Transcript Muscular System - Grafton School District

Muscular System
Chapter 9
3 types of muscular tissue:
Functions of muscular system
Stabilize joints
 Muscle tone
 Movement
 Maintain constant body temperature

Muscle structure
Fascia – connective
tissue around muscle,
becomes the tendon
 Origin – on stationary
bone
 Insertion – on the
moveable bone
 Fascicle – bundle of
muscle fibers
 Muscle fiber – muscle
cell
 Myofibril – made of
sarcomeres (in-between
two Z bands)
 Myo-filaments – actin
and myosin

Group Actions
Prime mover – the
muscle that causes
the desired
movement
 Antagonist – relax
during the action
 Synergists –
muscles that steady
the movement
(helpers)

The Neuromuscular Junction:
Neurons

Parts of :
 Cell body
 Dendrites – receive
impulse
 Axon – carries impulse
away
 Myelin sheath- white
fatty material
• Schwann cells (pns)
• Neurilemma (outside
the sheath)
• Nodes of Ranvier
The Nerve Impulse
Action potential – steps in the nerve
impulse
 3 stages of : polarization,
depolarization, repolarization

Step 1: Polarization
Resting state of a neuron
 Sodium/potassium pump – sodium ions
out of cells and potassium ions into cells

Polarization continued
Inside of the cell is – charged
 Outside of cell is + charged
 Due to sodium-potassium pump

– 2 K+ ions go in as 3 Na++ go out
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Step 3: repolarization
Return to resting state
 Due to the pumping out of K+.
 Na+ blocked
 Inside of cell negative


Continues to synapse
The Sliding Filament theory:
Step 1: Neuromuscular Junction
Action potential –
the reversal of
charges across the
plasma membrane.
 Nerve impulse
arrives at axon
terminal releasing
acetylcholine (Ach)

Step 1: Neuromuscular Junction

Ach diffuses across
synaptic cleft, binds
to receptors in the
motor end plate.
 Triggers action
potential
 Acetylcholinersteras
e in cleft destroys
Ach to stop action
potential
Disorders at the neuromuscular
junction
Myasthenia
gravis
Curare
Botulism
tetanus
Step 2:

Sarcoplasmic
reticulum stimulated
to release calcium
ions.
Step 3

Release of Calcium
causes shift in
troponin (actin)
 Active site on Actin
is uncovered
Step 4

Myosin and ATP
combines with
active site on actin
causing formation of
a crossbridge
Step 5 - 7




Energy released
causing filaments to
slide past each other
(power strokes)
ATP converted ADP
Troponin slides back
Cycle repeats if enough
calcium and ATP are
present
Energy for contraction
ATP (respiration)
 Creatine phosphate-can be stored
longer and more abundant than ATP
 Glycogen-storage of glucose in liver

Oxygen Debt-strenuous exercise

Lack of oxygen
availability
 Accumulation of
lactic acid
(soreness)
 Become short of
breath to metabolize
lactic acid
Muscular Responses

All or nothing response single fiber
contracts only maximally
– Threshold stimulus

Recruitment -
Types of Whole muscle contraction
Twitch contraction – not a usual
method of muscle contraction
Summation 
Muscle not allowed
to relax in-between
contractions
 Stronger contraction
Tetanus

sustained muscle
contraction
(maintaining posture
or tone)
 Usual means of
movement
Isotonic vs. Isometric

Isotonic contraction
 Movement produced
as a muscle pulls on
an attached bone
toward a stationary
structure

Isometric
contraction
 Muscle tension, no
shortening of
muscles
 No movement
Muscle Fiber types
Based on genetics
 Classified by respiration and the speed
of contraction
 Strength Training can influence

Fast Twitch Fibers




Energy for quick,
forceful contractions
Contraction 2-3 times
faster than slow twitch
Anaerobic respiration
Short term activities –
basketball, sprinting,
volleyball
Slow twitch muscle fibers

Aerobic respiration
 Slow contracting
 Endurance type
activities
 Ex. Long distance
running, soccer,
football, basketball