Chapter 9
Muscular System
Function of Skeletal Muscles
• The functions include movement, heat
production, and posture.
– Movement - contraction of muscles.
– Heat production - maintains
homeostasis of temperature.
– Posture - maintenance of partial
muscle contraction.
• Allows sitting, standing
Muscle and Muscle Fiber
Structure
• A muscle is composed
of many muscle fibers
(muscle fiber =
muscle cell). The
individual muscles are
separated from each
other and held in place
by a covering called
the FASCIA. This
fascia also forms
TENDONS and
APONEUROSES
connecting muscles to
bones and muscles to
muscles.
Microscopic Structure of Skeletal
Muscles
• Composed of bundles of
fibers, not cells.
• Fibers:
– Sarcolemma - plasma
membrane of the muscle.
– Sarcoplasma - cytoplasm
of a fiber.
– Sarcoplasmic reticulum –
like the endoplasmic
reticulum, tunnels
throughout fiber.
– Contains many
mitochondria and several
nuclei - more ATP
production.
Microscopic Structure of
Skeletal Muscles Continued
• Fibers:
– Myofibrils bundles of very
fine fibers that
extend through
the sarcoplasm.
– Each myofibril
is made of many
protein
filaments called
myofilaments.
2 Types of Myofilaments
• Myosin -Thick
filaments
• Actin - Thin
filaments
Movement
•
Actin and Myosin
filaments are arranged in
an overlapping pattern of
light (“I” bands) and
dark (“A” bands). In the
middle of each “I” band
is a line called a “Z” line.
The section of a
myofibril from one Z-line
to the next Z-line is
called a SARCOMERE.
The arrangement of
these sarcomeres next
to each other produces
the STRIATIONS of the
skeletal muscle fibers.
Movement Continued
•
•
•
•
Myosin and actin interact
Myofibrils pull toward
sarcomere
Sarcomeres shorten,
myofibrils shorten,
muscle shortens =
contraction.
All-or-None Law
– contract with all force
possible under
conditions or do not
contract at all.
•
•
•
•
•
Energy Sources
ATP - Adenosine
Triphosphate
Breakdown bonds
between the phosphate
groups provides energy
for contraction.
Creatine Phosphate
provides energy for the
regeneration of ATP.
For more intense
contractions, generation
of ATP comes from food
intake - Cellular
respiration.
ATP is made in the
mitochondria.
Energy Sources Continued
• Only 25% of energy produced during
cellular respiration is used in metabolic
processes – the rest is in the form of
HEAT. This is what produces our body
heat and maintains body temperature.
More muscle activity = more heat.
Connective Tissue Components
•
•
•
Epimysium - sheath
that envelopes each
muscle
Perimysium extension of sheath
between fiber
bundles - like a
partition.
Endomysium extension of sheath
between individual
fibers.
•
Connective Tissue
Components Continued
Tendon - extention of
three above structures
from the muscle to its
other end which is
continuous with the
periosteum (fiberous
tissue that covers bone)
–
•
Shin splints - tendon not
torn because of strength,
but can be pulled away from
bone.
Tendon sheath - tube
shaped structure, encloses
certain tendons - ex.
wrist, ankle
–
–
Lined with synovial fluid
Allows easy movement
Connective Tissue
Components Continued
•
Deep fascia extension from epi,
peri, and endomysium
of muscles and their
attachment to bone.
Review: http://www.biologycorner.com/anatomy/chap8.html
Muscle Names
Reason for muscle
names
• Action - Flexor,
extensor
• Direction of fibers
• Location - Femoris
• Number of
divisions
• Shape
• Points of
attachment
Examples:
Deltoid - shaped like a triangle
Orbicularis - orbit, circular muscle
Major/Minor - large/small or sometimes upper and lower
Vastus - large
Dorsi or Dorsal - backside
Infra / Supra - lower and upper
Longis / Brevis - long/ short (brief)
Medialis / Lateralus - medial (toward the inside), lateral
(toward the outside)
Some muscles are named for the region or the bone they are
attached to, for example:
biceps femoris - two headed muscle attached to the femur
extensor carpi radialis longus - long muscle that runs the
length of the radius (bone) to the carpals (wrist bones) that
extends the fingers
Muscle Groupings
• Muscles are grouped according to
location.
• Muscles are grouped according to
function.
5
2
1
6
7
3
4
Trapezius
Anterior
Muscles
1
2
3
4
14
5
6
15
16
7
9
10
19
18
20
11
21
12
13
Posterior
Muscles
1
2
3
6
12
13
7
9
8
10
15 Rectus femoris
14
11
16
Principles of Skeletal Muscle Function
Contract only
if stimulated
(nerves)
Principles of Skeletal Muscle
Function Continued
• Types of Contractions
– Tonic - continual, partial contraction - tautness (occurs only
when awake).
– Isotonic - contraction remains the same, but length of muscle
changes = shortens (walking, running, lifting an object).
– Isometric - muscle length remains the same, muscle tension
increases (push against wall).
– Convulsions - abnormal, uncoordinated contractions.
Principles of Skeletal Muscle
Function Continued
•Produce movement by pulling on bones
•Bones serve as levers, and joints serve as
fulcrums of the levers.
•Muscles move parts other than where they
lie.
Principles of Skeletal Muscle
Function Continued
•Act in groups
•Prime movers - contraction produces movement
(primarily responsible for producing an action).
•Antagonists - relaxation of muscle while prime
movers are contracting.
* antagonist of a flexor is an extensor*
•Synergists - contract at same time as prime,
assist in movement.
Skeletal Muscle Contraction
•Neurotransmitter must
stimulate muscle acetylcholine for muscle
contraction.
•ATP must be present at
the same time
•Decrease acetylcholine
= muscle relaxation
Energy Sources for Contraction
Creatine phosphate
1. contains high energy phosphate
bonds
2. stores excess energy released
from mitochondria
3. decrease ATP---- energy from
creatine turns to ADP—ADP is
coverted to ATP
4. creatine is depleted rapidly in
active muscles
5. can ingest extra creatine to
increase body supply.
Muscle Fatigue
•Inability of muscle to
contract
•Due to accumulation
of lactic acid
•Could coincide with
cramping due to a lack
of ATP
Rigor Mortis
• Partial muscle contraction after death
•Can continue for 72 hours
Posture
Maintenance
1. Muscles exert continual pull on bone
in opposite direction (extensors).
2. Tonicity (elastic tension of living
muscles) allows pull against gravity
a. Absent during sleep
b. Will not counteract gravity
c. Cannot sleep standing up
Posture Continued
Importance of good posture
1. Decreases work on muscles
2. Bad posture puts strain on ligaments
3. Bad posture interferes with
respiration, digestion, etc…