CNS Flashcards
What is the key learning point for neurons?
Neurons do not regenerate - lack of oxygen leads to permanent cellular death. There is no ability to store O2 in the CNS tissues, and the central neurons do not undergo mitosis.
What colour are myelinated cells?
white
What are the types of neuroglial cells?
astrocytes oligodentroglia ependyma microglia Schwann cells
What are the basic characteristics of astrocytes?
- part of the blood brain barrier, nutrition
- support brain framework (neurons and capillaries)
- largest and most numerous
- synaptic conductivity
What are the basic characteristics of oligodendroglia?
helps form myelin sheath in the CNS
What are the basic characteristics of the ependyma?
- forms choroid plexus
- secretes cerebrospinal fluid
- lines the ventricles and spinal cord
What are the basic functions of the microglia?
eliminates waste by phagocytosis
Describe the polarity of the neuron at rest.
inside cell membrane negative (K+ in cell)
outside cell membrane positive (Na)
What is the minimum threshold to achieve action potential?
-60mV
What are the steps of impulse transmission?
slow influx of sodium (RMP changes from -70mC to -35mV), rapid sodium influx (sodium channels open, RMP +70 to +90mV), depolarization: K+ channels open (K+ efflux promotes onset of repolarization), repolarization: sodium-potassium pump: re-establish RMP
What is the target for acetylcholine?
motor nerves to muscles
What does a lack of dopamine in the brain lead to?
parkinsons
What does norepinephrine do?
increase heart rate, and stimulates fight or flight
What are the characteristics of the cranium?
- inside is jagged
- eight flat irregular shaped bones fused together during childhood
- solid, non-expanding
- function to protect the brain
What is the foramen magnum?
opening at the base to allow brainstem to project and connect to the spinal cord
What are the layers of the meninges and where are they located?
Dura mater - outermost, tough, adhered to the skull, covers brain and spinal cord to S2
Arachnoid - delicate, fragile, vascular, spiderweb, spongy, connects dura to pia, acts as a cushion
Pia mater - adheres directly to brain tissue
Describe the characteristics of the neural ventricals.
lateral ventricles - foramen of monroe
third ventricle - aqueduct of sylvius
fourth ventricle - foramen of lushka, foramen of magendie
Describe the pathway of CSF
lateral ventricles - foramen of monroe - third ventricle - cerebral aqueduct - fourth ventricle - central canal or subarachnoid via foramen of lushka and mangendie - reabsorbed by arachnoid villi into venous system
What are the basic functions of the frontal lobe?
logical thinking, short term memory, personality and judgement
What are the functions of the parietal lobes?
sensory receiving and interpreting, speech, grammar, and hand skills
What are the functions of the temporal lobe?
auditory receiving and interpretation, emotion, personality, behaviour, memory storage
What is the function of the Wernicke area?
understanding spoken and written word
What is the function of the occipital lobe?
visual receiving and interpretation
What are the functions of the thalamus?
consciousness, pain, attention span, damage can mean permanent coma, sorts information that goes to cerebral cortex (auditory, visual, taste, touch)
What are the functions of the hypothalamus?
thermostat, internal homeostatsis, controls autonomic nervous system, afferent impulses, uses pituitary for communication.
What are the characteristics of the pituitary gland?
attached to the hypothalamus at the base of the brain, the master gland, secretes 9 hormones, controls/influences all other endocrine glands, growth, metabolic rate, sexuality
What are the characteristics of the cerebellum?
surrounds the brainstem
helps provide smooth, coordinated body movement,
motor planning
muscle memory
fine movement
balance through feedback loops
no initiation of movement - send/receive impulses for muscle activity
Your patient has an injured Cerebellum. What physical findings would you see in ataxia?
preservation of motor strength, lack of coordination, staggering gait, lack of ocntrol, injury, parkinsons, alzheimers
What are the characteristics of the midbrain?
located below the cerebrum and above the pons, contains cranial nerve 3 and 4 and the visual reflex, functions to relay stimuli involved in voluntary movement.
What are the characteristics of the pons?
a bridge - connects midbrain with the medulla
contains respiratory centres - pneumotaxic control (breathing patterns)
Regulates consciousness
cranial nerves 5, 6, 7,8
What are the characteristics of the medulla?
- most inferior part of the brainstem
- connects higher levels of the brain to the spinal cord
- not life sustaining without stimuli
- swallow, gag, sneeze
- crossing of voluntary motor fibres occurs here
- cranial nerves 9, 10, 11, 12
Describe the characteristics of the reticular activating system
functions:
-sensation
-movement
-regulates arousal (consciousness)
-regulates sleep-wake transitions
controls overall central nervous system activity
sorting through white noise for pertinent information
Damage to the reticular activating system will have what effect on your patient?
altered LOC, impaired sleep-wake cycle, impaired attention span
Describe the characteristics of the blood-brain barrier
a physiological mechanism that alters permeability of the brain capillaries
permeable to water, oxygen, carbon dioxide and glucose
regulates transport of ions and waste products
What are the requirements to allow a substance to pass through the blood brain barrier?
particle size, lipid solubilit, protein-binding potential
Describe the blood supply to the brain.
- internal carotids and verebral arteriers (anterior and posterior sections, branch off the aortic arch, connect at the circle of willis)
- anterior circulation: internal carotids (provide 80% blood to cerebral hemispheres
- brain uses 20% total cardiac output (required flow 750ml/min)
What are the functions of the circle of willis?
connects anterior and posterior circulation
- anterior and posterior cerebral arteries (back to front)
- anterior and posterior communicating arteries (side to side)
- vertebral arteries
What type of nerve is in the dorsal root?
afferent
What type of nerve is in the ventral root?
efferent
What is the GCS scale for Best “eye” opening
4 - spontaneously
3 - to speech
2 - to pain
1 - none
What is the GCS for best “verbal” response?
5 - oriented 4 - confused 3 - inappropriate words 2 - mumbled/incoherent 1 - none
What is the GCS best “motor” response?
6 - obeys command 5 - localize 4 - flexion withdrawal 3 - abnormal flexion 2 - abnormal extension 1 - none
How would you differentiate between localizing and withdrawal to painful stimuli?
local - crosses midline to attempt to remove painful stimulus
withdraw - moves body away
What are some intracranial causes of altered LOC?
- space occupying lesions
- head injury
- seizures, epilepsy
- infections
- degenerative conditions
- secondary insult
What are some extracrainial causes of altered LOC?
- metabolic causes
- respiratory involvement
- cardiovascular instability
- sepsis, shock and trauma
- liver, renal and endocrine dysfunction
- pharmacologic agents
- multi-organ dysfunction
- fluid/electrolyte imbalance
- acid/base imbalance
What is central pontine demyelination?
too rapid sodium correction - locked in syndrome - can be permanent
- decreases nerve ability to communicate
- requiring ventilation and inotropes until reversed, if possible
What is the monro-kellie doctrine?
- three components of the cranial vault - blood (10%) brain (80%) CSF (10%)
- increase in volume of one intracranial element must be compensated by a decrease in one or more of other components
- total volume remains fixed
- dynamic equilibrium
What are the compensatory mechanisms of the monro-kellie doctrine?
- displacing CSF to lumbar cistern
- increasing CSF absorption
- compression low-pressure venous system
What is brain compliance?
adaptive capacity of the brain to maintain intracranial equilibrium in response to both physiologic and external changes
-measure of brain stiffness
What is normal ICP?
0-15
When do we treat ICP?
greater than 20 ICP
Describe the characteristics of central perfusion pressure?
- blood pressure gradient across the brain
- prevent extension of brain injury due to ischemia
- formula: CPP=MAP-ICP
- goal 60-80
What is the rationale for active cooling?
decreases cerebral oxygen demand
decrease intracranial pressure
suppresses the inflammatory response
-reduce intracellular acidosis
What are the clinical findings for a basal skull fracture?
- fragility of the bones in the sinuses make them susceptible to breaking which can lead to meningeal or dural tears
- bleeding can occur with basal skull fracture and manifests as racoon eyes and battle’s sign
Describe racoon eyes
always bilateral, venous blood pooling as a result of fracture
Describe Battle’s sign
unilateral, boggy, behind one ear, could affect cranial nerve, Bell’s palsy and hearing
What is the significance, symptoms, and type of CSF leaks in a basal skull fracture?
nuchal rigidity, headaches, nausea, otorrhea (ear drum must be ruptured also), rhinorrhea
Describe the primary and secondary traumatic brain injury
Primary injury - neurons and glial cells are directly damaged
Secondary injury - cerebral edema, biochemical/inflammatory responses, tissue hypoxia/decreased cerebral blood flow
Describe the characteristics of a diffuse axonal injury?
generalized axonal shearing (stretching and tearing) of axons
mild - GCS 13-15
moderate - GCS 9-12
Severe - GCS 3-8
May not be visible on a CT or MRI unless there is a bleed because it is electrical
hyperexcitability of neurons
severe form of concussion
What are the four goals of patient management of ischemic stroke?
restore cerebral blood flow
prevent thrombolysis
neuroprotection
supportive care
Why are dextrose solutions contraindicated in acute brain injury?
because the brain will quickly remove the glucose from the solution, leaving a lot of free water, which will then follow osmotic pressure to move into the tissues, increasing edema and ICP
Describe the characteristics of spinal shock
occurs immediately or within several hours of original insult
occurs with SCI above T6
loss of motor, sensory, reflex, and autonomic function below the level of injury
instant, flaccid paralysis
can last up to 6 weeks
Describe the characteristics of neurogenic shock
loss of sympathetic input to the heart and decreased peripheral vascular resistance
hypotension
bradycardia
loss of ability to sweat below the injury
IV fluids needed
no fight or flight response
What is the disability associated with a spinal cord injury at C1-2
usually fatal
What is the disability associated with a spinal cord injury at C3
quadrapalegia
What is the disability associated with a spinal cord injury at C4-5?
variable function, neck, arms, shoulder, muscles, diaphragm impairment. C3, 4, 5 keeps the diaphragm alive
What is the disability associated with a spinal cord injury at T1-12
paraplegia, respiratory issues, upper thoracic innervates the intercostals (T6 and above)
What is the disability associated with a spinal cord injury at L1-5?
paraplegia
mixed picture of motor and sensory loss
What is autonomic dysreflexia?
a medical emergency - occurs after the acute (shock) phase of SCI
patient is susceptible for life
stimulation of sensory receptors below the level of injury
triggered by noxious stimuli below injury (T6 or above)
What are the signs and symptoms of autonomic dysreflexia?
throbbing headache hypertension stimulation of vagus nerve flushing blurred vision seizure and stroke
What are the steps of autonomic dysreflexia?
- noxious stimuli
- afferent input
- massive sympathetic response
- widespread vasoconstriction
- baroreceptors in the blood vessels detect hypertensive crisis
- bradycardia
How is brain death diagnosed?
lack of corneal reflex
lack of oculocephalic reflex (dolls eyes)
lack of oculovestibular reflex (eyes moving towards ear being stimulated with flush of water)
apnea testing for 3 minutes, 6 minutes, 10 minutes with ABGs
Ancillary testing - cerebral blood flow studies (anything past the circle of willis?)
