lateral geniculate nucleus

Examples of lateral geniculate nucleus in the following topics:

• Optic (II) Nerve

  • Most of the axons of the optic nerve terminate in the lateral geniculate nucleus (where information is relayed to the visual cortex), while other axons terminate in the pretectal nucleus and are involved in reflexive eye movements.

• Thalamus

  • The thalamus derives its blood supply from four arteries including the polar artery (posterior communicating artery), paramedian thalamic-subthalamic arteries, inferolateral (thalamogeniculate) arteries, and posterior (medial and lateral) choroidal arteries.
  • 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.

• Facial (VII) Nerve

  • The motor part of the facial nerve arises from the facial nerve nucleus in the pons, while the sensory part of the facial nerve arises from the nervus intermedius.
  • The facial nerve forms the geniculate ganglion prior to entering the facial canal.

• Nuclear Size and Density

  • Rutherford was able to put an upper limit on the radius of the gold nucleus of 34 femtometers (fm).
  • Later studies found an empirical relation between the charge radius and the mass number, $A$, for heavier nuclei ($A>20$): $R \approx r\cdot A^{1/3}$ where $r$ is an empirical constant of 1.2–1.5 fm.
  • This gives a charge radius for the gold nucleus ($A=197$) of about 7.5 fm.
  • The nuclear density for a typical nucleus can be approximately calculated from the size of the nucleus:
  • Note that the image is not to scale; in reality the nucleus is vastly smaller than the electron shell.

• Endosymbiotic Theory and the Evolution of Eukaryotes

  • However, the role of endosymbiosis in the development of the nucleus is more controversial.
  • There are several other competing hypotheses as to the origin of eukaryotes and the nucleus.
  • One idea about how the eukaryotic nucleus evolved is that prokaryotic cells produced an additional membrane which surrounded the bacterial chromosome.
  • If the eukaryotic nucleus evolved this way, we would expect one of the two types of prokaryotes to be more closely-related to eukaryotes.
  • Another hypothesis, the nucleus-first hypothesis, proposes the nucleus evolved in prokaryotes first, followed by a later fusion of the new eukaryote with bacteria that became mitochondria.

• Oculomotor (III) Nerve

  • The oculomotor nucleus originates at the level of the superior colliculus.
  • The muscles it controls are the striated muscle in the levator palpebrae superioris and all extraocular muscles, except for the superior oblique muscle and the lateral rectus muscle.
  • The Edinger-Westphal nucleus supplies parasympathetic fibers to the eye via the ciliary ganglion, and controls the pupillae muscle (affecting pupil constriction) and the ciliary muscle (affecting accommodation).
  • It then runs along the lateral wall of the cavernous sinus, above the other orbital nerves, receiving in its course one or two filaments from the cavernous plexus of the sympathetic nervous system, and a communicating branch from the ophthalmic division of the trigeminal nerve.
  • It then divides into two branches that enter the orbit through the superior orbital fissure, between the two heads of the lateral rectus (a muscle on the lateral side of the eyeball in the orbit).

• Characteristics of Eukaryotic DNA

  • Prokaryotic cells are known to be much less complex than eukaryotic cells since eukaryotic cells are considered to be present at a later point of evolution.
  • The single characteristic that is both necessary and sufficient to define an organism as a eukaryote is a nucleus surrounded by a nuclear envelope with nuclear pores.
  • All extant eukaryotes have cells with nuclei; most of a eukaryotic cell's genetic material is contained within the nucleus.
  • Because eukaryotes have mitochondria and prokaryotes do not, eukaryotic cells contain mitochondrial DNA in addition to DNA contained in the nucleus and ribosomes.
  • Eukaryotic DNA is stored in a nucleus, whereas prokaryotic DNA is in the cytoplasm in the form of a nucleoid.

• Cartilaginous Joints: Symphyses

  • The discs consist of an outer annulus fibrosus that surrounds the inner nucleus pulposus.
  • The annulus fibrosus and the nucleus pulposus distribute pressure evenly across the disc.
  • The nucleus pulposus contains loose fibers suspended in a mucoprotein gel with the consistency of jelly.
  • The disc can be likened to a jelly doughnut with the annulus fibrosis as the dough and the nucleus pulposis as the jelly.
  • The lateral and superior view of an invertebral disc, including the vertebral body, intervertebral foramen, anulus fibrosis, and nucleus pulposus.

• Medulla Oblongata

  • A stroke can injure the pyramidal tract, medial lemniscus, and the hypoglossal nucleus.
  • These are the fasciculus gracilis, lying medially next to the midline, and the fasciculus cuneatus, lying laterally.
  • They are caused by masses of gray matter known as the nucleus gracilis and the nucleus cuneatus.
  • The lower part of the medulla, immediately lateral to the fasciculus cuneatus, is marked by another longitudinal elevation known as the tuberculum cinereum.
  • It is caused by an underlying collection of gray matter known as the spinal nucleus of the trigeminal nerve.

• Phylogeny of the Eukarya

  • Eukaryotes are very diverse in phylogenic terms, the common feature being a membrane bound nucleus.
  • The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried.
  • The last common ancestor of all eukaryotes is believed to have been a phagotrophic protist with a nucleus, at least one centriole and cilium, facultatively aerobic mitochondria, sex (meiosis), a dormant cyst with a cell wall of chitin, cellulose, and peroxisomes.
  • Later endosymbiosis led to the spread of plastids in some lineages.