#14116 - Brainstem And Cerebellum - Neuroscience 1

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[hide]

• Hypoglossal nucleus (XII) - motor

• Dorsal motor nucleus of vagus nerve (X) - visceromotor

• Nucleus ambiguus (IX, X, XI) - motor

• Solitary nucleus (VII, IX, X) - sensory

• Spinal trigeminal nucleus (V) - sensory (crude touch, temperature and pain)

• Inferior olivary nucleus afferent fibres to cerebellum

Core: brainstem nuclei

Core: dorsal column nuclei

The dorsal column nuclei (nucleus gracilis and nucleus cuneatus) contain the cell bodies of second-order neurons of the dorsal columns.

They can be seen just ventral to the fasciculus gracilis and fasciculus cuneatus in the caudal and mid medulla.

Core: olivary nuclei

The inferior olivary nucleus can be seen in the rostral medulla, just dorsal and lateral to the pyramids.

The superior olivary nucleus is on the dorsal surface of the trapezoid body, which is in the pontine tegmentum.

Core: pontine nuclei

Primary motor cortex –corticopontine fibres ipsilateral pontine nucleus –pontocerebellar projection contralateral cerebellum via the middle cerebellar peduncle.

Core: periaqueductal grey

Locations of nuclei

-The trigeminal sensory nucleus takes the position of the dorsal horn in the transition from spinal cord to medulla. It extends up to the pons. The more caudal part of this nucleus (medulla) is the spinal nucleus. The more rostral part (pons) is the principal nucleus.

-The solitary nucleus also runs the full length of the medulla, receiving visceral and taste sensation from VII, X and XI.

-In the rostral medulla are:

• The hypoglossal nucleus, just lateral to the midline.

• The dorsal motor nucleus of the vagus, just lateral to the hypoglossal nucleus.

• The vestibular nucleus in the lateral part of the floor of the fourth ventricle.

• The cochlear nucleus, dorsally and laterally to the inferior cerebellar peduncles.

• The nucleus ambiguus, just dorsal to the inferior olivary nucleus.

In the pontine tegmentum are:

• The abducens nucleus

• The facial motor nucleus

• The trigeminal motor nucleus

• Between the floor of the fourth ventricle in the pons and the lateral edge of the PAG in the midbrain is the mesencephalic nucleus.

In the ventral part of the PAG in the midbrain are:

• The trochlear nucleus at the level of the inferior colliculi

• The ocolomotor nucleus and Edinger-Westphal nucleus at the level of the superior colliculi.

Auditory pathways

-Bilateral upward projection

Vestibular system (balance)

Taste and visceral afferents terminate in solitary nucleus (7,9,10)

Somatosensory pathways

-Discriminative touch- dorsal columns to dorsal column nuclei, medial leminiscus to thalamus-medial leminiscus

-Anterolateral system-second order dorsal horn projection neurons through spinothalamic tract. Also spinoreticular, spinomesencephalic, spinothalamic

Trigeminal pathways (somatosensation from face)

-Second order projections from spinal trigeminal nucleus (pain and temp) cross and join the anterolateral projection to the thalamus

Descending pathways- corticospinal tracts

-cortical spinal tract descend through cerebral peduncle,

-Corticopontine- descend through pons

-Corticobulbar- ventral medulla

Medial longitudinal fasciculus

-Inter connections between oculomotor nulcei and vestibular system – oculomotor complex, trochlear nucleus, abducens nucleus

-Continous with tectospinal tract which controls neck movements

Cerebellum

-The cerebellum develops in the roof of the IVth ventricle.

-The cerebellum lies underneath the tentorium cerebelli and posterior to the fourth ventricle, pons and medulla.

-It consists of two ovoid cerebellar hemispheres joined in the midline by the narrow median vermis.

Core:...