Muscles Flashcards
What are the different types of muscles?
Striated: cardiac and skeletal!
smooth
How is a muscle fiber innervated?
by only one nerve ending!!
though one nerve ending can innervate multiple muscle fibers…
What is the structure of a skeletal muscle?
it is made of fascicles!
which contain bundle of muscle fibers/cells (myofiber)
within each fiber you have myofibrils (composed of thick and thin filaments)
What is a myofribril?
composed of many repeating sarcomeres
which are basic contractile units
Explain the different components of a sarcomere.
lengh: z line to z line
I band: thin filaments (actin) LIGHT
H zone: thick filaments (myosin)
A band: overlapping DARK
M line: has proteins to anchor thick filaments
Z line: attach actin
Tell me about the thick filaments
aka myosin
it binds actin @ the globular head
has ATPase activity
Tell me about thin filaments
aka actin
has binding site for myosin
but at rest it is blocked by troponin-tropomyosin complex
when active: Ca binds to troponin C –> tropomyosin goes away!
the binding site is now free
What is the function of T-tubules?
invagination of sarcolemma (plasma membr) into muscle fiber
- brings the AP
- next to SR
- have DHPR that sense voltage
What is the function of the SR?
stores calcium!
released by activating RyR
What is the function of SERCA?
pump calcium back into the SR
-works with ATP
What happens in Excitation-Contraction (EC) coupling?
- Ca entry into axon causes fusion and exocytosis of Ach into NMJ
- Ach binds to channels that cause sodium influx
- Causes depolarization-> AP
- AP travels along sarcolemma and into the T-tubule to bring deep into the muscle
- The depolarization (by Na) activates DHPR (voltage sensor)
- DHPR has a conformational change that activates RYR
- BOOM! Ca is released from SR
- Ca initiates muscle contraction
- Ca binds to troponin C: disables the complex
- Myosin can bind actin
- form crossbrides! power stroke - SERCA pumps Ca back into the SR: muscle relaxes
Cross bridge cycling
Can stop at 2 spots
- When have relaxed muscle but high actin affinity
- Actin and myosin are attached and can’t separate cuz no ATP (rigor mortis)
Explanation:
- myosin head binds ATP
- ATP hydrolyzed: high energy configuration
- Ca comes in and binds to tropomyosin: lower affinity for actin so get’s out of the way and leaves the myosin binding site open
- tin and myosin bind!
- remove the ADP+Pi = powerstroke
- ATP binds to head again: cause detachment of myosin and actin
How do you regulate the strength of a muscle contraction?
skeletal muscle
- twitch summation: multiple AP’s can add up cuz accumulate Ca
- recuit more motor units: stronger contraction
- thicker muscle fibers: if have sarcomeres in parallel (stacked) the forces will be added up
- length-tension relationship: sarcomeres need to be at ideal length at the start of contraction (if too long not enough cross bridges but if too short steric hindrance)
What are the differences between skeletal muscle and cardiac muscle? [striated muscles]
- skeletal doesn’t require extracell Ca (DHPR voltage sensor)
- cardiac needs it to release Ca from SR (CICR) - skeletal muscle can recruit more motor units
- cardiac doesn’t have summation so vary amount of Ca
So now that we finished striated muscle. What’s different in smooth muscle?
no T-tubules! instead have coeval (invaginations)
instead of z-lines have dense bodies
