300-14 The Meninges and Cerebral Hemispheres 2023 (4).pdf

Meninges & the Cerebral Hemispheres Images from Human Anatomy 6th ed., © 2009, by Martini, Timmins and Talitsch, denoted by “Ma”. Images from Human Anatomy, 2nd ed., © 2008 by McKinley & O’Loughlin, denoted by “Mc”. Organization of Lecture 1. Overview of the brain, cerebral meninges, dural venous...

Meninges & the Cerebral Hemispheres Images from Human Anatomy 6th ed., © 2009, by Martini, Timmins and Talitsch, denoted by “Ma”. Images from Human Anatomy, 2nd ed., © 2008 by McKinley & O’Loughlin, denoted by “Mc”. Organization of Lecture 1. Overview of the brain, cerebral meninges, dural venous sinuses (slides 3 - 15). 2. The ventricular system (slides 16 - 24). 3. Cerebral hemispheres and functional localization, the diencephalon (slides 25 - 38). 2 An Overview of the Brain A. Cerebral hemispheres • bilaterally paired; separated by the longitudinal fissure • anatomically ~ symmetrical • functionally asymmetrical A B B. Diencephalon • grey matter buried within the cerebral hemispheres • includes the paired thalami, hypothalamus, epithalamus C E D C. Brainstem • includes the midbrain, pons & medulla • contains vital autonomic centres, cranial nerve nuclei, white matter tracts Ma15.1 D. Cerebellum • consists of bilaterally paired cerebellar hemispheres • separated from the cerebral hemispheres by the transverse fissure (E) 3 Cerebral Cortex • a layer of grey matter (neuronal cell bodies) 4-6 mm thick • highly folded in sulci (grooves) and gyri (bumps) which ↑ surface area – sulcus (singular), gyrus (singular) – particularly deep sulci are called fissures • variability in sulci & gyri between brains and between hemispheres of the same brain • however, some sulci and gyri are fairly consistent between brains and are named • these are used as landmarks to divide the brain into anatomical regions, called lobes…. 4 Lobes of the Cerebral Hemispheres CENTRAL SULCUS FRONTAL LOBE PARIETAL LOBE TEMPORAL LOBE LATERAL FISSURE Mc15.1 PARIETOOCCIPITAL FISSURE (on medial surface) OCCIPITAL LOBE PREOCCIPITAL NOTCH 5 Lobes of the Cerebral Hemisphere 6 7 A. skin Coverings of the Brain B. periosteum C. cranium Mc15.4 D. dura mater E. periosteal layer A B C E F I J K L M H F. meningeal layer G. dural reflection H. dural venous sinus D I. subdural space – “potential” space J. arachnoid mater K. subarachnoid space – contains CSF, BVs L. pia mater G M. cerebral cortex 8 Loose connective tissue and periosteum of cranium ANTERIOR Cranium Dura mater Epicranial aponeurosis Subarachnoid space Arachnoid mater Scalp Cerebral cortex covered by pia mater POSTERIOR Ma16.4 The Dural Reflections in a Coronal MRI A FN-C9 A. falx cerebri B. parietal lobe C B C. lateral fissure D. temporal lobe E. tentorium cerebelli D E F F. cerebellum 10 Midsagittal view Dural Reflections A • meninges form rigid folds in major fissures: A. falx cerebri in longitudinal fissure – separates right and left cerebral hemispheres B. tentorium cerebelli in transverse fissure B C – separates occipital lobe of cerebrum from cerebellum C. diaphragma sellae Pituitary gland Ma16.3 Sella turcica of sphenoid – stabilizes position of the pituitary gland in the skull base 11 The Dural Reflections in a Sagittal MRI A. frontal lobe FN-S1 D B. parietal lobe B A C. occipital lobe C E D. tentorium cerebelli F H E. brainstem G F. cerebellum G. foramen magnum H. spinal cord 12 Dural Venous Sinuses I B A Note the dural reflections, the falx cerebri and tentorium cerebelli. Note the related dural venous sinuses: • in margins of dural reflections; i.e. between periosteal and meningeal layers of dura mater C • drain venous blood from the brain into R & L internal jugular veins A. superior sagittal sinus D B. inferior sagittal sinus C. straight sinus D. confluence of sinuses Ma16.3 Note the dural reflections in bold. Note their related sinuses. Mc15.5 14 Dural Venous Sinuses and Cerebral Venous Drainage 2 4 Superior sagittal sinus Dura mater Subdural “space” Subarachnoid space Ma16.5 3 Subdural “space” Subarachnoid space Arachnoid mater Arachnoid trabeculae Pia mater Arachnoid granulation Falx cerebri Cranial Meninges Cerebral cortex Cerebral vein 1 Cerebral cortex Perivascular space D Dural Venous Sinuses II E A. confluence of sinuses F C B A B. transverse sinus C. sigmoid sinus to jugular foramen D. cavernous sinus receives ophthalmic veins from orbit D E F Ma6.11 A C B E. superior petrosal sinus F. inferior petrosal sinus Diaphragma sellae over pituitary gland Crista galli Tentorium cerebelli Ma16.23 Falx cerebri (cut) Tentorium cerebelli (cut edge) Superior view The Ventricular System • the nervous system originates from a hollow, fluid-filled tube, the neural tube • cells of tube wall proliferate, differentiate forming cells of the nervous system • enclosed fluid-filled space, the neural canal forms the ventricular spaces of the CNS • contains cerebrospinal fluid (CSF), produced by the choroid plexus within the ventricles 18 Choroid Plexus in the Lateral Ventricle Remember: TJs between the ependymal cells of the choroid plexus forms the blood-CSF barrier. Coronal section through the cerebrum Choroid plexus 19 Structural Characteristics of Neural Capillaries Remember: TJs between the endothelial cells of the cerebral BVs forms the blood-ISF barrier. Capillaries in neural tissue are of the continuous type. Capillaries in many other tissues are fenestrated. 20 B BBB Breakdown A • results in ↑ permeability of brain capillaries • causes vasogenic edema, which ↑ intracranial pressure and can act like a space occupying lesion C • in imaging, seen with contrast agent, that doesn’t cross intact BBB • BBB breakdown occurs in tumors, arteriovenous malformations, inflammation (2° to stroke, MS, etc.) A. Normal brain with contrast B. Gadolinium-enhanced MRI showing BBB breakdown in a glioblastoma multiforme. 21 C. Gadolinium-enhanced MRI showing BBB breakdown due to inflammation in active MS lesions. The Ventricular System • ventricular spaces are associated with subdivisions of the nervous system: CEREBRAL HEMISPHERES A. BILATERALLY PAIRED LATERAL VENTRICLES DIENCEPHALON B. THIRD VENTRICLE MIDBRAIN C. CEREBRAL AQUEDUCT PONS, MEDULLA, CEREBELLUM D. FOURTH VENTRICLE SPINAL CORD E. CENTRAL CANAL A A B B C C Lateral view Ma16.2 D D E Anterior view E 22 Continuity of the Ventricular System A B Ma16.2 C A D Lateral view E H F G A. R, L lateral ventricles B. interventricular foramen C. third ventricle D. cerebral aqueduct E. fourth ventricle F. central canal Fourth ventricle is continuous with the subarachnoid space through the median aperture (G) and the lateral apertures (H). A C B D E H F G (very) Schematic coronal section 23 Choroid plexus in lateral ventricle Arachnoid granulations The Circulation of CSF • CSF is produced by the choroid plexus, present in all ventricles • total volume CSF ~150 mL • produce ~ 500 mL / day Choroid plexus of third ventricle Aqueduct of midbrain Choroid plexus of fourth ventricle Subarachnoid space Central canal • ∴ turned over 3 times per day • CSF circulates through ventricles, enters subarachnoid space via median and lateral apertures of fourth ventricle • circulates in subarachnoid space Lumbar cistern Ma16.7 NEXT SLIDE Choroid plexus in lateral ventricle Arachnoid granulations The Circulation of CSF • CSF is returned to venous blood via arachnoid granulations in dural venous sinuses Dural venous sinus Choroid plexus of third ventricle Aqueduct of midbrain Choroid plexus of fourth ventricle • Also along the sheaths of cranial and spinal nerves to surrounding lymphatics Cranium Dura mater (endosteal layer) Central canal Arachnoid granulation Subarachnoid space Arachnoid trabecula Central canal Lumbar cistern Dura mater (meningeal layer) Cerebral cortex Ma15.6 Pia mater Subarachnoid space Arachnoid mater 25 MRI of normal ventricles MRI of ventricles in hydrocephalus 26 Midsagittal section Association tracts Parietal lobe Corpus callosum Commissural tracts (in corpus callosum) • cerebral hemispheres receive sensory information from, issue motor commands to, the opposite side of the body • the cerebral cortex is grey matter Frontal lobe Temporal lobe The Medullary Centre Occipital lobe Coronal section • subcortical white matter – carries afferent information toward neuronal cell bodies of cerebral ctx – carries efferent information away from neuronal cell bodies of cerebral ctx – may be association, commissural or projection fibres Cerebral nuclei • buried within are grey matter structures – the basal nuclei (ganglia) Projection tracts Mc15.13 Thalamus – diencephalon (thalamus, hypothalamus, epithalamus) 27 28 Functional Localization in the Cerebral Cortex Motor Output • movement is planned and initiated in specific dedicated cortical areas Sensory Input • all sensory modalities ultimately reach the cerebral cortex, most after a relay in the thalamus • each modality has an area dedicated to it’s perception, its 1º sensory cortex; e.g. 1° somatosensory ctx, 1° visual ctx, 1° auditory ctx, etc. • each modality has an area dedicated to it’s interpretation, its association cortex; e.g. somatosensory assn. ctx, visual assn. ctx, auditory assn. ctx. • input from the various sensory modalities are integrated in the multimodal association cortices 29 Major Sulci & Gyri of the Cerebral Hemispheres Lateral view B A C D M L J G I F H E K Ma15.9 Left lateral view 30 Lobes of the Cerebral Hemisphere 31 32 Functional Localization in the Cerebral Cortex I A. 1º Motor Cortex (precentral gyrus) Superior view B A • control of voluntary, skilled mvt Hip Knee Ankle Toes • somatotopic representation of the contralateral half of body, the motor homunculus • area ∝ precision of movement of body part, not its size Pharynx Coronal section through precentral gyrus B. Premotor Ctx, Supplementary Motor Area (adjacent portions of frontal lobe) • fxn. in programming of, preparation for, mvt and control of posture Mc15.12 Lateral Medial 33 Functional Localization in the Cerebral Cortex II Superior view C. 1º Somatosensory Cortex (postcentral gyrus) C D Hip Leg Foot Toes Genitals • perception of somatosensation • somatotopic representation of the contralateral half of body, the sensory homunculus • area ∝ density of sensory innervation of a given body part, not its size Coronal section through postcentral gyrus Intra-abdominal D. Somatosensory Association Cortex (adjacent portions of parietal lobe) • interpretation of somatosensation Medial Mc15.12 Lateral • conscious awareness of the contralateral half of the body 34 Coronal MRI 35 Functional Localization in the Cerebral Cortex III E. 1º Visual Cortex (on either side of the calcarine fissure in the occipital lobe) • functions in visual perception F. Visual Association Cortex (remainder of occipital lobe) • interpretation of visual images in the context of past experience • lesion causes deficit in visual interpretation and recognition G. 1º Auditory Cortex (portions of temporal lobe within lateral fissure) • conscious perception of sound • organized as a “tonotopic” map of cochlear duct H. Auditory Association Cortex (adjacent portions of temporal lobe) • interpretation of auditory input in the context of past experience, etc. • in dominant hemisphere, adjacent to sensory speech or “Wernicke’s” area • in the nondominant hemisphere, the corresponding area interprets prosidy 36 Functional Localization in the Cerebral Cortex IV I. Motor Speech Area (portions of frontal lobe ant. to precentral gyrus) • in the dominant (usually the left) hemisphere only; a.k.a. “Broca’s area” • functions in motor aspects of speech • in the nondominant hemisphere, the corresponding area controls prosidy J. 1 ° Gustatory Cortex (inf. part of postcentral gyrus and insula) • conscious perception of taste K. 1° Olfactory Cortex (temporal lobe) • conscious perception of smell Multimodal Association Cortices L. Prefrontal Cortex (frontal lobe) • integrates information from various assn. cortices • higher intellectual functions e.g. reasoning, prediction, emotion M. Inferior portions of parietal lobe • interface between somatosensory, visual and auditory association cortices 37 The Basal Nuclei A B • includes the A. caudate B. putamen C. globus pallidus or “pallidum” D. substantia nigra & subthalamus Functions • refine normal voluntary mvt. • not directly connected to spinal cord; i.e. do not directly control movement • diseases of basal nuclei present with: – hypokinesis (without paralysis) or hyperkinesis D Coronal section Mc15.14 C – altered posture and muscle tone – altered cognition, behavioural disturbances – eg. Parkinsonism 38 The Diencephalon I • thalamus, hypothalamus & epithalamus Thalamus: Functional Organization of Nuclei Sensory Nuclei • vision (lateral geniculate nucleus) • hearing (medial geniculate nucleus) • somatic sensation, conscious proprioception, taste (ventral posterior) Motor Nuclei Mc15.16 • associated with basal nuclei & cerebellum • movement planning & control (VA, VL) Limbic Nuclei Medial group Posteri • emotions, mood (ant. nuc. group) or group Anterior Lateral group MG group Association (multimodal) Nuclei LG • integrates sensory information; connects VA VL VP Ventral group with association cortices Intrinsic & diffuse-projecting Nuclei 39 Left anterolateral view • influences levels of arousal A. The Hypothalamus The Diencephalon II • maintains homeostasis via neural & hormonal means in response to interoceptive & limbic input B A • regulates reproductive, autonomic and instinctive functions, food & water intake, circadian rhythms, emotional aspects of behaviour…. B. The Epithalamus • includes the pineal gland – secretes melatonin Midsagittal section Mc15.15 – fxn. in circadian rhythm & onset of puberty 40 41 The Diencephalon in MRI A B A. B. C. D. Midsagittal section C D Thalamus Hypothalamus Epithalamus Area of subthalamus FN-S1 42 The Cerebral Hemispheres in Axon-Stained Section LATERAL VENTRICLES CEREBRAL CORTEX (grey matter) SUBCORTICAL WHITE MATTER THALAMUS (grey matter) BASAL NUCLEI (GANGLIA) (grey matter) THIRD VENTRICLE HYPOTHALAMUS (grey matter) CGS Coronal section 43 The Cerebral Hemispheres in Coronal MRI LATERAL VENTRICLES CEREBRAL CORTEX (grey matter) SUBCORTICAL WHITE MATTER DIENCEPHALON (grey matter) BASAL NUCLEI (GANGLIA) (grey matter) THIRD VENTRICLE FN-C15 44