Neuroanat 2_Telencephalon and meninges_2023_Student - Tagged.pdf

Organisation of the central nervous system: Telencephalon and the meninges Professor Andrew Dilley Previous lecture • Development of the central nervous system • Anatomy of the spinal cord • Anatomy of the brainstem • Anatomy of the cerebellum • Anatomy of the diencephalon Telencephalon Telen...

Organisation of the central nervous system: Telencephalon and the meninges Professor Andrew Dilley Previous lecture • Development of the central nervous system • Anatomy of the spinal cord • Anatomy of the brainstem • Anatomy of the cerebellum • Anatomy of the diencephalon Telencephalon Telencephalon • Telencephalon is superior to the diencephalon • Comprises the cerebral hemispheres/cerebral cortex, components of the basal ganglia and the limbic system Telencephalon (Cerebral hemispheres) Midsagittal MRI showing the telencephalon Cerebral hemispheres • Cerebral hemispheres are divided into lobes Central sulcus • Outer layer is the cerebral cortex (divides frontal from parietal lobe) • Highly folded structure (gyri and sulci) Parietal lobe Frontal lobe Lateral sulcus (divides temporal from parietal lobe) Temporal lobe Occipital lobe = Neocortex Functional areas of cortex • The cortex of each lobe has a different sensory or motor function Primary motor cortex (precentral gyrus) Central sulcus Somatosensory cortex (postcentral gyrus) Visual cortex Motor speech area of Broca Motor Sensory Association/cognition Prefrontal cortex 80% of cortex is involved in association (perception of world) and cognition Auditory cortex Olfactory cortex Gustatory (taste) cortex (part of insula) Corpus callosum • White matter tract linking the cerebral hemispheres Corpus callosum Midsagittal Coronal MRI showing the corpus callosum Subcortical structures • Lots of brain nuclei and white matter tracts deep within the telencephalon • Interconnected to form important neural pathways, which include the basal ganglia and limbic system Basal ganglia • Involved in control of posture and movement • Series of interconnected nuclei at base of forebrain: Lentiform nucleus Putamen Globus pallidus Corpus striatum Caudate nucleus Ventral • Connects to the motor cortex and the substantia nigra in the midbrain Clinical: Disorders of the basal ganglia cause abnormalities in movement, muscle tone and posture Corpus striatum • Lentiform nucleus is lens shaped • Caudate nucleus is C-shaped and sits in wall of lateral ventricle (see ventricular system lecture) Body of caudate nucleus Head of caudate nucleus Rostral Lentiform nucleus Tail of caudate nucleus Lentiform and caudate nuclei • Lentiform nucleus sits lateral to caudate nucleus Rostral Caudate nucleus (Head) A Lentiform nucleus Gp P B B P Gp A (Tail) Caudate nucleus (Head) Nucleus accumbens (Reward centre) Rostral slice MRI showing the basal ganglia The capsules • Important white matter tracts either side of the lentiform nucleus • Internal capsule connects cortex to brainstem (Internal to lentiform nucleus) Rostral Internal capsule Claustrum Coronal External capsule (External to lentiform nucleus) Horizontal Limbic system • Involved in emotional processing, autonomic functions, learning and memory • Limbic system* refers to structures on the medial border of the hemispheres • Connects to the endocrine and autonomic areas (hypothalamus), and prefrontal cortex * Limbus means edge/border Limbic system components • Spans the telencephalon and diencephalon • Main components include: Cingulate cortex MRI showing parts of the limbic system Fornix Thalamus (anterior) Hippocampal formation Mammillary bodies Amygdala Entorhinal cortex Hippocampal formation • Hippocampus is a major part of the hippocampal formation Rostral • It resembles a sea horse • Involved in spatial memory Hippocampus lateral Medial MRI showing the hippocampus Dentate gyrus Subiculum Entorhinal cortex LHS Coronal Hippocampus sits in floor of lateral ventricle (see ventricular system lecture) Fornix • The fornix is an important connecting pathway within the limbic system • The semi-circular white matter tract connects the hippocampus and mammillary bodies Body of fornix Fornix Coronal Mammillary body Hippocampus • The mammillary bodies are involved with memory Caudal Amygdala • Almond-shaped nuclei on medial side of temporal lobe • At tip of inferior horn lateral ventricle (Fused to tail of caudate nucleus) • Involved in the emotional processing of fear and rage MRI showing the amygdala Amygdala Hippocampus Caudal Meninges Meninges • Central nervous system is surrounded by the meninges • Consists of three layers: SKULL Dura Mater Arachnoid Mater Outer Cerebrospinal fluid Pia Mater BRAIN Inner • Multiple functions: Protects brain Prevents movement of brain Forms fluid filled cavity to cushion the brain against trauma Dura mater • Dense fibrous membrane • Cranial dura consists of two layers : Endosteal layer – Lines inside of cranium Meningeal layer – Lines brain and spinal cord • Spinal dura only has one layer Coronal Dura mater blood and nerve supply Blood supply • Own blood supply via the middle meningeal artery • Enters middle cranial fossa through foramen spinosum • Sits within the endosteal layer of dura Branch of maxillary artery (from external carotid artery) Nerve supply • Mainly by the trigeminal (CN 5) nerve Dura is the only part of the CNS with a sensory supply Clinical: Meningeal headache Activation of nociceptors in dura (due to inflammation or change in intracranial pressure) Meningeal layer of dura • Forms a series of septa • Divide cranial cavity into compartments Falx cerebri Tentorium cerebelli Falx cerebri Separates the cerebral hemispheres Tentorium cerebelli Separate cerebellar hemispheres from the cerebral hemispheres Falx cerebelli Falx cerebelli Separate cerebellar hemispheres Christa galli (ethmoid bone) Tentorium cerebelli Sphenoid bone Clinical: Haematomas • Dura is important to understand clinically: Extradural (epidural) haematoma • Blood collects in space between skull and dura • Trauma to middle meningeal artery Subdural haematoma • Blood collects between dura and arachnoid Called the ‘subdural space’ • Trauma to bridging veins CT scans Arachnoid mater • Thin avascular translucent layer lining the dura Subarachnoid space Arachnoid • Space below arachnoid • Contains cerebrospinal fluid • Contains cerebral vessels Subarachnoid space Arachnoid granulations • Herniations of arachnoid into venous sinuses (see Ventricular system lecture) Trabeculae (Projections of arachnoid) Clinical: Subarachnoid haemorrhage Bleed into subarachnoid space; caused by a ruptured aneurysm or major trauma Pia mater • Very thin vascular membrane • Closely invests brain • Arachnoid and pia are called the leptomeninges Clinical: Meningitis (leptomeningitis) Inflammation of the leptomeninges Pneumococcal meningitis Dural venous sinuses • Spaces formed between the endosteal and meningeal layers of the dura - No valves are present • Drain blood and cerebrospinal fluid from brain • Drain into internal jugular veins Sinuses closely associated with the dural folds Falx cerebri Tentorium cerebelli Superior sagittal sinus Network of dural venous sinuses 1. Superior sagittal (FC) 2. Inferior sagittal (FC) 1 2 3. Straight 4. Occipital (FCe) 6 7. Cavernous 5. Confluence of sinuses 6. Transverse (TC) 7 8. Superior petrosal 7 9 4 6 8 9 TC FCe 5 3 FC 9. Sigmoid Internal jugular vein 8 Ophthalmic veins Internal jugular veins Venous system • Sinuses drain blood from: Cranium via diploic veins Extracranial sites via Superiorveins cerebral veins emissary Brain via cerebral veins Bridging vein (bridges across arachnoid and meningeal dura) Clinical: Emissary veins provide route of infection into cranial cavity Cavernous sinus Lesser wing • Paired sinus • located against the sphenoid bone • Many structures pass through the sinus Greater wing Cranial nerves (CN3-6: oculomotor, trochlear, trigeminal, abducent) Internal carotid arteries Cavernous sinus • Receives blood from sphenoparietal sinus*, cerebral, ophthalmic and emissary veins (infratemporal fossa region) Clinical: Route of infection (Extracranial to intracranial sites) Inflammation of structures passing through cavernous sinus * Summary • Anatomy of the cerebral hemispheres • Anatomy of the limbic system • Anatomy of the basal ganglia • Structure of the meninges • Dural venous sinuses Next Lecture: Ventricular system and cerebrospinal fluid