Unit 3 Lecture 26 Flashcards
Compare and contrast the structure and function of cardiac muscle and skeletal muscle - describe the differences between cardiac muscle and skeletal muscle related to motor units, speed of contraction, and the involvement of the nervous system in contraction - understand the functions of smooth muscle compared to skeletal muscle - describe the basic structure of smooth muscle and the general steps of contraction
What are the three types of muscle?
Cardiac, smooth, and skeletal
What do all muscle types do?
Generate tension
The mechanisms in all three types of muscles rely on what themes?
- Sliding filaments (actin and myosin)
2. Regulation of cytoplasmic (Ca2+)
Calcium is required to start what?
Contraction
What is the function of cardiac muscle?
Pumps blood
- contraction of cardiac muscle around a specific volume increases pressure so the blood can be pushed through the circulatory system
What are features of cardiac muscle (compared to skeletal muscle)
- smaller cells (branched)
- less extensive T-tubule and SR system
- myofibrils also organized into sarcomeres
- extensive cell-to-cell interactions called intercalated discs
What do intercalated discs contain?
- sarcoplasm- to- sarcoplasm channels called gap junctions
- desmosomes
Define desmosomes
A structure by which two adjacent cells are attached, formed from protein plaques in the cell membranes linked by filaments
What is the anatomy of cardiac muscle?
cardiac muscle fiber, Intercalated discs, opening of transverse tubule, gap junctions, nucleus, sarcolemma (w thin/ thick filament etc) mitochondrion, desmosomes, and sarcoplasmic reticulum
What cardiac muscle functions are similar to skeletal muscle?
The sliding filament model still applies
What is the sliding filament model?
- Crossbridge cycling occurs
2. Ca2+ interacts with regulatory proteins on the thin filaments
What is the crossbridge cycle?
- starting point: Ca2+is released into the sarcoplasm, exposing myosin binding sites on actin (myosin head already up)
1. Myosin head binds to actin, forming crossbridge
2. mysosin crossbridge rotate toward center of the sarcomere (power stroke)
3. As myosin heads bind ATP, the crossbridge detatch from actin
4. Myosin heads hydrolyze ATP and become reoriented and enlarged
What cardiac muscle functions are different with skeletal muscle
- There is not enough Ca2+ released by the SR during E-C coupling to support cardiac muscle contraction
- Contractions are NOT initiated by an electrical signal
- There are no motor units, and every cardiac cell contracts with every heartbeat
- every heart beat is a “twitch” (no cardiac tetanus)
How does the body get more Ca2+?
- It gets extracellular Ca2+
- extracellular Ca2+ is required every time the muscle fibers contract beat-to-beat)
How is cardiac muscle contraction initiated?
- pacemaker cells : creates electrical (and contractile) activity which spontaneously generates AP’s
- cardiac muscle has its own rhythm = autorhythmicity
- cardiac muscle contraction is a “twitch” - not long contraction (= not tetanus)
