The Brain PDF

The Brain Ugbai Teklay MSc, Fellow HEA Lecturer/EF Biological Sciences  Learning Outcomes  Name the three meningeal layers and describe their function.  Discuss the formation and function of cerebral spinal fluid and the role of the blood brain barrier.  Identify the four main region...

The Brain Ugbai Teklay MSc, Fellow HEA Lecturer/EF Biological Sciences  Learning Outcomes  Name the three meningeal layers and describe their function.  Discuss the formation and function of cerebral spinal fluid and the role of the blood brain barrier.  Identify the four main regions of the brain i.e.: cerebrum, diencephalon, brainstem, cerebellum and describe their function.  Protective Covering of the Brain The brain is protected by the cranial bones and cranial meninges. Surrounding the brain there are three membranous layers known as the meninges. The meninges function to protect and support the brain, prevent the spread of infection, and hold the cerebrospinal fluid.  The Meninges The cranial meninges are continuous with spinal meninges and are named dura mater, arachnoid mater and pia mater. From superficial to deep, the meninges are: dura mater, arachnoid mater and pia mater. The dura mater, outermost layer, helps to hold the brain in place. Cranial Bones and Meninges Copyright ©2017 John Wiley & Sons, Inc. 5  The Meninges The arachnoid mater is the middle layer that has a spider web-like appearance. The pia mater is the innermost layer which is very thin and transparent and lies directly on the surface of the brain. Between the pia mater and the arachnoid mater is the subarachnoid space in which the cerebrospinal fluid (CSF) is circulated. Importance of Blood Flow to the Brain Blood flows to the brain mainly via blood vessels that branch from the cerebral arterial circle (circle of wills) at the base of the brain. Veins return blood from the head to the heart. 7 Importance of Blood Flow to the Brain The brain utilizes about 20% of the body’s oxygen supply. Any interruption of the oxygen supply can result in weakening, permanent damage, or death of brain cells Glucose deficiency may produce mental confusion, dizziness, convulsions, and unconsciousness 8  Blood Brain Barrier (BBB) The BBB protects brain cells from harmful substances and pathogens by serving as a selective barrier to prevent passage of many substances from the blood into the brain. Nutrients, some amino acids and electrolytes are pumped into CSF but metabolic waste such as urea, creatinine; and toxins cannot reach CSF. 9  Blood Brain Barrier (BBB) BBB may also prevent entry of drugs as therapy for brain cancer or other CNS disorders An injury to the brain due to trauma, inflammation, or toxins causes breakdown of the BBB, permitting the passage of normally restricted substances into the brain tissue 10  Cerebrospinal Fluid The cerebrospinal fluid (CSF) is formed by filtration from networks of capillaries called choroid plexuses located in the ventricle walls. The choroid plexuses make CSF. The ependymal cells form a blood-CSF barrier, controlling substances passing from the blood to CSF. 11 Cerebrospinal Fluid The CSF bathes the brain and spinal cord and provides mechanical and chemical protection, and circulation of essential nutrients. Copyright ©2017 John Wiley & Sons, Inc. 12 Principal Parts of the Brain Copyright ©2017 John Wiley & Sons, Inc. 13 Cerebrum  Largest part of brain (83% of the total mass)  Longitudinal fissure split in 2 left and right cerebral hemispheres  Each cerebral hemisphere is divided into lobes.  Cerebrum Gyrus (pl. = gyri) Sulcus (pl. = sulci) Grey Matter White Matter Left Hemisphere Right Hemisphere Corpus callosum  Cerebrum  Surface is grey matter, deeper is white matter  Surface is convoluted to increase surface area (for more neurons)  Cerebrum is conscious brain  Gyri and sulci. Big sulci distinguish between different lobes Cerebrum  Each hemisphere of the cerebrum has 4 lobes: Frontal Parietal Occipital Temporal Copyright ©2017 John Wiley & Sons, Inc.  Frontal Lobe  Largest lobe and is found at the front of the brain  Function- The “mind” with higher order functioning and memory and control of voluntary movements.  Parietal Lobe  Posteriorly, it is separated from the occipital lobe by the parietal-occipital sulcus.  Multiple functions related to integrated sensations necessary to carry out complex mathematics, reading, writing and visual skills.  Temporal Lobe  Auditory cortex  Special senses (hearing, smell).  Some influence over personality and emotional response  Occipital Lobe  Primary visual cortex lies in extreme posterior  Much of the lobe is occupied by the visual association area-visual interpretation. Cerebellum  Small part of brain beneath occipital lobe- Latin for ‘little brain’  connected to cerebrum via brainstem Cerebellum Cerebellum  Similar anatomy to cerebrum, has 2 hemispheres  Cerebellum is unconscious (subconscious) brain  It has to learn its skills (not present at birth)  Functions: it controls muscle coordination, maintains balance and equilibrium, makes motor movements more efficient The Brain Stem  Positioned at the base of the brain just above spinal cord  Made up from separate components: Midbrain Pons The midbrain Medulla oblongata The pons The medulla oblongata The Brain Stem  The brainstem contains the vital centres that regulate:  Cardiac centre- regulates the heart rate and force of contraction.  Vasomotor centre- regulates blood vessel diameter- blood pressure control.  Respiratory centre- regulates respiratory movements.  In addition, it is responsible for reflexes: swallow, cough, sneeze, blink…. The Diencephalon The diencephalon is composed of the: Thalamus Hypothalamus Epithalamus Copyright ©2017 John Wiley & Sons, Inc. 27 Summary of Functions of the Diencephalon Part Function A cadaver photograph shows a sagittal section of the brain, Blank highlighting the anterior thalamus, posterior epithalamus, and inferior hypothalamus. Thalamus: Relays almost all sensory input to cerebral cortex. Contributes to motor functions by transmitting information from cerebellum and basal nuclei to primary motor area of cerebral cortex. Plays role in maintenance of consciousness. Hypothalamus: Controls and integrates activities of autonomic nervous system. Produces hormones, including releasing hormones, inhibiting hormones, oxytocin, and antidiuretic hormone (ADH). Regulates emotional and behavioral patterns (together with limbic system). Contains feeding and satiety centers (regulate eating), thirst center (regulates drinking), and suprachiasmatic nucleus (regulates circadian rhythms). Controls body temperature by serving as body's thermostat. Epithalamus: Consists Copyright ©2017 of &pineal John Wiley gland (secretes melatonin) Sons, Inc. 28 and habenular nuclei (involved in olfaction).  References Tortora's Principles of Anatomy and Physiology, 17th Edition, Global Edition. Anatomy TV (Primal Pictures). Available through OvidSP. Any Questions ?