The Human Brain : From Neurone to Nervous System
CONNECTIONS OF THE THALAMUS AND AREAS OF THE CORTEX
- Thalamic nuclei process signals in the pathways of sensory systems, the initiation and coordination of movement, and the sleep-waking cycle.
Below the thalamus is the hypothalamus, a small area that regulates many physiological functions.
The thalamus consists of many nuclei with different functions, separated from each other by bands of axons called laminae. Each side of the thalamus is concerned with sensory information from the contralateral side of the body, and objects in the contralateral visual and auditory fields.
Some thalamic nuclei process sensory inputs and relaying their messages to the cortex. The posterior thalamus is concerned with sensory functions: neurones of the Lateral Geniculate Nucleus (or Body) process visual signals and send their axons to the visual cortex in a fan-shaped arrangement of axons called the optic radiation; the axons arising from the lateral geniculate nucleus spread out to reach a large area of cortex around the calcarine fissure in the occipital lobe. The Medial Geniculate nucleus processes auditory signals.
- Ventral and anterior thalamic nuclei are concerned with motor functions, and relay infomation from the basal ganglia and cerebellum to motor areas of the cortex. Other anterior thalamic nuclei connect with the limbic system.
- The thalamus is surrounded by a shell of neurones, the reticular nucleus of the thalamus (RNT), a non-specific nucleus involved in the sleep-waking cycle.
On the outer surface of the thalamus is a thick band of white matter called the internal capsule that contains many axons arising within the thalamus towards the cerebral cortex. It also contains axons connecting the cerebral cortex with other parts of the CNS including the spinal cord.
Key Words: Thalamic nuclei and connections; medial and lateral geniculae nuclei; sensory and motor functions of the thalamus.