HUMB1001 Lecture Notes - Lecture 3: Endoplasmic Reticulum, Skeletal Muscle, Myofilament
How do we move?
Functions of the Muscular System:
❖ Movement of the body
❖ Maintenance of posture
❖ Respiration (thoracic muscles)
❖ Production of body heat
❖ Communication
❖ Constriction of organs and vessels
❖ Contraction of the heart
General properties of Muscles
❖ Contractility: ability of a muscle to shorten with force to produce tension
❖ Excitability: capacity of muscle to respond to a stimulus (from our nerves or hormones) must
be capable of transmitting an action potential.
❖ Extensibility: muscle can be stretched to its normal resting length and beyond to a limited
degree
❖ Elasticity: ability of muscle to recoil to original resting length after stretched
Types of Muscle Tissue:
• Skeletal Muscle
o Makes up of 40% of body weight
o Responsible for locomotion, respiration, posture, mastication, facial
expressions
o Generally attach to bone
• Smooth Muscle
o Found in hollow organs and tubes
▪ E.g. bronchioles, gut, blood vessels, iris of the eye
• Cardiac
o Found only in the heart
o To move blood
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Connective Tissue Coverings of Skeletal Muscle
❖ Surrounds and supports muscle fibres
❖ Providing passage for nerves and blood vessels
❖ Mechanism of joining muscle-tendon-
bone
o Transferring the force created
by the shortening of the muscle
through to a tendon then to
bones
❖ Connective Tissue Layers
o Epimysium: surrounds a whole
muscle
o Perimysium: surrounds a group
of muscle fibres. Each group
called a fascicle
o Endomysium: surrounds
individual muscle fibres
Structure of a skeletal muscle fibre
• Muscle fibre (=muscle cell) & wrapped in
endomysium
• Sarcolemma (=plasma membrane)
• Sarcoplasm (=cytoplasm)
• Multiple nuclei at periphery
• Lots of mitochondria
• Myofibrils: cylindrical organelles within
sarcoplasm
• Sarcoplasmic reticulum (=smooth
endoplasmic reticulum)
o Storage area Ca2+
o Terminal cisterna are enlarged sarcoplasmic
reticulum located either side of the T-tubule
• Transverse (T) tubule invaginations
(morphogenetic process by which an embryo
takes form) of sarcolemma with run deep into
the muscle cell
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Myofibrils
❖ Myofilaments: within myofibrils thread like protein strands
o Thin (actin, includes troponin and tropomyosin)
o Thick (myosin)
❖ Striated appearance
o I Bands: (light band)
▪ Z disks in the middle: attachment of thin filaments and thick myofilaments
through Titin
o A Bands: (dark band)
▪ Length of thick filament
o H Zone: region in A band where actin and myosin do not overlap
▪ M ling: in the middle, attachment point for thick myofilaments
o Sarcomere: highly ordered repeating units of myofilaments
▪ From z disk to z disk
▪ Unit of contraction for skeletal muscle
Myosin (thick) Myofilament
• Myosin: A large elongated protein
made of many myosin molecules;
look like golf clubs
• Myosin heads can bend at hinge
region, which allows binding to
the active sites on the actin
molecules to form cross-bridges.
Myosi heads are oked upright ready for atio whe ATP attahes to the hige setio ad
broken down to ADP + P + energy.
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Document Summary
Contractility: ability of a muscle to shorten with force to produce tension. Excitability: capacity of muscle to respond to a stimulus (from our nerves or hormones) must be capable of transmitting an action potential. Extensibility: muscle can be stretched to its normal resting length and beyond to a limited degree. Elasticity: ability of muscle to recoil to original resting length after stretched. Providing passage for nerves and blood vessels. Mechanism of joining muscle-tendon- bone: transferring the force created by the shortening of the muscle through to a tendon then to bones. Connective tissue layers: epimysium: surrounds a whole muscle, perimysium: surrounds a group of muscle fibres. Each group called a fascicle: endomysium: surrounds individual muscle fibres. Myofilaments: within myofibrils thread like protein strands: thin (actin, includes troponin and tropomyosin, thick (myosin) I bands: (light band: z disks in the middle: attachment of thin filaments and thick myofilaments through titin, a bands: (dark band)
