Brainstem Anatomy Flashcards
What is the function of the brainstem?
- performs spinal cord-like functions for the regions of the head and neck
- contains vital centres for the control of:
- cardiorespiratory function
- posture and movement
- wakefulness and sleep
- is the conduit (channel) for important tracts:
–> ascending sensory tracts from the spinal cord
–> descending motor tracts from the forebrain (telencephalon + diencephalon)
What are the components of the brainstem?
Midbrain, pons and medulla oblongata
What are the external features of the ventral (anterior) brainstem?
Pyramids, base of pons (basis pontis) and cerebral peduncles.
Describe the pyramids of the ventral (anterior) surface of the brainstem.
The pyramids are 2 white columns that form the medulla oblongata ventromedially.
i. Formed by a bundle of axon fibres called the corticospinal tract, which transmit information from the cerebral cortex –> spinal cord
ii. Pyramidal decussation: junction of the medulla and spinal cord, 90% of fibres from each pyramid cross the midline to enter the opposite side of the spinal cord
iii. Ventral median sulcus: separate the pyramids
iv. Olives: 2 large swelling visible lateral to the pyramids in the upper (rostral) part of the medulla
Describe the base of pons on the ventral surface of the brainstem.
Forms the ventral surface of the pons, with the basilar groove in the midline (occupied by the basilar artery.
i. Middle cerebellar peduncle (MCP): extension of the base of the pons laterally on each side that enters the cerebellum
1) Largest cranial nerve CN5 arises from the MCP
2) Is the largest of the 3 cerebellar peduncles
Describe the cerebral peduncles on the ventral surface of the brainstem.
The cerebral peduncles are 2 massive white structures that forms the ventral surface of the midbrain.
i. Interpeduncular fossa: separates the 2 cerebral peduncles.
What are the 4 key landmarks on the dorsal (posterior) surface of the brainstem.
Gracile fasciculus + cuneate fasciculus, fourth ventricle, isthmus and superior + inferior colliculi.
How does the fourth ventricle form in the brainstem?
In the more rostral medulla, the gracile and cuneate fasciculi gradually disappear as the central canal opens out to form the fourth ventricle.
Outline the gracile and cuneate fasciculus.
These are 2 paired white columns that form the dorsal surface of the medulla.
i. Function: carry somatosensory information from the limbs and trunk.
1) Gracile: lower limb and trunk
2) Cuneate: upper limb and trunk
What is the exact location of the 4th ventricle?
Between the cerebellum behind and the medulla and pons in front.
What is the rhomboid fossa and what are its key features?
The rhomboid fossa is the floor of the 4th ventricle. Its key features are:
1) Median fissure (in the midline)
2) Sulcus limitans: structure lateral to the median eminences, which is a foetal remnant separating basal plate (motor) from alar plate (sensory) derivatives.
3) Medial eminences: elevation between the median fissure and sulcus limitans (region for motor neuron)
4) Vestibular + acoustic area: area lateral to the sulcus limitans (region for sensory neuron)
5) Roof: superior and inferior medullary vela
6) Lateral boundaries:
a) Cuneate tubercle
b) ICP
c) SCP
What is the isthmus?
Junction between pons and midbrain.
What are the superior and inferior colliculi?
Paired structures forming the dorsal surface of the midbrain (collectively referred to as the tectum)
What are the 2 key internal features of the brainstem?
Tegmentum and Ascending/Descending tracts
Outline the tegmentum (internal feature of brainstem).
The tegmentum is the central core of the brain stem located between the ventricles and the basal part of the brainstem.
It contains:
1) Reticular formation: structure containing various nuclei + numerous ascending and descending tracts
2) Cranial nerves nuclei:
a) Only thing to know here is the prominent spinal nucleus of the trigeminal nerve, which replaces the dorsal horn of the spinal cord and extends throughout the medulla.
