Cns

• Overview of the Nervous System

  2023-2024

  
• Nervous System


  The system concerned with monitoring the changes in both external and internal environments and dealing with these changes

  
• Nervous System


  • Formed of nerve cells (neurons) which receive stimuli from the receptors present all over the body, deal with these stimuli, and send the proper impulses to the effector organs (muscles or glands)
• Classification of the Nervous System

  • Central nervous system
  • Peripheral nervous system

  
• Central nervous system


  • Brain: inside the skull
  • Spinal cord: Inside the vertebral column

  
• Peripheral nervous system


  • Somatic nerves: carrying motor & sensory fibers which supply the skeletal muscles and skin of the body
  • Autonomic nerves: carrying motor & sensory fibers which supply the viscera of the body

  
• Parts of the Brain

  • Cerebral hemispheres (Cerebrum)
  • Diencephalon
  • Brain stem
  • Cerebellum

  
• Cerebral hemispheres (Cerebrum)


  Formed of 4 lobes including the frontal, parietal, occipital and temporal lobes

  
• Diencephalon


  Divided into thalamus, subthalamus, hypothalamus, epithalamus and metathalamus
• Brain stem


  Formed of midbrain, pons and medulla oblongata

  
• Spinal Cord


  • 45 cm tube which is present inside the vertebral column
  • Begins as continuation of the lower border of medulla oblongata at the foramen magnum
  • 31 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal)
  • Two enlargements, one in the cervical and one in the lumbar regions, where the nerve plexuses arise
  • Tapering end called conus medullaris which ends at the level of lower border of L1 vertebra
  • Outer white matter (nerve fibres): it contains the nervous tracts
  • Inner grey matter (nerve cells): it is H-shaped making horns including dorsal horns, ventral horns, and lateral horns
  • Central Canal

  
• Cerebral hemispheres


  Separated by the longitudinal fissure, and are connected by the largest commissural fibers, "the corpus callosum"
• Sulci of the cerebral hemispheres

  • Central
  • Lateral
  • Parieto-occipital

  
• Lobes of the cerebral hemispheres

  • Frontal (motor activity and thinking)
  • Parietal (sensory)
  • Temporal (auditory or hearing)
  • Occipital (vision)
  • Limbic (emotions, memory, and basic behavior)

  
• Interior of Cerebral Hemisphere

  • White matter
  • Grey matter
  • Cavity (e.g. corpus callosum, internal capsule, basal nuclei, lateral ventricle)

  
• Ventricles of the Brain

  • Lateral Ventricle
  • Third Ventricle
  • Fourth Ventricle
• Lateral Ventricle


  Cavity of the cerebral hemisphere, with a body and 3 horns (anterior, posterior and inferior), communicates with the third ventricle through the inter-ventricular foramen
• Third Ventricle


  Cavity of Diencephalon between the 2 thalami, communicates in front with lateral ventricles and behind with the aqueduct of the midbrain
• Fourth Ventricle


  Situated between the cerebellum (behind) and the pons and upper part of the medulla (in front), diamond-shaped when seen from behind but tent-shaped when seen from the side, with a floor, roof, and four angles, connected to the aqueduct of sylvius above and the central canal of the medulla below, and connected to the subarachnoid space through apertures in the roof
• Diencephalon


  Includes the thalamus, hypothalamus, and epithalamus
• Brain stem


  Includes the midbrain, pons, and medulla oblongata

  
• Cranial Nerves


  • I: Olfactory nerve
  • II: Optic nerve
  • III: Oculomotor nerve
  • IV: Trochlear nerve
  • V: Trigeminal nerve
  • VI: Abducent nerve
  • VII: Facial nerve
  • VIII: Auditory nerve
  • IX: Glossopharyngeal nerve
  • X: Vagus nerve
  • XI: Accessory nerve
  • XII: Hypoglossal nerve
• Meninges


  • Pia mater
  • Arachnoid mater
  • Dura mater
• Subarachnoid space


  Narrow space between pia mater and arachnoid mater, containing the blood vessels of the brain and the cerebrospinal fluid (CSF)
• Arachnoid villi and granulations

  Pedunculated projections from the arachnoid mater which push themselves inside the dural venous sinuses, serving as the channels for drainage of the CSF back to the blood stream
• Cerebrospinal Fluid (CSF)


  Fluid which circulates in the ventricles and the central canals of the CNS and also fills the subarachnoid space and cisterns, secreted by the choroid plexuses in the ventricles of the brain
• CSF Circulation


  1. Circulates in the ventricles and the central canals of the CNS

  2. Drains out from the 4th ventricle through apertures to reach the subarachnoid space

  3. Flows over the surface of the brain and the spinal cord

  4. Leaves the subarachnoid space by means of the arachnoid villi and granulations to drain into the dural venous sinuses
• Functions of CSF


  • Takes the place of lymph in the CNS, protects the brain and spinal cord, regulates intracranial pressure
• Any obstruction to the normal passage of the CSF especially at the narrow foramina and canals causes increased intracranial pressure and dilatation of the ventricles; a condition known as hydrocephalus
• CSF Circulation


  1. CSF flows over the surface of the brain and the spinal cord

  2. CSF leaves the subarachnoid space by means of the arachnoid villi and granulations to drain into the dural venous sinuses
• Functions of CSF


  • Takes the place of lymph in the CNS which is devoid of lymph vessels
  • Principal medium for removal of the waste products of the nerve cell activity
  • Acts as a protective water cushion which protects the brain and the spinal cord and minimize the effects of any trauma
  • Regulation of the intracranial pressure due to changes in the flow of cerebral circulation
• Skull


  • Skeleton of the head and face which is formed of 21 fixed bones in addition to one movable bone which is the mandible
  • Fixed bones articulate together by fibrous joints called sutures
  • Cranium denotes the part of skull enclosing & protecting the brain
  • Facial skeleton denotes the part of front of skull below the orbital cavity
  • Calvaria means the skull cap or vault
  • Described externally from five aspects, each one is known as norma
  • Interior of skull (cranial cavity) is described after removal of skull cap
• Norma Verticalis (Superior View of Skull)

  • Four bones: Frontal bone anteriorly, 2 parietal bones in the middle and occipital bone posteriorly
  • Three sutures: Coronal, sagittal and lambdoid suture

  
• Norma Frontalis (Anterior View of Skull)


  • Formed of a frontal bone, 2 maxillary bones, 2 nasal bones, 2 zygomatic bones and mandible
  • Orbital Opening is nearly quadrangular, bounded by supra-orbital margin, infra-orbital margin, lateral margin, and medial margin
• Norma Occipitalis (Posterior View of Skull)


  • Consists of posterior parts of the 2 parietal bones, squamous part of occipital bone and mastoid part of temporal bones
  • Sutures between the bones are sagital and lambdoid sutures

  
• Norma Lateralis (Lateral View of Skull)

  • Includes temporal bone, greater wing of sphenoid, parietal, zygomatic bone, nasal bone, maxillary bone, parts of frontal and occipital bones, and lateral aspect of mandible
  • Important features: External auditory meatus & zygomatic arch
• Cranial Cavity


  • Space within the cranium that contains the brain, meninges, cranial nerves, blood vessels and pituitary gland
  • Has roof and a floor
  • Roof is inner surface of skull vault
  • Floor is divided into 3 fossae: Anterior, middle and posterior cranial fossae
  • Important features: pituitary fossa & foramina for cranial nerves

  
• Mandible


  • Skeleton of the lower jaw which is formed of a body and 2 rami
  • Body is horse shoe-shaped which is convex forwards, with upper alveolar margin and lower border, and outer and inner surfaces
• Scalp


  • Soft tissues that covers the vault of skull
  • Extends from the superciliary arches (eye brows) anteriorly to the superior nuchal lines posteriorly, and on each side to the zygomatic arch
  • Consists of 5 layers from superficial to deep: skin, connective tissue, epicranial (or galeal) aponeurosis, loose areolar connective tissue, and pericranium

  
• The scalp proper is the first 3 layers which are closely adherent together & moves as one unite