Lesson 15 Action and Support: The Muscles and Skeleton Introduction to Life Processes - SCI 102 1
Muscle Contraction Muscles: tissues that produce movement by contracting Vertebrates have three types of muscles (muscle tissue) Skeletal Cardiac Smooth Introduction to Life Processes - SCI 102 2
Muscle Contraction Vertebrate skeletal muscles have highly organized, repeating structures Skeletal muscles move the skeleton and appear striated This type of muscle tissue consists of a series of nested, repeating parts Introduction to Life Processes - SCI 102 3
Muscle Contraction Parts of skeletal muscle Tendons: muscles are encased in connective tissue sheaths Muscle fibers are individual cells found within the sheath Muscle fibers contain myofibrils encased in the sarcoplasmic reticulum Each myofibril consists of repeating elements called sarcomeres, which contain the protein filaments that make up muscles The filaments of myofibrils are made of myosin and actin, each of which interacts with the other to contract the muscle fiber Introduction to Life Processes - SCI 102 4
Muscle Contraction Muscle fibers contract through interactions between thin and thick filaments The sliding-filament mechanism describes how thick and thin filaments slide over each other, shortening muscle length Each spherical actin molecule has a myosin binding site Myosin binding sites are blocked by tropomyosin During contraction, tropomyosin moves aside and exposes the myosin binding sites The myosin heads bind to actin The myosin heads pull the thin filaments toward the sarcomere center, sliding over the thick filaments Introduction to Life Processes - SCI 102 5
Muscle Contraction Muscle contraction uses the energy of ATP Energy from ATP is used to extend the head on the myosin filament so it can flex the thin filament toward the center of the sarcomere A skeletal muscle s reserves of ATP are used up quickly Muscle cells carry creatine phosphate These molecules in muscle tissue quickly resynthesize ATP from ADP, but only last a few seconds Glycolysis can provide some ATP for short activities Cellular respiration provides ATP for prolonged activity Glucose and fatty acids are used to form ATP An oxygen source is required for efficient ATP formation Introduction to Life Processes - SCI 102 6
Muscle Contraction The nervous system controls the contraction of skeletal muscles Motor neurons excite skeletal muscle fibers at neuromuscular junctions Motor neurons release neurotransmitters that diffuse across the synaptic cleft to receptors on the muscle fiber, triggering an action potential Introduction to Life Processes - SCI 102 7
Muscle Contraction The action potential travels along the muscle fiber cell membrane and passes down T tubules, causing the sarcoplasmic reticulum to release calcium ions into the myofibril cytoplasm Calcium ions bind to troponin accessory proteins Calcium-troponin binding causes tropomyosin to shift position, exposing myosin binding sites on actin Myosin heads bind to actin The actin filaments slide past the myosin filaments, shortening the muscle fiber When the action potential is over, calcium is actively transported back into the sarcoplasmic reticulum Calcium is removed from the accessory proteins that block the actin binding sites, and the muscle relaxes Introduction to Life Processes - SCI 102 8
Muscle Contraction The nervous system controls the contraction of skeletal muscles The size of motor units and the frequency of action potentials determine the force of muscle contraction A motor unit is one branched motor neuron synapsing with many muscle fibers The size of a motor unit regulates the type of movement it can generate The nervous system controls the strength of muscle contractions by varying the number of muscle fibers stimulated and the frequency of action potentials to each fiber Introduction to Life Processes - SCI 102 9
Muscle Contraction Fast-twitch and slow-twitch muscle fibers are specialized for different types of activity Muscle fibers come in two basic types, slow-twitch and fast-twitch Slow-twitch fibers contract with less power than fast-twitch Fast-twitch fibers contract powerfully but fatigue more quickly Introduction to Life Processes - SCI 102 10
Muscle Contraction: Leg Muscles Leg muscle contractions The strength of leg muscle contractions when lifting a heavy object is determined by: The frequency of action potentials and number of muscle fibers stimulated The largest motor units in the human muscles are found in the leg muscles Introduction to Life Processes - SCI 102 11
Muscle Contraction: Leg Muscles Leg muscle fibers Fast-twitch muscle fibers Contain fewer mitochondria than slow-twitch fibers Are found in the legs of sprinters Slow-twitch fibers Have more mitochondria Contract with less power than fast-twitch fibers but can keep contracting for a long period of time Are found in the legs of marathon runners Introduction to Life Processes - SCI 102 12
Cardiac, Smooth, and Skeletal Muscle The three muscle types differ from each other structurally and functionally Type of Muscle Property Smooth Cardiac Skeletal Muscle appearance Nonstriated Striated Striated Cell shape Tapered at both ends Branched Tapered at both ends Number of nuclei One per cell One per cell Many per cell Speed of contraction Slow Intermediate Slow to rapid Contraction stimuli Spontaneous, stretch, nervous system, hormones Spontaneous Nervous system Function Controls movement of substances through hollow organs and tubes Pumps blood Moves the skeleton Under voluntary control? No No Yes Introduction to Life Processes - SCI 102 13
Cardiac, Smooth, and Skeletal Muscle Cardiac muscle powers the heart The structure and contraction mechanism is similar to that of skeletal muscle One main difference is that cardiac muscle fibers are connected to each other by intercalated discs Unlike skeletal muscle, cardiac muscle can generate its own contractions The heart s pacemaker does this Gap junctions allow for the synchronization of contractions by allowing action potentials to travel from muscle cell to muscle cell Introduction to Life Processes - SCI 102 14
Cardiac, Smooth, and Skeletal Muscle Smooth muscle produces slow, involuntary contractions Smooth muscle surrounds blood vessels and most hollow organs Smooth muscle cells are not striated because the thin and thick filaments are scattered throughout the cell Contractions are initiated by stretch, hormones, or the nervous system and are slow and sustained Introduction to Life Processes - SCI 102 15
Cardiac, Smooth, and Skeletal Muscle When a person builds up muscle strength, the muscle becomes resistant to fatigue In a strong muscle, there are often elevated levels of ATP to give the muscle the extra energy it needs Example: marathon runner s leg muscles are resistant to fatigue Introduction to Life Processes - SCI 102 16
Cardiac, Smooth, and Skeletal Muscle People who work out often (bikers, athletes, trainers for the Olympics) often require rapid bursts of high-energy muscle output Many of these people will spend money on dietary supplements such as: Amino acids, which are used by the body as building blocks to make more high-protein muscle cells Energy increasers, which are used to increase energy or provide more endurance during workouts Many supplements contain creatine, which can donate phosphate ions to regenerate ATP when there is a lack of oxygen Introduction to Life Processes - SCI 102 17
Muscles and Skeletons Work Together to Provide Movement The actions of antagonistic muscles on skeletons move animal bodies Three different types of skeletons are seen in the animal kingdom Coordinated movement of an animal s body is produced by alternating contractions of antagonistic muscles Introduction to Life Processes - SCI 102 18
Muscles and Skeletons Work Together to Provide Movement Worms, cnidarians, and many mollusks have a hydrostatic skeleton made of fluid and muscle Muscles around fluid cause shape changes and locomotion The bodies of arthropods are encased by rigid exoskeletons Movement occurs at joints and is based on antagonistic muscles Arthropods must molt periodically in order to grow Endoskeletons are rigid structures found inside echinoderms and chordates Movement occurs at joints and is facilitated by antagonistic muscles Introduction to Life Processes - SCI 102 19
Muscles and Skeletons Work Together to Provide Movement Endoskeleton Rigid internal skeleton found in vertebrae (animals with a backbone and humans), as well as in seas stars and related animals The vertebrate endoskeleton serves multiple functions It supports the body and protects internal organs It allows locomotion in many different forms It participates in sensory function in the middle ear Bones produce blood cells Bones store calcium and phosphorus Introduction to Life Processes - SCI 102 20
Muscles and Skeletons Work Together to Provide Movement The vertebrate skeleton consists of two parts The axial skeleton includes the head, vertebral column, and rib cage The appendicular skeleton includes the pectoral and pelvic girdle and the appendages attached to them Introduction to Life Processes - SCI 102 21
Muscles and Skeletons Work Together to Provide Movement The vertebrate skeleton is composed of: Cartilage Ligaments Bone Introduction to Life Processes - SCI 102 22
Muscles and Skeletons Work Together to Provide Movement Cartilage provides flexible support and connections During embryonic development, most of the skeleton is composed of cartilage, which is later replaced by bone Cartilage covers the ends of bones and provides flexible support to other parts of the body The living cells of cartilage are called chondrocytes They secrete the collagen matrix Cartilage lacks blood vessels, and is slow to heal Introduction to Life Processes - SCI 102 23
Muscles and Skeletons Work Together to Provide Movement Cartilage plays many roles in the vertebrae skeleton Examples: The entire skeleton of sharks, and many other fish, is composed of cartilage Cartilage covers the ends of bones at the joints Cartilage supports the flexible portions of the body (ear, nose) Provides the framework for the larynx, trachea, and bronchi of the respiratory system Introduction to Life Processes - SCI 102 24
Muscles and Skeletons Work Together to Provide Movement Composition of cartilage Contains large amounts of glycoproteins Often has elastic fibers Lacks blood vessels Damage to cartilage tends to heal slowly because of the lack of blood vessels Introduction to Life Processes - SCI 102 25
Muscles and Skeletons Work Together to Provide Movement Ligaments connect bone to bone in joints Are mainly made up of wavy collagen fibers Do not have significant amounts of elastic fibers Introduction to Life Processes - SCI 102 26
Muscles and Skeletons Work Together to Provide Movement Bone provides a strong, rigid framework for the body Bone consists of a hard outer shell of compact bone that encloses spongy bone in its interior Compact bone is arranged in osteons, in which collagen and calcium phosphate surround a central canal containing blood vessels Spongy bone is lightweight, rich in blood vessels, and porous There are three types of bone cells Osteoclasts break down bone Osteoblasts are bone-forming cells Osteocytes are mature bone cells Introduction to Life Processes - SCI 102 27
Muscles and Skeletons Work Together to Provide Movement Bone remodeling allows skeletal repair Bone remodeling occurs through the coordinated activity of osteoblasts and osteoclasts Bones become thicker and larger as a person grows Bone remodeling varies with age The ultimate bone remodeling occurs after a fracture Healing begins when a cartilage callus forms at the break site The cartilage is replaced by bone Introduction to Life Processes - SCI 102 28
Muscles and Skeletons Work Together to Provide Movement Bone strength is increased when it is given moderate stress from weight-bearing exercises Many people hope that they will one day be able to travel into space for extended periods of time This comes with health risks to the bones and muscles Under weightless conditions, space travelers will lose bone and muscle mass because there is no pull of gravity to strengthen the bones and muscles. To maintain bone and muscle mass, they will have to do special, weightbearing exercises each day. If they do not do exercise, their bones and muscles will atrophy (deteriorate), which could have additional negative side effects on their body physiology. Introduction to Life Processes - SCI 102 29
Muscles and Skeletons Work Together to Provide Movement Antagonistic muscles move joints in the vertebrate skeleton Joints are held together by ligaments, which are strong and flexible Tendons hold muscles to bones The origin of any joint is where muscle is attached to the immovable bone on one side of a joint Movement occurs in antagonistic muscle pairs when one muscle flexes while the other is passively extended The insertion is where muscle is attached to the movable bone on one side of a joint Introduction to Life Processes - SCI 102 30
Muscles and Skeletons Work Together to Provide Movement Antagonistic muscles move joints in the vertebrate skeleton Hinge joints move in two dimensions Examples: elbows, knees, fingers Ball-and-socket joints allow movement in many planes The round end of one bone fits into a hollow depression in another Allow movement in several directions Examples: hips, shoulder Introduction to Life Processes - SCI 102 31
Muscles and Skeletons Work Together to Provide Movement The knee joint If there would be a ball-and-socket joint in the knee, there would be decreased joint stability and the person would be unable to stand properly The anterior cruciate ligament (ACL) is one of the major knee joint ligaments in humans, and damage to this ligament is fairly common in athletes. An ACL tear is most often a sports-related injury but can also result from accidents, falls, and work-related injuries. Most sports-related ACL tears occur when a person pivots or lands from a jump. Instability or weakness of the knee joint happens when a person has a torn ACL Introduction to Life Processes - SCI 102 32
Muscles and Skeletons Work Together to Provide Movement The biceps femoris bends the leg back when crouching Introduction to Life Processes - SCI 102 33