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Essentials of Human Anatomy Nervous System II Chapter 7 Dr Fadel Naim Ass. Prof. Faculty of Medicine IUG Brain • An adult brain weighs between 1.35 and 1.4 kilograms (kg) (around 3 pounds) and has a volume of about 1200 cubic centimeters (cc). • Brain size is not directly correlated with intelligence • It is not the physical size of the brain that determines intelligence—it is the number of active synapses. Functions of the Brain • interprets sensations • determines perception • stores memory • reasoning • makes decisions • coordinates muscular movements • regulates visceral activities • determines personality 3 The Brain’s 4 Major Regions • Prosencephalon (forebrain) – Telencephalon: cerebrum – Diencephalon: epithalamus, thalamus,hypothalamus • Mesencephalon (midbrain) – Mesencephalon: cerebral peduncles, colliculi • Rhombencephalon (hindbrain) – Metencephalon: pons, cerebellum – Myelencephalon: medulla oblongata The Brain’s 4 Major Regions • The cerebrum is divided into two halves, called the left and right cerebral hemispheres. • Each hemisphere is subdivided into five functional areas called lobes. • Outer surface of an adult brain exhibits folds called gyri (gyrus) and shallow depressions between those folds called sulci (sulcus). • The brain is associated with 12 pairs of cranial nerves. Lobes of Cerebral Hemispheres 1. Frontal 2. Parietal 3. Temporal 4. Occipital 5. Insula 8 Functional Regions of Cerebral Cortex Cerebral Cortex – thin layer of gray matter that constitutes the outermost portion of cerebrum; contains 75% of all neurons in nervous system 9 Diencephalon • between cerebral hemispheres and above the brainstem • surrounds third ventricle 12 Diencephalon Thalamus • gateway for sensory impulses heading to cerebral cortex • receives all sensory impulses (except smell) • channels impulses to appropriate part of cerebral cortex for interpretation Hypothalamus maintains homeostasis by regulating visceral activities links nervous and 13 Diencephalon Limbic System Consists of • portions of frontal lobe • portions of temporal lobe • hypothalamus • thalamus • basal nuclei • other deep nuclei Functions • controls emotions • produces feelings • interprets sensory impulses 14 Brain Stem Three Parts 1. Midbrain 2. Pons 3. Medulla Oblongata 15 Midbrain • between diencephalon and pons • contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain 16 Pons • rounded bulge on underside of brainstem • between medulla oblongata and midbrain • helps regulate rate and depth of breathing • relays nerve impulses to and from medulla oblongata and cerebellum 17 Medulla Oblongata • enlarged continuation of spinal cord • conducts ascending and descending impulses between brain and spinal cord • contains cardiac, vasomotor, and respiratory control centers • contains various nonvital reflex control centers (coughing, sneezing, swallowing, vomiting) 18 Cerebellum • inferior to occipital lobes • posterior to pons and medulla oblongata • two hemispheres • vermis connects hemispheres • cerebellar cortex – gray matter • arbor vitae – white matter • cerebellar peduncles – nerve fiber tracts • dentate nucleus – largest nucleus in cerebellum • integrates sensory information concerning position of body parts • coordinates skeletal muscle activity • maintains posture 19 Cranial Nerves 22 membranes surrounding CNS • protect CNS • three layers • dura mater – outer, tough • arachnoid mater – thin, weblike • pia mater – inner, very thin Meninges 23 Spinal Meninges Three membranes surround all of CNS 1) Dura mater - "tough mother", strong 2) Arachnoid meninx spidery looking, carries blood vessels, etc. 3) Pia mater 2) Arachnoid Subarachnoid space 1) Dura mater 3) Pia mater - "delicate mother", adheres tightly to surface of spinal cord Ventricles • interconnected cavities • within cerebral hemispheres and brain stem • continuous with central canal of spinal cord • filled with cerebrospinal fluid (CSF) • lateral ventricles • third ventricle • fourth ventricle • cerebral aqueduct 25 Cerebrospinal Fluid • secreted by choroid plexus • circulates in ventricles, central canal of spinal cord, and subarachnoid space • completely surrounds brain and spinal cord • clear liquid • nutritive and protective • helps maintain stable ion concentrations in CNS 26 Lumbar Puncture (= Spinal Tap) L3 L4 For clinical examination of CSF or administration of radiopaque dyes, drugs and sometimes anesthetics However: mostly “epidurals” for anesthetics THE END