neuroanatomy Flashcards
lecture 3
1
Q
2 types of cells in the brain
A
neurons and glia
2
Q
glia cells
A
keep the brain alive, provide nutrients, provide physical support, regulate extracellular fluid
3
Q
neuron cells
A
do the ‘psychology’ bit, many types
4
Q
how many neurons and glia are there in the brain
A
around 86 million for both
5
Q
by adulthood, how many connections should we have between neurons
A
100 trillion
6
Q
5 types of glial cells
A
astrocyte, microglia, oligodendrocyte, satellite cells and Schwann cells
7
Q
astrocyte function
A
star shaped cells that provide physical and nutritional support for neurons
8
Q
microglia
A
like astrocytes, digest parts of dead neurons
9
Q
oligodendrocyte
A
provide the insulation (myelin) to neurons in the central nervous system
10
Q
satellite cells
A
physical support to neurons in the peripheral nervous system
11
Q
schwann cells
A
provide the insulation (myelin) to neurons in the peripheral nervous system
12
Q
cell body
A
metabolic centre of a neuron
13
Q
dendrites
A
short processes emanating from the cell body, which receive most of the synaptic contracts from other neurons
14
Q
axon hillock
A
cone shaped region at the junction between the axon and cell body
15
Q
axon
A
long, narrow process that projects from the cell body
16
Q
myelin sheath
A
fatty insulin around many axons
17
Q
nodes of ranvier
A
gaps between sections of myelin
18
Q
axon terminals
A
branching processes at the end of the axon
19
Q
terminal buttons
A
button like endings of the axonal branches
20
Q
what speed do nerve impulses travel across the axon
A
around 100mph
21
Q
cell membrane
A
defines cell boundary, consists of a lipid bilayer, embedded with a variety of protein molecules with specific functions
22
Q
lipid bilayer
A
double layer of fat like molecules
23
Q
2 things inside the cell body
A
cytoplasm, mitochondria, nucleus, mictrotubles
24
Q
cytoplasm
A
jellylike substance that fits the cell
25
mitochondria
organelles in the cytoplasm responsible for extracting energy from nutrients, generates most of the chemical energy needed to power the cells
26
nucleus
part of the cell containing chromosomes
27
microtubules
means of rapid transport within neurons
28
what does a neuron do
processes and transmits information, forms connections between different areas
29
what are bundles of axons called in the central NS
tracts/pathways
30
what are clusters of cell bodies called in the central NS
nuclei
31
what are enclosed, cable like bundle of nerve fibres (axons) called in the peripheral NS
nerve
32
what are clusters of cell bodies called in the peripheral NS
ganglia
33
experiment of squid axons
Squid axons will stay alive in sea water for a couple of days
The experiment measures the electrical charge generated by an axon
Wire electrode is placed in the sea water, a glass microelectrode is inserted into the axon, the voltmeter measures the charge across the membrane
Shows that the inside of the axon is negatively charged with respect to the outside
34
membrane potential
measuring the charge across the cell membrane / difference in the electrical charge between the inside and outside of the neutron
35
resting potential
stable, negative charge of a neuron (-70mV) when its not actively sending a signal
36
action potential
rapid, all or nothing electrical impulse that travels down the axon when the neuron reaches the threshold of excitation
37
refractory period
brief time after an action potential during which a neuron is unable, or less likely to fire another action potential due to temporary inactivation of ion channels and restoration of resting potentials
38
threshold of excitation
minimum membrane potential a neuron must reach to trigger an action potential, typically around -55mV
39
repolarisation
return of the membrane potential to a negative value after depolarisation, primarily due to the outflow of potassium ions
40
depolarisation
process where the neurons membrane potential becomes less negative due to the influx of sodium ions, moving it closer to the threshold
41
hyperpolarisation
temporary increase in the negativity of the membrane potential beyond the resting potential, making the neuron less likely to fire another action potential
42
what 2 types of fluid contain different ions
intracellular and extracellular
43
ion
number of protons determine the element, atom of any given element with more or fewer electrons
44
isotope
atom to any given element with more or fewer neutrons than usual
45
since electrons are negatively charged, what does removing an electron do to the electrical change
increases electrical charge
46
cations
positively charged ion
47
anions
negatively charged ion
48
structure of an atom
protons and neutrons inside the nucleus, electrons surround the nucleus
49
what fluid is the organic anions (A-) in
intracellular fluid
50
what fluid is the chloride ions (Cl-) in
predominantly in the extracelluar fluid
51
what fluid is the sodium ions (Na+) in
predominately in the extracellular fluid
52
what fluid is the potassium ions (K+) in
predominately in the intracellular fluid
53
2 main forces controlling the pull of ions
electrostatic force and diffusion
54
electrostatic force
opposites attract - particles with the same charge repel whilst the opposite charge attracts
55
what do anions repel in electrostatic force
anions
56
what do cations repel in electrostatic force
cations
57
what do anions attract in electrostatic force
cations
58
diffusion
molecules like to spread out evenly - molecules want to distribute themselves evenly throughout a solution in which they are dissolved, move from regions of high concentration to regions of low concentration
59
what is cell membrane normally impermeable to
sodium
60
cell membranes contain ion channels
gates which allow ions to enter or leave the cell, these are voltage dependent (only open when depolarisation has been reached)
61
what happens if the threshold of excitation is reached
sodium channels are open, allowing sodium to rush into the cell - action potential has been triggered
62
ligands
molecules that bind together, ligand gates only open when a certain molecule is bound to it
63
mechanically gated ion channels
open in response to a change of shape
64
1st step of neural transmission
threshold of excitation is reached, and sodium channels open allowing sodium to enter the cell, action potential begins, rapid change in membrane potential
65
2nd step of neural transmission
potassium channels open allowing potassium to leave the cell, channels require a larger depolarisation than sodium to allow activation
66
3rd step of neural transmission
action potential reaches its peak, sodium channels before refractory so no more sodium can enter cell, they won’t reopen again until the membrane has reached its resting potential
67
4th step of neural transmission
potassium continues to leave the cell (inside of cell is now +ye so K+ is driven out by diffusion and electrostatic pressure), allows membrane potential to return to resting level (repolarisation)
68
5th step of neural transmission
potassium channels start to close and sodium channels rest for another action potential
69
6th step of neural transmission
because potassium channels close slowly, membrane overshoots its resting potential for a while (hyperpolarisation)
70
what is used in order to maintain a higher concentration of sodium in the extracellular fluid
sodium potassium pump
71
sodium potassium pump
Sodium potassium pump binds 3 sodium ions and a molecule of ATP
Splitting of ATP provides energy to change the shape of the channel, the sodium ions are driven through the channel
Sodium ions are released to the outside of the membrane, and the new shape of the channel allows 2 potassium ions to bind
Release of the phosphate allows the channel to revert to its original form, releasing the potassium ions on the inside of the membrane
72
myelinated axons
insulates axon preventing ions passing through cell membrane, nodes of rangier are areas free of myelin which have concentrations of ion channels, action potential jumps along the axon, myelination increases speed of axonal conduction
73
Loewi
proved chemical transmission across the synapse using frog hearts which are supplied by 2 peripheral nerves, 1 had the vagus nerve interact, the other had it removed. hearts placed into fluid baths which stimulated vagus nerve in heart A but heart B was slowed - fluid must contain a substance secreted by vagus nerve projecting to heart
74
small neurotransmitters
packed into vesicles by the terminals Golgi complex, vesicles are stored next to the presynaptic membrane
75
large neurotransmitters
assembled in cytoplasm of the cell body and paicked into vesicles by Golgi complex, transported to the terminals by mictrotubules
76
how are neurotransmitters released
Presynaptic membrane has many voltage-activated calcium channels
Action potential causes these channels to open, allowing calcium into the button
Increases in calcium causes the vesicles to fuse with the presynaptic membrane and empty their contents into the synaptic cleft
77
what happens when the neurotransmitter binds with the postsynaptic receptor
causes neurotransmitter dependent ion channels to open in cell membrane, of this signal is sufficient, may trigger action potential
78
what will opening a sodium channel cause
depolarisation - excitatory postsynaptic potential
79
what will opening a potassium channel cause
hyperpolarisation - inhibitory postsynaptic potential
80
how does neurotransmitter stop having its action (2 methods)
reuptake or enzyme degradation
81
reuptake
once released, neurotransmitters are almost immediately drawn back into presynaptic cell
82
enzyme degradation
enzymes in synaptic cleft break the neurotransmitters apart so they can no longer have an effect
83
agonist
activates receptor
84
antagonist
blocks receptor, producing no effect
