Describe how neurons in the central nervous system communicate. Using examples, discuss how this has helped us to understand human behaviour.
Human cognition, emotion, motivation and ultimately life is made possible by neurons in the central nervous system (CNS). This essay will briefly describe the processes involved in neuronal communication and discuss how this knowledge has helped improve our understanding of human behaviour, specifically with regards to neurological and psychological disorders.
Neurons connected to motor neurons in the somatic nervous system control the bodies conscious action whilst neurons in the automatic nervous system control involuntary action which keeps the heart pumping and internal processes working. The soma of a neuron is electrically charged reacting to electrical disturbances from either sensory or neighbouring neurons via it's dendrites. These brief changes of electrical voltage (action potentials) are conducted away from the soma and along the neurons axon. Action potentials travel quickly to the tip of the axon (synapse) where it stimulates the secretion of a particular neurotransmitter. The neurotransmitter acts as a chemical message able to bridge the fluid filled synaptic gap between neighbouring neurons so that communication between cells can occur. The amount of neurotransmitter released into the synaptic gap depends on the frequency of the incoming action potential. On reaching compatible receptors on the postsynaptic neuron the neurotransmitter has an effect on the neighbouring cells action potential, either creating anew or increasing the frequency of an already present action potential (excitation) or suppressing action potential activity (inhibition). Crucially the neurotransmitter only has a short time to stimulate the receptors as it is quickly taken back by the presynaptic neuron in the process of 're-uptake'. In this way the brain can receive incoming messages from the external world, process the information and transmit instructions of response to the body which reacts appropriately.
Understanding the biological behaviour of neurons and applying this knowledge to symptoms of neurological disease has led to some important discoveries and theories regarding the nature of the brain and it's relationship to human behaviour. For example neuronal activity can explain why the breaking or blocking of a blood vessel (a stroke) and resulting lesion in a region of the motor cortex can cause loss of speech and use of corresponding limbs, neurons are no longer able to communicate to the appropriate motor neurons (Toates, 2007). The inherent adaptability or 'plasticity' of the brains neurons which enables other brain regions to take over a damaged region (Mareschal, Johnson and Grayson, 2004) also offers an explanation for the recovery of bodily function seen in stroke patients. However the vast differences in levels and speed of recovery in stroke patients indicates that the creation of new connections is most likely affected by many variables placing limits on theories of cause and effect.
In recent years non-invasive methods such as positron emission tomography (PET) and magnetic resonance imaging (MRI) have revolutionised biological psychology research. Researchers are now able to provide visual evidence of participants neuronal activity as cognitive and motor tasks are performed. This has armed psychology with credible biologically based data with which to generate hypothesis regarding the relationship between neurons and human behaviour. However Toates (2007) warns that the interpretation of material data in itself may limit the reliability of it's use as evidence.
A further area of psychological interest enriched by our understanding of neuronal systems is that of mood disorders. For example depression is argued to be caused by abnormalities in the neurotransmission of key neural systems including the serotonergic synapse which...