Work through the text, deleting the inappropriate items in the [square brackets], or filling in any blank spaces. It might be a good idea to take a copy of this file, or print it out, to work on.
The membranes also contain pores of [carbohydrate / lipid / protein] molecules, which provide channels for the passage of ions or small molecules.
Ions are electrically charged particles. Cations are ions carrying a [positive / negative] charge; anions carry [positive / negative] charges.
In extracellular fluid, the principal cation is [sodium / potassium / calcium] and the principal anion is [chloride / nitrate / organic anion].
In intracellular fluid. the principal cation is [sodium / potassium / calcium] and the principal anion is [chloride / nitrate / organic anion].
If an ion or molecule can pass through a membrane, the membrane is said to be...................... to that ion or molecule.
Ions may pass through channels in cell membranes by a passive process (one that does not require energy) called ...........…… For any given ion, the rate and direction of this movement are determined by ................. and .............................. gradients.
When there are different initial concentrations of a permeable ion on either side of a membrane, there will be a net movement of the ion from the region of [higher / lower] concentration to the region of [higher / lower] concentration. When the concentrations of the ion on each side of the membrane become equal. a state of ............................ is said to exist. In this state, movements of the ion [continue / cease].
In the resting state, the inside of a neuron carries a voltage which is about 70mV more [negative / positive] than the extracellular fluid.
The inside of all cells is negatively charged with respect to the outside and so cations will tend to be [repelled from / attracted to] the inside of the cell.
In the resting cell, the membrane permeability to sodium ions (Na+) is [ greater / less] than the permeability to potassium ions (K+).
Sodium and potassium ions may also cross the cell membrane (`uphill') against the concentration gradient by an active process involving the ................... By this means. Na+ are moved [into / out of] the cell, in exchange for K+, which are moved in the [same / opposite] direction.
Changing the membrane potential of a neuron from the resting membrane potential of -70mV to a new value of around -90mV is described as [depolarisation / repolarisation / hvperpolarisation].
The normal stimulus for initiating an action potential in a nerve axon is [ hyperpolarisation /
depolarisation ] of the membrane.
When the action potential threshold is exceeded, there is a transient [opening / closing] of channels permeable to [Na+ / K+] ions, which [enter / leave] the cell, making the voltage inside the axon more [positive / negative] than it was at rest. This phase of the action potential involves [positive / negative] feedback.
After the peak of the action potential. the membrane potential returns towards its resting value. This involves ions moving by [ diffusion./ active transport]. The recovery phase is due mainly to [K+ / Na+ / Cl-] passing out of the cell through ion specific channels.
If the sodium/potassium pump is blocked, immediately afterwards the duration of an action potential will be [prolonged / shortened / unaltered ].
Following the initiation of an action potential. the axon undergoes a ................... period, during which another action potential cannot be produced. This period of complete inexcitability is due to [reversal of ionic concentration gradients / inhibition of the Na-K pump / inactivation of sodium channels].
The amplitude of the action potential is [dependent on / independent of ] the strength of the stimulus; thus the action potential is described as a [graded / all-or-nothing] event.
Action potentials propagate along the length of an axon by spread of local electrical currents that [depolarise / hyperpolarise] regions of resting nerve membrane lying [behind /ahead of] the active region.
The velocity of propagation of the action potential depends on the axon diameter and whether or not the axon is myelinated. Increasing axon diameter will [increase / decrease] conduction velocity. For a given axon diameter, conduction velocity will be faster if the axon is [mvelinated / unmyelinated].
Myelin is produced by the membrane of .................... cells, which wrap round the axon. The presence of a myelin sheath acts as an insulator, [increasing / decreasing] the resistance of the membrane to ions. At intervals along a myelinated axon, there are gaps in the myelin sheath at [nodes of Ranvier / synaptic clefts / dendrites] . In a myelinated axon, the action potential is said to spread by ...................... conduction.
Chemical transmitters are stored in [vesicles / mitochondria / chromosomes] in the terminal bouton of the [pre- / post-] synaptic cell.
Action potentials arriving at the terminal bouton of a neuron will cause [depolarisation / hyperpolarisation] of the presynaptic cell. This is followed by an [increase / decrease] in the concentration of calcium ions in the terminal, which brings about release of [one /many] molecule(s) of transmitter.
The transmitter [diffuses / is pumped] across the synaptic [cleft / node / knob], to act on [protein / lipid] receptor molecules on the post-synaptic cell membrane. The time interval between transmitter release and its action on the post-synaptic cell is of the order of [0.1 / 1.0 / 10] ms.
The action of the transmitter acetylcholine (ACh) is terminated by the action of the enzyme .............................., which is situated on the [pre- / post-] synaptic membrane.
Administration of a poison which inactivates this enzyme will [prolong / reduce] the duration of action of ACh.
At a nerve-nerve synapse, the post-synaptic neuron may be depolarised or hyperpolarised, depending on the nature of the transmitter and type of receptor involved. At an excitatory synapse, the transmitter will [depolarise / hvperpolarise] the post-synaptic neuron, producing an [EPSP / IPSP ].
An individual neuron will receive inputs from many other neurons: this is known as [convergence / divergence] of inputs. For a single neuron, all these inputs are likely to have [the same / different] effect(s) on the membrane potential.
The effects of several synaptic inputs may combine or summate. If two or more excitatory inputs to different parts of a given neuron are activated at the same moment [spatial / temporal] summation occurs. Summation between excitatory and inhibitory inputs [can / cannot] occur.