Introduction to
Muscle Anatomy
Types of Muscle
1. Skeletal
Longitudinal
Cells
View
– Elongated
– Multi nucleated
Notice striations
and nuclei
– Striated – striped
appearance around outside
of cell.
– Voluntary
– Produces powerful
contractions
– Tires easily, needs rest
(fatigue).
Cross Section
– Covers bony skeleton
Notice nuclei
(motility)
around outside
of cell.
Skeletal Muscle Composite Sketch
2. Smooth
– Spindle-shaped Cell
– Single nucleus in each
cell
– No Striations
– Involuntary
– Slow, sustained
contractions
– In hollow visceral
Cross organs
Section (stomach,
Nucleus
is in center respiratory
bladder,
of cell. Cells much
passages)
smaller.
Smooth Muscle Composite Sketch
3. Cardiac (Heart)
– Branched cell
– Contain intercalated
discs
– Single nucleus in each
cell
– Striations
– Involuntary
– Steady, constant
contractions
– Never tires
Cardiac Muscle Composite Sketch
Muscle Functions
• Produce movement
– locomotion & manipulation
– Help blood move through veins & food
thru small intestines
• Maintain posture
• Stabilize joints
• Body temp homeostasis
– Shivering: movement produces heat
energy
Axon of
neuron
Muscle Requirements
Motor end
plate
(terminus)
• Demands continuous oxygen/nutrient
supply.
– Lots of arteries/capillaries to muscle.
• Each muscle cell w/ its own nerve ending
controlling its activity.
• Produce much metabolic waste due to
constant activity.
Muscle Attachments
• Most muscles span joints
• Attaches to bone in two places: (video)
1. Insertion: the moveable bone
• Bicep insertion is the radius
2. Origin: the stationary bone
• bicep originates in two different places in scapula
• Attachment types
1. Direct: attaches right onto bone
- ex. intercostal muscles of ribs
2. Indirect: via tendon or aponeurosis (sheet-like
tendon) to connect to bone
- leaves bone markings such as tubercle
Muscle Organization
Muscles are complex bundled
structures: fibers within fibers
Muscle
organization
Muscle
(organ)
Fascicle
Muscle fiber (cell)
Myofibril
Sarcomere
Myofilaments:
Actin & Myosin
Muscle Fibers
• A Muscle Fiber = Muscle Cell
• HUGE cell:
– 10 - 100m in diameter
– can be hundreds of centimeters long (created by cytoplasmic
fusion of multiple embryonic cells)
– extends the length of the muscle
• Main content: bundles of proteins (actin
and myosin)
• Multinucleated
– to maintain high rate of protein synthesis.
– Muscle fiber nucleus = myonucleus
Insulation of Muscles
•Muscle cells must be insulated
from one another by specialized
membranes
•Muscle cells work electrically
– if not insulated, nerves cannot
control individual muscles.
• Epimysium surrounds entire
muscle
– Dense CT that merges
with tendon
– Epi = outer
– Mys = muscle
• Perimysium surrounds muscle
fascicles
– Peri = around
– Within a muscle fascicle
are many muscle fibers
• Endomysium surrounds
muscle fiber
– Endo = within
Structural Terminology Associated
with Muscle Fibers
Prefixes: myo, mys, and sarco all refer to muscle
• Sacroplasmic Reticulum = Smooth ER of muscle
(regulates calcium levels for muscle contraction)
• Sarcoplasm = Cytoplasm
– To maintain ATP production during cellular respiration,
contains high amounts of:
• mitochondria
• glycosomes that store sugar
• oxygen binding protein called myoglobin
• Sarcolemma = Plasma Membrane
• T tubules - The sarcolemma of muscle cells are not
just on the outside, rather forms tubes that dive into
the muscle cells
• Myosin and Actin= muscle proteins that create
muscle cytoskeletal filaments for contraction
myofibril
Sarcoplasmic
Reticulum
T-tubule
sarcolemma
Myosin (red) and
Actin (blue)
Microstructures
• Each muscle fiber (muscle cell), is
composed of many myofibrils.
– Organized system of cytoskeleton filaments of
actin and myosin proteins that do the actual
contracting
– Myofibrils are NOT CELLS
– A sarcomere is one segment of a myofibril
(muscle segments).
– The series of sarcomeres produce the striated
appearance of muscles
Muscle Fiber
Sarcomere
Sarcomere organization
• Myofibril composed of repeating series of
sarcomeres with dark A and light I bands.
• I bands intersected by Z discs mark the
outer edges of each sarcomere.
• Contraction happens within one
sarcomere.
Sarcomere Banding Pattern
How do muscle contract?
Let’s sketch the sarcomere
together and discuss the sliding
filament model of muscle
contraction