TEST 1 REVIEW Flashcards
afferent
from receptor to brain
efferent
from brain to organ
Peripheral nervous system maintains homeostasis through
dual innervation, antagonistic action between parasympathetic and sympathetic nervous systems
purkinje neuron
major output neuron of the cerebellum
Astrocytes
glial cells – involved in blood brain barrier maintenance by enveloping endothelial capillaries, development of new circuits, repair, release gliotransmitters, and tripartite system of connection
where are action potentials generated
axon hillock
the four functional neural zones
reception, integration, conduction, transmission
location of signal reception
dendrites and cell body
location of signal integration
axon hillock
location of signal conduction
AP travelling down axon
location of signal transmission
release of NT at axon terminals
differences between axons and dendrites
Axons do not branch dendrites taper as well as branch, dendrites have spines and axons are smooth
depolarization
membrane becomes less negative
repolarization
membrane returns to resting value
hyperpolarization
membrane becomes more negative
equilibrium potential
potential at which an ion is at equilibrium across the membrane i.e. there is no net movement of that ion across the membrane, calculated using the Nernst equation
goldman equation
weighted average of equilibrium potentials for all ions with permeability to that cell
electrotonic current spread
charge spreads through cytoplasm causing changes in adjacent membrane potential, no contribution from VG channels, primarily ligand gated
Characteristics of APs
Triggered by net graded potential reaching threshold potential at axon hillock, Caused by opening and closing of ion gated channels, Do not degrade over time, travel long distances, All or none size, duration, and shape which are the same in a given neuron but not necessarily among a population of neurons, Occur IN axons, Self propagating, Electrotonic spread, Have a regenerative cycle
Channel activity in an AP
o VG Na channel opens in depolarization
o VG K channels open more slowly in repolarization
o VG Na channels close and K channels close more slowly in hyperpolarization
Hodgkin cycle
a positive feedback loop that drives depolarization – opening of Na channels causes influx of Na causing further depolarization and more Na channels to open
VG Na channels at rest
activation gate closed
VG Na channels during depolarization
activation gate open
VG Na channels during repolarization
inactivation gate closed, activation gate open
Saltatory conduction
APs leap from node to node, does not degrade like regular electrotonic current spread because APs are regenerated at nodes – the alternating of electrotonic conduction with new APs along the axon
cause of absolute refractory period
closure of inactivation gate of Na channels during hyperpolarization
Factors that lower intracellular Ca
o Binding with intracellular buffers
o Ca ATPases
[Ca] at high frequency APs
Ca influx is greater than removal, ↑ [Ca], many synaptic vesicles release their contents, high [neurotransmitter] in synapse
Electrochemical driving force
|Vm – Eion|
Cholinergic transmission
acetyl CoA (from mitochondria) + choline»_space;choline acetyl transferase»_space; Ach, released by exocytosis, broken down by AchE in synapse, choline re-entered by presynaptic cell while acetate diffuses out of the synapse
Electrical synapse
gap junction - allows movement of small molecules/ions without having to cross membrane
gap junction
Made with 1 hemmichannel/cell, connexon formed of 6 connexins
Chemical synapse
chemical messenger crosses synaptic cleft – increases diversity of signals that can be passed through the synaptic cleft
PNS chemical synapses
axon terminals, varicosities
CNS chemical synapses
En passant synapse, spine synapse
Characteristics of NTs
o Synthesized in neurons
o Released at presynaptic cell following depolarization
o Bind to postsynaptic receptor and cause a detectable effect
o Mechanism of inactivation
Types of NTs
o Amino acids o Neuropeptides o Biogenic amines o Acetylcholine o Miscellaneous (gases, purines)
Inhibitory NTs
cause hyperpolarization of postsynaptic cells (IPSP), make cell less likely to generate AP
Excitatory NTs
cause depolarization of membrane (EPSP), make cell more likely to generate AP
Ionotropic receptors
ligand gated ion channels, fast e.g. nicotinic Ach receptors
Metabotropic receptors
changes shape, formation of second messenger, alters opening of ion channel, slow, leads to long term changes via second messengers
Nicotinic receptor
always excitatory, ionotropic, 5 subunits, Na, Ca in
Muscarinic receptor
metabotropic, g-protein coupled, 7TM subunits, activates cAMP (PKA)
Biogenic amines
serotonin and the catecholamines
catecholamines
tyrosine derived - NE, E, dopamine
Synaptic facilitation
repeated AP results in increased Ca released in axon terminal, increased NT released
Synaptic depression
repeated APs decrease NT release, progressive depletion of readily releasable pool
Post-tetanic potentiation
train of high frequency APs leads to increased NT release, believed to involve Ca dependent increase in NT containing vesicles in axon terminal which might lead to recruitment of vesicles from reserve pool
Alzheimer’s treatment
AchE inhibitors; found reduced level of Ach in the brain of alzheimers patients, wanted to increase Ach in brain to help that, but problem is Ach deficiency is symptom, problem is the plaques that cause NT reduction
Depression treatment
Prozac – selective serotonin reuptake inhibitor, treats symptom not cause
Generator potential
sensory receptor IS the primary afferent neuron
Receptor potential
sensory receptor is separate from the primary afferent neuron – requires an NT from receptor to afferent neuron creating a graded potential that triggers an AP
Telereceptors
detect distant stimuli
Exteroreceptors
detect stimuli on outside of body
Interoreceptors
stimuli inside the body
Stimulus modality
what type of energy the stimulus responds to
Adequate stimulus
preferred stimulus modality
ampullae of lorenzini
detect pressure, temperature, electrical fields at end of canal at the base of which lies gel that is in constant contact with water – receptor potentials
Theory of labeled lines
discrete pathway from the sensory cell to the integrating centre
Lateral inhibition
signals from neurons at the centre of a receptive field inhibit neurons on the periphery – to determine locations of stimuli
Dynamic range
range of stimulus intensities over which a receptor can increase its response
threshold of detection
response 50% of the time in one receptor
large dynamic range
large change in stimulus causes a small change in firing frequency – poor sensory discrimination
narrow dynamic range
small change in stimulus causes a large change in AP frequency – good sensory discrimination
range fractionation
groups of receptors work together to increase dynamic range without decreasing sensory discrimination
Weber-fechner law
resolution of perception diminishes for stimuli of greater magnitude
Phasic receptors
produce APs at the beginning and/or end of the stimulus, encode change in stimulus but not stimulus duration
Tonic receptors
produce APs as long as the stimulus continues, encode stimulus duration
olfactory receptor cells
are ciliated bipolar neurons with odorant receptor proteins in cilia
odorant receptor protein
Each olfactory neuron expresses one, but receptors can recognize more than one odorant
odorant response
Odorant binds receptor causing conformational change, Golf activates adenylate cyclase increasing cAMP, which opens cAMP gated ion channels causing Ca and Na to enter cell – generator potential – Ca activates Cl (out) channels increasing depolarization, generator potential opens VG Na channels – AP
Vomeronasal organ
detects pheromones – structurally and molecularly distinct from the olfactory epithelium, connected to oral or nasal cavity, GPCR activates PLC system which opens ion channels causing depolarization
Invertebrate olfactory system
located in many parts of the body but mainly on antennae in arthropods
Sensilla
hair like projections of cuticle, contain odorant bipolar neurons which have GPCRs that cause cAMP formation, opening of ion channels and depolarization
Taste receptor cells
epithelial cells release NTs and express more than one kind of receptor protein, a single primary afferent taste neuron may synapse with more than one receptor cell with diverse signal transduction mechanisms
salty taste transduction mechanism
Na ions depolarize receptor cell membrane through open ion channels
sour taste transduction mechanism
protons enter through channel and block K channel leading to depolarization
sweet, bitter, umami taste transduction mechanisms
activation of PLC, PIP, IP3, causing release of Ca into cytoplasm from ER that opens Na channels causing depolarization and NT release
Invertebrate taste
located on sensilla inside and outside mouth, on legs, and wing margin, bipolar sensory neurons that express only one receptor protein (each), more similar to vertebrate olfactory neurons
Mechanoreceptors
linked to ECM and alter channel permeability
ENaC
epithelial sodium channels
TRP channels
transient receptor potential channels (allow K and Ca to cross)
Vertebrate tactile receptors
widely dispersed in skin, isolated, free nerve endings maybe wrapped in accessory structure
Pacinian corpuscle
free nerve ending with 60-70 layers of membranes with gel in between, pressure and vibration, transient depolarization at onset and offset of stimulus
Merkel’s disk
free nerve endings associated with an enlarged epidermal cell with small receptive fields, slowly adapting tonic receptors – most sensitive to indentation
Root hair plexus
free nerve endings wrapped around basis of hair follicles, rapidly adapting phasic receptors, sensitive to changes in movement
Trichoid receptor
hairlike projection of cuticle, bipolar sensory neuron, TRP channel, also used in olfaction and gustation
Campaniform receptor
dome shaped bulge od cuticle, sense deformation of cuticle as it moves, bipolar sensory neuron, used in proprioception
Muscle spindles
monitor muscle length (skeletal)
Golgi tendon organs
monitor muscle tension
Joint capsule receptors
located in capsules that enclose joints, monitor pressure, tension, and movement
Statocysts
organ of equilibrium in aquatic invertebrates, hollow fluid filled cavities lined with mechanosensory neurons, Contain statoliths
statoliths
dense particles of calcium carbonate, their movement stimulates mechanoreceptors
Vertebrate hair cells
modified epithelial cells NOT neurons with cilia on apical surface all connected by tip links
kinocilium
one true cilium on each hair cell
stereocilia
microvilli made of actin bundles 20-300 on each, pivot along base in response to movement, oriented according to size
stereocilia moving away from kinocilium
blocks K channel opening and NT release so there is no AP generation in primary afferent neuron
stereocilia moving towards kinocilium
opens K channels and causes NT release for AP generation in PAN
endolymph
fluid bathing apical side that is high in K, concentration is actively maintained in vestibular apparatus and cochlea, high K low Na
perilymph
fluid bathing basal side, similar to CSF, high Na low K, fills cochlear ducts
Vestibular apparatus
3 semicircular canals with ampulla at one end and 2 sac like swellings of utricle and saccule, lagena is extension of saccule that in birds and mammals becomes cochlear duct or cochlea
macula
in utricle and saccule, mineralized otoliths in gelatinous matrix that have hair cell cilia embedded, detect linear acceleration and tilting of head when inertial force causes hair bundle movement
crista
in ampullae of semicircular canals – has gelatinous matrix in cupula that DOES NOT have otoliths but does have stereocilia embedded, detect angular acceleration by inertial force of fluid movement causing hair bundle movement - pressure of endolymph in opposite direction of movement
Push-pull system
one canal is stimulated, partner on other side is inhibited, direction of movement determined by comparing contralateral canals
cochlea
coiled in mammals, contains organ of corti
organ of corti
has hair cells on basilar membrane, inner rows of sensory receptors and stereocilia embedded in tectorial membrane
Sound transduction
vibrations to oval window, pressure waves in perilymph of vestibular duct, basilar membrane vibrates, stereocilia bend, opens TRP channels, K in for depolarization, hair cells release glutamate which excites afferent neuron, round window dissipates energy
sound frequency detection
basilar membrane is stiff and narrow at proximal end and flexible and wide at distal end, high frequency at proximal end
sound location detection
brain uses time lags and differences in intensity to detect location, head rotation localizes sound
ciliary photoreceptor cells
have a single highly folded cilium that forms disks containing photopigments
rhabdomeric photoreceptor cells
have microvillar projections that contain photopigments – outfoldings of apical surface
Vertebrate photoreceptors
ciliary – rods (dim) and cones (bright), have inner segment which forms synapses with other cells and outer segment with photopigments
Chromophore
pigment derived from vitamin A (e.g. retinal) that has C=C bonds, when light is absorbed bond changes cis to trans
Photoreceptor protein
e.g. opsin GPCR – structure determines photopigment sensitivity
Rhabdomeric phototransduction
o Chromophore absorbs energy from photon and changes conformation (isomerizes cis-trans)
o Activated chromophore dissociates from opsin – bleaching
o Opsin activates g-protein which activates PLC, converting PIP to DAG and IP3, DAG activates a TRP channel, Ca and Na enter and depolarize cell
ciliary phototransduction
o Chromophore absorbs energy from photon and changes conformation (isomerizes cis-trans)
o Activated chromophore dissociates from opsin – bleaching
o Opsin activates Gi called transducin, which activates PDE which converts cGMP to GMP, decreased [cGMP] closes Na channel, decreasing [Na] hyperpolarizes cell
flat sheet eyes
some sense of light direction/intensity, larval eyes or accessory adult eyes, no image formation
cup shaped eyes
retinal sheet is folded into narrow aperture that allows discrimination of light direction and intensity, light/dark
camera eyes
most vertebrates, lens in aperture improves clarity and intensity by refracting light and focusing it on one point on retina
compound eyes
found in annelids, molluscs, arthropods – convex retina, detection of movement and wide field of view
composition of compound eyes
Composed of ommatidia – the photoreceptor – forms images by each ommatidia operating independently and forming part of an image that the neurons interconnect, OR, ommatidia work together to form image
limitations of compound eyes
size limited by wave properties of light, number of ommatidia limited by size - resolving power can be increased by reducing size or increasing number of ommatidia
3 layers of vertebrate vesicular eye
sclera, uvea, retina
sclera
white of eye, support and protection, has cornea – anterior modification
uvea
choroid, ciliary body, iris – for nutrition gas exchange and reducing reflection, tapetum in nocturnal animals as reflective modification
retina
lines inside of choroid, light sensitive
aqueous humor
fluid in anterior chamber
iris
pigmented smooth muscle regulating size of pupil
ciliary body
muscles that change lens shape
lens
behind iris, focus images on retina
vitreous humor
gelatinous mass in posterior chamber
layers of cells in vertebrate vesicular eye
ganglion cells, amacrine, bipolar, horizontal, rods/cones – axons of ganlions exit retina at optic disk
fovea
region in centre of retina where overlying bipolar and ganglion cells are pushed away leaving only cones, provides sharpest image
rods
use principle of convergence – many rods converge on one bipolar cell, many bipolar cells on one ganglion cell – gives large receptive field and fuzzy image
cones
no convergence, one cone/bipolar cell/ganglion cell, smaller receptive field, high resolution image, less convergence = greater acuity
Center-surround organization of signal processing
enhances perception of borders and contrast, lateral inhibition from horizontal cells in surround
On center ganglion cells
light in centre of receptive field causes hyperpolarization of photoreceptor and reduced release of I glutamate, bipolar cells depolarize, increase NT release, and ganglion fire
off centre ganglion cells
light in centre of receptive field, photoreceptor hyperpolarization, reduced e glutamate, bipolar cell hyperpolarization, decreased NT release, ganglion inhibition
visual signal processing
optic nerves > optic chiasm > optic tract > lateral geniculate nucleus > visual cortex
Alpha 1 adrenergic receptor sensitivity
more sensitive to NE than E
alpha 1 adrenergic receptor cascade
NE binds GPCR and activates PLC > PIP > DAG + IP3 > PKC > activates Ca channel
alpha 1 adrenergic receptor action
Vasoconstriction to nonessential tissues
alpha 2 adrenergic receptor sensitivity
NE>E
alpha 2 adrenergic receptor cascade
NE binds GPCR, Gi subunit inactivates AC, decreased cAMP levels, inactivates PKA, dephosphorylates Ca channels
alpha 2 adrenergic receptor action
Negative feedback loop inhibiting NE release
beta 1 adrenergic receptor sensitivity
NE = E
beta 1 adrenergic receptor cascade
NE/E binds, GPCR activates AC, increased cAMP activates PKA, activates Ca channels
beta 1 adrenergic receptor action
Greater contractive force in heart
beta 2 adrenergic receptor sensitivity
E>NE
beta 2 adrenergic receptor cascade
E binds, GPCR activates AC, increased cAMP activates PKA, inactivates MLCK
beta 2 adrenergic receptor action
PKA hyperpolarizes cell making it more prone to contraction – vasodilation
