Anatomy Of The Human Nervous System

By Tiffany Tseng. May 7th 2016

Have you ever wondered what allows you to taste that delicious lasagna you had for lunch? Or how your body knows to increase your heart rate when you run, or why you feel sadness when your dear friend moved away? Well, your nervous systems handle it all. The human nervous system is a complex organ system that relays information and signals through a network of nerves to coordinate a person's actions, thoughts, emotions and feelings.

Basic Structures and Parts

The most basic structure of the nervous system is a neuron, which bundle together to form nerve fibers. Along these nerve fibers, they relay information via electrical or chemical impulses known as synapses. Nerve fibers are intertwined and spread throughout each section of the nervous system, and synapses allow each division to communicate effectively with each other. (See below for a comprehensive flow chart of the human nervous system)

Central Nervous System (CNS)

The central nervous system, often abbreviated as CNS, consists of the brain and the spinal cord. Working along with the peripheral nervous system, the CNS is considered the "control center" of the entire nervous system, as it processes all information relayed by the peripheral nervous system and makes meaning of it. Different parts of the brain allow people to have feelings, emotions, while dictating decisions, behaviors and thought processes. The central nervous system is protected by the skull and the spinal cord, as well as a membrane known as the blood brain barrier, which keeps toxins out.

Peripheral Nervous System (PNS)

The peripheral nervous system, often abbreviated as PNS, consists of all nerves and ganglion outside of the brain and the spinal cord. Its main function is to relay all sensory and motor information to the central nervous system for processing, and carry out subsequent commands. Unlike the central nervous system, the PNS does not have protective coverings and is more prone to injuries. The peripheral nervous system is further divided into the sensory, somatic and autonomic nervous systems.

  • Sensory system: The sensory system is responsible for all the sensory information of the body. Sensations such as vision, hearing, touch, taste and smell are processed here and relayed back to the central nervous system.
  • Somatic nervous system (SNS): The somatic nervous system is a division of the peripheral nervous system, and consists of voluntary controls that can only take place when a person is conscious. Motor neurons of the SNS are connected to the skeletal muscles of the body. One example would be the contraction of your arm muscles when you raise your arm, or the movement of your legs when you walk or run. At the same time, if you step on a nail, there is a pain signal.
  • Autonomic nervous system (ANS): The autonomic nervous system governs involuntary actions of the smooth organ muscles. For example, food digestion is an involuntary action of the ANS that people's consciousness cannot control directly. It is separated into the sympathetic and parasympathetic divisions for different types of reaction.

Sympathetic nervous division: The sympathetic division of the autonomic nervous system deals with emergency situations of the body by increasing alertness and metabolic activity, and places the body in survival mode. Hence, it is also known as the "fight or flight" division. The sympathetic nervous division fires up when the body is under stress, fear, or when the "survival instincts" kick in. The rush of adrenaline commonly referred to is a product of the sympathetic nervous system in action.

Some examples of the sympathetic activity of the body include:

  • Pupil dilation
  • Increased heart rate
  • Faster breathing
  • Inhibits digestion
  • Inhibits urination
  • Release of sexual climax

Parasympathetic nervous division: The parasympathetic division of the ANS deals primarily with energy conservation of the body and nutrient replenishment. Hence, it is often referred to as the "rest and digest" division. Parasympathetic activities happen when the body is relaxed and resting. It works closely with the sympathetic division to maintain an internal balance of the human body.

Some examples of parasympathetic activity of the body include:

  • Pupil constriction
  • Salivation
  • Urination and defecation
  • Decreased heart rate
  • Slower breathing
  • Sexual arousal

How Does It Come Together?

The nervous system is an intricate information relay system. Here is a summary of relations between the systems:

Nervous System

*Chart provided by Tiffany Tseng


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