Test: The Bases of Human Behaviour- 2 - Grade 11 MCQ

The brain sits at the top of the spinal cord like a huge walnut on a stick. At the back is the cerebellum (Latin for ‘little brain’) – resembling a piece of knotted rope, it plays a key role in making movement smooth and efficient. The spinal cord, made up of both axons and ganglia, gives us some essential reflexes. You can withdraw your hand from a fire before the information from your fingers has reached your brain: the spinal circuitry is complex enough to go it alone.
It is also complex enough to contribute to other motor sequences, like those involved in walking. Mammalian brains are made in two halves, or hemispheres – again like a walnut. What this view hides are the numerous subcortical structures. These subcortical regions process sensory input and relay it to appropriate areas of the cortex, or process motor output before relaying it to the spinal cord and from there to the peripheral nervous system.
But the brain should not be thought of as a sort of cognitive sandwich, with sensory information as the input, motor responses as the output, and cognition as the filling. Brain function is much more highly integrated than that. The motor and sensory systems are interactive, and each can directly modify activity in the other.

LTP and LTD represent changes in the responses of target neuron’s to given levels of stimulation, with LTP referring to a lasting increased response and LTD referring to a lasting decreased response. LTP and LTD are not directly related to a person’s potential or mental health.

Early research on seizures advanced our understanding of the idea that brain regions have specialised functions and special roles, and that the removal of the part of the cortex contributing to the seizure activity may reduce seizures. Seizures are caused by electrical discharges, not chemical. Patterns of seizure activity can be detected.

There is much more to chemical neurotransmission than signal amplification and one-way information flow. There are also inhibitory neurotransmitters, which reduce the excitability of a cell. If a cell has a constant but low level of incoming stimulation that keeps it firing at a regular rate, an inhibitory transmitter can reduce that firing. And if a target cell is quiescent, an inhibitory neurotransmitter can prevent it from being excited. The classic inhibitory neurotransmitter is GABA (gamma-amino-butyric acid). GABA works by increasing chloride ion flow into the interior of the cell. Since chloride ions are negatively charged, they increase the cell’s negativity. This is called hyperpolarization. It is harder to excite an action potential in a hyperpolarized cell.

Within each region of the neocortex there may be further, more specialized, modules. In the visual system, for example, separate modules for colour, form and motion speed up visual processing by handling all these attributes in parallel. This high level of specialization means that damage restricted to particular cortical regions can have very precise effects. For example, people with a condition called prosopagnosia are unable to recognize particular people’s faces, despite other visual abilities remaining quite normal.
If you ask neuroscientists whether they would prefer to lose a cubic centimetre of cortex or a cubic centimetre of some subcortical region, they would probably choose to give up some cortex. This is because damage to the subcortex tends to be more profoundly disabling. For example, the loss of neurons in a small subcortical region called the substantia nigra results in Parkinson’s disease, which eventually causes almost complete motor disability.
The functions of the different areas of the cortex have, until recently, been determined either by experimental studies of monkeys (which have a much more highly developed neocortex than animals like rats) or by neuropsychological studies of the effects of brain damage in clinical patients. The development of functional neuro-imaging methods has given us a new way to study the roles of different brain areas in cognition in healthy humans by allowing us to observe which brain regions are active.

Antagonists block the effects of neurotransmitters whereas agonists mimic the effects of neurotransmitters. The synapse is the gap between the axon terminal and the dendrite in which the neurotransmitters are released. Glial cells support the neurons.

Severe hemi-neglect often results from damage to the right parietal lobe. Patients with hemi-neglect may ignore the entire left half of the world, so that they eat only the food from the right side of their plates, shave only the right side of their face, and, when dressing, pull their trousers on to their right leg only. Neglect of the right-hand side of the world, resulting from left cerebral hemisphere damage, is much rarer. The underlying reasons for this are not yet certain, but it suggests that the right hemisphere might be able to support bilateral spatial attentional processes, whereas the left hemisphere (perhaps because of its own specialized allocation to language processing) can only support unilateral spatial attention. This would mean that when the left hemisphere is damaged, the right takes over processes that would normally depend on the left hemisphere. But when the right hemisphere is damaged, the left presumably continues to support its usual processing of events in the right half of the world, but cannot take over processing of events on the left.

Neurons are integrators. They can have a vast number of different inputs, but what they produce is a single output signal, which they transmit to their own targets. How is this done? The key lies in the electrical potentials they generate. There is a small voltage difference between the inside and the outside of the neuron, known as the neuronal resting potential. The mechanisms which generate this resting potential include membrane pumps. Some pumps move ions inwards and others move them outwards.
The inputs to neurons are tiny amounts of chemical neurotransmitters. The target cell has specialized receptor sites, which respond to particular neurotransmitters by subtly changing the cell’s electrical potential for a short time. If enough signals come in together, then the total change can become big enough for the target cell to ‘fire’ – or to transmit an output signal along its axon to modify the activity in its own target cells.

Action potentials are the electrical signal or output of a neuron and neurotransmitters are the chemical signal or output of the neuron. The resting potential is the electrical gradient balance of the neuron when it is in a resting state. Depolarization refers to the change from resting potential to an action potential as a result of an influx of positive ions that make the inside of the cell less negative. Hyperpolarization refers to the change in the cell after an action potential, where the inside of the cell is more negative than it is at rest, which makes it very difficult to induce another action potential in the cell.

Because of the functional roles of different parts of the brain, the loss of a cubic centimeter of subcortex would be most disabling and the loss of some cortex would be least disabling.