From StudyingMed

< AEB
Jump to: navigation, search

This learning activity is not yet finished -- we still have to improve it to reach our stringent standards. Please help out!

The bones of the skull

  • Made up of 2 groups:
    • Bones of the face
    • Bones bounding the cranial cavity
      • Holds the brain, its coverings (meninges) and blood vessels

Bones of the cranial cavity

  • Made up of unpaired and paired bones
    • Paired (2)
      • Parietal
      • Temporal
    • Unpaired (4)
      • Frontal (but develops in embryo as a pair)
      • Occipital
      • Ethmoid
      • Sphenoid
  • Facial: nasal, zygoma, maxilla, mandible, frontal
  • These are joined by short fibrous bands of tissue that form suture joints (fibrous joints)
    • Fibres are short (<1mm), therefore there is zero movement at these joints
    • Coronal suture = between frontal bone and parietal bones
    • Sagittal suture = between parietal bones
    • Bregma = intersection between coronal and sagittal sutures (a region)
    • Lambdoid suture (region = lambda)
      • Between parietal and occipital bones
  • External occipital protuberance = palpable point on back of skull
  • These bones develop from membranous ossification - at birth there are spaces between skull bones covered only by membranes, so that the skull is flexible for childbirth
    • Bregma is last place for skull bones to come together (anterior fontanelle; closed up by 12 months)
  • Superior and posterior views
    • Superior
      • Junction between frontal and 2 parietal bones is the bregma
      • Junction between the occipital and 2 parietal bones is the lambda
    • Posterior
      • Palpable midline swelling is known as the external occipital protuberance (inion)
  • Lateral wall
    • Made up of parts of the frontal, parietal, temporal sphenoid and occipital bones
    • The greater wing of the sphenoid bone is anterior to the squamous part of the temporal bone (between temporal bone and zygoma)
    • The area where the frontal, parietal, sphenoid and temporal bones meet is called the pterion (the temple: if it fractures, bones can splinter and rupture arteries underneath; can be fatal). One fingerbreadth behind zygomatic arch and one fingerbreadth behind orbit

The temporal bone

  • Contains the external acoustic meatus (EAM)
  • Made up of several parts
    • Squamous part – thin, fractures easily
      • Forms the roof of the EAM
      • Has a zygomatic process that articulates anteriorly with the zygoma (cheek bone; zygomatic arch)
    • Mastoid process – palpable just behind and below the ear
    • Styloid process (often breaks off), for attachment of muscles
    • Petrous part – extends inwards and is not externally visible
      • Contains spaces for the middle and inner ears
      • Forms a ridge that extends backwards
  • The ridge of the lesser wing and the ridge of the petrous part of the temporal bone divide the cranial cavity into three fossae.


Interior (floor) of cranial cavity

Floor of the cranial cavity
  • Divided into 3 cavities: the anterior, middle and posterior cranial fossae
    • Anterior cranial fossa
      • Orbital plate of the frontal bone (forms the roof of orbit)
      • Cribriform plate of the ethmoid bone (has small perforations for olfactory nerves); forms the roof of the nasal cavity
    • Middle cranial fossa
      • Sphenoid bone
        • Central body with paired anterior and posterior clinoid processes projecting upwards (anterior projects posteriorly and vice versa); note that the body has no suture with the basilar part of the occipital bone - they're fused perfectly
          • Body has a central depression (pituitary/hypophyseal fossa) where the pituitary gland (hypophysis) sits; sella turcica
          • Greater and lesser sings of the sphenoid project laterally
    • Lesser wings form the boundary for the anterior and middle fossae - forms a ridge extending anteriorly and laterally
    • Greater wings form the floor and part of the lateral wall of the middle fossa
      • Greater separated from lesser by the superior orbital fissure
      • Temporal bone (squamous part)
        • Forms the remainder of the floor and lateral wall
      • Foramina
        • Foramen rotundum, foramen ovale, foramen spinosum, foramen lacerum (note that carotid canal is within foramen lacerum, but the two have distinct external openings)
      • Posterior boundary is formed by the petrous part of the temporal bone
    • Posterior cranial fossa
      • Occipital bone:
        • Foramen magnum at centre
    • Anterior is the flat basilar part that fuses anteriorly with the body of the sphenoid forming the clivus
  • Jugular foramen is located between the basilar occipital and petrous temporal bones
  • Hypoglossal canal can be seen either side of the foramen magnum
  • Internal acoustic meatus – located on the posterior surface of the petrous temporal bone
  • Internal occipital protuberance is opposite the external occipital protuberance &inside

Foramina

  • Optic canal (medial to anterior clinoid process)
  • Superior orbital fissure (slit between lesser and greater wings of the sphenoid)
  • Heading backwards: foramen rotundum and foramen ovale, then foramen spinosum (for CN, CN and BV)
  • Jagged outline = foramen lacerum (lateral to the posterior clinoid process)
  • Internal acoustic meatus = between petrous part of temporal bone and the posterior cranial cavity
  • Jugular foramen = large foramen between the occipital bone and the temporal bone
  • Foramen magnum = big one in the middle for the spinal cord
  • Side of foramen magnum = hypoglossal canal

Occipital bone

  • Clivus = basilar part of occipital bone = fused with sphenoid
  • Internal occipital protuberance = a bump in the occipital bone at the posterior of the occipital bone, on the inside

Brain

  • Weighs about 1400g (normal range 1100-1800g); proportional to body size (height); boys have larger brains, but female brains are more connected synaptically
    • Occupies the cranial cavity of the skull
    • 100 billion neurons and 10x that glial cells (supporting cells)
  • Develops from the neural tube
    • Following closure, 3 swellings (primary vesicles) appear (week 5)
      • These become the hindbrain, midbrain and forebrain of the adult
  • The hindbrain
    • Made up of the medulla oblongata, the pons and the cerebellum
  • The midbrain
    • Relatively small and located in front of the pons
  • The brainstem
    • The medulla, pons and midbrain
    • Functions: those vital for life – cardiovascular and respiratory centres
  • The cerebellum (little brain)
    • Attached to the back of the pons
    • Covered in a layer of grey matter (cerebellar cortex) which is folded to increase SA
      • Has a cauliflower-like appearance
    • Functions: coordination of voluntary movement and maintenance of balance

Forebrain

  • Primary brain vesicles = prosencephalon (subdivide to two), mesencephalon, and rhombencephalon (subdivides) (forebrain, midbrain and hindbrain)
  • Secondary brain vesicles = P (telencephalon (cerebral hemispheres) and diencephalon), M, R (metencephalon (medulla and pons) and myelencephalon)
  • A system of spaces remains in the adult brain to form the ventricles
  • Two main parts:
    • Diencephalon and the Telencephalon (cerebral hemispheres)
  • Diencephalon
    • In front of the midbrain
    • 2 main parts (has 4 total parts)
      • 1. Thalamus (largest)
        • Larger
        • A relay station for distributing information to the cerebral cortex (outer covering of the cerebral hemisphere) - all sensory information except smell goes through the thalamus, which is headed up to the surface of the hemispheres (cerebral cortex; to correct area)
      • 2. Hypothalamus
        • Small
        • Lies beneath the thalamus
        • Central control centre for the maintenance of homeostasis (a constant internal body environment)
        • Acts by neural connections to other brain structures or by hormone production
      • Optic nerve grows out of diencephalon (projects forwards from in front of hypothalamus)
  • Cerebral hemispheres a.k.a. cerebrum (telencephalon)
    • Form the largest part of the brain
    • Two hemispheres are joined by the corpus callosum (a massive bundle of white matter)
      • Each hemisphere is covered by a 2.5-4mm thick layer of grey matter (cerebral cortex) o Cerebral cortex
      • Site where the highest levels of neural processing occur
      • Allows us to consciously perceive sensory stimuli, to think and make decisions
      • Highly folded to increase SA
      • Grooves are sulci, ridges are gyri – patterns are regular
      • Each cortex of each hemisphere is divided into 4 lobes (frontal, temporal, parietal, occipital)
  • Brain: ventral = inferior; dorsal = superior

Ventral surface

  • Medulla oblongata (bottom, to spinal cord)
  • Pons (blob at base of midbrain); forms a bridge between the two hemispheres of the cerebellum (cerebellum is covered in grey matter and also has gyri and sulci; mirrors the cerebrum). Cerebellum is also divided into hemispheres like cerebrum, but used for balance/posture and motor coordination (timing and force of muscle contraction; it is highly affected by alcohol; drunkenness simulates cerebellar dysfunction).
  • Cerebellum (fluffy bit)
  • Midbrain is a small bit between the pons and forebrain
    • Superior colliculus (bump at top) - vision
      • In humans, most of our visual processing takes place in the forebrain; superior colliculus in humans is mainly related to reflex behaviours
    • Inferior colliculus - hearing
  • Brainstem = medulla + pons + brainstem
    • Vital part of brain - contains autonomic control centres (respiratory centres in medulla; because breathing in is an active process and needs neural regulation. It also has cardiovascular regulation, and also regulates consciousness and sleep. There are also cranial nerves coming out of the brainstem. You can live without a forebrain, as a vegetable).

Ventricular system

  • Brain develops from a hollow neural tube
    • Cavity at the centre remains – the ventricular system
      • Spaces are filled with cerebrospinal fluid (CSF)
  • Central canal of the spinal cord continues into the medulla forming the fourth ventricle
    • Lies between the cerebellum, the pons and medulla
  • Ventricle closes again to form the cerebral aqueduct in the midbrain before opening into the third ventricle, a slit
    • Separates the two thalami and has the hypothalamus as its floor
  • Interventricular foramen (just in front of each thalamus) opens into the lateral ventricles (one in each hemisphere)
    • Lateral ventricle: C-shaped cavity in each cerebral hemisphere

Cerebri

  • Corpus callosum = big C-shaped band of white matter communicating between hemispheres (whose surfaces are covered in folded grey matter)
  • Folds (gyri) with grooves (sulci) going down to corpus callosum
  • Cerebral cortex: lateral view
    • Divided into lobes
  • The sulci are very regular. Two important landmarks
    • Lateral sulcus (lateral fissure) = 2cm deep, running superiorly and posteriorly
    • As you go from anterior to posterior, you find two sulci that run straight down, on either side of a very deep central sulcus
      • Precentral gyri and postcentral gyri lie between these two straight sulci and the central sulcus
    • Parieto-occipital sulcus comes in from posterior and goes inferiorly and anteriorly (visible medial surface)
      • Central sulcus may also peek around to medial surface
  • Using the sulci we divide the cerebral cortex into lobes, by extending lateral lobe back to parieto-occipital lobe
    • Frontal lobe = in front of central sulcus
    • Occipital lobe = behind occipital lobe
    • Temporal lobe = below lateral sulcus
    • Parietal lobe = between central sulcus, parieto-occipital sulcus and lateral sulcus
  • There is grey matter buried inside lateral ventricles (?) called basal ganglia.