Biology 121 Anatomy and physiology. Lecture 5 Chapter 7 The Muscular System. VIII. The Muscular System A. Introduction 1. Kinds of Muscle (3 types). a. Skeletal- striated, voluntary
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The Muscular System
1. Kinds of Muscle (3 types).
a. Skeletal-striated, voluntary
b. Smooth-nonstriated, involuntary
c. Cardiac-striated, involuntary
2. Number of skeletal muscles.
a. Approximately 700
3. Purpose of skeletal muscle.
a. Movement-by shortening (contraction) usually in pairs
b. Maintain posture
c. Support soft tissue and organs
d. Maintain body temperature
e. Guard entrances and exits
a. Excitability (irritability).-responds to stimulation
b. Contractility-shortens or contracts upon stimulation
c. Elasticity – can be stretched.
C. Structure of Skeletal muscle
-Skeletal muscle is an organ composed of
a. muscle tissue (muscle fibers or cells)
b. connective- binds muscle forms tendons
c. Blood vessels and nerves
-provide oxygen and nutrients
-nerves transmit signals from brain/ sp. cord
C. Structure of a Skeletal Muscle continued (bundles of bundles) 1. Muscle –covered with connective tissue: epimysium.
epimysium=collagen separates muscle from surrounding organs
2. perimysium-divides muscle into compartments of muscle fibers (facscicles)- this layer has blood vessels and nerves
3. Each individual muscle fiber (cell) within a fascicle are bound to adjacent fibers with endomysium
Epimysium, perimysium, endomysium
Come together to form tendons
= cell membrane
Calcium store: releases calcium when stimulated causes myofilaments to interact
Thin and Thick Filaments
Myosin can bind and pull on actin
Overlapping arrangement of myofilaments is called a sarcomere=the unit of contraction
Pattern of light and dark is called??
Calcium binds troponin and causing tropomyosin to move aside
This exposes the myosin binding site on actin
Myosin-actin releases ADP causes myosin head to pull on actin
ATP binds to Myosin enabling myosin to release actin
NOTE: ATP IS REQUIRED TO RELEASE MYOSIN CROSSBRIDGE
ATP is split causing myosin to “cock”
Figure 7-3 A band stays the same length, H and I bands become smaller
1. Motor unit – A nerve fiber and all the muscle fibers
2. Neuromuscular junction – location where the
nerves motor end plate
contacts the muscle
3. Neurotransmitter and action potential (impulses)
a. Charges at membrane
1.) Resting potential -70 mV (millivolts)
a.) More Na+ outside cell than within
b.) More K+ inside than out
b. The sodium-potassium exchange pump uses ATP
to move Na+outand K+ in to repolarize the cell
(-70mV +30) (+30mV -70)
-Action potentials are electrical currents (Ions) that flow across a membrane through ion channels
-The channels are normally closed and Na,K pump establishes resting potential (-70mV)
-An action potential causes ion channels to open allowing ions to flood into the cell . Result: the membrane to become temporarily +30mV
-The flip in potential causes nearby channels to also open = spread of the action potential down the cell membrane
After a period of time the Na K pump restores the resting potential
Common in eye
1 motor nerve controls 100’s of muscle cells
No fine control ut lots of force
Common in muscles of the back
a. Impulse and T-tubules
b. Calcium release and its role
c. ATP and its role with actin and myosin
d. Shortening of sarcomere
2. Impulse enters t tubule
1. Impulse spreads from nerve across sarcolemma
3. Impulse spreads from t tubule into SR causing Ca release
a. Source of ATP
1.) The liver stores glucose as animal starch
2.) The Kreb’s cycle and ETS may provide sustained
energy as ATPif sufficient oxygen is available.
3.) Glycolysis may anaerobically supply small
bursts of ATP energy quickly
4.) Phosphocreatine (PC) may recharge ATP for
5-10 second bursts of energy
PC + ADP + P ATP + creatine (C)
1.) If O2 is lacking, pyruvate lactic acid
causing muscle fatigue, burning, soreness
2.) To recover you stop activity, deliver O2to cells
to make ATP. Lactic acid leaves muscles and
may be converted back to pyruvate, glucose or
glycogen in the liver, (reverse glycolysis).
1. Tonic – partially contracted muscle, different motor
groups contracting at different times.
2. Isotonic – shortening of cells, no increase in tension.
3. Isometric – no shortening, but increase in tension.
4. Tetanic – maximal, sustained contraction due to
rapid-firing stimuli. Muscle never gets to
5. Twitch – contraction due to a single stimulus.
1. Origin – attached end of muscle that does not move.
2. Insertion – attached end of muscle that moves.
3. Action – movement produced by the muscle.
a. Prime mover (agonist) – muscle mostly responsible
b. Antagonist - muscle whose action opposes
c. Synergist – muscle that helps a prime mover.
May add pull to prime mover near
1.) Fixator – a synergist that stabilizes the origin of a
a. Prime Mover – biceps brachii
b. Antagonist – triceps brachii
c. Syngergist – brachialis
5. EXTENSION OF ELBOW:
a. Prime Mover – triceps brachii
b. Antagonist – biceps brachii
c. Fixator - brachialis
1. Action – adductor, abductor, extensor, flexor.
2. Shape – Deltoid, orbicularis, serratus.
3. Location – anterior, external, rectus.
4. Origin or Insertion points – biceps, triceps,
5. Number of units makeup – (same as above).
6. Size – maximus, minimus.
7. Direction of fibers – oblique, rectus, transverse.