Ch 9 Part 2) Muscles Flashcards
1
Q
Excitiable Cells
A
- Nuerons and Muscle Cells are both excitable
- Capaible of AP
- AP crosses from Nueron to Muscle cell via Nuerotransmitter Acetylcholine (ACh)
- Ion channels play major role in changing channels
- Chemically gated) activated via chemical messanger (nuerotransmittter)
- Voltage Gated) Activated via voltage changes in membrane potential
2
Q
Nueromuscular Juntion
A
- Point where Axon branches end and form synapse with the muscle
- Also called the motor end plate
3
Q
Events At Nueromuscular Juntion (6)
A
1.)AP arrives at axon terminal
2.)Voltage-gated calcium channels open, calcium enters
motor neuron
3.)Calcium entry causes release of ACh
neurotransmitter into synpatic cleft
- )ACh diffuses across to ACh receptors (Na+ chemical
gates) on sarcolemma
5.)ACh binding to receptors, opens gates, allowing Na+
to enter resulting in end plate potential
6.)Acetylcholinesterase degrades ACh
4
Q
Generation of AP across Sarcolemma
A
- Sarcolemma (plasma membrane) is polarized meaning there is a voltage across the membrane
- Three steps
- Generation of End Plate (nueromuscular juntion) Potential
- Na+ diffuses into cell (some K+ out) making inside less negatice
- In a local depolarization event called End Plate Potential
- Depolarization
- Generation and propagation of the AP
- Once threshold is passed, Na+ channels open which leads to muscle fiber contration
- This potential runs down the sarcolemma along voltage gated channels
- Repolarization
- Resoration of resting Conditions
- Na+ channels close and K+ channels open
- K+ channels bring membrane back to orginal voltage (no hyperpolarzation
- Refractory Period) Muscle fiber cannot be stimulated until repolarization is complete.
5
Q
Excitation-Contraction (E-C) coupling
A
- Events that transmit AP along sarcolemma (Excitation)
are coupled to sliding of myofilaments (Contraction)- AP propagates along sarcolemma into T tubules where voltage protiens sense a change and release Ca2+
- Ca2+ leads to contraction
6
Q
Calcium Concentration Effects
A
- Low Ca2+ concentration
- Tropomyosin blocks active sites on actin
- Myosin heads cannot attach to actin
- Muscle fiber remains Relaxed
- Higher Ca2+ concentation
- Ca2+ binds to trononin
- Troponin changes shape of tropomyosin moving it away from the acitin active sites
- Myosin heads attach to actin forming the cross bridge
7
Q
Four Steps of the Cross Bridge Cycle
A
- Cross bridge formation)
- High-energy Myosin head attaches to Actin thin filament active site
- Working (power) stroke)
- myosin head pivots and pull thin filament toward M line
- Cross bridge detachment:
- ATP attaches to myosin head, causing cross bridge to detach
- Cocking of myosin head:
- energy from hydrolysis of ATP “cocks” myosin head into high-energy state
- This energy will be used for power stroke in next cross bridge cycle
8
Q
Rigor Mortis
A
- 3-4 hours after death the muscle stiffens because ATP is no longer synthsized
- ATP releases muscle contraction and starts a new one.
9
Q
Diffrent types of contraction
A
- Isometric Contraction
- Muscle tension increases but does not shorten
- Will not exceed load (pushing on wall)
- Isotonic Contraction
- Muscle shortens because tension exceeds the load
- (picking up a book)
10
Q
Motor Unit
A
- Each muscle is served by at least one motor nerve
- Motor nerve contains hunderds of axons for motor nuerons
- Axons branch which form NMJ with each single fiber
- Motor Unit
- Nerve-Muscle functional unit
- Each fiber recives imput from one nueron but each nueron can controll up to 4 to several hundred fibers
- The smaller the number of nerve fibers the greater the control of the mucsles (Eyes vs hip muscles)
11
Q
Muscle Twitch
A
- Simplest contraction resulting from a muscle fiber’s response to a single Action Potential from motor neuron
- Three Phases
- ) Latent Period) events of excitation-contration coupling
- No muscle tension produces
- ) Period of Contraction) Cross bridge formation
- Muscle tension increases
- Period of relaxation) Ca2+ reenters into SR
- Tension declines to zero
- A muscle contracts faster than it relaxes.
- Diffrences in strength and duration is due to variation in metabolic properties.
12
Q
Graded Muscle Response
A
- A normal, smooth muscle contraaction
- Varries in strength based on demands placed on it
- Referred to as Graded Response
- Brain Derermines strength of muscle contraction by
- The rate of AP’s firing along axon (frequency)
- Number of motor nuerons (Strength)
13
Q
Response to Change in Stimulus Frequency
A
- The Nervous system achives greater muscular force by increasing the Firing Rate (frequency) of motor nuerons.
- If twitches are delivered in rapid sucession, the subsequent twitches will be stronger than the first
- This summation of twitch strength is known as Wave (Temporal) Summation.
- Muscle fibers do not relax completeley between twitches, so each twitch produces more force than the last.
14
Q
Tetanus (different types)
A
- Unfused (incomplete) tetanus
- Occurs when muscle stimilus frequency continues to get stronger
- Will eventually sustain a quivering contraction
- Fused (complete) Tetanus
- Muscle tension reaches maxiumum when stimuli frequency continues to increase
- Contractions “fuse” into one long contraction which leads to muscle fatuige.
15
Q
Response to Change in Stimulus Strength.
A
- Recruitment (Multiple Motor unit summation)
- (stronger) Stimilus is sent to more muscle fibers
- Leads to more precise control and
- Types of Stimilus Involved
- Subthreshold Stimilus) not strong enough to cause a contraction
- Threshold Stimulus) Stimulus is strong enough to cause at least one contraction
- Maximal Stimulus) Strongest stimilus that produces maximal force
- All motor units are used
