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 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 Frontal Parietal Temporal Occipital Insula 8 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 9

Diencephalon between cerebral hemispheres and above the brainstem surrounds third ventricle 12 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 endocrine systems 13 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 14

Brain Stem Three Parts Midbrain Pons Medulla Oblongata 15 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 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 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 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 19

Cranial Nerves 22 22

Meninges membranes surrounding CNS protect CNS three layers dura mater – outer, tough arachnoid mater – thin, weblike pia mater – inner, very thin Meninges 23 23

Spinal Meninges Three membranes surround all of CNS 3) Pia mater 1) Dura mater - "tough mother", strong 2) Arachnoid meninx - spidery looking, carries blood vessels, etc. Subarachnoid space 3) Pia mater - "delicate mother", adheres tightly to surface of spinal cord 3) Pia mater 2) Arachnoid 1) Dura mater

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 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 26

Lumbar Puncture (= Spinal Tap) For clinical examination of CSF or administration of radiopaque dyes, drugs and sometimes anesthetics However: mostly “epidurals” for anesthetics

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