Chapter 38: Nervous and Sensory Systems

The nervous system is organized hierarchically, from simple diffuse nerve nets in cnidarians to centralized brains in vertebrates. The central nervous system integrates sensory information and coordinates responses, while the peripheral nervous system transmits signals between the CNS and body tissues through afferent sensory pathways and efferent motor pathways. The autonomic division controls involuntary functions through three branches: the sympathetic system mobilizes energy during stress, the parasympathetic system promotes recovery during rest, and the enteric system manages gastrointestinal processes. Glial cells provide essential support, including myelin formation for signal conduction speed and astrocyte involvement in maintaining the blood-brain barrier. The vertebrate brain shows regional specialization where the brainstem controls vital functions like respiration and heart rate, the cerebellum coordinates movement and equilibrium, and the diencephalon regulates sensory relay and homeostatic balance through structures like the hypothalamus and suprachiasmatic nucleus. The cerebrum's hemispheres exhibit functional lateralization, with the left hemisphere controlling language production and analytical thinking while the right excels at spatial processing and pattern recognition. The limbic system generates emotions and consolidates memories through coordinated activity among the amygdala, hippocampus, and thalamus. Neuroplasticity enables synaptic strengthening and weakening in response to experience, supporting learning and memory formation while contributing to conditions like autism and addiction. The sensory systems convert physical and chemical stimuli into neural signals through specialized receptors: mechanoreceptors detect touch and sound, chemoreceptors process smell and taste, thermoreceptors monitor temperature, and nociceptors signal pain. The ear translates sound vibrations into neural impulses via the cochlea's hair cells, which encode pitch by location and volume by firing rate. Vision relies on photoreceptors in the retina, where rods enable low-light detection and cones mediate color discrimination through distinct photopsins that respond to different wavelengths.