Nervous System

Overview of Nervous System

The nervous system is the most complex and highly organized body system. It contains two major parts, the central nervous system and the peripheral nervous system. The central nervous system is considered as the primary command center of the body that controls the body’s responses to external stimuli, as well as internal functions and processes of the body systems such as heartbeat, breathing, and digestion. The peripheral nervous system consists of all of the parts of the nervous system outside of the brain and spinal cord. It connects the central nervous system to every other part of the body. The two systems work together to ensure the normal function of the nervous system.

Structure of Nervous System

Neurons and neuroglia are two classes of cells in the nervous system.

• Neurons are the fundamental units of the brain and nervous system and responsible for communicates with other cells via specialized connections called synapses. They are typically divided into three types based on their function: afferent neurons, efferent neurons, and interneurons.
• Neuroglia are non-neuronal cells that can provide support and nutrition for nerve cells, form myelin sheath, and participate in signal transmission in the nervous system.

Sensory System

The sensory system is a part of the nervous system that processes sensory information. It receives stimuli such as light waves and sound waves and converts them into neural signals which can be recognized by the nervous system. The sensory system is composed of sensory receptors receiving stimuli from the internal and external environment, neural pathways transmitting the stimuli to the brain, and parts of the brain involved in sensory perception. Human sensory system includes the following subsystems.

Visual system Auditory system Somatosensory system

Gustatory system Olfactory system Vestibular system

Motor System

The motor system is a highly complex system in the nervous system, responsible for voluntary and involuntary movement. It is composed of a set of central and peripheral structures. Central structures include cerebral cortex, brainstem, spinal cord, and pyramidal system that consists of the upper motor neurons, extrapyramidal system, cerebellum, and the lower motor neurons in the brainstem and the spinal cord. Peripheral structures include skeletal muscles and neural connections with muscle tissues.

Neurotransmitter System

Neurotransmitter is a chemical messenger that transmits a signal from a neuron across the synapse to a target cell (e.g., another neural cell, muscle cell, or gland cell) in which a specific response will be induced. Neurotransmitter is synthesized in and released from nerve endings into the synaptic cleft. The neurotransmitter then binds to receptor proteins on the cellular membrane of the target cell, leading to an excited or inhibited response of the target cell. There are more than 40 neurotransmitters in the human nervous system. The most important neurotransmitters include acetylcholine, dopamine, norepinephrine, gamma-aminobutyric acid (GABA), purines, glutamate, aspartate, serotonin, and histamine.

Fig.2 Generic Neurotransmitter System.

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