Muscular system flashcards

Skeletal muscle is striated and tubular, it has many nuclei, it contracts voluntarily and is usually attached to skeleton bone. Smooth muscle is not striated, cells have one nucleus, contracts involuntarily and is found in the walls of internal organs. Cardiac muscle is striated, tubular and branched, cells have one nucleus, contracts involuntarily and found in the walls of the heart.

They support the body, move bones, maintain body temperature, protect internal organs and stabilize joints.

Muscle contraction causes movement of bones at a joint. Muscles shorten when they contract expand when they relax. Muscles can only pull they cannot push. Muscles come in pairs because every action of one muscle has another doing the opposite action (antagonistic pairs), the pair of muscles are arranged around a joint.

A flexor is a muscle that conracts to bend a joint, extensor relaxes (ex bicep). An extensor contracts to straighten a joint and the flexor relaxes (ex tricep).

A muscle lies along a length of bone, attached at both ends by a tendon. A muscle fibre bundle is a fascicle (section) of muscle fibres. A layer of connective tissue wraps around each bundle. Blood vessels and nerves run between the bundles.

Muscle --> Muscle fibre bundle --> muscle fibre --> myofibrils --> myofilaments.

It is a long single muscle cell bound by a membrane called the sarcolemma (regulates entry and exits into cell). Components found in a muscle fibre are myoglobin (oxygen binding pigment that stores oxygen for cellular respiration), sacroplasm (cytoplasm, stores myoglobin and glycogen), sacroplasmic reticulum (organelle in sarcoplasm that stores calcium ions) and myofibrils.

Myofibril is an organized budle of myofilaments that are responsible for muscle contraction. Striations are formed due to a contractile unit called a sarcomere that repeat along the length of the myofibril. Myofilaments have two types, thin and thick filament. Each contains their own specific protein structure that is responsible for muscle contraction. These proteins are actin and myosin.

Actin is thin filament, two strands are wrapped around each other. Myosin consists of two strands as well but they are 10x longer and wrapped tighter, one end has a long rod the other has a globular head.

Myosin heads bind to actin through chemical bonds, then the myosin head flexes backwards and inwards a few nanometers pulling the attached actin too. Then ATP provides energy to release the myosin head and reposition it before each flex. Then myosin attaches further along the filament and continues to flex and slide the actin.

Each actin in anchored at one end of its filament at a postion in the striated muscle tissue called the z-line, because actin is anchored as actin moves past myosin it drags the z line with it. since their are two different actin filaments in a sarcomere both are pulled inwards in opposing directions and they pull the z lines together causing the z line to shrink and muscles to contract. eventually myosin will hit the z line and be unable to flex further.

Calcium ions (Ca2+) from the sarcoplasmic reticulum bind with toponin to make the troponin-tropomyosin complex reposition so myosin heads are able to attach to the binding sites of actin. Nerve impulses release Ca2+ to diffuse into myofibrils and they cause it to return back through active transport.

Because ATP produced before exercise only lasts a few secons and during exercise muscles require a continuous supply of ATP.

Creating Phosphate is a high energy compound that builds up when a muscle is resting. It cannot directly participate in muscle contraction so it make ATP through the reaction: creatine phosphate + ADP --> creatine + ATP. It is the first way to get ATP before oxygen enters the mitochondria to facilitate aerobic cellular respiration and it only provides enough energy for about 8 seconds of intense activity then needs to be rebuilt by resting.

It usually provides most of a muscles ATP its reaction is glucose + oxygen + ADP --> carbon dioxide + water + ATP. Muscle fibres use glucose and fatty acids from glycogen and fats that are stores in muscle cell to produce ATP. Myoglobin is an oxygen carrying muscle that temporarily stores oxygen (more than hemoglobin) and makes it availible to the mitochondria when cellular respiration begins. CO2 leaves through the lungs, water diffuses into extracellular space and heat from the reaction warms the entire body.

Lactate fermentation, the 2nd form of anaerobic respiration provides ATP without consuming oxygen. Glucose is broken down to produce lactate through the following reaction: glucose + ADP --> lactate (lactic acid) + ATP. the buildup of lactate in a muscle fibre majes the sarcoplasm more acidic which eventually causes enzymes to stop functioning well. This results in oxygen deficiency because lactate requires oxygen to be metabolized completely (causes panting). This happens at the same time as aerobic respiration.

Muscles are controlled by electrical impulses from the nervous system, each muscle fibre has a minimum voltage required to cause it to contract. If the minimum is reached the fibre will contract, it will not contract harder or faster if their is more voltage. This single contraction only lasts a fraction of a second and is called a muscle twitch. Strength of a muscle contraction can vary depending on the number of muscle fibres contracting in it.

First comes the stimulus which is the signal recieved. Then there is the latent period, the time between the stimulation and initiation of contraction. Then comes the contraction period (muscle contracts), and last the relaxation period (muscle returns to original length).

slow twitch fibres contract slowly, use ATP efficiently, resist fatigue and only tire when fuel is gone, produce most of their energy aerobically and are dark in colour due to having myoglobin. They also have many mitochondria and blood vessels. Fast twitch fibres are adapted for rapid generation of power, produce most of their energy anaerobically (but can fatigue quickly if lactate acumulates), are rich in glycogen but have fewer mitochondria and blood vessels and are light in colour due to having little to no myoglobin.

Atrophy is a condition in which muscles are impaired due to lack of use, their size, tone and power reduce. Atrophy can be reversed by physical therapy but dead muscle fibres cannot be replaces. Hypertrophy is the opposite it is the exercise induced increase in muscle mass (no new fibres are created).