Session 3 Flashcards
(24 cards)
Meninges
Three Membranous Layers that Surround and Protect the Brain and Spinal Cord
Pia mater -microscopically thin, delicate adherent to surface of brain, follows every fold
Arachnoid mater - microscopically thin, delicate adherent to surface of brain, follows every fold Space (subarachnoid) - CSF - Cerebral vessels suppling/draining brain
(Leptomeninges - pia and arachnoid mater)
Dura mater - Potential subdural space
Dural Folds and Sinuses
- Dura fuses with the periosteum lining inner table of skull bones
- Dura effectively then has two layers (while within the skull) – Periosteal –part against the inner table of bone – Meningeal = part adjacent to arachnoid
- For most part two layers closely adhered (appearing as a single layer) – but areas where they separate
- Separation of two layers forms – Dural folds – Dural venous sinuses (spaces which are filled with venous blood =venous channels)
Venous Sinuses
panopto
Dural Folds
Help to Stabilise the Brain and act as Rigid Dividers
A rise in pressure inside the skull e.g. secondary to a bleed can lead to compression and displacement (herniation) of parts of brain under rigid dural folds (1-3) and/or through foramen magnum (4)
use slide 10 lec 1
Dural Venous Sinuses
Venous blood filled spaces created by separation of meningeal from periosteal layer of dura
• Found throughout the skull, surrounding the brain within the areas where two layers of dura separate to create a ‘space’
• Dural venous sinuses connected to each other, and receive blood from cerebral veins (draining brain)
• Eventually dural venous sinuses drain into internal jugular vein
How does blood drain the brain
slide 12 lec 1
sinuses of the brain
slide 13lec 1
Cerebral Veins within Subarachnoid Space
Cerebral Veins within Subarachnoid Space Drain into Dural Venous Sinuses
Sub dural space
Subdural space: potential space between dura and arachnoid (archoid is pushed up against it by pressure of CSF within subarachnoid space
Scalp and emissary Veins
Scalp Veins Also Connect with Dural Venous Sinuses
Emissary veins traverse through the skull
Intracranial Haemorrhage
Head trauma can lead to bleeding in ‘spaces’ between meningeal layers
• Blood vessels run along or traverse between the meningeal layers
• Injury and bleeding from these blood vessels will cause accumulation of blood in the ‘space’ between the meningeal layers – Extradural – Subdural – Subarachnoid
• Bleeding can also occur within the brain tissue itself (e.g. contusions, tearing of white matter) – Intracerebral haemorrhage
• Addition of ‘volume’ to an already fixed space (the skull) leads to rise in pressure and damage to brain tissue, brainstem and other important structures e.g. cranial nerves
Extradural Haemorrhage
Arterial Bleed
Subdural Haemorrhage
Venous bleed usually from bridging veins
Subarachnoid Haemorrhage
Arterial bleed
• Secondary to trauma or spontaneous rupture of blood vessel e.g. aneurysm – Usually a branch of ‘Circle of Willis’ (the arterial circuit responsible for supplying brain structures)
• Blood leaks into subarachnoid space, mixing with CSF – Sudden, often fatal
• CT imaging of head – 93% picked up if within 24 hours; 100% if within 6 hours – Lumbar puncture-if CT inconclusive: sample CSF to identify presence of blood (haemoglobin degradation products)
Treatment of head intracranial bleed
craniotomy use slide 21
Neural networks
The brain works like a vast ‘computer’, with many layers of processing. The strengths of individual synapses within the network determines the behaviour of that network. Learning is the process whereby the strengths of these synapses is changed in order to match up a stimulus with an appropriate behaviour
Basic components of the CNS compared to PNS
CNS Cerebral hemispheres Brainstem and cerebellum Spinal cord
PNS Dorsal and ventral roots Spinal nerves Peripheral nerves
Anatomical terminology and the CNS
Because the human brain ‘flexes’ at around the level of the midbrain, the superior part of the hemisphere is actually dorsal. The inferior brain is actually ventral. Therefore dorsal/ventral brain structures are not necessarily closest to the back/belly respectively.
Remember that in imaging, right and left are reversed
Parts of the brainstem
• Midbrain (mesencephalon) • Eye movements and reflex responses to sound and vision • Pons • Feeding • Sleep • Medulla • Cardiovascular and respiratory centres • Contains a major motor pathway (medullary pyramids, which ultimately decussate)
Decussation
The fact that the body is controlled by the contralateral side of the brain has been appreciated since the time of the ancients
Sulci, gyri and fissures
Sulcus(pl. sulci): A ‘groove or furrow’ in the brain separating adjacent gyri Gyrus(pl. gyri): A ‘ridge or fold’ in the brain Fissure: A large ‘crack’ or ‘split’ between adjacent large areas of the brain
The lateral aspect of the cerebral hemisphere
Frontal lobe: Higher cognition, motor function, speech Parietal lobe: Sensation, spatial awareness
Temporal lobe: Memory, smell, hearing Occipital lobe: Vision Cerebellum: Co-ordination and motor learning
The inferior aspect of the cerebral hemisphere
Optic chiasm: A site where fibres in the visual system cross over Uncus: Part of the temporal lobe that can herniate, compressing the midbrain Medullary pyramids: Location of descending motor fibres (each has around 1 million axons!)
The medial aspect of the cerebral hemisphere
Corpus callosum: Fibres connecting the two cerebral hemispheres Thalamus: Sensory relay station projecting to sensory cortex
Hypothalamus: Essential centre for homeostasis
