Lecture 25. Muscle and Muscle Contraction Flashcards
What do all muscles do?
Transduce chemical and electrical commands to produce a mechanical response (motor output)
What are the two types of muscular contraction?
Isometric and isotonic
What are the three types of muscle?
Cardiac
Smooth (glands, blood vessels, gut, etc)
Skeletal (striated)
What is the structure of cardiac muscle?
Myocytes 15 μm in diameter, 100 μm length
Linked together via intercalated disks (irregular)
Electrically coupled via gap junctions
Similar to skeletal muscle (sacromeres, T tubules and SR)
Properties of cardiac muscle cells
Differences between atria, conducting system
and ventricles
Striated like skeletal muscle
Shows myogenic activity
Cells are electrically coupled
T system (ventricular muscle)
Controlled by autonomic nervous system and hormones
What are the properties of smooth muscles?
Muscle of internal organs (blood vessels, gut, glands etc)
Heterogeneous
Can maintain a steady level of tension (tone)
Produce slow long lasting contractions
Spindle-shaped cells linked together by mechanical and electrical junctions
No cross striations but does contain actin and myosin: loose lattice
Innervated by the ANS (varicosities)
Very plastic properties: can adjust length over a much wider range than skeletal or cardiac muscle
What is the individual unit of muscle?
Sacromere
What does the force produced by muscle contraction depend on?
- Number of active muscle fibres
(recruitment) - Frequency of stimulation (temporal summation, tetanus vs twitch)
- Rate at which muscle shortens
- Cross sectional area of the muscle
- Initial resting length of the muscle
What is the thick filament in a sacromere called?
Mysoin
What is the thin filament in a sacromere called?
Actin
The cross-bridge cycle
- ATP binds to myosin head, causing the disassociation of the actin-myosin complex
- ATP is hydrolysed, causing myosin heads to return to their resting conformation
- A cross-bridge forms and the myosin head binds to a new position on actin
- P is released. Myosin heads change conformation, resulting in the power stroke. The filaments slide past each other
- ADP is released
What are the properties of slow-twitch fibres?
Metabolism: oxidative phosphorylation
Number of mitochondria: High
Glycogen storage: high
Contraction rate: slow (~15 mm per second)
Relaxation rate: slow
Can maintain tension for prolonged periods Resistant to fatigue
What is an example of slow-twitch fibres?
Muscles that maintain body posture such as soleus muscle of lower leg
What are the properties of type IIa (fast oxidative fibres)?
Metabolism: oxidative phosphorylation
Number of Mitochondria: very high
Glycogen storage: high
Fatigue resistant
What are the properties of type IIb (large diameter, white muscle)
Metabolism: glycolytic (anaerobic)
Number of mitochondria: fewer (limited blood supply)
Glycogen storage: high
Rapid fatigue
Required for short periods i.e. sprinting
