Chapter 10- Muscles Flashcards
Myology
scientific study of muscles
how much mass do muscles account for
~45%
functions of muscles
maintain posture and body position movement heat production guard orifices support visceral organs
properties of muscle tissue
Excitability
-the ability to receive and respond to electrical or chemical stimuli
Contractility
-the ability to shorten forcibly when stimulated
Extensibility
-ability to be stretched without damaging the tissue
Elasticity
-ability to return to original shape after being stretched
composition of mucles
- muscles are organs
- consist of many tissue types
- connective tissue
- arteries/veins
- nerves
- lymphatics
- contractile muscle cells
skeletal muscle characteristics
- attaches to bone, skin, or fascia
- striated with light and dark bands
- voluntary control
- long, thin and multi-nucleated fibers
- arranged into packages that attach to and cover the bony skeleton
- contracts rapidly, but tire easily
- may exert great force
- fiber=1 muscle cells
muscle structure
- belly: main portion of a muscle (thick part)
- belly is attached to tendons
- tendons are attached to bone
fascia
- deep fascia
- -dense irregular CT around muscle
- -holds it in place and separates it form other muscles
- subcutaneous fascia
- -loose CT beneath skin, surrounds several muscles
skeletal muscle organization
- many muscle fibers are bundled together into groups called fascicles
- 10-100 muscle cells
- several fascicles make up a muscle (so several hundred fibers(cells))
skeletal muscle CT
- epimysium
- perimysium
- endomysium
epimysium
surrounds the whole muscle
perimysium
surrounds fascicles
endomysium
separates individual muscle fibers
tendon formed from what
all connective tissue extended beyond the muscle belly
aponeuroses
tendons that form thick flattened sheets
myoblasts
embryonic cells that fuse to form muscle fibers
-causes the length and multinucleation
myosatellite cells
myoblasts that do not fuse
-assist in repair of damaged cells
fiber structure
- sarcoplasm: fiber cytoplasm
- sarcolemma: plasma membrane of a fiber
- transverse (T) tubule: extensions of the sarcolemma into the sarcoplasm
myofibrils
contractile organelles
-extend the length of fiber
sarcoplasmic reticulum
surrounds the myofibrils
- similar to ER
- contains calcium ions which tell muscle to contract
sarcomere
functional unit of the myofibril
-made of thick and thin filaments
thick filaments
myosin
-twisted protein with globular heads
thin filament
actin -structural protein -coiled "beads" regulatory proteins -allow/prohibit attachment between actin and myosin -tropomyosin -troponin
sarcomere bands
cause the striated appearance bands -A band: entire thick filament range -I band: only thin filaments -H band: only thick filaments - Zone of overlap: both filaments
Sarcomere lines
divide and flank the sarcomere
- Z line:
- -end of sarcomere
- -made of actin protein
- -anchor thin filaments
- M line:
- -middle of the sarcomere
- -stabilize thick filaments
structural proteins
titin: anchors a thick filament to a Z line
- accounts for elasticity and extensibility
nebulin: holds F actin together on thin filaments (runs through center)
actinin: makes up Z line
sliding filament theory
actin slides over myosin
- zone of overlap enlarges
- h band shrinks
- I band shrinks
- A band remains the same
- Z line moves closer to A band
Neuromuscular junction is made up of
- motor unit
- neuromuscular junction
- synaptic termical
- motor end plate
- synaptic cleft
- neurotransmitter
motor unit
neuron and all the muscle cells stimulated by the neuron
neuromuscular junction
point of contact between the neuron and the muscle
synaptic cleft
end of axon that contacts motor end plate
neurotransmitter
chemical released into synaptic cleft
-acetylcholine
events of muscle contraction
Ach stored in synaptic vesicles
- impulse reaches end of neuron-Ach released
- Ach crosses gap and binds to receptors
- impulse tracels through motor end plate down T-tubules to SR
- Ca2+ ions diffuse out of SR into sarcoplasm
- Ca2+ exposes the active site
- myosin binds to active site
- ATP is used and contraction occurs
- contraction continues as long as Ca2+ concentration is high
- Ach decomposed by acetylcholinesterase
- Ca ions transported back to SR
- actin and myosin links broken
- cross bridges moved back
- active site is blocked again
acetylcholinesterase
breaks down acetylcholine
tension produced by muscle
determined by
-frequency of stimulation
-number of motor units stimulated
brain tells muscle how much tension to apply
all or none law
all fibers in a motor unit full contract if stimulated
recruitment
steady increase in tension by increasing the number of contracting motor units
tetanus
muscle never begins to relax, continuous fused contraction
muscle tone
- motor units contract randomly
- tension, but no movement
- can stabilize joints, hold objects in place, maintain posture
hypertrophy
-constant, exhaustive stimulation increases the number of organelles/proteins in a fiber increases: -mitochondria -glycolytic enzyme reserves -myofibrils (more and thicker) -filaments within myofibrils Muscle fibers DO NOT reproduce
atrophy
-lack of constant motor neuron stimulation reduces organelles and proteins
-due to:
age
hormones
lack of use
nerve damage
-reversible if fiber is not dead
muscle attachments
- origin: attachment site that does not move
- insertion: attachment site that moves
- force= tension
- fascicle arrangement varies based on position of muscle
parallel muscles
-fascicles parallel to long axis
-unidirectional force
ex= biceps brachii
convergent muscles
- fan shaped
- multi-directional force
- versatility
- generates least amount of force
- not all parts pulling in same direction at same time
ex. pectoralis major
pennate muscles
feather shaped -fascicles oblique to long axis -tendon passes THROUGH the muscle -greatest force ex=deltoid, quadricep con=distance. cannot pull as far because of angle
circular muscles
-concentric fascicles around opening
-contraction decreases lumen diameter
ex= orbicularis oculi (eye)
mouth
articulations and muscle actions: uniaxial
rotation around one axis
movements: rotation (atlantoaxial); pivot joints
Angular: knee, IP joints
articulations and muscle actions: biaxial
movement occurs along 2 axes angular motions: -flexion/extension -abduction/adduction -ex: ellipsoidal joint, radiocarpal, metacarpal phelange, carpometacarpal (2-5)
articulations and muscle actions: multiaxial
-movement on all axes
-angular motion: same as biaxial
-rotation
-circumduction
ex=ball-and-socket
Actions: agonist
main muscle causing directional force
-this can be any muscle of interest
actions: antagonist
muscle that contracts to oppose the agonist
ex=bicep brachii vs tricep brachii
actions: synergist
muscle that assits/modifies movement
ex=brachialis and pronator teres
actions: fixator
muscle that stabilizes elements associated with agonists
-deltoid stabilizes glenohumeral joint
levers
lever systems modify movements
- can change:
- magnitude of force
- speed
- direction
- distance of limb movement
components of lever system
- lever(L): skeletal element
- effort (E): applied force (muscle pulling)
- fulcrum (F): joint
- resistance (R): body part or object moved
types of levers: first class
teeter totter/see saw -R opposite of E with central F ex= neck extension -E=neck extensors F=atlanto-occipital joint -R=skull
Second class levers
-wheel barrow
-E opposite of R to move R
Ex=plantar flexion
-E=calf
-F=MP joint
-R=weight of body
Third class levers
-shovel, broom
-E in between F and R
Ex= elbow flexion
-E= biceps brachii
-F=elbow joint
-R=weight distal to joint
types of skeletal muscle fibers: fast fibers
-fast acting; high energy requirements
-anaerobic
-large diameter
-densely packed myofibrils
-large glycogen reserves
-few mitochondria
-rapid, powerful, brief contractions
LIGHTER, less myoglobin
types of skeletal muscle fibers: slow fibers
-more myoglbin; slower sustained contraction
-aerobic
-smaller diameter
-longer to contract
-contract for longer time
DARKER b/c myoglobin
types of skeletal muscle fibers: intermediate fibers
- attributes of both
- similar to fast fibers
- greater resistance to fatigue
- exercise (or lack of) can change one muscle type to another
smooth muscle characteristics
-attached to hair follicles in skin
-in walls of hollow organs and blood vessels
-nonstriated
-involuntary control
-contractions are slow and sustained
-spindle shaped
-very elastic
do not fuse like muscle cells do
smooth muscles
characteristics:
- contract slowly
- resistant to fatigue
- stimulated by:
- nervous system
- hormones
- ions
- stretching
smooth muscle types: single unit
- many gap junctions
- sheets of spindle shaped cells
- contract together
ex: BV’s, digestive tract, resp. tract, urinary tract. - either closed or open, no precision
smooth muscle types: multi-unit
- no or few gap junctions
- separate fibers; contract independently
- only contract when stimulated by motor nerve
- ex: walls of large BV’s, uterus, iris of the eye
- lots of precision, degree of refinement/contraction
cardiac muscle characteristics
-striated in appearance
-involuntary control
-autorhythmic
network of fibers with intercalated disks at ends
-found only in heart
