The Motor System Muscles Muscles n Howstuffworks Cardiac

The Motor System Muscles

Muscles n Howstuffworks "Cardiac and Smooth Muscle" The 3 main types of Muscles

n The body has more then 600 muscles!

Muscles n 3 main types of muscles: n 1) Cardiac Muscles: heart muscles Found only in the heart n Involuntary contraction and relaxation. Why? It is controlled by nerves of the autonomic nervous system and always has to be pumping in order to pump blood (which contains oxygen, nutrients, and other important molecules) to all of the cells of the body. n

Cardiac Muscles -The heart beats non-stop because of these striated muscle cells. -Cardiac muscle is myogenic, meaning that it is self-excitable stimulating contraction without a required electrical impulse coming from the central nervous system. -A single cardiac muscle cell, if left without input, will contract rhythmically at a steady rate; if two cardiac muscle cells are in contact, whichever one contracts first will stimulate the other to contract, and so on. This is heavily regulated by the autonomic nervous system

2) Smooth Muscles: found in the lining of many organs -Found in the hollow parts of the body, for instance the lining of organs such as: the stomach, esophagus, uterus, and walls of blood vessels. -Smooth muscle contractions are required for such things as: pushing food through the digestive system or pushing a baby through the vagina. -Similar to cardiac muscles contraction, smooth muscle contraction is involuntary

Smooth Muscles -This type of muscle shows no cross stripes (non-striated muscle cells) under microscopic magnification. It consists of narrow spindleshaped cells with a centrally located nucleus. Smoothmuscle tissue contract slowly and automatically.

3) Skeletal Muscles: muscles that are attached to bone -Unlike cardiac and smooth muscles, these type of muscles are voluntarily controlled -These muscles allow you to walk, talk, ride a bike, swim, jump, etc. -Skeletal muscles attach to bones by tendons -Skeletal muscles are key in helping you keep warm. 80% or all energy used in muscle contraction is lost as heat!

Skeletal Muscles -Similar to cardiac muscles, Skeletal muscles are striated. -Like all muscles, skeletal muscles shorten when they contract and lengthen when they relax. The arm bends upwards when muscles contract and pull it upwards. -The central nervous system sends excitatory or inhibitory nerve impulses to the skeletal muscles which either cause the muscle to contract or relax, never to do both at one time.

Skeletal Muscles Cont…. n n Skeletal muscle is composed of many bundles of cells called fiber. The fibers are enclosed within a membrane called sarcolemma Within the muscle fiber there are many myofilaments bundles together n There are two main types of myofilament which contain different contractile units: n n n 1) Thin Myofilament: composed of actin (light bands) 2) Thick Myofilament: composed of myosin (dark bands) These two types of myofilament overlap to produce a striated (striped) appearance

Structure of Skeletal Muscles n n n An individual section of the myofilament is called a sarcomere The length of one sarcomere is defined by the Z-Line. The Z-lines anchors the actin to each other and to the bone. The length of the myosin is defined by the A-Band. It contains both actin and myosin. The I-Band only contains actin and it is the space in between 2 myosin. The H-Zone is the empty space between 2 actin. Myosin is only found in this space

Muscles Contraction (The Sliding Filament Theory) n During each contraction: n n n 1) A neurotransmitter is released from a nerve to the muscles, signaling contraction 2) The muscle cell’s endoplasmic reticulum release Calcium (Ca 2+ ions) near the actin 3) Calcium ions attach to the actin and this then allows myosin to attach to the actin as well, forming an ‘Actin. Myosin Cross-Bridge’ 4) The actin and myosin attach and de-attach, over an over. With each re-attachment of the actin the muscle fibers get pulled closer together. This carries on until full contraction of the muscles occurs. Untitled Document

n Calcium ions also start the break down of ATP, which allows the actin to de-attach each time from the myosin and also provides the energy for contraction to occur. (Recall: when ATP is broken down, energy is given off) If no ATP is present, rigor mortis occurs: This occurs after death, myosin and actin stay attached, thus muscles stay fully contracted. The body is stiff as a board! n Muscle. Animation n

Complications of the muscular system n n Muscle soreness, burning, fatigue, tightness, etc. , is due to the fact that very little ATP can be stored in the muscle tissue. As a result, Aerobic Cellular Respiration constantly provides/replenishes most of the energy (in the form of ATP). As soon as the ATP is used up and converted back to ADP, a compound called creatine phosphate, ensures all ADP is converted back to ATP n n Creatine is a supplement often used by many sports to increase muscle strength Fatigue will only occur if ATP demands can not be met. Lactic acid begins to build up, muscles tighten up, and fatigue takes over.

n n n Atrophy: the reduction in size, tone and power of a muscle due to decreased use and stimulation, which can eventually lead to permanent loss of muscle function. Hypertrophy: an exercise-induced increase in muscle mass resulting from an increase in the size of individual muscle fibres. Note- neither of these involve a change in the number of muscle fibres.

Muscle Twitch n Muscle twitch – is a muscle contraction that lasts a fraction of a second that occurs in three stages: n n n Latent stage – time between stimulus and initiation of the contraction Contraction stage – time it takes for the muscle fibers to shorten Relaxation stage – time it takes for the muscle to return to its regular length.

n n Slow twitch – smaller muscle fibers that contract slowly and resist fatigue because they are surrounded by more blood vessels and have more mitochondria. i. e. soleus muscle in the leg, postural back muscles Fast twitch– larger muscle fibers that contract quickly to give more power, but depend upon anaerobic energy production. They are rich in glycogen, and have fewer mitochondria and blood vessels surrounding them. i. e. lateral rectus muscle in the eye, biceps

The effects of exercise n n Endurance training – increases the development of slow-twitch muscle fibres and has no impact on the size of the muscles. Resistance / strength training – thickens fast-twitch muscles, causing an increase in muscle size.

n n Tetanus: a state of constant muscle contraction. Often caused by bites, or rusted metals entering the blood stream. Muscle spasms: involuntary contraction of a muscle. Often caused by a pinched nerve.