NS Anatomy 1 PDF

Lec 1: Brain and Spinal cord Nervous tissue divisions: 1. Central Nervous System: Brain & Spinal Cord 2. Peripheral Nervous System: Peripheral nerves (cranial and spinal) & ganglia Nerves according to function is divided into: - Sensory (somatic and visceral, visceral divided to sympatheti...

Lec 1: Brain and Spinal cord Nervous tissue divisions: 1. Central Nervous System: Brain & Spinal Cord 2. Peripheral Nervous System: Peripheral nerves (cranial and spinal) & ganglia Nerves according to function is divided into: - Sensory (somatic and visceral, visceral divided to sympathetic and parasympathetic) - motor General term: - Aggregation of neuronal cell bodies in the CNS → nucleus - Aggregation of neuronal cell bodies in the PNS → ganglion - Aggregation of axons in the CNS → tracts - Aggregation of axons in the pns → nerves Directional terms: Above the brain stem: o Dorsal means superior o Ventral means inferior o Rostral means anterior o Caudal means posterior Within the brain stem and below: o Dorsal means Posterior o Ventral means Anterior o Rostral means Superior o Caudal means Inferior Major Parts of The Brain Forebrain (Prosencephalon): Cerebrum & Diencephalon Midbrain (Mesencephalon): Midbrain Hindbrain (Rhombencephalon): Pons, Medulla oblongata, & Cerebellum ✓ Neurulation of nervous system starts at 3rd week of pregnancy  Cerebrum Largest part of brain → occupy anterior cranial fossa and middle cranial fossa 2 hemispheres: (Rt. & Lf.) separated by a midline fissure (longitudinal fissure)→ occupied by extension from meninges (specifically dura matter) → falx cerebri External Aspect of Cerebrum o Folded into Gyri & Sulci to increase surface area o Subdivided by sulci into lobes: 1. Frontal 2. Parietal 3. Occipital 4. Temporal 5. Insula (deep withing the lateral fissure) Internal Structure of Cerebrum o Outer Layer: ▪ The Cerebral Cortex ▪ Gray matter → contain aggregation of cell bodies and a little amount of connective tissue ▪ folded from outside into: gyri & sulci o Inner Layer: ▪ white matter → contains bundle of axons (tracts) ▪ basal nuclei is cluster of subcortical nuclei deep to cerebral hemispheres cerebrum landmarks o Each hemisphere is divided into lobes by: ▪ Lateral fissure → between frontal lobe, parietal lobe above and temporal lobe below ▪ Central sulcus → between frontal lobe anteriorly and parietal lobe posteriorly ▪ Parieto-occipital sulcus (only on the medial surface) ▪ And two imaginary lines 1st line extends from pre-occipital notch inferiorly to the superior surface of the cerebrum. o Separates between occipital lobe posteriorly and parietal & temporal lobes anteriorly. 2nd line extends between the posterior ramus of lateral fissure to the 1st line. o Separates between parietal lobe superiorly and temporal lobe inferiorly.  The Diencephalon o Masses of gray matter located around third ventricle Thalamus → dorsally Hypothalamus → ventrally Subthalamus Epithalamus The brainstem Extend between the diencephalon and the spinal cord. Midbrain → superiorly Pons → middle Medulla → inferiorly The Cerebellum Posterior cranial fossa below the occipital lobe Contain most of the neurons Has connections with: spinal cord, brainstem, and thalamus Spinal Cord Externally Extends from the medulla oblongata to the superior border of the L2 in an adult o Conus medullaris → where the spinal cord tapers off inferiorly to its termination o Filum terminale → a prolongation of the pia mater attached to the posterior aspect of coccyx o Cauda equina → the inferior nerve roots of the spinal nerves that descend from the lower part of the spinal cord Internally it is a butterfly shaped inner grey matter surrounded by white matter. o The anterior median fissure o The post. median sulcus o The gray commissure (cross the midline) o Central canal (contain CSF) o Anterior (ventral) & posterior white commissure  The grey matter of the spinal cord o The anterior (ventral) grey horn o The posterior (dorsal) grey horns o The lateral grey horns (present only in the thoracic, upper lumber, and sacral segments) The white matter of the spinal cord (have ascending sensory tract and descending motor tract) o Anterior (ventral) white columns o Posterior (dorsal) white columns o Lateral white columns Spinal nerves o 31 pairs Emerges from a spinal segment ✓ 8 pairs of cervical nerves (C1–C8) ✓ 12 pairs of thoracic nerves (T1–T120 ✓ 5 pairs of lumbar nerves (L1–L5) ✓ 5 pairs of sacral nerves (S1–S5) ✓ 1 pair of coccygeal nerves (Co1) o Two roots: ✓ The anterior or ventral root (motor) ✓ The posterior or dorsal root (sensory) ✓ The posterior or dorsal root ganglion o Spinal nerve divides into several branches called rami: ✓ The posterior (dorsal) ramus ✓ The anterior (ventral) ramus ✓ Gray and white rami (contribute to the ANS) ✓ The meningeal branch - The anterior rami of the spinal nerves form networks called plexuses, except for thoracic Cells of the CNS o Two major cell types: 1. Nerve cells (Neurons) 2. Neuroglial cells (Glia) 1. Nerve cells o The structural and functional units of NS, Components: ▪ Cell body ▪ Extensions (neurite): Dendrites and Axon o Types: ▪ Based on number of branches: Multipolar neuron (most on neurons)→ 1 axon and at least 2 dendrites Bipolar neuron (in retina and CN8) Unipolar neuron→ has short single process that immediately divides into 2 processes, 1st called central and go toward CNS and 2nd called peripheral go toward periphery (neurons in the dorsal root ganglia) ▪ Based on function: Sensory neurons Motor neurons ▪ Based on termination sites of axon: Local circuit neurons (interneurons)→ for processing and integration of info Projection neurons ▪ Golgi Classification (depend on used stain) Golgi type I: large neurons within brain region (eg: pyramidal cells→ large motor neuron within somatomotor area (precentral gyrus)) Golgi type II: small local circuit neurons  ❖ Neurites o Dendrites: ▪ Tapers (decrease diameter) from cell body ▪ Dendritic spines which are areas of synapse ▪ Brings action potential toward cell body o Axon: ▪ Uniform diameter ▪ Has Collateral branches ▪ Synaptic terminals ▪ Take action potential away from cell body ✓ Neuronal Synapses (Axo-dentritic, Axo-axonic, Axo-somatic) o Chemical: ▪ Neurotransmitters (presynaptic) ▪ Receptors (postsynaptic) o Electrical: ▪ Gap junctions ▪ Faster conduction ▪ Low resistance ▪ Bidirectional 2. Neuroglia a. Astrocytes o Have many cytoplasmic process and Perivascular feet o Form Internal Glial limiting membrane o Form External Glial limiting membrane o 2 types: o Fibrous astrocytes: found in white matter o Protoplasmic: found in gray matter o Functions: o Framework support o Supports blood brain barrier o Recycling of neurotransmitters  b. Oligodendrocytes oSmall cell body oConspicuous cytoplasm oLong thin processes rich in microtubules oForm a segment of myelin sheath around more than one axon in the CNS (while schwann cells form segment of the myelin sheath only around one axon in the PNS) c. Microglia o The macrophage of the CNS o Small cells o Elongated nuclei o Several short branched processes o Evenly distributed in gray & white matter d. Ependyma o Simple cuboidal to columnar epithelium o Lines the ventricular system - Ependomocytes o majority o ciliated o no tight junctions - Tanycytes o long basal processes o at the floor of 3rd ventricle - Choroidal epithelial cells o Cover choroid plexus o Ciliated o Tight junctions → Forms Blood-CSF barrier The Blood-Brain Barrier Protects brain from harmful substances and pathogens Components: 1. Tight junctions between endothelial cells 2. Thick basement membrane 3. Processes of astrocytes → press up against the capillaries  meninges, ventricles and CSF The cranial meninges: 3 layers of connective tissue that: 1- Protect the brain 2- Provide supporting framework for arteries and vein 3- Enclose fluid filled cavity (CSF) The 3 layers are: 1- Dura matter 2- Arachnoid mater 3- Pia matter - Meninges fuse with the epinurium of the cranial nerves at skull foramina (don’t pass beyond the Foramina), while they cover the optic nerve all through. Dura mater - Most external part - It is avascular double layered membrane, which are: 1- External periosteal layer→ periosteum of calvarian bones 2- Internal meningeal layer → it’s tough thick fibrous membrane that continues at foramen magnum to spinal cord - Brain venous sinuses are located between periosteal and meningeal layers of dura Dural reflections Folding of internal meningeal layer between brain compartments( septa) to restrict the rotatory displacement of the brain There is 4 main reflections: 1- Falx cerebri → occupy longitudinal fissure separates between 2 hemisphere 2- Falx cerebelli → separates between 2 cerebellar hemispheres 3- Tentorium cerebelli → separates between occipital lobe superiorly and cerebellum inferiorly 4- Sellar diaphragm →covering the sella turcica, with a pituitary stalk penetrating the diaphragm. Innervation of dura meter - Above tentorium cerebelli → trigeminal nerve. o Pain is referred to the skin overlaying the dura mater - Below tentoium cerebelli → upper cervical spinal nerves from posterior rami of cervical spinal nerves (greater occipital nerve) o Pain is referred to the back of the head Arachnoid mater - It’s thin intermediate layer that attaches to pia mater through web-like arachnoid trabeculae - It’s avascular layer Arachnoid space - Is located between arachnoid and pia - Contains: arachnoid trabeculae and CSF Lumbar cistern: located at L4 (for lumber puncture) Arachnoid villi: empty CSF into superior sagittal sinus - Have valve like function - Group of them called arachnoid granulation Pia mater - It’s very thin and delicate membrane that is highly vascularized - It adhere to brain surface and flows its contours - It extend at the conus medullaris as filum terminale Meningeal spaces 1- Epidural space: between dura and bone - Its not presented normally → it happens pathologically (eg, hemorrhage) 2- Subdural space: between arachnoid and pia - It’s not present normally 3- Subarachnoid space: between pia and arachnoid - It’s a real space that contain CSF Ventricles of the brain - 4 CSF filled cavaties located within the brain o 2 lateral ventricels o 3rd ventricle o 4th ventricle - Lined by ependymal - Contain specialized vascular structure for CSF production( choroid plexus) - Connected to each other and to other 2 CSF filled spaces (subarachnoid and simple canal of spinal cord) Lateral ventricle - Its C shape - Parts: o Anterior horn → (in frontal lobe) o Body → (in parietal lobe) o Posterior horn → (extending posteriorly and may or may not extend to the occipital lobe) o Inferior horn → (extending more laterally and inferiorly within the temporal lobe) - The atrium is where 3 parts meet each other - Each lateral ventricle is connected to the 3rd ventricle through interventricular foramen (foramen of minro)→ at the junction of anterior horn and body of lateral ventricle - Location: a) The roof for: - Anterior horn & body → Corpus callosum - Inferior horn → Tail of caudate nucleus b) The floor for: - Body → Thalamus - Inferior horn → Hippocampus c) The lateral wall of: - Anterior horn & body → Caudate nucleus d) Medial wall → Septum pellucidum third ventricle (ventricle of the diencephalon) - Narrow cavity between the two thalami and floor is formed by the hypothalamus. - Communicates with lateral ventricles via foramen of Monro. - Communicates with fourth ventricle through cerebral aqueduct that runs through the midbrain Cerebral Aqueduct - ¾ inch long with no choroid plexus. - Represents a passageway for the CSF from the 3rd ventricle to the 4th ventricle. - In the midbrain fourth ventricle - Ventricle of the hindbrain. - Tent shaped cavity - Bounded anteriorly by bones & medulla oblongata and posteriorly by the cerebellum. - Communicates with the subarachnoid space through: - Median foramen of Magendie in the roof - 2 lateral foramina of Luschka Choroid plexus - Present in all ventricles - Production and secretion of CSF - Found at the junction of the body and & inferior horn and continue within the roof of the inferior horn. - For third and fourth ventricles, choroid plexus are located within the roof. - Components: 1. Endothelial layer (fenestrated) 2. Pial membrane 3. Choroidal epithelial cells joined by tight junction Blood-CSF barrier A- Blood brain barrier → tight junction between endothelial cells B- Blood CSF barrier → tight junction between choroid plexus endocytes ( choroid epithelial cells) CSF - Made by choroid plexus (about 500 ml/day) - Distributed in ventricles and subarachnoid space - Clear and colorless - Circulation: lateral ventricles→ 3rd ventricles → 4th ventricles → subarachnoid space arachnoid granulation → dural venous sinuses