Muscles, Muscles, Muscles                                                                                                                                               9/12/2018

Muscular System Functions Body movement Maintenance of posture Respiration Production of body heat Communication Constriction of organs and vessels Heart beat

The human body http://www.gwc.maricopa.edu/class/bio201/muscle/mustut.htm 9/12/2018

About how many muscles do you think the human body has? Answer = 650 9/12/2018

Types of Muscle Contractions Isometric: No change in length but tension increases Postural muscles of body Isotonic: Change in length but tension constant Concentric: Overcomes opposing resistance and muscle shortens Eccentric: Tension maintained but muscle lengthens Muscle tone: Constant tension by muscles for long periods of time

Three potential actions during muscle contraction: Biceps muscle shortens during contraction shortening isometric Most likely to cause muscle injury lengthening Biceps muscle lengthens during contraction

Muscle Tissue Types Skeletal Smooth Cardiac Attached to bones Nuclei multiple and peripherally located Striated, Voluntary and involuntary (reflexes) Smooth Walls of hollow organs, blood vessels, eye, glands, skin Single nucleus centrally located Not striated, involuntary, gap junctions in visceral smooth Cardiac Heart Striations, involuntary, intercalated disks

Muscle Teamwork Agonist (prime mover): - the muscle or group of muscles producing a desired effect Antagonist: - the muscle or group of muscles opposing the action Synergist: - the muscles surrounding the joint being moved Fixators: - the muscle or group of muscles that steady joints closer to the body axis so that the desired action can occur

Skeletal Muscle An organ consisting of skeletal muscle tissue, nervous tissue, blood, and connective tissues Fascia separates one muscle fiber from the next and holds it in place. These can be continuous with tendons, and intertwines to periosteum to connect it to a bone Fascia can also form aponeuroses which are broad sheets of connective tissues connecting to other muscles

Refresher Course in Muscle Physiology Structural hierarchy of skeletal muscle 4/11/2003 Muscle A little less than half of the body’s mass is composed of skeletal muscle, with most muscles linked to bones by tendons through which the forces and movements developed during contractions are transmitted to the skeleton. Muscle fibers Muscle fiber Myofibril Sarcomere Modified from McMahon, Muscles, Reflexes and Locomotion Princeton University Press, 1984. EB2003--Susan Brooks

Components of skeletal muscle d) myofibril c) muscle fibre b) muscle fibre bundle a) Muscle belly Sport Books Publisher

Organization I:

Organization II:

Organization III:

Muscle Fibres Cylinder-shaped cells that make up skeletal muscle Each fibre is made up of a number of myofilaments Diameter of fibre (0.05-0.10 mm) Length of fibre (appr. 15 cm) Surrounded by a connective tissue sheath called Sarcolemma Many fibres are enclosed by connective tissue sheath Perimycium to form bundle of fibres Each fibre contains contractile machinery and cell organelles Activated through impulses via motor end plate Group of fibres activated via same nerve: motor unit Each fibre has capillaries that supply nutrients and eliminate waste Sport Books Publisher

More Skeletal Muscle Epimysium: layer of connective tissue surrounding muscle Perimyseum: extend in from epimysium and separate muscle into compartments. Fascicles: separated muscle fibers Endomysium: thin membrane housing the fascicles

Parts of a Muscle

Muscle fibre:

Internal organization:

Organization of myofilaments II:

Muscles contract when the nervous systems causes muscle filaments to move. Muscle fibers are cells of the muscular system. muscle muscle fiber

Myofibrils are long strands of protein in the muscle fiber.

Each myofibril is divided into sarcomeres. Sarcomeres contain filaments that cause contraction. myofibril muscle fiber muscle sarcomere

Skeletal Muscle Fibers Single cell Responds to stimulus…contraction Sarcolemma: its membrane Sarcoplasm: its cytoplasm Many nuclei and mitochondria Sarcoplasm contains myofibrils: threadlike, parallel fibers containing actin and myosin

Each myofibril is divided into sarcomeres. Sarcomeres contain filaments that cause contraction. Actin filaments are pulled during contraction. Myosin filaments pull actin during contraction. CONTRACTION RELAXATION M line myosin Z line

Actin and myosin Patterns of these creates striations I bands: light bands, actin connected to Z lines A bands: thick myosin filaments overlapping actin filaments. This area encompasses the overlapping of thick/thin filaments and the central H Zone, plus the M Line A Sarcomere goes from one Z line to the next

High microscope magnification of sarcomeres within a myofibril Sport Books Publisher

Sarcomere Sarcoplasmic reticulum: Like ER, but surrounding each myofibril, and running parallel to it Transverse tubule: runs laterally across cell, reaches all the way across Transverse tubules cross SR at cisternae: enlarged pockets on SR. The SR and Transverse tubule initiate contractions

Excitation-Contraction Coupling Mechanism where an action potential causes muscle fiber contraction Involves Sarcolemma Transverse or T tubules Terminal cisternae Sarcoplasmic reticulum Ca2+ Troponin

Motor Units A motor neuron and the muscle fibers it controls A motor neuron causes all fibers that are linked to it to contract simultaneously

Neuromuscular Junction Each skeletal muscle attached to a motor neuron This connection is called a neuromuscular junction The fiber membrane here is called the Motor End Plate, which is full of mitochondria, and the sarcolemma is very folded The nerve end is loaded with vesicles containing neurotransmitters These neurotransmitters (acetylcholine) cross the synapse and stimulate a muscle contraction http://www.blackwellpublishing.com/matthews/myosin.html

Neuron stimulates muscle at the neuromuscular junction.

Energy Sources for Contraction ATP allows contractions to occur Creatine Phosphate is the first store of energy to recharge ADP back to ATP Creatine Phosphate stores are limited, and after it is exhausted, cell respiration supplies the ATP to get the job done.

Muscle Contractions: Once upon a time, there was a neurotransmitter released… Sliding Filament Theory: The head of a myosin cross bridge attaches to an actin and bends slightly, pulling the actin filament with it. It then releases, straightens, and grabs another actin binding site further up. Repeat as necessary. Myosin cross bridges contain ATPase which releases energy from ATP to fuel contraction Acetylcholinesterase decomposes acetylcholine, which stops continuous contractions from one impulse http://www.sci.sdsu.edu/movies/actin_myosin.html

Neuron stimulates muscle at the neuromuscular junction. Neurotransmitters cause calcium channels in the sarcomere to open. regulatory protein Calcium exposes binding sites. Myosin binds to actin and pulls it. As the sarcomere shortens, the muscle contracts. myosin actin Z line

Cross-bridge formation:

Sarcomere Shortening

Slow and Fast Fibers Slow-twitch or high-oxidative Contract more slowly, smaller in diameter, better blood supply, more mitochondria, more fatigue-resistant than fast-twitch Fast-twitch or low-oxidative Respond rapidly to nervous stimulation, contain myosin to break down ATP more rapidly, less blood supply, fewer and smaller mitochondria than slow-twitch Distribution of fast-twitch and slow twitch Most muscles have both but varies for each muscle Effects of exercise Hypertrophies: Increases in muscle size Atrophies: Decreases in muscle size

Fatigue Decreased capacity to work and reduced efficiency of performance Types: Psychological Depends on emotional state of individual Muscular Results from ATP depletion Synaptic Occurs in neuromuscular junction due to lack of acetylcholine

Effects of Aging on Skeletal Muscle Reduced muscle mass Increased time for muscle to contract in response to nervous stimuli Reduced stamina Increased recovery time Loss of muscle fibers Decreased density of capillaries in muscle