Biology 4

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Resting Neurone

1. More K+ ions inside the cell and more Na+ out of the cell. 

2. (Using ATP), Na+/K+ oumos can AT both ions accross the membrane. 

3. 3Na+ out of cell for every 2K+ into cell. 

4. Membrane is more permeable to K+ so many diffuse out of cell (leaky)

5. Maintains voltage of -60mV

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The Refractory Period

1. Chance for cell to recover and restore the ion balance using the Na+/K+ pump.

2. Difficult for another AP to occor without cell recovery. 

3. Ensures that APs are being trasmitted in 1 single direction. 

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The Mylinated Sheath

1. Mylinated sheath = fattym insulative material

2. Specilised cells = Schwaan cells 

3. Sheath prevents the diffision of ions, so transmission of ions consists by "jumping" from 1 node of Ranvier to another = SALTATORY CONDUCTION 

4. Local current is also elongated to ensure ions "jump"

5. Reduces distance travelled by ions therefore APs = faster

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The synapse

1. AP arrives at synaptic knob of the pre-synpatic neurone. 

2. Triggers the Ca2+ v.g.c to open causing Ca2+ to diffuse in. 

3. Influx of Ca2+ causes vesicles of ACETYCHOLINE to duse with the presynaptic membane. 

4. Via exocytosis, ACETYLCHOLINE is released into the synaptic cleft, which diffuses down the concentration gradient and into the post-synpatic membane. 

5. ACETYLCHOLINE binds to its receptors on the Na+ channels causing channels to open and letting the Na+ to diffuse in. 

6. Influz of Na+ triggers the AP as normal. 

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Acetylcholine

1. Acetylcholine is broken down with ACETYLCHONESTERASE 

2. products are recycled

3. If not, effective endless nerve impulses -> paralysis or eventually death due to ASPYXIATION

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Roles of the Synapse

1. Convergence: signals from different parts of the central part, can trigger the same response. 

2. Divergance: Allows a signal to be transmitted from 1 neurone to several areas simultanseously. 

3. Allows movememt of signal in one direction

4. Low level signals can be amplified with summation

5. ACCLIMITISATION: neurones run out of vesicles and become fatigued preventing overstimulation 

BIGGER SIGNALS DEPEND ON THE INTENSITY OF STIMULUS AND THE FREQUENCY OF AP TRANSMISSIONS. 

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Adrenaline

1. every receptor of Adrenaline has an enzyme ADENYL CYCLASE 

2. Adrenaline = 1st messenger; from blood binds to the crecptor on target tissue, activating ADENYL CYCLASE

3. ADENYL CYCLASE: converts ATP-> cAMP

4. cAMP= 2nd messenger and actvates a cascade of enzyme controlled reactions. 

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