• Hugo Creeth

Brain - Basics

Updated: Oct 4, 2019

The brain is a complex and delightfully fascinating organ, it weighs around 1.2 kg and is jam packed with upwards of one hundred billion nerve cells and over one hundred trillion connections between them. It is these countless interconnections that attributes the brain with a host of abilities that makes us, US. The brain is the control centre that controls every action, sensation and thought (conscious or unconscious).



That being said, the brain is just one part of the core central nervous system...


The Central Nervous System


The central nervous system (CNS) has two distinct parts:

  1. The Spinal Cord

  2. The Brain

The brain is the control centre and is itself divided into a number of regions each with distinct functions. These regions are as follows:

Hinbrain

  • Medulla Oblongata - often just known as the medulla. It is vital for autonomic functions, including: digestion, breathing and heart rate. The medulla is historically called the "bulb" but is still the term used for certain clinical conditions affecting the medulla i.e. bulbar palsy.

  • Pons Varolli - Which literally means "bridge" was named after an Italian surgeon Costanzo Varolio who discovered it during is many dissections. It consists of white matter that conveys information about movement to cerebellum from the cerebrum. It is only 1 inch in size and amongst its functions it contains numerous nuclei that relay varying types of information, for example the pneumotaxic center that regulates the seamless switch from inhalation to exhalation. As well as these functions research has pointed to the pons being critically linked to sleep paralysis and dreaming.

  • Cerebellum - translates from Latin to mean "little brain". It is connected to brain stem via peduncles and is fundamentally involved with movement and learning motor skills. Although it possibly involved with some cognitive functions such as attention and some aspects of language.

Midbrain


Controls many sensory and motor functions e.g. eye movement, but is also utilised for temperature regulation.

  1. Tectum - Auditory and visual reflexes. It is the "ceiling" of the midbrain.

  2. Tegmentum - region of the midbrain that forms the "floor".

  3. Cerebral peduncles - link the brainstem to the thalami, and ultimately the cerebrum.

N.B. The midbrain plus the pons and the medulla are collectively known as the "Brainstem".


Inter-brain


Also known as the Diencephalon, the interbrain (sometimes incorporated into the forebrain, below) consists of two regions:

  • Thalamus - This structure sits on top of the brain stem and processes information reaching the cerebral cortex as well as the regulation of consciousness (including sleep).

  • Hypothalamus - regulates autonomic, endocrine and visceral functions. Its most important role however is to link the nervous system to the endocrine system via the pituitary gland

Forebrain

The Cerebrum as it is more formally known contains two cerebral hemispheres:


  • Limbic System -

  1. Amygdala - An "almond" shaped structure, this region is responsible for emotions.

  2. Hippocampus - coming from the latin word for "sea-horse" due to its shape, this structure is heavily involved in memory.


  • Cerebral Cortex - heavily wrinkled outer layer of the brain. It is the most recently developed part of the brain. It makes up 80% of the brains volume and is divided into two hemispheres (Left and Right) joined by the corpus callosum. These hemispheres contain four major lobes (each coming in pairs):

  1. Frontal Lobe - Located behind the forehead at the top. Its equates to 30% of the cortex. It is involved with voluntary muscles, intelligence and personality.

  2. Parietal Lobe - found on the top of the head towards the back, it is vital for spatial location, pain perception, touch and temperature. (N.B. It is said that Albert Einsteins Parietal Lobe was 15% larger than most)

  3. Occipital Lobe - this is the smallest pair of lobes. It is the "Visual Processing Centre" and is located at the back of the skull, which is somewhat counterintuitive with respects to the eyes location

  4. Temporal Lobe - Found above the ears it is subsequently involved in hearing, language processing and memory (it is linked to the Hippocampus in the Limbic System).

The lobes of the cerebral cortex are named from the skull bones that overlie them. It is in the cerebral cortex that most of our cognitive abilities occur. Each lobe has several characteristic deep infoldings that are evolutionary in origin. These infoldings allow for more nerve tissue/cells to be packed into a limited space. The crests of the convolutions are known as "gyri" and the grooves are called "sulci" (or "fissures").

  • Subcortical Structures - consists of three deep lying structures:

  1. Basal Ganglia - sandwiched between the thalamus and cerebral cortex this densely packed cluster of neurons regulates motor performance.

  2. Amygdaloid Nuclei - coordinate the autonomic and endocrine responses of emotional states.

  3. Olfactory Bulb - As the name suggests this structure in the mammalian brain is conducive to our sense of smell.




The brain is far more complex than this article suggests with many more structures and cells that all combine to perform a huge number of different functions. These will be described in more detail in future articles and also reported as more and more information is unearthed. It was in 2013 that in the USA the BRAIN initiative began in an attempt to produce a more dynamic map of the human brain, with a budget of over $100 million. This is an exciting time to be part of such research as we continue to gain more and more knowledge about the structure that allows us to think.


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