Focuses on the structure of the body parts and their
Study of the body function
Study of how body structures and functions are
altered when exposed to acute bouts of exercise.
Chronic adaptations to exercise.
Concepts of exercise physiology to training the athlete
and enhancing the athletes sport performance.
Thus it is derived from exercise physiology.
Structure & Function of
the Exercising Muscle
Types of muscle
Plasma membrane that surrounds the fiber
Apart of a larger unit called the sarcolemma (plasma
membrane + basement membrane)
@ the end of the muscle fiber it blends with the
tendon which inserts into the bone.
Appears as a series of shallow folds along the surface
of the fiber when contracted or rested.
Has junctional folds in the innervation zone at the
Assists with maintaining acid – base balance
Transports metabolites from the capillaries into the
Satellite cells (growth and development) located in
between plasmalemma and the basement membrane
Gelatin like substance that fills the space between the
protein, minerals, glycogen, fats, and necessary
Differs from the cytoplasm of most cells because it
contains large quantity of stored glycogen and oxygen
binding compound myoglobin.
Extensions of the plasmalemma that passes laterally
through the muscle fiber.
Interconnected to allow nerve impulses received to be
transmitted rapidly to individual myofibrils.
Provides pathways from outside to its
interior, allowing substances to enter and waste
products to leave
Longitudinal network of tubules
Membranous channels parallel the myofibrils and loop
Storage site for calcium
Contractile elements of the skeletal muscle
Appear as long strands of smaller subunits called the
Skeletal muscle has distinct striped appearance.
BASIC functional unit of a myofibril and the BASIC
contractile unit of the muscle.
Each myofibril consists of numerous sarcomere
joined end to end at the Z disks
2/3 of the skeletal muscle protein is myosin, principal
protein of the thick filament.
Each myosin molecule composed of two protein strands
One end of each strand is folded into a globular head –
Myosin head protrudes from the thick filament to form
cross bridges onto the thin filaments.
Titin – array of fine filaments that stabilizes the myosin
from Z to M line.
Composed of three different protein molecules:
One end attached to the Z line and the opposite
extending to the center of the sarcomere, lying in
space between the thick filaments.
Anchoring protein for actin
Plays a regulatory role in mediating actin and myosin
Each thin filament contains active binding sites to
which myosin heads can bind.
Backbone of the thin filament
Individual actin molecules are globular proteins joined end
to end like stands twisted into a helical pattern
Tube shaped protein that twists around the actin strands
Attached at regular intervals to both the actin strands and
Neuron that connects with and innervates many
Single motor neuron and all the muscle fibers it
supplies are collectively termed a motor unit.
Communication between the nervous system and
muscular system occurs at the neuromuscular
junction (gap between the α-motor neuron and the
Action potentials (AP) are electrical signals
propagated from the brain or spinal cord to the α-
From the α-motor neuron dendrites (specialized
receptors on the neuron’s cell body) the AP travels
down the axon to the axon terminals located close to
@ the terminals the nerve ending secretes
achetylcholine (Ach) which binds to the receptors on
Enough ACh has to bind to the receptors to allow for
the AP to be transmitted to the ful length of the
This open ions gates in the muscle cell membrane
and allows sodium to enter, depolarization.
An AP MUST be generated in the muscle before the
muscle cell can act.
Role of Calcium in the
The AP travels over the T-tubules to the interior of
The arrival of the electrical charge causes the SR to
release large quantity of calcium (Ca) into the
@ rest tropomyosin covers the myosin binding sites
on the actin, hence preventing the binding of the
Once the Ca ions are released from the SR they bind
to the troponin on the actin molecule.
Troponin has a strong affinity for Ca and is believed
to initiate the contraction process by moving the
tropomyosin molecules off the myosin-binding sites
on the actin molecules.
Once lifted off the the myosin heads can attached to
the binding sites on the actin molecules.
Sliding Filament Theory
Once the myosin cross bridges are activated they
bind to actin conformational change in the cross
bridge causing the myosin head to tilt (power
stroke) dragging the thin filament towards the
center of the sarcomere pulling of the thin
filament past the thick filament shortens the
sarcomere and generates force.
Immediately after the myosin head tilts it breaks
away from the active site, rotates back to its original
position and attaches to a new active site.
Repeated attachments and power strokes cause the
filament to slide past one another, hence the term
sliding filament theory.
This process continues until the end of the myosin
touches the Z disks, or until the Ca is pumped back
into the SR
Energy for Muscle
Muscle contraction is a process that requires energy.
In addition to the binding site for actin, the myosin
head contains a binding site for adenosine
Myosin MUST bind with ATP for muscle contraction
to occur, because ATP supplies the needed energy.
Adenosine triphosphatase (ATPase) – located on the
myosin head, splits the ATP to adenosine
diphosphate (ADP), inorganic phosphate, and energy.
Energy released from the ATP is used to power the
tilting of the myosin head.
Thus, ATP is the chemical source of energy for
End of Muscle
Muscle contraction will continue as long as calcium is
available in the sarcoplasm.
@ the end of muscle contraction, Ca is pumped back into
the SR where it is stored until a new AP arrives.
Ca is returned to the SR by an active Ca – pumping system.
This system is energy demanding and hence relies on ATP.
Thus contraction and relaxation phases requires energy.
Once Ca is pumped back into the SR, troponin and
tropomyosin return to the resting conformation.
Blocking the linking of myosin cross bridges and
actin molecules, and stops the use of ATP.
Resulting in the thick and thin filaments returning to
their relaxed original state.