1
Q
what are the 3 functions of the nervous systems
A
- receive info - using sensory neurons (receptors) to receive from external env
- integrates info - organizes the info and brings it together with already stored info
- transduces info - sends appropriate signals to appropriate target
2
Q
what are the two main parts of the nervous system ?
A
- central nervous system (CNS)
- makes up the brain and spinal cord - peripheral nervus system (PNS)
- part of system outside brain and spinal cord
- consist of sensory (afferent) and motor (efferent) neurons
3
Q
what are the two type of cells found in nervous system ?
A
- neurons - info centres
- glial cells - support cells
4
Q
define neurons
A
- generate and transmit electrical impulses often over long distances
5
Q
explain the soma + bundles in PNS & CNS
A
- cell body
- contains the nucleus and all biosynthetic machinery
- centre of chemical processes, keeps cell alive and functioning
- terminology for bundles of cells body in NS
PSN = ganglia
CNS = nuclei
6
Q
explain the dendrites
A
- slender processes that receive info
- transmit electrical signals towards soma
7
Q
explain the axon + bundles in CNS & PNS
A
- cytoplasmic extension that sets out info
- transmit electrical signal away from soma
-terminology for bundles of axons in NS
PSN = nerves
CNS = tracts
8
Q
explain axon terminals
A
- end of an axon
- connection between neuron and other cells
- participate as a part of the synapse (where info is passes) -> presynaptic
9
Q
what are pseudounipolaer neurons
A
pseudounipolar
- somatic sensory neurons meaning sensations from skin, joints, muscles (ex in hands)
- axon & dendrites fuse during development into a single process
10
Q
what are bipolar neurons
A
bipolar
- smell/vision sensory neurons
- contain a single axon & dendrite
11
Q
what are multipolar neurons
A
multipolar (CNS and Efferent)
- have a single axon process
- have 2 or more dendrites
Multipolar = many inputs, one output → common for decision-making and motor control neurons.
12
Q
explain afferent (sensory) neurons
A
- receive info from receptor cells
- they then transmit the sensory info to the CNS
- cell bodies are located outside of CNS
- long cytoplasmic extensions transmit info to cells within CNS
13
Q
explain interneurons
A
- decide what to do
- located inside CNS
- make up 96% of neurons
- transmit info signals within CNS, either laterally within spinal cord or vertically to the brain
- integrate info received from afferent neurons and previous info and transmit signal to efferent neurons
14
Q
quick difference between efferent and afferent
A
afferent = to CNS
efferent = exits CNS
15
Q
explain efferent motor neurons
A
- receive info from interneurons
- efferent cell bodies are located within CNS
- cytoplasmic extensions transmit info to effectos
- effector carry out the message
- effectors = muscles, glands
16
Q
explain general glial cells
A
- associated with neurons
- do not carry info long distance but do communicate with nearby neurons using electrical and chemical signals
- serve neurons in 2 ways
1. aid in nerve impulse conduction
2. maintain the microenvironment around neurons
17
Q
explain schwann glial cells
A
Schwann cells
- special glial cells that are wrapped around axons
- forms myelin - layers of membrane wrapped around axon.
- myelin acts as a electrical insulator
18
Q
explain satellite
glial cells + diagrams
A
satellite cells
- non-mylenating Schwann cells
- support nerve bodies (soma)
19
Q
explain oligodneria glial cells
A
Oligodneria
- CNS version of Schwann cells
- wrap around axon and forms myelin to insulate axon
20
Q
explain Astroglia glial cells
A
Astroglia
- small star shaped cells
- regulate blood flow in the brain
- contacts blood vessels and neurons (blood brain barrier)
- maintain neuron microenviormnt, extracellular fluid around neurons
21
Q
explain microglia glial cells
A
Microglia
- very small specialized immune cell (macrophage like)
- function is to remove damaged cells and foreign invaders
22
Q
explain Ependymal glial cells
A
Ependymal
- epithelial cells that produce cerebral spinal fluid (CSF)
- creates selectively permeable barrier between compartments if brain
23
Q
how do neurons transmit electrical impulses ?
A
via energy stored as an electrochemical gradient
24
Q
what are the electrical principles
A
- body is electrically neutral. law of conservation of electrical change means charge in a process is 0
- opp attract like repel
- separating opps requires energy
- cell membrane is insulator which allows for seperation of electrical charge
- there is an electrical gradient. ICF = neg ECF = pos
- ion channels allow electrical charge to move through the membrane
25
explain membrane potential m
- all living cells have a membrane potential , they are polarized electrically
- there is a relative difference in cations and anions on either side of membrane
- difference of electrical potential between inside and outside of a cell is membrane potential
- excitable tissues (nervous & muscle) use rapid change of membrane potential when they are excited which allows neurons to conduct an electrical signal and muscles to contract
- membrane potential is measure in millivolts (mV)
26
what is the first property that determines membrane potential
unequal distribution of key ions between ICF and ECF
- Na+, Ca2+, and Cl- are higher in ECF
- K+ is higher in ICF
- anions (large neg intercellular proteins) are higher In ICF
27
what is the second property that determines membrane potential
selective movement of these ions across the membrane
- due to size anions do not travel across membrane
- conc differences of Na+ and K+ are maintained by the Na+-K+ pump (uses ATP for energy to drive ions against gradient)
- ions can move cross membrane through specific protein channels -> channels can be passive (leak) or gated
- easier for K+ to move passively due to large number of passive channels for K+ compared to Na+
28
what is equilibrium potential ?
- membrane potential that exactly opposes the conc gradient of an ion -> where electrical and chemical forces acting on an ion are equal and opposite
- for any single ion you can calculate electrical potential of the cell needed to generate an equilibrium state, if you know conc gradient by Nernst equation
29
explain equilibrium potential specifics
EP for K+ is -90mV
EP for Na+ is +60mV - both are hypothetical and will never reach it
- cell will never reach equilibrium because cell would be static and stop
30
explain Nernst equation
Eion = EP for any single ion
61 = is a constant
z = electrical charge of ion
- equation looks at what membrane potential would be if the membrane was permeable to only one ion (eg. only Na+, K+)
- but in living systems there are multiple ions that contribute to membrane potential
31
explain resting membrane potential
- charge difference between inside and outside of a cell at REST
- typical for neuron is -70mV (close to K+ as it is no.1 contributor)
32
why is it called resting membrane potential?
resting = membrane potential is at resting state
membrane potential = the electrical and chemical gradients caused by ions (source of stored potential energy)
33
what happens to a nueron after it sends a signal ?
neuron is no longer at rest -> moves away from resting membrane potential
34
what sets the resting membrane potential?
the conc of each ion and their relative permeability
- Na+, Ca2+, Cl- higher ECF
K+ higher ICF
35
how does permeability work in cell membrane ?
- more permeable to certain ions
- some can cross much more easy than others ex. K+ much better than Na+
- the ion contribution to resting potential is proportional to its permeability
- the more easier it can cross membrane, the more important it is to resting potential
- molecules that cannot cross do not contribute to resting potential (Ca2+)
- GHK equation predicts membrane potential using multiple ions
36
basic GHK equation
- considers membrane potential for each ion
37
how are electrical signals created ?
when there is a change in permeability of the cell to a given ion, then the ion can move down (leave) its electrochemical gradient
- NAK pump offsets passive movement of NAK at rest
- very few ions can cause a change in resting potential (-70mV)
- open NA = NA enter
- open K = K can leave
38
explain depolarization
- decrease in membrane potential difference
- cell membrane potential becomes less negative
39
explain hyperpolarization
- an increase in membrane potential difference
- cell membrane potential becomes more negative
40
how is ion permeability controlled ?
- neurons contain a variety of gated ion channels that regulate movement of ions
- gated ion channels can be controlled by stimuli
41
explain mechanically gated ion channels
Mechanically gated
- found in sensory neurons
- open in response to physical forces (stretch)
42
explain ligand gated ion channel
LIgand Gated
- respond to ligands such as neurotransmitters
43
explain volatge gated ion channels
Voltage gated
- respond to changes of voltage
- important in initiation and conduction of electrical signals along the axon
44
what are the 4 major types of selective ion channels in the neuron
1. Na+
2. K+
3. Ca2+
4. Cl-
45
what are the two types of signals generated by neurons ?
1. short distance signals
- short distances -> graded potentials
2. long distance signals
-long distances -> action potentials
46
what are the charectaristcis of graded potentials
- depolar or hyppol
- occur in dendrites or cell body of neurons
- triggered by open/closing of ion channel
- started by ions entering cell from ECF
- graded because amplitude of potential is proportional to the triggering event
- short distance through neuron
- lose energy strength
47
why do graded potentials lose energy ?
Current leak
- some positive charges leak back with the depolarization wave
Cytoplasmic resistance
- cytoplasm restricts flow of the current
- greater impact closer to the flow problem point (like throwing a rock in a lake, wave gets smaller as distance from rock grows)
48
what causes and how do the ions to enter the cell ?
it is initiated by the neurotransmitters (molecules released by neurons) binding to membrane receptors & opening ion channels
49
what are the events that follow the binding of a nuerotransmitter on an ion channel
1. ion channels open
2. ions move into (Na) or out (K) the neuron along their electrochemical gradient
3. wave of depol or hyperpol spreads through the cell
50
how does signal strength of a neurotransmitter work?
- determined by # of ions entering cell
- graded potentials diminish in strength as distance increases. as they are meant for short distance
51
explain depolarizing graded potentials ?
- makes membrane potential less neg
- brings membrane potential closer to threshold potential (-55mV)
- Excitatory Post Synaptic Potentials (EPSP) bc they increase the chance of exciting the axon to fire
52
explain hyperpolarizing graded potentials ?
- hyperpolarize cell membrane potential
- makes mem potential more negative
- takes membrane potential further from threshold potential
- called Inhibitory Post Synaptic Potentials (IPSP) bc they decrease the chance of exciting the axon to fire
- inhibit cell from firing action potential
53
what are the charectaristics of action potentials ?
- differ from graded potentials in 2 ways
1. all action potentials are identical
- no volume control they are only on or off
2. they do not diminish in strength as they travel long distances
- single is strong over the entire journey
54
how are action potentials initiated, specifically the location of initiation ?
- action potentials start at the trigger zone
- known as the integrating center of neuron
- trigger zone is different for various kinds of neurons
- in sensory (afferent) it is adjacent to the receptor
- in efferent neurons & interneurons it is the axon hillock and the initial segment (very first part of axon)
55
how are action potentials initiated, specifically the trigger ?
Graded potentials sum at the axon hillock.
If membrane reaches threshold (~–55 mV) → Na⁺ channels open → action potential fires.
If threshold isn’t reached → no action potential.
56
what are phases 1-3 of action potential
1. resting membrane potential is at -70mV
2. depolarizing stimulus
3. membrane depolarizes to threshold -> voltage gated Na+ & K+ channels begin to open
57
what are phases 4-6 of action potential
4. rising phase (depol) -> rapid Na+ entry depolarizes the cell (to a max of aprox +30mV)
5. Na+ channels close and slower K+ channels open -> results in a peak of the AP
6. repol phase -> K+ exit results in membrane potential travel towards resting membrane potential
58
what are phases 7-9 of action potential
7. hyperpol phase (undershoot) -> membrane potential overshoots resting potential bc K+ channels remain open and additional K+ exits the cell
8. voltage gated K+ channels close -> less K+ leaks out of cell
9. membrane returns to resting ion perm ->retention of K+ and leak of Na+ into tor axon brings membrane potential back to -70mV
59
generally describe sodium gated ion channels
- have two gates
- important to regulate ion movement during an AP
60
explain the state of the activation gate of voltage gated ion channels
closed at resting mem potential to prevent Na+ influx
61
explain the inactivation gate of voltage gated ion channel
ball and chain of amino acids on cytoplasmic side of the membrane is open at resting membrane potential
62
what are the sequence of events impacting the voltage gated Na+ channel
resting - closed - open
threshold reached - opening - open
depol - open - open
peak - open - closing
after peak - closed - closed
63
how does the mem potential return to the resting level?
Na⁺ stops, K⁺ drops, pump resets.
K+ ions leave the cell -> falling phase of AP
- neurons also have voltage gated K+ channels in their membranes
- slower to open than Na+ channel -> depol to threshold triggers opening of K+ channels
- gating tential (full opening) is around +30mV
- compared to full opening at -55mV for Na+ channel
64
BIOL 273
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