Changes

*Those animals with a better sense of smell have more highly innervated olfactory epithelium.

*Those animals with a better sense of smell have more highly innervated olfactory epithelium.

*It is the mucous membrane of the dorsal nasal conchae that is sensitive to smell. Here, odourants dissolve in the mucous membrane, and it is these odourants that are recognised by the olfactory sensory receptors. Sensory cilia, that are present on the surface of the olfactory receptors, project into the film of mucous.

*It is the mucous membrane of the dorsal nasal conchae that is sensitive to smell. Here, odourants dissolve in the mucous membrane, and it is these odourants that are recognised by the olfactory sensory receptors. Sensory cilia, that are present on the surface of the olfactory receptors, project into the film of mucous.

*The mucous also contains antibodies, to prevent infection. This is because the olfactory neurones provide a direct passage, via the olfactory nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|CN I]]), to the brain.

*The mucous also contains antibodies, to prevent infection. This is because the olfactory neurones provide a direct passage, via the olfactory nerve ([[Cranial Nerves - Anatomy & Physiology|CN I]]), to the brain.

==Vasculature==

==Vasculature==

==Innervation==

==Innervation==

*Sensory innervation is provided by the olfactory nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|CN I]]).

*Sensory innervation is provided by the olfactory nerve ([[Cranial Nerves - Anatomy & Physiology|CN I]]).

==Central Olfactory Pathways==

==Central Olfactory Pathways==

*The olfactory receptors are embedded in the mucous membrane within the nasal cavity. They are bipolar neurones, and are covered with cilia (non-motile).

*The olfactory receptors are embedded in the mucous membrane within the nasal cavity. They are bipolar neurones, and are covered with cilia (non-motile).

*It is thought that these cilia contain the active sites for the olfactory transduction process.

*It is thought that these cilia contain the active sites for the olfactory transduction process.

*The axons from the olfactory receptors join together and become the olfactory nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|CN I]]). The axons pass through the perforations in the cribriform plate of the ethmoid bone, and enter the olfactory bulb.

*The axons from the olfactory receptors join together and become the olfactory nerve ([[Cranial Nerves - Anatomy & Physiology|CN I]]). The axons pass through the perforations in the cribriform plate of the ethmoid bone, and enter the olfactory bulb.

*Once the axons have entered the olfactory bulb, the olfactory nerve synapses on mitral cells. The axons from these cells then project into the olfactory cortex of the cerebral hemispheres, via the olfactory tract.

*Once the axons have entered the olfactory bulb, the olfactory nerve synapses on mitral cells. The axons from these cells then project into the olfactory cortex of the cerebral hemispheres, via the olfactory tract.

*The olfactory cortex is the only region within the cerebral hemispheres that receives direct sensory input without any information first passing through the thalamus. This is because the olfactory system evolved before the thalamus.

*The olfactory cortex is the only region within the cerebral hemispheres that receives direct sensory input without any information first passing through the thalamus. This is because the olfactory system evolved before the thalamus.

*It is positioned at the base of the nasal cavity, within the roof of the mouth, and is separated into two parts by the nasal septum. It is situated close to the vomer and nasal bones, hence the name vomeronasal organ.

*It is positioned at the base of the nasal cavity, within the roof of the mouth, and is separated into two parts by the nasal septum. It is situated close to the vomer and nasal bones, hence the name vomeronasal organ.

*It is contained within a bony capsule which opens into the base of the nasal cavity, and is lined with olfactory mucosa.

*It is contained within a bony capsule which opens into the base of the nasal cavity, and is lined with olfactory mucosa.

*The vomeronasal organ contains sensory chemoreceptors, and is involved in the first processing step of the accessory olfactory system. The vomeronasal organ carries information via the olfactory nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|CN I]]), which travels through the cribrifrom plate, to the accessory olfactory bulb (the vomeronasal bulb), and then to the hypothalamus. The sensory receptors are found on the medial inner surface of the vomeronasal organ. The lateral inner surface is covered with sensory cilia. Basal cells are also found in this region. The dorsal and ventral inner surfaces of the vomeronasal organ comprise the vomeronasal glands, which function to fill the organ with fluid.

*The vomeronasal organ contains sensory chemoreceptors, and is involved in the first processing step of the accessory olfactory system. The vomeronasal organ carries information via the olfactory nerve ([[Cranial Nerves - Anatomy & Physiology|CN I]]), which travels through the cribrifrom plate, to the accessory olfactory bulb (the vomeronasal bulb), and then to the hypothalamus. The sensory receptors are found on the medial inner surface of the vomeronasal organ. The lateral inner surface is covered with sensory cilia. Basal cells are also found in this region. The dorsal and ventral inner surfaces of the vomeronasal organ comprise the vomeronasal glands, which function to fill the organ with fluid.

*The function of the vomeronasal organ is carried out by the sensory chemoreceptors. They can detect specific chemical compounds, including pheromones (although pheromones can also be detected by the normal olfactory pathway).  

*The function of the vomeronasal organ is carried out by the sensory chemoreceptors. They can detect specific chemical compounds, including pheromones (although pheromones can also be detected by the normal olfactory pathway).  

*As the information that is picked up by the vomeronasal organ is sent to the accessory olfactory bulb and then the hypothalamus, as opposed to the olfactory bulb and then the cerbral cortex, this may explain why some specific chemical compounds within scents may induce aggressive or mating behaviour.

*As the information that is picked up by the vomeronasal organ is sent to the accessory olfactory bulb and then the hypothalamus, as opposed to the olfactory bulb and then the cerbral cortex, this may explain why some specific chemical compounds within scents may induce aggressive or mating behaviour.