Understanding the Human Nervous System
The nervous system relies on neurons to function. It comprises three interconnected systems:
- The Central Nervous System (CNS): Consists of the brain (cerebrum, cerebellum, and brainstem) and part of the spinal cord. Structurally protected by the skull and spine. The brain has three main structures: the cerebrum, cerebellum, and brainstem. The brain lobes are often color-coded: pink for parietal, green for temporal, and blue for occipital. The visual cortex is located at the back of the brain.
- Peripheral Nervous System (PNS): Located outside the CNS, it mainly includes the spinal cord and the nerves that exit the spinal column (spinal nerves). These nerves extend to the upper and lower limbs.
- Autonomic Nervous System (ANS): Controls involuntary functions, often involving hormone regulation. It is further divided into two branches:
- Sympathetic Nervous System: Activated during stressful or “fight-or-flight” situations. For example, it dilates the pupils.
- Parasympathetic Nervous System: Promotes relaxation and rest. For example, it returns the pupils to their normal size.
Central Nervous System Features
The CNS consists of the brain and a small part of the spinal cord. It processes information rapidly, enabling various functions.
Brain Components:
- Cerebral Hemispheres
- Diencephalon: Thalamus and Hypothalamus
- Brainstem:
- Mesencephalon (Midbrain)
- Pons
- Medulla Oblongata
- Cerebellum
- Spinal Cord: Protected by the spine and skull.
The spinal cord is protected by the meninges, which are three layers of membranes:
- Dura Mater: The outermost, tough, fibrous layer. It extends from the skull to the sacral canal. It has two parts:
- Cranial Dura Mater: Forms ducts around the skull, creating venous sinuses.
- Spinal Dura Mater: Connects with nerves throughout the body.
- Arachnoid Mater: The middle layer, separated from the dura mater by the subdural space. It appears transparent.
- Pia Mater: The innermost, thin layer, closely attached to the brain and spinal cord. It contains numerous small blood vessels. The subarachnoid space, between the arachnoid and pia mater, contains cerebrospinal fluid.
Brain Anatomy
The brainstem consists of three parts: the mesencephalon (midbrain), pons, and medulla oblongata.
The brain is the largest and most prominent organ of the nervous system. Key sensory functions include speech, smell, and sight. It weighs approximately 1.1 to 1.5 kg. Nociceptive (pain) and proprioceptive (body position) senses work in conjunction with the sense organs. The brain is divided into two hemispheres connected by the corpus callosum.
Brain lobes are separated by the fissures of Rolando and Sylvius. Another fissure, the internal perpendicular fissure, extends deep within the brain. The wrinkles in the brain are called sulci or gyri. The brain is composed of gray matter on the periphery and white matter internally.
Underside: At the base of the brain are structures related to sight and smell, including the olfactory bulbs, optic chiasm, pituitary gland, and mammillary bodies.
Brain Functions: Thought, feeling, movement, will, instinct, intelligence, memory, reasoning, written language, spoken language, vision, and hearing.