3.6.2 nervous coordination

• Explain resting potential

  3Na+ actively transported out of axon, 2K+ actively transported into axon both using carrier proteins, occurs due to sodium potassium pump More Na+ in tissue fluid, more K+ in cytoplasm of axon, an electrochemical gradient is created Facilitated diffusion moves Na+ into axon and K+ out of axon, channel protein has gates which are closed for Na+ movement (membrane is less permeable to Na+) Inside of axon is -ve charged compared to tissue fluid making it polarised
• What’s a nerve impulse

  Reversal of electrical potential difference across the axon membrane Has resting potential and action potential
• What happens during depolarisation

  Energy from a stimulus causes some sodium voltage gated channels in axon to open, Na+ diffuses (facilitated diffusion)into axon, reverse potential difference across membrane 40mV action potential is established
• What happens during repolarisation

  40mV action potential is established, voltage gates on Na+ channels close, voltage gates of K+ open, electrical gradient allows K+ to diffuse out of axon
• What happens during hyperpolarisation

  K+ ions diffusing out of axon cause an overshoot of electrical gradient, inside of axon is more negative than tissue fluid Gates on K+ ion channels are closed Sodium potassium pump continues, resting potential reestablished
• What’s action potential

  Neurones voltage increase beyond a set point, continual wave of depolarisation, generates nervous impulse
• What’s the passage of an action potential across an unmyelinated axon

  Resting potential, Na+ in tissue fluid, -ve charge inside axon, axon membrane is polarised Depolarisation, Na+ moves into axon, inside is now +ve, membrane is depolarised Localised electrical current by Na+ cause sodium voltage gates channels to close, potassium ones open, moves along axon membrane Axon membrane behind action potential is repolarised, sodium potassium pump continues across the axon
• What’s the all or nothing principal

  If depolarisation doesn’t exceed threshold voltage then an action potential isn’t generated If a stimulus triggers depolarisation, there will be a peak to the same max voltage, larger stimuli increase frequency of action potentials Ensures animals only respond to large stimuli
• What’s the passage of an action potential across a myelinated axon

  Action potential can occur at nodes of ranvier, action potential jumps between adjacent nodes this is called saltatory conduction Action potential passes along a myelinated neurone faster
• What’s the refractory period

  After an action potential is created Na+ voltage gated channels close prevents Na+ moving into the cell
• What’s the importance of the refractory period

  Action potentials propagated in one direction, action potential move from active to resting, cannot be propagated into a refractory region, move in one direction Production of discreet impulses, new action potential can’t be formed immediately after another due to refractory period, ensures action potentials are separated Limits number of action potentials, action potentials are separated from each other, only a certain amount can pass in a given time, strength of stimulus that can be detected is limited
• What shows the strength of a stimulus

  Frequency of action potentials
• What factors effect the speed of conduction of an action potential

  Myelination and saltatory conduction Axon diameter Tenperature
• How does myelination and saltatory conduction effect speed of an action potential

  Myeline sheath acts as electrical insulator, causes action potential to jump between adjacent nodes of ranvier this is called saltatory conduction
• How does the diameter of an axon effect the speed of an action potential

  Greater axon diameter means faster speed of conductance, less leakage of ions, easier to maintain membrane potential
• How does temperature effect the speed of an action potential

  Only in cold blooded animals Higher temperature increases rate of diffusion for ions Enzymes work faster at higher temps up to an optimal temp, respiration releases energy for active transport, faster movement of ions Higher temps increase the speed and strength of muscle contractions
• What’s a synapse

  Where one neurone communicates with another or with an effector
• Structure of a synapse

  Synaptic cleft, small gap Presynaptic neurones, releases neurotransmitter Synaptic knob, swollen end of Presynaptic neurone, lord of mitochondria, manufactures neurotransmitters Synaptic vesicles, stows neurotransmitters Postsynaptic neurones, specific receptor proteins on membrane to receive neurotransmitter
• What’s a neuromuscular junction

  Motor neurone meters skeletal muscle fibre, many of these junctions spread across muscle for rapid and coordinated contraction Nerve impulse received at junction, synaptic vesicles fuse with Presynaptic membrane releasing acetylcholine, diffuses into Postsynaptic membrane, more permeable to Na+, Na+ enters, membrane depolarised, acetylcholine broken down by acetylcholinesterase, choline and acetyl diffuse back into neurone, recombine using energy from mitochondria
• What’s unidirectionality

  Synapses only pass info from Presynaptic neurone to Postsynaptic neurone
• What’s summation

  Spatial summation, different Presynaptic neurones release enough neurotransmitter to exceed threshold of Postsynaptic neurone, trigger new action potential Temporal summation, single Presynaptic neurone releases neurotransmitter lots of times in a short period, if the conc of neurotransmitter exceeds threshold of Postsynaptic neurone, new action potential is triggered
• What’s inhibition by inhibitory synapses

  Presynaptic neurone releases neurotransmitter binds to Cl- protein channels on Postsynaptic neurone, Cl- protein channel opens, Cl- moves into Postsynaptic neurone by facilitated diffusion, K+ channels also open, K+ moves out of Postsynaptic neurone into synapse, inside of Postsynaptic membrane is more -ve than outside, hyperpolarisation, more Na+ ions needed to produce action potential
• Cholinergic synapse vs neuromuscular junction

  Both neurotransmitters acetylcholine transported by diffusion Both have receptors on which bind to acetylcholine causing influx of Na+ Both use Na+ K+ pump to depolarise axon Both use acetylcholinesterase to hydrolyse acetylcholine NMJ Links neurones to muscle Only involves motor neurones Action potential ends CS Links neurones to neurones, or neurones to effectors Uses motor, sensory and intermediate neurones A new action potential can be produced
• How movement of K+ and Na+ controlled

  Channel proteins across the phospholipid bilayer, contain specific gates,if open all the time ions can move through by facilitated diffusion Carrier proteins actively transport Na+ and K+ ions through the sodium potassium pump