01 Neurophysiology Flashcards
1
Q
Neurons can
A
receive and transmit impulses
conduct electrical impulses by varying the voltage gradient across their cell membranes
communicate with target cells like other neurons, muscles, glands through chemical or electrical synapses
2
Q
Neurons can be classified according to (2 things)
A
function and morphology
3
Q
function classifications
A
sensory, motor, interneurons
4
Q
morphology classifications
A
multipolar, bipolar, unipolar, pseudounipolar
5
Q
multipolar cells and example
A
2 or more dendrites and a single axon (motorneurons of the spinal cord)
6
Q
bipolar cells and example
A
one dendrite and one axon (sensory neurons in the olfactory mucosa)
7
Q
unipolar cells
A
no dendrites, only an axon (which is rare in vertebrates)
8
Q
pseudounipolar cells and example
A
a single neural process formed by fusion and bifurcation of a dentrite and axon
process functions in an axon-like manner, carrying signals from a peripheral sensroy region toward the CNS (dorsal root ganglion neurons)
9
Q
organelles in the cell body
A
- free ribosomes
- rough endoplasmic reticulum (RER)
- Golgi complex
- smooth endoplasmic reticulum
- mitochondria
- endosomes, lysosomes, vesicles
- cytoskeletal components
10
Q
free ribosomes
A
protein synthesis
11
Q
rough ER
A
synthesis of proteins to be packaged (identifiable as Nissl bodies using light microscopy)
12
Q
Golgi complex
A
modification and packaging of protein, enzymes, chemical messengers
13
Q
smooth ER
A
synthesis of lipids and carbohydrates
14
Q
mitochondria
A
energy production (which is mainly used for threshold stabilization)
15
Q
endosomes, lysosomes, vesicles
A
transportation
16
Q
cytoskeletal components and their purpose
A
- microfilaments (cell membrane)
- neurofilaments (assist with development and regeneration of axons and dendrites)
- microtubules (maintain cell shape and aid in transport to and from soma)
- material produced in the cell body that can be transported to the axon via anterograde transport
- material can be transported via retrograde transport to the soma (ex: horseradish peroxidase)
17
Q
3 types of neural processes/neurites
A
dendrites, axons, axon terminals
18
Q
dendrites
A
- transmit signals to the cell body
- relatively short, branching extensions of the soma
- variable number per neuron (can have none or many)
- surface area can increase with more branching
- prominal region may contain organelles
19
Q
axons
A
- transmit impulses away from the soma
- 1 (or none in rare, specialized cases)
- axon does not have free ribosomes or RER
- axon has mitochondria, SER< vesicles, neurofilaments, and microtubules
- originates from axon hillock
20
Q
3 regions of the axon
A
- initial segment - transition zone containing voltage-gated sodium channels, where action potentials are generated
- axon proper - can be short or up to a meter long. has a constant diameter. larger diameters have higher conduction velocities. may have collaterals
- terminals/boutons/end feet - axon may branch, forming a terminal arborization and enabling synaptic contact with many targets (other neurons, muslces, or glands)
21
Q
myelinated neurons
A
- oligodendrocytes in CNS
- Schwann cells in PNS
- short myelinated segments are internodes and nodes of Ranvier are the spaces between them
- ion channels are concentrated at the nodes of Ranvier
22
Q
divergence
A
to extend in different directions from a common point. one action potential projecting to many targets
23
Q
convergence
A
tending to meet at a point. many inputs converge into one signal
24
Q
feedback
A
activity in a neuron can influence the probability of additional activity in the same neuron, either directly or via interneuron
25
recurrent excitation (feedforward)
makes excitatory even last longer and with more excitation
26
recurrent inhibition (feedback)
creates specific timing patterns by inhibition of cells at a specific time
27
parallel processing
you don't have to finish one before starting another; many processes can happen at once
28
synapse and the 2 types
a specialized intercellular junction that permits communication between neurons in the CNS or between a neuron and an effector cell
1. chemical - presynaptic cell releases neurotransmitters into the synaptic cleft. the neurotransmitter binds to receptors on the postsynaptic cell membrane causing an effect
(most common in mammals)
2. electrical - gap junction - ions or small molecules go from one cell to another through channels present in the cell membrane of both cells
29
chemical synapse types
ionotropic - neurotransmitter binds to receptors on the postsynaptic membrane which opens the ion channel
----- EPSP and IPSP
metabotropic - neurotransmitters that are neuromodulators bind to G-protein coupled receptors and have a slower, indirect effect on ion channels through second messenger systems; slower/not as strong
30
synapses can have a variety of configurations
- axodendritic (most common)
- axoaxonic
- axosomatic
- dendrodendritic
31
Resting membrane potential
- resting potential is about -70 mV which is polarized
- membrane potential represents stored energy that can be released as an action potential when the cell is stimulated
- inside of the cell is negatively charged compared to the outside of the cell
32
resting membrane potential is established by
chemical forces - tend to distribute each ion evenly inside and outside the cell by diffusion through non-gated ion channels
electrical forces - tend to equalize the electrical charge inside vs outside the cell (opposite charges attract and similar charges repel)
the sodium-potassium pump - an active transport protein uses energy in the form of ATP to move Na+ out of the cell and move K+ into the cell
33
initiation of an action potential
- summation of all EPSPs and IPSPs onto a postsynaptic cell changes action potential at the axon hillock where AP is initiated
34
threshold level of depolarizaiton and what happens
-55mV
voltage-gated Na+ channels will open and Na+ ions will flow into the cell to depolarize it rapidly
35
propagation of the action potential
advancement of an action potential in a single direction along the length of the membrane
36
unmyelinated axon AP propagation
propagation flows directly down axon in linear fashion
37
myelinated axon AP propagation
propagation jumps between nodes of Ranvier
saltatory conduction
much faster
38
refractory state
can not be influenced by changes in membrane potential
39
exception to normal uni directional signaling
peripheral nerve is stimulated artificially using electrical stimulation
- Na+ channels are not in the refractory state when the stimulation is delivered to a point along the axon, propagation occurs in both directions
- retrograde component dissipates when it reaches the cell body or when it collides with another action potential traveling in anterograde direction
40
transmission at chemical synapse
- arrival of an AP at the terminal opens voltage-gated calcium channels
- Ca+2 influx into the axon terminal
- Ca+2 triggers the fusion of synaptic vesicles with the presynaptic membrane
- exocytosis = the NT is released into the synaptic cleft where it diffuses across the cleft
- binds to a receptor on the postsynaptic membrane
41
presynaptic inhibition
neural inhibition in which an interneuron reduces the influx of Ca+2 into the presynaptic neuron
reduces the likelihood that the NT will be released
42
3 main types of NTs
1. amino acids
2. amines
3. peptides
43
amino acid NTs
small molecules that are fast acting
- examples of excitatory NTs = glutamate and aspartate
- examples of inhibitory NTs = GABA and glycine
- can be either excitatory or inhibitory
44
amines NTs
small molecules that are neuromodulators
- typically binds to G - protein-coupled receptors and has a slower effect with second messenger systems
- can be either excitatory or inhibitory
- examples: acetylcholine, serotonin, histamines, and catecholamines (dopamine, epinephrine, norepinephrine)
45
peptide amino acids
- large molecules that act via 2nd messenger systems
- can be either excitatory or inhibitory
- dynorphin, beta-endorphin, enkephalin, and substance P
46
are there more neurons or glia cells
glia outnumber neurons by 10 to 1
47
2 types of astrocytes
1. fibrous astrocytes in white matter
2. protoplasmic astrocytes in grey matter which surround synapses and have receptors for NT on their cell membranes
48
astrocyte functions
- physical and nutritional support of neurons
- separate neurons from each other, and occupy most space in the CNS
- surround neural elements and form a perivascular covering around the blood vessels
- control concentrations of ions in the extracellular space
- metabolize extracellular neurotransmitters
- regulate development, stabilization, and functions of synapses
- provide a scaffold during development, for newly formed neurons to migrate to the final destination
49
oligodendroglia
mostly in white matter (some in grey matter)
form myelin sheath around axons by enveloping the axon and layering membrane
cytoplasm gets squeezed out between layers of myelin. creates tight wrappings of cell membranes (composed of 70-80% lipids)
high electrical resistance with low conductivity
1 oligodendrocyte can myelinate up to 30 axons
50
microglia
- small macrophages in CNS
- remove pathogens and cellular debris by phagocytosis after neural damage
- participate in inflammatory and degenerative reactions
51
ependymal cells
- the lining of ventricles of the brain and the central canal of the spinal cord
- have cilia that help circulate cerebrospinal fluid
- participate in forming choroid plexus and producing CSF
- ex: tanycytes
52
tanycytes
modified ependymal cells in 3rd ventricle that have long processes that extend to the hypothalamus and are thought to deliver CSF to hypothalamus
53
glial scar tissue
after neural injury, astrocytes, oligodendroglia an microglia all proliferate and form glial scar tissue, isolating the damaged tissue and inhibiting neural repair
54
number of neurons and synapses
100 billion neurons
each with 7,000 contacts/synapses
total for 500 trillion synapses in the brain
55
anterograde
from soma to terminal
56
retrograde
from terminal to soma
57
myelin has high/low electrical resistance
high -- it repels electricity so that is why electricity hops around
58
Na+ K+ Cl- order inside/outside
Inside: K+ and protein
Outside: Na+ and Cl-
59
Nernst equation
1 ion species at a time
equilibrium potentials when held constant of just one species
- Ex: when Na+ channels become more permeable, more Na+ flows in and brings the threshold closer to +60
