Neuro Physiology Flashcards
What are the functions of glial cells? (5)
- produce myelin sheets
- modulate growth of damaged or developing neurons
- buffer extracellular neurotransmitter and K+ concentrations
- forms contacts between neurons
- immune responses of the nervous system
Where do afferent sensory versus efferent motor axons exit or enter the spinal cord?
afferent sensory - enter through the dorsal roots
efferent motor - exit through the ventral roots
What part of the brain does the hypothalamus belong to?
Diencephalon - forebrain
Name these structures
What are the 3 protective layers of the CNS?
- Pia mater - single layer fibroblasts
- Arachnoid - spiderweb appearance, thin layer fibroblasts (subarachnoid space with CNS between pia mater and arachnoid
- Dura mater - thick layer fibroblasts
What is axoplasmic transport?
transport of proteins/macromolecules produced in the neuron cell body and carried through the axon to the presynaptic terminals
needed transprot because axons are not able to produce proteins themselves / lack ribosomes
What are PNS versus CNS glial cells called?
- PNS Swann cells
- CNS Oligodendrocytes
What are the indentation between myelin sheets called?
nodes of Ranvier
What is the normal resting membrane potentia of neurons?
-70 mV
Describe the differences between postsynaptic Na+ versus K+ channel opening
If neurotransmitter opens Na+ channels»_space; moves membrane potential towards more positive»_space; triggering depolarization = excitatory postsynaptic potential
If neurotransmitter open K+ channel»_space; moves membrane potential more towards hyperpolarzied (i.e., more negative)»_space; inhibitory postsynaptic potential
What is destroyed in Coonhound paralysis?
myelin sheets
Besides surgery list 4 treatment options for insulinomas
- glucocorticoids - increases gluconeogenesis
- diazoxide - inhibits insulin secretion
- somatostatin - increases gluconeogenesis
- streptozocin - toxic to beta cells
What trigger release of presynaptic vesicles?
increase in IC Ca++
What is synaptobrevin and syntaxin/SNAP-25?
binding proteins at the presynaptic membrane that bind and align acetylcholine filled vesicles
What does Ca++ bind to to cause vesicle release at the presynaptic membrane?
synaptotagmin
What receptors does acetylcholine bind to at the postsynaptic membrane in neuromuscular junctions?
nicotinic acetylcholine receptors
when bound - channel opens - Na+ diffuses into the cell»_space; depolarizaiton»_space; excitatory nerve impulse
List examples for these major neurotransmitter classes:
- amino acids
- amines
- catecholamines
- peptides
- opioids
- purines
- gases
How does tetanus excert its effects?
tetanospasmin - blocks synaptic release of GABA and glycine by cleaving synaptobrevin (vesicle binding protein)
i.e., blocks release of inhibitory neurotransmitters
What are intrafusal versus extrafusal muscle fibers innervated by?
extrafusal - alpha motor neurons
intrafusal - gamma motor neurons
What neurons typically malfunction to cause LMN signs. Where are these neurons located and what do they innervate?
alpha motor neurons
cell bodies + dendrites located in the CNS (ventral horn spinal cord or brainstem if CN)
axons innervate the extrafusal skeletal muscle fibers
What are the 4 hallmarks of LMN signs?
- paralysis or paresis - flaccid
- loss of reflex arch - loss of segmental and intersegmental reflexes
- muscle atrophy - within days of the injury
- changes on electromyography within a few days
where are upper motor neurons located?
completely in the CNS»_space; influence the lower motro neurons»_space; send axons down the spinal cord or into the brain stem to control LMNs
What are the hallmarks of UMN injuries/disease?
- inappropriate or abnormal movement (spinal cord injury often causes weakness, brain orignin rigidity, circling, seizures, inappropriate movements)
- no muscle atrophy - LMN still intact
- retained but exaggerated segmental reflexes - loss of UMN inhibitory control
- normal electromyogram
Where does the motor neuron unit exit the spinal cord?
ventral horn of spinal cord gray matter
With LR and LH weakness and proprioceptive deficits, what are differentials for neurolocalizaiton?
- right motor cortex
- right corticospinal tract
- left cervical spinal cord
When assessing physiologic nystagmus, what reflex is assessed?
Vestibuloocular reflex
What are the hallmark signs of cerebellar disease?
- wide-stance ataxia
- dysmetria (inappropriate measure of muscle contractions) - exaggerated goose-stepping
- asynergia
- Intention tremors
Where do the sympathetic and parasympathetic nervous systems originate?
sympathetic - thoracolumbar spinal cord
parasympathetic - brainstem and sacral spinal cord
What 3 tissues does the autonomic nervous system affect?
- smooth muscles
- glandular tissue
- cardiac muscles
Which cranial nerves are part of the parasympathetic system?
- oculomotor (CN III)
- facial (CN VII)
- glossopharyngeal (CN IX)
- vagus (CN X)
What nerves are formed by the sacral part of the parasympathetic nervous system?
pelvic nerves
How is norepinephrine removed from the synpatic cleft?
reuptake by the presynaptic neuron
How are norepinephrine and epinephrien removed from the circulation?
enzymatic breakdown
* catechol-O-methyltransferase
* monoamine oxidase
highest cc in liver and kidneys
What are the two different receptors stimulated by acetylcholine?
Muscarinic acetylcholine receptor
* G-protein couple
* target cells of postganglionic parasympathetic neurons and cholinergic postganglionic neurons of the sympathetic nervous system
Nicotinic receptors
* ligand-gated ion channels
* at synapses between autonomic preganglionic and postganglionic neurons
* at somatic neuromuscular junctions
Why does sympathetic stimulation typically last longer than parasympathetic stimulation?
because of circulating norepinephrine and epinephrine
Describe how urine storage is facilitated
facilitated mainnly by the sympathetic nervous system
* lumbar splanchnic nerves - inhibits contraction of the destrusor muscle
* inhibit parasympathetic postganglionic neurons that would otherwise cause detrusor contraction
* contracts smooth muscle internal sphincter (neck of bladder)
* somatic motor neurons»_space; external sphincter contraction (urethralis muscle)
Describe how urine voiding is facilitated
- contraction of the detrusor muscle via parasympathetic nervous system (pelvic nerves)
- inhibition of sympathetically mediated storage reflex
both controlled by the pontine micturition center (PMC)
PMC can be overriden by conscious control
What structures must be intact for a normal direct PLR response?
- retina
- CN II
- CN III
- brainstem
- iris
How is aqueous humor formed?
active transport of Na, Cl, HCO3- into the posterior chamber»_space; draws in water
flows from posterior into anterior chamber due to pressure gradient
absorbed into the venous system at the angle between the cornea and the iris
Where is CSF formed?
choroid plexus of the ventricles
List 3 functions of the CSF
- cushions the brains against trauma
- helps maintain a consistent EC environment for neurons
- removes potentially harmful cellular metabolites
What are the 4 ventricles?
- 2 lateral ventricles, left and right
- third ventricle at the midline of the diencephalon
- fourth ventricle: between cerebellum and dorsal surfac of hindbrain
How does blood pressure of CSF pressure affect CSF formation?
independent - formation is almost constant
Name 3 drugs that could reduce CSF production/volume
- acetazolamide (carbonic anhydrase inhibitor)
- furosemide
- PPIs - proton-pump inhibitors (reduce NaKATPase activity in the choroid plexus)
What characteristics facilitate the BBB selectivity?
- tight junctions
- no open clefts (usually present in capillaries in other organs)
What molecules can cross the BBB easily?
- lipophilic
- minimally protein-bound
- small and uncharged
otherwise»_space; carrier-mediated transport
What are the parts of the neuromuscular bundle?
- surrounding pericytes
- glial astrocytic “end-feet”
- neurons
How can you measure CSF pressure and what is normal in dogs?
manometer through a needle placed in the cisterna magna
normal < 180 mm CSF
