Muscular system

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Muscular System Study Guide

The muscular system is responsible for movement, stabilizing joints, maintaining posture, and generating heat

Irritability is The ability to receive and respond to stimuli.

Contractility is the ability to shorten with adequate stimuli

How does a muscle contract? A nerve impulse reaches the end of the nerve a neurotransmitter is released.

• The neurotransmitter that stimulates skeletal muscle is acetylcholine (Ach)
  When enough acetylcholine is released, sodium ions (Na+) will rush into the muscle.

• This rush of ions creates an electrical current known as the action potential.

• The action potential travels over the entire muscle causing it to contract.

The Sliding Filament Theory:

• Muscle fibers contract when the sarcomere shortens.

• The sarcomere shortens when the actin fibers slide past the myosin filaments

• Myosin moves the actin.

• The sliding filament theory refers to the movement of actin in relation to myosin.

• ATP supplies the energy for muscle contraction.

• Myosin filaments do all the work.
  The actin filaments just sit there.

Aerobic Respiration - ATP is made by aerobic respiration

• 1 glucose - 36 ATP

• Fairly slow - needs continuous supply of oxygen

Anaerobic Respiration and

Lactic Acid Formation

• No oxygen

• 2 ATP per glucose

• Lactic acid is made and builds up in muscles

• 5X faster than aerobic

• 30-40 seconds of strenuous exercise

• Problems: needs lots of glucose

• Small amount of ATP produced per glucose

• Lactic acid

Aerobic or Endurance Excercise

• Stronger more flexible muscles with greater resistance to fatigue

• Blood supply increases as cells form more mitochondria and store more oxygen

Body Benefits

1. Overall body metabolism is more efficient

2. Improves digestion

3. Skeleton stronger

4. Heart pumps more blood with each beat

5. Fat deposits cleared

6. Lungs are more efficient at gas exchange

Resistance or Isometric

Exercise

• A few minutes every other day

• Muscles increase in size because muscle cells increase in size (not increase in number of cells)

• Amount of reinforcing connective tissue also increases

Types of Muscles

• Muscles cannot push. They can only pull.

• So most body movements are a result of the activity of pairs or teams of muscles acting together or against each other
  Muscle groups are arranged on the skeleton so that whatever one muscle can do, another group of muscles can do in reverse

Slow Twitch Muscle Fibers -Legs

• Steadier tug

• More endurance

• Aerobic energy production - tire when fuel is gone

• Sports useful in: long distance running, biking, jogging, swimming

• Color: dark

• Many mitochondria, dense capillary beds which draw more blood and oxygen

Fast Twitch Muscle Fibers -Breasts

• Anaerobic - tire quick because of lactic acid build up

• Designed for strength

• Explosions of energy

• Sports useful in: sprinting, weight lifting

• Color: white

• Few mitochondria, few blood cells

Types of Muscle Tissue and How They Contract

1. Skeletal Muscle

• Voluntary muscle attached to bones.

• Contraction is initiated by nervous signals.

• Responsible for movements of the body.

2. Cardiac Muscle

• Involuntary muscle found in the heart.

• Contractions are regulated by electrical impulses generated within the heart muscle itself (pacemaker cells).

• Striated and branched.

3. Smooth Muscle

• Involuntary muscle found in the walls of hollow organs (e.g., intestines, blood vessels).

• Contractions are controlled by the autonomic nervous system and hormones.

Acetylcholine

• Acetylcholine (ACh) is a neurotransmitter that plays a critical role in transmitting signals from nerves to muscles.

• It binds to receptors on muscle cells to initiate the contraction process.

Sliding Filament Theory

• Sliding Filament Theory explains how muscles contract by the sliding of actin and myosin filaments:

1. Myosin heads bind to actin filaments to form cross-bridges.

2. The myosin heads then pull on the actin filaments, causing the filaments to slide past each other.

3. This shortens the muscle fiber and generates contraction.

Motor Unit

• A motor unit consists of a motor neuron and the muscle fibers it controls.

• The motor neuron sends a signal to the muscle fibers, causing them to contract.

• Larger muscles have more motor units for stronger contractions, while smaller muscles may have fewer motor units for more precise movements.

Positive Effects of Aerobic Exercise

• Increased endurance and muscle efficiency.

• Improved cardiovascular health.

• Better oxygen delivery to muscles.

• Enhanced ability to burn fat for energy.

• Increased mitochondrial density in muscles for more efficient ATP production.

Three Ways ATP is Supplied to Muscles

1. Creatine Phosphate (CP) Breakdown:

• Provides ATP rapidly for short bursts of activity.

• Lasts for about 10-15 seconds.

2. Anaerobic Respiration:

• Occurs without oxygen, produces ATP quickly, but also generates lactic acid, leading to muscle fatigue.

• Lasts for 1-3 minutes.

3. Aerobic Respiration:

• Requires oxygen to produce ATP efficiently.

• Preferred during prolonged, moderate activity (e.g., running, swimming).

How Muscles Move Bones

• Muscles contract, shortening the muscle fibers.

• When muscles contract, they pull on tendons, which are attached to bones.

• This movement allows bones to rotate at joints, resulting in body movements.

Muscle Fiber

• Muscle fibers are elongated cells with many nuclei.

• They contain myofibrils which are made up of sarcomeres, the functional units of muscle contraction.

Three Types of Muscle Tissue and Their Characteristics

1. Skeletal Muscle

• Voluntary, striated, multinucleated fibers.

• Attach to bones and control movement.

2. Cardiac Muscle

• Involuntary, striated, single nucleus, branched fibers.

• Found in the heart and helps pump blood.

3. Smooth Muscle

• Involuntary, non-striated, single nucleus fibers.

• Found in the walls of hollow organs like blood vessels and the digestive tract.

Two Protein Filaments in Muscles

1. Actin (Thin Filament)

• Composed of globular subunits that form long chains.

• Helps in forming the cross-bridges with myosin for muscle contraction.

2. Myosin (Thick Filament)

• Contains myosin heads that bind to actin and pull it to contract the muscle.

Muscle Hierarchy

1. Fascicle: A bundle of muscle fibers (cells).

2. Muscle Fiber (Cell): The individual muscle cells that contract.

3. Myofibril: Long, thread-like structures within muscle fibers that contain the actin and myosin filaments.

4. Sarcomere: The functional unit of muscle contraction, defined by the area between two Z-discs in a myofibril.

Muscle Vocabulary

1. Anabolic Steroids: Synthetic substances that mimic the effects of testosterone and increase muscle growth but have harmful side effects.

2. Isometric Contractions: Muscle contractions where the muscle generates tension without changing length (e.g., holding a plank).

3. Isotonic Contractions: Muscle contractions where the muscle changes length (e.g., lifting weights).

4. Sarcomere: The repeating unit in myofibrils responsible for muscle contraction.

5. Atrophy: The decrease in muscle size due to lack of use or illness.

6. Lactic Acid: A byproduct of anaerobic respiration, leading to muscle fatigue.

7. Irritability: The ability of muscle fibers to respond to stimuli (e.g., nerve impulses).

8. Nerve Impulse: Electrical signals sent through neurons to initiate muscle contraction.

9. Hypertrophy: The increase in muscle size from strength training.

10. Anaerobic Respiration: ATP production without oxygen, often resulting in lactic acid buildup.

11. Contractility: The ability of muscle fibers to contract in response to stimuli.

12. Fatigued: The state of being unable to continue contracting due to energy depletion.

13. Aerobic Respiration: ATP production with oxygen, leading to more efficient energy production for prolonged activity.

Perimysium, Epimysium, Endomysium, Fascicle, Myofibril, Sarcomere

• Perimysium: Connective tissue surrounding a muscle fascicle.

• Epimysium: Connective tissue surrounding the entire muscle.

• Endomysium: Connective tissue surrounding individual muscle fibers.

• Fascicle: A bundle of muscle fibers.

• Myofibril: Substructures inside muscle fibers, made of sarcomeres, that help in contraction.

• Sarcomere: The contractile unit of a muscle, consisting of actin and myosin filaments.

Major Muscles and Their Locations

1. Eye Muscles: Control eye movements.

2. Forehead (Frontalis): Raises eyebrows and wrinkles forehead.

3. Mouth (Orbicularis oris): Allows for movements like closing the mouth and pursing lips.

4. Shoulder (Deltoid): Moves the arm in various directions.

5. Upper Back (Trapezius): Moves and stabilizes the shoulder blades.

6. Lower Back (Latissimus Dorsi): Extends, adducts, and rotates the arm.

7. Biceps (Biceps Brachii): Flexes the elbow.

8. Chest (Pectoralis Major): Moves the arm and shoulder.

9. Abs (Rectus Abdominis): Flexes the spine and compresses the abdominal contents.

10. Obliques: Rotates and laterally flexes the trunk.

11. Gastrocnemius: Primary calf muscle involved in plantar flexion.

12. Femur Muscles (Quadriceps & Hamstrings): The quadriceps extend the knee, while the hamstrings flex it.

13. Sternocleidomastoid: Rotates and tilts the head, flexes the neck.

14. Sartorius: Flexes, abducts, and externally rotates the hip.

This guide is designed to provide you with the key concepts and vocabulary for your muscular system study. You can use it to prepare for quizzes, tests, or to deepen your understanding of the muscular system.