Hormuzdi Physiology Flashcards
Which ions have an excitatory effect (depolarizing) on a cell when they influx?
Na+
Ca+
(increase positive charge)
Which ion has an inhibitory effect (hyperpolarizing) on a cell with influx?
Cl-
increase negative charge
Which ion has an inhibitory effect (hyperpolarizing) on a cell with efflux?
K+
increase negative charge
What would be the effect of an Na channel antagonist on neurotransmission? Give an example of a drug that works like this
Closes Na channel, stops Na influx, hyperpolarizing (inhibitory) effect, cell relaxes
e.g. lidocaine in anaesthesia
Influx of which ion, in response to depolarization, causes exocytosis of neurotransmitter at the synaptic cleft?
Ca
What are the 2 main types of receptor neurotransmitter can act on in the postsynaptic cell?
Ionotropic receptor (direct) Metabotropic receptor (indirect)
What is the structural/mechanical differences between ionotropic and metabotropic receptors?
Ionotropic = channel molecule Metabotropic = signalling molecule
The action of a metabotropic receptor is sufficient to illicit an action potential. True/False?
False
Which receptor does ACh act on in autonomic ganglia - ionotropic or metabotropic?
Both!
ACh acting on ionotropic receptors illicits a fast/slow epsp
What type of channels are associated with it?
ACh acting on ionotropic receptors illicits a fast epsp
Na+ and K+ channels
ACh acting on metabotropic receptors illicits a fast/slow epsp
What type of channels are associated with it?
ACh acting on metabotropic receptors illicits a slow epsp
K+ channel
Out of ACh, GABA, glycine and glutamine, which are excitatory and which are inhibitory neurotransmitters?
Excitatory: ACh, glutamine
Inhibitory: GABA, glycine
GABAa is the ionotropic/metabotropic receptor and GABAb is the ionotropic/metabotropic receptor
GABAa is the ionotropic receptor and GABAb is the metabotropic receptor
How do benzodiazepines and barbiturates work in terms of GABA inhibition?
Positively modulate GABAa receptor to enhance GABA neuro-inhibition
What is the normal frequency range for sound that humans can hear?
20-20,000 Hz
Which ossicle converts rhythmic sound energy to mechanical energy in the middle ear?
Stapes at oval window
What is impedance matching of sound?
Ossicles overcome loss of sound pressure caused by fluid by amplifying stimulus by 30dB
What are the 3 fluid-filled cavities of the cochlea?
Scala vestibuli, tympani and media
Which membrane separates the scala vestibuli and media?
Reissner’s membrane
Which membrane separates the scala media and tympani?
Basilar membrane
Which fluid - endolymph or perilymph - is present in the scala media?
Endolymph
Which fluid - endolymph or perilymph - is present in the scala vestibuli?
Perilymph
Which fluid - endolymph or perilymph - is present in the scala tympani?
Perilymph
The basilar membrane is flexible and vibrates with fluid motion. Which end of the membrane is wider and how does this relate to pitch?
Wide at apex of cochlea, narrow at base
High pitch/frequency received at base
Stereocilia transduction is caused by K efflux. True/False?
False!
K influx causes depolarisation in this case
The auditory system has two types of hair cell - describe their function
Inner hair cells perceive sound (CN VIII)
Outer hair cells regulate sound (superior olivary complex)
What are the two methods by which the auditory nerve codes frequency of sound?
Place code (area of basilar membrane) Temporal code (no. of action potential peaks)
Which vestibular structures aid head rotation?
Semicircular canals
Which vestibular structures aid translational (linear) head movement?
Utricle
Saccule
(otolith organs)
What displaces hair cells in the vestibular labyrinth?
Acceleration/gravity
List the 3 main vestibular reflexes
Vestibulo-ocular reflex (keep eyes still in space when head moves)
Vestibulo-colic reflex (keeps head still in space)
Vestibulo-spinal reflex (adjusts posture for rapid changes in position)
At rest, photoreceptors are depolarised. True/False?
True
What causes depolarisation in photoreceptors?
Dark current at rest involving Na influx through cGMP channel
What causes hyperpolarisation in photoreceptors?
Light causes less Na influx so Vm is closer to Ek which causes K efflux
Which cells - ganglion, bipolar or photoreceptors - generate action potentials?
Ganglion cells
What are the two possible end routes for neurotransmitters?
Return to terminal fro reuse
Pass onto glial cells
What technique do metabotropic receptors have to use to help stimulate the release of neurotransmitters?
Modulatory synaptic actions
What types of ionotropic receptors exist in glutamate?
NON-NMDA: permeable to Na, K
NMDA: permeable to Na, K, Ca
What part of glutamate reception is targeted by anaestheisa?
NMDA receptor, focusing on Ca influx
The GABAa inotropic receptor is associated with what type of ion channel?
Cl- channel
The GABAb metabotropic receptor is associated with what type of ion channel?
K+ channel
Baclofen targets what receptor used by GABA neurotransmitters?
GABAb receptor
What type of receptor and channel does glycine act on?
Ionotropic receptor
Cl channel
What is an epsp. and ipsp.?
Excitatory postsynaptic potential (depolarizing rmp) and creates an AP if threshold is reached Inhibitory PSP (hyperpolarizing rmp) which inhibits APs
What is meant by ‘interneurone’?
Locally acting neurone that releases neurotransmitter (typically GABA, glycine) to cause an ipsp.
What is meant by ‘projection neurone’?
Convey signals to other parts of brain, usually glutamate to cause an epsp.
An excitatory neurone releases a depolarising/ hyperpolarising neurotransmitter e.g. glutamate/ GABA
Depolarising
Glutamate
An inhibitory neurone releases a depolarising/ hyperpolarising neurotransmitter e.g. glutamate/ GABA
Hyperpolarising
GABA
Neurotransmitters are released in single vesicles called…
Quanta
What is meant by the term ‘synaptic integration’?
Summation of psp allows multiple synaptic inputs to be integrated
What is the difference between spatial and temporal summation?
SPATIAL: summation of epsps and ipsps are spatially distributed but timed together
TEMPORAL: epsps occur in temporal sequence such that the threshold is triggered
Which neurotransmitter is involved in regulating the responsive cation entry of ions by hair cells?
Glutamate - excitatory signal
The otilith organs are involved in what type of movement?
Tilt and acceleration
How are sound vibrations transmitted to the auditory cortex?
Vibrates eardrum and otilith organs Spreads to cochlea Vibration of air converted to fluid Captured by hair cells Transduction (conversion to neural energy) ---> Auditory cortex
What are the three mechanisms which cause amplification in the middle ear?
Area ration of ear drum to stapes
Lever action of ossicles
Buckling of ear drum
Where do scala vestibuli and scala tympani connect?
At helicotremia
Which protein in outer hair cells can change the length of the cell, and increase transduction?
Prestin
Outline the central auditory pathway
(Right and left cochlear impulses cros) Eighth CN Cochlear nucleus Superior olivary nuclei Lateral lemniscus Inferior colliculus (MGN ---> auditory cortex)
What are the three cochlear nuclei, branches of CNVIII?
Dorsal cochlear nucleus
Posteroventral cochlear nucleus
Anteroventral cochlear nucleus
Where does locating sound occur?
Medial and lateral olive
What type of fluid is contained within SCC?
Endolymph
How many SCC are there?
3 push-pull pairs of fluid-filled canals (right angles to each other)
Hair cells in the macula are divided by _____ into two populations with opposing polarities
What is it’s function?
Striola
Allow all organs to have multidirectional sensitivity
What type of crystals respond to tilt and are on the otilithic membrane?
CaCO3
Give examples of agents that can be ‘ototoxic’ and contribute to vestibular system dysfunction
Aminoglycoside antibiotics
Chemo agents
Alcohol
List the stages of the direct pathway for signal transmission in the retina. Is this the same as light?
Photoreceptors ----> Horizontal cells Bipolar cells ----> Amacrine cells Ganglion cells CNII (ganglion cell axons)
Light travels in opposite direction: ganglion cells, bipolar cells, photoreceptors
What chemical is composed of opsin and 11-cis retinal? What is the activated form of 11-cis retinal?
Rhodopsin
Trans-retinol
Rod cells have less acuity than cone cells. True/ False? Why?
True
Used in dim light, cells have increased convergence and therefore increased sensitivity and reduced acuity. The opposite is true in cones.
Ionotropic bipolar cells respond negatively to glutamate. True/ False?
False
Metabotropic bipolar cells respond negatively, and ionotropic respond positively.
What is the role of lateral inhibition in vision?
Exaggerates the difference in stimulus intensity detected by adjacent neurones, via inhibitory interneurones, and aids with localization
What type of retinal cells interconnect a group of surround neurones?
Horizontal cells
An on-center cell is stimulated when the center of its receptive field is exposed to light/dark, and is inhibited when the ______ is exposed to light/dark. Off-center cells have just the opposite reaction.
Light
Surround
Light
Which neurotransmitter is involved in inhibiting on and off-centre cells? What does this do?
GABA
Increase the response of the centre on bipolar cells
What is the function of central surround organization?
Sharpens boundary between objects of different luminance
Which process is important in modifying receptive fields of ganglion cells to have a centre surround organisation?
Lateral inhibition
List the three types of retinal ganglion cells which give information about different receptive fields.
M (movement)
P (form and colour)
Non M and P (colour)
What type of ganglion cells is involved in giving information about light and dark?
On and off centre ganglion cells
What type of ganglion cell is involved in giving information about colour?
Opponent ganglion cells
What type of hemiretina - nasal or temporal - crosses at chiasm to form optic tracts?
Nasal
Which part of the retina occupies the largest area of the visual cortex?
Centre of retina - the FOVEA
An injury to CNII in the visual pathway would cause what visual defect?
Monocular blindness
An injury to the optic chiasm in the visual pathway would cause what visual defect?
Bitemporal haemanopia
An injury to the optic tract in the visual pathway would cause what visual defect?
Contralateral haemanopia
An injury to the optic radiation in the visual pathway would cause what visual defect?
Quadrantic haemanopia
An injury to the striate cortex in the visual pathway would cause what visual defect?
Foveal sparing
What layer are the first binocular neurones found in in the striate cortex?
Layer 3
What is the purpose of the ocular dominance columns?
Neurones coming from the eye only act on a particular area of cortex on contralateral side
The peak frequency of the cortical receptive fields of the striate cortex depends on…
The particular orientation
What is the ‘competition hypothesis’?
Connection from two eyes compete in cortex and affect the ocular dominance columns
What is the effect of monocular deprivation during development?
Active afferents in one eye remain and reduce in the other which affects the structure of the cerebral cortex
