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Gayathri Mani

Central Nervous System Study Guide

Prepare to be amazed at how the CNS, which comprises the brain and the spinal cord, beautifully works together to keep our bodies alive and functioning!

Lesson Objectives

  • Understand the different, important parts that make up the CNS and their functions
  • Briefly understand differences between the CNS and the PNS

The Central Nervous System (CNS)

The human nervous system is split into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

The CNS consists of the brain and the spinal chord.

  • It is termed 'central' because it coordinates activity across the whole organism.
  • It is a highly complex organ system and is therefore, well protected

CNS Characteristics

  • The CNS is housed within a triple-layered, protective membrane called the meninges
  • The brain and spinal column are also additionally protected by two bony structures - the skull and the vertebral column, respectively.

The Brain

The brain is highly complex and is made up of the cerebrum, cerebellum, subcortical structures, and the brain stem.

brain function

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The brain can be broadly divided into 4 lobes:

  • Temporal lobe: Contains regions dedicated to processing sensory information that are particularly important for hearing, linguistic functions, and memory formation. It also receives auditory information from the ears and secondary areas to help us understand what we hear!
  • Occipital Lobe: Controls visual processing. It receives stimuli from the eyes and relays the information to relevant areas that in turn interpret depth, distance, location and the identity of the object we see.
  • Frontal Lobe: Controls higher executive functions including processing of emotions, planning, reasoning, and problem solving. Often injury or damage to the frontal lobe can result in personality changes! It is also majorly responsible for voluntary movement.
  • Parietal Lobe: Located behind the frontal lobe. It helps in processing sensory information including touch, spatial awareness, temperature, pain, pressure and navigation. This lobe helps us distinguish objects through touch alone through texture and spatial awareness.

The Spinal Cord

The spinal cord runs down the length of our backs, and is the primary connection between the brain and the rest of the body.

The spinal cord

  • Originates from the brainstem
  • Consists of 5 segments (cervical, thoracic, lumbar, sacral, and coccygeal)
  • Has 31 spinal nerves that enter into the spinal cord from the brain stem

Spinal Cord Functions:

  • Connects with nerves from the PNS that come in from other parts of the body such as the skin, muscles, and joints. Information travels from the brain —> spinal cord —> muscles or vice versa, i.e., sense organs —> spinal cord —>brain
  • It also controls your reflexes! The spinal cord contains reflexive circuits that help us react quickly in situations that may be harmful to our bodies, e.g. pulling our arm back if we accidentally touch a flame
  • The reflex circuits can also control movements like running and walking without necessarily relying on input from the brain

White and Grey Matter

The CNS is said to broadly consist of white and grey matter.

The colors actually come from the presence of corresponding parts of neurons. Both types of tissue contain glial cells, which aid in the protection of neurons.

  • Grey matter is made up of clusters of neuronal bodies
  • White matter is made up of the myelin that surround the axons

The brain is seen to have a superficial coating of grey matter on the outside, while its inner layers are comprised largely of white matter.

HOWEVER,

The spinal chord displays the OPPOSITE - the inner layers comprise grey matter, while the outer layers have white matter. This contributes to the spinal chord's characteristic 'butterfly-shaped' cross-section!

spinal chord

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CNS vs PNS: Differences

  • The PNS refers to any part of the nervous system that lies outside of the brain and the spinal chord, whereas the CNS comprises the brain and the spinal chord alone
  • Nerve axons in the PNS are long, and can stretch up to 1 metre in length! The CNS has relatively shorter axons (rarely longer than a few mm) in comparison.
  • The CNS does not have the ability to regerate itself. The PNS however does - if you severe a nerve in your finger, it will grow back!

We hope you enjoyed studying this lesson and learned something cool about the Central Nervous System! Join our Discord community to get any questions you may have answered and to engage with other students just like you! Don't forget to download our App and check out our awesome VR room for this guide - we promise, it makes studying much more fun 😎

Sources

  1. All about the central nervous system. https://www.medicalnewstoday.com/articles/307076#cns-diseases. Accessed Oct 27, 2021.

  2. Central Nervous System. https://www.kenhub.com/en/library/anatomy/the-central-nervous-system. Accessed Oct 27, 2021.