What is the difference between the central nervous system CNS and the peripheral nervous system PNS in terms of their functions?

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The central nervous system (CNS) is made up of the brain and spinal cord. It is one of 2 parts of the nervous system. The other part is the peripheral nervous system, which consists of nerves that connect the brain and spinal cord to the rest of the body.

The central nervous system is the body’s processing centre. The brain controls most of the functions of the body, including awareness, movement, thinking, speech, and the 5 senses of seeing, hearing, feeling, tasting and smelling.

The spinal cord is an extension of the brain. It carries messages to and from the brain via the network of peripheral nerves connected to it.

Nerves also connect the spinal cord to a part of the brain called the brainstem.

What are the parts of the central nervous system?

The nervous system is made up of basic units called neurons. The neurons are arranged in networks that carry electrical or chemical messages to and from the brain.

The tissue of the central nervous system is made up of grey matter and white matter. Grey matter is made up of neurons, cells and blood vessels. White matter is made up of axons, which are long cords that extend from the neurons. They are coated in myelin, which is a fatty insulation.

The brain and spinal cord are protected from damage by a clear liquid called cerebrospinal fluid, 3 layers of membranes called the meninges, and the hard bones of the skull and backbone.

The brain

The brain is made up of different parts. These include the cerebrum, the cerebellum, the thalamus, the hypothalamus and the brainstem.

The cerebrum is the largest part of the brain. It controls intelligence, memory, personality, emotion, speech, and ability to feel and move. It is divided into left and right hemispheres, linked by a band of nerve fibres in the centre of the brain called the corpus callosum.

Each hemisphere is divided into 4 lobes, or sections, which are all connected.

• The frontal lobes control movement, speech and some of the functions of the mind like behaviour, mood, memory and organisation.
• The temporal lobes play an important part in memory, hearing, speech and language.
• The parietal lobes play an important part in taste, touch, temperature and pain, and also in the understanding of numbers, awareness of the body and feeling of space.
• The occipital lobes are vital for being able to see clearly.

Deep inside the brain are the thalamus and the hypothalamus. The thalamus moves information to and from the lobes, and controls movements and memory. The hypothalamus controls appetite, thirst and body temperature, and produces hormones that control the release of other hormones in the pituitary gland.

At the base of the brain is the brainstem. It is important for breathing, blood pressure and how the body reacts to danger.

Learning Outcomes

• Differentiate between the central and peripheral nervous systems

The nervous system has three main functions: sensory input, integration of data and motor output. Sensory input is when the body gathers information or data, by way of neurons, glia and synapses. The nervous system is composed of excitable nerve cells (neurons) and synapses that form between the neurons and connect them to centers throughout the body or to other neurons. These neurons operate on excitation or inhibition, and although nerve cells can vary in size and location, their communication with one another determines their function. These nerves conduct impulses from sensory receptors to the brain and spinal cord. The data is then processed by way of integration of data, which occurs only in the brain. After the brain has processed the information, impulses are then conducted from the brain and spinal cord to muscles and glands, which is called motor output. Glia cells are found within tissues and are not excitable but help with myelination, ionic regulation and extracellular fluid.

Figure 1. The central and peripheral nervous systems

The nervous system is comprised of two major parts, or subdivisions, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and spinal cord. The brain is the body’s “control center.” The CNS has various centers located within it that carry out the sensory, motor and integration of data. These centers can be subdivided to Lower Centers (including the spinal cord and brain stem) and Higher centers communicating with the brain via effectors.

The PNS is a vast network of spinal and cranial nerves that are linked to the brain and the spinal cord. It contains sensory receptors which help in processing changes in the internal and external environment. This information is sent to the CNS via afferent sensory nerves. The PNS is then subdivided into the autonomic nervous system and the somatic nervous system. The autonomic has involuntary control of internal organs, blood vessels, smooth and cardiac muscles. The somatic has voluntary control of skin, bones, joints, and skeletal muscle. The two systems function together, by way of nerves from the PNS entering and becoming part of the CNS, and vice versa.

We’ll further discuss the components and roles of these systems later in this module.

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Updated March 13, 2018

By Lawrence Adams

The human nervous system is a complicated system of connecting neurons and associated cells. The nervous system allows us to think, breathe and feel. Scientists categorize the nervous system into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). These parts of the nervous system differ in their structures and physiological functions.

The CNS consists of the brain and spinal cord, while the PNS includes all other nervous system tissue. All sensory receptors, sensory neurons and motor neurons are part of the PNS. The bones of the skull and spinal vertebrae encase all CNS neurons. Neurons in the PNS are not encased in bone; rather, they travel through or lie on top of muscle, organ and skin tissue. Groups of neurons form in both the CNS and the PNS. In the CNS, a group of neurons is called a nucleus. In the PNS, a group of cell bodies is known as a ganglion, while a bundle of neuron tracts is called a nerve.

The primary purpose of the CNS is to organize and analyze information. Nervous system impulses run to and from the brain via the spinal cord. Different areas of the brain process sensory and motor information, allowing us to observe and react to our environment. The central purpose of the PNS is to follow the commands of the CNS. Neurons in the PNS gather sensory information from the environment and relay it to the CNS. After the CNS processes the information, the PNS responds to its commands by changing motor output.

The brain and spinal cord are broken down by their general purposes. For example, the brain consists of the cerebrum, diencephalon, midbrain and hindbrain. Each brain region performs a specific set of tasks. The PNS is divided into the somatic nervous system and the autonomic nervous system. The somatic nervous system consists of consciously controlled nerves that receive sensory information and execute motor commands. The autonomic nervous system operates without conscious commands from the brain. It monitors heart rate, digestive activity, breathing, salivation and sexual arousal.

Experts divide the nervous system into the CNS and PNS to classify its important functions. However, both parts of the nervous system work in tandem and are essential to life. Without the PNS, the CNS would not have any sensory input to process, making it impossible to react to the environment. Likewise, the PNS relies upon the CNS to coordinate information from different body parts and make decisions about how you should react in a given situation. These two parts of the nervous system work together in synchrony to create our conscious experience of everyday life.