The CNS Flashcards
types of cells of the NS
- the neuron
- neuroglia
types of neurglial cells
- astrocytes
- oligodendrocytes
- ependymal cells
neuron
- brains immune cells
- protect against injury and disease
astrocytes
- metabolic buffer, detoxifies
- modulate how neurons communicate
- surround blood vessels
oligodendrocytes
- produce myelin
- myelin wraps around axons as insulation
ependymal cells
- lines spinal cord and ventricles of brain
- produces CSF
where does sensory information go to in the brain
- medulla, pons, mesencephalon
- cerebellum
- thalamus
- cerebral cortex
- SC at all levels
what are effectors
- muscles or glands
- anatomical features that do the function the brain tells them to do
major levels of CNS function
- SC
- lower brain or subcortical level
- higher brain or cortical level
spinal cord level of CNS function
- upper levels send signals to SC
- SC performs functions necessary
lower brain function
- subconscious activity
- controlled by:
- medulla
- pons
- mesencephalon
- hypothalamus
- thalamus
- cerebellum
- basal ganglia
higher brain function
- done by cerebral cortex
- essential for thought processes
- cannot function by itself
cerebral cortex function
- thinking
- learning
- remembering
thalamus function
- interprets sensory messages like pain, temp, pressure
hypothalamus function
- controls homeostatic functions
- i.e. temp, respiration, HR
cerebellum function
- muscle tone
- posture
- balance
brain stem function
- HR and breathing
- plays role in consciousness
blood brain barrier
- selectively inhibits substances that reach the brain or CSF
components of the BBB
- capillaries
- astrocyte foot
- efflux transporters
role of capillaries in BBB
- have continuous tight junctions
- limit passage of most substances
astrocyte foot in BBB
- surrounds BV
- allows small and lipophilic molecules
- contributes to brain swelling
efflux transporters
- proteins
- help expel foreign substances that pass through capillaries
where does wallerian degeneration occur
in the distal axon of a severed axon
characteristics of wallerian degeneration
- swelling in distal axon
- neurofilament hypertrophy
- myelin sheath disintegrates
- axon degenerates and disappears
what happens at the proximal end of an injured axon?
- similar to wallerian degeneration but only to the next node of ranvier
what happens to the cell body of an injured nerve
- swells
- undergoes apoptosis
what happens 7-14 days after nerve injury
- new terminal sprouts project form proximal segment
- increase incidence of scar formation
astrocyte reaction to injury
- causes cellular swelling
- due to hypoxia, hypoglycemia, or toxic injuries
oligodendrocyte reaction to injury
- results in demyelinating disorders
where is CSF produced
choroid plexus of each ventricle
CSF function
- shock absorber for brain
- deliver nutrients and remove waste from brain
- regulate ICP
hydrocephalus
- increase in CSF within ventricles
- due to reduce flow or decreased resorption of CSF
what is the result of hydrocephalus in infancy?
enlargement of head due to unfused cranial sutures
what is the result of hydrocephalus after infancy?
expansion of ventricles and increased ICP
cerebral autoregulation
- BF maintained at constant levels
- range of 60- 150 mmHg
when is cerebral autoregulation lost?
at 180 mmHg
what is the result of lost cerebral autoregulation?
- cerebral vasodiation
- cerebral edema
what are the types of cerebral edema?
- vasogenic
- cytotoxic
vasogenic edema
- irreversible increase in extracellular fluid
- caused by BBB disruption and increased vascular permeability
cytotoxic edema
- reversible
- increase in fluid secondary to neuronal, glial, or endothelial damage
- caused by hypoxia or ischemia
intracranial components
- cerebral parenchyma
- CSF
- Blood
ICP
- pressure inside cranial cavity
- normally <15 mmHg
- pathologic HTN > 20 mmHg
intracranial compliance
- displacement of CSF into thecal sac
- decrease in volume of cerebral venous blood via venoconstriction and extracranial drainage
what happens if ICP increase?
blood supply to brain decreases and results in cerebral ischemia
herniation
- displacement of brain tissue past dural folds or through openings in skull
- due to increased ICP
when do you often see herniation?
- cerebral edema
- increased CSF volume
- mass lesions
what is the most common type of herniation
- tonsillar herniation
- causes brainstem to compress
- compromises vital respiratory and cardiac centers in medulla
causes of hypoxia
- low partial pressure of oxygen
- impaired o2 carrying capacity
- toxins
- ischemia
broad classifications of ischemia
- global
- focal
global cerebral ischemia
- happens when BP is less than 50 mmHg
- usually due to cardiac arrest
- outcome depends on duration
- severe global ischemia -> brain dead pt
focal cerebral ischemia
- cerebral artery occlusion leading to focal ischemia then infarction
- causes are embolic infarction or thrombotic occlusions
clinical deficits due to ischemia depend on
- duration of ischemia
- magnitude and rapidity of reduction of flow
cerebrovascular disease classifications
- intrinsic issue of vessels
- process might originate elsewhere
- result of inadequate cerebral BF
- rupture of vessles
cerebrovascular disease classifications that can cause TIA or ischemic stroke
- when issue is intrinsic
- when process originates elsewhere
- when there is inadequate BF
cerebrovascular disease classifications that can cause hemorrhagic strokes
- when vessels rupture
TIA
- transient neurologic dysfunction due to ischemia
- no acute infarction
ischemic stroke
- infarction due to ischemia
- causes permanent damage
mechanisms of TIA
- large artery TIA due to atherosclerosis
- embolic TIA
- lacunar/ small artery due HTN
what is the penumbra
- area surrounding infarcted brain tissue that have the potential to recover
mechanism of ischemic cell injury
- inhibition of protein synthesis
- glucose utilization increases
- anaerobic glycolysis and tissue acidosis
- neuronal electrical failure
- membrane failure
- cell death
what happens if the brain structural integrity is lost
- breakdown of BBB
- cerebral edema
- hemorrhage into brain parenchyma
what is matrix metalloprotease (MMP)
protease that mediates loss of brain structural integrity