Question

Topic: Neuroscience

1. (a) How do neurons communicate with each other? What is this process called? Explain in detail how information from one neuron gets passed on to another and do not leave out any stages in this process.

Key words you must use in your explanation: synapse, post and pre-synaptic neuron and their structures, vesicles, neurotransmitters, receptors, excitatory and inhibitory.

(b) In the beginning of our lecture on neuroscience, we discussed a quote from Hippocrates that summarizes the neurosciences perspective on the human mind. Please explain the main message or “essence” of this quote. Is Hippocrates a monist or a dualist?

Answer 1

Neurons communicate at their meeting points called synapses. The small gaps separating the neurons are referred to as synaptic clefts. These synapses are not merely gaps but are functional links between the two neurons. Signals are transferred in only one direction across the synapse.

Synapses can be either chemical or electrical.

Chemical synapses

The space between the pre- and postsynaptic neurons is called the synaptic cleft. The key feature of all chemical synapses is the presence of small, membrane-bound organelles called synaptic vesicles within the presynaptic terminal. These spherical organelles are filed with one or more neurotransmitters, the chemical signals secreted from the presynaptic neuron, and it is these chemical agents acting as messengers between the communicating neurons that give this type of synapse its name. there are many kinds of neurotransmitters, the best-studied example being acetylcholine.

Transmission at chemical synapses occurs when an action potential invades the terminal of presynaptic neurons. The change in membrane potential caused by the arrival of the action potential leads to the opening of voltage-gated calcium channels in the pre-synaptic membrane. The opening of these channels causes a rapid influx of Ca2+ into the pre-synaptic terminal, resulting in a transient increase in the Ca2+ concentration of the cytoplasm. The elevation of the presynaptic Ca2+ concentration allows synaptic vesicles to fuse with the plasma membrane of the presynaptic neuron. The Ca2+ dependent fusion of synaptic vesicles with the terminal membrane causes their contents, most importantly the neurotransmitters, to be released into the synaptic cleft.

Following exocytosis, neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the membrane of the postsynaptic neuron. The binding of neurotransmitters to the receptors causes the channels in the postsynaptic membrane to open (sometimes close), changing the ability of ions to flow into or out of the post-synaptic cells. the resulting neurotransmitter induced current flow alters the conductance and usually the membrane potential of the postsynaptic neuron, increasing or decreasing the probability that the neuron will fire an action potential. In this way, information is passed from one neuron to another neuron.

Types of chemical synapses- Excitatory or Inhibitory

The action of neurotransmitters may promote or inhibit the generation of an action potential in the post-synaptic cell. Binding of a neurotransmitter to an excitatory receptor opens a channel that allows Na+ ions or both Na+ and K+ ions. These non-voltage gated ion channels can be part of the receptor protein or can be a separate protein that opens in response to a cytosolic signal generated by the activated receptor. Channel opening leads to the depolarization of the postsynaptic plasma membrane, promoting the generation of an action potential.

In contrast, binding of a neurotransmitter to an inhibitory receptor on the post-synaptic cell causes opening of K+ or Cl- channels. The resulting membrane hyperpolarization inhibits generation of an action potential in the postsynaptic cell.