Page - 32 - in Cyborg Mind - What Brain–Computer and Mind–Cyberspace Interfaces Mean for Cyberneuroethics

32 • Cyborg Mind place producing a number of substances required for normal neurological functioning. Information in the nervous system is coded as electrical-chemical messages and sent through chains of neurons, usually going in one direction, from the dendrites through the cell body and along the axon, which is then connected to a dendrite or cell body of a neighbouring neuron. The very small interconnecting gaps between neurons are called synapses and occur at the point where one neuron touches another, and are the places where signals are transferred. When a neuron transmits a message to a neighbour, it initiates an electrical signal to the synapse, eliciting the release of a small package of chemicals. These chemicals travel across the microscopic gap between the two cells, triggering a shock wave through a pulse of voltage in the second neuron, which then moves down its exten- sions. The nature of the response depends on the types of cells and the types of chemicals released. Neurons are usually specialised in different ways in order to fulfil specific tasks. The number, length and pattern of the extensions that develop from the cell, the connections these make with other neurons, the neurotransmit- ters that are released to the neighbouring cell and the surface channels of receptors all make a neuron very specific in its role.1 This form of organisa- tion of the neurons is the basis of a kind of regional specialisation of function and is believed to increase the speed of communication.2 The brain makes up the largest portion, is the major functional unit and is often referred to as the main structure of the central nervous system. The spinal cord, on the other hand, has certain processing abilities relating to, for example, spinal locomotion and process reflexes. The Spinal Cord The spinal cord is the main pathway supporting information between the brain and the peripheral nervous system. Extending from the base of the brainstem is a bundle of neurons making up nerve fibres reaching down through a protective channel in a person’s spinal column. It is a major trunk route directing signals from the brain to the body and vice versa. However, it would be a mistake to see the spinal cord as a passive con- duit of information. Much of the basic functional control of a person’s body is organised within the spinal cord protected by the bony spinal column, with a length of about 45 cm in men and 43 cm in women, made up of bones called vertebrae. Although the spinal column is somewhat flex- ible, some of the vertebrae in the lower parts of the column may become fused. This open access edition has been made available under a CC-BY-NC-ND 4.0 license thanks to the support of Knowledge Unlatched. Not for resale.