Download muscular system - Norwell Public Schools

MUSCULAR SYSTEM
ROLES OF MUSCLES IN BODY
• Produces
movement
• Maintains
posture
• Stabilizes
joints
• Generates
• Vital
heat
for maintaining body temperature.
TYPES OF MUSCLE
•Skeletal – striated & voluntary
•Smooth – involuntary
•Cardiac - heart
SKELETAL MUSCLE
• Muscle
attached to the skeleton.
• Striated
muscle.
• Contains
more than one nuclei per cell
• Contraction
is under voluntary control.
SKELETAL FIBER STRUCTURE
• Muscle
is made up of thousands of cylindrical muscle fibers.
•
Run from origin to insertion.
•
Bound together by connective tissue.
• Each
fiber contains:
•
Array of myofibrils that are stacked lengthwise.
•
Run the entire length of the fiber
SKELETAL FIBER STRUCTURE
• Many
mitochondria for
energy.
• Extensive
smooth
endoplasmic reticulum
• Many
nuclei: each muscle fiber
develops from the fusion of
many cells
CARDIAC MUSCLE
• Striated
• Each cell contains sarcomeres with sliding filaments of
actin and myosin.
CARDIAC MUSCLE
•
The myofibrils of each cell are branched.
• The branches interlock with adjacent fibers by adherens
junctions.
•Enable heart to contract forcefully without ripping the
fibers apart.
• The action potential that triggers the heartbeat is
generated within the heart itself.
CARDIAC MUSCLE
• Action
potential that drives contraction of the heart
passes from fiber to fiber through gap junctions.
• All
fibers contract in a synchronous wave
• Sweeps
from atria down through ventricles and pumps
blood out of the heart.
• Refractory
period is longer than the period it takes for
the muscle to contract (systole) and relax (diastole).
• Has
richer supply of mitochondria than skeletal muscle.
SMOOTH MUSCLE
• Made
• No
of single, spindle-shaped cells.
visible striations
SMOOTH MUSCLE
• Cells
contain thick (myosin) and thin (actin) filaments.
• Slide
against each other to produce contraction of the cell.
• Does
not depend on somatic motor neurons to be stimulated.
• Motor
neurons (of the autonomic system) reach smooth
muscle and can stimulate it — involuntary action based on
stimulus response.
MUSCLE STRUCTURE
Muscles are composed of many fibers that are
arranged in bundles called FASCICLES
Individual muscles are separated by FASCIA, which
also forms tendons (connects muscles to bones).
MUSCLE FIBER MADE OF MYOFIBRILS
Myofibrils = individual muscle fibers --> made of myofilaments
MYOFIBRIL
• Contains
• ACTIN
protein filaments
(thin) and MYOSIN (thick)
• These
filaments overlap to form dark and light bands on the
muscle fiber.
•A
•I
• In
band = dark • thick (myosin)
band = light • thin (actin)
the middle of each I band are Z lines.
• Sarcomere
is section of myofibril from one Z line to the other
MYOFIBRILS ARE A SERIES OF
CONNECTED SARCOMERES
SARCOMERE
• Basic
contracting unit of muscle.
• The
entire array of thick and thin filaments between the
Z disks is called a sarcomere.
•Z
lines on either end.
• Contains
one A-band and 21/2 I-bands
SARCOMERE STRUCTURE
• The
striations are caused
by alignment of bands.
prominent: A and I
bands and Z line.
• Most
•A
band: 2 proteins
overlap.
•I
band: only the actin
protein.
SARCOMERE STRUCTURE
• The
H zone: Part of the
A band where thick and
thin filaments do not
overlap.
•M
line runs through
center of the
sarcomere.
• Provides
a scaffold for
the assembly of
myosin molecules in
the thick filament
SARCOMERE STRUCTURE
• When
muscle contracts
the actin filaments slide
into the A band,
overlapping with myosin.
•Z
lines move closer
together
•I
band becomes shorter
•A
band stays at the
same length
IT IS IMPORTANT TO REMEMBER THE
MUSCLE HIERARCHY
myosin
myofibrils
fascicles
myofilaments
actin
muscle fiber
myofilament
epimysium
myofibrils
muscle
sarcomere