THE MUSCULAR SYSTEM

To understand the structure of muscle.

To explain the components and significance of the sarcomere.

To identify the parts of the neuromuscular junction

To explain how muscle contracts.

OBJECTIVES

MUSCULAR MOVEMENT skeletal muscles come in

antagonistic pairsflexor vs. extensor

They contract (shorten) when activatedTendons (t=two!)

connect bone to muscle

ligamentsconnect bone to bone

Composed of skeletal muscle tissue, nervous tissue, blood, and connective tissues.

SKELETAL MUSCLE

Fascia: layers of fibrous connective tissue that separate an individual muscle from adjacent muscles.

Epimysium: tissue closely surrounding muscle

Perimysium: separates muscle tissue into small compartments.

Fascicles: bundles of skeletal muscle fibers

Endomysium: surrounds each fiber within a fascicle.

CONNECTIVE TISSUE COVERINGS

STRUCTURE OF STRIATED SKELETAL MUSCLE

Muscle Fiber muscle cell

divided into sections = sarcomeres

Sarcomere functional unit of muscle

contraction alternating bands of

thin (actin) & thick (myosin) protein filaments

THICK & THIN FILAMENTS

Myosin tails aligned together & heads pointed away from center of sarcomere

THIN FILAMENTS: ACTIN Complex of proteins

braid of actin molecules & tropomyosin fibers tropomyosin fibers secured with troponin molecules which block the

spot where the myosin fiber will attach. (this must be moved in order for the muscle to contract)

SLIDING FILAMENT THEORY Sliding filament theory

Thin filaments of sarcomere slide toward M line after the

myosin crossbridges form

The width of the A band remains the same

Z lines move closer together

WHAT AM I?

Place where a motor neuron meets a muscle cell

Action potential travels down neuron, stimulates release of acetylcholine from vesicles, received by receptors on muscle cell, action potential is propogated and stimulates contraction.

NEUROMUSCULAR JUNCTION

Animation

STEPS OF CONTRACTION1. A. Upon stimulation, Ca2+ binds to receptor on

troponin molecule.

B. The troponin–tropomyosin complex changes,

exposing the active site of actin.

2. The myosin head attaches to actin, forming a cross-

bridge.

STEPS OF CONTRACTION

3. The attached myosin head bends/pivots towards the sarcomere, and ADP and P are released.

4. The cross- bridges detach when the myosin head binds another ATP molecule.

5. The detached myosin head is reactivated as ATPase splits the ATP and captures the released energy.

MOLECULAR EVENTS OF THE CONTRACTION PROCESS

Figure 7-5

MOLECULAR EVENTS OF THE CONTRACTION PROCESS

Figure 7-5

MOLECULAR EVENTS OF THE CONTRACTION PROCESS

Figure 7-5

MOLECULAR EVENTS OF THE CONTRACTION PROCESS

Figure 7-5

MOLECULAR EVENTS OF THE CONTRACTION PROCESS

Figure 7-5

MOLECULAR EVENTS OF THE CONTRACTION PROCESS

Figure 7-5

Put it all together…1

ATP

2

3

4

5

7

6

ATP

DO NOW

Read the article and answer the questions.

OBJECTIVES

To understand how muscles “grow” and explain the benefits of resistance workouts.

To identify the parts of a myogram and explain the different graphs used to depict muscle contraction.

To build on prior knowledge from Biology to explain muscular fatigue.

TENSION PRODUCTION

The all-or-none principle

As a whole, a muscle fiber either contracts

completely or does not contract at all

NUMBER OF MUSCLE FIBERS ACTIVATED

Recruitment (multiple motor unit

summation)

In a whole muscle or group of muscles, increasing

tension is produced by slowly increasing the

size or number of motor units stimulated

MOTOR UNITS

Figure 7-8

NUMBER OF MUSCLE FIBERS ACTIVATED

Muscle tone

The normal tension and firmness of a muscle at

rest

Muscle units actively maintain body position,

without motion

Increasing muscle tone increases metabolic

energy used, even at rest

MUSCLE CONTRACTIONA muscle fiber will contract after threshold stimulus has been reached.

Once stimulated, the entire fiber completely contracts which is called the all-or-none response.

*the extent of shortening depends on resistance.

MYOGRAMTwitch= single muscle

contractionLatent period: time

between stimulation and response

Period of contraction: muscle is contracted

Relaxation: fiber returns to former length

TYPES OF GRAPHS Twitch- full contraction

Summation- force of each twitch combines

Incomplete tetanus- minimal amt. of relaxation after each stimulus

Complete tetanus- no relaxation, continuous calcium ion deposit

ATP AND MUSCLE CONTRACTION

Sustained muscle contraction uses a lot of

ATP energy

Muscles store enough energy to start

contraction

Muscle fibers must manufacture more ATP

as needed

MUSCLE FATIGUE Cells undergo both aerobic and anaerobic respiration to supply ample atp

(lactic acid fermentation)

Lactic acid creates an oxygen debt because the liver cells must now use oxygen to break down the lactic acid (can take several hours)

Lactic acid lowers the ph, which diminishes the muscle fibers response to stimulation

More exercise = more glycolytic enzymes = increased capacity for glycolysis= increased capacity for aerobic respiration!! … start working out

HYPERTROPHY VS. ATROPHYHypertrophy- muscles

respond to exercise and enlarge Slow twitch fibers activated

by low intensity exercise such as swimming or running, develop more mitochondria and capillaries, prolonging fatigue

Fast twitch fibers activated by weight lifting can produce new myofilaments & enlarge the muscle (they are still fatigable)

Atrophy- when regular exercise stops, capillary networks shrink, mitochondria decrease, actin & myosin decrease, and muscle shrinks.

TETANUS

Caused by Clostridium bacteria present in soil

Bacteria produces a neurotoxin which blocks the release of inhibitory neurotransmitters.

ISOMETRIC VS. ISOTONIC

Isometric- no change in muscle length

Isotonic- muscle length changes

MUSCLES OF THE FACE