Section 6:Nervous coordination and muscles Flashcards
What are the two main features of the synapse?
Undirectionality and summation
Three points
What is meant by undirectionality and why it occurs?
Postsynaptic and presynaptic
Passes impulses from presynaptic membrane to postsynaptic membrane. This is because:
* Synaptic vesicles containing neurotransmitter only produced in presynaptic neurone
* Receptor protiens for neurotransmitter only in postsynaptic membrane
* Channel proteins for neurotransmitter for Na+ only on postsynaptic membrane
What is meant by summation?
Ensures that the neurotransmitter levels reach and exceed the thershold to trigger an action potential
What are the two types of summation?
Spatial and temporal
Describe spatial summation
No. of presynaptic neurones form synapses with one postsynaptic neurone~each neurone releases transmitter,exceeds threshold + initatiates action potential and causes depolorisation
Describe temporal summation
No. of action potentials have to arrive at the same presynaptic neurone before there wiill enough transmitter released to exceed threshold + initiate an action potential
Describe the difference between low and high frequency action potential for temporal summation
- Low-frequency~neurotransmitters broken down rapidly=Conc is below threshold to trigger an action potnetial
- High-frequency~neurotransmitter release in a short time=Conc is above threshold to trigger an action potential
What are the two types of syanpses?
Excitatory and inhibitory
Describe the role/function of an excitatory syanspe
Impulse passed from presynaptic neurone to a postsynaptic neurone~new action potential is created in postsynaptic neurone=action potential is passed from presynaptic neurone to postsynaptic neurone
Excitatory neurotransmitter is acetylecholine
Describe the basic role/function fo an inhibitory synapse
Impulses can be stopped/slowed at synapses by neurotransmitters~makes it less likely that an action potential is created
Inhibitory neurotransmitter is GABA
Four points
Describe what happens at an inhibitory synapse
- Presynaptic neurone releases neurotransmitter that binds to Cl- channels on postsynaptic membrane~open channels,Cl- flow into postsynaptic neurone via FD
- Neurotransmitter causes K+ channels to open=K+ move out of neurone into the synapse via SD
- Combined effect of Cl- diffusing in and K+ diffusing out~inside of postsynaptic membrane becomes more negative than resting (hyperpolorised)
- Less likely a new action potential with be created as a larger influx of Na+ will be needed
Explain how the release of acetylcholine reduces the membrane potential of the postsynaptic membrane
Acetylcholine binds to receptor site of Ca2+ channels causing them to open
Ca2+ diffuses in which causes the membrane to depolorise
Explain how a lower temperature leads to slower nerve impulse conduction
Decrease in temeprature,decreases KE=Decreasing the rate of diffusion of Na+ ions
Takes longer for depolorisation to occur and to trigger an action potential
Give a basic description of each
Give three factors that affect the speed of nerve impulse conduction
- Axon diameter~greater diameter,greater rate of transmission
- Temperature~speeds up rate of diffusion via increased KE
- Myelinated sheath~insulates the axon via saltatory conduction
Threshold
What does the ‘all or nothing’ principle mean?
Action potential can only be generated if the stimulus recahes and exceeds a certain theshold
An axon cannot send a mild or strong response
Two factors
What affects the perception of the size of an action potential?
- Number of impulses sent
- Having different neurones with different theshold values
Describe how the strength of impulses affect action potential
- Increased strengths of stimuli will give increased frequency of action potential
- Size of action potentials remain the same
How is it caused
What is a refractory period?
A brief period of time between the triggering of an impulse and when it is available for another
Voltage gated Na+ channels closeprvent inward movement of Na+
Three points
What are the consequences of a refractory period?
- Impulses can only travel in one direction
- Produces discreat impulses
- Limits the number of action potentials
Describe the events at a synapse
- Action potential arrives at the end of the neurone~Ca2+ channels opne in postsynaptic membrane
- Ca2+ enter by FD=causes vesicles containing neurotransmitter to fuse with presynaptic membrane
- Neurotransmitter diffuse across synaptic cleft,binds to receptor sites on postsynaptic membrane
- Na+ channels open and Na+ enters postsynaptic membrane
- Action potential is generated~neurotransmitter hydrolysed and diffuses back across the cleft into presynaptic nueorne where it is resynthesized
Describe the two ways in which drugs can affect synapses
- Stimulate~creates more action potential=drug mimmics effect of neurotransmitter or inhibits enzymes which breaks down neurotransmitter
- Inhibit~prevents action potential in postsynaptic neurone=drug could inhibit release of neurotransmitter or block receptor on Na+/K+ channels on postsynaptic membrane
What are the three types if muscles and what kind of control is there over each?
- Skeletal~voluntary
- Cardiac~involuntary
- Smooth~involuntary
What are three charcateristics of all muscle fibres?
- Made of muscle cells fused together so they share nuclei and cytoplasm
- Contains lots of mitochondria and sacroplasmic reticulum
- Surrounded by a membrane called the sarcolemma
What fillaments are in each band
Describe the structure of a sacromere
A-band=myosin and actin fillaments
I-band=actin fillaments
H zone=myosin fillaments
Z line
What are three differences between actin and myosin fillaments?
- Myosin=attached to centre of sacromere~long-rod shaped fibrous proteins with ‘head’ and ‘tail’
- Actin=attached to Z line~2 strands twisted around each other~associated with 2 proteins (tropomyosin and troponin)
When a muscle contracts what changes happen to the sacromere?
- I band is narrower
- Z lines move closer
- H zone is narrower
- A band stays the same length
