CNS: Intro to Brain and Ventricles, Medulla Oblongata, Pons, Mid-Brain and Cerebellum

The brain does everything in regards to…

  • Heart rate, respiratory rate, blood pressure
  • Autonomic nervous system
  • Endocrine system
  • Sensory-motor integration
  • Intelligence(s)
  • Memory
  • Consciousness

Four main regions of the brain

  • Cerebral hemispheres (2)
  • Diencephalon
  • Brain stem (Midbrain, Pons, and Medulla oblongata)
  • Cerebellum

White and Gray Matter Distribution (in general)

  • White matter is external
  • Gray matter is centrally located
  • There’s an additional layer of gray matter internal to the white matter in the cerebrum and cerebellum called the cortex.

Ventricles are CSF filled cavities (the things in blue) situated deep inside the brain.

The two lateral ventricles have anterior, posterior and inferior horns.

The interventricular foramen connects the lateral ventricles and the third ventricle.

The cerebral aqueduct connects the third and fourth ventricles together.

The fourth ventricle has a few holes called apertures, named by their relative positions, such as the lateral aperture and median aperture.  The two lateral apertures provide a conduit for cerebrospinal fluid to flow from the brain’s ventricular system into the subarachnoid space.  The flow of the CSF can be seen in this article.

Let’s start with the most caudal part of the brain – The Brain Stem

The brain stem is the most primitive part of the brain and is responsible for all automatic behavior (breathing, heart rate/force, blood pressure, hiccup/sneeze/cough/swallow).  This is what connects the cerebrum and the spinal cord together and it’s heavily involved with the cranial nerves that innervate the face and neck.

The medulla oblongata is the lower half of the brainstem.  Where the spinal cord ends and the medulla oblongata starts anatomically is the location of the magnum foramen.

Two front columns are called the pyramids where tracts of voluntary motor fibers run together.  The decussation of pyramids cross fibers from one side of the brain to the other through the cerebral cortex.
The olives are a relay station just anterior to the pyramids.
The medulla oblongata is anterior to the 4th ventricle wall (look how similar the shape is).

The medulla contains brain nuclei (nerve cell bodies) called the Reticular Formation.  These nuclei control the reflexes of the nearby cranial nerves while the rest control visceral functions.

The Pons

Superior to the medulla oblongata is the Pons (latin for bridge). It is also inferior to the midbrain, and ventral to the cerebellum.

When we move up from the mint-green section (the medulla oblongata), we reach the white area, the pons, and it’s full of horizontal running fibers.  Here are the ventral, lateral and dorsal views of the pons:

The Mid Brain

The mid brain includes the cereberal peduncles plus two superior colliculi and two inferior colluculi.  The four colliculi create the corpora quadrigemina of tectum.

The cerebral aqueduct (mentioned earlier with the ventricles) runs through the mid brain and periaqueductal gray matter surrounds the cerebral aqueduct.

Function: has to do with fight or flight reaction: Links the cerebrum’s perception of fear to the autonomic physiological reactions to fear… it can suppress pain or raise heart rate and blood pressure.

Superior colliculus looks like balls.  The inferior colliculus looks like… a tadpole or something.
Superior colliculi contain brain nuclei that act in visual reflexes such as tracking. Inferior colliculi contain brain nuclei that act in auditory reflexes such as turning toward a sound

Review the Location of the Medulla Oblongata, Pons and Midbrain:

The Cerebellum

Located dorsal to the pons and medulla and separated from them by the 4th ventricle.
Smooths and coordinates body movements. Helps maintain equilibrium and posture.

The cerebellum is useful in athletes as its involved with muscle memory and motor skills. A little bit of language/problem solving as well but it’s more so involved with something that has a lot of steps to it (like dancing).

  • Arbor vitae (white) contains axons that carry info to and from cerebellar cortex
  • Cerebellar cortex (gray) generates instructions on how to correct movements
  • Deep cerebellar nuclei (gray) relay these instructions to other parts of the brain

The cerebellum has to do with learning a new motor skill.  Once mastered, skill becomes automatic – “motor memory” or “muscle memory.”  It also plays a role in cognition, language, problem-solving, task planning by recognizing previous events.

Review… the superior, middle (it’s actually lateral) and inferior peduncles.  The peduncles are just fibers that don’t intermingle.  The pons is on top so it sends to the middle peduncle. 

Use this Table of Contents to go to the next article

Painting by Michael Reedy
The Basics. Start here. This is your Foundation.


The Autonomic Nervous System

Specialized Systems