Download The Muscular System and Integumentary System

The Muscular System and
Integumentary System
Ms. Hoffman
September 13, 2004
How do Muscles and Bones
Interact?
• Skeletal muscles generate force and produce movement by
contracting, or pulling on body parts
• Skeletal muscles are joined together by tough connective
tissues called tendons
• Tendons are attached so that they pull on bones and make
them work like levers
• Most skeletal muscles work in opposing pairs
• When one muscle contracts, the other relaxes
• Ex. When the biceps muscle contracts, the triceps is
relaxed and you can curl your arm
• Ex. When the biceps muscle relaxes, the triceps muscle
contracts and you can extend your arm
What is Muscle Tone?
• Skeletal muscles remain in a state of partial
contraction
• At all times, a few muscle cells are being
stimulated while others are not
• Limited stimulation causes a tightening of some
muscles called resting muscle tone
• Resting muscle tone is responsible for keeping the
back and legs straight and the head upright, even
when you are relaxed
• Regular exercise increases muscle tone
Muscles
• Provide the forces that put the body into
motion
• More than 40% of the mass of the average
human body is muscle
• Fxns: regulate blood pressure, move food
through the digestive system, power every
movement in the body
Types of Muscle Tissue
• Muscle tissue is found everywhere in the
body…from beneath the skin to deep within
the body
• There are three different types of muscle
tissue: skeletal, smooth, and cardiac
• Each type of muscle tissue has a different
structure and plays a different role in the
body
Skeletal Muscles
• Usually are attached to bones
• Responsible for voluntary movements like dancing, running, jumping
• Have alternating light and dark bands or stripes called striations when
viewed under the microscope
• Most skeletal muscles are controlled by the central nervous system
• Skeletal muscle cells are large cells, have many nuclei, and vary in
length from 1 mm – 30 cm
• May be referred to as muscle fibers because these muscle cells are so
long and slender
• Complete skeletal muscles consists of: muscle fibers, connective
tissues, blood vessels, and nerves
Skeletal Muscle
Smooth Muscles
• Usually are not under voluntary control
• Spindle-shaped, one nucleus, no striations
• Found in hollow structures like the stomach, blood
vessels, and small and large intestines
• Fxns: move food through your digestive tract,
control the way blood flows through your
circulatory system, decrease the size of the pupils
of your eyes in bright light
• May function without nervous stimulation
• Connected to one another by gap junctions that
allow electrical impulses to travel directly from
one muscle cell to a neighboring muscle cell
Smooth Muscle
Cardiac Muscle
• Only found in the heart
• Striated like skeletal muscle
• Usually only have one nucleus like smooth
muscle
• Usually not under the direct control of the
central nervous system
• Cardiac cells are connected to their
neighboring cells by gap junctions
Cardiac Muscle
Muscle Contraction
• Muscle fibers in skeletal muscles are made of
smaller structures called myofibrils
• Each myofibril is made of even smaller structures
called filaments
• Thick and thin filaments alternate to create the
striated appearance of muscle cells
• Thick filaments are made of a protein called
myosin
• Thin filaments are made of a protein called actin
Muscle Contraction
• Myosin and actin filaments are arranged
along a muscle fiber in units called
sarcomeres
• Sarcomeres are separated from each other
by regions called Z discs
• During relaxation of a muscle there are no
thin actin filaments in the center of a
sarcomere
Muscle Contraction
• Myosin and actin filaments are what cause muscles to
contract
• A muscle contracts when the thin actin filaments in a
muscle fiber slide over the thick myosin filaments
• For contraction to occur, the thick myosin filaments must
form a cross-bridge with the thin actin filament
• The cross-bridge changes shape and pulls on the actin
filament which slides toward the center of the sarcomere
• The distance between the Z discs decreases
• The cross-bridge detaches from the actin filament and the
cycle is repeated when the myosin binds to another site on
the actin filament
What Supplies the Energy for
Muscle Contraction?
• The energy of muscle contraction is
supplied by ATP
• One molecule of ATP supplies the energy
for one interaction between a myosin crossbridge and an actin filament
• Lots of ATP is needed!
• ATP can be produced by cells via cellular
respiration
Controlling Muscle Contractions
• Motor neurons connect the central nervous
system (brain and spinal cord) to skeletal
muscle cells
• Impulses from motor neurons control the
contraction of skeletal muscle fibers
• Neuromuscular junction- the point of
contact between a motor neuron and a
skeletal muscle cell
Controlling Muscle Contractions
• At the neuromuscular junction there are pockets (vesicles)
in the terminals of the motor neuron that release a
neurotransmitter called acetylcholine
• Neurotransmitters are chemicals used by neurons to
transmit an impulse across a synapse (space where a
message can be relayed) to another cell
• Acetylcholine molecules cross the synapse and cause an
impulse in the cell membranes of the muscle fiber
• This impulse causes calcium ions to be releases within the
fiber
• The calcium ions affect proteins that regulate how the actin
and myosin filaments interact
• The contraction of a muscle fiber is an all- or -none
process