6B Nervous coordination

• What is a resting potential?

  The difference in electric charge between the inside and outside of a neuron's cell membrane when no impulses are being transmitted.
• What is the resting potential (number)?

  -70MV
• Which factor establishes and maintains the resting potential?

  - Na/K pump.
• How does the Na/K pump maintain resting potential?

  The membrane is more permeable to K+ than Na+ so It actively transport 3 Na+ out for every 2 K+ in, meaning there is a larger conc of positive ions outside the axon than inside.
• What is the first step of an action potential?

  Stimuli excites the cell membrane of the neuron, causing a sodium ion channel to open. The membrane becomes more permeable to sodium allowing them to diffuse down the electrochemical gradient into the neuron. This makes the inside of the neuron less negative.
• What is the second step of an action potential?

  Depolarisation - if the potential difference reaches -55MV, more sodium channels open causing more sodium to rapidly diffuse into the neuron.
• What is the third step of a action potential?

  Repolarisation - at a potential difference of +30MV the sodium channels close and potassium channels open. The membrane is more permeable to potassium so potassium ions diffuse out, decreasing the positivity inside the neuron.
• What is the fourth step of an action potential?

  Hypoerlarisation - potassium ion cannels are slow to close so there is a slight overshoot where too many ions diffuse out of the neuron. This causes the potential difference to be slightly more negative than the resting potential.
• What is the fifth step of an action potential?

  Resting potential - the ion channels are reset and the Na/K pump returns it to the resting potential.
• What is the sixth step of an action potential?

  Refractory period - ion channels are recovering and cannot be opened for a period of time.
• What is a wave of depolarisation and why does it occur?

  When an action potential occurs some sodium ions diffuse sideways causing sodium ion channels nearby to open and sodium ions diffuse into the next region.
• Why do refractory periods occur?

  To ensure action potentials don't overlap but pass along as discrete (separate) impulses. To ensure action potentials are unidirectional (one way). To ensure there is a limit to how many impulses can be transmitted in a certain time.
• What is the all or nothing principle?

  if the threshold is not reached, an action potential will not fire. If the threshold is reached, an action potential will fire independent of the size of the stimulus. A bigger stimulus wont cause a bigger action potential but will increase frequency.
• What three factors affect the speed of action potentials?

  myelination, axon diameter, temperature.
• How does myelination affect the speed of action potentials?

  Schwann cells make up myelin sheaths that act as an electrical insulator for neurons. Between these Schwann cells are nodes of ranvier where sodium ion channels are concentrated. In a myelinated neuron, depolarisation occurs at the notes of ranvier where sodium ion channels are concentrated. because of this the cytoplasm conducts enough electrical charge to depolarise the next node. This is called saltatory conduction and is faster than conduction in a non myelinated neuron.
• How does axon diameter affect the speed of action potentials?

  the greater the axon diameter, the faster the conduction. This is because there is less resistance to the flow of ions in the cytoplasm.
• How does temperature affect the speed of action potentials?

  an increase in temperature increases the speed of conduction.This is because it increases the speed that ions diffuse. But after 40 degrees the proteins denature
• Describe the process of synaptic transmission?

  when an action potential reaches the presynaptic knob, it causes the vesicles to fuse with the presynaptic membrane and release neurontransmitters into the synaptic cleft. the neurotransmitters then bind to complimentary receptors on the post synaptic membrane. when neurotransmitters bind to the specific receptors, it can trigger an action potential in the post synaptic neuron. neurotransmitters are then removed from the cleft and broken down by enzymes.
• What do we call synapses that use acetylcholine?

  Cholinergic synapses.
• Describe the process of synaptic transmission in a cholinergic synapse.

  action potential arrives at the synaptic knob. This stimulates voltage gated calcium ion channels to open. The calcium ions diffuse into the synaptic knob. this stimulates the vesicles to fuse with the presynaptic membrane.this releases ACh into the synaptic cleft (exocytosis). ACh diffuses across the synaptic cleft and binds to cholinergic receptors on the post synaptic membrane. Sodium ions in the postsynaptic neuron then open. This causes depolarisation and an action potential occurs. ACh is removed from the cleft and broken down by AChE (enzyme).
• What are the two types of neurotransmitters?

  excitatory and inhibitory.
• What do excitatory neurotransmitters do?

  Depolarise the post synaptic membrane increasing the chance of action potentials.
• What do inhibitory neurotransmitters do?

  Hyperpolarise the post synaptic membrane decreasing the chance of an action potential.
• What is summation?

  The idea that all of the effects of neurotransmitters are summed together to determine weather the action potential will fire.
• Give and example of an exhitatory neurotransmitter.

  ACh in the CNS.
• Give an example of an inhibitory neurotransmitter.

  ACh in the heart.
• What are the two types of summation?

  Spatial and temporal.
• What is spatial summation?

  When many neurons connect to one and the net effect of the neurotransmitters is summed.
• What is temporal summation.

  When many neurotransmitters arrive in quick sucession and the net effect is summed.
• What are neuromuscular junctions?

  Synapses between a motor neuron and muscle cell.
• Describe synaptic transmission at neuromuscular junctions.

  action potential occurs.Calcium ions diffuse into the neuron.ACh containing vesicles fuse with the presynaptic membrane.ACh diffuses across the synaptic cleft.ACh binds to nicotine cholinergic receptors.
• What are the differences between cholinergic synapses and transmuscular junctions.

  Cholinergic synapse

  • ACh neurotransmitter

  • Found between neurons

  • Can be exhitatory or inhibitory

  • Stimulated by action potential

  
  

  Neurotransmuscluar junction

  • ACh neurotransmitter

  • Found between a motor neuron and a muscle

  • Only excitatory

  • Stimulated by action potential
• Name 5 different ways that drugs can affect the action of neurotransmitters at synapses.

  drugs that are the same shape as neurotransmitters (agonists) so they mimic the neurotransmitters actions and cause more receptors to be activated. Some drugs inhibit the enzyme that breaks down the neurotransmitter so receptors are activated more often. Some drugs stimulate the release of neurotransmitters so more receptors are activated. Some drugs block receptors (antagonists) so fewer receptors will be activated. Some drugs inhibit the release of neurotransmitter so less receptors are activated.
• What muscles do we use to move?

  Skeletal.
• How are skeletal muscles attached to bones?

  by tendons.
• How are bones attached to eachother?

  by ligaments.
• How do bones move?

  A pair of skeletal muscles (antagonistic pair) contract (agonist) and relax (antagonist) against the incompressible (rigid) bones.
• How does your arm move?

  Biceps contract and triceps relaxes so the arm flex's at the elbow and moves up. Ticeps contract and biceps relax so the arm extends and moves back down.
• Are muscles stimuli, effectors, or receptors?

  Effectors.
• What stimulates muscles to contract?

  motor neurons.