brain information and facts

brain  information  and facts

The brain is one of the most complex and magnificent organs in the human body. Our brain gives us awareness of ourselves and of our environment, processing a constant stream of sensory data. It controls our muscle movements, the secretions of our glands, and even our breathing and internal temperature. Every creative thought, feeling, and plan is developed by our brain. The brain’s neurons record the memory of every event in our lives.

Anatomy of the Brain

There are different ways of dividing the brain anatomically into regions. Let’s use a common method and divide the brain into three main regions based on embryonic development: the forebrain, midbrain and hindbrain. Under these divisions:

1. 

• The forebrain (or prosencephalon) is made up of our incredible cerebrum, thalamus, hypothalamus and pineal gland among other features. Neuroanatomists call the cerebral area the telencephalon and use the term diencephalon (or interbrain) to refer to the area where our thalamus, hypothalamus and pineal gland reside.

2. 

• The midbrain (or mesencephalon), located near the very center of the brain between the interbrain and the hindbrain, is composed of a portion of the brainstem.

3. 

• The hindbrain (or rhombencephalon) consists of the remaining brainstem as well as our cerebellum and pons. Neuroanatomists have a word to describe the brainstem sub-region of our hindbrain, calling it the myelencephalon, while they use the word metencephalon in reference to our cerebellum and pons collectively.

Anatomy of the brain 

The largest part of the human brain is the cerebrum, which is divided into two hemispheres, according to the mayfield  clinic . Underneath lies the brainstem, and behind that sits the cerebellum. The outermost layer of the cerebrum is the cerebral cortex, which consists of four lobes: the frontal, parietal, temporal and occipital.

Like all vertebrate brains, the human brain develops from three sections known as the forebrain, midbrain and hindbrain. Each of these contains fluid-filled cavities called ventricles. The forebrain develops into the cerebrum and underlying structures; the midbrain becomes part of the brainstem; and the hindbrain gives rise to regions of the brainstem and the cerebellum.

The cerebral cortex is greatly enlarged in human brains and is considered the seat of complex thought. Visual processing takes place in the occipital lobe, near the back of the skull. The temporal lobe processes sound and language, and includes the hippocampus and amygdala, which play roles in memory and emotion, respectively. The parietal lobe integrates input from different senses and is important for spatial orientation and navigation.

Right brain – left brain

The cerebrum is divided into two halves: the right and left hemispheres . They are joined by a bundle of fibers called the corpus callosum that transmits messages from one side to the other. Each hemisphere controls the opposite side of the body. If a stroke occurs on the right side of the brain, your left arm or leg may be weak or paralyzed.

Not all functions of the hemispheres are shared. In general, the left hemisphere controls speech, comprehension, arithmetic, and writing. The right hemisphere controls creativity, spatial ability, artistic, and musical skills. The left hemisphere is dominant in hand use and language in about 92% of people.

The cerebrum is the largest part of the human brain, and is divided into nearly

symmetrical left and right hemispheres by a deep groove, the longitudinal

fissure. The outer part of the cerebrum is the cerebral cortex, made up of grey

matter arranged in layers. It is 2 to 4 millimetres (0.079 to 0.157 in) thick, and

deeply folded to give a convoluted appearance.Beneath the cortex is the white

matter of the brain. The largest part of the cerebral cortex is the neocortex, which

has six neuronal layers. The rest of the cortex is of allocortex, which has three or

four layers. The hemispheres are connected by five commissures that span the

longitudinal fissure, the largest of these is the corpus callosum. The surface of the

brain is folded into ridges (gyri) and grooves (sulci), many of which are named,

usually according to their position, such as thef rontal gyrus of the frontal lobe or the

central sulcus separating the central regions of the hemispheres. There are many

small variations in the secondary and tertiary folds. Each hemisphere is

conventionally divided into four lobes; the frontal lobe, parietal lobe, temporal lobe,

and occipital lobe, named according to the skull bones that overlie them. Each

lobe is associated with one or two specialised functions though there is some

functional overlap between them.

The cortex is mapped by divisions into about fifty different functional areas known

as Brodmann's areas. These areas are distinctly different when seen under a

microscope.[19] The cortex is divided into two main functional areas – a motor cortex and a sensory cortex The primary motor

Cerebrum

Major gyri and sulci on the lateral

surface of the cortex

Lobes of the brain

cortex, which sends axons down to motor neurons in the brainstem and spinal cord, occupies the rear portion of the frontal lobe,

directly in front of the somatosensory area. The primary sensory areas receive signals from the sensory nerves and tracts by way of

relay nuclei in the thalamus. Primary sensory areas include the visual cortex of the occipital lobe, the auditory cortex in parts of the

temporal lobe and insular cortex, and the somatosensory cortex in the parietal lobe. The remaining parts of the cortex, are called the

association areas. These areas receive input from the sensory areas and lower parts of the brain and are involved in the complex

cognitive processes of perception, thought, and decision-making. The main functions of the frontal lobe are to control attention,

abstract thinking, behaviour, problem solving tasks, and physical reactions and personality. The occipital lobe is the smallest

lobe; its main functions are visual reception, visual-spatial processing, movement, and colour recognition. There is a smaller

occipital lobule in the lobe known as the cuneus. The temporal lobe controls auditory and visual memories, language, and some

hearing and speech.

The cerebrum contains the ventricles where the cerebrospinal fluid is produced and circulated.

Below the corpus callosum is the septum pellucidum, a membrane that separates the lateral

ventricles. Beneath the lateral ventricles is the thalamus and to the front and below this is the

hypothalamus. The hypothalamus leads on to the pituitary gland. At the back of the thalamus

is the brainstem.

The basal ganglia, also called basal nuclei, are a set of structures deep within the hemispheres

involved in behaviour and movement regulation. The largest component is the striatum,

others are the globus pallidus, the substantia nigra and the subthalamic nucleus.Part of the

dorsal striatum, the putamen, and the globus pallidus, lie separated from the lateral ventricles

and thalamus by the internal capsule, whereas the caudate nucleus stretches around and abuts

the lateral ventricles on their outer sides. At the deepest part of the lateral sulcus between

the insular cortex and the striatum is a thin neuronal sheet called the claustrum. Some

sources include this with the basal ganglia.

Below and in front of the striatum are a number of basal forebrain structures. These include

the nucleus accumbens, nucleus basalis, diagonal band of Broca, substantia innominata, and the medial septal nucleus. These

structures are important in producing the neurotransmitter, acetylcholine, which is then distributed widely throughout the brain. The

basal forebrain, in particular the nucleus basalis, is considered to be the major cholinergic output of the central nervous system to the

striatum and neocortex.

The cerebellum is divided into an anterior lobe, a posterior lobe, and the flocculonodular

lobe. The anterior and posterior lobes are connected in the middle by the vermis. The

cerebellum has a much thinner outer cortex that is narrowly furrowed horizontally. Viewed

from underneath between the two lobes is the third lobe the flocculonodular lobe.The

cerebellum rests at the back of the cranial cavity, lying beneath the occipital lobes, and is

separated from these by the cerebellar tentorium, a sheet of fibre.

It is connected to the midbrain of the brainstem by the superior cerebellar peduncles, to the

pons by the middle cerebellar peduncles, and to the medulla by the inferior cerebellar

peduncles. The cerebellum consists of an inner medulla of white matter and an outer

cortex of richly folded grey matter. The cerebellum's anterior and posterior lobes appear to

play a role in the coordination and smoothing of complex motor movements, and the

flocculonodular lobe in the maintenance of balance although debate exists as to its

cognitive, behavioural and motor functions.

Cortical folds and white

matter in horizontal bisection

of head

Cerebellum

Human brain viewed from

below, showing cerebellum

and brainstem

Brainstem

The brainstem lies beneath the cerebrum and consists of the midbrain, pons and medulla. It lies in the back part of the skull, resting

on the part of the base known as the clivus, and ends at the foramen magnum, a large opening in the occipital bone. The brainstem

continues below this as the spinal cord, protected by the vertebral column.

Ten of the twelve pairs of cranial nerves[a] emerge directly from the brainstem. The brainstem also contains many cranial nerve

nuclei and nuclei of peripheral nerves, as well as nuclei involved in the regulation of many essential processes including breathing,

control of eye movements and balance. The reticular formation, a network of nuclei of ill-defined formation, is present within

and along the length of the brainstem. Many nerve tracts, which transmit information to and from the cerebral cortex to the rest of

the body, pass through the brainstem.

The human brain is primarily composed of neurons, glial cells, neural stem cells, and blood vessels. Types of neuron include

interneurons, pyramidal cells including Betz cells, motor neurons (upper and lower motor neurons), and cerebellar Purkinje cells.

Betz cells are the largest cells (by size of cell body) in the nervous system.The adult human brain is estimated to contain 86±8

billion neurons, with a roughly equal number (85±10 billion) of non-neuronal cells. Out of these neurons, 16 billion (19%) are

located in the cerebral cortex, and 69 billion (80%) are in the cerebellum.

Types of glial cell are astrocytes (including Bergmann glia), oligodendrocytes, ependymal cells (including tanycytes), radial glial

cells and microglia. Astrocytes are the largest of the glial cells. They are stellate cells with many processes radiating from their cell

bodies. Some of these processes end as perivascular end-feet on capillary walls. The glia limitans of the cortex is made up of

astrocyte foot processes that serve in part to contain the cells of the brain.

Mast cells are white blood cells that interact in the neuroimmune system in the brain.Mast cells in the central nervous system are

present in the meninges they mediate neuroimmune responses in inflammatory conditions and help to maintain the blood–brain

barrier, particularly in brain regions where the barrier is absent. Across systems, mast cells serve as the main effector cell

through which pathogens can afect the gut–brain axis.

Some 400 genes are shown to be brain-specific. In all neurons, ELAVL3 is expressed, and in pyramidal neurons, NRGN and REEP2

are also expressed. GAD1 – essential for the biosynthesis of the neurotransmitter GABA – is expressed in interneurons. Proteins

expressed in glial cells are astrocyte markers GFAP, and S100B. Myelin basic protein, and the transcription factor, OLIG2 are

expressed in oligodendrocytes.

Cerebrospinal fluid is a clear, colourless transcellular fluid that circulates around the

brain in the subarachnoid space, in the ventricular system, and in the central canal of

the spinal cord. It also fills some gaps in the subarachnoid space, known as

subarachnoid cisterns. The four ventricles, two lateral, a third, and a fourth

ventricle, all contain choroid plexus that produces cerebrospinal fluid. The third

ventricle lies in the midline and is connected to the lateral ventricles.A single

duct, the cerebral aqueduct between the pons and the cerebellum, connects the third

ventricle to the fourth ventricle. Three separate openings, the middle and two

lateral apertures, drain the cerebrospinal fluid from the fourth ventricle to the

cisterna magna one of the major cisterns. From here, cerebrospinal fluid circulates

around the brain and spinal cord in the subarachnoid space, between the arachnoid

mater and pia mater. At any one time, there is about 150mL of cerebrospinal

fluid – most within the subarachnoid space. It is constantly being regenerated and absorbed, and replaces about once every 5–6

hours.

Microanatomy

Cerebrospinal fluid

Cerebrospinal fluid circulates in

spaces around and within the brain

In other parts of the body, circulation in the lymphatic system clears extracellular waste products from the cell tissue. For the

tissue of the brain, such a system has not yet been identified. However, the presence of a glymphatic or paravascular system has

been proposed. Newer studies (2015) from two laboratories have shown the presence of meningeal lymphatic vessels

running alongside the blood vessels, and these have been shown with lymph valves, to be more extensive at the base of the brain

where they exit with the cranial nerves.

The internal carotid arteries supply oxygenated blood to the front of the brain and the

vertebral arteries supply blood to the back of the brain. These two circulations join

together in the circle of Willis, a ring of connected arteries that lies in the interpeduncular

cistern between the midbrain and pons.

The internal carotid arteries are branches of the common carotid arteries. They enter the

cranium through the carotid canal, travel through the cavernous sinus and enter the

subarachnoid space. They then enter the circle of Willis, with two branches, the anterior

cerebral arteries emerging. These branches travel forward and then upward along the

longitudinal fissure, and supply the front and midline parts of the brain. One or more small

anterior communicating arteries join the two anterior cerebral arteries shortly after they

emerge as branches. The internal carotid arteries continue forward as the middle cerebral

arteries. They travel sideways along the sphenoid bone of the eye socket, then upwards

through the insula cortex, where final branches arise. The middle cerebral arteries send

branches along their length.

The vertebral arteries emerge as branches of the left and right subclavian arteries. They travel

upward through transverse foramina – spaces in the cervical vertebrae and then

emerge as two vessels, one on the left and one on the right of the medulla. They

give off one of the three cerebellar branches. The vertebral arteries join in front of

the middle part of the medulla to form the larger basilar artery, which sends multiple

branches to supply the medulla and pons, and the two other anterior and superior

cerebellar branches.Finally, the basilar artery divides into two posterior cerebral

arteries. These travel outwards, around the superior cerebellar peduncles, and along

the top of the cerebellar tentorium, where it sends branches to supply the temporal

and occipital lobes. Each posterior cerebral artery sends a small posterior

communicating artery to join with the internal carotid arteries.

Cerebral veins drain deoxygenated blood from the brain. The brain has two main

networks of veins: an exterior or superficial network, on the surface of the cerebrum that has three branches, and an interior network.

These two networks communicate via anastomosing (joining) veins. The veins of the brain drain into larger cavities the dural

venous sinuses usually situated between the dura mater and the covering of the skull. Blood from the cerebellum and midbrain

drains into the great cerebral vein. Blood from the medulla and pons of the brainstem have a variable pattern of drainage, either into

the spinal veins or into adjacent cerebral veins.

Motor control

The motor system of the brain is responsible for the generation and control of

movement.Generated movements pass from the brain through nerves to motor

neurons in the body, which control the action of muscles. The corticospinal tract

carries movements from the brain, through the spinal cord, to the torso and

limbs.The cranial nerves carry movements related to the eyes, mouth and face.

Gross movement – such as locomotion and the movement of arms and legs – is

generated in the motor cortex, divided into three parts: the primary motor cortex,

found in the prefrontal gyrus and has sections dedicated to the movement of

different body parts. These movements are supported and regulated by two other

areas, lying anterior to the primary motor cortex: the premotor area and the supplementary motor area.The hands and mouth have

a much larger area dedicated to them than other body parts, allowing finer movement; this has been visualised in a motor cortical

homunculus.Impulses generated from the motor cortex travel along the corticospinal tract along the front of the medulla and

cross over (decussate) at the medullary pyramids. These then travel down the spinal cord, with most connecting to interneurons, in

turn connecting to lower motor neurons within the grey matter that then transmit the impulse to move to muscles themselves. The

cerebellum and basal ganglia, play a role in fine, complex and coordinated muscle movements.Connections between the cortex

and the basal ganglia control muscle tone, posture and movement initiation, and are referred to as the                 extrapyramidal system.

sensory

The sensory nervous system is involved with the reception and processing of

sensory information. This information is received through the cranial nerves,

through tracts in the spinal cord, and directly at centres of the brain exposed to the

blood. The brain also receives and interprets information from the special senses

(vision, smell, hearing, and taste). Mixed motor and sensory signals are also

integrated.

From the skin, the brain receives information about fine touch, pressure, pain,

vibration and temperature. From the joints, the brain receives information aboujto int

position.The sensory cortex is found just near the motor cortex, and, like the motor cortex,

has areas related to sensation from different body parts. Sensation collected by a sensory

receptor on the skin is changed to a nerve signal, that is passed up a series of neurons through

tracts in the spinal cord. The dorsal column–medial lemniscus pathway contains information

about fine touch, vibration and position of joints. Neurons travel up the back part of the spinal

cord to the back part of the medulla, where they connect with "second order" neurons that

immediately swap sides. These neurons then travel upwards into the ventrobasal complex in

the thalamus where they connect with "third order" neurons, and travel up to the sensory

cortex.The spinothalamic tract carries information about pain, temperature, and gross

touch. Neurons travel up the spinal cord and connect with second-order neurons in the

reticular formation of the brainstem for pain and temperature, and also at the ventrobasal

complex of the medulla for gross touch.

Neurotransmission

Brain activity is made possible by the interconnections of neurons that are linked together to reach their targets.A neuron

consists of a cell body, axon, and dendrites. Dendrites are often extensive branches that receive information in the form of signals

from the axon terminals of other neurons. The signals received may cause the neuron to initiate an action potential (an

electrochemical signal or nerve impulse) which is sent along its axon to the axon terminal, to connect with the dendrites or with the

cell body of another neuron. An action potential is initiated at the initial segment of an axon, which contains a complex of

proteins. When an action potential, reaches the axon terminal it triggers the release of a neurotransmitter at a synapse that

propagates a signal that acts on the target cell.These chemical neurotransmitters include dopamine, serotonin, GABA,

glutamate, and acetylcholine.GABA is the major inhibitory neurotransmitter in the brain, and glutamate is the major excitatory

neurotransmitter.Neurons link at synapses to form neural pathways, neural circuits, and large elaborate network systems such as

the salience network and the default mode network, and the activity between them is driven by the process of neurotransmission.