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Year 1 Revisio– Central Nervous System Omar SalimILOs • structures and broad functions, and the differences between grey and white matterent • Identify the major structural features of the brain and understand the broad functions of different areas (cerebral hemispheres, lobes, brainstem, cerebellum) • Give an overview of the structure and function of the spinal cord • Outline the locations and functions of the meninges and cerebrospinal fluid • Understand the functional importance of the blood-brain barrier and outline its structureNervous System Divisions • CNS – brain + spinal cord • PNS – cranial nerves + spinal nervesCell Types Glia (aka Neuroglia) • Comprise ~1/2 volume brain & SC • Generally smaller than neurons • 4 main functions: • Surround neurons & hold them in place • Supply nutrients & oxygen to neurons • Insulate neurons • Destroy pathogens & remove dead neurons • Examples • CNS – oligodendrocytes, astrocytes, microglia, ependymal cells • PNS – Schwann cells, satellite cellsAstrocytes • Star shaped cells, largest & most numerous type of glial cell • Supply nutrients to CNS neurons. • Contain microfilaments à considerable strength à support neurones. • Processes wrapped around blood capillaries, maintain selective permeability of endothelial cells à isolate neurons from harmful substances in bloodOligodendrocytes • Resemble astrocytes but smaller with fewer processes. • Form and maintain myelin sheath around CNS axons. Microglia • Function as phagocytes. Like tissue macrophages, remove cellular debris formed during development of the nervous system. Phagocytose microbes + damaged nervous tissue.Ependymal Cells • Cuboidal/columnar, form single layer with microvilli & cilia • Line ventricles of brain & SC central canal (spaces filled with CSF à protects & nourishes brain & SC) • Produce, monitor & assist in circulation of CSF Schwann Cells • Form myelin sheath around PNS axons. • Single oligodendrocyte myelinates several axons, but each Schwann cell myelinates one axon. • Participate in axon regeneration, more easily accomplished in PNS than CNSNeurons • Excitable cells required for generation and transmission of signals. • Comprise dendrite, cell body, axon & nerve terminals. • Axon is typically myelinated with gaps in between – Nodes of Ranvier. Terms: • Grey matter àcell bodies • White matter àaxonsBrain Gross Anatomy • Vast majority is neocortex (cerebral cortex) • Gyri (folds) & sulci (grooves) • parietal/temporal lobesfrontal and • Lateral sulcus around temporal lobe Frontal Lobe • Movement, decision-making, problem solving, planning. 3 main divisions: • Prefrontal cortex - personality expression, planning of complex cognitive behaviours • Premotor cortex + primary motor cortex – voluntary muscle movement Parietal Lobe • Processing tactile sensory information e.g. pressure, touch, and pain. • Somatosensory cortex located here. Essential for processing body's senses, situational/spatial awarenessOccipital Lobe • Main centre for visual processing. • Contains primary visual cortex – receives visual input from retina via optic nerve. These visual signals are interpreted in occipital lobes. Temporal Lobe • Structures of limbic system including olfactory cortex, amygdala & hippocampus (memory) • Important role in organising sensory input, auditory perception (primary auditory cortex), language & speech production, memory. • Wernicke’s area - language understanding & processing, found in dominant cerebral hemisphere (left in 90%) • Broca’s area - motor aspect of speechMotor Homunculus Sensory HomunculusMedulla Oblongata • Autonomic/involuntary functions essential for life e.g. breathing, heart rate, blood pressure, swallowing. Pons • Connects cerebral cortex with medulla oblongata. • Communication and coordination centre between two hemispheres of brain. • As part of brainstem, helps in transferring messages between various parts of brain and spinal cord.Thalamus (Relay Station) • Grey matter relay station under cerebral cortex – receives auditory, somatosensory & visual sensory signals and relays them to cortex. Hypothalamus • Control centre for many autonomic functions of PNS inc. hunger, thirst, maintenance of body temperature. • Endocrine (hormone secreting) functions, connects with pituitary gland à important for maintaining homeostasisCerebellum • Controls motor movement coordination, balance, equilibrium & muscle tone. • Relays information between body muscles & areas of cerebral cortex involved in motor control. Amygdala • Groups of neurons deep within medial temporal lobes • Processing & memory of emotional reactions. • Part of limbic system – variety of functions inc. emotion, behaviour, long-term memory Hippocampus • Limbic system structure important for forming, organising & storing memories.Basal Ganglia • Collection of nuclei strongly connected to cerebral cortex & brainstem • “Action selection” centre – influence motor activity & motor control • Corpus Striatum – made up of caudate nucleus, putamen & globus pallidus • Subthalamic nuclei – produce excitatory neurotransmitter glutamate. • Substantia nigra – midbrain structure, produces neurotransmitter dopamine. Damage to this area causes Parkinson’s disease.• Two hemispheres connected through the corpus callosum = bundle of white matter tracts. Parts: • Body • Genu • Rostrum • SpleniumMeninges and CSF • Membranes that envelop brain + SC for protection. • Dura mater – outermost layer, thick, inelastic. Epidural space between dura mater and inner surface of vertebral canal). • Arachnoid mater – middle cushioning layer, thin & fibrous. Subarachnoid space between arachnoid and pia mater – has trabeculae (spider web-like), contains CSF. • Pia mater – innermost layer, envelopes brain & spinal cord. Has underlying subpial space. Attaches SC to arachnoid via denticulate ligaments• Cranial dura mater has 2 layers → superficial layer (periosteum of skull) and deep layer (dura mater proper) • Cranial cavity has 2 dural reflections (sheet- like protrusions into the cranial cavity): • Tentorium Cerebelli (between occipital lobes and cerebellum) • Falx Cerebri (between cerebral hemispheres in the longitudinal cerebral fissure) Cerebrospinal Fluid (CSF) • A filtrate of blood, made in choroid plexus within ventricles • Produce ~500ml/day • ~140ml circulates throughout subarachnoid space • Affords mechanical and immunological protection to brain & spinal cord • Reabsorbed into venous drainage system of head Lateral ventricles à interventricular foramen à third ventricle à cerebral aqueduct (of midbrain)fourth ventricle à central column of medulla & spinal cordVertebral Column • Vertebral column - strong, flexible, bony column that: 1. Encloses & protects spinal cord 2. Articulates with skull (atlas), ribs (thoracic vertebrae) & hip girdle (sacrum) and provides attachment for back muscles 3. Allows movement & enhances flexibility of trunk (flexion, extension & rotation) 4. Supports head and trunk • 33 vertebrae in infants, 26 in adults • 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fuse), 4 coccygeal (fuse)• Facet / Intervertebral Joint → fix direction of movement • Ligaments (strong bands of fibrous tissue) → prevent excessive movement • Supraspinous Ligaments → C7 to sacrum (tips of spinous processes) • Interspinous Ligaments → C1 to Sacrum (in between spinous processes) • Ligamenta Flava → between adjacent laminae • Longitudinal Ligaments → between adjacent bodies • Intervertebral Discs → carries most of weight & absorbs vertical shock • Annulus Fibrosus → outer fibrous ring consisting of concentric fibrocartilage • Nucleus Pulposus → inner soft, pulpy and highly elastic substanceSpinal Cord • Part of CNS enclosed within vertebral column → consists of nerves cells and tracts. Functions: • Nerve impulse propagation → controls movement of trunk and limbs • Information integration → integrates incoming and outgoing information for spinal reflexes • Central canal surrounded by grey & white matter • Organised segmentally: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal • Total segments31 • Each segment gives rise to pair of spinal nerves• Upper limit: continuation of medulla oblongata • Lower limit: conus medullaris (L1/2 border); there branches of spinal nerves taper to becomes cauda equina • Spinal dura mater anchored to coccyx by filum terminale• Transverse section of spinal cord – central grey matter, surrounding white matter • In the cord, grey matter is subdivided into horns • Posterior (dorsal) grey horns contain cell bodies (in dorsal root ganglia) and axons of incoming sensory neurons • Anterior (ventral) grey horns contain somatic motor nuclei • Lateral grey horns contain autonomic motor nuclei, only present in thoracic & upper lumbar segments of SCmatter comprises tracts ofhite myelinated axons arranged in columns/funiculi • Each column contains axons carrying similar information and have similar origins and sites of termination • Note: column/funiculus contain ≥1 tracts or fasciculi • Ascending (sensory) tracts e.g. touch, pain • Descending (motor) tractsBlood-Brain Barrier • Highly selective semi-permeable border of endothelial cells, stops solutes in blood non-selectively crossing into CSF. • Formed by endothelial cells of capillary wall, astrocyte end-feetensheathing capillary & pericytes embedded in capillary basement membrane. • Allows passage of some small molecules by passive diffusion • Blood brain barrier functions: • Maintains constant environment • Protects brain from foreign substances & • Comprises vascular endothelial cells with tight junctions to prevent leakage