Nervous system Flashcards
Resting membrane potential (Vr) is …..
It is caused by …..
the difference in potential between the inside and the outside of the cell at rest.
- Normal value is -60 mV, while for heart & skeletal muscles -90mV
- Caused by different distribution of ions and selective permeability of the cell membrane. The membrane is permeable to K, and impermeably to intracellular anions
Concentration gradient is …
the force that drives diffusion across a membrane so that the ions concentrations are equal on both sides of the membrane
Electrical gradient is …..
the force that drives diffusion across a membrane so that charges tend to equalize on both sides of the membrane
The Na-K pump maintains ….. & …..
low intracellular Na, High intracellular K
* For every 3 Na leaving the cell, 2 K enter. The result is +ve charge loss
Diffusion of an ion through a channel depends on ……. & ……
Ion size and charge,, and the channel size and charge
Ion channels are either ….. or ……
ligand gated, or voltage gated
* Voltage gated Ca channels are more abundant at axon terminals where Ca is needed for neurotransmitter release
Neurons possess the ability to …….
regulate their resistance because of their ion channels
A threshold potential (Vt) is …..
potential required to generate an action potential. It is about -50 mV
The all or none response means …….
any stimulus at or above the threshold intensity will generate the same action potential with constant amplitude
Axon hillock is ……
where the action potential starts and propagates in both directions.
* Most of the Na channels are located here, not at the soma
A hyperpolarizing pulse is ……, while a depolarizing pulse is ……..
- Hyperpolarizing pulse changes Vm so that the inside is more -ve. More intense stimuli is needed to generate AP
- Depolarizing pulse changes Vm so that the inside of the cell is less negative
When the tendency of K to leave is equal to the tendency of the membrane to pull back K, the membrane is ….
at rest (stable)
When the membrane reaches threshold, the magnitude of the response is greater because of …….
active participation of the membrane in which the inward movement of +ve ions overwhelms the repolarization process
The action of local anesthetic is by ……
blocking the Na influx, thereby inhibiting depolarization.
* LA affects smaller nerve fibers first (C fibers, small pain fibers, large A proprioceptive fibers)
Action potential continues ….. the stimuli discontiunues
after
After AP, the membrane is repolarized below ……
the resting potential
The absolute refractory period occurs ….., because ……
during the peak and first half of the falling phase of AP.
* No AP can be elicited at this period, because Na channels can not open and K is still elevated and flowing outward
The relative refractory period is ……
when the inactivation of Na channels is ending and the efflux of K is diminishing, here, a stronger than normal stimulus can initiate another AP
* This phase follows the absolute phase
The power of …….. is needed to re establish the resting potential
Na-K pump
Saltatory conduction is ……
the movement of AP from one node to another. It is much more faster than in unmyelinated axons
* Electrochemical basis behind saltatory conduction is ↓ membrane
capacitance (increase distance between charges; less charges necessary).
The greater the diameter of an axon, the ……
greater the speed of conduction
Why impulses are conducted in one direction only??
because:
- synapses permits transmission in one direction only
- The moving impulse doesn’t depolarize the spot behind it because it is either hyperpolarized or refractory
Orthodromic impulses are ….., while antidromic impulses are ……
- occur in normal direction of conduction
* occur in the opposing direction (only experimentally)
How is gradation of sensory impulse possible?
because many axons with different thresholds are present at the same sensory location
Mixed nerves have a compound action potential because …..
of the different conduction speed
see p. 470
What are the two types of synapses?
- Bridged: electrical synapses, separated by a 2nm gap (gap junctions). Like the myocardium
- Unbridged: or chemical synapses, separated by synaptic cleft (30 nm gap)
When AP reaches the tip of an axon, this leads to ……
activation of voltage gated Ca channels, influx of Ca, then fusion of synaptic vesicles with the plasma membrane.
* The neurotransmitter is either degraded or taken back up by the nerve terminal
…. molecules of Ach bind to the nicotinic receptor
two
* in the presynaptic cell, Ach is generated from acetyl-CoA with choline, catalyzed by transferase enzyme
In the post synaptic neuron, the opening of the channels allow both Na & K to flow down their concentration gradient, however, Na influx dominates, why??
because Na flows down its concentration & electrical gradient
EPSP must be conducted electronically to ……, only there AP is generated if EPSP exceeds the threshold
axon hillock of the post synaptic neuron
* The axon hillock contains many low threshold voltage gated channels
IPSP causes ….. , because ….
hyperpolarization of the neuron
it opens voltage gated K channels, or may cause inward flux of Cl
AP is generated only when …… + ….. are equal to /more than ….
ESPS + IPSP
Vt
Spatial summation means ……
Temporal summation means …..
- The summing of simulataneous inputs from different presynaptic neurons.
- the additive effect on the post synaptic cell is caused by repeated rapid firing of a single presynaptic neuron
Lowering extra cellular Ca concentration …… the synaptic transmission
reduces
* the opposite is also true
Miniature end plate potentials are …..
spontaneous potentials with out signal that releases Ach in the cleft.. Do not cause AP as they are not enough to reach Vt
The ability to change the amount of Ca entering the terminal is called …..
synaptic plasticity
* Long term potentiation is an example, and is the basis of memory and learning
The ANS doesn’t have the same specialization of directed transmitter release. T/F
True
Different neurotransmitters can not coexist in a single neuron. T/F??
False
Ach is found in ….
while norepinephrine is found in …
- neuromuscular junction
- all preganglionic neurons of ANS
- post ganglionic neurons of the parasympathetic system
* nor epinephrine is found in post ganglionic sympathetic neurons
The primary excitatory neurotransmitter in the CNS is ……, while glycin is ……, and GABA is ……
glutamate
glycin is inhibitor in the spinal cord
GABA is inhibitor in basal ganglia, cerebellar Purkinje cells (increase Cl influx)
* See p. 473 for the rest of the transmitters
The result of transmitter-receptor interaction depends on ….
the receptor type
The methods of eliminating the transmitter-receptor interaction is by …., ….. &…..
- enzyme degradation
- reuptake by presynaptic cell
- diffusion of neurotransmitter away from receptor
Mysthenia gravis is caused by ….., resulting in ….. . The treatment is ….
antibodies to the Ach receptos, muscle weakness
* Muscle function worsens after repeated use
Tx is anti AchE medication (prevents Ach degradation), steroids or cytotoxic agents
* It doesn’t affect all muscles equally
* This is a post synaptic disease
Eaton Lambert disease is different from Mysthenia gravis in …. . The main cause is
the muscle improves after repeated use, and it affects the presynaptic neuron
* Main cause is antibodies against the voltage gated Ca channels, which prevent Ach release
Black widow venom causes …
complete depletion of Ach reservoir at the neuromuscular junction, with severe muscle spasm
Clostridium Botulinum toxins cause ….
blockage of the transmitter release and quick paralysis
The smooth muscle neuroeffector junction could be …… or ….
adrenergic or cholinergic
The neuromuscular junction of smooth muscle is different from skeletal muscles junctions by ….
- smaller clefts, with no secondary folds
- Could be cholinergic (Ach), or noradrenergic (norepinephrine, inactivated by reuptake)
- Transverse T tubules are absent in smooth muscles
Visceral effectors are ……
autonomous (visceral smooth muscles contract without innervation)
* However ANS is needed to coordinated the visceral function
In the ANS, the preganglionic neuron is ….., while the post ganglionic is ….
slightly myelinated
unmyelinated
* ANS conduction is 100 times slower than skeletal motor conduction
The sympathetic system extends from …. to ….
T1 to L2
Preganglionic sympathetic fibers, along with the motor neurons, leave the spinal cord in …… . The sympathetic fibers then leave in….
ventral root white ramus (myelinated) to join the sympathetic chain
The sympathetic chain contains …..
the cell bodies of the postganglionic sympathetic fibers
* not all preganglionic neurons synapse in the sympathetic chain
Each presynaptic neuron synapses with ……, while the post synaptic soma synapse with ….
many postsynaptic neurons (divergence)
many presynaptic neurons (convergence)
The sympathetic chain is also called ……, runs on each side of
paravertebral ganglia spinal cord (extends the whole length, not just T1 to L3)
Splanchnic nerves pass ……. to end in …..
Prevertebral ganglia are ….
through the sympathetic ganglia without synapsing
end in neural plexus, like the celiac ganglia
* prevertebral ganglia are sympathetic ganglia that receive the splanchnic nerves. It has long preganglionic fibers, and supply the viscera
Nerves for the adrenal medulla pass ….
the sympathetic chain without synapsing, to end in cells analogous to postganglionic neurons (in the medulla)
All preganglionic neurons are …..
cholinergic neurons
The sympathetic ganglion function is regulated by ……..
small intensity fluorescent cells, which releases dopamine in the ganglionic blood vessels
* SIF cells are neural crest derivatives, and innervated by the preganglionic neurons
Post ganglionic sympathetic neurons have ……, either go back through …. to ….., or …
long axons, gray ramus, spinal nerves, take a vascular route with major blood vessels (supplying the blood vessel lining and the target area)
Sympathetic postsynaptic neurons are noradrenergic except
neurons to sweat gland and skeletal muscles vasculature which are cholinergic,
and the postganglionic neurons in the adrenal medulla which release epinephrine plus norepinephrine
Cervical ganglia are …
paravertebral
The superior cervical ganglion supplies….., the middle and inferior supply…..
- lower 4 cranial nerves, pharynx, ext & int carotid arteries, and the cardiac nerve
- heart, lungs, blood vessels to the upper extremities
- The middle and inferior are fused in stellate ganglion
Thoracic chain ganglia is ……, supply ….
paravertebral, 12 in number
GIT up to the left colic flexture
Lumbar and sacral ganglia are ….., supplying …..
paravertebral (5 lumbar, 4 sacral)
GIT below the left colic flexture, ext. genitalia & uterus, bladder
Horner’s syndrome is caused by ….
a lesion to the superior cervical ganglion
Sympathetic system functions are ……
- CO increase
- O2 concentration increase (due to bronchodilation). blood glucose increase (due to glycogenolysis)
- blood to GIT decrease, also motility
- muscular vessels dilated, cutaneous constricted
- goose bumps, mydriasis
- release of epinephrine from medulla
Parasympathetic system consist of ……..
cranial nerves III, VII, IX , X
and the sacral division S2, S3, S4 (supply structures below the left flexture)
Parasympathetic preganglionic fibers are …., the preganglionic sympathetics are …….
very long and terminate close to the effectors
- Preganglionic sympathetic fibers are short, while the post ganglionic are long
- There is little divergence and convergence in the parasympathetic system, unlike the sympathetic
Parasympathetic preganglionic fibers are ….., the postganglionic are …
always excitatory
mixed, and may also contain sympathetic receptors (especially in the GIT)
Sweat glands, arrector pili and blood vessels are innervated by ….
sympathetic system (unopposed)
Function of parasympathetic fibers via X are …., while those of VII & IX are ….. , those of III cause ….., while the sacral functions are ….
- relaxes sphincter, increases peristalsis, activates digestion, slows HR
- increase (with the sympathetic) salivary secretion
- miosis
- defecation, bladder contraction (urination. Sympathetic inhibits bladder contraction), and erection (ejaculation is under sympathetic though)
- Bronchoconstriction
Adrenergic receptors are two types, Alpha receptors are ……., while beta receptors are ……
All these receptors are associated with ….. on the membrane
excitatory
inhibitory, except in the heart (β1)
G protein (G protein coupled receptors)
* Alpha are sensitive to epi>norepi>isoproterenol
* Beta are sensitive to isoproterenol>epi>norepi
* β2 receptors causes bronchodilation and vasodilation
Cholinergic receptors are two types: nicotinic which are always ……. and can be blocked by …..
, and muscarinic which are ……. and blocked by …..
excitatory, curare (at neuromuscular junction) & hexamethonium (at ganglia) but not by atropine
inhibitory or excitatory, atropine (not curare or hexamethonium)
Nicotinic receptors are found in ……., while muscarinic receptors are …..
neuromuscular junction, ganglia & between pre and post ganglionic neurons
muscarinic found at postganglionic parasympathetic synapses on effectors
Tonic activity enables …..
finer control by the opposing effect of sympathetic and parasympathetic system on an effector
The somatic sensory system is of 3 categories based on the source of signal. What are these categories?
- exterceptive
- proprioceptive
- interoceptive (monitors internal events, such as blood pressure)
Nociceptors are ….
free nerve ending of A delta (mylinated) and C fibers (unmyelinated)..
Conducts pain and temp over 45
* C fibers activation is perceived as sickening, burning sensation
Cold and warm receptors are connected by ….
A delta and C fibers
What are the types of mechaoreceptors??
- Rapidly adapting: respond to onset and termination of stimulus. Connected by A beta & delta. Example is hair follicle receptor, Meissner corpuscle (palm, two point discrimination), Pacinian corpuscle (subcutaneous, ligaments). These are encapsulated
- Slowly adapting: Connected by A beta fibers. Type I (Merkel cell, non corpuscle) produce sustained response to static stimuli (eg. indentation of skin). Type II (ruffini corpuscle) is sensitive to skin stretch
What are the four nuclei in the spinal gray matter??
- Post. marginal nucleus: integrates afferents information
- Substantia gelatinosa: relays pain and temp
- Nucleus proprius: integrates sensory information
- Clark’s nucleus: relays limb position to the cerebellum (proprioceptive)
The pupil size ranges from …… and reduces entering light by factor of …..
2 - 8 mm
16
Accommodation is ……
constriction of pupil upon focusing on near subject..
* Mediated via different pathway than light reflex
Light-Near dissociation occurs in …..
tertiary syphilis, called Argyl Robertson pupil.
Light reflex is lost, but accommodation is preserved
Viewing a near object causes the contraction of …..
ciliary muscle to thicken the lens; and at the same time, medial recti contract to direct the gaze medially.
- Mediated by CN III and visual cortex
- Ciliary body produces the aqueous humor
Approximately 75% of light refraction is performed by …..
the cornea
What are the two types of receptors in the retina?
- Rods: contains rhodopsin, which consists of light trapping scotopsin & retinal. Sees only shades of gray
- Cones: responsible for color vision and visual acuity. Contain iodopsin
* Oxidation of Vit. A (retinol) produces retinal
see P. 482 for the table
Rhodopsin functions by …..
absorbing light and inducing conformational changes which alter visual cell permeability to Na
* Rods are peripherally located
Rods and cones in the dark are always ….
depolarized and release transmitter that inhibits the bipolar cell.
- They don’t generate AP
- There are more rods than cones
Ganglionic cells are responsible for ….
transmission of visual information to the brain
Amacrine cells are ……
interneurons in the retina, connecting the rods and cones
Brodmann area 17 is ….., and it contains …… & ……
the visual cortex
pyramidal cells: projects axons to other areas of the brain
stellate cells: integrates visual input
Vibration of the ossicles produces ….
pressure changes in the fluid of the inner ear
Tympanic reflex occur when ……
tensor tympani and stapedius contract and lock the ossicles in place during loud sound to prevent damage to the inner ear
Organ of Corti function is ……
transduction of physical forces into bioelectrical impulses
* It is resting on the basilar membrane
Organ of Corti consists of …… that are embedded in …..
hair cells (innervated by CN VIII) tectorial membrane
Movement of the perilymph (…..) moves the …… which in turn triggers …… deformation
(scala vestibuli)
basilar membrane
hair cells deformation
The movement of the Stapes produces pressure waves in perilymph of ……
scala vestibuli, causing displacement of the basilar membrane
The stapes end of the base is ….. compliant than the apex end, and responds to ….. frequency sounds
less, high
- the apex responds to low frequency sounds
- the basilar membrane is tonotopically organized, and so is the CN VIII fibers
Sound representation is …… in the cortex
bilateral
* although, individual hemispheres is more concerned in sound localization from the contralateral auditory hemisphere
Crossed and uncrossed fibers from the cochlear nucleus of medulla pass in …..
lateral lemniscus, inf. colliculus, medial geniculate body, then superior temporal gyrus
Semicircular canals have enlarged portion called ….., which contains the receptor organ ……., which is embedded in …. .
Distortion of of the hair cells leads to …… or ….. depending on the direction
ampulla
crista ampullaris (has hair cells)
gelatinous cupula
depolarization or hyperpolarization
The ampulla detects ….. acceleration
angular
The utricle and the saccule contain the receptor ….. that have hair cells with …. at the tip. They detect …..
maculae
otoliths
linear acceleration
* Hair cells are also embedded in gelatinous mass
A delta and C fibers synapse on ……
neurons in the dorsal horn
Spinal pain projections (spinothalamic tract) terminate in …., ……. & …….
thalamus, superior & inferior colliculus, tegmental reticular formation
The gate control theory of pain suggests that …..
afferents other than the pain fibers inhibit the incoming pain signal in the dorsal horn
Endorphine prevents the release of …… from C afferent fibers
substance P
The olfactory epithelium is composed of ……, that are bathed in ……
bipolar hair cells (primary neurons)
special fluid (to dissolve gas, from Bowman’s glands)
* Their axons (unmyelinated) penetrate the cribriform plate, to form the olfactory nerve
The first synapse of the olfactory nerve is in ….
the olfactory bulb (ipsilateral fibers synapse here)
The olfactory tracts are …..
projections from the olfactory bulb to the olfactory cortex
* Doesn’t have a relay in the thalamus
At the apex of the taste buds, …… admits the stimulus
pores
All portions of the tongue respond to all four tastes. T/F ???
True
but to varying degree
SNARE protein facilitates ….
vesicle exocytosis
* located in the presynaptic neurons
Foliate and fungiform papillae are ……, while the circumvallate and the filliform are.
not keratinized
