Muscular System Flashcards
Functions of Muscle Tissue
- Movement
- Postural Maintenance
- Joint Stabilization
- Heat Generation
- Support Organs
- Guard Orifices
Functional Properties of Muscle
Contractility - cells shorten, generating pulling force
Excitability - nerve impulses stimulate contraction
Extensibility - can be stretched back to original length by opposing muscle
Elasticity - can recoil after stretching
Types of Muscle Tissue
Skeletal, Cardiac and Smooth
Muscle Fibers
- single cells of skeletal and smooth muscles
Cardiac Muscle Fiber
long row of joined cardiac muscle cells
myofilaments
proteinaceous filaments that make up muscle fibers
sarcolemma
plasma membrane of striated muscle fiber
sarcoplasm
cytoplasm of muscle cell
sarcoplasmic reticulum
- smooth ER of muscle cell
- stores and pumps calcium ions for excitation of muscle fiber in terminal cisternae
- meshwork around each myofibril
myocardium
thick layer of cardiac muscle tissue in heart wall
intercalated discs
microscopic identifying features of cardiac muscle, they are the junctions between cells
Longitudinal Layer of Smooth Muscle
runs parallel to organs long axis
Circular Layer of Smooth Muscle
runs perpendicular to long axis of organ (around circumference)
Six Locations of Smooth Muscle
- walls of circulatory vessels
- respiratory tubes
- digestive tubes
- urinary organs
- reproductive organs
- inside the eye
Smooth Muscle Structure/Function
- non-striated cells without sarcomeres
- thin + thick filaments
- slow sustained contraction
Single Muscle as Organ
- muscle tissue
- connective tissue
- blood vessels
- nerves
Epimysium
dense CT around an entire muscle
Perimysium
fibrous CT around each fascicle
endomysium
fine sheath of CT (reticular fibers) around each muscle cell
aponeuroses
- thin flattened sheets of tendon
ex: rectus abdominis
Skeletal Muscle Structure Overview (from largest unit to smallest)
A muscle is made of bundles of fascicles which are made up of bundles of myofibers (muscle cells) which are made up of bundles of myofibrils which are made up of bundles of myofilaments
Myosin
protein component of thick myofilaments
- look like braided golf clubs
Actin
protein component of thin myofilaments
Myofibrils
- long unbranched rods of myofilaments within sarcoplasm
- specialized contractile organelles
Sarcomere
section of a myofibril between two Z lines
Dark segment of a sarcomere that contains the full length of a thick myosin filament
A (anisotropic) band
light segments of 2 adjacent sarcomeres (split by Z disc) that contains only thin actin filament
I (isotropic) band
brighter zone of the a band that contains only thick filaments and is the middle of each sarcomere
H band
(german “heller” = brighter)
very middle of sarcomere, in middle of H zone
M line
(german “Mittelscheibe)
boundaries of each sarcomere that bisect I bands, occuring where there are only actin filaments
Z disc or line
troponin
regulatory protein that holds tropomyosin in place on actin filaments, keeping muscle relaxed by preventing myosin crossbridge formation
tropomyosin
two-stranded alpha-helical coiled coil protein that wraps around actin filaments, preventing myosin crossbridge formation
crossbridge formation
when heads of myosin molecules bind to active sites on actin molecules causing muscle contraction
tunnel-like infoldings of sarcolemma that penetrate cell and carry eletric current to its interior
T (transverse) Tubules
Triad
a T-tubule and 2 terminal cisternae of the sarcoplasmic reticulum
motor unit
each motor neuron and all the muscle fibers it innervates
fine control = fewer fibers per unit (eyes)
more strength = more fibers per unit (large skeletal muscles)
synapse
connection between nerve fiber and target cell
neuromuscular junction
specific name for synapse btwn motor nerve and muscle fiber
bulbous swelling at end of motor nerve above motor end plate
synaptic knob (terminal or bouton)
gap between synaptic knob and motor end plate
synaptic cleft
small packets of neurotransmitters within a synaptic knob before they are exocytotically released into the synaptic cleft
synaptic vesicles
Skeletal Muscle Fiber Types
- naming based on speed of contraction and mode of ATP production
- Slow Oxidative (red/ dark-staining)
- Fast Glycolytic (white/ non-staining)
- Fast Oxidative (intermediate/ lighter-staining)
Slow Oxidative Fibers
- stain darkly due to abundant myoglobin
- contract slowly and for longer
ex: back muscles, support muscles
seen as dark cells in picture
Intermediate Fast Oxidative Fibers
- stain less darkly than red
- contract faster/ more powerfully than slow oxidative
- abundant in lower limbs and contract for longer periods
seen as slightly larger/lighter than dark red cells in picture:
Fast Glycolytic Fibers
- little myoglobin, don’t stain
- largest diameter of three types
- anaerobic glycolysis
- contract rapidly but fatigue easily
- found in upper limbs for large work loads
- most abundant fiber type
origin
less movable attachment
ex: biceps brachii to humerus
insertion
more movable attachment
ex: biceps brachii to tibia
two types of muscle attachments
direct/fleshy attachment - short connective tissue fibers
indirect attachment - CT forms tendon or aponeurosis
4 Fascicle Arrangments
- convergent (pec major)
- parallel (biceps brachii)
- circular (AKA sphincters, ex: orbicularis oris)
- pennate (“feather like”)
Convergent Fascicle Arrangement
- broad origin with fascicles converging on tendon at insertion
Parallel Fascicle Arrangement
- fascicles run parallel to long axis
Circular Fascicle Arrangement
- arranged in concentric rings
- surround body openings and AKA sphincters
ex: orbicularis oculi
Pennate Fascicle Arrangement
- feather-like with short fascicles attaching obliquely to tendon
- Unipennate - fascicles in one side of tendon
- Bipennate - fascicles in either side of tendon
- Multipennate - fascicles on all sides of tendon
4 Functional Groups of Muscle
- Prime Mover
- Antagonist
- Synergist
- Fixator
Prime Mover
- primarily responsible for producing a certain movement
ex: diaphragm for inspiration
Antagonist
- opposes or reverses movement of prime mover
ex: internal intercostals in inspiration (depress rib cage, causing exhalation)
Synergist
- helps prime mover by adding force and/or reducing undesirable movement
ex: external intercostals in inspiration (elevate ribcage)
Fixator
- type of synergist that holds a bone firmly in place
Muscle Naming Criteria
- Location (intercostal)
- Shape (deltoid)
- Relative Size (maximus/minimus, longus/brevis)
- Direction of Fascicles and Fibers (transversus)
- Attachment Location (sternocleidomastoid)
- Number of Origins (bi-, tri-, quadriceps)
- Action (flexor, extensor)
