Brainstem

Original Editor - Wendy Walker

Lead Editors - Lucinda hampton, Olajumoke Ogunleye, Evan Thomas, Pacifique Dusabeyezu, Wendy Walker, Kim Jackson, Garima Gedamkar, WikiSysop, Aya Alhindi, Tarina van der Stockt, Daniele Barilla and Carina Therese Magtibay

Description

The Brainstem lies at the base of the brain and the top of the spinal cord. Image: The 3 structures of the brainstem.

The brainstem is the structure that connects the cerebrum of the brain to the spinal cord and cerebellum.  

• It is composed of four sections in descending order: the diencephalon, midbrain, pons, and medulla oblongata.  
• It is responsible for many vital functions of life, such as breathing, consciousness, blood pressure, heart rate, and sleep.  

The brainstem contains many critical collections of white and grey matter.  

• The grey matter within the brainstem consists of nerve cell bodies and form many important brainstem nuclei. Ten of the twelve cranial nerves arise from their cranial nerve nuclei in the brainstem  
• The white matter tracts of the brainstem include axons of nerves traversing their course to different structures; the axons originate from cell bodies located elsewhere within the central nervous system (CNS). Some of the white matter tract cell bodies are located within the brainstem as well. These tracts travel both to the brain (afferent) and from the brain (efferent) such as the somatosensory pathways and the corticospinal tracts, respectively.  

Structure

The brainstem is generally said to be composed of three parts.

Components, from above downward:

1. Midbrain (or Mesencephalon)
2. Pons (part of the metencephalon)
3. Medulla AKA Medulla Oblongata (myelencephalon)

Midbrain:

This consists of 3 parts: the tectum, the tegmentum and paired cerebral peduncles. These peduncles are the anterior part of the midbrain that connects the remainder of the brainstem to the thalami. They are paired, separated by the interpeduncular cistern, and contain the large white matter tracts that run to and from the cerebrum.The substantia nigra lies in the cerebral peduncles.

Pons:

Consists of a posterior part, the tegmentum, and an anterior basilar part.

Medulla:

The "bulb" is an archaic term for the medulla oblongata, and in modern clinical usage the word bulbar (e.g. bulbar palsy) is retained for terms that relate to the medulla oblongata. The word bulbar can refer to the nerves and tracts connected to the medulla, and also by association to the muscles thus innervated, such as those of the tongue, pharynx and larynx.

Anatomical Relations

The brainstem is located in posterior cranial fossa.

Above, the midbrain is continuous with the cerebral hemisphere.
Below, the medulla is continuous with the spinal cord.
Posteriorly, the pons and medulla are separated from the cerebellum by the fourth ventricle.

Function

The brainstem has three broad functions:

1. Serves as a conduit for the ascending tracts and descending tracts connecting the spinal cord to the different parts of the higher centres in the forebrain

2. Contains important reflex centres associated with the control of:

• respiration
• cardiovascular system
• consciousness

3. Contains the nuclei of Cranial Nerves III to XII.

The brain stem is responsible for, and regulatory of, the following functions of the human body:

• Alertness
• Attention
• Arousal
• Breathing
• Heart rate
• Blood pressure
• Conveys information and signals shared between the peripheral nerves and spinal cord to the upper brain
• Other autonomic functions such as digestion, salivation, perspiration, dilation or contraction of the pupils, urination, etc.
  

Clinical Significance

A Stroke affecting the brainstem can cause severe symptoms which include:

• Problems with vital functions, such as breathing - frequently resulting in death
• Difficulty using with chewing, swallowing, and speaking
• Weakness or paralysis in the arms, legs, and/or face
• Problems with balance or sensation
• Hearing loss
• Vision problems
• Vertigo
• Locked-in Syndrome
• Coma 

The 9 minute video below gives a good summary of brainstem and stroke

Brainstem lesions frequently occur in Multiple Sclerosis, with visual problems including blurred double vision being a common early symptom of MS.

Central pontine myelinolysis is a concentrated, frequently symmetric, noninflammatory demyelination within the pons.