2 primary cell types in nervous system

1
2 primary cell types in nervous system

• neurons 10 to 100 billion neurons
• Role
• 2. glial cells
• provide support, nutrients, myelin, cleanup, etc.
  for neurons

2
(No Transcript)
3
(No Transcript)
4
2 primary cell types in nervous system

• neurons 10 to 100 billion neurons
• can vary tremendously in size and shape but all
  have 3 components
• cell body or soma
• contains genetic material, provides nutrients,

5
2 primary cell types in nervous system

• 1. neurons 10 to 100 billion neurons
• Role
• can vary tremendously in size and shape but all
  have 3 components
• cell body or soma
• contains genetic material, provides nutrients,
• dendrites
• axon

6
How do neurons communicate?

• within neurons electrically
• between neurons - chemically

7
Neuron receiving info
Information traveling down neuron
8
Ramon Y Cajal

• developed Golgi Stain
• first determined space between neurons
• synapse

9
A brief discussion about communication within a
neuron

• changes in electrical potential

10
Neurons can exist in one of 3 states

• the resting state
• the active state or action potential
• neuron is firing
• conveying info to other neurons or organs
• the recovery or refractory state

11
How do we know about what is happening in the
neuron?

• giant squid axon
• why was work done with the giant squid axon?

12
(No Transcript)
13
(No Transcript)
14
At rest

• inside of the axon has a slightly negative charge
  relative to outside the axon
• called the membrane or resting potential
• ( -60 mV)
• why?

15
Neuron stimulated

• see depolarization (change from negative inside
  neuron to more positive)
• threshold if a great enough depolarization
  occurs, an action potential will occur
• action potential very quick - milliseconds

16
When the action potential occurs..

• see depolarization (change from negative (
  -60mV) inside neuron to more positive ( 30 mV))

17
threshold
resting potential
18

• hyperpolarization
• after action potential return to negative
  (actually a more negative state than to begin
  with)

19
What causes these changes in electrical potential?

• All axons and cells have a membrane
• thin bilayer that surrounds cell allowing some
  chemicals and ions in but keeping others out
• axons also have a large number of protein
  channels that when open allow ions (charged
  molecules) to flow in or out

20
(No Transcript)
21
What causes these changes in electrical potential?

• Ions flowing across the membrane causes the
  changes in the potential
• Ions are molecules that contain a positive or
  negative charge
• anion negative charge
• cation positive charge

22
Some important ions for neuronal communication

• Na sodium
• HIGHER CONCENTRATION OUTSIDE THE AXON
• Cl- chloride
• HIGHER CONCENTRATION OUTSIDE AXON
• K potassium
• higher concentration inside the axon
• A- anions -large (-) molecules with a negative
  charge (stuck inside the axon)

23
OUTSIDE AXON (EXTRACELLULAR FLUID)
INSIDE AXON (intracellular)
Na
Cl-
Na
Cl-
A-
Cl-
Cl-
A-
Cl-
Na
Na
Cl-
Cl-
A-
Na
Na
Na
A-
Na
Cl-
Na
Na
A-
Cl-
Na
Cl-
Cl-
Na
Na
A-
Cl-
Cl-
Cl-
Cl-
Na and Cl- are in higher concentration in the
extracellular fluid
Neuron at Rest
24
INSIDE AXON
OUTSIDE AXON (EXTRACELLULAR FLUID)
Cl-
K
K
K
Cl-
A-
Na
Cl-
Na
A-
K
Na
A-
Cl-
Na
A-
K
Na
Cl-
Na
K
K
K and negative anions are in higher
concentration in the intracellular or inside the
axon
Neuron at Rest
25
Some forces that play a role in maintaining
membrane potential

• concentration gradient
• ions diffuse from higher concentration to lower
  concentration

26
What would each ion do if the ion channel opened
based on the concentration gradient?
Na
K
Cl-
27
Some forces that play a role in maintaining
membrane potential

• concentration gradient
• ions diffuse from higher concentration to lower
  concentration
• electrical gradient -
• opposite charges attract so ions are attracted to
  an environment that has a charge that is opposite
  of the charge they carry!

28
example of electrostatic forces
29
What would each ion do if the ion channel opened
based on electrostatic forces ?
Na
K
Cl-
30
What drives the action potential?

• opening of Na channels and influx of Na ions

31
(No Transcript)
32
What happens if sodium channels are blocked?

• lidocaine, novocaine, cocaine
• TTX tetrototoxin
• Sagitoxin-
• red tides

33
(No Transcript)
34

• http//faculty.washington.edu/chudler/ap.html

35
What about communication between neurons?
36
(No Transcript)
37
Communication between neurons

• most psychoactive drugs work via this mechanism
• chemical transmission via the synapse
• neurotransmitters

38
label some things

• presynaptic ending axon releases chemical if
  the neuron generated an action potential

39
presynaptic ending (axon)
40
label some things

• presynaptic ending axon releases chemical if
  the neuron generated an acton potential
• postsynaptic ending can be dendrite, cell body,
  or axon
• receives chemical signal from neuron
• synapse tiny gap between neurons

41
Other things to notice in presynaptic ending

• Ca channels -
• synaptic vesicles
• contain neurotransmitter

42
(No Transcript)
43
What happens at level of synapse when an action
potential occurs?

• Ca2 enters presynaptic ending via Ca channels
• synaptic vesicles bind to presynaptic ending and
  release their neurotransmitter
• Neurotransmitter crosses synapse and binds to
  receptor on postsynaptic side

44

• http//www.williams.edu/imput/synapse/pages/II.htm
  l

45
postsynaptic receptors

• protein embedded in membrane
• mechanism for neurotransmitter to influence
  postsynaptic activity by binding to receptor

46
What happens when neurotransmitter binds to the
postsynaptic receptor?

• can cause the opening of localized ion channels
  in the postsynaptic ending
• Na or
• K or
• Cl-

47
What happens when neurotransmitter binds to the
postsynaptic receptor?

• can cause the opening of localized ion channels
  in the postsynaptic ending
• IF
• Na channels open - Na enters
• local excitation (or depolarization)
• K or
• Cl-

48
What happens when neurotransmitter binds to the
postsynaptic receptor?

• can cause the opening of localized ion channels
  in the postsynaptic ending
• IF
• Na
• K channels open K leaves the cell
• causes local inhibition or hyperpolarization
• Cl-

49
What happens when neurotransmitter binds to the
postsynaptic receptor?

• can cause the opening of localized ion channels
  in the postsynaptic ending
• IF
• Na
• K or
• Cl- channels open influx of Cl-
• causes local inhibition or hyperpolarization

50

• Graded Potentials-
• these local changes in ion flow are called graded
  potentials
• has impact in limited region
• increases or decreases the likelihood of the
  neuron receiving info to generate an action
  potential.

51
How do graded potentials contribute to the
likelihood of an action potential?

• graded potentials are summed at axon hillock if
  great enough depolarization to reach threshold
  axon generates an action potential

52
What happens when neurotransmitter binds to the
postsynaptic receptor?

• if Na channels open - increases likelihood of
  generating an action potential
• if K channels open - - decreases the likelihood
  of an action potential
• if Cl- channels open - decreases the likelihood
  of an action potential

53
(No Transcript)
54
(No Transcript)
55
Ways that graded potentials differ from action
potentials

• Graded Potentials-
• action potentials are all or none while graded
  potentials decrease over space and time
• localized has impact in limited region
• action potentials always excitatory while graded
  potentials can be excitatory or inhibitory

56
Two types of graded potentials

• excitatory -
• EPSPs excitatory postsynaptic potentials
• Na ion channels
• IPSPs inhibitory postsynaptic potentials
• K or Cl- ion channels

57
(No Transcript)
58
2 ways that neurotransmitter exert these effects

• ionotrophic - directly opening the ion channel
• occurs and terminates very quickly

59
(No Transcript)
60
2 ways that neurotransmitter exert these effects

• ionotrophic - directly opening the ion channel
• occurs and terminates very quickly
• metabotropic - more indirect
• ultimately opens ion channel via stimulating a
  chemical reaction through a "second messenger
  system"
• takes longer but lasts longer

61
(No Transcript)
62
How do we get rid of the transmitter from the
synapse?

• 2 main ways
• 1. reuptake - most common
• transporter on presynaptic ending
• a means of recycling
• a common way for drugs to alter normal
  communication

63
transporter
64

• enzyme degradation
• enzyme - speeds up a reaction
• ex. acetylcholine (ACh) is broken down by
  acetylcholinesterase (AChE)

65

• http//et.middlebury.edu/scivizlab/animations/neur
  otransmission/lowres/normal.mov

66
NT binding to postsynaptic receptor

• lock and key analogy

67
Neurotransmitter represents a key Receptor
represents the lock Other keys can represent
drugs
68
What are possibilities?

• agonist mimics the neurotransmitter
• antagonist blocks the neurotransmitter
• partial agonists/ partial antagonists