Neuro Flashcards
Neurons
Generate action potentials
Transmitter cells
Carry messages to and from the brain and spinal cord.
Glial Cells
Support and protect neurons.
Do not generate action potentials but have a resting potential
CNS: Astrocytes, Microglia, Oligodendroglia, Ependymal cells.
PNS: Schwann Cells (myelin), Satellite cells
Produce cerebral spinal fluid.
Neurons can synapse with
neurons, muscle, glands
Synaptic Transmission
A small burst of neurotransmitters is released
The neurotransmitters stimulate or inhibit action potentials
Neurotransmitters
either destroyed by enzymes or reabsorbed
recycled for the next transmission
Electrical impulses
Info passed between neurons by chemicals
Can be excitatory or inhibitory
Along the axons, the information passes electrically
Neurons cont
Do not have the ability to divide
Losses due to aging or injury cannot be replaced
Not all cell death results in loss of functioning
Undamaged neurons in the brain will assume functions of damaged neurons (“plasticity”)
require constant oxygen and glucose supply
vulnerable to hypoxia and hypoglycemia
Myelin
Lipoprotein
Increases speed of conduction, large axons:
- Are “insulation”
- Prevent leakage of electric current
- Layers w/spaces (nodes of Ranvier) between cells
- Impulse “jumps” from node to node
“Unmyelinated” axons – smaller, slower
The Neurological System Consists of three main components
spinal cord, brain, peripheral nerves
Central Nervous system: Brain and spinal cord
Peripheral nervous system: nerves
Peripheral nervous system
Autonomic nervous system: sympathetic (fight or flight) nervous system and parasympathetic (rest and digest)
Somatic nervous system: sensory nerves and motor nerves
Cerebrum
includes lobes Frontal Parietal Occipital lobe Temporal lobe
Diencephalon
thalamus
hypothalamus
Cerebellum
balance and coordination
Brain stem
midbrain, pons, medulla oblongata
3 meninges
Dura mater, arachnoid mater, pia mater
Dura mater
outer, lines skull
Arachnoid mater
middle, contains blood vessels
Pia mater
inner, covers brain
3 potential spaces
epidural, subdural, subarachnoid
epidural
outside dura
subdural
between dura and arachnoid
subarachnoid
deep to arachnoid, filled with CSF
Cerebrospinal Fluid (CSF)
Made in choroid plexuses (roofs of ventricles)
Filtration of plasma from capillaries through ependymal cells (electrolytes, glucose)
Cushions and nourishes brain
Useful for diagnosing meningitis, bleeds, MS
Hydrocephalus: excessive accumulation of CSF
Blood supply to the brain
Supplied by the internal carotid and vertebral arteries
Arterial circle (circle of Willis) helps ensure flow
800 to 1000 mL per minute
CO2 level affects CNS blood flow
Increases in CO2 will increase cerebral blood flow & arterial blood pressure.
Circle of Willis
Anterior Cerebral Artery, middle cerebral artery, posterior cerebral artery, lenticulostriate arteries
Anterior Cerebral artery
supplies frontal lobes
Middle Cerebral Artery
Artery-frontal lobe
& the lateral surface of the temporal and parietal lobe (includes motor, sensory, speech)
*Most frequently occluded artery in a stroke.
Posterior Cerebral Artery
temporal & occipital lobes of cerebral hemispheres.
Lenticulostriate arteries
small, deep penetrating arteries known as the lenticulostriate arteries branch from the middle cerebral artery
How does autoregulation of cerebral blood flow work?
The arteries that comprise the circle of Willis in the brain normally maintain a constant flow of blood within the brain
Autoregulation
means that the cerebral arteries constrict or dilate to keep the CPP between 50-150mmHg
CPP (cerebral perfusion pressure)
the pressure required to perfuse the brain with blood
MAP (mean arterial pressure)
it is the average blood pressure in the arteries. MAP is a more accurate way to measure “blood pressure” in the vessels.
ICP
intracranial pressure
Autoregulation is achieved by
combination of 4 factors:
- BP (MAP)
- Metabolic– CO2, others
- Autonomic receptors (smaller role)
- Arterial oxygen level
BP (MAP)
the cerebral arteries constrict or dilate in response to changes in BP (ie. MAP) or intracranial pressure (ICP)
Metabolic–CO2
CO2 is a potent vasodilator
increased CO2/decreased BP –> vasodilation decreased CO2/increased BP–> vasoconstriction
Arterial oxygen level
low arterial oxygen tension has profound effects on cerebral blood flow. When PO2 falls below 50mmHg there is a rapid increase in cerebral blood flow (CBF) and arterial blood volume.
Cranial nerves
12 of cranial nerves branch directly from the base of the brain.
some carry sensory fibers, others only carry motor fibers
some carry both
each nerve travels from the brain through the foramen ovale to its destination
On old olympus towering tops, a finn and german viewed some hops
Some say marry money but my brother says bad business marry money
white matter
comprised of nerve fiber tracts/ pathways
Gray matter
neurons
ascending fibers/afferent tracts
carry sensory information the body back to the brain
descending fibers/efferent tracts
carry motor impulses from the brain to the PNS
nerves
bundles of nerve fibers. Each fiber is part of the neuron
works like an information highway
31 spinal nerve pairs
8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal
ganglia
collections of nerve cell bodies outside the CNS
Spinal nerves
arise from dorsal and ventral surfaces of the spinal cord
Spinal nerve
comprised of a dorsal root adn a ventral root. Each root formed from 6-8 rootlets
Somatic
voluntary
31 pairs of spinal nerves
12 pairs of cranial nerves
Automatic
involuntary
smooth muscle
cardiac muscle
glands
Check and balance system
Sympathetic nervous system
Parasympathetic nervous system
Sensory nerves
afferent nerves
input: sensory
afferent: to brain
motor nerves
efferent nerves
output: motor
efferent: from brain
interneurons
connect the sensory and motor neurons in the spinal cord
Dermatome
area of the skin innervated by a given pair of spinal sensory nerves
What can be fixed in nervous system:
severed peripheral nerves:
- can regenerate to a point to reestablish connections
What cannot be fixed in the nervous system:
severed brain and spinal cord axons
- results in paralysis and loss of sensation below the area of damage
Autonomic nervous system
controls smooth muscles
unconscious response that affects such activities as heart rate, blood pressure, intestinal motility
sympathetic nervous
fight or flight response
aided by adrenal medulla via epinephrine and norepinephrine secretion
stimulates the adrenergic receptors
parasympathetic nervous system
rest and digest response
stimulates the cholinergic receptors
The two subdivisions have an antagonistic effect with each other
Adrenergic (SNS) & Cholinergic (PNS) receptors
These receptors are found in certain target organs:
The heart, lungs, gastrointestinal tract, the bladder, and the muscles.
Order of Neurological Assessment
Mental status cranial nerves motor system sensory system reflexes
Assessing Consciousness
alert, confused, delirious, lethargic, obtunded, stuporous, comatose
Glasgow Coma Scale (GCS)
Evaluates neurological functioning.
Used after TBI or other neurological injuries.
Looks at purposeful response to the environment in 3 areas:
Eye opening
Motor response
Verbal response
Increased Intracranial Pressure (ICP)
Increased ICP is increased volume in the cranial.
Skull: rigid, does not expand in adults.
Brain occupies 80% of the skull.
Monro-Kelli hypothesis
Volume increase: compensated for by shifts in CSF & blood volume.
Causes: traumatic brain injury, tumor, hydrocephalus, cerebral edema, and hemorrhage
Monro-Kelli hypothesis
increase in volume of one component must be compensated by a decrease in volume of another
Fontanelles
close by age 3 years usually
Increased ICP compensatory mechanisms
autoregulation, Cushing’s reflex, Cushing’s triad
Autoregulation (normal response)
the blood vessels dilate to increase blood flow and constrict if ICP increases. This acts up to a certain point.
Cushing’s reflex (normal response)
the hypothalamus increases sympathetic stimulation when the mean arterial pressure drops below the ICP.
Causes vasoconstriction, increased cardiac contractility, and increased cardiac output.
Cushing’s triad (what you see when things go bad…..very very bad)
increased blood pressure, bradycardia, and Cheyne-Stokes respiratory pattern.
Cushing’s Triad 3 primary signs that often indicate an increase in intracranial pressure (ICP)
increase systolic BP
decrease in pulse
decrease in respiration
Symptoms of increased ICP are opposite of SHOCK
decrease in BP
increase in pulse
increase in respiration
Cushing’s syndrome
a disease state resulting from the elevated levels of blood cortisol
Herniation
Feared complication of increased ICP
Refers to displacement of brain tissue
transtentorial (central) herniation
cerebral blood flow, CSF, reticular activation system, and respirations are impaired
Uncal herniation
puts pressure on cranial nerve III, the posterior cerebral artery, and the reticular activation system
Cerebellar, or tonsillar (intrafratentorial), herniation
compresses the brain stem and vital centers, causing death
Manifestations of Increased ICP
Decreasing level of consciousness Vomiting (often projectile) Rising blood pressure Increasing pulse pressure Bradycardia Papilledema Fixed and dilated pupils Posturing
Increased ICP diagnosis
History & physical exam
Glasgow Coma scale
Head CT, MRI
ICP monitoring
Increased ICP treatment
depends on cause (bleed, tumor, hydrocephalus, meningitis). Respiratory support Semi-Fowler’s positioning Decrease edema, swelling Prevent seizures Reduce brain metabolism No activities that increase ICP Control glucose level Stress ulcer prevention
Cerebral perfusion pressure
pressure in brain
the pressure required to “perfuse” all of the tissue of the brain with blood.
Without sufficient blood perfusion any living tissue dies
Homeostasis in the Cranium
CCP= MAP-ICP
Where, CPP is cerebral perfusion pressure
MAP is mean arterial pressure
ICP is intracranial pressure
If MAP decreases then CPP decreases
If ICP increases then CPP decreases
we do not want CPP to decrease in most circumstances