Anatomy Of Brain PDF

Anatomy and physiology of Brain By Huma Murtaza Senior lecturer Ripha International University Introduction  The brain is an amazing three-pound organ that controls all functions of the body, interprets information from the outside world, and...

Anatomy and physiology of Brain By Huma Murtaza Senior lecturer Ripha International University Introduction  The 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.  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 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.  The brain is composed of the  cerebrum  cerebellum  and brainstem  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 & 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. Lobes of brain  The cerebral hemispheres have distinct fissures, which divide the brain into lobes.  Each hemisphere has 4 lobes:  Frontal  Temporal  Parietal  and occipital  Frontal lobe  Personality, behavior, emotions  Judgment, planning, problem solving  Speech: speaking and writing (Broca’s area)  Body movement (motor strip)  Intelligence, concentration, self awareness  Parietal lobe  Interprets language, words  Sense of touch, pain, temperature (sensory strip)  Interprets signals from vision, hearing, motor, sensory and memory  Spatial and visual perception  Occipital lobe  Interprets vision (color, light, movement)  Temporal lobe  Understanding language (Wernicke’s area)  Memory  Hearing  Sequencing and organization 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.  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. 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  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 has some role in sexual development. Thalamus  This consist of two masses of grey and white matter situated within the cerebral hemispheres just below the corpus collusum one on each side of third ventricle.  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. Brain stem  Mid brain: it is an area of the brain situated around the cerebral aqueduct between the cerebrum above and the pons below.  It consist of nuclei and nerve fibers which connect the cerebrum with lower parts of brain and spinal cord.  The nuclei act as a relay centre for ascendind and descending nerve fibers.  Pons:  The pons is situated in front of the cerebellum below the midbrain and above the medullae oblongata.  It consist mainly of nerve fibers (white matter) that forms a bridge between the two hemispheres of the cerebellum, and of fibers passing between the higher levels of brain and spinal cord.  Medulla oblongata :  It extends from pons above and is continuous with the spinal cord below.  It is about 2.5cm long.  And is lie just within the cranium above the foramen magnum. 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; 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. Ventricles and CSF  The brain has hollow fluid-filled cavities called ventricles.  Inside the ventricles is a ribbon-like 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). Blood supply  Blood is carried to the brain by two paired arteries, the internal carotid arteries and the vertebral arteries.  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  The venous circulation of the brain is very different from that of the rest of the body.  The major vein collectors are integrated into the dura to form venous sinuses.  The venous sinuses collect the blood from the brain and pass it to the internal jugular veins.  All sinuses eventually drain to the sigmoid sinuses, which exit the skull and form the jugular veins.  These two jugular veins are essentially the only drainage of the brain. 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.  Glial 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.