Brainstem And Cerebellum Notes

Brainstem

Components of brain stem: Midbrain, pons, medulla

Medulla: the pyramids (medial) and olives (lateral), which are both visible on the ventral surface. It also contains the dorsal coloumn nuclei

Pons: Pontine nuclei, fibres and floor of the 4^th ventrlice.

Midbrain: The midbrain comprises the tectum (or corpora quadrigemina), tegmentum, the cerebral aqueduct (or ventricular mesocoelia or "iter"), and the cerebral peduncles, as well as several nuclei and fasciculi. the dorsal region is known as the tectum, which is composed largely of two superior and two inferior colliculi. The ventral region is known as the tegmentum. The cerebral aqueduct is also found in this region

Core: cerebral peduncles

At the ventral border of the tegmentum are the crura cerebri (sometimes called cerebral peduncles but this is technically the entire mesencephalon apart from the tectum).

Midbrain

Brainstem components and functions

-Cranial nerves: 3-12

-Ascending and descending tracts originating in the brainstem

-Sensory nuclei/tracts of auditory, vestibular, taste/visceral sensory

-Interconnections vestibular with oculomotor (3,4,5) nuclei

-Diffuse amine fountains- NA, 5-HT, DA

-Passage and relay of tracts originating outside the brainstem

-Ascending somatosensory tracts- medial leminiscus, anterolateral system

-Descending corticospinal, corticobulbal, corticopontine tractics

-Cerebellar connections

-Pontine nuclei, inferior olivary nuclei, lateral reticular nuclei

-Integrative functions- reticular formation; phsycological centers

Cranial nerves

Cranial nerve nuclei: cranial nerve nucleus is a collection of neurons (gray matter) in the brain stem that is associated with one or more cranial nerves. Axons carrying information to and from the cranial nerves form a synapse first at these nuclei. Lesions occurring at these nuclei can lead to effects resembling those seen by the severing of nerve(s) they are associated with. All the nuclei except that of the trochlear nerve (CN IV) supply nerves of the same side of the body.

-In the brainstem folding is less, so alar plate –dorsal (sensory) lies lateral and basal plate (motor)-ventral lies more medial

In general, motor nuclei are closer to the front (ventral), and sensory nuclei and neurons are closer to the back (dorsal). This arrangement mirrors the arrangement of tracts in the spinal cord.

• Close to the midline are the motor efferent nuclei/somatic motor, such as the oculomotor nucleus, which control skeletal muscle.

• Just lateral to this are the branchiomotor / special visceral efferent nuclei- innervate muscles from branchial arches

  • Trigeminal nerve (5), facial nerve (7), glossopharangeal nerve (9), vagus nerve (10) and acessory nerve (11)

• Lateral to the branchio motor lies the parasympathetic (General visceral)

• There is a separation, called the sulcus limitans, and lateral to this are the sensory nuclei. Near the sulcus limitans are the visceral afferent nuclei (taste, carotid body, carotid sinus), namely the solitary tract nucleus.

• More lateral, but also less posterior, are the general somatic afferent nuclei. This is the trigeminal nucleus.

• Back at the dorsal surface of the brainstem, and more lateral are the special somatic afferents, this handles sensation such as hearing and balance balance.

• Another area, not on the dorsum of the brainstem, is where the branchial efferent nuclei reside. These formed from the branchial arches, in the embryo. This area is a bit below the autonomic motor nuclei, and includes the nucleus ambiguus, facial nerve nucleus, as well as the motor part of the trigeminal nerve nucleus.

Rostral caudal organisation of the cranial nerve motor nulcei reflect their developomental origin

-Cranial motor nulcei- related to rhombomeres-compartments in hindbrain each with a specific identity

-Each branchial arch motor nerve is derived from rhombomere pairs

-V, trigeminal nerve- 1^st arch (rhombomere 2+3)

-VII: facial- 2^nd arch (rhombomere 4+5)

-IX: Glossopharyngeal- 3^rd arch – rhombomere 6

-X: vagus, XI accessory- 4^th +6^th arch- rhombomere 7+8

-To see what rhombomere they arise from use fluorescent dyes which are used to trace axons back to cell bodies as they are retrogradely transported

-Rhombomere identity is determined by unique HOX gene code- Hox genes are the vertebrate homologues of Antennapedia-class heomeotic genes of drosophila

-E.g R1/2 boundary is determined by Hox D2, R6/7 Boundary is determined by HOXD4 (more posterior expression)

-Altering Hox gene expression alters identity of neurons

-E.g Facial nerve- three components- sensory, branchiomotor, parasympathetic. Motor componenet has unusual corse looping around abducens nucleus before exiting the brainstem. Facial motor neurons migrate first caudally, medial to abducent nucleus, then laterally t their final position. Axons loop around the abducent nucleus-facial colliculus in floor of 4^th ventricle

-In mice lacking Hoxb1- failure to correctly specify rhombomere 4 derivatives-facial paralysis

Rhombomeric origins and HOX coding don’t explain the position of the sensory nuclei

V: Somatosensory: face, mouth

VII : viscerosensory : taste buds

VIII: special somatosensory : vestibule, cochlea

IX: Viscerosensory: oropharynx, carotid body

X: viserosensory: great vessels, lungs, foregut, midgut

Nuclei present in the Midbrain[hide]

• Mesencephalic trigeminal nucleus (V) - sensory

• Red nucleus - motor, extrapyramidal

• Trochlear nucleus (IV) - motor

• Oculomotor nucleus (III) - motor

• Edinger-Westphal nucleus (III) - visceromotor

Nuclei present in the Pons[hide]

• Cochlear nuclei (VIII) - sensory

  • Dorsal cochlear nucleus

  • Ventral cochlear nucleus

• Vestibular nuclei (VIII) - sensory

• Salivary nuclei - visceromotor

  • Inferior salivary nucleus (IX)

  • Superior salivary nucleus (VII)

• Facial nucleus (VII) - motor

• Abducens nucleus (VI) - motor

• Trigeminal motor nucleus (V) - motor

• Main trigeminal nucleus (V) - sensory (fine touch and vibration)

Nuclei present in the medulla...

Buy the full version of these notes or essay plans and more in our Neuroscience 1 Notes.