Download The Muscular System

The Muscular System
The Muscular System
 Myology = The study of muscles
 Functions of muscle tissue:
 Move the body by pulling bones
 Maintain body positions by continuous muscle
contraction (ex. Neck holding up the head)
 Move substances within the body such as
blood, reproductive cells and food.
 Produce heat- muscle contraction generates
thermal energy
 Regulate organ volume (controls opening
from the bladder, stomach, and rectum)
There are 3 types of muscle tissue
 Skeletal
 Smooth
 Cardiac
Skeletal Muscle Characteristics
 Most are attached by
tendons to bones
 Cells- called muscle fibersare multinucleate
 Striated – have visible
banding
 Voluntary – subject to
conscious control
 Cells are surrounded and
bundled by connective tissue
= great force, but tires easily
Smooth Muscle Characteristics
 Has no striations
 Spindle-shaped cells
 Muscle fibers have a
single nucleus
 Involuntary – no
conscious control
 Found mainly in the
walls of hollow organs
and structures
 Slow, sustained and
tireless
Cardiac Muscle Characteristics
 Has striations
 Muscle fibers
branch and contain
a single nucleus
 Joined to another
muscle cell at an
intercalated disc
 Involuntary
 Found only in the
heart
 Steady pace!
Naming of Skeletal Muscles
 Location of the muscles origin and
insertion
 Example: sterno (on the sternum)
 Shape of the muscle
 Example: deltoid (triangular)
 Action of the muscle
 Example: flexor and extensor (flexes or
extends a bone)
Naming of Skeletal Muscles
 Direction of muscle fibers
 Example: rectus (straight)
 Relative size of the muscle
 Example: maximus (largest)
Naming of Skeletal Muscles
 Location of the muscle
Example: many muscles are named
for bones (e.g., temporalis)
 Number of origins
Example: triceps (three heads)
Connective Tissue Wrappings of
Skeletal Muscle
 Epimysium –
covers the
entire skeletal
muscle
 Fascia – on the
outside of the
epimysium
Connective Tissue Wrappings of
Skeletal Muscle
 Perimysium –
around a
fascicle (bundle
of fibers)
 Endomysium –
around single
muscle fiber
(cell)
Microscopic Anatomy of Skeletal
Muscle
 Sarcolemma – specialized plasma
membrane of a muscle fiber
 Sarcoplasm- cytoplasm of the muscle
fiber
 Sarcoplasmic reticulum – network of
tubules in the muscle fiber that store
calcium ions for muscle contraction
 Myoglobin- pigment in the sarcoplasm
that stores oxygen
Microscopic Anatomy of Skeletal
Muscle
 Myofibril- Cylindrical structure within a
muscle fiber
 Bundles of thick and thin filament (makes
muscle striated)
 I band =
light band (thin)
 A band =
dark band (thick)
Microscopic Anatomy of Skeletal
Muscle
 Sarcomere
 Contractile units of a muscle fiber which are
separated by Z discs
Microscopic Anatomy of Skeletal Muscle
 Organization of the sarcomere
 Thick myofilaments = myosin filaments= have
extensions called “heads”
 Thin myofilaments = actin filaments
 Myosin and actin somewhat overlap
 Actin are anchored at the z-disc
Quick Review
1. For cardiac, smooth and skeletal muscle,
indicate if they are: striated or not; voluntary
or not; multinucleated or not
2. What are the differences in shape between
the different muscle cells?
3. What is the outermost connective tissue layer
of skeletal muscle?
4. What are bundles of muscle fibers called?
5. What tissue layer surrounds each muscle
fiber?
Quick Review cont…..
6. What is the plasma membrane of a muscle fiber
called?
7. What is the cylindrical unit inside a muscle cell?
8. What are the 2 myofilaments in a muscle fiber?
9. What is another term for the thick band?
9. What is another term for the thin band?
10. What is the region between z-discs called?
11. What is the region where the actin filaments are
anchored?
12. Where are calcium ions stored in a muscle fiber?
The Sliding Filament Theory of Muscle
Contraction
1. Activation by a nerve causes myosin heads to
attach to binding sites on the adjacent thin
filament.
2. Myosin heads flex inward then reach ahead to
attach to the next site of the thin filament.
3. This continued forward grabbing causes a
sliding of the myosin along the actin.
4. The result is that the sarcomere shortens, thus
shortening the entire muscle.
5. Myosin heads attach and detach to actin due
to ATP (energy stored in mitochondria) and Ca+
(stored in sarcoplasmic reticulum).
Nerve Stimulus to Muscles
 Neuromuscular
junctions – Where
motor neurons
(nerve cells) and
muscle fibers
associate
Nerve Stimulus to Muscles
 Synaptic cleft –
gap between
nerve and
muscle
 Nerve and
muscle do not
make contact
 Area between
nerve and muscle
is filled with fluid
Transmission of Nerve Impulse to
Muscle
 Neurotransmitter – chemical released by a nerve
to communicate with another nerve or muscle
 The neurotransmitter for skeletal muscle is
acetylcholine (ACh)
 ACh attaches to receptors on the sarcolemma
 Sarcolemma allows sodium (Na+) to enter the
muscle fiber
 Sodium rushing into the cell initiates muscle
contraction by causing the release of Ca+ from
the sarcoplasmic reticulum.
Contraction of a Skeletal Muscle
• What happens if NMJs are blocked?
– No muscle contraction!!
• Why would someone want to
purposely block NMJs?
– No muscle contraction= No
wrinkles!!
• What is a drug that does that?
– BOTOX!!
Botox “before” and “after”
What causes a muscle to relax
after contraction?
• The enzyme acetylcholinesterase rapidly
breaks down acetylcholine in the synaptic
cleft, preventing it from continuing to
signal to the muscle fiber.
• Ca2+ ions are transported from the
sarcoplasm back into the sarcoplasmic
reticulum for storage.
• The actin filaments slide back to their
relaxed positions
Muscle Fatigue and Oxygen Debt
 Muscle fatigue is the inability to contract
after prolonged activity.
 What are some possible reasons for why this
happens?
 The common reason for muscle fatigue is
oxygen debt
 Oxygen debt is the amount of oxygen
taken into the body after exercise to
“repay” what was taken from the
myoglobin.
Muscle Fatigue and Oxygen Debt
 Under anaerobic (low oxygen) conditions
(during exercise when not taking in enough
oxygen), muscle cells go through
fermentation to produce energy. This
results in a build up of lactic acid in the
muscles. This is a very inefficient energy
producing process.
 Increasing acidity (from lactic acid) and lack
of ATP causes the muscle to contract less.
 The body uses oxygen debt to remove
lactic acid and produce more ATP.
Muscles and Body Movements
 Movement is
attained due to
a muscle
moving an
attached bone
Figure 6.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Muscles and Body Movements
 Muscles are
attached to at
least two points
 Point of Origin –
attachment to an
immovable bone
 Point of Insertion
–attachment to a
moveable bone
Figure 6.12

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
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
 Flexor- bends a joint
 Extensor- straightens a joint
Example:
 Biceps curl Prime mover- Biceps brachii
 Antagonistic muscle- Triceps brachii
 Synergist muscle- Pectoralis major
 Flexor- Biceps brachii
 Extensor- Triceps brachii
Disorders relating to the
Muscular System
• Muscular Dystrophy: inherited, muscle
enlarge due to increased fat and connective
tissue, but fibers degenerate and atrophy
• Duchenne MD: lacking a protein to
maintain the sarcolemma
• Myasthemia Gravis: progressive weakness
due to a shortage of acetylcholine receptors