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
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).
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
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
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
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