Download Muscular System

Muscular
System- Part 1
Unit 5
Miss Wheeler
Fun Facts!
›  The
tongue is the strongest muscle in your body
›  The smallest muscles in the body are in the
middle ear
›  The largest muscle in the body is the gluteus
maximus
›  It takes 17 muscles to smile, and 43 muscles to
frown
›  The heart is the only muscle that never gets tired
Muscle Functions
1. 
2. 
3. 
4. 
Produce movement
Maintain posture
Stabilize joints
Generate Heat
Characteristics of Muscles
›  Muscle
cells (called muscle fibers) are
elongated
›  All muscles share some terminology:
›  Myo
- muscle
›  Mys - muscle
›  Sarco – flesh
›  Epi- upon
›  Peri- around
›  Endo- inner
Muscle Tissue
›  Three
1. 
2. 
3. 
muscle types (you already know these):
Smooth Muscle
Cardiac Muscle
Skeletal Muscle
Smooth Muscle
›  How
blood and food
move
›  No striations
›  Single nucleus
›  Involuntary
›  Spindle-shaped cells
›  Found in walls of hollow
organs (intestines, blood
vessels)
Cardiac Muscle
›  Makes
your heart beat
›  Striations
›  Single nucleus
›  Involuntary
›  Cells jointed to each other at intercalated discs
›  Found only in the heart
Skeletal Muscle
›  Moves
your bones
›  Striated
›  Multi-nucleated
›  Voluntary
›  Cells are surrounded
and bundled by
connective tissue
›  Most are attached to
bones by tendons
Try This!
A. Smooth
B. Cardiac
______________ involuntary
______________ striated
______________ moves bones
______________ voluntary
______________ this picture à
C. Skeletal
Structures of Skeletal Muscle
›  Epimysium-
covers the
entire skeletal muscle
›  Perimysium- covers a
bundle of fibers
(fascicle)
›  Endomysium- covers a
single muscle fiber (cell)
Structures of Skeletal Muscle
›  Sarcolemma-
muscle
fiber membrane
›  Sarcoplasm- cytoplasm
of muscle fiber
›  Sarcoplasmic
Reticulum- transport
(ER). Store calcium
›  Myofibrils- organelle
structure that takes up
most of the space in a
muscle fiber
›  Myofilaments- threadlike proteins that make
up a myofibril
Structure of Skeletal Muscle
Structure of Skeletal Muscle
›  Myofibrils
are made of myofilaments that form a
unit called a sarcomere with light and dark bands.
ACTIN = thin filaments; form light band (I band)
MYOSIN = thick filaments; form dark band (A band)
Try This!
Muscle
composed of
bundles
composed of
cells
composed of
fibrils
composed of
filaments
Individual types
light
dark
Twizzler Analogy
Many packages of
Twizzlers together =
fascicle
Find a fascicle on your
diagram
Twizzler Analogy
1 package of
Twizzlers =
The packaging =
Twizzler Analogy
1 bundle of
Twizzlers =
1 Twizzler strand =
Twizzler Analogy
Try This!
Now try making your own model
of a skeletal muscle using only
the materials you are given.
Muscle Contraction
How
muscles
contract to
move the
skeleton
Review
›  Muscle
fiber à
myofibrils à
myofilaments
›  Myofibrils are
made of units
called sarcomeres,
made of thick
(myosin) and thin
(actin) filaments
›  Sarcomeres
stretch from Z line
to Z line
Muscle Contraction
THE BIG PICTURE
›  Thick (myosin) and thin (actin) filaments slide over
one another to shorten the muscle during
contraction
Where Does It Start?
Skeletal muscle contraction begins
at the neuromuscular junction.
What do you think the neuromuscular junction
is?
Neuron
Axon terminal
Cell body
Axon
Motor unit = motor
neuron & muscle
fiber that it
activates
More motor units =
stronger
contractions of the
muscle
Acetylcholine
Sarcoplasmic
Reticulum
Muscle Contraction
1. 
2. 
3. 
4. 
5. 
6. 
Nerve impulse releases acetylcholine
(neurotransmitter) into neuromuscular junction
Sends action potential through T-tubules to the
sarcoplasmic reticulum (SR)
Ca2+ (calcium) is released from SR to sarcomeres
Calcium binds to troponin on thin filaments, which
then shift the tropomyosin to expose binding site
on actin
Myosin head from thick filaments binds to actin
thin filaments using energy from ATP (cross-bridge)
Thick filament pulls thin filament toward the
center, shortening the sarcomere and causing
muscle contraction
Steps #1-3
Acetylcholine
Sarcoplasmic
Reticulum
Sarcomere Contraction
Steps #4-6
Sliding Filament Theory
›  Actin
and myosin filaments “slide” past each other
as a muscle contracts
Contraction Video
https://www.youtube.com/watch?v=BMT4PtXRCVA
Sliding Filament Analogy
›  Boat
= myosin (thick filament)
›  Oar/paddle = myosin arm
›  Water = actin (thin filament)
›  Life ring = calcium
Resting Muscle
1. 
2. 
ATP binds to myosin arm
ATP breaks down into ADP + P, reading to
be activated
Step 1. Action Potential
1. 
2. 
A nerve action potential releases
acetylcholine
Signal gets sent to sarcoplasmic
reticulum, which releases calcium
Step 2. Myosin-Actin Binding
1. 
2. 
3. 
Calcium binds to troponin
Causes tropomyosin to move out of the way of
the actin binding site
Actin and myosin bind using energy from ATP
Step 3. Row, row, row your boat
1. 
2. 
Myosin arm pivots so myosin and actin slide
past each other, shortening the sarcomere
ADP and P released
Quick Write
1. 
What chemical helps expose the binding site on
actin?
2. 
What is the source of energy for a contraction?
3. 
What happens to the length of the sarcomere
during a contraction?
Types of Muscle Contractions
›  Isotonic
Contractions- the myofilaments are
successful in their sliding movements. The muscle
shortens, and movement occurs
›  Ex.
Bending the knee, smiling
›  Isometric
Contractions- contractions in which the
muscles do not shorten. Tension develops in the
muscle and it attempts to slide the filaments
›  Ex.
When you push against a wall or try to lift a very
heavy object
Types of Muscle Contractions
Isotonic Contractions
Isometric Contractions