The Muscular System

SAP2. Students will analyze the interdependence of the integumentary, skeletal, and muscular systems as these relate to the protection,

support and movement of the human body.

Explain how the skeletal structures provide support and protection for tissues, and function together with the muscular system to make movements possible.

Types of Muscular Tissue

• Muscular tissue makes up 40% - 50% of the total body weight.

• Skeletal muscle – attached to bones and moves parts of the skeleton. It is striated (has light and dark bands). It can contract and relax by conscious control (voluntary).

• Cardiac muscle – found only in the heart. It is also striated. It is involuntary

• Smooth muscle – located in walls of internal structures (blood vessels, airways, the stomach the intestines). It helps control digestion, blood pressure regulation. It is nonstriated and involuntary.

Functions of the Muscular Tissue

1.Producing body movements – walking, running

2.Stabilizing body positions – sitting, standing, holding the head upright

3.Regulating organ volume – sphincters prevent outflow of the contents of a hollow organ: storage of urine, food in the stomach,

Functions of the Muscular Tissue

4. Moving substances within the body – cardiac muscle contractions pumps blood through the body, contraction and relaxation of muscle in blood vessels regulate blood flow

5. Producing heat – as muscles contract they produce heat that is used to maintain a normal body temperature (homeostasis). Involuntary contractions (shivering) can help warm the body by increasing rate of heat production.

Skeletal Muscle Tissue

• Perimysium – Surrounds bundles of 10 – 100 muscle fibers call fascicles

• Endomysium – wraps around each individual muscle fiber

• Tendon- cord of dense connective tissue composed of bundles of collagen fibers. They attach muscle to bone.

Skeletal Muscle (pg. 174)

QuizYourself

Histology (study of the microscopic structure of tissues)• Muscle fibers are arranged parallel to each other. Each

fiber is covered by a membrane called the sarcolemma.

• The muscle fibers cytoplasm is called sarcoplasm which has many mitochondria that produce large amounts of ATP when a muscle contracts.

• Throughout the sarcoplasm is sarcoplasmic reticulum which are tubules that stores calcium ions which are required for muscle contraction. Myoglobin (a red pigment) is also in the sarcoplasm and it stores oxygen to be used by the mitochondria to generate ATP.

Muscular Atrophy

• Is a wasting away of muscle. The muscle fibers decrease in size because of loss of myofibrils.

•How does it happen? People who are bedridden, limbs that have been in casts

Muscular hypertrophy

• Is an increase in muscle fiber diameter due to the production of more myofibrils, mitochondria, sarcoplasmic reticulum, etc.

• It results from forceful, repetitive activity such as strength training. Since they contain more myofibrils they are capable of contractions that are more forceful.

Botulinum Toxin

• It blocks the release of acetylcholine (ACh) at the neuromuscular junction.

• It is used as a medicine.

• Helps patients with crossed eyes and uncontrollable blinking

• Cosmetic treatment to relax muscles that cause facial wrinkles (Botox)

• Stops back pain due to spasms in the lumbar region

Rigor Mortis

• When a person dies, Ca begins to leak out of the sarcoplasmic reticulum and binds to troponin, causing the filaments to slide. ATP production has ceased so the crossbridges cannot detach from actin. The resulting stiffness of the muscles is rigor mortis, rigidity of death. It begins 3-4 hours after death and lasts for about 24 hours.

Muscle Tone

• Even when a muscle is not contracting, a small number of motor units are involuntarily activated to produce a sustained contraction of their muscle fibers. To sustain muscle tone small groups of motor units are alternately active and inactive in a constantly shifting pattern. This keeps skeletal muscles firm but does not produce movement.

• Example: the tone of muscles in the back of the neck keeps the head upright and prevents it from slumping forward.

• Therefore, tone is established by neurons in the brain and spinal cord that excite the muscles neurons.

Energy for Contraction

• Muscles must have ATP and Calcium to contract

• As muscles become more active more ATP is needed.

• The ATP inside the muscle fibers is only enough to power a contraction for a few seconds!

• If exercise is continued it must synthesize more ATP. It comes from 3 sources.

Energy for Contraction

• 1. Creatine phosphate which comes from excess ATP. It is an energy-rich molecule that is unique to muscle fibers. A phosphate from ATP is transferred to creatine (a small amino acie-like molecule that is synthesized in the liver, kidneys and pancreas and comes from milk, red meat and fish) forming creatine phosphate and ADP. It provides about 15 seconds of energy. Read blue box on pg 182-183

• 2. Anaerobic cellular respiration – without the use of oxygen…..Through the conversion of creatine phosphate and glycolysis (from ATP) it can provide energy for about 30 to 40 seconds of maximal muscle activity

Energy for Contraction

• 3. Aerobic cellular respiration – oxygen requiring reactions that produce ATP in mitochondria. Muscle fibers get oxygen from the blood and from myoglobin (which is a protein found in the sarcoplasm)

• Aerobic respiration yields much more ATP!!!!!

Muscle Fatigue

• The inability for a muscle to contract forcefully after prolonged activity.

• A big factor in fatigue is a decline in the Ca level in the sarcoplasm, a depletion of creatine phosphate, insufficient oxygen, build up of lactic acid and ADP, and failure of nerve impulses

Cardiac Muscle

• Skeletal muscle contracts when stimulated by a nerve impulse

• Cardiac muscle fibers act as a pacemaker to initiate each cardiac contraction. The built in rhythm is called autorhythmicity. Several hormones and neurotransmitters can increase or decrease heart rate by speeding or slowing the hearts pacemaker.

• Beats about 75 times per minute.

• The mitochondria in cardiac fibers are larger and more numerous than skeletal muscle.

Aging

• At about 30 years old……humans begin a slow progressive loss of skeletal muscle mass that is replace by connective tissue and adipose tissue (fat)

• Due to……….decline in physical activity!

• In addition….there is a decrease in muscle reflexes and flexibility.

• So we need to stay active!!!!! Aerobic activities and strength training !!!!!!

Muscles producing movement

• As we saw in the chicken wing…..muscles are not directly attached to bones. They are attached by tendons. When a muscle contracts it pulls one bone toward another. The 2 bones don’t move equally. One is held at almost its original position called the origin. The other end is attached by a tendon to the movable bone called the insertion. Think of bending your arm. The humerus is the point of origin. The radius and ulna are the point of insertion. Look at Figure 8.12 on pg 189

Stretching

• Read the Focus on Wellness on pg 190

• When does tissue stretch the best?

• How do you increase flexibility?

Neuromuscular disease

• When skeletal muscle function is abnormal due to disease or damage of components of a motor unit, somatic motor neurons and neuromuscular junctions or muscle fibers.

Duchenne muscular dystrophy

• The most common form of muscular dystrophy (muscle destroying disease – progressive degeneration of muscle fibers).

• Strikes boys (because it is on the X chromosome…males only have one)

• By 12 they are unable to walk.

• By 20 – 30 respiratory/cardiac failure which eventually causes death

Fibromyalgia

• A painful disorder that usually appears at 25-50 years of age

• Mostly women

• A striking pain that results from pressure at specific “striking points”.

Myalgia

• Pain in or associated with muscles

Myositis

• Inflammation of muscle fibers/cells.