Neurotransmitters are chemical messages that transfer signals within the nervous system. ![]() From this, very short postganglionic fibres terminate dirctly onto the cells of the effector organ itself. These fibres are very long and only terminate at near the effector organs. Parasympathetic preganglionic fibres originate from the head and lower back areas of the CNS. From this, long postganglionic fibres terminate on the appropriate effector organ. These fibres synapse with the postganglionic neurons on either side of the spinal cord. Sympathetic nerve preganglionic fibres originate in the chest and abdominal regions of the spinal cord. The autonomic nervous system is divided into two componens – the sympathetic nervous system and the parasympathetic nervous system. All output carried out by the autonomic system originates in the CNS, and the CNS in turn receives input from the somatic nervous system described later in this article. The peripheral nervous system is closely connected to the CNS. Part of this second neuron (the postganglionic fibre) then innervates the effector organ in the body. Part of the neuron, namely the axon, synapses with the cell body of the second neuron. The cell body of the first neuron in the chain is located within the CNS. The efferent division of the PNS can be divided into two components – the autonomic nervous system and the somatic nervous system.Ī pathway in the autonomic nervous system extends from the CNS to an innervated organ. These efferent neurons are part of the PNS. As part of the regulation process, the CNS initiates electrical signals known as action potentials in the outgoing (efferent) neurons whose nerve endings (known as axons) terminate on these organs. The efferent division is generally a link between the central nervous system and the effector organs so that the CNS can regulate the various responses. The efferent division sends information from the nervous system to the organs of the body which then carry out the appropriate response. ![]() The afferent division of the PNS can be understood by looking at how various special senses function individually – for example, the sense of hearing or the sense of vision. This sensory information is characterised by our senses including vision, hearing, taste and smell. Afferent inputs that reach conscious awareness are known as sensory afferents and transmit sensory information. Subconscious information from the internal organs is transmitted via an incoming pathway called a visceral afferent. Although we are not conscious of this information being processed, this system is vital for determining a suitable outgoing response to maintain the normal functioning of the body. Afferent division of the PNSĪfferent information is sent towards the nervous system regarding the internal environment of the body such as information about blood pressure. The PNS can be divided into two components – the afferent division and the efferent division.
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