2. Neuroanatomy

3. Neuroanatomy refers to the study of the parts and function of neurons.
Neurons are individual nerve cells.
The entirety of the human body’s neurons make up the nervous system, from the brain to the tips of the toes.

4. Neuron The basic building block of the nervous system -- a nerve cell
Neurons perform three basic tasks
Receive information
Carry the information
Pass the information on to the next neuron

5. The Basic Parts of a Neuron

6. A. Dendrites
Thin, branching fibers lined with receptors at which the dendrite receives information from other neurons. The greater the surface area, the greater the amount of information. Some dendrites are covered with spines which greatly increase its surface area.

7. B. Cell Body/Soma
Contains the (C) nucleus and other parts of the cell needed to sustain life

8. D. Axon
Wire-like structure ending in the terminal buttons that extends from the cell body

9. E. Myelin Sheath
An insulating, fatty covering around the axon that speeds neural transmissions. Axons that are myelinated appear white. Known as “white matter.”

10. F. Schwann Cells
Provide for the growth of the myelin sheath.

11. G. Nodes of Ranvier
Regularly spaced gaps in the myelin sheath around an axon or nerve fiber. This is where depolarization takes place.

12. H. Terminal Buttons
The branched end of the axon that contains neurotransmitters

13. Neural Transmission

14. Synapse
The space between the terminal buttons on one neuron and dendrites of the next neuron

15. Neurotransmitters
Chemicals contained in the terminal buttons that enable neurons to communicate.
Neurotransmitters fit into receptor sites on the dendrites of neurons like a key fits into a lock.

17. Neurotransmitters

18. At the terminal buttons, neurotransmitters are released into the synapse and passed along to the dendrites of the next neuron.

19. If enough neurotransmitters have been sent, the next neuron will fire
If enough neurotransmitters have been sent, the next neuron will fire. If not, the message ends. This is called the all-or-nothing principle.

20. All-or-None Principle
The principle that if a neuron fires it will always fire at the same intensity
All action potentials are of the same strength.
A neuron does NOT fire at 30%, 45% or 90% but at 100% each time it fires.

23. Resting Potential
The state of a neuron when it is at rest and capable of generating an action potential
The neuron is set and ready to fire

24. Resting Potential
While in resting potential, a neuron is said to be “Polarized”
negative ions are within the cell. Surrounding the cell are positively charged ions.
The ions cannot mix while in this stage

25. A neuron has a pre-set level of stimulation that needs to be met or exceeded in order for it to pass the received impulses on to the next neuron. This is called a neuron’s threshold.

26. If the threshold has been met a chain reaction begins.
The cell becomes depolarized and allows positively charged ions into the axon at the nodes of ranvier.

28. Axon – inside and out

29. Action Potential
This mix of positive and negative ions causes an electrical charge to form (an action potential).
A brief electrical charge that travels down the axon of the neuron.
A neural impulse
Considered an “on” condition of the neuron

30. Once the refractory period is complete the neuron can fire again
The “recharging phase” when a neuron, after firing, cannot generate another action potential
Once the refractory period is complete the neuron can fire again

31. Refractory Period
Excess neurotransmitters are reabsorbed by the sending neuron – this is called re-uptake
The cell becoming polarized once again.

35. Neuron firing like a Toilet
Like a Neuron, a toilet has an action potential. When you flush, an “impulse” is sent down the sewer pipe

36. Neuron firing like a Toilet
2. Like a neuron, a toilet has a refractory period. There is a short delay after flushing when the toilet cannot be flushed again because the tank is being refilled

37. Neuron firing like a Toilet
Like a Neuron, a toilet has a resting potential. The toilet is “charged” when there is water in the tank and it is capable of being flushed again
Like a Neuron, a toilet operates on the all-or-none principle – it always flushes with the same intensity, no matter how much force you apply to the handle

39. Click here to see a neuron in action!
Click here to see a quick summary!

40. Depending on what type of neurotransmitter has been released, the next neuron will react differently.
….so, since the entire body is a connection of nerves, …

41. Inhibitory vs Excitatory
Inhibitory neurotransmitters decrease the likelihood of the firing action potential of a cell while
Excitatory neurotransmitters increase the likelihood of action potential

42. Acetylcholine (ACh)
Excitatory
Involved in muscle action, learning, and memory
Undersupply - Alzheimer’s disease

43. Dopamine
Inhibitory:
Pleasure, Reward and Motivation, Motor Control over Voluntary Movements
Excessive dopamine linked to schizophrenia;

44. Serotonin Inhibitory Affects mood, hunger, sleep, and arousal
Undersupply is linked to depression; Prozac and other anti-depressants raise serotonin levels

45. Epinephrine and Norepinephrine
Excitatory: Used for arousal in the flight/fight response, plays a role in learning and memory retrieval
Adrenaline Burst of Energy (small amounts in brain)
Undersupply can depress mood

46. GABA
Inhibitory:
offsets excitatory messages (see Glutamate); helps regulate daily sleep-wake cycles
Undersupply linked to anxiety, seizures, tremors, and insomnia

47. Glutamate Excitatory Involved in memory, learning and movement
Oversupply can overstimulate the brain, producing migraines or seizures (epilepsy)

48. Endorphins
Inhibitory: Natural opiates that are involved in pain perception and positive emotions
released in response to pain and vigorous exercise

49. Drugs and Chemicals Interact with Neural Transmission

50. Some drugs that people put into their bodies are classified as agonists.
Agonists may either speed up the neural process, cause an over-release or absorption of a neurotransmitter, or block the re-uptake process.

51. Prozac blocking the re-uptake of Serotonin

52. Some agonists mimic the effects of a naturally occurring neurotransmitter
Agonist (like morphine – replacing natural endorphines)
Dendrite of receiving Neuron

53. If re-uptake is blocked, the lingering neurotransmitters in the synapse will continue to be absorbed until it is gone.
Therefore, a lingering feeling will occur

54. Cocaine – blocks the re-uptake of dopamine
Examples of Agonists
Cocaine – blocks the re-uptake of dopamine
MDMA (Ecstasy) – blocks the reuptake of serotonin
Repeated use destroys serotonin producing cells

55. Some drugs that people put into their bodies are classified as antagonists.
Antagonists may slow or stop the transmission of a neurotransmitter, or they may bind themselves to receptors on a neuron’s dendrite, thus not allowing a message to be passed on.

56. Examples of Antagonists
Curare – a poison that stops the flow of Ach – causes paralysis
Antagonist (like curare)
Neurotransmitter (such as Ach)
Dendrite of receiving Neuron

57. There are three types of neurons:
Afferent Neurons (Sensory Neurons)
Interneurons
Efferent Neurons (Motor Neurons)

58. Types of Neurons
Afferents, or “sensory neurons”, carry information from the body to the brain

59. Types of Neurons
Interneurons, found in the spinal cord and the brain
interpret incoming information and determine the next course of action

60. Types of Neurons
Efferents, or “motor neurons”, carry information from the spinal cord or the brain to the rest of the body in order to initiate behavior

61. The exceptions to the “general pathway” of neural activity are reflexes.

62. Reflexes are controlled by the spinal cord without any conscious effort on behalf of the brain.

63. Reflexes are primitive responses
protect our bodies from danger

64. Yawning (too much carbon dioxide in the blood)
Reflex
Coughing
Blinking
Yawning (too much carbon dioxide in the blood)
….etc…….

65. Reflex Sensory to spinal cord to motor… no brain processing involved….