Pathways in the Central Nervous System

In this section on pathways, we will cover the important pathways that make up the central nervous system. The ascending and descending tracts are the first two articles, which cover the anatomy of the sensory and motor pathways of the central nervous system respectively. There are also articles on the visual pathways and auditory pathways to help you understand the intricacies of these important senses.

The ascending tracts refer to the neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex. In some texts, ascending tracts are also known as somatosensory pathways or systems. Functionally, the ascending tracts can be divided into the type of information they transmit – conscious or unconscious. In this article, we shall look at the anatomy of the ascending tracts, and consider their clinical implications.

We will discuss the descending tracts. The descending tracts are the pathways by which motor signals are sent from the brain to lower motor neurones. The lower motor neurones then directly innervate muscles to produce movement. There are no synapses within the descending pathways. At the termination of the descending tracts, the neurones synapse with a lower motor neurone. Thus, all the neurones within the descending motor system are classed as upper motor neurones. Their cell bodies are found in the cerebral cortex or the brain stem, with their axons remaining within the CNS.

The auditory pathway conveys the special sense of hearing. Information travels from the receptors in the organ of Corti of the inner ear (cochlear hair cells) to the central nervous system, carried by the vestibulocochlear nerve (CN VIII). This pathway ultimately reaches the primary auditory cortex for conscious perception. In addition, unconscious processing of auditory information occurs in parallel. In this article, we will discuss the anatomy of the auditory pathway – its components, anatomical course and relevant anatomical landmarks.