Brain stem and cranial nerves Flashcards
What are the major parts of the brainstem?
Midbrain - divided into dorsal tectum and ventral tegmentum
Pons - lies between medulla and the midbrain
Medulla oblongata - conical continuation of the spinal cord within the skull, beginning at the foramen magnum. It’s limited above by the caudal border of the pons and the bulbopontine sulcus.
How can the midbrain be divided up?
The midbrain can be divided into the tectum and the paired cerebral peduncles. Internally, the cerebral peduncles are further separated by the substania nigra into the crus cerebri (anterior) and the tegmentum (posterior).
What makes up the tectum?
The tectum houses four rounded prominences named colliculi (collectively the corpora quadrigemina) which sit directly inferior to the pineal gland. The colliculi are separated by the cruciform sulcus.
Superior colliculi - part of the visual system, concerned with eye reflexes
Inferior colliculi - part of the auditory system, concerned with the reflex of looking towards a loud noise
What are the cerebral peduncles?
The paired cerebral peduncles extend from the cerebral hemispheres to converge as they meet the pons. They are separated anteriorly in the midline by the interpeduncular fossa
What are the crus cerebri?
The crus cerebri is the anterior portion of the cerebral peduncle which contains the motor tracts, travelling from the cerebral cortex to the pons and spine. It contains the following tracts:
Frontopontine fibres – located most medially.
Corticospinal fibres – motor fibres from the primary motor cortex.
Corticobulbar tracts – motor fibres from the primary motor cortex.
Temporopontine fibres – located posterolaterally.
What are the different parts of the substantia nigra?
The substantia nigra – a pigmented nucleus that separates the two regions of the cerebral peduncles. It is further broken down into the pars reticulata (anterior) and pars compacta (posterior).
Which nerves can be found in the periaquaductal grey matter?
Within the periaqueductal gray matter lies the mesencephalic nucleus of the trigeminal nerve, as well as the trochlear nucleus with its fibres continuing around the gray matter to exit the midbrain.
What is the structure of the pons?
It is a group of nerves that function as a connection between the cerebrum and cerebellum.
The anterior or ventral surface of the pons is marked by a bulging formed by the transverse pontocerebellar fibers. The basilar groove demarcates the midline of the ventral surface and is where the basilar artery is located.
What is the pontomedullary junction?
The pontomedullary junction is an important anatomical landmark defined by the angle between the lower border of the pons and the superior border of the medulla.
Which cranial nerves come from the pons?
CNV, VI, VII, VIII originate from the ventral surface of the pons.
How is the pons connected to the cerebellum?
The pons is intimately related to the cerebellum, and is connected to it by the middle cerebellar peduncles. Removal of the cerebellum will reveal the underlying fourth ventricle.
What marks the floor of the fourth ventricle?
The medial eminence marks the midline of the floor of the fourth ventricle
What is the facial colliculus?
The facial colliculus is a bulge formed by the fibers of the facial nerve looping around the abducens nucleus.
What is the stria medullaris?
The stria medullaris of the fourth ventricle is a bundle of nerve fibers crossing transversely from the lateral aspect into the midline. They mark the posterior border between the pons and the medulla.
What is the cerebellopontine junction?
The angle formed at the junction of the pons, medulla, and cerebellum is another anatomical landmark and is named cerebellopontine angle.
What are the two major parts of the pons?
The ventral pons contains the pontine nuclei, which are responsible for coordinating movement. Fibers from the pontine nuclei cross the midline, and form the middle cerebellar peduncles on their way to the cerebellum.
The tegmentum is the evolutionarily older part of the pons which forms part of the reticular formation – a set of nuclei found throughout the brainstem that are responsible for arousal and attentiveness.
What tracts go through the pons?
Descending corticospinal tracts – responsible for voluntary motor control of the body.
Descending corticobulbar tracts – responsible for voluntary motor control of face, head and neck.
Ascending medial lemniscus tracts – responsible for fine touch, vibration and proprioception.
Ascending spinothalamic tracts – responsible for pain and temperature sensation
