WHEN BLOOD CLOTS - EFFECT ON WEEK 9 - THE NERVOUS SYSTEM Flashcards
The blood brain barrier
anatomical barrier between the blood capillaries and the brain tissue preventing toxins in blood from entering the brain tissue.
Made of
- endothelial cells
- connective tissue
- nervous tissue
Made of a selective permeable barrier
- endothelial cells - the cell wall of the capillary. Are extremely tight and act as a barrier. Surrounded by pericytes, that make up muscle tissue surrounding the capillary
- Basil lamina - connective tissue that maintains the structural integrity of the capillary.
- Astrocytes - star shaped cells bound to the lamina that stimulate contraction of endothelial cells - generating vasoconstriction
Endothelium consists of transporter proteins that channels nutrients in and waste products out.
Anterior blood supply of the brain comes from… (+anatomy)
anterior supply of the brain comes from the L and R carotid arteries, which then become the internal carotid arteries (after splitting from the external carotids)
- these sit at the front of your neck where you can feel a pulse
- they come (almost) straight of the aortic arch splitting from the subclavian artery
Posterior blood supply of the brain comes from… (+anatomy)
posterior supply to the brain comes from the L and R vertebral arteries
- split from the subclavian artery (distally to carotid split)
- pass through the vertebrae
- when neck in extreme rotation/extension, the artery is under a lot of stress.
What is the circle of willis (revise diagram)
the network of blood vessels created once the internal carotid arteries and the vertebral arteries reach the underside of the brain. It is complicated because it is designed to ensure that there is more than one way for blood to get to brain tissues, so if one part gets damaged or blocked, there is an alternate route for blood from the heart.
4 parts to internal carotid artery
- cervical - from bifurcation to the carotid canal
- petrous - from the carotid canal at the base of the skull to the carotid canal in the middle cranial fossa
- cavernous - sits in the cavernous sinus
- cerebral - where the artery reaches the circle of Willis
Frontal Lobe of the brain functional areas
- primary motor cortex
- premotor/supplementary motor cortex (planning coordination of movement
- frontal eye field
- Prefrontal cortex (executive function, behaviour, personality)
- brocas area (muscles + production of speech)
Paritetal lobe functional areas
- primary somatosensory cortex (awareness of somatic sensations)
- somatosensory association area (processing of somatic sensations)
- posterior association area (visual, auditory somatosensory areas meet)
Occipital lobe functional areas
- primary visual cortex (awareness of visual cortex)
- visual association area (processing of visual stimuli)
temporal functional areas
- primary auditory cortex
- auditory association area
- Wernickes area (comprehension of written and spoken language)
- primary olfactory cortex/association area (awareness and processing of smell)
Stroke - description
Caused by the interruption of blood flow to the brain. Brain cells begin to die due to lack of blood flow, leading to a multitude of effects, dependent on the location and severity of the interruption.
Lack of blood flow to brain tissue = no glucose or oxygen = no energy
- leads to build up of Na+ and Ca2+ in the cells.
- increased Na leads to the absorption of water, leading to cytotoxic oedema, creating swelling in the brain
Types of stroke
2 types of Stroke
Ischaemic (75% of all strokes)
A stroke can be caused by the blood supply being blocked. This is called anischaemic stroke. It is the most common type of stroke.
Usually it is a blood clot that blocks the blood supply. Clots help to stop bleeding from wounds, but they can also form withinblood vessels, which are the tubes or pipes that carry blood around the body.
Haemorrhagic stroke (25%)
A stroke can be caused by bleeding. This is called ahaemorrhagic stroke.
Blood can leak from a broken or burstblood vessel, which is one of the tubes or pipes that carry blood around the body. The leaking blood is like a bruise that injures part of the brain
Hamorrhagic stroke types + causes
Haemorrhagic
- Long term low grade damage - high blood pressure, smoking
- Atherosclerosis -> aneurysms (expansion of vessel, collecting blood. can lead to haemmorhage)
- Head trauma -> blood vessels shearing & tearing
Types
-
intracerebral - inside the brain (more common)
- intraparenchymal (just the brain tissue)
- intraventricular - into ventricles (CSF production)
- subarachnoid - bleeding occuring between the pia and arachnoid matter of the meninges (rare)
Ischemic stroke forms
-
embolism - a travelling mass (blood clot) gets stuck in cerebral arteries
- often formed in heart
- or as an effect of atherosclerosis (cholesterol)
-
thrombotic - clot arises in cerebral/basilar arteries
- commonly happens in middle cerebral arteries, internal carotid arteries and basilar artery.
- Lacunar - artery walls thicken, limiting BF
-
watershed - cerberal hypoperfusion - limiting blood flow to the brain
- blood flows from in to out and out to in inside the brain
- with watershed, hypoperfusion disallows central parts of the hemispheres from being provided with oxygenated blood.
- the deprived area is known as the watershed area
Lacunar strokes
Lacunar Stroke
- form of ischemic stroke
- most commonly effects the deep branches of the MCA that feed the basal ganglia (lenticulate vessels)
- lacunar = lake, after stroke the brain tissue develops fluid filled pockets called cysts that look like lakes
- usually occurs due to hyaline arteriolosclerosis
- arteriole walls is pushed into the interstitual space
- hypertension or diabetes
- increases thickness of arteriole wall
- arteriole walls is pushed into the interstitual space
Stroke risk factors
- high BP
- heart disease
- smoking
- history of TIA’s (transient-ischemic attack)
- Dyslipidemia
- genetic predisposition
- older age (55+)
