Human Anatomy Lecture 15 - Brain (Part 2) PDF

Academic year 2022-2023 ‫فرع جراحة الفم والوجه والفكين‬ ‫كلية طب االسنان‬ 2ed year Human Anatomy Lecture 15...

Academic year 2022-2023 ‫فرع جراحة الفم والوجه والفكين‬ ‫كلية طب االسنان‬ 2ed year Human Anatomy Lecture 15 Brain (part 2) By:Dr.Nada hashim AL JASSIM Snell R.S. Clinical Anatomy by regions, 9th Edition, Lippincott Williams & Wilkins, [2012 For more detailed instructions, any question, cases need help please post to the telegram group of the session  THE BRAIN  ANATOMICAL REGIONS  A. Cerebrum  B. Diencephalon  Thalamus  Hypothalamus  C. Brain Stem  Midbrain  Pons  Medulla oblongata  D. Cerebellum  THE BRAIN  FUNCTIONAL REGIONS  A. MOTOR AREAS  B. SENSORY AREAS  C. HIGHER FUNCTIONS  The Brain Since the brain is so important, it is protected by the skull,  cerebrospinal fluid which cushions it, meninges which are membranes that surround the brain and only let certain substances cross through to the brain.  CEREBRUM 5  The brain is divided into parts, and is bilaterally symmetrical.  In general, the left side controls the right half of the body, and the right side of the brain controls the left half of the body.  The largest portion is the CEREBRUM, which makes up 80% of the brain.  The cerebrum controls logical thought and conscious awareness of the environment, and the sensory and motor activity.  The cerebrum is made up mostly of grey matter (cell bodies, dendrites, and unmyelinated axons).  GYRUS AND SULCUS  The superficial region of the brain (and all other organs) is called the cortex.  The surface is not smooth, it’s convoluted. Each bump on the surface of the cerebrum is called a GYRUS, and each shallow groove on the surface of the cerebrum is called a SULCUS.  The cerebrum is divided into 2 halves called CEREBRAL HEMISPHERES, which are separated by the longitudinal fissure.  Each hemisphere is divided into lobes, named for the bones on top of them. The Cerebral Hemispheres and lobes 8 The Cerebral Hemispheres and lobes Central sulcus  The FRONTAL LOBE and PARIETAL LOBE are separated by the CENTRAL SULCUS.  The TEMPORAL LOBE is between the parietal and frontal lobe, separated by the LATERAL SULCUS.  The OCCIPITAL LOBE does not have a real border; it’s just a region. Lateral sulcus  CORPUS CALLOSUM  If you slice the brain down the center in a mid- sagittal section, you will slice through a white colored tissue called the CORPUS CALLOSUM, which is the area that connects the right and left halves of the brain.  Diencephalon Consists of two parts:  Thalamus  The superior portion of the diencephalon  Processes sensory information according to importance  Major relay station for sensory impulses to the cerebrum  Hypothalamus  The inferior portion of the diencephalon  Makes hormones which maintains the homeostasis of the body  13 Thalamus Hypothalamus Pituitary gland  HYPOTHALAMUS  The hypothalamus synthesizes and secretes hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones.  By secreting hormones, the hypothalamus controls blood pressure, body temperature, hunger, thirst, fatigue, sleep, autonomic nervous reflexes, and circadian cycles.  BRAIN STEM – MIDBRAIN – PONS – MEDULLA OBLONGATA  Midbrain  The top of the brain stem is the MIDBRAIN.  It controls automatic behaviors (fight or flight)  The midbrain also contains a pigmented area called the substantia nigra.  The Substantia nigra is involved in addictions and in initiating body movement.  The substantia nigra secretes the neurotransmitter dopamine.  When the neurons in the substantia nigra become damaged, dopamine levels decrease, causing Parkinson's Disease.  Treatment is to replace the dopamine  Pons Farther down the brainstem is the PONS, which relays sensory information between the cerebellum (for balance) and cerebrum (conscious awareness). 18 Midbrain Pons Medulla Oblongata  Medulla Oblongata  At the base of the brainstem is the MEDULLA OBLONGATA, which contains the cardiac, respiratory, vomiting and vasomotor (blood vessel constriction) centers.  It controls the nerves that effect the heart rate, blood pressure, and breathing.  Damage here causes coma.  What’s the difference in function between the medulla oblongata and the hypothalamus?  The medulla oblongata controls blood pressure directly (using nerves),  and the hypothalamus controls it indirectly (using hormones).  Reticular Formation  The reticular formation is a group of cells scattered throughout the brainstem.  They play a role in rousing and maintaining consciousness.  PINEAL BODY (Pineal gland)  The PINEAL BODY secretes melatonin.  melatonin helps us sleep  Production of melatonin by the pineal gland is inhibited by light and permitted by darkness.  Secretion peaks in the middle of the night, with normal variations in timing according to an individual's chronotype.  23 Pineal body  CEREBELLUM  The cerebellum is the second largest  portion of the brain, is responsible for balance and muscle coordination  Cerebellar Function Evaluation  Finger to nose  Heel to shin  Ataxic gait of alcoholism 25  MENINGES These are tissues that cover the entire CNS. They are three layers that serve to protect and cushion the brain. 26  Meninges 1. DURA MATER is the thickest and most superficial of the meninges. 2. ARACHNOID MATER is the middle layer and is not nearly as dense. It also does not go down into the sulci, it only covers over the top of the gyri. 3. PIA MATER is the thin, shiny layer that DOES follow the brain surface into the sulci.  SUBDURAL SPACE is between the dura mater and the arachnoid mater. It has a venous blood.  The SUBARACHNOID SPACE is between the arachnoid and pia mater, and is filled with CEREBRAL SPINAL FLUID (CSF).  1. DURA MATER (“Tough mother”) Dense regular connective tissue, like a tendon or ligament. It consists of two layers. Under the skull is the first layer of dura mater, called the PERIOSTEAL LAYER. Just under this is the second layer, called the MENINGEAL LAYER. There are these two layers everywhere except around the spinal cord, where it’s just one layer, the meningeal layer of the dura mater; no periosteal layer.  Between the meningeal and periosteal layers of the dura mater are DURAL SINUSES, which are filled with venous blood which is drained from the brain.  The dura and arachnoid mater both have lots of blood vessels, which might rupture in an injury,  called a SUBDURAL or SUBARACHNOID HEMORRHAGE, which is potentially fatal. In some areas within the skull, the meningeal layer of the dura mater folds inwards as Dural Folds (Refections) to limit the rotational displacement of the brain. They divide the cranial cavity into several compartments.  There are 4 dural foldes 1-The tentorium cerebelli exists between and separates the cerebellum and brainstem (Infratentorium Compartment) from the occipital lobes of the cerebrum (Supratentorium Compartment). 2-The falx cerebri, which separates the two hemispheres of the brain, is located in the longitudinal cerebral fissure between the hemispheres 3-The falx cerebelli is a vertical dural fold that lies inferior to the tentorium cerebelli in the posterior part of the posterior cranial fossa. It partially separates the cerebellar hemispheres. 4-The diaphragma sellae is the smallest dural fold and is a circular sheet of dura that forming a partial roof over the Pituitary fossa and covers the pituitary gland  VENTRICLES OF THE BRAIN  The brain contains hollow spaces called ventricles, which are filled with CSF. They are extensive. The names are simple.  LATERAL VENTRICLE is the largest, extends throughout the cerebrum. It is between the corpus callosum and the fornix.  THIRD VENTRICLE: it looks like a cavity between the fornix and a red arch.  FOURTH VENTRICLE is at the base of the cerebellum; it is continuous with the central canal of the spinal cord, and also with the subarachnoid space.  CEREBRAL AQUEDUCT: connects the 3rd and 4th ventricles. The used CSF drains out of the brain at the aqueduct and returns to the blood circulation. The ventricles, subarachnoid space, and cerebral aqueduct are filled with CSF. The subdural space is NOT filled with CSF; it is filled with venous blood. VENTRICLES OF THE BRAIN (blue) 34  35 Fornix Lateral 3rd ventricle ventricle Cerebral aqueduct mammillary body Fourth ventricle  CerebroSpinal Fluid (CSF)  CSF is similar to plasma because it is derived from plasma.  CSF is made in the ventricles by a group of capillaries called the CHOROID PLEXUS.  The choroid plexus capillaries have holes that allow the blood plasma to leak into the subarachnoid space. It is now called cerebrospinal fluid (CSF).  CerebroSpinal Fluid (CSF)  The CSF that has been depleted of its nutrients is absorbed back into the blood through the ARACHNOID GRANULATIONS.  Arachnoid granulations are on top of the finger-like projections (arachnoid villi), which are small protrusions of the arachnoid mater (the thin second layer covering the brain) through the dura mater (the thick outer layer).  They protrude into the venous sinuses of the brain, and allow cerebrospinal fluid (CSF) to circulate from the brain into the venous (blue) blood to return to the heart.  800ml of CSF is made per day, but there is actually only 150 ml there because the extra is continually removed from the brain and returned to the bloodstream. FUNCTION OF FLUID-FILLED VENTRICLES  1. Allows the brain to float. The brain has CSF on the outside as well..  2. It cushions..  3. Acts as the lymphatic system of the brain (it doesn’t have one).  PROBLEMS WITH MENINGES  HYDROCEPHALY is accumulation of CSF inside the ventricles.  It is usually congenital, caused by a blockage of the cerebral aqueduct. The CSF is made but can’t leave, and the brain gets expanded.  MENINGITIS is inflammation of the meninges caused by bacteria, viruses, or fungus THANK YOU