1. Cellular Anatomy Lecture 2
Psychology 210
Cellular Anatomy
Lecture 2

2. Cells of the Nervous System
Neurons
Information processing and communicating nerve cells
Glia
Addressed later

3. What do you know about neurons coming into this class?
How does a neuron communicate with another neuron?
What type of signal is processed in a neuron?
What are the parts of a neuron?

4. Parts of a Neuron 3 main parts Dendrites Soma (cell body) Axon
Receive information
Soma (cell body)
Cellular maintenance
Axon
Transmits information

5. Dendrites Tree like processes Receives information from other neurons
Dendritic spines
Create more area for axons to transmit information
Change depending on the amount of activity
This is one of the suggested bases for learning and memory
A neuron can have multiple dendrites

6. The soma Nucleus- contains DNA Nucleolus- constructs ribosomes
Endoplasmic reticulum- contains ribosomes that construct proteins
Golgi apparatus- “packages” proteins
Mitochondria- produces energy

7. The Axon Transmits information to other neurons Myelin sheath
insulation that aids in the speed of the neural transmission
Axon terminal
End of the axon
Contains neurotransmitters
Also called terminal buttons

8. More on the Axon Axon hillock Nodes of Ranvier
Where the action potential begins
Nodes of Ranvier
Segments of bare axon not covered by myelin

9. Giant Squid Used to study axons in the 1930s-1940s
Extra large axon visible to the eye
Doesn’t have myelin, so it is extra large to add conductance

10. Characterization of neurons
Sensory neurons
Translates incoming sensory information into an electrical signal
Afferent Neurons
Conduct information towards the brain from the muscles and senses
Interneurons
Neurons in the spinal cord and the brain that both communicate a signal and process that signal
Efferent Neurons
Conduct information away from the brain to the muscles and senses
Motor Neurons
Translates electrical signal to the muscles and glands

11. Not all neurons look the same
Named by the number of extensions from the cell body
Unipolar
One extension that branches into dendrites and an axon
Bipolar
Two extensions: one axon and one dendrite
Multipolar
Many extensions: one axon, many dendrites

12. Unipolar Neurons Found primarily in human embryos and invertebrates
Sensory neurons that conduct impulses into the brain

13. Bipolar Neurons
Found primarily as sensory neurons in vision, audition and olfaction

14. Multipolar neurons Found everywhere else Brain
Peripheral autonomic nervous system
Spinal cord

15. What happens in a nerve
Neurons communicate information to other neurons
The signal itself is an electrical signal within the neuron
Action Potential
From neuron to neuron, communication is chemical

16. The Resting Potential Two forces at work in a neuron
Potassium Ions
Two forces at work in a neuron
Force 1: Equilibrium: the idea that the concentration of a molecule tries to remain constant throughout the medium (substance)

17. The Resting Potential
Ex. Smells: the garbage begins to smell in one spot, but the smell slowly expands throughout the house
The smell gets lighter and lighter as it expands throughout the house
It tries to spread out as evenly as possible

18. Status of the main players (ions)
Sodium (Na+): more of it outside of the neuron
Potassium (K+): more of it inside of the neuron
Chloride (Cl-): more of it outside of the neuron

19. Based on equilibrium…
What does Na+, K+, and Cl- want to do? Are they “happy” where they are?
What direction will they move if allowed?

20. Due to equilibrium… Na+ wants to move inside the neuron
K+ wants to move outside the neuron
Cl- wants to move inside the neuron

21. What about charge? Does charge play a role in things?
According to charge, how might the ions react?

22. How do charges react to each other?
Opposites attract
Like charges repel

23. One more piece to the puzzle
There are large molecules inside the neuron with negative charges

24. Now which way do the ions want to go?
Potassium:
Which way does equilibrium push?
What about the charge?

25. Now which way do the ions want to go?
Chloride:
Which way does equilibrium push?
What about the charge?

26. Now which way do the ions want to go?
Sodium:
Which way does equilibrium push?
What about the charge?

27. At rest Resting potential -70mV Potassium can cross the membrane
Sodium and Chloride cannot cross the membrane
What will potassium want to do at rest?

28. Stimulation
When stimulated by another neuron, some Na+ channels are opened
K+ channels close

29. The action potential
If the signal is strong enough, it makes it to the axon hillock
If strong enough, an action potential is generated
Threshold
Begins an action potential

30. The action potential
Depolarization: occurs when Na+ flows into the cell
Due to Na+ channels opening

31. The action potential
Now, there is more of a positive charge inside than outside (the Na stops coming in for the same reasons the K did originally, a balance of two forces) this represents the peak of the AP
At the beginning of the AP, Na channels open and Na enters the cell

32. How’s potassium feeling now?
Sodium moving inside the cell made the inside of the cell more positive
This repels potassium to move outside

33. The action potential
K+ channels open at the peak and K+ flows out of the cell
This repolarizes the cell and even overshoots the resting potential of before
Called hyperpolarization
Then the Na/K pump brings the K back inside the cell and the Na back outside the cell
2 K for every 3 Na
Uses energy (ATP)

34. The action potential
At the peak, K+ channels open and K+ exits the cell
Conditions are now back where they started in terms of potential and charge, but the ions are in opposite positions

35. The action potential
The Sodium Potassium pump restores the original environment of the resting potential so that the neuron can fire yet again
This is known as the refractory period

36. Graded Potentials Action Potentials are referred to as “all-or-none”
Either get an action potential or not
Inputs that don’t reach threshold: Graded Potentials
Can add up across synapses/inputs to reach threshold

37. Saltatory Conduction Insulation is not perfect
Signal loses strength down the axon
Regeneration of the Action Potential occurs at each break in the myelin

38. At the Axon Terminal Vesicles containing neurotransmitters are present
When an action potential reaches the axon terminal, Ca2+ channels open up and this causes the fusing of the vesicles to the membrane and the release of the neurotransmitters into the synaptic cleft

39. In the Synaptic Cleft
Neurotransmitters cross the membrane and bind to receptors on the receiving neuron
Depending on the neurotransmitter, it can either excite or inhibit the post-synaptic neuron
Excitatory Postsynaptic Potential (EPSP)- the excitation of the receiving neuron
Inhibitory Postsynaptic Potential (IPSP)- the inhibition of the receiving neuron

40. Neurotransmitters Various chemicals
Can either excite the receiving neuron or inhibit it
Acetylcholine- an excitatory NT typically found in the muscles
GABA- an inhibitory NT typically found elsewhere in the nervous system

41. How transmission occurs
Multiple synapses on each neuronal dendrite
Some can excite while others inhibit
Axon potentials can be created by multiple EPSPs from multiple neurons
Called Spatial Summation

42. How transmission occurs
One synapse can fire repeatedly on the same dendrite within a short temporal window (time period)
Axon potentials can be created by multiple EPSPs from a single neuron
Called Temporal Summation

43. Summary: One last thing
Transmission within the neuron is electric
Via action potentials
Transmission between neurons is chemical
Via neurotransmitters

44. Glial cells Astrocytes- structural support and blood brain barrier
Oligodendrocytes- myelination of axons CNS
Schwann cells- myelination of axons PNS
Microglia- clean up