THE BIOLOGY OF LEARNING

It seems that learning is as natural as breathing. Since our birth, we have been learning numerous things about the world around us and about ourselves. Initially, this process appears to be purely physical (biological). Later on, learning involves not only biological processes, but also psychological and behavioural aspects.


Of neurones, synapses and action potentials

At a fundamental level, learning consists of information processing and recall. This is, of course, a very simplistic view of learning. Biologically,‘information’ is not a tangible object - i.e., there is no physical entity that can be construed as information. In all multicellular animals, learning appears to be the product of a special type of cell - theneurone (or nerve cell).

A neurone is a type of‘electrically-excitable’ cell. Other examples of electrically-excitable cells muscle cells, endocrine cells and toxin cells (to name a few). Thd‘electric’ part of this description comes from the part played by electrically charged atoms (i.e. ions - cations (positively charged) and anions (negatively charged)). The outer membrane of neurones is impermeable to these ions. Two specific ions are important in this regard - sodium (Na+) and potassium (K+). Different concentrations of these ions accumulate across the plasma membranes of neurones. Since the membrane is very thin, the separation of these ions at the membrane causes‘gradients’. to form. These gradients are called ‘electrochemical’ gradients. However, situated on these membranes are certain proteins called ion channels. These channels act as molecular gates that permit the movement of sodium orpotassium ions through them. As a result, these ions can move from the interior of the cell (cytoplasm) to the exterior space. These channels are normally closed, but when a neurone isstimulated, these channels will open temporarily. This will cause the ions to move across the cell’s membrane, a movement that is driven by concentration differences. Themovement of those ions also causes electrical charges (i.e. the charges on the ions) to move. Moving charges resemble an electrical current. This current is also called a nerve impulse or an action potential.

Neurones are oddly-shaped cells with various projections. These projections are used for communicating with neighbouring cells. Projections called dendritesreceive signals, while projections called axons transmit signals. Indeed, when a neurone is activated, the nerveimp usetravels along the axons until it reaches the end of the cell. Once there, the action potential causes the cell to release chemicalls called neurotransmitters. The junction between two neurones is called a synapse. The activatedneurone at the synapse releases neurotransmitters which cross the synaptic space and land on the other neurone. This activates the second neurone, which forms a new nerve impulse. Hence, the nerve signal moves from one neurone to the next, until iteventually reaches its destination.

Nerve impules form the basis of physical sensations. Information from sensory organs reach the brain using this mechanism. The brain, which is also a conglomeration of neurones, processes the incoming nerve impulses. Somehow these nerve impulses are converted into a tangible reality of ourselves and the world around us. Scientists are still attempting to unravel the complexity of the human brain and the manner in which it functions.



Sham Nair 2014