Brain Anatomy and Functions

Brain Anatomy and Functions

• > 1
• Overview
• The human brain is an amazing three-pound organ
• that controls all functions of the body, interprets
• information from the outside world, and embodies
• the essence of the mind and soul. Intelligence,
• creativity, emotion, and memory are a few of the
• many things governed by the brain. Protected
• within the skull, the brain is composed of the
• cerebrum, cerebellum, and brainstem.
• The brain receives information through our five
• senses: sight, smell, touch, taste, and hearing –
• often many at one time. It assembles the messages
• in a way that has meaning for us, and can store
• that information in our memory. The brain controls
• our thoughts, memory and speech, movement of
• the arms and legs, and the function of many organs
• within our body.
• The central nervous system (CNS) is composed of
• the brain and spinal cord. The peripheral nervous
• system (PNS) is composed of spinal nerves that
• branch from the spinal cord and cranial nerves that
• branch from the brain.
• Brain
• The brain is composed of the cerebrum, cerebellum,
• and brainstem (Fig. 1).
• Cerebrum: is the largest part of the brain and is
• composed of right and left hemispheres. It
• performs higher functions like interpreting touch,
• vision and hearing, as well as speech, reasoning,
• emotions, learning, and fine control of movement.
• Cerebellum: is located under the cerebrum. Its
• function is to coordinate muscle movements,
• maintain posture, and balance.
• Brainstem: acts as a relay center connecting the
• cerebrum and cerebellum to the spinal cord. It
• performs many automatic functions such as
• breathing, heart rate, body temperature, wake and
• sleep cycles, digestion, sneezing, coughing,
• vomiting, and swallowing.
• Right brain – left brain
• The cerebrum is divided into two halves: the right
• and left hemispheres (Fig. 2). They are joined by a
• bundle of fibers called the corpus callosum that
• transmits messages from one side to the other.
• Anatomy of the Brain
• Figure 1. The brain has three main parts:
• the cerebrum cerebellum, and brainstem.
• Figure 2. The cerebrum is divided into left and right
• hemispheres. The two sides are connected
• fibers corpus callosum.> 2
• 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.
• Lobes of the brain
• The cerebral hemispheres have distinct fissures,
• which divide the brain into lobes. Each hemisphere
• has 4 lobes: frontal, temporal, parietal, and
• occipital (Fig 3). Each lobe may be divided, once
• again, into areas that serve very specific functions.
• It’s important to understand that each lobe of the
• brain does not function alone. There are very
• complex relationships between the lobes of the
• brain and between the right and left hemispheres.
• Language
• In general, the left hemisphere of the brain is
• responsible for language and speech and is called
• the "dominant" hemisphere. The right hemisphere
• plays a large part in interpreting visual information
• and spatial processing. In about one third of people
• who are left-handed, speech function may be
• located on the right side of the brain. Left-handed
• people may need special testing to determine if
• their speech center is on the left or right side prior
• to any surgery in that area.
• Aphasia is a disturbance of language affecting
• speech production, comprehension, reading or
• writing, due to brain injury. The type of aphasia
• depends on the brain area damaged.
• Broca’s area: lies in the left frontal lobe (Fig 3). If
• this area is damaged, one may have difficulty
• moving the tongue or facial muscles to produce the
• sounds of speech. A person can still read and
• understand spoken language but has difficulty in
• speaking and writing (i.e. forming letters and
• words, doesn't write within lines) – called Broca's
• aphasia.
• Wernicke's area: lies in the left temporal lobe (Fig
• 3). Damage to this area causes Wernicke's aphasia.
• The person may speak in long sentences that have
• no meaning, add unnecessary words, and even
• create new words. They can make speech sounds,
• however they have difficulty understanding speech
• and are therefore unaware of their mistakes.
• Figure 3. The cerebrum is divided into four lobes:
• frontal, parietal, temporal, and occipital.
• Frontal lobe (blue)
• Personality, behavior, emotions
• Judgment, planning, problem solving
• Speech: speaking and writing (Broca’s area)
• Body movement (motor strip)
• Intelligence, concentration, self awareness
• Parietal lobe (orange)
• Interprets language, words
• Sense of touch, pain, temperature (sensory
• strip)
• Interprets vision, hearing, sensory and
• memory
• Spatial and visual perception
• Occipital lobe (purple)
• Interprets vision (color, light, movement)
• Temporal lobe (green)
• Understanding language (Wernicke’s area)
• Memory
• Hearing
• Sequencing and organization> 3
• Cortex
• The surface of the cerebrum is called the cortex. It
• has a folded appearance with hills and valleys. The
• cortex contains 16 billion neurons (the cerebellum
• has 70 billion = 86 billion total) that are arranged in
• specific layers. The nerve cell bodies color the
• cortex grey-brown giving it its name – gray matter
• (Fig. 4). Beneath the cortex are long nerve fibers
• (axons) that connect brain areas to each other —
• called white matter.
• The folding of the cortex increases the brain’s
• surface area allowing more neurons to fit inside the
• skull and enabling higher functions. Each fold is
• called a gyrus, and each groove between folds is
• called a sulcus (Fig. 4). There are names for the
• folds and grooves that help define specific brain
• regions.
• Deep structures
• Pathways called white matter tracts connect areas
• of the cortex to each other. Messages can travel
• from one gyrus to another, from one lobe to
• another, from one side of the brain to the other,
• and to structures deep in the brain (Fig. 5).
• Hypothalamus: is located in the floor of the third
• ventricle and is the master control of the autonomic
• system. It plays a role in controlling behaviors such
• as hunger, thirst, sleep, and sexual response. It
• also regulates body temperature, blood pressure,
• emotions, and secretion of hormones.
• Pituitary gland: lies in a small pocket of bone at
• the skull base called the sella turcica. The pituitary
• gland is connected to the hypothalamus of the brain
• by the pituitary stalk. Known as the “master gland,”
• it controls other endocrine glands in the body. It
• secretes hormones that control sexual
• development, promote bone and muscle growth,
• and respond to stress.
• Pineal gland: is located behind the third ventricle.
• It helps regulate the body’s internal clock and
• circadian rhythms by secreting melatonin. It has
• some role in sexual development.
• Thalamus: serves as a relay station for almost all
• information that comes and goes to the cortex. It
• plays a role in pain sensation, attention, alertness
• and memory.
• Basal ganglia: includes the caudate, putamen and
• globus pallidus. These nuclei work with the
• cerebellum to coordinate fine motions, such as
• fingertip movements.
• Limbic system: is the center of our emotions,
• learning, and memory. Included in this system are
• the cingulate gyri, hypothalamus, amygdala
• (emotional reactions) and hippocampus (memory).
• Figure 4. The cortex contains neurons (grey matter),
• which are interconnected to other brain areas by axons
• (white matter). The cortex has a folded appearance. A fold
• is called a gyrus and the valley between is a sulcus.
• Figure 5. Coronal cross-section showing some of the deep
• structures of the brain.> 4
• Memory
• Memory is a complex process that includes three
• phases: encoding (deciding what information is
• important), storing, and recalling. Different areas of
• the brain are involved in different types of memory

(Fig. 6). Your brain has to pay attention and rehearse in order for an event to move from shortterm to long-term memory – called encoding.

• Short-term memory, also called working
• memory, occurs in the prefrontal cortex. It
• stores information for about one minute and its
• capacity is limited to about 7 items. For
• example, it enables you to dial a phone number
• someone just told you. It also intervenes during
• reading, to memorize the sentence you have
• just read, so that the next one makes sense.
• Long-term memory is processed in the
• hippocampus of the temporal lobe and is
• activated when you want to memorize
• something for a longer time. This memory has
• unlimited content and duration capacity. It
• contains personal memories as well as facts and
• figures.
• Skill memory is processed in the cerebellum,
• which relays information to the basal ganglia. It
• stores procedural learned memories like tying a
• shoe, playing an instrument, or riding a bike.
• Ventricles and cerebrospinal fluid

The brain has hollow fluid-filled cavities called ventricles (Fig. 7). Inside the ventricles is a ribbonlike structure called the choroid plexus that makes clear colorless cerebrospinal fluid (CSF). CSF flows within and around the brain and spinal cord to help cushion it from injury. This circulating fluid is constantly being absorbed and replenished.

• There are two ventricles deep within the cerebral
• hemispheres called the lateral ventricles. They both
• connect with the third ventricle through a separate
• opening called the foramen of Monro. The third
• ventricle connects with the fourth ventricle through
• a long narrow tube called the aqueduct of Sylvius.
• From the fourth ventricle, CSF flows into the
• subarachnoid space where it bathes and cushions
• the brain. CSF is recycled (or absorbed) by special
• structures in the superior sagittal sinus called
• arachnoid villi.
• A balance is maintained between the amount of CSF
• that is absorbed and the amount that is produced.
• A disruption or blockage in the system can cause a
• build up of CSF, which can cause enlargement of
• the ventricles (hydrocephalus) or cause a collection
• of fluid in the spinal cord (syringomyelia).
• Figure 6. Structures of the limbic system involved in
• memory formation. The prefrontal cortex holds recent
• events briefly in short-term memory. The hippocampus is
• responsible for encoding long-term memory.
• Figure 7. CSF is produced inside the ventricles deep within
• the brain. CSF fluid circulates inside the brain and spinal
• cord and then outside to the subarachnoid space. Common
• sites of obstruction: 1) foramen of Monro, 2) aqueduct of
• Sylvius, and 3) obex.> 5
• Skull
• The purpose of the bony skull is to protect the brain
• from injury. The skull is formed from 8 bones that
• fuse together along suture lines. These bones
• include the frontal, parietal (2), temporal (2),
• sphenoid, occipital and ethmoid (Fig. 8). The face is
• formed from 14 paired bones: the maxilla, zygoma,
• nasal, palatine, lacrimal, inferior nasal conchae,
• mandible, and vomer.
• Inside the skull are three distinct areas: anterior
• fossa, middle fossa, and posterior fossa (Fig. 9).
• Doctors sometimes refer to a tumor’s location by
• these terms, e.g., middle fossa meningioma.
• Similar to cables coming out the back of a
• computer, all the arteries, veins and nerves exit the
• base of the skull through holes, called foramina.
• The big hole in the middle (foramen magnum) is
• where the spinal cord exits.
• Cranial nerves
• The brain communicates with the body through the
• spinal cord and twelve pairs of cranial nerves (Fig.
• 9). Ten of the twelve pairs of cranial nerves that
• control hearing, eye movement, facial sensations,
• taste, swallowing and movement of the face, neck,
• shoulder and tongue muscles originate in the
• brainstem. The cranial nerves for smell and vision
• originate in the cerebrum.
• The Roman numeral, name, and main function of

the twelve cranial nerves:

No. Name Function

• I olfactory smell
• II optic sight
• III oculomotor moves eye, pupil
• IV trochlear moves eye
• V trigeminal face sensation
• VI abducens moves eye
• VII facial moves face, salivate
• VIII vestibulocochlear hearing & balance
• IX glossopharyngeal taste, swallow
• X vagus heart rate, digestion
• XI accessory moves head
• XII hypoglossal moves tongue
• Figure 8. The brain is protected inside the skull.
• The skull is formed from 8 bones.
• Figure 9. A view of the cranial nerves at the base of the
• skull with the brain removed. Cranial nerves originate
• from the brainstem, exit the skull through holes called
• foramina, and travel to the parts of the body they
• innervate. The brainstem exits the skull through the
• foramen magnum. The base of the skull is divided into 3
• regions: anterior, middle and posterior fossae.> 6
• Meninges
• The brain and spinal cord are covered and protected
• by three layers of tissue called meninges. From the
• outermost layer inward they are: the dura mater,
• arachnoid mater, and pia mater.
• Dura mater: is a strong, thick membrane that
• closely lines the inside of the skull; its two layers,
• the periosteal and meningeal dura, are fused and
• separate only to form venous sinuses. The dura
• creates little folds or compartments. There are two
• special dural folds, the falx and the tentorium. The
• falx separates the right and left hemispheres of the
• brain and the tentorium separates the cerebrum
• from the cerebellum.
• Arachnoid mater: is a thin, web-like membrane
• that covers the entire brain. The arachnoid is made
• of elastic tissue. The space between the dura and
• arachnoid membranes is called the subdural space.
• Pia mater: hugs the surface of the brain following
• its folds and grooves. The pia mater has many
• blood vessels that reach deep into the brain. The
• space between the arachnoid and pia is called the
• subarachnoid space. It is here where the
• cerebrospinal fluid bathes and cushions the brain.
• Blood supply
• Blood is carried to the brain by two paired arteries,
• the carotid arteries and the vertebral arteries (Fig.
• 10). The internal carotid arteries supply most of the
• cerebrum. The vertebral arteries supply the
• cerebellum, brainstem, and the underside of the
• cerebrum. After passing through the skull, the right
• and left vertebral arteries join together to form the
• basilar artery. The basilar artery and the internal
• carotid arteries “communicate” with each other at
• the base of the brain called the Circle of Willis (Fig.
• 11). The communication between the internal
• carotid and vertebral-basilar systems is an
• important safety feature of the brain. If one of the
• major vessels becomes blocked, it is possible for
• collateral blood flow to come across the Circle of
• Willis and prevent brain damage.
• The venous circulation of the brain is very different
• than the rest of the body. Usually arteries and
• veins run together as they supply and drain specific
• areas of the body. So one would think there would
• be a pair of vertebral veins and internal carotid
• veins. However, this is not the case. The major vein
• collectors are integrated into the dura to form
• venous sinuses – not to be confused with the air
• sinuses in the face and nasal region. The venous
• sinuses collect the blood from the brain and pass it
• to the internal jugular veins. The superior and
• inferior sagittal sinuses drain the cerebrum, the
• cavernous sinuses drains the anterior skull base. All
• sinuses eventually drain to the sigmoid sinuses,
• which exit the skull as the jugular veins. The two
• jugular veins are the only drainage of the brain.
• Figure 10. The common carotid artery courses up the neck
• and divides into the internal and external carotid arteries.
• The brain’s anterior circulation is fed
• carotid arteries (ICA) and the posterior circulation is fed
• by the vertebral arteries. The two systems connect at the
• Circle of Willis (green circle).
• Figure 11. Top view of the circle of Willis. The internal
• carotid and vertebral-basilar systems are joined by the
• anterior communicating (Acom) and posterior

communicating (Pcom) arteries.> 7

Mayfield Certified Health Info materials are written and developed by the Mayfield Clinic. We comply with the HONcode standard for trustworthy health information. This information is not intended to replace the medical advice of your health care provider. © Mayfield Clinic 1998-2018.

• updated > 4.2018
• reviewed by > Tonya Hines, CMI, Mayfield Clinic, Cincinnati, Ohio
• Cells of the brain
• The brain is made up of two types of cells: nerve
• cells (neurons) and glia cells.
• Nerve cells
• There are many sizes and shapes of neurons, but
• all consist of a cell body, dendrites and an axon.
• The neuron conveys information through electrical
• and chemical signals. Try to picture electrical wiring
• in your home. An electrical circuit is made up of
• numerous wires connected in such a way that when
• a light switch is turned on, a light bulb will beam. A
• neuron that is excited will transmit its energy to
• neurons within its vicinity.
• Neurons transmit their energy, or “talk”, to each
• other across a tiny gap called a synapse (Fig. 12). A
• neuron has many arms called dendrites, which act
• like antennae picking up messages from other
• nerve cells. These messages are passed to the cell
• body, which determines if the message should be
• passed along. Important messages are passed to
• the end of the axon where sacs containing
• neurotransmitters open into the synapse. The
• neurotransmitter molecules cross the synapse and
• fit into special receptors on the receiving nerve cell,
• which stimulates that cell to pass on the message.
• Glia cells
• Glia (Greek word meaning glue) are the cells of the
• brain that provide neurons with nourishment,
• protection, and structural support. There are about
• 10 to 50 times more glia than nerve cells and are
• the most common type of cells involved in brain
• tumors.
• Astroglia or astrocytes are the caretakers —
• they regulate the blood brain barrier, allowing
• nutrients and molecules to interact with
• neurons. They control homeostasis, neuronal
• defense and repair, scar formation, and also
• affect electrical impulses.
• Oligodendroglia cells create a fatty substance
• called myelin that insulates axons – allowing
• electrical messages to travel faster.
• Ependymal cells line the ventricles and secrete
• cerebrospinal fluid (CSF).
• Microglia are the brain’s immune cells,
• protecting it from invaders and cleaning up
• debris. They also prune synapses.
• Sources & links
• If you have more questions, please contact Mayfield
• Brain & Spine at 800-325-7787 or 513-221-1100.
• Links
• brainfacts.org
• thebrain.mcgill.ca
• Figure 12. Nerve cells consist of a cell body, dendrites
• and axon. Neurons communicate with each other by
• exchanging neurotransmitters across a tiny gap called

a synapse.