Seminar 6 The Muscular System

Introduction Muscular tissue enables the body and its parts to move Movement caused by ability of muscle cells (called fibers) to shorten or contract Muscle cells shorten by converting chemical energy (obtained from food) into mechanical energy, which causes movement Three types of muscle tissue exist in body

3 Types of muscle Skeletal Cardiac Smooth

Parts of a Skeletal muscle Origin—attachment to the bone that remains relatively stationary or fixed when movement at the joint occurs Insertion—point of attachment to the bone that moves when a muscle contracts Body—main part of the muscle

Microscopic Structures Here’s the breakdown: Muscle >bundles of fibers>individual muscle fibers>sarcomeres>myofilaments A sarcomere is a contractile unit of a muscle fiber. Fibers contain thick myofilaments (myosin) and thin myofilaments (actin).

Figure 8-3, page 232

Sliding Filament Theory Actin and myosin myofilaments slide past each other in a “ratchet” motion What two things are required for this contraction to occur?

Motor Unit – how we get muscles to move! Stimulation of a muscle happens by a nerve impulse . Each muscle has specific nerves that function to make it move!!! A motor neuron is the specialized nerve that transmits an impulse to a muscle, causing contraction Neuromuscular Junction is the exact spot where the nerve enters the muscle

What are the functions of the muscular system?

Functions of the muscular system: Movement Posture Heat production

Movement Prime Mover Synergist Antagonist The main muscle responsible for a particular movement Synergist The muscle(s) that assist the prime mover with a particular motion Antagonist The muscle that works in opposition to the above

Posture Tonic muscle contraction allows us to maintain good posture

Heat Production Requires ATP Contraction of muscle fibers produces heat

Muscle Fatigue – what causes it? Reduced strength of muscle contraction Caused by repeated muscle stimulation without adequate periods of rest Repeated muscular contraction depletes cellular ATP stores Contraction in the absence of adequate oxygen produces lactic acid What is meant by Oxygen Debt?

Motor Unit Each muscle of the body has a particular nerve or several nerves that “innervate” that muscle. The muscle and the nerve that supplies it’s innervation are known as a motor unit.

Types of skeletal muscle contractions Twitch Tetanic Isotonic Isometric

Twitch Tetanic Isotonic Isometric

Effects of Exercise on Skeletal Muscles Improves muscle tone Improves posture Results in more efficient heart and lung functioning Reduces fatigue

Effects of Exercise on Skeletal Muscles Prolonged inactivity causes disuse, called atrophy Regular exercise increases muscle size, called hypertrophy

The Step Test – The question Why do breathing and heart rate remain elevated after exercise stops?

The Step Test – The answer Stored ATP is quickly depleted, and if oxygen supplies are not sufficient, muscle cells switch to energy conversion that does not require oxygen. However, this energy conversion produces lactic acid. The “oxygen debt” is paid when labored breathing and an increased heart rate are required to remove lactic acid and replace depleted energy reserves, even after exercise has ended.

Step Test – 2nd question Why would a “physically fit” person return to normal breathing and heart rate levels more quickly than an unfit person?

Step Test – 2nd answer increased efficiency of the respiratory and circulatory systems an increase in the number of blood vessels in muscles more efficient delivery of oxygen and glucose to muscle fibers more oxygen is available = the less “oxygen debt” there will be in the muscles.

Step Test – 3rd question Aerobic training also increases the number of mitochondria in muscle fibers. Why would this benefit the muscle contraction process?

Step Test – 3rd answer Mitochondria are cellular organelles that convert glucose to ATP Contraction of muscle cells requires ATP an increase in the number of mitochondria in a muscle cell increases the speed with which ATP is produced in the cell. Mitochondria = ATP

Body movements Figure 8-11 Rotation Adduction and abduction Pronation and supination Dorsiflexion and plantarflexion

Exercise – Learning activity Let’s say we want to strengthen the various muscles listed here…. Biceps brachii Pectoralis major Gluteus maximus Gastrocnemius Rectus abdominus What exercises should we do?

Exercise – Learning activity Let’s say we want to strengthen the various muscles listed here…. Biceps brachii = arm curls Pectoralis major = push ups Gluteus maximus = squats Gastrocnemius = foot flexion and extension Rectus abdominus = sit-ups

Muscle disorders Strain—injury from overexertion or trauma Cramps are painful muscle spasms (involuntary twitches) Infections Muscular dystrophy Myasthenia gravis

Review Function of the muscular system Structure of a muscle Types of muscle tissue How a contraction occurs Types of contractions How exercise affects muscle