nucleus

Examples of nucleus in the following topics:

• Clusters of Neuronal Cell Bodies

  • A nucleus can either by a relatively compact collection of neurons or a distinctly identifiable group of neurons spread over a large area.
  • In neuroanatomy, a nucleus is a brain structure consisting of a relatively compact cluster of neurons.
  • In anatomical sections, a nucleus shows up as a region of gray matter, often bordered by white matter.
  • In addition, nucleus can refer to an identifiable distinct group of neurons that can spread over an extended area.
  • For example, the reticular nucleus of the thalamus is a thin layer of inhibitory neurons that surround the thalamus.

• Pons

  • Within the pons is the pneumotaxic center, a nucleus in the pons that regulates the change from inspiration to expiration.
  • The alar plate produces sensory neuroblasts, which will give rise to the solitary nucleus and its special visceral afferent column, the cochlear and vestibular nuclei (which form the special somatic afferent fibers of the vestibulocochlear nerve), the spinal and principal trigeminal nerve nuclei (which form the general somatic afferent column of the trigeminal nerve), and the pontine nuclei, which is involved in motor activity.
  • Basal plate neuroblasts give rise to the abducent nucleus (forms the general somatic efferent fibers), the facial and motor trigeminal nuclei (form the special visceral efferent column), and the superior salivatory nucleus, which forms the general visceral efferent fibers of the facial nerve.
  • the chief or pontine nucleus of the trigeminal nerve sensory nucleus (V)- mid-pons

• Trochlear (IV) Nerve

  • The nucleus of the trochlear nerve is located in the caudal mesencephalon beneath the cerebral aqueduct.
  • It is immediately below the nucleus of the oculomotor nerve (III) in the rostral mesencephalon.
  • The trochlear nucleus is unique in that its axons run dorsally and cross the midline before emerging from the brainstem.
  • Thus a lesion of the trochlear nucleus affects the contralateral eye.
  • A peripheral lesion is damage to the bundle of nerves, in contrast to a central lesion, which is a damage to the trochlear nucleus.

• Cartilaginous Joints: Symphyses

  • Discs consist of an outer annulus fibrosus, which surrounds the inner nucleus pulposus.
  • The strong annular fibers contain the nucleus pulposus and distribute pressure evenly across the disc.
  • The nucleus pulposus contains loose fibers suspended in a mucoprotein gel with the consistency of jelly.
  • The nucleus of the disc acts as a shock absorber, absorbing the impact of the body's daily activities and keeping the two vertebrae separated.
  • The disc can be likened to a jelly doughnut: whereby the annulus fibrosis is similar to the dough and the nucleus pulposis is the jelly.

• Thalamus

  • In particular, every sensory system (with the exception of the olfactory system) has a thalamic nucleus that receives sensory signals and sends them to the associated primary cortical area.
  • For the visual system, for example, inputs from the retina are sent to the lateral geniculate nucleus of the thalamus, which in turn projects to the primary visual cortex in the occipital lobe.
  • Similarly, the medial geniculate nucleus acts as a key auditory relay between the inferior colliculus of the midbrain and the primary auditory cortex.
  • The ventral posterior nucleus is a key somatosensory relay, which sends touch and proprioceptive information to the primary somatosensory cortex.

• Vagus (X) Nerve

  • The dorsal nucleus of vagus nerve - Sends parasympathetic output to the viscera, especially the intestines.
  • The nucleus ambiguus - Sends parasympathetic output to the heart (slowing it down).
  • The solitary nucleus - Receives afferent taste information and primary afferents from visceral organs.
  • The spinal trigeminal nucleus — Receives information about deep/crude touch, pain, and temperature of the outer ear, the dura of the posterior cranial fossa and the mucosa of the larynx.

• Medulla Oblongata

  • A stroke can injure the pyramidal tract, medial lemniscus, and the hypoglossal nucleus.
  • It is caused by a large mass of gray matter known as the inferior olivary nucleus.
  • They are caused by masses of gray matter known as the nucleus gracilis and the nucleus cuneatus.
  • It is caused by an underlying collection of gray matter known as the spinal nucleus of the trigeminal nerve.
  • The gray matter of this nucleus is covered by a layer of nerve fibers that form the spinal tract of the trigeminal nerve.

• Direct Gene Activation and the Second-Messenger System

  • Upon binding to a ligand, heat shock proteins dissociate from the receptor allowing for homo-dimerization of the receptor, translocation into the nucleus, and binding to specific sequences of DNA known as hormone response elements (HREs).
  • Type II receptors are retained in the nucleus and bind as hetero-dimers to DNA .
  • Hormone action is mediated and amplified within a cell by the action of second messenger mechanisms (molecules which relay signals from receptors on the cell surface to target molecules inside the cell in the cytoplasm or nucleus).
  • Hormone binding to the NR triggers dissociation of heat shock proteins (HSP), dimerization, and translocation to the nucleus, where the NR binds to a specific sequence of DNA known as a hormone response element (HRE).
  • This figure depicts the mechanism of a class II nuclear receptor (NR), which, regardless of ligand-binding status, is located in the nucleus bound to DNA.

• Hypothalamus

  • The extreme lateral part of the ventromedial nucleus of the hypothalamus is responsible for the control of food intake.
  • Medial parts of the nucleus have a controlling effect on the lateral part.
  • Bilateral lesion of the medial part of the ventromedial nucleus causes hyperphagia and obesity.
  • Further lesion of the lateral part of the ventromedial nucleus in the same animal produces complete cessation of food intake.
  • Some differences are apparent even in gross neuroanatomy: most notable is the sexually dimorphic nucleus within the preoptic area.

• Somatic Sensory Pathways to the Cerebellum

  • This is in contrast with the dorsal spinocerebellar tract (C8 - L2/L3), which only has one unilateral axon that has its cell body in Clarke's nucleus (only at the level of C8 - L2/L3).
  • These central processes travel through the dorsal horn where they synapse with second order neurons of Clarke's nucleus.
  • Axon fibers from Clarke's nucleus convey this proprioceptive information in the spinal cord in the peripheral region of the posteriolateral funiculus ipsilaterally until it reaches the cerebellum, where unconscious proprioceptive information is processed.