Download Muscular System

MUSCULAR SYSTEM
I. Overview
A.Muscles – 40-50% of body mass
B.Functions
1.
2.
3.
4.
5.
6.
skeletal movement
control of organ and vessel size
maintain posture and position
support soft tissue
guard entrances and exits
maintain body temperature
(85%)
C. 3 Kinds of Muscle Tissue
1.Skeletal
– Striated
– Voluntary
AKA: Somatic
Tissue
C. 3 Kinds of Muscle Tissue
2. Cardiac
–
–
–
–
Heart muscle
Branched cells
Multinucleiated
Thick striations
•
•
–
–
Intercalated discs
Increase speed of
impulses
Involuntary
AKA Visceral Tissue
C. 3 Kinds of Muscle Tissue
3. Smooth
–
–
–
–
Spindle shaped
Nonstriated
Involuntary
Found around hollow
organs such as arteries,
esophagus, stomach
D. Muscle Characteristics
1. Contractility
Ability to shorten and
exert tension
2. Excitability
Ability to respond
3. Extensibility
Ability to contract after
being stretched
4. Elasticity
Ability to regain initial
length after contraction
I. Overview
E. Each muscle is an
organ comprised of
1. Muscle tissue
2. Connective tissues
3. Nervous tissue
4. Blood
II. Anatomy of Skeletal Muscle
A.Connective Tissue
1. Superficial
Fascia
Surround and
separate each
muscle
A. Connective Tissue
2. Deep
a. Epimysium whole muscle
b. Perimysium bundles of fibers
(fascicles)
c. Endomysium single muscle
fiber
A. Connective Tissue
3. Tendons
a. Formed from the union of
all three deep fascia
b. Connect
muscle to
bone
A. Connective Tissue
4. Aponeurosis – flat sheet
B. Muscle Fibers
1. Each muscle fiber
a.is a single, long, cylindrical
muscle cell.
– Sarcolemma (cell membrane)
– Sarcoplasm (cytoplasm)
• Many mitochondria
• Nuclei
• Sarcoplasmic reticulum
B. Muscle Fibers
1. Each muscle fiber
b. is wrapped in endomysium
1. Each muscle fiber
c. is a bundle of myofibrils which
is made of a budle of
myofilaments
B. Muscle Fibers
2. Fascicles:
a. a bundle of
muscle
fibers
b. wrapped in
perimysium
B. Muscle Fibers
3. Myofibrils
a. made of thin and thick
filaments
B. Muscle Fibers
3. Myofibrils
b. Thick filaments made up of
the protein myosin.
c. Thin filaments are made up
of the protein actin.
Thick filaments
Thin filaments
Tropomyosin and troponin are regulatory proteins
Actin and myosin are contractile proteins.
B. Muscle Fibers
3. Myofibril
d. Together, the thick and
thin filaments make up the
striations
B. Muscle Fibers
4. Sarcomeres
a. Contractile unit of a muscle
b. Consists of overlapping thick
and thin filaments
Sarcomere
B. Muscle Fibers
4. Sarcomere
c. Muscle contraction
results from thick and thin
filaments sliding past one
another.
C. Neuromuscular Junction
1. Where the
neuron and
muscle fiber
meet
2.The neuron and muscle fibers
it controls make up a motor
unit (2-2000 fibers/unit)
MOTOR UNIT
C. Neuromuscular Junction
3. When
stimulated, all
of the muscle
fibers of a
motor unit
contract all at once.
C. Neuromuscular Junction
4. Anatomy
Axon terminal – nerve end
• Produces a neurotransmitter
- acetycholine (Ach)
C. Neuromuscular Junction
4. Anatomy
Motor end
plate –
site on
muscle
with
Motor
end plate
acetycholine receptors
Synaptic cleft - space between
the nerve & motor end plate
III. Skeletal Muscle Contraction
A. Initiation events
1. nerve impulse
2. ACh released
3. Ach binds to
receptor on
muscle
4. Enzyme
(Acetylcholine
esterase
removes ACh
III. Skeletal Muscle Contraction
B. Action Potential
1. ACh causes to Na+ to diffuse
into cell
2. If threshold is reached, action
potential occurs
- impulse travels along
membrane resulting in
contraction
III. Skeletal Muscle Contraction
C. Sliding Filament Theory
1.Action potential causes Ca++
release from S.R
2.Ca++ binds to thin filament
3.Thin filament rotates exposing
binding site for myosin
4.Myosin binds actin
» uses ATP to "rachet" once
» releases, "and binds to next
actin
Calcium is the "switch" that turns
muscle "on and off" (contracting and
relaxing).
III. Skeletal Muscle Contraction
D. How Neurotoxins Work
1.cobra toxin and curare
– block Ach receptors
– cause flaccid paralysis, potentially
fatal respiratory arrest
2.nerve gas and insecticides
• inhibit AchE
• cause potentially fatal paralytic
convulsions
How a Nerve Gas Works
Normal
Nerve Gas
Effect of Atropine on the Transmission
of Acetylcholine in the presence of a
nerve agent
III. Skeletal Muscle Contraction
D. How Neurotoxins Work
3.Botulism toxin and curare
– block Ach release
– cause flaccid paralysis, potentially
fatal respiratory arrest
4.Tetanus toxin
• cause excessive Ach release from
motor neurons
• causes potentially fatal paralytic
convulsions (“lock jaw”)
III. Skeletal Muscle Contraction
E. Rigor Mortis
•
•
•
•
Ca++ pumps run out of ATP
Ca++ cannot be removed
continuous contraction
eventually tissues break down
IV. Energy Metabolism in Sk.Ms.
A. Aerobic Respiration
1.Most efficient use of glucose
Sources of glucose include blood
glucose and stored glycogen
2.36ATP/glucose
3.requires oxygen
4.occurs in mitochondria
– Muscle cells have more
mitochondria than any other cell
– Require a steady supply of O2
B. Creatine-phosphagen system
1.During rest, muscles store
energy as creatine
phosphokinase (CPK or CK)
2.During intense exercise, ATP
is depleted first, then CK is
used to convert ADP back to
ATP
C. Lactic Acid Pathway
1.Anaerobic use of glucose
2.2 ATP/ glucose
3.Lactic acid produced as waste
product – Oxygen Debt
– Is toxic to tissue
– Can be recycled in liver
V. Muscle Twitch
-cycle of contraction and
relaxation
V. Muscle Twitch
-cycle of contraction and
relaxation
A. Reasons for varying degrees
1. The number of muscle fibers
innervated by a single neuron
varies
2. Some motor units have lower
thresholds than others
3. Muscle fibers differ functionally:
fast twitch – slow twitch fibers
V. Muscle Twitch
B. Fast vs Slow Twitch Fibers
1. Differ in
– How they make ATP
– Speed of ATP break down
– Mitochondria content
– How fast they fatigue
B. Fast vs Slow Twitch Fibers
2. Slow Twitch Fibers
–
–
–
–
–
–
Smallest fibers
Fatigue resistant
Aerobic ATP production
Many mitochondria
Slow contractions
Example: uroanal muscles
B. Fast vs Slow Twitch Fibers
2. Oxidative Fast Twitch Fibers
–
–
–
–
–
Fatigue resistant
Aerobic ATP production
Many mitochondria
Fast contractions
Example: arm muscles
B. Fast vs Slow Twitch Fibers
3. Glycolytic Fast Twitch Fibers
– Largest fibers
– Fatigue easily
– Anaerobic ATP production
– Few mitochondria
– Strong fast contractions
– Example: sprinter’s leg muscles
B. Fast vs Slow Twitch Fibers
4. Muscles have combination of all
three fibers
– The number of each type varies
from individual to individual
Endurance running - slow and fast
oxidative fibers
Sprints - fast oxidative fibers and some
fast glycolytic fibers
Powerlifting - fast glycolytic fibers &
some fast oxidative
Old age - increase in slow oxidative
fibers
B. Fast vs Slow Twitch Fibers
4. Muscles have combination of
all three fibers
– Training/conditioning can
change the predominant fiber
type in muscles
Anabolic steroids
– similar to testosterone
– large doses required for good
effect
– Side effects:
– overall - kidney and heart damage,
aggressiveness
– females - sterility, facial hair,
breast & uterine atrophy
– males - baldness, atrophy of testis
Sports injuries - RICE therapy
– Rest
– Ice
– Compression
– Elevation
V. Skeletal Muscle
A. Muslce Attachments
1.Origin - tendons attach muscle
to a stationary bone
2.Insertion - muscle attaches to
moving bone (usually distal)
V. Skeletal Muscle
B. Lever Systems
1.lever - rod that moves at the
fulcrum (fixed point)
2.fulcrum typically the joint moving
3.Resistance - gravity pulling on
body
4.Effort - muscle contraction
V. Skeletal Muscle
B. Lever Systems
4. Movement
occurs when
E > R
– First class
levers - E F R
V. Skeletal Muscle
B. Lever Systems
4. Movement
occurs when
E > R
– 2nd class
levers – F R E
V. Skeletal Muscle
B. Lever Systems
4. Movement
occurs when
E > R
– 3rd class
levers – F E R
most common
V. Skeletal Muscle
C. Muscle Groups
1.Many muscles are required for
any given movement
– 1 muscle moves arm up
– another muscle
moves arm
down
C. Muscle Groups
2. Muscles work
together
– Agonist
> Prime mover
> muscle that causes a
movement
– Antagonist
> opposes the muscle that
stretches
Ex. Arm flexion
Biceps – Agonist (prime mover)
Triceps -- Antagonist
Uncurl arm -- roles are reversed
C. Muscle Groups
2. Muscles work
together
– Synergist
> Assists the prime mover
– Fixator
> auxiliary muscles that
steady a movement
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