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# Human Nervous System ## Central Nervous System (CNS) The CNS consists of the brain and spinal cord. * **Composition:** * A large number of association neurons. * A mix of white and gray matter. * White matter (myelinated neurons) is responsible for the white appearance a...

# Human Nervous System ## Central Nervous System (CNS) The CNS consists of the brain and spinal cord. * **Composition:** * A large number of association neurons. * A mix of white and gray matter. * White matter (myelinated neurons) is responsible for the white appearance and transmits signals throughout the CNS. Unmyelinated neurons are involved in interpretation and decision-making. * Connective tissue called neuroglia holds the CNS together. * Neuroglia also produces myelin for the white matter. * **Protective Layers:** The CNS is covered by meninges, membranes that contain blood vessels supplying the brain and spinal cord. They also produce cerebrospinal fluid (CSF). CSF fills the spaces within the CNS and bathes the tissue, nourishing it and acting as a shock absorber. * **Location:** The brain is encased within the skull, and the spinal cord lies within the vertebral column. ## Peripheral Nervous System (PNS) The PNS consists of receptors and nerves. * **Function of Receptors:** Receptors identify stimuli in the environment, including the five senses: sight, sound, taste, smell, and touch. ## Cerebrum * **Structure:** The cerebrum is the largest part of the brain, characterized by folds called convolutions (gyri), with deeper grooves called sulci. This structure increases the surface area. * **Function:** This increased surface area allows for more complex signals and decisions to be processed. * **Hemispheres:** The cerebrum is divided into two hemispheres (left and right) separated by the longitudinal fissure. They communicate through the corpus callosum. * **Lobes:** Each hemisphere is further divided into five lobes (frontal, parietal, temporal, occipital, and insula). * **Locations:** The frontal, parietal, temporal, and occipital lobes are located on the surface of the brain. The insula is located deeper within the hemisphere. * **Fissures:** Fissures (deep grooves) separate the lobes. The central sulcus separates the frontal and parietal lobes. The lateral sulcus separates the parietal and temporal lobes. A parieto-occipital fissure separates the parietal and occipital lobes. * **Function of Lobes:** Different areas in different lobes are responsible for specific functions. For example, the frontal lobe is the motor center, controlling voluntary movements. Lobes work together to form decisions.