Anatomy - Olfaction and Limbic System

Dentate Gyrus

From: Entorhinal cortex (via perforant pathway). To: Hippocampus (via mossy fibers)

Hippocampus

From: Dentate gyrus (via mossy fibers), Septum (via fornix), Limbic lobe (via cingulum). To: Mammillary bodies, Anterior thalamus, Septal area, Tuber cinereum (via fornix), Subcallosal area (via longitudinal striae)

Septal Area

From: Olfactory bulb, Amygdala, Fornix.To: Medial forebrain bundle, Hypothalamus, Habenula

Amygdala

From: Primitive temporal cortex, Sensory association cortex, Opposite amygdala (via anterior commissure). To: Hypothalamus (direct amygdalofugal pathway), Septal area, Hypothalamus (via stria terminalis)

Limbic lobe

Was so named because this cortical complex forms a limbus (border) between the diencephalon and the more lateral neocortex of the telencephalic hemispheres

Limbic lobe

Consists of a ring of cortex outside the corpus callosum, largely made up of the subcallosal and cingulate gyri as well as the parahippocampal gyrus

Limbic System

Includes the functionally interrelated limbic lobe (parahippocampal, cingulate, and subcallosal gyri), the amygdala, and the hippocampal formation and associated structures

Olfactory receptors

Are specialized neurons located in the olfactory mucous membranes, a portion of the nasal mucosa blanketed by a thin layer of mucus, produced by Bowman’s glands

Olfactory receptors

Are highly sensitive and respond with depolarizations when confronted with odor-producing molecules that dissolve in the mucous layer

Olfactory receptors

Contain, in their membranes, specialized odorant receptors that are coupled to G-protein molecules, which link these receptors to adenylate cyclase

Cyclic Adenosine Monophosphate (cAMP)

When a specific odoriferous molecule binds to the appropriate olfactory receptor, it activates the G-protein molecule, which, via adenylate cyclase, generates?

Olfactory bulb

The axons of the olfactory receptors travel within 10–15 olfactory nerves to convey the sensation of smell from upper nasal mucosa through the cribriform plate to the?

Olfactory sulcus

The olfactory bulb and olfactory tract (peduncle) lie in here on the orbital surface of the frontal lobe

Mitral cells

Within the olfactory bulb, the olfactory receptor axons terminate in specialized synaptic arrangement (termed glomeruli) on the dendrites of?

Spatial Map

Olfactory neurons expressing a specific odorant receptor (and thus responsive to a specific odorant stimulus) project precisely to a small number of glomeruli within the olfactory bulb. Thus, there appears to be a this structure within the olfactory bulb that identifies the receptors that have been stimulated

Mitral Cells

Send their axons posteriorly via the olfactory tracts to reach the olfactory projection area in the cortex

Lateral Olfactory Stria

A fiber bundle that projects laterally along the floor of the lateral fissure. Enters the olfactory projection area near the uncus in the temporal lobe

Medial Olfactory Stria

The small medial olfactory stria passes medially and ascends toward the subcallosal gyrus, located near the inferior part of the corpus callosum. Carries the axons of some mitral cells to the anterior olfactory nucleus

Anterior Olfactory Nucleus

Sends its axons back to the olfactory bulbs on both sides, presumably as part of a feedback circuit that modulates the sensitivity of olfactory sensation

Anterior Perforated Substance

A thin layer of gray matter with many openings that permit the small lenticulostriate arteries to enter the brain. Extends from the olfactory striae to the optic tract. Serves a role in olfactory reflex reactions together with the medial stria

Hippocampal Formation

A primitive cortical structure that has been folded in and rolled up so that it is submerged deep into the parahippocampal gyrus

Industrium griseum

What is the other term for supracallosal gyrus which is the gray matter on top of the corpus callosum?

Hippocampal Formation

Receives input from many cortical regions that are relayed to it via the entorhinal cortex, which projects to the dentate gyrus via the perforant pathways

Dentate gyrus

A thin, scalloped strip of cortex that lies on the upper surface of the parahippocampal gyrus. Serves as an input station for the hippocampal formation. One of the few regions of the mammalian brain where neurogenesis continues through adulthood

Neurogenesis

Term for the production of new neurons

Hippocampus

Also called Ammon's horn. Extends the length of the floor of the inferior horn of the lateral ventricle and becomes continuous with the fornix below the splenium of the corpus callosum

Sommer sector

The hippocampus has been divided into several sectors partly on the basis of fiber connections and partly because pathologic processes such as ischemia, produce neuronal injury that is most severe in a portion of the hippocampus, namely?

Dendrite, Pyramidal cell, Axon

The dentate gyrus and the hippocampus itself show the histologic features of an archicortex with three layers, namely?

Juxtallocortex (Mesocortex)

The transitional cortex from the archicortex of the hippocampal formation to the six-layered neocortex (in this area called the subiculum) is ______________, with four or five distinct cortical layers

Temporal neocortex

The hippocampus receives input from many parts of the neocortex, especially the?

Mossy fibers

Granule cells of the dentate gyrus send axons (__________) that terminate on pyramidal neurons in the CA3 region of the hippocampus

Schaffer collaterals

Collateral branches (termed __________) from the CA3 neurons project to the CA1 region

Fornix

The major outflow tract from the hippocampus. An arched white fiber tract extending from the hippocampal formation to the diencephalon and septal area. Carries some incoming axons into the hippocampus and constitutes the major outflow pathway from the hippocampus

Fornix

Its fibers start as the alveus, a white layer on the ventricular surface of the hippocampus that contains fibers from the dentate gyrus and the hippocampus

Hippocampal Commissure

A variable collection of transverse fibers connecting the two crura of the fornix.

Mamillary bodies

Many axons in the fornix terminate in the __________ of the hypothalamus

Entorhinal cortex

Much of the hippocampal input is relayed via the __________ from the temporal neocortex

Papez Circuit

Named after the neuroanatomist who defined it. Ties together the cerebral cortex and the hypothalamus. It provides an anatomic substrate for the convergence of cognitive (cortical) activities, emotional experience, and expression

Subcallosal gyrus

The portion of gray matter that covers the inferior aspect of the rostrum of the corpus callosum

Cingulate gyrus and Parahippocampal gyrus

The subcallosal gyrus continues posteriorly as the?

Supracallosal gyrus (Indusium griseum)

A thin layer of gray matter that extends from the subcallosal gyrus and covers the upper surface of the corpus callosum

Medial and Lateral Longitudinal Striae

Delicate longitudinal strands that extend along the upper surface of the corpus callosum to and from the hippocampal formation

Anterior Commissure

It is a band-like tract of white fibers that crosses the midline to join both cerebral hemispheres

Interbulbar system

A fiber system in the anterior commissure that joins both anterior olfactory nuclei near the olfactory bulbs

Intertemporal system

A fiber system in the anterior commissure that connects the temporal lobe areas of both cerebral hemispheres

Septal Area (Septal Nuclei) (Septal Complex)

An area of gray matter lying above the lamina terminalis and below the rostrum of the corpus callosum, near and around the anterior commissure. A focal point within the limbic system

Septal Area

Connected with the olfactory lobe, amygdala, hippocampus, and the hypothalamus. A “pleasure center” in the brain. Rats with electrodes implanted in the septal area will press a bar repeatedly to receive stimuli in this part of the brain

Septum lucidum

A portion of the septal area, that is a double sheet of gray matter below the genu of the corpus callosum

Amygdala (Amygdaloid Nuclear Complex)

A gray matter mass that lies in the medial temporal pole between the uncus and the parahippocampal gyrus. Situated just anterior to the tip of the anterior horn of the lateral ventricle

Stria terminalis, Amygdalofugal pathway

What are the fiber connections of the amygdala?

Basolateral Nuclear Group

Receives higher-order sensory information from the association area in the frontal, temporal, and insular cortex. Axons run back from the amygdala to the association regions of the cortex

Corticomedial Nuclear Group

Located close to the olfactory cortex. Interconnected with it, as well as the olfactory bulb. Connections also run, via the stria terminalis and amygdalofugal pathway, to and from the brainstem and hypothalamus. Activity of neurons within the amygdala is increased during states of apprehension

Modulating hypothalamic activity

The amygdala also appears to participate in regulating endocrine activity, sexual behavior, and food and water intake, possibly by?

Septal Area

Because it is a pivotal region with afferent fibers from the olfactory and limbic systems and efferent fibers to the hypothalamus, epithalamus, and midbrain, no single function can be ascribed to the area

Antipsychotic drugs

May act in part by modifying dopaminergic inputs from the midbrain to the septal area

Bulimia

Lesions in the lateral amygdala induce unrestrained eating called?

Amygdalectomy

In some cases, this has been performed to suppress these antisocial traits in patients, has sometimes been followed by hypersexuality

Hippocampus

Involved in converting short-term memory (up to 60 minutes) to long-term memory (several days or more)

Anterograde amnesia

Patients with bilateral damage to the hippocampus can demonstrate no new long-term memories can be established

Long-term potentiation

A process whereby synaptic strength is increased when specific efferent inputs to the hippocampus are excited in a paired manner, provides a cellular-molecular basis for understanding the role of the hippocampus in memory and learning

Place cells

The hippocampus contains “__________” that encode spatial memory.

Kluver-Bucy syndrome

This disturbance of the limbic system activity occurs in patients with bilateral temporal lobe lesions. Manifestations are Hyperorality, Hypersexuality, Psychic blindness/Visual agnosia, Personality changes

Hyperorality

Tendency to place objects in the mouth and indiscriminately eating/chewing said objects and all kinds of food

Psychomotor (Complex partial) Seizures

The temporal lobe (especially the hippocampus and amygdala) has a lower threshold for epileptic seizure activity than the other cortical areas. Seizures that originate in these regions, called?

Temporal lobe epilepsy

May include abnormal sensations, especially bizarre olfactory sensations, sometimes called uncinate fits, as well as repeated involuntary movements such as chewing, swallowing, and lip smacking; disorders of consciousness; memory loss; hallucinations; and disorders of recall and recognition