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CH 6 Muscular System Notes Part I

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Lori Richardson

on 8 March 2015

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Transcript of CH 6 Muscular System Notes Part I

Chapter 6
Muscular System
How Many Muscles in the Body?
656 to 850
Fun Facts
Muscles can account for about 50% your body weight.
Muscles can only pull, they cannot, as some people assume, push.
The longest muscle has muscle cells that can be over a foot long.
The hardest working muscles in the body are the muscles in the eye.
The smallest muscles are in the middle of the ear.
There are 640 individual names for muscles.
It takes 17 muscles in the body to smile.
There are muscles in the root of our hair that gives us goose bumps!
Major Muscle Groups
Upper body:
trapezius
deltoids
latissimus dorsi
pectorals
biceps brachii
triceps brachii
Lower body:
quadriceps
hamstrings
gluteals
abdominals
gastrocnemius
Three basic muscle types are found in the body
Skeletal muscle
Cardiac muscle
Smooth muscle
Muscle cells are elongated (muscle cell = muscle fiber)
Contraction is due to the movement of microfilaments
Prefix myo refers to muscle
Prefix mys refers to muscle
Prefix sarco refers to flesh
Characteristics of Muscles
Skeletal Muscle Characteristics
Attached by tendons to bones
Cells are multinucleate
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by connective tissue
Endomysium – around single muscle fiber
Perimysium – around a fascicle (bundle) of fibers
Epimysium – covers the entire skeletal muscle
Fascia – on the outside of the epimysium
Skeletal Muscle Attachment
Tendon
cord-like structure
Aponeuroses
sheet-like structure
Sites of muscle attachment
Bones
Cartilages
Connective tissue coverings
Smooth Muscle Characteristics
Has no striations
Spindle-shaped cells
Single nucleus
Involuntary – no conscious control
Found mainly in the walls of hollow organs
Has striations
Usually has a single nucleus
Joined to another muscle cell at an intercalated disc
Involuntary
Found only in the heart
Cardiac Muscle Characteristics
Produce movement
Maintain posture
Stabilize joints
Generate heat
Functions of Muscles
Microscopic Anatomy of Skeletal Muscle
Cells are multinucleate
Nuclei are just beneath the sarcolemma
Sarcolemma – specialized plasma membrane
Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum that stores calcium
Bundles of myofilaments aligned to give distinct bands
I band = light band
A band = dark band
Myofibril
Contractile unit of a muscle fiber
Sarcomere
Thick filaments
Composed of the protein myosin
Has ATP enzymes
Organization of the Sarcomere
Thin filaments
Composed of the protein actin
Myosin filaments have heads (cross bridges)
At rest, there is a bare zone that lacks actin filaments
Skeletal muscles must be stimulated by a nerve to contract
The neurotransmitter for skeletal muscle is acetylcholine
Irritability
– ability to receive and respond to a stimulus
Contractility
– ability to shorten when an adequate stimulus is received
Neuromuscular junctions
– association site of nerve and muscle
Neurotransmitter
– chemical released by nerve upon arrival of nerve impulse
Muscle Contraction
Neurotransmitter attaches to receptors on the sarcolemma
Sarcolemma becomes permeable to sodium (Na+)
Sodium rushing into the cell generates an action potential
Once started, muscle contraction cannot be stopped
Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament
Myosin heads then bind to the next site of the thin filament
This continued action causes a sliding of the myosin along the actin
The result is that the muscle is shortened (contracted)
Muscle fiber contraction is “all or none”
Types of Mucscle Responses
Single, brief contraction
Not a normal muscle function
Twitch
One contraction is immediately followed by another
The muscle does not completely return to a resting state
Tetanus
Some relaxation occurs between contractions
Unfused (incomplete) tetanus
No evidence of relaxation before the following contractions
The result is a sustained muscle contraction
Fused (complete) tetanus
Energy for Muscles
Muscle force depends upon the number of fibers stimulated
Initially, muscles used stored ATP for energy
Only 4-6 seconds worth of ATP is stored by muscles
After this initial time, other pathways must be utilized to produce ATP

Aerobic Respiration
Occurs in the mitochondria
Glucose is broken down to carbon dioxide and water, releasing energy
This is a slower reaction that requires continuous oxygen

Anaerobic glycolysis
Reaction that breaks down glucose without oxygen
Glucose is broken down to pyruvic acid to produce some ATP
Pyruvic acid is converted to lactic acid
Muscle Fatigue and Oxygen Debt
The common reason for muscle fatigue is oxygen debt
Oxygen is required to get rid of accumulated lactic acid
Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

Types of Muscle Contractions
Myofilaments are able to slide past each other during contractions
The muscle shortens
Isotonic
Tension in the muscles increases
The muscle is unable to shorten
Isometric
Movement is attained due to a muscle moving an attached bone
Muscles are attached to at least two points
Origin – attachment to an immovable bone
Insertion – attachment to a moveable bone
Increase in muscle size
Increase in muscle strength
Increase in muscle efficiency
Muscle becomes more fatigue resistant
Results of increased muscle use
Flexion
Extension
Rotation
Abduction
Circumduction
Body Movements
Types of Muscles
Prime mover
– muscle with the major responsibility for a certain movement
Antagonist
– muscle that opposes or reverses a prime mover
Synergist
– muscle that aids a prime mover in a movement and helps prevent rotation
Fixator
– stabilizes the origin of a prime mover
Naming Muscles
Direction
Size
Shape
Action
Location
Number of Origins
Location of Origins
Part 2
The Basics
Part 1
WARNING
The following contains
strong language and
scenes that may be
uncomfortable for some
viewers to watch
30 Minute
Song and Dance Challenge
Using the following terms, your team has 30 minutes to come up with a song and a dance demonstration these moves:
Flexion
Extension
Hyperextension
Rotation
Abduction
Adduction
Circumduction
Inversion
Eversion
Dorsiflexion
Plantar Flexion
Supination
Pronation
Opposition
1. A signal is sent from the brain or the spinal cord to the muscle via neurons

2. An action potential is generated in the neuron, releasing Ca++ in axon terminal

3. The influx of calcium ions causes acetylcholine (ACh) to be released in the synaptic cleft
Breaking It Down into 9 Easy Steps
4. ACh binds to the ACh receptors on the sarcolemma

5. Na++ enter the sarcolemma, changing its polarity and creating an action potential

6. Ca++ are released by the sarcoplasmic reticulum

Breaking It Down into 9 Easy Steps
7. Ca++ bind with troponin, causing the tropomyosin to shift and expose the myosin binding sites on actin

8. Myosin binds to actin

9. Myosin head bends and actin slides over the myosin surface

Breaking It Down into 9 Easy Steps
Full transcript