Crown (anatomy)

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Crown
Cranium - neurocranium superior view 2.jpg
A birds-eye view of the crown, which is the highest point of the skull.
Details
System Skeletal system
InsertionsScalp, meninges, bones
ArticulationsSutures
Anatomical terms of bone

The crown is the top portion of the head behind the vertex. The anatomy of the crown varies between different organisms. The human crown is made of three layers of the scalp above the skull. The crown also covers a range of bone sutures, and contains blood vessels and branches of the trigeminal nerve.

Contents

The structure of the human crown provides a protective cavity for the brain and optimizes the crown's ability to ensure the neocortex is safe. Different parts of the neocortex, such as the frontal lobe and the parietal lobe, are protected by the meninges and bone structures. Other organisms, such as whales, have their blowholes on their crown, causing a flattened head shape. Some bird species have a crest located on their crown, used for communication and courtship.

Macroevolution of the human crown has led to different structures between modern and archaic human species, such as significant changes to the cranial vault. The human crown is prone to different injuries and disorders with various causes, medical signs and symptoms, methods of diagnosis, and treatments. For example, illnesses such as cerebrospinal fluid leak, which results in intense headaches that are localised underneath the crown. Other diseases include meningioma, a tumor surrounding essential blood vessels and nerves that may be near the crown, causing symptoms such as memory loss.

Structure

The crown is at the top of the human skull, and contains the different layers of the scalp. [1] The scalp has three distinct layers including the cutaneous layer, a subcutaneous connective tissue layer, and a muscular layer. [1] The crown covers bone layers of the skull. It is between 4 and 7 millimetres (0.16 and 0.28 in) thick, and varies between different people. [2] It tends to increase in thickness with age. [2]

The frontal and parietal bones are joined by the coronal suture. The two separate parietal bones are connected at the sagittal suture. Sobo 1909 46.png
The frontal and parietal bones are joined by the coronal suture. The two separate parietal bones are connected at the sagittal suture.
The blowhole of sperm whales is located on the crown of the head and allows the whale to breathe. Sperm whale blowhole Vincze.jpg
The blowhole of sperm whales is located on the crown of the head and allows the whale to breathe.

Below the crown, the frontal bone and the parietal bones are separated by a range of fibrous joints called sutures. The sutures are an essential part of growth and development, allowing the skull to expand as the brain increases in size. Different sutures between the frontal and parietal bones of the skull expand in specific directions, causing a symmetrically shaped human head. [3] The frontal bone and the parietal bones are joined at the frontal suture. The frontal bone has a number of parts, including the squamous part, the orbital part, and the nasal parts. The frontal bone connects to the parietal bone at the coronal suture to shape the crown and sides of the skull. The two separate parietal bones are joined at the sagittal suture, ensuring the crown is stable. [4] Other structures of the human crown include blood vessels and nerves, which are essential for the allocation of nutrients to the brain, and the transmission of information to the brain. The superficial temporal artery branches from the common external carotid artery and delivers oxygenated blood to the crown. [5] The crown also contains branches of the trigeminal nerve. [2]

The pileated woodpecker on a tree branch, showing its crest which is under the pileum and the crown of the head. Woodpecker 20040529 151837 1c.jpeg
The pileated woodpecker on a tree branch, showing its crest which is under the pileum and the crown of the head.

Organisms such as whales and birds have different crown structures and species use them in different situations. Sperm whales have their blowholes situated asymmetrically on the crown of the head to breathe, causing a flattened head shape. [6] In bird anatomy, the crown is the top of the head, or more specifically the zone from the frons, or forehead, extending posteriorly to the occiput and laterally on both sides to the temples. The upper part of the head, including frons, crown, and occiput, is called the pileum. [7] A bird with a crest covering the pileum is described as "pileated" such as the pileated woodpecker. [8] The range of feathers that make up the crest determines the bird's emotions and courtship behaviors. [9] For instance, bird species such as the northern cardinal move the crest intensely to signify dominance and communication. [6]

Function

The main function of the crown is to protect the brain from specific physical injuries. The neurocranium has the frontal and parietal bones that make up the crown and protect parts of the brain including the frontal lobe as well as the parietal lobe. [10] The three membranes of the meninges ensures stability and prevents injuries directed to these lobes. [10] For instance, the meninges which include flexible sheets between the brain, spinal cord, and skull aim to protect the frontal lobe, located behind the forehead. The cerebrospinal fluid within the ventricles of the skull reduces the extent of the injury by acting as a cushion. [11] Protecting the frontal lobe allows humans to perform motor movements and to execute functions. The parietal lobe of the neocortex which contains a strip targeting the sense of touch and allows for the representation of space for action is protected due to the thick layers of the crown. [12]

Injuries and Diseases

The crown or human head is subjected to a range of injuries and diseases causing the brain to be vulnerable. The extent of the injuries and diseases directed to the human crown causes additional implications to the brain, impacting the individual's ability to function normally. The range of injuries and disorders have specific causes, medical signs and symptoms, diagnosis methods and treatments.

Cerebrospinal fluid leak (CSF leak)

A common disease associated with the crown includes the cerebrospinal fluid leak, which involves the excess removal of fluid within the meninges. The cerebrospinal fluid leak is mainly caused by a head, brain, or spinal injury which tears the meninges membrane. The excessive leakage of the cerebrospinal fluid leads to symptoms that include intense headaches often localised to the crown. [13] An extreme sign of this disorder includes the leakage of fluid from the patient's ears and nose. [13] The diagnosis of the cerebrospinal fluid leak is determined from examinations including a computerised tomography scan which involves an X-ray image of parts of the skull including the crown. [14] Health professionals offer treatments to manage the symptoms associated with the disease. For example, consuming fluids such as water aims to stop excess leakage and reduce headaches, and antibiotics are also provided if signs of infection are clear such as fever and chills. [15]

Meningioma

Meningioma is a cranial disorder and is characterised by tumor growth on the meninges, surrounding the blood vessels and nerves near the crown. The causes of the disorder include a rapid division of cells around the area. The patients that have meningioma develop signs and symptoms including amnesia and epileptic seizures. [16] The direct impact to the frontal lobe of the brain causes symptoms such as weakness to the arms and legs. Diagnosis is made via imaging tests such as magnetic resonance imaging (MRI) which involves high-frequency radio waves and a strong magnetic field allowing for the measurement of protons in the water. [17] The treatments involve surgery to remove the tumor from the patient's meninges and the extent of the surgery depends on the size and aggression of the meningioma. [18]

An obvious fracture to the crown of the skull causing damage to the brain. Cleidocranial2.jpg
An obvious fracture to the crown of the skull causing damage to the brain.

Fractures

Bone fractures to the crown of the head are linear or depressed and range in severity based on the impact to the skull. The linear fracture involves a break to the skull whereas the depressed fracture results in the scatter of skull fragments. [19] The skull fractures are mainly caused by incidents involving a vehicle, assault, or a fall. In more severe cases, penetrating skull fractures are caused by an object such as a metal rod or bullet breaking through the skull completely. Based on the severity of the fracture, symptoms may include nausea, memory loss, concussion, bruise, and lethargy. Another symptom such as bleeding results in the build-up of pressure in the skull since it is an enclosed cavity and thus pushes the brain to the brainstem opening leading to a coma. [20] Diagnosis occurs due to a range of physical exams which identifies the extent of the injury and possible treatments. For example, the computerised tomography scan identifies the site of the fracture and any associated injuries to the brain, whereas magnetic resonance imaging highlights the damaged tissue. The treatments of severe skull fractures include surgery and medication to avoid infection, however, for linear fractures treatment involves rest for approximately 5 to 10 days, so that the crown can heal. [21]

Gorham Disease

Gorham disease is a condition that targets the human musculoskeletal system including the crown of the skull. The chronic disorder involves the progressive loss of bone, although, symptoms such as intense pain are not evident during the initial stages. [22] The cause of the Gorham disease has not been discovered, however, cells associated with the breakdown of fragile and old bones which include osteoclasts are considered to be the main link towards identifying the cause. The symptoms of the disease are clear after a fracture to the crown of the skull causing patients to experience abnormal deformities as well as issues to the nervous system. [23] Diagnosis occurs through physical exams such as X-rays and magnetic resonance imaging which find the decrease in bone mass (osteolysis) and deformities. Treatment of the disease involves a range of techniques to prevent spread from the skull to the spine or chest of the patient. Chemotherapy and surgery, as well as lifestyle changes such as consuming a diet of high protein, aim to minimise the severity of the disease. [24]

Evolution

The macroevolution of the human species resulted in changes such as the increase in bone and muscle structures that support the crown of the head, compared to primates. Modern human species have a cranial base which is more angled and a cranial vault that is rounded, compared to archaic human species. Modern human species have their temporal lobes positioned under the cranial base signifying the increase in the size of the human brain and skull. [25]

The sagittal vault's morphology, which is the area that joins the two parietal bones together to make up the structure of the crown, has remained the same for archaic and modern human species. The cartilage embedded within the skull plays a major role in the changes of the crown. [26] The cartilage evident within the cranium were an essential part in defending the central nervous system, however, over time the cartilage began to shape the crown by a process known as endochondral ossification. This process involves the replacement of grown cartilage with bone to develop the bone structure of the skull. [27]

See also

Related Research Articles

<span class="mw-page-title-main">Cerebrospinal fluid</span> Clear, colorless bodily fluid found in the brain and spinal cord

Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates.

<span class="mw-page-title-main">Head injury</span> Serious trauma to the cranium

A head injury is any injury that results in trauma to the skull or brain. The terms traumatic brain injury and head injury are often used interchangeably in the medical literature. Because head injuries cover such a broad scope of injuries, there are many causes—including accidents, falls, physical assault, or traffic accidents—that can cause head injuries.

<span class="mw-page-title-main">Skull</span> Bony structure that forms the head in vertebrates

The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone, however two parts are more prominent: the cranium and the mandible. In humans, these two parts are the neurocranium (braincase) and the viscerocranium that includes the mandible as its largest bone. The skull forms the anterior-most portion of the skeleton and is a product of cephalisation—housing the brain, and several sensory structures such as the eyes, ears, nose, and mouth. In humans, these sensory structures are part of the facial skeleton.

<span class="mw-page-title-main">Fontanelle</span> Anatomical feature of the infant human skull

A fontanelle is an anatomical feature of the infant human skull comprising soft membranous gaps (sutures) between the cranial bones that make up the calvaria of a fetus or an infant. Fontanelles allow for stretching and deformation of the neurocranium both during birth and later as the brain expands faster than the surrounding bone can grow. Premature complete ossification of the sutures is called craniosynostosis.

<span class="mw-page-title-main">Meninges</span> Three membranes that envelop the brain and spinal cord

In anatomy, the meninges are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in the subarachnoid space between the arachnoid mater and the pia mater. The primary function of the meninges is to protect the central nervous system.

<span class="mw-page-title-main">Pia mater</span> Delicate innermost layer of the meninges, the membranes surrounding the brain and spinal cord

Pia mater, often referred to as simply the pia, is the delicate innermost layer of the meninges, the membranes surrounding the brain and spinal cord. Pia mater is medieval Latin meaning "tender mother". The other two meningeal membranes are the dura mater and the arachnoid mater. Both the pia and arachnoid mater are derivatives of the neural crest while the dura is derived from embryonic mesoderm. The pia mater is a thin fibrous tissue that is permeable to water and small solutes. The pia mater allows blood vessels to pass through and nourish the brain. The perivascular space between blood vessels and pia mater is proposed to be part of a pseudolymphatic system for the brain. When the pia mater becomes irritated and inflamed the result is meningitis.

<span class="mw-page-title-main">Dura mater</span> Outermost layer of the protective tissues around the central nervous system (meninges)

In neuroanatomy, dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous system. The other two meningeal layers are the arachnoid mater and the pia mater. It envelops the arachnoid mater, which is responsible for keeping in the cerebrospinal fluid. It is derived primarily from the neural crest cell population, with postnatal contributions of the paraxial mesoderm.

<span class="mw-page-title-main">Subdural hematoma</span> Hematoma usually associated with traumatic brain injury

A subdural hematoma (SDH) is a type of bleeding in which a collection of blood—usually but not always associated with a traumatic brain injury—gathers between the inner layer of the dura mater and the arachnoid mater of the meninges surrounding the brain. It usually results from tears in bridging veins that cross the subdural space.

<span class="mw-page-title-main">Intracranial hemorrhage</span> Hemorrhage, or bleeding, within the skull

Intracranial hemorrhage (ICH), also known as intracranial bleed, is bleeding within the skull. Subtypes are intracerebral bleeds, subarachnoid bleeds, epidural bleeds, and subdural bleeds.

<span class="mw-page-title-main">Craniosynostosis</span> Premature fusion of bones in the skull

Craniosynostosis is a condition in which one or more of the fibrous sutures in a young infant's skull prematurely fuses by turning into bone (ossification), thereby changing the growth pattern of the skull. Because the skull cannot expand perpendicular to the fused suture, it compensates by growing more in the direction parallel to the closed sutures. Sometimes the resulting growth pattern provides the necessary space for the growing brain, but results in an abnormal head shape and abnormal facial features. In cases in which the compensation does not effectively provide enough space for the growing brain, craniosynostosis results in increased intracranial pressure leading possibly to visual impairment, sleeping impairment, eating difficulties, or an impairment of mental development combined with a significant reduction in IQ.

<span class="mw-page-title-main">Cribriform plate</span> Part of the ethmoid bone in the skull

In mammalian anatomy, the cribriform plate, horizontal lamina or lamina cribrosa is part of the ethmoid bone. It is received into the ethmoidal notch of the frontal bone and roofs in the nasal cavities. It supports the olfactory bulb, and is perforated by olfactory foramina for the passage of the olfactory nerves to the roof of the nasal cavity to convey smell to the brain. The foramina at the medial part of the groove allow the passage of the nerves to the upper part of the nasal septum while the foramina at the lateral part transmit the nerves to the superior nasal concha.

<span class="mw-page-title-main">Skull fracture</span> Medical condition

A skull fracture is a break in one or more of the eight bones that form the cranial portion of the skull, usually occurring as a result of blunt force trauma. If the force of the impact is excessive, the bone may fracture at or near the site of the impact and cause damage to the underlying structures within the skull such as the membranes, blood vessels, and brain.

<span class="mw-page-title-main">Basilar skull fracture</span> Medical condition

A basilar skull fracture is a break of a bone in the base of the skull. Symptoms may include bruising behind the ears, bruising around the eyes, or blood behind the ear drum. A cerebrospinal fluid (CSF) leak occurs in about 20% of cases and may result in fluid leaking from the nose or ear. Meningitis occurs in about 14% of cases. Other complications include injuries to the cranial nerves or blood vessels.

<span class="mw-page-title-main">Cranial cavity</span> Space inside the skull formed by eight cranial bones known as the neurocranium

The cranial cavity, also known as intracranial space, is the space within the skull that accommodates the brain. The skull minus the mandible is called the cranium. The cavity is formed by eight cranial bones known as the neurocranium that in humans includes the skull cap and forms the protective case around the brain. The remainder of the skull is called the facial skeleton. Meninges are protective membranes that surround the brain to minimize damage to the brain in the case of head trauma. Meningitis is the inflammation of meninges caused by bacterial or viral infections.

<span class="mw-page-title-main">Superior sagittal sinus</span> Anatomical structure of the brain

The superior sagittal sinus, within the human head, is an unpaired area along the attached margin of the falx cerebri. It allows blood to drain from the lateral aspects of anterior cerebral hemispheres to the confluence of sinuses. Cerebrospinal fluid drains through arachnoid granulations into the superior sagittal sinus and is returned to venous circulation.

<span class="mw-page-title-main">Head and neck anatomy</span>

This article describes the anatomy of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat.

<span class="mw-page-title-main">Fibrous joint</span> Fixed joints between bones held together by dense, fibrous tissue

In anatomy, fibrous joints are joints connected by fibrous tissue, consisting mainly of collagen. These are fixed joints where bones are united by a layer of white fibrous tissue of varying thickness. In the skull, the joints between the bones are called sutures. Such immovable joints are also referred to as synarthroses.

Cerebrospinal fluid rhinorrhoea refers to the drainage of cerebrospinal fluid through the nose (rhinorrhoea). It is typically caused by a basilar skull fracture, which presents complications such as infection. It may be diagnosed using brain scans, and by testing to see if discharge from the nose is cerebrospinal fluid. Treatment may be conservative, but usually involves neurosurgery.

<span class="mw-page-title-main">Cerebrospinal fluid leak</span> Medical condition

A cerebrospinal fluid leak is a medical condition where the cerebrospinal fluid (CSF) that surrounds the brain and spinal cord leaks out of one or more holes or tears in the dura mater. A CSF leak is classed as either nonspontaneous (primary), having a known cause, or spontaneous (secondary) where the cause is not readily evident. Causes of a primary CSF leak are those of trauma including from an accident or intentional injury, or arising from a medical intervention known as iatrogenic. A basilar skull fracture as a cause can give the sign of CSF leakage from the ear nose or mouth. A lumbar puncture can give the symptom of a post-dural-puncture headache.

The following outline is provided as an overview of and topical guide to the human brain:

References

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  13. 1 2 "Cerebrospinal Fluid (CSF) Leak - Symptoms and Causes". www.pennmedicine.org. Retrieved 2020-10-20.
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