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HUMAN ANATOMY LECTURE ELEVEN BRAIN AND SPINAL CORD BRAIN Part of CNS contained in cranial cavity • Control center for many body functions • Divided into (i) midbrain (brainstem) - connects spinal cord to brain - reflexes necessary for survival (ii) hindbrain - control of locomotion, balance, posture (iii) forebrain - higher level processes, autonomic functions, thoughts, memories, intellectual functions • Covered by neural cortex with elevated ridges (GYRI), shallow depressions (SULCI) and deep grooves (FISSURES) SAGITTAL SECTION OF BRAIN PARTS OF THE BRAIN BRAINSTEM • Connects spinal cord to brain - all signal must pass through • Controls life-sustaining processes Medulla Oblongata • Continuous with spinal cord • All communication to and from brain through ascending and descending nerve tracts • Contains control centers: cardiovascular - heart rate, blood vessel diameter respiration – breathing reflex centers - swallowing, vomiting, hiccupping, coughing, sneezing Pons • Superior to medulla oblongata • Links cerebellum to rest of brain • Contains sleep centers • Respiratory center coordinates with medulla Midbrain (mesencephalon) • Superior to pons • Ascending and descending nerve tracts • Four mounds on dorsal surface called CORPORA QUADRIGEMINA - two inferior COLLICULI are auditory nerve pathways - two superior COLLICULI are involved in visual reflexes • Contains a black mass called SUBSTANTIA NIGRA that is involved with regulation of general body movements HINDBRAIN Cerebellum • • Attached to brainstem, posterior to pons Gray matter (cortex) folded in ridges with white matter inbetween resembles tree (ARBOR VITAE) CEREBELLAR PEDUNCLES - tracts that communicate with other areas of brain FLOCCULONODULAR LOBE -controls balance and eye movements VERMIS - controls posture, fine motor coordination, smooth movements LATERAL HEMISPHERES - works with cerebrum to plan, practice, learn complex movements FOREBRAIN - DIENCEPHALON • Between brainstem and cerebrum • Integrates conscious and unconscious sensory info and motor commands Thalamus • Right and left halves are separated by the 3rd ventricle of the brain • Receives sensory info - filtered and relayed to cerebrum • Emotional awareness, mood regulation, motivation Epithalamus • Superior and posterior to thalamus PINEAL BODY - endocrine gland that helps regulate biological clock, causes sleepiness, may influence puberty HABENULAR NUCLEUS emotional and visceral responses to odors Hypothalamus • Collection of fibers under thalamus • Controls secretion of hormones from posterior pituitary gland • Maintains homeostasis, central role in control of body temperature, hunger, thirst, urination • “feel good” emotions like sexual pleasure, satiation also rage and fear MAMMARY BODIES - process emotional responses and memories to odor INFUNDIBULUM - stalk extending from floor to posterior pituitary gland Hypophysis (Pituitary Gland) • Pea sized gland that rests in the depression (sella turica) of the sphenoid bone • Divided into anterior and posterior halves and attached to hypothalamus by infundibulum • Both halves secrete hormones FOREBRAIN - CEREBRUM • Largest portion of the brain • Divided into right and left hemispheres • Higher level functions, memory, conscious thought, language Cerebral Cortex (gray matter) • Outer surface with gyri, sulci and fissures: LATERAL FISSURE separates hemispheres LATERAL SULCUS separates temporal lobe from frontal and parietal lobe CENTRAL SULCUS separates frontal and parietal lobes • Hemispheres divided into lobes: FRONTAL LOBE - voluntary motor function, motivation, mood, aggression PARIETAL LOBE - reception and evaluation of some sensory info OCCIPITAL LOBE - visual input TEMPERAL LOBE - sound, smell, memory, abstract thought Cerebral Medulla • White matter found under cortex ASSOCIATED FIBERS -connections within the same hemisphere COMMISSURAL FIBERS – connects the hemispheres PROJECTION FIBERS - tracts between cerebrum and rest of brain and spinal cord Basal Nuclei (Basal Ganglia) • Masses of gray matter deep within white matter of hemispheres • Linked to all other areas of brain • Function in subconscious motor control and coordination STRUCTURES OF THE BRAIN Cranial Meninges • Continuous with spinal meninges • Surround and protect brain – stability and shock absorption (i) Dura Mater - superficial double layer, elastic, dense collagen fibers - outer layer connected to periosteum of skull - inner layer folds into: FALX CEREBRI - inbetween cerebral hemispheres TENTORIUM CEREBELLI - inbetween cerebellum and cerebrum FALX CEREBELLI – between cerebellar hemispheres (ii) Arachnoid Mater/Subdural Space • Thin, wispy layer over brain surface - not following folds • Projections allow CSF to be reabsorbed into blood • Subdural space inbetween dura and arachnoid layer - small amount of fluid (iii) Pia Mater/Subarachnoid Space • Thin, delicate membrane closely attached to brain and spinal cord • Follows contours of brain • Highly vascularized - brings blood to ependymal cells lining ventricles • Subarachnoid space - contains weblike strands of arachnoid mater, blood vessels, cerebrospinal fluid Ventricles • Fluid filled cavities in the brain • Lined with EPENDYMAL CELLS (produce CSF) LATERAL VENTRICLES - within cerebral hemispheres - separated by SEPTUM PELLUCIDUM THIRD VENTRICLE - within diencephalon INTERVENTRICULAR FORAMINA - join lateral and third ventricles FOURTH VENTRICLE - base of cerebellum CEREBRAL AQUADUCT - joins third and fourth ventricles - continuous with spinal cord and connected to subarachnoid space through holes (formamina) in walls and roof of 4th ventricle Cerebrospinal Fluid (CSF) • Bathes brain and spinal cord forming protective cushion • Transports nutrients, chemical messengers and waste products CHOROID PLEXUS – within ventricles, produces CSF - composed of ependymal cells, support tissues and blood vessels - removes waste products from CSF ARACHNOID GRANULATIONS - masses of arachnoid tissue in dural sinus where CSF passes into blood stream Flow of CSF • • • • CSF from lateral ventricles flows through foramina to 3rd ventricle CSF flows from 3rd ventricle through cerebral aquaduct to 4th ventricle CSF exits 4th ventricle into subarachnoid space - some enters central canal of spinal cord CSF flows through subarachnoid space to arachnoid granulations in superior sagittal sinus where it enters venous circulation Flow of Cerebrospinal Fluid • From lateral ventricles through foramina to 3rd ventricle • 3rd ventricle through cerebral aquaduct to 4th ventricle • Exits 4th ventricle into subarachnoid space - some enters central canal of spinal cord • Subarachnoid space to arachnoid granulations in superior sagittal sinus where it enters venous circulation BRAIN BLOOD SUPPLY • Brain requires tremendous amount of blood • Receives blood through arteries - internal carotids and vertebral arteries which join to form basilar artery. Carotids plus basilar form CIRCLE OF WILLIS (cerebral arterial circle) • Blood leaves brain through internal jugular veins Blood-Brain Barrier • Separates neural tissue from general blood supply • Endothelial cells lining capillaries interconnected by tight junctions preventing diffusion of materials into brain • Astrocytes release chemicals that control permeability of endothelium - only lipid soluble materials diffuse - CO2, O2, nicotine, ethanol, heroin - water soluble materials mediated transport – A.A., glucose, H2O Arteries of the Brain SPINAL CORD • Extends from foramen magnum to second lumbar vertebra • Gives rise to 31 pairs of spinal nerves • Divided into specialized areas: CERVICAL ENLARGEMENT - supplies upper limbs LUMBOSACRAL ENLARGEMENT supplies lower limbs CONUS MEDULLARIS - tapered inferior end CAUDA EQUINA - origins of spinal nerves extending from lumbosacral enlargement and conus medullaris Spinal Cord Cross Section of a Spinal Cord Cross Section of a Spinal Cord Cross Section ANTERIOR MEDIAN FISSURE and POSTERIOR MEDIAN SULCUS - deep clefts partially separating left and right halves White Matter (outside area) • myelinated axons form ascending and descending nerve tracts or columns (dorsal, ventral and lateral columns) Gray Matter (inside area) • unmyelinated axons, cell bodies/nuclei, dendrites surrounding central canal • divided into horns: - posterior horn (sensory neurons) - anterior horn (motor neurons) - lateral horn (sympathetic autonomic neurons) Commissures - connections between the left and right halves of the white matter and the gray matter Roots - spinal nerves arise as rootlets and combine to form roots that exit through intevertebral foramen • DORSAL ROOT - afferent neurons (coming into spinal cord) • VENTRAL ROOT - efferent neurons (leaving the spinal cord) • Dorsal and ventral roots combine to form spinal nerves Dorsal Root Ganglion • collections of cell bodies from afferent (sensory) neurons form dorsal roots • efferent (motor) neuron cell bodies are found in anterior and lateral horns of gray matter anterior horn - somatic motor neurons lateral horn - autonomic neurons • axons of efferent neurons form ventral roots and pass into spinal nerves