Nasal Cavity

Olfaction & Filtration

A sagittal section A cut or slice of the body or an organ for study. of the headRounded proximal end that fits into the acetabulum of the hip bone. shows the extent of the nasal cavityThe internal space behind the nose that filters, warms, and humidifies incoming air.. This little space right here between the palatineL-shaped bones forming posterior part of hard palate and floor of nasal cavity. bone and the tongue itself is the oral cavity. You can breathe through the oral cavity, but it’s not as good as breathing through the nose. The oral cavity is really designed for eating foods, not inhaling air.

One of the reasons you want to breathe through your nose is olfaction, or the process of sensing smells.  Cranial nerve #1, the olfactory nerve, has dendritesBranch-like extensions from a neuron that receive signals from other neurons. that extend through the cribriform plates of the ethmoidLight, spongy bone between the eyes; forms nasal septum and medial orbit walls. bone. These dendrites hang down into the nasalTwo small rectangular bones forming the bridge of the nose. cavity.  As air enters the nasal cavity, these dendrites send action potentials to the cerebrumThe largest part of the brain, responsible for thought, memory, and voluntary movements. concerning the smells. 

The nasal cavity is capable of some filtrationThe process by which fluid moves out of capillaries into surrounding tissues due to hydrostatic pre of the incoming air that the oral cavity cannot do.  Nasal hairs, macroscopic structures, are covered in mucus allowing them to trap large particulates you might inhale.  There are also microscopic ciliaHair-like projections on the surface of some cells that move fluids or particles., little hairlike projections off the epithelial cellsThe basic structural and functional units of life. lining the nasal cavity.  These cilia can wave in unison. They aim to move the mucus toward the opening of the nose, called the nasal vestibuleThe area between the labia minora.. 

Nasal Cavity

This large open space is the nasal cavity. It is lined with a mucus membrane called the respiratory mucosaThe innermost lining of the digestive tract that contains mucus-secreting cells for protection and a.  These are folds of the nasal mucosa.

The nasal cavity is not just an open void.  There are structures in there that warm air. They also humidify it. These are two things you want your air to be as you inhale it.  These are two benefits of breathing through your nose. Additionialy, your nose aids in olfaction and filtration. 

On a frontalForehead bone; forms the front part of the skull and roof of the orbits. Smooth and curved. section, we see these twists ad turns in the nasal cavity.  These twists and turns are formed by the nasal conchaeCurved, scroll-like bones inside nasal cavity; increase surface area for air warming and filtration. and then are lined by the nasal mucosal folds.  This creates a cavernous nasal cavity. Air is trapped and forced to recirculate just a little longer than it would before being sucked down the pharynxThe muscular passageway connecting the mouth to the esophagus and larynx.. Then, it moves through the windpipe and into the cul-de-sac of the lungs.

The air circulates in the nasal cavity. It is exposed to the capillary plexuses located just deepAway from the surface of the body. to the respiratory mucosa. This allows the air to receive heat and humidity from your blood.

Nasal Mucosa

The nasal cavity as with all open spaces in the body is lined with epithelial tissue. Specifically this epithelial tissue of the respiratory mucosa is pseudostratified columnar epithelia. Recall that this type of epithelia has columnar shaped cells. All these cells touch the basement membrane, making one layer of column-shaped cells. Therefore, this epithelia looks like it is stratified, or made of many layers, but it is not.  

Cillia or fine little extracellular hairs project from the apical surface of the cells.  All of the big bubbly ovals in this picture were once called goblet cells. They now have a name more specific to their purpose, which is secreting mucus. These mucus cells exocytosisThe process of expelling materials from a cell via vesicles that fuse with the plasma membrane. their mucus onto the apical surface of the pseudostratified columnar epithelium.

Sinuses

Sinuses do not contribute to the conductionThe transmission of nerve impulses along neurons. or exchange of gases during respirationThe process of gas exchange, including ventilation, external and internal respiration.. They are still considered to be part of the respiratory systemThe organ system responsible for gas exchange (oxygen and carbon dioxide).. Sinuses are open areas in the skull. They are intended to lighten the skull by filling space with fluid instead of brain or bone. 

The sphenoidButterfly-shaped bone in the middle cranial floor; unites cranial and facial bones. sinus is embedded in the sphenoid bone.  The frontal sinus is in the frontal bone.  This is why if your doctor suspects a sinus infection, they may push on your forehead. They do this to see if it causes pain. 

Sinus infections are commonly caused by bacteria invading these open cavities. As a defense mechanism, your sinusesAir-filled spaces in the skull that lighten it and help humidify air. will begin to weep more fluid into the open spaces. This causes the open space to fill and creates pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange.. Sinus infections are called sinusitis whereas infections of the nasal mucosa are called rhinitis.  Yes, the word rhinitis derives from the same word that rhinoceros does.

Why Breathe through the Nose?

The structures of the nasal cavity include the mucus cells and the blood vessels beneath the surface. The conchaeCurved bony structures in the nasal cavity that increase surface area and help warm, humidify, and f and the meatusesAir passageways between the nasal conchae that direct airflow through the nasal cavity. also play essential roles. All contribute to the warming and humidifying of air as it enters your respiratory system. Have you ever felt like saying, “The cold air took my breath away”? This can happen when you breathe through your mouthThe opening of the digestive tract where food enters and mastication begins. in the winter. The temperature is in single digits during this.

Cold air holds less moisture or humidity then hot air. This is why it only gets humid in the summer. If you had taken that breath through your nose, the air would have spent more time in the nasal cavity. This warms and humidifies the air before it descends into your lungs. This is why athletes are advised to breathe through their noses. It applies whether in warm humid air or cold dry air.