Download Effectors - Virtual Medical Academy

FUNCTION OF SKELETON:
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Support the body against the pull of gravity.
Protects soft parts. Ex: skull and ribcage.
Storage area of calcium and phosphorus salts.
Provide sites for muscle attachment.
Long bones permit flexible body movements.
Blood cells originate in the red bone marrow.
DIVISION OF THE SKELTON:
1) Axial skeleton:
 Lies in the mid-line of the body.
 Consist of the skull, vertebral column, sternum & ribs.
2) Appandicular skeleton:
 Includes bones of the girdles (pectoral & pelvic). &
appendages (upper and lower limbs).
It is hollow.
The cavity is bounded by compact bone.
Spongy bones and cartilage at the end.
Joints join the bone together.
Join the bones together.
Immovable joints: ex: structures between the bones in the skull.
Slightly movable joints: ex: intevertebral joints.
Freely movable joints: ex: humorous and scapula, hip joint, elbow
joint.
A.
Macroscopic structure:
Muscles attached to the bones by tendons.
During contraction, one bone remains fairly stationary and
the other one moves.
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Tendon: fibrous connective tissues attache the muscle to the
bone.
Origin: is on the stationary bone.
Insertion: is on the bone that moves during contraction.
The muscle contains fascicles.
Fascicles: is a group of muscle fibers.
Both fascicles and fibers are covered with connective tissue.
Muscle is covered with fascia.
B.
Microscopic structures:
The plasma membrane of muscle cell (fiber) is sarcolemma.
The cytoplasm -sarcoplasm- which contains:
1. The endoplasmic reticulum (sarcoplasmic reticulum)
it contains Ca+2.
2. Glycogen which provide energy for muscle
contraction.
The sarcolemma forms T (transverse) tubules.
T tubules: penetrate into the cell , they came into contact
with sarcoplasmic reticulum.
Each muscle fiber contains many myofibrils (the
contractile portion of muscle fiber).
The filaments inside myofibril are the myofilaments.
The contractile unit is sarcomere.
Extend between two dark lines ( Z lines).
Contains two types of protein myofilaments.
Myosin filaments (thick filaments) : made up of myosin.
Actin filaments (thin filaments) : made up of actin, troponin and
tropomyosin.
I band: light band, contains actin filaments only.
A band: dark band contains overlapping of actin & myosin.
H band: part of a band, contains myosin filaments only.
Consist of:
1. Bulbs: at the end of axons of motor neurons.
2. Sarcolemma: of the skeletal muscle.
3. Synaptic cleft: (gap) in between.
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1- Axon bulbs contain vesicles filled with neurotransmitter
(acetylcholine).
2- Nerve impulses travel down motor neuron.
3- Synaptic vesicles release Ach into synaptic cleft.
4- Ach bind to the receptors in the sarcolemma.
5- Sarcolemmas generate impulses that spread over the sarcolemma and
down T tubules to sarcoplasmic reticulum.
6- Ca+2 released the filaments slide, sarcomere contracts, the sarcomeres
shorted, muscle fiber contracts, and finally muscle contracts.
 The actin (thin) filaments slide past the myosin the ( thick)
filaments.
 I band shortened and the H band almost or completely
disappears.
 Myosin filament use ATP to pull the actin filaments toward the
center of the sarcomere.
ADP
ATP
Actin + Myosin
Actomyosin
Ca
+2
1- Actin and myosin filament: myosin filaments pull the actin filaments
toward the center of the sarcomere.
2- Ca+ ions: binds to actin filaments.
3- ATP: ATP activates myosin heads to form cross bridges between actin
and myosin.
Sources of ATP in muscle contraction:
1- Cereatin phosphate:
Cereatin –P + ADP
ATP + Cereatin
2- Aerobic respiration:
 Need oxygen to produce ATP.
 Used for long time.
 Glucose
CO2+ H2O+ ATP
3- Anaerobic respiration:
 Glucose
lactic acid + ATP
 Used for short time (lactic acid produce fatigue).
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