Muscular System Flashcards
skeletal muscles
functions
characteristics
Main Functions:
* Movement
* Heat production
* Posture
has crosswise stripes, or striations
Contractions can be voluntarily controlled
Characteristics of skeletal muscle
fibres:
* Excitability
* Contractility
* Extensibility
contract due to acetylcholine and relax because acetylcholine esterase breaks it down
Cardiac Muscle
- Striated involuntary muscle
- Only in the heart
- Intercalated disks between fibres – forms continuous, electrically coupled mass (syncytium)
- Single impulse across sarcolemma – coordinated pumping action
- Self-exciting
- Prolonged contractions
- won’t produce tetanus
- doesn’t fatigue (use up all the ATP available)
- Sparse SR, forms diads with T-tubules
- Mechanism of contraction and energy sources
Smooth Muscle
also called nonstriated, involuntary, or visceral muscle
Found in walls of hollow visceral structures such as digestive tract, blood vessels, and ureters
changing pupil diameter
two types of smooth muscle multiunit (if one fiber is stimulated then the others are as well ) and visceral
has autorhythmicity like cardiac muscle but used for peristalsis
aCH and norep
multiunit helps to move hormones
- No T-tubules, loosely arranged SR
- Ca++ comes from outside of cell, binds to calmodulin to trigger contraction
Overview of the Muscle Fibre
(Cell)
Sarcolemma – cell membrane
* Sarcoplasm – cytoplasm
* Lots of mitochondria, several nuclei
Sarcomeres
smallest functioning unit of muscle
* composed of actin (thin) and myosin (thick) protein myofilaments
* one sarcomere extends from “Z Line to Z line
causes striations
Myofibrils
“straw-like” structures extending length of cell (about 1-3 µm in diameter)
* composed of myofilaments
Myofilaments
Very fine filaments of 2 types: thick filaments and thin filaments
* Filaments are organized into sarcomeres
4 different kinds of protein molecules make up myofilaments -thin filments
Myosin
* Actin-2 helical strands of fibrous actin with binding sites (strung together like beads)
* Tropomyosin -Protein; wraps around within the groove formed by helix of actin
* Troponin -3 binding subunits binds to actin, tropmysosin, ca2
Thick Filaments
Myosin
* “thick” rods shaped like a golf club
Myosin Heads
* contain ATPase
* have binding site for actin myofilament
Mechanism of Contraction
Excitation of the Sarcolemma
Motor neurons connect to the sarcolemma and form a
neuromuscular junction
* Neurotransmitter acetylcholine (Ach) is released and initiates an electrical impulse
Mechanism of Contraction
Sliding Filament Theory
ATP binds to myosin head
ca released and binds to trop
troponin/tropmyosin binding complex is changed
actin binding sites unblock so myosin heads can bind
ATP realeased
ADP released and actin/myosin bond is broken
. If ATP and Ca2+ are available, more cross bridges are formed
Mechanism of Contraction
Relaxation
- SR actively pumps Ca++ back into sacs
- Tropomyosin moves back to cover actin active sites – myosin heads are blocked
Energy Sources for
Contraction
ATP
* Hydrolysis of ATP
* Muscle fibres must continuously resynthesize ATP
* Creatine phosphate (CP) can be used as backup energy
* ATP and CP resynthesized by cellular respiration
Glucose –
catabolized in sarcoplasm and mitochondria, energy
transferred to ATP and CP molecules
* glucose stored as glycogen (uninterrupted supply)
* glucose from blood stream
Oxygen as energy source
from blood –carried by hemoglobin, aerobic respiration
* Stored in cells attached to myoglobin
Anaerobic Respiration
pyruvic acid will be converted to lactic acid that accumalates in the cell
* diffuses out of the cell and taken to liver
* can be converted to glucose by liver or to pyruvic acid by cardiac muscle
Motor Unit**
is a nerve cell that transmits an impulse to a muscle, causing contraction
Twitch Contraction
quick, jerky responses to a stimulus— are
laboratory phenomena and do not play a significant role in
normal muscular activity
Latent period – impulse along sarcolemma and down T-tubules resulting in release of Ca++ ions
2. Contraction phase – binding of Ca++ to troponin and sliding of myofilaments
3. Relaxation phase – sliding ceases
“All Or None Principle”
of Muscle Contraction
when motor unit receives a stimulus strong enough to generate a response. The muscle fibres in the unit will all contract at the same time to the most possible extent
Muscles exhibit graded contractions (when stimuli is applied to a nerve) in two ways
Multiple Motor Unit (Spatial) Summation
* increasing the strength of stimulus increases the strength of contraction by recruiting more units
Wave Summation and Tetanization
* increasing frequency of stimulation to a muscle cell before it has relaxed from a previous stimulus building on the stimuli causes a wave pattern sustained contraction is called tetany or tetanus
isometric**
Types of Contractions
- muscle contractions that do not produce movement;
- e.g. Postural muscles maintain same length
Isotonic
Types of Contractions
- Contraction of a muscle that produces movement at a joint
- e.g. Most arm and finger movements
Types of Smooth Muscle
Visceral (single unit) Muscle
- Large sheets, gap junctions between individual fibres
- Muscular layer in walls of hollow structures
- Autorhythmicity
- Example of movement: peristalis
Multiunit Muscle
Types of Smooth Muscle
Made up of many independent single-cell units
* Responds to nervous system input
* Can be found as sheets, bundles, or single fibres
