Muscular System
Anatomy of Muscle Fibrils
Physiology of Muscle Contraction
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Did you know that ?
- More than 50% of body weight is
muscle !
- Muscle is made up of proteins
and water
• Muscles are responsible for all movement
of the body
• There are three basic types of muscle
• Skeletal (Striated or Voluntary)
• Cardiac (Heart)
• Smooth (Involuntary)
The Muscular System
3 Types of Muscles
Info About Muscles
• Only body tissue able
to contract
• Create movement by
flexing and
extending joints
• Body energy
converters (many
muscle cells contain
many mitochondria)
• Produce external movement
• Maintain posture – hold body still or in a
particular position
• Stabilize joints
• Movement of substances inside the body
– cardiac and smooth (visceral) muscles
transport blood and food
• Generate heat by contractions – High
metabolic rate of contracting produces
lots of waste heat; small contractions to
maintain body temperature
Functions of Muscles
Skeletal
Cardiac
Smooth
Three types of muscle
All muscles share some terminology
• Prefixes myo and mys refer to
muscle
• Prefix sarco refers to flesh
Muscle Terms
Classification of Muscle
Skeletal
Cardiac
Smooth
Limbs
Heart
Viscera
Movement
Heartbeat
Move food & and
other substances
through the body
Striated and
Striated
Not striated
Branched
Multi- nucleated
Uni-nucleated
Uni-nucleated Fibers in sheets
Fibers in bundles
Lots of mitochondria
Voluntary
Involuntary
Involuntary
Contracts in short,
strong bursts
All fibers contract at
the same time
Contracts slowly, but
steadily
Skeletal Muscle
• Also called Striated Muscle
• Always connect to skeleton in at
least one place
• Most attached to two bones by
a tendon
• Act independently of
neighboring muscle fibers
• Striated - have stripes, banding
• Multi-nucleated - cells have more than
one nucleus
• Voluntary - subject to conscious
control, CNS
• Long cylindrical fibers are arranged in
bundles
Skeletal or Striated
Muscle
• Muscles move by shortening
their length, pulling on tendons,
and moving bones closer to
each other.
• Tendons – strong collagen
fibers
• One bone is pulled toward the
other bone, which remains
stationary.
Muscles move Bones
• Muscle connected to stationary bone by
tendons at the Origin. The basis for the
action.
• Muscle connected to moving bone by tendons
at the Insertion. The effects of the action.
• Muscles are always attached to at least 2
points
• Movement is attained due to a muscle moving
an attached bone
How are Muscles
Attached to Bone?
Insertion
Origin
Muscle Attachments
• Location
• Origin and Insertion
• Number of Origins
• Shape, Size and Direction
• Function
Naming Muscles
The layers of connective tissue are the
cement that holds the muscle cells and
bundles together
• Epimysium – surrounds the whole muscle
• Perimysium – surrounds the Fascicle
(individual bundles of muscle cells)
• Endomysium – surrounds the Muscle
Fiber (Muscle Cell)
Three types of
Connective Tissue
Bone to Muscle Fiber / cell
Progression of Anatomy
• Each Muscle Cell or Fiber is long and
cylindrical
• 50-60 mm in diameter, and up to 10 cm long
(length is greater than width)
• The contractile elements of skeletal muscle
cells are Myofibrils
• Sarcolemma – special cell membrane that
conducts electrochemical signals
Structure of skeletal
muscle
Vesicles and Tubules that surround
the Muscle Fiber (cell)
• T-System or Tubules – connect to
sarcolemma and transmits the nerve
impulse to the middle of the cell and all the
thousands of myofibrils that make up the
muscle cell
• Sarcoplasmic Reticulum - forms a curtain
around each myofibril and a storehouse of
the calcium ions (Ca + 2) that are part of the
contraction mechanism
Sarcotubular System
Sarcomere
Myofibrils – muscle fiber structure;
contractile elements
A Bands - Dark and thick – Myosin
H Band (zone) – darker area in the middle
of the A Band
I Bands – Light and thin – Actin
Z Line (band, disc) – narrow, dark band in
the central region of the I Band
Sarcomere – area between two Z Lines –
functional unit of muscle fiber
Dark and Light Bands
1. Neuroelectrical Factors – Nerve impulse causes
Potassium ions (K +) and Sodium ions (Na¯ ) to
switch places across the cell membrane and create
an Action Potential that travels along the TSystem.
2. Chemical Interactions – Actin unites with Myosin
to form Actomyosin.
3. Energy Sources – ATP
3 Factors cause a
Muscle Contraction
Where Does the Energy
Come From?
• This all happens in the Mitochondria
• Energy is stored in the muscles in the
form of ATP
• ATP comes from the breakdown of
glucose during Cellular Respiration
• Acetylcholine – released from
synaptic vesicles, stimulates a muscle
impulse
• Cholinesterase – enzyme that stops
action of acetylcholine
Neurotransmitters
• More Potassium ions inside the cell than outside.
More Sodium ions outside the cell than inside.
Inside the cell is negatively charged and outside is
positively charged – Resting Potential
• At the neuromuscular junction (end of the axon), a
nerve impulse causes release of acetylcholine from
the synaptic vesicles into the synaptic cleft.
• Acetylcholine diffuses across the neuromuscular
junction and binds to receptors on the sarcolemma
(muscle cell membrane).
Steps in a Contraction 1
Action Potential
• Impulse spreads across sarcolemma and increases
the permeability to K+ ions (depolarization) - the
potassium ions rush outside the cell and the sodium
ions rush inside the cell. This creates an electrical
potential - and the Action Potential is generated.
• Action Potential travels by way of the T-Tubules to
all the cells and causes the Sarcoplasmic
Reticulum to release Calcium ions that diffuse into
the sarcoplasm.
Steps in a Contraction 2
• The Calcium ion concentration at the myofilaments
increases and negates the troponin and
tropomyosin which keeps the filaments apart. This
causes the formation of cross bridges between the
actin and myosin filaments and they slide between
each other and make Actomyosin. The Z Lines
move together.
• Contraction – the formation of the Actomyosin
shortens the myofibril which shortens the muscle
fibers which shortens the muscles
Steps in a Contraction 3
Actin and Myocin
• Sodium –Potassium Pump operation restores the
Na and K distribution to the resting potential.
Calcium ions are actively reabsorbed (Calcium
Pump using ATP) into the Sarcoplasmic Reticulum
and the concentration in the myofilaments
decreases.
• Contraction stops. The Z Lines move apart. The
muscle cell relaxes and lengthens. Enzyme
Cholinesterase stops action of the Acetylcholine.
Steps in a Contraction 4
• Muscle Fatigue - a muscle is tired and unable to
contract because of lack of oxygen, energy (ATP)
and too many waste products.
• Oxygen Debt - the amount of oxygen that the
body needs to restore muscle cells to resting state.
You feel out of breath!
Too Little Oxygen & ATP
Too Much CO₂
• Motor Unit – one motor neuron and the muscle
fibers (cells) that it sends impulses to; they all
contract together
• Average 150 muscle cells
• 200 muscle cells for gross movement (hand)
• 10 muscle cells for fine movement (eye)
• Muscle Cells have four properties:
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Excitability – stimulated by a nerve cell (neuron)
Conductivity – response can travel throughout cells
Contractility – the response to the stimulus
Elasticity – return to original shape after contraction
Contraction Physiology
Contraction Cycle - Latent Period to Contraction
Period (Shortening of fibers) to Relaxation Period
Strength of contraction depends on:
•
•
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•
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Number of Motor Units sending signals
Strength of stimulus
Duration of stimulus
Speed of application
Weight of the load (table vs. coffee cup)
Temperature of the body (98.6⁰)
Contractions
A stimulus that elicits a response
will produce a maximum
contraction. The contraction
occurs or it does not.
All or None Law
Single nerve impulse of a motor
neuron will cause a motor unit to
contract briefly before relaxing
• A single brief small contraction
• Not a normal muscle function
Muscle Twitch
Motor neuron provides many nerve impulses in
rapid succession, the muscle has a complete and
lasting contraction.
• One contraction immediately followed by another
• Effects are compounded
• Remains in tetanus until the nerve signal slows or
the muscle too fatigued to continue
• Muscle never completely returns to a relaxed
state
Muscle Tetanus
A natural condition of in which a muscle
stays partially contracted at all times.
• Some muscle cells will always be contracting while
other muscle cells are at rest.
• Maintain body posture without tiring
• Slight and steady pull on attached bones
• Pressure on abdominal contents
• Blood pressure in arteries and veins
• Assists in digestion in stomach and intestines
• Prevents damage to muscle and joints from sudden
movements
Muscle Tone
• Isotonic Contraction – tone or tension
remains the same; the muscles become
shorter and thicker; lifting a weight
• Isometric Contraction – muscles remain at
a constant length while the tension against
the muscle increases; push against a wall or
lift a large rock
Two types of Contractions
• Isotonic - muscles shorten and
movement occurs ( most normal
exercise)
• Isometric - tension in muscles
increases, no movement occurs
(pushing one hand against the other);
help develop tone or firmness in
muscles
Exercise and Muscles
• Hypertrophy – increase in size due to
repeated forceful contractions
(exercise); 75% maximum effort
• Atrophy – disuse or very low intensity
use causes muscle to shrink – fibers
shorten and replaced with fat and
connective tissue (CT).
More or Less
• No striations
• Spindle shaped
• Single nucleus
• Involuntary - no conscious
control, ANS
• Found mainly in the walls of hollow
organs
Smooth Muscle
• Lines walls of viscera
• Hollow Structures
• Intestines
• Blood Vessels
• Urinary Bladder
Location of Smooth
Muscle
Hollow Organs
• 2-Layer Arrangement
• longitudinal and
circular layers
• Alternate contraction
of circular &
longitudinal muscle
in the intestine leads
to peristalsis
Intestines
• Elongated Spindle shaped
uni-nucleated cells
• Striations not observed
• Actin and myosin filaments are
present (protein fibers) but not as
regularly arranged
Structure of smooth muscle
• Slower and more rhythmic
contractions
• Greater extensibility of the muscle
• Slow wave of contraction over the
entire muscle mass
Physiology of Smooth
Muscle
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Striations – very strong cells
Branching or y-shaped cells
Involuntary – ANS – autorhythmic
Uni-nucleated
Found only in the heart – responsible for
pumping blood
• Cells connected by Intercalculated Discs
that spread signals quickly from cell to cell to
beat as a unit
Cardiac Muscle
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•
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Main muscle of heart
Pumping mass of heart
Critical in humans
Heart muscle cells
behave as one unit
• Heart always contracts
to full extent
Cardiac muscle
Structure of cardiac
muscle
• Cardiac muscle cells (fibers) are short,
branched and interconnected
• Cells are striated & usually have 1
nucleus
• Adjacent cardiac cells are joined via
electrical synapses (gap junctions)
• These gap junctions appear as dark
lines and are called Intercalated Discs
• Rapid rhythm of contractions
• Impulse – contract – relax - another
impulse – contract…
• About 75 contractions per minute
• Fibrillation – rapid uncontrolled
contractions of individual cells; blood is
not pumped properly
Contractions of Cardiac
Muscle
Muscle Control
Type of
muscle
Skeletal
Skeletal
Cardiac
Smooth
Nervous
control
Controlled
by CNS
Regulated
by ANS
Controlled
by ANS
Type of
control
Example
Voluntary
Lifting a
glass
Involuntary
Heart
beating
Involuntary Peristalsis
END OF ANATOMY AND
PHYSIOLOGY
Types of Musculo-Skeletal Movement
Flexion
Extension
Hyperextension
Abduction, Adduction &
Circumduction
Rotation
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Inversion- turn sole of foot medially
Eversion- turn sole of foot laterally
Pronation- palm facing down
Supination- palm facing up
Opposition- thumb touches tips of fingers on the same
hand
More Types of
Movement……
The Skeletal Muscles
There are about 650 muscles in the
human body. They enable us to
move, maintain posture and
generate heat. In this section we
will only study a sample of the major
muscles.
Sternocleidomastoideus
Flexes and Rotates Head
Masseter
Elevate Mandible
Temporalis
Elevate & Retract Mandible
Trapezius
Extend Head, Adduct, Elevate or
Depress Scapula
Latissimus Dorsi
Extend, Adduct & Rotate Arm Medially
Deltoid
Abduct, Flex & Extend Arm
Pectoralis Major
Flexes, adducts & rotates arm medially
Biceps Brachii
Flexes Elbow Joint
Triceps Brachii
Extend Elbow Joint
Rectus Abdominus
Flexes Abdomen
External Oblique
Compress Abdomen
External Intercostals
Elevate ribs
Internal Intercostals
Depress ribs
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Flexor carpi—Flexes wrist
Extensor carpi—Extends wrist
Flexor digitorum—Flexes fingers
Extensor digitorum—Extends fingers
Pronator—Pronates
Supinator—Supinates
Forearm Muscles
Diaphragm
Inspiration
Gluteus Maximus
Extends & Rotates
Thigh Laterally
Rectus Femoris
Flexes Thigh,
Extends Lower Leg
Gracilis
Adducts and Flexes Thigh
Sartorius
Flexes Thigh, &
Rotates Thigh
Laterally
Biceps Femoris
Extends Thigh &
Flexes Lower Leg
Gastrocnemius
Plantar Flexes Foot
& Flex Lower Leg
Tibialis Anterior
Dorsiflexes and Inverts Foot