The brain is a brilliant organ, and there is still so much to find out about it and how it functions. The brain gives us meaning to the world, and all that is associated with it. This meaning is determined by the five senses of the brain; sight, hearing, smell, touch, and taste, these senses are often received via multiple signals at the same time.
There are many different sections of the brain, these control humans, thoughts, speech, memory, limbs, and other important functions of the human body. The brain also regulates heart, and breathing rhythms according to different environmental situations.
Brains vary in weight from birth to adulthood, with the brain weighing on average one pound at birth, and grows to weigh around 2.7 pounds for an adult female, and an adult male brain weighs around three pounds.
The Nervous System
The nervous system is divided between the central nervous system (CNS) and the peripheral nervous system. The CNS is located within the brain, its cranial nerves, and the spinal cord. Whereas, the peripheral nervous system is made up of the spinal nerves, that shoot from the spinal cord, and the autonomous nervous system. The nervous system is divided between the sympathetic and parasympathetic nervous systems.
How brain cells are structured
The brain is mainly made from two cell types, neurons and glial cells, sometimes known as neuroglia or glia. Neurons are cells within the nervous system that transmit and receive information to other nerve cells, muscle, or gland cells. Glial cells are nonneuronal cells that maintain homeostasis, provide nutrition and support, form myelin to protect neurons, and helps signal transmission in the nervous system. They are the most abundant cell types within the CNS and include; oligodendrocytes, astrocytes, ependymal cells, Schwann cells – which are named after German physiologist Theodor Schwann, microglia, and satellite cells.
The Meninges
The brain is protected by a shell, which is called the cranium, the purpose of the cranium is to protect the brain from damage. Located between the skull and the brain is the meninges, the meninges consist of three layers of tissue, these protect and cover the brain, and spinal cord. These three layers of tissue from the outermost layer are the pia mater, arachnoid, and the dura mater.
Dura Mater
The dura mater located in the brain is made from two layers of whitish, nonelastic membrane. The outer layer is known as the periosteum. The inner layer, dura, lines the inside of the complete skull, it is composed of many small compartments, parts of the brain are secured in these compartments, gaining protection. The dura has two special folds, called the tentorium, which separates the top and bottom of the brain.
Arachnoid
The second layer of the meninges known as the arachnoid, is thin and quite delicate, and covers the entire brain. A space located between the dura and the arachnoid membranes called the subdural space can be opened by the separation of the arachnoid mater via the dura mater as a result of trauma. The arachnoid is a delicate section within the brain and is composed of elastic tissue, and blood vessels, of a multitude of different sizes.
Pia Mater
The pia mater is located closest to the surface of the brain. The pia mater is covered in may blood vessels that travel into deep areas of the brain. The pia which again covers all of the brains surface, follows the brain’s folds. Major arteries that supply the brain, provide the pia with its blood supply. Where the pia and the arachnoid are separated is named the subarachnoid space, within this space is where cerebrospinal fluid flows.
Cerebrospinal Fluid
Cerebrospinal fluid (CSF) surrounds the brain and the spinal cord. The fluid is clear and watery, and help to protect the brain and spinal cord from injury. The cerebrospinal fluid circulates through ventricles around the spinal cord, and the brain, cerebrospinal fluid is constantly absorbed by the brain, and is constantly being reproduced. Specialized structures within the ventricles, called the choroid plexus, reproduce cerebrospinal fluid. The correct equilibrium of the cerebrospinal fluid is regulated by the three control systems within the brain, the autonomic nervous system influences choroid plexus CSF secretion, with activation of the sympathetic nervous system increasing secretion and the parasympathetic nervous system decreasing it.
The Ventricular System
The ventricular system stems into four different ventricles, these ventricles are connected via multiple holes, medically known as foramen
Enclosed in the cerebral hemispheres are two ventricles named the lateral ventricles. These lateral ventricles communicate with another ventricle called the Formen of Monro, which is located in a separate opening. The Foramen of Munro is located in the center of the brain, with the thalamus and hypothalamus making up its walls.
The Formen of Munro ventricle is connected to the Aqueduct of Sylvius, via a long tube.
Cerebrospinal fluid (CSF) travels through the Aqueduct of the Sylvius ventricle, supplying the brain, and spinal cord, via another series of foramen.
The brains sections and functions
Brainstem
The brainstem is the lower part of the brain, it is located at the front of the cerebellum, and is attached to the spinal cord. The brain stem includes; the pons, the midbrain, and the medulla oblongata. The brainstem is looked at as an information center, which transmits, and receives information around the body, and the cerebral cortex. The msot basic survival mechanisms are regulated in the brainstem.
It is also here that ocular motion is regulated by the midbrain, ocular motion or ocular motor skills can be described as the location and fixation of objects by the eye. This allows the eye to coordinate smooth focus, and movements of the eyes to focus and follow what is been seen. The pons regulates coordinating eye and facial movements, hearing and balance, and facial movements.
Many simple or primitive functions that are essential for survival are located here.
The medulla oblongata is a long stem-like section that regulates human blood pressure, breathing, swallowing, and heart rhythms. The brainstem and the pons, send messages to the cortex, which consecutively sends the information to the spinal cord, and the spinal cords associated nerve system. If serious damage is inflicted to these regions of the brain, it may cause brain death, as humans can not survive without these basic functions.
The reticular activating system (RAS) is located within the pons, midbrain, medulla, and part of the thalamus. The reticular activating system controls wakefulness, control of the circadian rhythm, and promotes attention spans.
Located within the brain stem are ten out of the 12 cranial nerves, these, control; eye movement, facial sensations, hearing, taste, swallowing, and movements associated with; tongue muscles, face, neck, and shoulders.
Cerebellum
The cerebellum is located at the rear of the brain, under the occipital lobes. The fold of dura or otherwise known as the tentorium separates the cerebellum from the cerebrum. The cerebellum promotes accuracy for fine motor movements, these movements could be associated with, surgeons performing surgery. Other roles the cerebellum promotes are; a sense of balance, maintain posture, control muscle tone, and limb movements, such as flexion, and extension. Also, the cerebellum is fundamental in enabling a human to perform rapid and repetitive actions, such as video gaming.
Cerebrum
The cerebrum is the largest component of the brain, and is divided into two individual sections, these are the right and left cerebral hemispheres. The two hemispheres are separated by a fissure or otherwise known as a groove, this is called the great longitudinal fissure. The right and left cerebral hemispheres are joined by the corpus callosum, the corpus callosum passes messages from one half of the hemisphere to the other. The cerebrum’s surface contains billions of neurons, and glia, which form the cerebral cortex.
The cerebral cortex, which is greyish in colour, is known as gray matter. When looking at the surface of the brain, it is wrinkled, these wrinkles in the cerebral cortex have sulci (small grooves), fissures (larger grooves), and bulges between the grooves, known as gyri. Below the cerebral cortex is a white coloured area called the white matter.
The cerebral hemispheres have several fissures, these fissures are divided into pairs of lobes (lobes meaning large areas of the brain). These lobes are named; frontal, parietal, temporal, and occipital. These lobes are also divided again into more specific functioning areas of the brain. These lobes function not alone, but in combined actions of the other lobes.
The brain delivers messages in many different ways, these messages are transported via pathways. If the brain incurs trauma, this may affect the transportation of information to the different lobes. This may lead to the loss of certain functions, such as; speech, follow instructions, or the ability to read. In a healthy brain, messages can be delivered to, one bulge to the other (gyri to gyri), from the left hemisphere to the right hemisphere, and from the lobes to other deep parts such as the thalamus, also deep structures of the brain to regions within the central nervous system.
Through research, scientists have determined that sending impulses to one hemisphere will send messages to the other hemisphere. Sending signals to the primary motor cortex located on the right hemisphere would cause the left side of the body to move. While stimulating the left primary motor cortex would cause the right side of the body to move. This determines that the left side of the brain controls the right side of the body, while the right side of the brain controls the left. So if a human has a tumor located on the right side of the brain, localized to the primary motor cortex, it will adversely affect the movement of the left associated limb.
Cranial Nerves
Cranial nerves originate from the brain, and these nerves are responsible for specific actions. There are a total of 12 pairs of cranial nerves, these are:
- Olfactory: Smell
- Trigeminal: Facial sensation
- Optic: Visual fields and ability to see
- Abducens: Eye movements
- Trochlear: Eye movements
- Oculomotor: Eye movements; eyelid opening
- Glossopharyngeal: Taste sensation; swallowing
- Facial: Eyelid closing; facial expression; taste sensation
- Auditory/vestibular: Hearing; sense of balance
- Accessory: Control of neck and shoulder muscles
- Vagus: Swallowing; taste sensation
- Hypoglossal: Tongue movement
Hypothalamus
The hypothalamus sends messages via nerve connections to the pituitary gland, and it processes information that is received from the autonomic nervous system. The hypothalamus controls actions such as sleeping, sexual behaviors, and eating. It also regulates, emotions, the temperature of the body, and secretions of hormones and movement.
The Lobes
Frontal Lobes
The brain’s frontal lobes are the largest of the four lobes. They control a multitude of different functions, to include; motor skills – speech, intellectual, voluntary movement, and behavioral functions. The primary motor cortex, and the precentral gyrus, are responsible for body movements. While the prefrontal cortex is a major contributor in memory, intelligence, temper, concentration, and personality. The premotor cortex is an area within the motor cortex. The function of the premotor cortex is to enable head movements, and to guide eye movements. The Broca’s area, normally located on the left side of the frontal lobe, is fundamental for language production.
Occipital Lobes
The occipital lobes contain the majority of the anatomical region of the visual cortex, and are located to the rear of the brain, these lobes enable the mammalian brain to receive and translate visual information. The right occipital lobe, receives and translates visual data from the left visual space, and the left occipital lobe receives and translates visual data from the right visual space. The primary visual cortex is named, Brodmann area 17, otherwise known as V1, meaning – visual one.
Parietal Lobes
The parietal lobes are located between the occipital, and frontal lobes, and above the temporal lobe. The name Parietal was though of. because of its proximity to the parietal bone, the wall of the cranium. The parietal lobes have 5 major functions; processing sensory information, motor functions, somatic sensation, attention, and visual.
Temporal Lobes
The temporal lobes filter sensory input into separate information, this information is then processed to be used for, language comprehension, visual memory, and emotion association.
Limbic System
The limbic system which utilises the; hippocampus, septal area, hypothalamus, part of the thalamus, and the amygdala. However, there is no universal agreement that wholly agrees on a total list of structures of the limbic system. The limbic system involves states such as; memories, addiction, sleep, motivation, social cognition, and arousal.
Pineal Gland
The exact functions of the pineal gland are still being debated, however it has been suggested by researchers that the pineal gland produces and regulates hormones to include melatonin. And that the pineal gland is partly responsible for functions such as; response to light conditions, sexual maturation, and sleep patterns (circadian rhythm).
Pituitary Gland
The pituitary gland – anterior and posterior, is attached to the pituitary fossa, or otherwise known as the sella turcica, located within a depression in the sphenoid bone. The pituitary gland is also known as the master gland, as it secretes various hormones.
Anterior pituitary
- Adrenocorticotrophic hormone (ACTH)
- Thyroid-stimulating hormone (TSH)
- Luteinising hormone (LH)
- Follicle-stimulating hormone (FSH)
- Prolactin (PRL)
- Growth hormone (GH)
- Melanocyte-stimulating hormone (MSH)
Posterior pituitary
Stored & secreted from the hypothalamus
- Anti-diuretic hormone (ADH)
- Oxytocin
The pituitary gland is responsible for:
- Growth and development
- The function of various body organs (i.e. kidneys, breasts and uterus)
- The function of other glands (i.e. thyroid, gonads, and adrenal glands)
Posterior Cranium Fossa
The posterior Fossa is located near the brainstem, and the cerebellum. The posterior cranium fossa contains the cerebellum, medulla, and pons.
Thalamus
The thalamus is located just above the brain stem, between the cerebral cortex and the midbrain. The thalamus mainly transmits motor and sensory information to the cerebral cortex. The thalamus consists of; the hypothalamus, epythalamus, ventral thalamus, and the dorsal thalamus.
