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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