Brainstem Flashcards
What are the 3 broad functions of the brainstem?
- Conduit: Allows passage of long pathways between the brain, brainstem, thalamus, cerebellum and spinal cord
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Integrative:
- Reticular formation: control of consciousness, cardiovascular and, respiratory functions, perception of pain.
- Influences motor patterns (e.g. balance, posture, muscle tone)
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Cranial nerves:
- Contains the nuclei of Cranial Nerves III to XII
- Head’s equivalent to spinal nerves plus sight, hearing, equilibrium and gustation
- Reflex centres
What is the reticular formation?
- A set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain.
- The neurons of the reticular formation make up a complex set of networks in the core of the brainstem that extend from the upper part of the midbrain to the lower part of the medulla oblongata.
What composes the brainstem?
- Midbrain
- Pons
- Medulla oblongata
What is the brainstem continuous with rostrally? (What is above it)
The midbrain is continuous with the diencephalon (D)
What is the brainstem continuous with caudally? (What is below it)
Medulla is continuous with the spinal cord (SC) at level of the foramen magnum
What is the brainstem continuous with ventrally? (in front of it)
The clivus of the occipital bone
What is the brainstem continuous with dorsally? (what is behind it)
The cerebellum
Running through the brainstem are components of the ventricular system. What are these components?
- IVth Ventricle (IVth) - between the pons/medulla anteriorly and cerebellum posteriorly
- Cerebral aquaduct (Caq) - at the level of the midbrain
How many cranial nerves arise from the brainstem?
10 out of 12 cranial nerves - these are part of the PNS and have motor and sensory parts (somatic and autonomic)
Revision of development from neural tube
At any level of brainstem, what 3 areas can be identified?
- Tectum (blue)
- Tegmentum (purple)
- Basal area (red)
Where is the tectum found?
The most dorsal area (roof) –> posterior to the ventricular system
Where is the tegmentum found?
Anterior to ventricular system
Where is the basal area found?
Most ventral part of brainstem
At the level of the midbrain, describe the locatio of the tectum, tegmentum and basal area in relation to cerebral aqueduct
- Tectum – located posterior to the cerebral aqueduct
- Tegmentum - anterior to cerebral aqueduct
- Basal - most ventral
Which area of the brainstem has most significant tectum?
Midbrain
What is found in the tegmentum?
- The tegmentum is the location of several cranial nerve (CN) nuclei
- Some pathways that pass through the brainstem
What is the basal area important for?
Descending motor fibres - fibres start in cortex and bring motor info down through the brainstem either to spinal cord, brainstem or cerebellum
What does locked in syndrome typically occur from? Why does it result in this syndrome?
- Results from stroke at level of pons
- Descending motor pathways are affected (in basal area)
- Paralysis of everything except eye movements
Why are most eye movements still intact in locked in syndrome?
Nerves that are responsible for eye movement arise above the pons
In locked in syndrome, why are people still able to breathe and heart is still functioning?
The tegmentum where we find these centres isn’t affected
What is the junction between the pons and the medulla called?
Pontomedullary junction (PMJ)
There are several structures visible on the anterior surface of the medulla. What are these?
- the three fissures/sulci
- the pyramids
- the olives
- five cranial nerves.
What fissure is found in the midline of the medulla?
Anterior median fissure - continuous along the length of the spinal cord.
What is the anterior median fissure temporarily interrupted by?
By the DECUSSATION of the pyramids
What is the pyramidal decussation?
marks the border between the spinal cord and the medulla oblongata.
What are the pyramids?
- Paired swellings of the medulla found between the anterior median fissure and the ventrolateral sulci
- Located on one either side of anterior median fissure
What is found under the pyramids?
These bumps exist as there is something underneath them - collections of white matter motor fibres coming from the cortex and descending down the CNS
What are descending tracts of the CNS?
The descending tracts are the pathways by which motor signals are sent from the brain to lower motor neurones. The lower motor neurones then directly innervate muscles to produce movement.
The motor tracts can be functionally divided into which two major groups?
- Pyramidal tracts
- Extrapyramidal tracts
Where do the pyramidal tracts originate? Where do they carry motor fibres to? What are they responsible for?
- These tracts originate in the cerebral cortex
- Carry motor fibres to the spinal cord and brain stem.
- They are responsible for the voluntary control of the musculature of the body and face.
What does the right hemisphere control?
The muscles on the left side of the body
What does the left hemisphere control?
Muscles on the right side of the body
As each hemisphere controls the opposite side of the body, the fibres coming from the right hemisphere need to cross the midline of the CNS. Where does this happen?
At the decussation of the pyramids
What is found lateral to the pyramids?
Another bump - the olives (paired)
What sulcus is located between the pyramids and the olives?
Antero-lateral sulcus
Which cranial nerve extends out of the antero-lateral sulcus?
The hypoglossal nerve (CN XII)
Where does the hypoglossal nerve (CN XII) emerge?
At the medulla between the pyramids and the olives (antero-lateral sulcus)
What 2 sulci are found on the anterior surface of the medulla?
- Antero-lateral sulcus
- Postero-lateral sulcus
Where is the postero-lateral sulcus located?
Lateral to the olives
What cranial nerves are found at the postero-lateral sulcus?
CN IX - glossopharyngeal nerve
CN X - vagus nerve
CN XI - spinal accessory nerve
Unlike the anterior surface of the medulla, the posterior surface is largely obstructed from view and is relatively devoid of features. In order to appreciate the posterior surface, what must be removed?
The cerebellum
The floor of the fourth ventricle can be seen in the dorsal surface of the medulla. What is this? What is it also known as?
- Also known as the rhomboid fossa
- This is a rhombus-shaped depression that is the anterior part of the fourth ventricle.
- Its anterior wall, formed by the back of the pons and the medulla oblongata, constitutes the floor of the fourth ventricle.
Similar to the anterior surface, the posterior surface has a midline structure. What is this?
The posterior median fissure
What is found lateral to the posterior median fissure?
The fasciculus gracilis / the gracile fasciculus
What does the gracile fasciculus contain?
White matter fibres travelling from the spinal cord and up towards the brainstem
What is found lateral to the gracile fasciculus?
The cuneate fasciculus