Usual set of notes

• Embryonic parts of the CNS and their adult derivatives


  • Prosencephalon
  • Mesencephalon
  • Rhombencephalon
• Embryonic structure


  1. Primary vesicle

  2. Secondary vesicle
• Adult brain derivates


  • Telencephalon
  • Diencephalon
  • Mesencephalon
  • Metencephalon
  • Myelencephalon

  
• Associated ventricular space


  • Lateral ventricles
  • Third ventricle
  • Cerebral aqueduct
  • Fourth ventricle
• Projection neurons


  • Cell body and dendrites located far away from the end of the axon
  • Connect different areas (e.g. spinal cord and cerebral cortex)
• Nuclear masses

  • Motor: basal ganglia (corpus striatum)
  • Sensory: diencephalon
• Interneurons


  • Form a communicating and integrating network between sensory and motor neurons
• Every function of the brain will have all 3 functions components
• Meninges


  Membranous coverings of the brain that lie immediately internal to the cranium

  
• Functions of meninges


  • Protect the brain
  • Form the supporting framework for arteries, veins and venous sinuses
  • Enclose a fluid-filled cavity (the subarachnoid space) which is vital to the normal function of the brain
• Layers of meninges


  • Dura mater
  • Arachnoid mater
  • Pia mater
• Leptomeninx


  Made of arachnoid and pia mater that are continuous membranes
• Subarachnoid space


  Separates pia and arachnoid and contains CSF
• Cranial dura mater


  • Thick, dense bilaminar membrane
  • Also called pachymeninx

  
• Layers of cranial dura mater


  • External periosteal layer
  • Internal meningeal layer

  
• External periosteal layer


  • Formed by the periosteum covering and internal surface of the calvaria
  • Tightly attached along suture lines and in the cranial base
  • Continuous at the cranial foramina with the periosteum on the external surface of the calvaria

  
• Internal meningeal layer


  • Strong fibrous membrane that is continuous with the spinal dura at the foramen magnum
  • Intimately fused with the periosteal layer and cannot be separated from it except at the dural venous sinuses and where the dural infoldings occur

  
• Dural infoldings


  • The internal meningeal layer reflects away from the external periosteal layer to form infoldings
  • They divide the cranial cavity into compartments
• Dural infoldings


  • Falx cerebri
  • Tentorium cerebelli
  • Falx cerebelli
  • Diaphragma sellae
• Falx cerebri


  • Largest dural infolding
  • Lies in the longitudinal cerebral fissure separating the right and left cerebral hemispheres
  • Attachments: in the median plane- internal surface of the calvaria, anteriorly- frontal crest of frontal bone and crista galli of ethmoid, posteriorly- internal occipital protuberance
  • Ends by becoming continuous with the tentorium cerebelli

  
• Tentorium cerebelli


  • Wide, crescent-shaped septum
  • Separates the occipital lobes of the cerebral hemispheres from the cerebellum
  • Attachments: rostrally- clinoid process of sphenoid, rostrolaterally- petrous part of temporal bone, posterolaterally- internal surface of the occipital bone and part of the parietal bone
  • The falx cerebri holds it up
  • Divides the cranial cavity into the supratentorial and infratentorial compartments
  • Tentorial notch: gap formed by the free concave anteromedial border through which brainstem passes

  
• Falx cerebelli


  • Vertical infolding that lies inferior to the tentorium cerebelli in the posterior part of the posterior cranial fossa
  • Attached to the internal occipital crest
  • Partially separates the cerebellar hemispheres

  
• Diaphragma sellae


  • Smallest infolding
  • Circular sheet suspended between the clinoid processes
  • Forms a partial roof over the hypophyseal fossa
  • Covers the pituitary gland and has an aperture for passage of infundibulum and hypophyseal veins

  
• Blood supply to dura mater


  • Middle meningeal aa. (from maxillary aa. from ECA)
  • Anterior and posterior ethmoidal aa. (from ophthalmic aa. from ICA)
  • Ascending pharyngeal aa. and occipital aa. (from ECA)
  • Vertebral aa. (from subclavian aa.)
• Innervation of dura mater


  • Ethmoidal nn. from ophthalmic nn. (CN V1)
  • Maxillary nn. (CN V2)
  • Mandibular nn (CN V3)
  • C2 and C3 via vagus (CN X) and hypoglossal (CN XII) nn.
• Pain fibres in dura mater


  • Most numerous where arteries and veins course in the dura
  • Pain from dura is usually referred and perceived as a headache in the cutaneous or mucosal region supplied by the involved nerve
• Cranial arachnoid and pia mater


  • Develop from a single layer of mesenchyme surrounding the embryonic brain
  • Indicated by web-like arachnoid trabeculae passing between the arachnoid and pia
  • Trabeculae- composed of flattened, irregularly shaped fibroblasts that bridge the subarachnoid space
  • The 2 meninges are continuous immediately proximal to the exit of each cranial nerve from the dura

  
• Cranial arachnoid mater


  • Contains fibroblasts, collagen fibres and elastic fibres
  • Avascular
  • Not attached to the dura mater but closely applied to the meningeal layer of the dura by the pressure of the CSF in the subarachnoid space
  • Arachnoid villi- evaginations of arachnoid projecting through dura into the dural venous sinuses and becomes large and aggregates with age

  
• Cranial pia mater


  • Highly vascularised by a network of fine blood vessels
  • Delicate layer only 2-3 cell layers thick
  • Adheres to the surface of the brain and follows all its contours
  • Pial coat- pia surrounding cerebral arteries for a short distance when they penetrate the cerebral cortex

  
• Epidural space


  Potential space between the cranium and the external periosteal layer of the dura that only becomes a space with pathology (e.g. blood from torn meningeal vessels)

  
• Subdural space


  Potential space between the dura and arachnoid that may develop in the dural border cell layer due to trauma
• Subarachnoid space


  Real space between the arachnoid and the pia that contains CSF, trabecular cells, arteries and veins

  
• Spinal epidural space


  Real space between the periosteum lining the bony wall of vertebral canal and spinal dura mater that contains fat and internal venous plexuses and runs the length of the vertebral canal

  
• Spinal dura mater


  • Separated from the periosteum-covered bone and the ligaments that form the walls of the vertebral canal by the epidural space
  • Forms the spinal dural sac that adheres to the margin of the foramen magnum of the cranium, is continuous with the meningeal layer of cranial dura mater, and is anchored inferiorly to the coccyx by the filum terminale externum
  • Has dural root sheaths evaginated by each pair of posterior and anterior roots of spinal nerves as they leave the spinal cord

  
• Spinal arachnoid mater


  • Encloses the CSF-filled subarachnoid space which contains the spinal cord, spinal nerve roots, and spinal ganglia
  • Not attached to the dura but held against inner surface of dura primarily by pressure of the CSF in the subarachnoid space

  
• Spinal pia mater


  • Thin, transparent and closely follows all the surface features of the spinal cord
  • Directly covers the roots of spinal nerves and the spinal blood vessels
  • Inferior to conus medullaris, pia continues as the filum terminale
  • Spinal cord is suspended in the dural sac by the filum terminale and the right and left denticulate ligaments

  
• Denticulate ligaments


  Run longitudinally on each side of the spinal cord, consisting of a fibrous sheet of pia extending midway between the posterior and anterior nerve roots from the lateral surface of the spinal cord, with 21 ligaments (20-22) that are thickened anteriorly to give a shine appearance in the midline (Linea splendens)

  
• Cerebral hemispheres


  • Cerebral cortex: composed of 6 layers of cell bodies called grey matter on the external surface
  • Have a series of elevations (gyri) and infoldings (sulci)
  • Divided into lobes: frontal, parietal, occipital, temporal and insula

  
• Cerebral fissures


  • Longitudinal fissure
  • Transverse fissure
• Cerebral lobes


  • Frontal lobe
  • Parietal lobe
  • Occipital lobe
  • Temporal lobe
  • Insula