Bio 150- Muscles Flashcards
General functions of the muscular system
-Body movement
-Maintenance of posture and stability
-Support soft tissues
-Guard “entrances and exits”
-Production of body heat
-Also:
Communication
Constriction of organs and vessels
Heart beat
Storage of nutrient reserves
Muscle tissue: defining characteristics
-Able to contract (“contractility”)
Can shorten forcibly
Causes movement of attached structures, or change in volume/pressure…
(note: lengthening of muscle is passive! Muscles can only “pull”, they can’t “push”!)
-Excitable! (“excitability”)
Muscle can respond to a stimulus (from nerves, hormones…)
-Conductivity
-Extensibility (can stretch)
-Elasticity (can recoil after being stretched)
Skeletal muscle
- Striated
- Attached to bone
- Cells are long and cylindrical, with many nuclei (peripherally located)
- Under voluntary control
- body movement
Smooth muscle
- Not striated
- Cells are spindle shaped, each with one central nucleus
- Involuntary control
Cardiac muscle
- Striated
- Cells are cylindrical and branched, each with one, central nucleus
- *intercalated discs (with gap junctions) join neighbouring cells
- Involuntary control
Skeletal muscles are made up of:
-Muscle fibers (cells): Number of fibers remains fairly constant after birth!
But they can increase in size
- Connective tissue
- (+blood vessels and nerves)
Muscle fiber
-Each muscle fiber (cell) is surrounded by sarcolemma (the cell’s plasma membrane)
-Sarcoplasm: cytoplasm
-Each fiber is surrounded by endomysium (CT)
-T tubules:
Invaginations of the sarcolemma
-Sarcoplasmic reticulum (SR):
Specialized smooth ER
-Triad:
T-tubules
Terminal cisterna (enlargement of SR near T tubules)
A bundle of fibers (and their endomysium) are surrounded by perimysium
This is called a
fascicle
Many fascicles are grouped together, and surrounded by
epimysium (dense CT)
CT layers form
tendon/ aponeurosis
Epimysium =
fascia
Nerve and blood supply to muscle
- An axon (of a motor neuron), an artery, and a vein tend to travel together through the CT layers
- Each axon branches so that each muscle fiber (=cell) receives a branch of an axon
- Arteries branch to form capillary beds (supply muscle tissue with O2, glucose, etc.)
Muscle fiber microstructure :Most of the cell is filled with
myofibrils
Each myofibril goes the length of the cell, and is made up of 2 main different protein filaments:
actin (thin) and myosin (thick)!
two myofilaments (actin and myosin, plus a 3rd called titin) form the
sarcomeres
The actin myofilaments are anchored by the
Z-disk
The myosin myofilaments are held in place by the titin filaments, and in the middle of the
H band
A sarcomere extends from
one Z-disk to the next Z-disk
I band
(isotropic, l-I-ght band)
Includes Z-disk; between the myosin myofilaments
A band
(anisotropic, d-A-rk band)
Extends the length of the myosin filaments
H zone
In the middle of the A band; only myosin (no actin)
Actin (thin) myofilaments
- Two strands of F actin (fibrous actin), plus tropomyosin and troponin molecules
- F actin is actually a chain of G actin molecules (globular)
- Allows for attachment of myosin heads!
Myosin myofilaments
-Each myosin myofilament is made up of many myosin molecules
Each one looks like a golf club!
-Rod portion + head
-The heads form cross-bridges with the actin
Titin myofilaments
- Very elastic
- Anchors myosin to the Z-disc
- Keeps actin and myosin in alignment
- Helps the muscle to resist extreme stretching
Origin:
the “fixed end”.
Belly:
thick midregion of the muscle.
Insertion:
the “moveable end”. Muscle contraction pulls the insertion point closer to the origin.
Agonist:
the “prime mover”
Synergist:
helps the agonist (e.g., stabilize?)
synergist is usually smaller than the agonist
Antagonist:
opposes the action of the agonist
Fixator:
prevents a bone from moving
Types of movements – Angular movements
Flexion
Extension
(Hyperextension)
Abduction
Adduction
Circumduction
Types of movements – Rotational movements
Lateral (external) rotation
Medial (internal) rotation
Right and left rotation
Pronation
Supination
Types of movements – Special movements
Eversion Inversion Dorsiflexion Plantar flexion Opposition Protraction Retraction Depression Elevation Lateral flexion
