Seminar 6 Seminar 6 The Muscular SystemThe Muscular System

IntroductionIntroductionMuscular 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 muscle3 Types of muscleSkeletalCardiacSmooth

Parts of a Skeletal muscleParts 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 StructuresMicroscopic 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 TheorySliding Filament TheoryActin 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 Motor Unit – how we get muscles to move!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 WHAT ARE THE FUNCTIONS OF THE FUNCTIONS OF THE MUSCULAR SYSTEM?MUSCULAR SYSTEM?

Functions of the muscular Functions of the muscular system:system:Movement

Posture

Heat production

MovementMovementPrime Mover

◦ 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

PosturePostureTonic muscle

contraction allows us to maintain good posture

Heat ProductionHeat ProductionRequires ATP

Contraction of muscle fibers produces heat

Muscle Fatigue – what Muscle Fatigue – what causes it?causes it?Reduced strength of muscle contractionCaused by repeated muscle stimulation

without adequate periods of restRepeated muscular contraction depletes

cellular ATP stores Contraction in the absence of adequate

oxygen produces lactic acidWhat is meant by Oxygen Debt?

Motor UnitMotor UnitEach 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 Types of skeletal muscle contractionscontractionsTwitchTetanicIsotonicIsometric

TwitchTetanicIsotonicIsometric

Effects of Exercise Effects of Exercise on Skeletal Muscleson Skeletal MusclesImproves muscle tone Improves postureResults in more efficient heart

and lung functioning Reduces fatigue

Effects of Exercise Effects of Exercise on Skeletal Muscleson Skeletal Muscles

Prolonged inactivity causes disuse, called atrophy

Regular exercise increases muscle size, called hypertrophy

The Step Test – The The Step Test – The questionquestionWhy do breathing and heart rate

remain elevated after exercise stops?

The Step Test – The The Step Test – The answeranswerStored 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 – 2Step Test – 2ndnd question questionWhy would a “physically fit”

person return to normal breathing and heart rate levels more quickly than an unfit person?

Step Test – 2Step Test – 2ndnd answer answerincreased 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 – 3Step Test – 3rdrd question questionAerobic training also increases

the number of mitochondria in muscle fibers.

Why would this benefit the muscle contraction process?

Step Test – 3Step Test – 3rdrd answer answerMitochondria are cellular organelles that

convert glucose to ATP Contraction of muscle cells requires ATPan 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 Body movements Figure 8-118-11RotationAdduction and abductionPronation and supinationDorsiflexion and plantarflexion

Exercise – Learning Exercise – Learning activityactivityLet’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 Exercise – Learning activityactivityLet’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 disordersMuscle disordersStrain—injury from overexertion

ortrauma

Cramps are painful muscle spasms (involuntary twitches)

InfectionsMuscular dystrophy Myasthenia gravis

ReviewReviewFunction of the muscular systemStructure of a muscleTypes of muscle tissueHow a contraction occursTypes of contractionsHow exercise affects muscle