Neurophysiology Flashcards
dorsal root
carries sensory (afferent) information to CNS
ventral root
carriers motor (efferent) information to muscles and glands
gray matter
consists of motor and sensory nuclei
white matter
consists of axons carrying information to and from the brain
ascending tracts
carry sensory info to the brain
descending tracts
carry commands to motor neurons
interneuron
found only in the CNS (spinal cord)
cerebrospinal fluid
- produced by the choroid plexus
- provides buoyancy, nutrients, waste removal, cushioning
hydrocephalus
elevated CSF, puts pressure on the brain
blood brain barrier
prevent things from getting in the brain
-astrocytes help form this
cerebrum
blanket covering the brain
cerbellum
regulates motor activity and contains half of all neurons in the brain
pons
regulates sleep and breathing, relays motor signals between cerebrum and cerebellum (if damaged, will see paralysis)
medulla oblongata
controls cardiovascular activity and respiration
wernicke’s area
sensory info: can hear, but not make sense
-if damaged will see fluent word use with little meaning
broca’s area
motor info: can make sense, but not respond well
-if damaged will see telegraphic speech
corpus callosum
communication between two hemispheres
- left: mathematic
- right: spacial/artistic
basal ganglia
action selection by disinhibition
- “prevented until needed”
- linked to OCD, Tourette’s, Parkinson’s
hippocampus
involved in memory and learning (short to long term)
amygdala
involved in memory and emotion (memories with strong emotional content)
thalamus
relay and integrate sensory and motor information
pineal gland
secrete melatonin (circadian rhythm)
hypothalamus
homeostasis
diencephalon
thalamus, pineal gland, hypothalamus, pituitary gland
-injury may result in amnesia
MRI
imaging of magnetic fields around water
PET
injection of a short half-life radioactive ligand to measure activity in the brain
EEG
used in sleep therapy and to localize seizure activity as in epilepsy
glial cells PNS
schwann cells form myelin sheath
glial cells CNS
oligodendrocytes form myelin sheath
capacitance
number of ions needed to change membrane voltage
conductance
ease of moving ions across membrane
potential of a neuron
- depolarize when sodium enters cell
- hyperpolarize when potassium exits and when chloride enters
Na-K Pump
concentrates potassium inside cell and depletes sodium inside
Na+ equilibrium potential
+60 mV
K+ equilibrium potential
-90 mV
Nernst equation
how will an ion try to drive a cell
open channels
“door” create water filled pore
- faster
- move with gradient (diffusion)
carriers
“revolving door” never form an open channel between two sides of the membrane
- slower
- do not have an equilibrium potential and do not use diffusion
primary active transport
energy dependent (ATP)
secondary active transport
uses concentration gradient for energy
channel properties
selectivity
conductivity
gating: voltage, ligand, mechanical
voltage gated sodium channels
4 domains with peptide crossing membrane 6 times
S4
forms voltage sensor
S5 and S6
form activation gate
P loop
ion selectivity
third cytoplasmic loop
forms inactivation gate
acetycholine receptor
-ligand gated
ionotropic glutamate receptors
- four subunits
- each subunit crosses membrane 3 times
ex) AMPA, NMDA, Kainate
excitatory ionotropic receptors
Ach and glutamate (Na and K)
inhibitory ionotropic receptors
GABA and glycine (Cl)
graded potential
- slow, analog, variable amplitude, usually produced at synapse
- get smaller with distance (can’t send info over long distances)
- can be depolarizing or hyperpolarizing
- signals can sum
action potential
- fast, short duration, fixed size, digital signals
- can only be depolarizng
- all or none
where is the action potential initiated?
trigger zone
action potentials are produced by graded potentials
at the trigger zone, graded potentials must be at least threshold voltage to evoke and AP
what determines the frequency of an AP?
the size of the graded potential
what determines size of graded potential?
strength of the stimulus
sodium current is regenerative
positive feedback mechanism, chain reaction
absolute refractory period
determined by Na channel inactivation
-cannot produce another AP
relative refractory period
determined by potassium channel after hyperpolarization
-stronger 2nd stimulus could produce another AP
miniaturization
myelin used to speed up conduction
saltatory conduction
“jumping” from one node to the next
multiple sclerosis
disease causes loss of myelin and slows conduction
hypokalemia
increased blood K+ conc. brings membrane closer to threshold
hyperkalemia
decreased blood K+ conc. hyperpolarizes membrane and makes neuron less likely to fire and AP in response to a stimulus that would normally be above threshold
chemical synapse
- depolarization
- calcium channels open and calcium enters
- neurotransmitter travels across synaptic cleft
- binds with receptors on postsynaptic cleft
SNARE proteins
attach the vesicle to the presynaptic membrane
Botulinum toxins
interfere with SNARE proteins and prevent ACh vesicle fusion
tetanus toxins
disrupts other SNARE proteins to prevent fusion of glycine vesicles
synaptotagmin
binds calcium and stimulates vesicle fusion
Acetylcholinesterase
enzyme that deactivates ACh
metabotropic receptors
G-protein coupled receptors and 7-transmembrane receptors
- activate G-proteins inside cell
- can stimulate production of second messengers, enzymes and molecules
- can be amplified
- are slower than ionotropic
cAMP
adenylyl cyclase an amplification enzyme, converts ATP to cAMP to activate protein kinase A, which phosphorylates other proteins to lead to a cellular response
glycine
major inhibitory transmitter in spinal cord
glutatmate
major excitatory transmitter in brain
IP3
second messenger that releases internal calcium stores
divergent pathway
one presynaptic neuron branches to affect a large number of postsynaptic nuerons
convergent pathway
many presynaptic neurons converge to influence a smaller number of postsynaptic neurons
(ex. rods in eye)
postsynaptic summation
multiple small graded potentials arrive at trigger zone together and sum to make an AP
temporal summation
quick second stimulation to sum two subthreshold potentials together to make an AP
spatial summation
two or more presynaptic inputs are active at same time and add together
summation can be negative
if there are more inhibitory neurons that fire than excitatory
presynaptic inhibition
hyperpolarize of suppress calcium channels at the synapse (no neurotransmitter release)
paired pulse facilitation
(presynaptic facilitation) Increased transmitter release during second pulse due to accumulated, residual calcium in the presynaptic terminal. Short term effect in response to rapid stimulation
NMDA receptor
unusual glutamate receptor
- permeable to Na, K, Cl
- Mg can plug the pore (very voltage dependent)
AMPA
glutamate receptor that works with NMDA
- fast brief depolarization by AMPA
- slower prolonged depolarization by NMDA
- much longer and stronger effect when paired
long term potentiation
High frequency stimulation of the presynaptic neuron causes strong activation of postsynaptic AMPA receptors and NMDA receptors
long term depression
Low frequency stimulation produces only a small rise in internal calcium in the postsynaptic cell.
small receptive fields
produce high resolution
convergence increases
receptive field sensitivity but reduces resolution
lateral inhibition
enhances perception of stimulus (improves resolution)
phasic sensory receptor
rapidly adapt to constant stimulus and turn off. the fire once more when stimulus turns off. (event detector)
tonic sensory receptor
slowly adapting receptors that respond for the duration of a stimulus (encode intensity and duration)
olfaction
- metabotropic pathway
1) odorant stimulates a membrane receptor
2) G protein (Golf) stimulated
3) stimulates adenylyl cyclase which produces cAMP
4) opens cationic excitatory channel
5) Ca opens an excitatory Cl channel
fovea
region of sharpest vision
- light strikes the photoreceptors here
- no rods, only cones
- highest spatial resolution
rhodopsin in photoreceptors
G-protein coupled receptor found in membranes of the outer segment of photoreceptors
phototransduction
1) light activates rhodopsin
2) rhodopsin stimulates PDE to break down cGMP
3) sodium channels begin to close and photoreceptor hyperpolarizes
4) less glutamate released
taste receptors that are GPCRs
sweet, bitter, umami
- increase IP3 and internal Ca
- activate TPR channels which allow Na influx
- activation of voltage-gated Ca channels and transmitter release
taste receptors that activate membrane channels
sour and salt
-sensitive to large changes in concentration
gustducin
activates g protein in sweet, bitter, umami taste buds
salt
- codes for high sodium
- na entering sodium channel
sour
- codes for spoiled food
- protons entering channel or blocking potassium channels, may directly activate a TRP channel
bitter
codes for poison
umami
codes for protein
sweet
codes for carbohydrate energy source
hair cells
-Movement of cilia in one direction adds tension
to the protein bridge, increasing the open time of the channel
-Movement in the opposite direction reduces the tension and reduces the open time of the mechanical channel.
location of hair cells
distal end- low frequency vibrations
proximal- high frequency
adaption in hair cells
calcium stimulates the movement of protein bridge attachments down along the cilia
paravertebral ganglia
Sympathetic nerves travel between these
prevertebral ganglia
nerves that supply GI tract
sympathetic nurotransmitters
acetylcholine (pre) and norepinephrine (post)
fight or flight
parasympathetic neurotransmitters
acetylcholine (pre and post)
rest and digest
adrenal gland
acts like sympathetic system under stress (postganglion)
preganglionic neurons
ionotropic receptors
postganglionic neurons
metabotropic receptors
what nerves stimulate sweat glands?
sympathetic
reciprocal inhibition
regulated contraction by controlling level of muscle excitation (inhibit motor neuron, not the muscle)
enteric system
- controls circular and longitudinal muscles
- ACh is excitatory
- NO is inhibitory
sympathetic role in GI
minimal, slow motility and decrease secretion
parasympathetic role in GI
dominant (the vagus nerve), and activates nicotinic receptors.
esophageal peristalsis
contraction- ACh released from ENS
relaxation- NO releases from myenteric ENS
relaxation of lower sphincter- NO
achlasia
failure to relax lower esophageal sphincter
skeletal muscle
- striated
- voluntary (somatic motor neuron)
- all or none
- fastest contraction
cardiac muscle
- striated
- involuntary
- graded potential
- slightly slower than skeletal contraction
smooth muscle
- smooth
- involuntary
- graded potential
- slow contraction
motor unit
number of muscle fibers innervated by one motor neuron
innervation ratio
number of muscle fibers per motor neuron
low ratio = fine control
motor pool
all the motor neurons that supply one muscle
small motor unit size
activates slow red muscles
- first to be activated
- last to stop contracting
- show less fatigue
large motor unit size
activates fast white muscles
sarcomere
the functional contractile unit in a muscle cell
-calcium and ATP required
actin
thin filament
myosin
thick filament
-has a head group that flips towards M line to pull actin
troponin
binds to intracellular calcium to initiate contraction
-moves tropomyosin to allow myosin to bind
tropomyosin
can lie on top of actin and blocks myosin head group to prevent the contraction
T tubule
brings action potentials into interior of muscle fiber
sarcoplasmic reticulum
stores calcium
power stroke
cause movement of actin towards center line
endplate potential
ACh produces a large depolarization of the motor end plate
relaxation of muscle contraction
slow twitch, tonic muscles pump calcium more slowly back into SR
unfused tetanus
stimuli are far enough apart to allow muscle to relax slightly between stimuli
complete tetanus
muscle reaches steady tension
muscle spindle reflex
the addition of a load stretches the muscle and the spindles creating a reflex contraction
low muscle tone
flaccidity, hypotonia
-down syndrome
high muscle tone
rigidity, hypertonia
-cerebral palsy
decerebrate rigidity
transection at midbrain resulting in increased tone in extensors of all 4 limbs
decorticate rigidity
local lesions of motor cortex, effects contralateral side of body
-increased tone in extensors on contralateral side of stroke
Golgi tendon organ
detects muscle tension
nuclear bag intrafusal fibers
relay movement and length information
nuclear chain intrafusal fibers
relay length information
alpha motor neurons
contract the muscle spindle
monosynaptic stretch reflex
involves only 2 neurons: sensory neuron from spindle and somatic motor neuron to muscle
ex) patellar reflex
polysynaptic reflex pathways
cause an arm/leg to be pulled away from a noxious stimulus
flexion reflexes
pull limbs away from painful stimuli
renshaw cell
inhibitory neuron in spinal cord
- stimulated by a motor neuron and feeds back to inhibit that same motor neuron
- excited by ACh and release glycine
strychnine
- inhibits glycine receptors
- leads to increased motor activity and tetanic contractions
clostridium tetani
- toxin inhibits glycine release from renshaw cells
- leads to tetanic contractions
