The olfactory tract (olfactory peduncle or olfactory stalk) is a

bilateral Bilateral may refer to any concept including two sides, in particular: *Bilateria, bilateral animals *Bilateralism, the political and cultural relations between two states *Bilateral, occurring on both sides of an organism ( Anatomical terms of l ...

bundle of

afferent nerve fiber Afferent nerve fibers are axons (nerve fibers) of sensory neurons that carry sensory information from sensory receptors to the central nervous system. Many afferent projections ''arrive'' at a particular brain region. In the peripheral nerv ...

s from the

mitral The mitral valve ( ), also known as the bicuspid valve or left atrioventricular valve, is one of the four heart valves. It has two Cusps of heart valves, cusps or flaps and lies between the atrium (heart), left atrium and the ventricle (heart), ...

and tufted cells of the

olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OF ...

that connects to several target regions in the brain, including the

piriform cortex The piriform cortex, or pyriform cortex, is a region in the brain, part of the rhinencephalon situated in the cerebrum. The function of the piriform cortex relates to the sense of smell. Structure The piriform cortex is part of the rhinencephal ...

amygdala The amygdala (; : amygdalae or amygdalas; also '; Latin from Greek language, Greek, , ', 'almond', 'tonsil') is a paired nucleus (neuroanatomy), nuclear complex present in the Cerebral hemisphere, cerebral hemispheres of vertebrates. It is c ...

, and

entorhinal cortex The entorhinal cortex (EC) is an area of the brain's allocortex, located in the medial temporal lobe, whose functions include being a widespread network hub for memory, navigation, and the perception of time.Integrating time from experience in t ...

. It is a narrow white band, triangular on

coronal section The dorsal plane (also known as the coronal plane or frontal plane, especially in human anatomy) is an anatomical plane that divides the body into dorsal and ventral sections. It is perpendicular to the sagittal and transverse planes. Human an ...

, the apex being directed upward. The term olfactory tract is a misnomer, as the olfactory peduncle is actually made up of the juxtaposition of two tracts, the medial olfactory tract (giving the medial and intermediate olfactory stria) and the lateral olfactory tract (giving the lateral and intermediate olfactory stria). However, the existence of the medial olfactory tract (and consequently the medial stria) is controversial in primates (including humans).

Structure

The olfactory peduncle and

lie in the olfactory sulcus a sulcus formed by the medial orbital gyrus on the inferior surface of each

frontal lobe The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a Sulcus (neur ...

. The olfactory peduncles lie in the sulci which run closely parallel to the midline. Fibers of the olfactory peduncle appear to end in the antero-lateral part of the olfactory tubercle, the dorsal and external parts of the

anterior olfactory nucleus The anterior olfactory nucleus (AON) also called the anterior olfactory cortex, is a major early processing area for olfaction located behind the olfactory bulb, and in the olfactory tract (olfactory peduncle). The AON connects the olfactory pro ...

, the frontal and temporal parts of the prepyriform area, the cortico-medial group of amygdala nuclei and the nucleus of the stria terminalis. The olfactory peduncle divides posteriorly into three main branches: the medial, intermediate and lateral striae. The olfactory peduncle thus terminates in a triangular structure called the olfactory trigone. Caudal to these elements is the

anterior perforated substance The anterior perforated substance is a part of the brain. It is bilateral. It is irregular and quadrilateral. It lies in front of the optic tract and behind the olfactory trigone. Structure The anterior perforated substance is bilateral. It ...

, the anterior part of which is marked by the relief of the olfactory tubercle. Finally, projections from the olfactory peduncle to the anterior olfactory nucleus are sometimes grouped together under the name of superior olfactory stria. The terms olfactory tubercle and olfactory trigone are commonly confused in the literature.

Medial olfactory stria

The medial olfactory stria is classically described as running medially behind the parolfactory area (hence its name) and terminating in the

subcallosal gyrus The subcallosal gyrus (paraterminal gyrus, peduncle of the corpus callosum) is a narrow lamina on the medial surface of the hemisphere in front of the lamina terminalis, behind the parolfactory area, and below the rostrum of the corpus callosum. ...

. However, this description has been rejected for some fifty years. The medial olfactory stria is now described as terminating much more medially, in the ventral tenia tecta.

Intermediate olfactory stria

The intermediate olfactory stria is the branch (or branches) extending from the medial or lateral olfactory striae to the olfactory tubercle and anterior perforated substance. Trolard's term "pectineal formation " is used to refer to multiple intermediate striae extending from the lateral olfactory stria.

Lateral olfactory stria

The lateral olfactory stria is directed across the lateral part of the anterior perforated substance and then bends abruptly medially toward the uncus of the

parahippocampal gyrus The parahippocampal gyrus (or hippocampal gyrus') is a grey matter cortical region, a gyrus of the brain that surrounds the hippocampus and is part of the limbic system. The region plays an important role in memory encoding and retrieval. It ha ...

Clinical significance

Destruction to the olfactory peduncle results in ipsilateral

anosmia Anosmia, also known as smell blindness, is the lack of ability to detect one or more smells. Anosmia may be temporary or permanent. It differs from hyposmia, which is a decreased sensitivity to some or all smells. Anosmia can be categorized int ...

(loss of the ability to smell). Anosmia either total or

partial Partial may refer to: Mathematics *Partial derivative, derivative with respect to one of several variables of a function, with the other variables held constant ** ∂, a symbol that can denote a partial derivative, sometimes pronounced "partial d ...

is a symptom of

Kallmann syndrome Kallmann syndrome (KS) is a hereditary, genetic disorder that prevents a person from starting or fully completing puberty. Kallmann syndrome is a form of a group of conditions termed hypogonadotropic hypogonadism. To distinguish it from other fo ...

genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosome abnormality. Although polygenic disorders ...

that results in disruption of the development of the olfactory peduncle. The depth of the olfactory sulcus is an indicator of such congenital anosmia.

Additional images

File:Gray732.png, Scheme of

rhinencephalon In animal anatomy, the rhinencephalon (from the Greek, ῥίς, ''rhis'' = "nose", and ἐγκέφαλος, ''enkephalos'' = "brain"), also called the smell-brain or olfactory brain, is a part of the brain involved with smell (i.e. olfaction). ...

. (Olfactory tract visible at left.) File:Gray724.png, Base of brain. File:Gray772.png, Plan of olfactory neurons. File:Gray729 olfactory sulcus.png, Orbital surface of frontal lobe olfactory sulcus shown in red.

References

External links

* {{Authority control Olfactory system