bone Cancer • Bone cancer is caused by a problem with the cells that make bone - Most commonly in children and adolescents • Osteosarcoma is the most common primary malignant bone cancer - Often occurs in the long bones at areas of rapid growth around the knees and shoulders The Muscular System • Skeletal muscle: one of the three types of muscle in humans; 639 pieces - Controlled by nerves Nourished by blood vessels Attached to bones at tendons - • Function: interact with bones to produce voluntary body movements 6 10/29/20 http://www.youronlinefitness.com/anatomy_chart.php • Mode of action: antagonistic pairs - Muscles can only contract but can’t return into their original positions - A pair of muscles pull in the opposite directions Example: Biceps: a two-headed muscle located in the front of the upper arm Triceps: a three-headed muscle on the back of the upper arm 7 10/29/20 To raise the forearm: biceps contract à pull triceps back into the original relaxed position To lower the forearm: triceps contract à pull biceps back into the original relaxed position (b) Triceps contracted (a) Biceps contracted Biceps relaxed Biceps contracted Triceps relaxed Tendon Triceps contracted Figure 19.10 Lecture Discussion • In gym exercise, which of the following is the best when you train muscles on the forearm: a. Quick up; quick down b. Quick up; slow down c. Slow up; quick down d. Slow up; slow down 8 10/29/20 Skeletal Muscle Structure • Skeletal muscles is composed of bundles of muscle fibers arranged in parallel - Each muscle fiber is a single cell, made of paralleled filaments called myofibrils - Each myofibril is made of sarcomeres, the units of contraction of a muscle fiber - Each sarcomere is composed of proteins actin and myosin • The parallel arrangement of fibers gives skeletal muscle its characteristic striated appearance (b) Myofibril (a) Skeletal muscle structure Myosin Sarcomere Outer sheath of a muscle Z disc One bundle of muscle fibers Actin Sarcomere Z disc Z disc Single muscle fiber (cell) Myofibril Figure 19.11 9 10/29/20 Sliding-Filament Mode of Muscle Contraction Myofibril Sarcomere Sarcomere between contractions Myosin head Actin Myosin ATP 1 ATP binds to myosin which is released from actin filament. 2 The use of ATP “cocks” the myosin 3 Myosin head binds to an actin molecule, drawing the actin filament towards center, shortening the sarcomere. ATP The same sarcomere contracted Figure 19.12 Discussion: Steps in Muscle Contraction Put these steps in their correct order: 7 Myosin changes shape, pulling actin toward the center of the __ sarcomere 3 Myosin is released from its binding on the actin filament __ 5 The myosin head changes shape by cocking back __ 2 ATP binds to myosin __ 8 The muscle fiber shortens __ 4 ATP is broken down __ 1 An action potential travels down a motor neuron to a muscle __ cell membrane 6 __The myosin head binds to an actin molecule 10 10/29/20 Sex Different in Skeletal Muscle • Arise due to levels of testosterone – a hormone produced by the testes - Men have larger and more muscle fibers = greater muscle mass - Women have more body fat under skin = smoother appearance of muscles Muscular Dystrophy • A group of muscle diseases that weaken the muscular system and hamper locomotion - Genetically inherited • Symptoms: - Skeletal muscle weakness - Defects in muscle proteins - Death of muscle cells and tissue 11