Central Nervous System Lecture Notes PDF

CENTRAL NERVOUS SYSTEM Dr S Ravi Shankar MBBS MD Dip Cardiology Associate Professor Faculty of Medicine UniKL RCMP LECTURE OUTLINE Classification of Nervous System (NS ) Types of glia & their functions Myelinat...

CENTRAL NERVOUS SYSTEM Dr S Ravi Shankar MBBS MD Dip Cardiology Associate Professor Faculty of Medicine UniKL RCMP LECTURE OUTLINE Classification of Nervous System (NS ) Types of glia & their functions Myelination in CNS versus peripheral nervous system Formation Circulation & Absorption of Cerebrospinal Fluid (CSF) Parts of the brain Cerebral Cortex : Lobes & Functions Functions of other parts of the brain  Nervous System Central Nervous System Peripheral Nervous System Brain Somatic Spinal Sensory Cord Visceral Motor Autonomic Somatic Parasympathetic Sympathetic  GLIAL CELLS Non neuronal cells / connective tissue of nervous system continue to undergo cell division in adulthood ability to proliferate - stroke Types : in vertebrate central nervous system (CNS) - Microglia : resemble tissue macrophages & not other neural cells scavenger cells : remove debris resulting from injury infection & disease - Macroglia : Astrocytes : Fibrous & Protoplasmic Oligodendrocytes cf Schwann cells (Peripheral NS) Ependymal Cells : produce cerebrospinal fluid (CSF)  Astrocytes Send processes to : - blood vessels & form blood brain barrier (BBB) - envelop synapses & surface of nerve cells & insulating synapse from its neighbours - Produce neurotropins : growth & repair - Supplement interstitial fluid in brain - Help maintain appropriate concentration of ions & neurotransmitters 1. Central Nervous System (CNS) – Oligodendrocytes: - Oligodendrocytes are the cells responsible for myelination in the CNS, which includes the brain and spinal cord. - In the CNS, a single oligodendrocyte can myelinate multiple axons or neurons at once. This means that one oligodendrocyte can wrap segments of myelin around several different axons, as shown in the diagram on the left. - The image also shows perineural oligodendrocytes, which are cells that provide support to neurons in the CNS by wrapping around their axons. 2. Peripheral Nervous System (PNS) – Schwann Cells: - In contrast to the CNS, myelination in the PNS is carried out by Schwann cells. - Each Schwann cell can myelinate only one axon. This is demonstrated in the diagram on the right, where the Schwann cell wraps around a single axon in layers to form the myelin sheath. - The diagram also shows structures like the Nodes of Ranvier, which are small gaps between segments of the myelin sheath. - - These nodes play a key role in speeding up nerve signal transmission by allowing the signal to "jump" from one node to the next. Summary of Key Differences: - Oligodendrocytes (CNS) can myelinate multiple neurons. - Schwann Cells (PNS) can only myelinate one neuron at a time. This myelin sheath is critical for efficient communication between neurons, ensuring rapid signal transmission across the nervous system.  Myelination Central Nervous System : Peripheral Nervous System : Oligodendrocytes Schwann Cell Ventricles of Brain Circulation & Absorption of Cerebrospinal Fluid (CSF) Formation of CSF ≈ 500 ml / day i.e 3 - 4 X of total volume 2/3 : choroid plexuses in ventricles Rest : Ependymal surfaces of all ventricle Arachnoidal membranes Brain itself through perivascular spaces In : Na + Cl - ( + 15 %) H2O Glucose (- 30 %) Out : HCO3 - & K + (- 40 %) 1. CSF Production: - CSF is produced in the choroid plexuses of the ventricles (specifically in the lateral, third, and fourth ventricles). 2. Flow of CSF: - CSF from the lateral ventricles flows through the interventricular foramina into the third ventricle. - CSF from the third ventricle flows through the cerebral aqueduct into the fourth ventricle. - From the fourth ventricle, the CSF enters the subarachnoid space via the lateral and median apertures. 3. CSF Absorption: - CSF circulates within the subarachnoid space, surrounding the brain and spinal cord. - It is absorbed into the bloodstream through arachnoid villi located in the dural venous sinuses. 4.Blood Circulation: - The venous blood, now containing absorbed CSF, returns to the heart and lungs to be oxygenated, continuing the systemic circulation. - This process helps cushion the brain, remove waste, and maintain a stable environment within the central nervous system.  Brain : Primary Portions Forebrain or Prosencephalon - rostral (head) portion Subdivisions : Telencephalon : Cerebrum or Cerebral Cortex ( 4 lobes) & Diencephalon : Thalamus Hypothalamus Pineal Gland Midbrain or Mesencephalon - middle portion connects forebrain to hindbrain Hindbrain or Rhombencephalon - caudal (tail) portion Subdivisions : Metencephalon - Pons & Cerebellum Myelencephalon - Medulla oblongata Note : Brain stem consists of midbrain pons and medulla  Cerebral Cortex Counts for 2 /3 of brain's mass & covers most other brain structures Consists of right & left hemispheres connected by the corpus callosum Gyrus : folds or ridges & Sulci : grooves Cranial nerves : 1st - Olfactory (smell) & 2nd - Optic (sight) Ventricles : 2 Lateral & third cerebral ventricles Sensory input : general / somatosensory & special ( sight smell taste hearing) Limbic system : amygdala & hippocampus : memory formation & emotions Higher Mental Functions : Language Memory Problem solving Motivation Reasoning & Abstract thinking  Cerebral Cortex : Lobes & Functions Receives & processes Planning & somatosensory information Execution Touch Pain of voluntary Temperature movement Receives & processes Receives & processes olfactory information visual information Receives & processes auditory information  Diencephalon Connects nervous system with endocrine system (pineal) endocrine system with nervous system (hypothalamus) Relays sensory information & plays a major role in sensory perception Regulates autonomic endocrine & motor functions Thalamus : Gate between cerebral cortex & other parts of brain & spinal cord for sensory perception & control of movement Role in the control of sleep & wake cycles Hypothalamus : Control center for many autonomic functions Secretes hormones As part of limbic system influences emotional responses  Midbrain (Mesencephalon) Connects the forebrain to the hindbrain Regulates movement & aids in processing of auditory & visual information Cranial Nerves: Oculomotor (III) Trochlear (IV): control eye & eyelid movement Cerebral aqueduct connects the third & fourth cerebral ventricles Tectum : dorsal portion composed of Superior colliculus : visual Inferior colliculus : auditory Cerebral peduncle: anterior portion consists of large bundles of nerve fiber Structures : Tegmentum : forms base of midbrain includes reticular formation & red nucleus Crus cerebri  Hindbrain or Rhombencephalon Metencephalon : Cranial Nerves : Trigeminal (V) Abducent (VI) Facial (VII) Vestibulocochlear (VIII) Myelencephalon : Cranial Nerves : Glossopharyngeal (IX) Vagus (X) Accessory (XI) Hypoglossal (XII) Fourth cerebral ventricle extends through this region Pons : control of autonomic functions & sleep & arousal Cerebellum : Coordination of fine movement Maintenance of balance & equilibrium maintenance Maintenance of muscle tone Medulla : Regulation of Autonomic functions : breathing & heart rate Reflex actions : swallowing & sneezing  Let’s Recollect Classify the nervous system Enumerate the different types of glia & state their functions Explain the difference in myelination in CNS & peripheral nervous system Explain the Formation Circulation & Absorption of Cerebrospinal Fluid (CSF) Enumerate parts of the brain Enumerate lobes of the cerebral cortex & list their functions Enumerate functions of cerebellum pons medulla thalamus & hypothalamus Thank You