1. Neurons: The Matter of the Mind
Chapter 7
Neurons: The Matter of the Mind

2. Cells of the Nervous System
Sensory (or afferent) neurons carry information toward the CNS from sensory receptors
Motor (or efferent) neurons carry information away from the CNS to an effector

3. Cells of the Nervous System
Association neurons (or interneurons) are located between sensory and motor neurons within the CNS where they integrate and interpret sensory signals

4. Types of Neurons in the Nervous System Sensory Motor Interneuron
Figure: 07-01
Title:
The nervous system.
Caption:
The nervous system consists of sensory neurons, interneurons, and motor neurons. Trace the pathway of the impulse from a sensory receptor that detects a change in the external or internal environment along a sensory neuron to an interneuron. In this diagram, only one sensory neuron is shown. An interneuron usually receives input from many sensory neurons. The interneuron integrates the information from the sensory neuron and stimulates a motor neuron. The motor neuron then conducts the information to a muscle or a gland (an effector).

5. Cells of the Nervous System
Glial cells (also called neuroglial cells) are more numerous than neurons and provide structural support, growth factors, and insulating sheaths around the nerves
They are able to reproduce, unlike neurons

6. Neurons (in red) and Glial Cells (in green) in muscle tissue

7. Function of Glial Cells
Protection/selective uptake - provides blood brain barrier
Guides neurons to proper destination (synapse)
Developing embryo
Adult
Nurture - Secrete nerve growth factors

8. Function of Glial Cells (cont.)
Clean-up - Mop-up chemicals & neurotransmitters
Insulation of neurons
Schwann cells in PNS
Oligodendrocyte in CNS

9. Neurons Have Dendrites, a Cell Body, and an Axon
Dendrites receive information from other neurons or from the environment
Dendrites carry information toward the cell body of a neuron

10. Neurons Have Dendrites, a Cell Body, and an Axon
A single long axon carries information away from the cell body

11. FIGURE 7.2
The structure of a neuron

12. Dendrites, Cell Body, and Axon
A nerve consists of parallel axons, dendrites, or both from many neurons
Nerves are covered with tough connective tissue

13. Dendrites, Cell Body, and Axon
Most axons outside of the CNS are electrically insulated by a myelin sheath

14. Dendrites, Cell Body, and Axon
Schwann cells (glial cells) form the myelin sheath, insulating it and allowing messages to travel faster as they jump from one node of Ranvier to the next in a type of transmission called saltatory conduction

15. FIGURE 7.3a
The myelin sheath. (a) An axon protected by a myelin sheath. The Schwann cells that form the myelin sheath are separated by nodes of Ranvier—areas of exposed axon that allow for saltatory conduction. (b) The myelin sheath forms from multiple wrappings of Schwann cell plasma membranes. (c) An electron micrograph of the cut end of a myelinated axon.

16. How a Schwann cell wraps around an axon to create a myelin sheath
FIGURE 7.3b
The myelin sheath. (a) An axon protected by a myelin sheath. The Schwann cells that form the myelin sheath are separated by nodes of Ranvier—areas of exposed axon that allow for saltatory conduction. (b) The myelin sheath forms from multiple wrappings of Schwann cell plasma membranes. (c) An electron micrograph of the cut end of a myelinated axon.

17. Cross section of an axon surrounded by myelin
FIGURE 7.3c
The myelin sheath. (a) An axon protected by a myelin sheath. The Schwann cells that form the myelin sheath are separated by nodes of Ranvier—areas of exposed axon that allow for saltatory conduction. (b) The myelin sheath forms from multiple wrappings of Schwann cell plasma membranes. (c) An electron micrograph of the cut end of a myelinated axon.

18. Dendrites, Cell Body, and Axon
The myelin sheath also facilitates nerve repair outside the CNS

19. Myelin Sheath on Neuron
Multiple sclerosis involves progressive destruction of myelin sheaths within the brain and spinal cord.

20. Depending on where the nerve damage occurs, MS can affect vision, sensation, coordination, movement, and bladder and bowel control.

21. Dendrite Axon Synapse Impulsive
The part of the neuron that carries impulses (info) away from the cell body is called ….
Dendrite
Axon
Synapse
Impulsive

22. Dendrites …. Carry information away from the cell body
Carry information toward the cell body
Receive information from other neurons

23. The myelin sheath Slows the conduction of nerve impulses
Is formed by Schwann cells wrapping around axons
Make saltatory conduction possible
Has gaps in it called “Nodes of Ranvier”

24. The Nerve Impulse Is an Electrochemical Signal
A nerve impulse, or action potential, is a bioelectrical signal involving sodium ions (Na+) and potassium ions (K+) that cross the cell membrane through the ion channels

25. FIGURE 7.4
The plasma membrane of a neuron provides two general ways for ions to enter or leave the cell: (1) diffusion through a channel or (2) active transport by a pump.

26. The Nerve Impulse
Na+ and K+ are transported across the membrane by the sodium-potassium pump

27. FIGURE 7.4
The plasma membrane of a neuron provides two general ways for ions to enter or leave the cell: (1) diffusion through a channel or (2) active transport by a pump.

28. Resting Membrane Potential
When a neuron is not conducting a nerve impulse, it is in a resting state
The sodium-potassium pump uses ATP to transport sodium ions out of and potassium ions into the neuron
The inside of a resting neuron has a negative charge relative to the outside

29. FIGURE 7.5a part 1
The resting state and the propagation of an action potential along an axon. (a) The sequential opening and closing of sodium-channel gates and potassium-channel gates produces the action potential. (b) The voltage across the membrane can be measured by electrodes placed inside and outside the axon. The graph shows the changes in voltage that accompany an action potential.

30. The Nerve Impulse
When the neuron is stimulated the sodium gates open and sodium ions enter the cell
The minimum charge that causes the sodium gates to open is called the threshold

31. Action Potential (aka, nerve impulse)
Na+ channels open: sodium moves into the axon
K+ channels open: potassium moves out of the axon
Re-establishment of the Na+ and K+ gradients by the normal activity of the sodium-potassium pump

32. FIGURE 7.5a part 2
The resting state and the propagation of an action potential along an axon. (a) The sequential opening and closing of sodium-channel gates and potassium-channel gates produces the action potential. (b) The voltage across the membrane can be measured by electrodes placed inside and outside the axon. The graph shows the changes in voltage that accompany an action potential.

33. Figure: 07-05b
Title:
The resting state and the propagation of an action potential along an axon.
Caption:
Bottom: charge restoration.

34. FIGURE 7.5b
The resting state and the propagation of an action potential along an axon. (a) The sequential opening and closing of sodium-channel gates and potassium-channel gates produces the action potential. (b) The voltage across the membrane can be measured by electrodes placed inside and outside the axon. The graph shows the changes in voltage that accompany an action potential.

35. The first and second events of an action potential are:
Ca++ gated channel opens then closes
Na+ pumped out and K+ pumped into the axon by the Na+/K+ pump
Na+ moves in then K+ moves out of the axon
Ca++ moves out of the SER and then is pumped back in

36. Axons…. Conduct impulses away from the cell body
Conduct information toward the cell body
Carry information both toward and away from the cell body

37. All-or-None and Self-Propagating Action Potentials
Action potentials are “all-or-none” responses
Action potentials are “self-propagating”
Electrical current reaches threshold throughout axon during spread of the action potential

38. Synaptic Transmission Is Communication between Neurons
Communication between neurons is by neurotransmitters; chemicals that cross the gap between two neurons

39. Communication between Neurons
A synapse is the junction between the presynaptic neuron, which sends a message to the postsynaptic neuron

40. FIGURE 7.6a
Structure of a synapse. (a) The synaptic knob at the end of the axon on the presynaptic neuron is separated from the dendrite or cell body of the postsynaptic neuron by a small gap called a synaptic cleft. Within the synaptic knob are small sacs, called synaptic vesicles, filled with neurotransmitter molecules. (b) An electron micrograph of a synapse.

41. FIGURE 7.6b
Structure of a synapse. (a) The synaptic knob at the end of the axon on the presynaptic neuron is separated from the dendrite or cell body of the postsynaptic neuron by a small gap called a synaptic cleft. Within the synaptic knob are small sacs, called synaptic vesicles, filled with neurotransmitter molecules. (b) An electron micrograph of a synapse.

42. FIGURE 7.8a
A neuron may have as many as 10,000 synapses at which it receives input from other neurons. Some synapses have an excitatory effect on the membrane of the postsynaptic neuron and increase the likelihood that the neuron will fire. Other synapses have an inhibitory effect and reduce the likelihood that the postsynaptic neuron will fire. The net effect of all the synapses determines whether an action potential is generated in the postsynaptic neuron. (The shape of the synaptic knobs shown in this electron micrograph is distorted as a result of the preparation process.)

43. FIGURE 7.8b
A neuron may have as many as 10,000 synapses at which it receives input from other neurons. Some synapses have an excitatory effect on the membrane of the postsynaptic neuron and increase the likelihood that the neuron will fire. Other synapses have an inhibitory effect and reduce the likelihood that the postsynaptic neuron will fire. The net effect of all the synapses determines whether an action potential is generated in the postsynaptic neuron. (The shape of the synaptic knobs shown in this electron micrograph is distorted as a result of the preparation process.)

44. Communication between Neurons
When an action potential (impulse) reaches the axon ending of the presynaptic neuron----
This causes the membrane of the synaptic vesicles to fuse with the plasma membrane and to release the neurotransmitter substances

45. FIGURE 7.7 part 1
Transmission across an excitatory synapse

46. Synaptic Vesicles …. Contain mitochondria Contain DNA
Contain neurotransmitters
Release neurotransmitters into the synaptic cleft

47. Communication between Neurons
Neurotransmitters diffuse across the synaptic cleft to the other side where they bind with receptors on the postsynaptic cell causing the ion channels to open

48. FIGURE 7.7 part 2
Transmission across an excitatory synapse

49. FIGURE 7.7 part 3
Transmission across an excitatory synapse

50. Presynaptic neurons signal postsynaptic neurons across the synaptic cleft by:
Electrons
Ions
ICBMs
Neruotransmitters
Texting

51. Communication between Neurons
After the neurotransmitter crosses the membrane, it is quickly broken down or pumped back into the synaptic knob of the presynaptic axon

52. Removal of Neurotransmitter from Synapse
Enzymatic breakdown
Re-uptake of neurotransmitter
Example: Dopamine transporter (re-uptake protein) knockout mouse is hyperactive and unresponsive to cocaine and amphetamines
Many drugs (legal and illegal), toxins, and venoms work at the level of the synapse

53. Communication between Neurons
If neurotransmission occurs at an excitatory synapse and enough receptor sites bind with neurotransmitter substances to cause depolarization to threshold value, an action potential is generated in the postsynaptic cell

54. Communication between Neurons
However, in an inhibitory synapse, the postsynaptic cell becomes more negatively charged and there is no action potential generated

55. Resting Membrane Potential, Graded Potential And Action Potential

56. Transfer of Information from Neuron to Post-Synaptic Membrane
Post-Synaptic Response
Release of neurotransmitter: graded potential achieved
Effects of neurotransmitter is either:
Excitatory: depolarize postsynaptic cell
Inhibitory: hyperpolarize postsynaptic cell
Role of postsynaptic neuron: integrates the relative amount of excitatory and inhibitory input

57. Points of Synaptic Regulation
Compensation (up or down regulation) occurs at several levels:
Release of Neurotransmitter
Reuptake of Neurotransmitter
Enzymatic Breakdown of Neurotransmitter
Post-synaptic Receptor for Nt

58. What would you expect to happen in the synapses of a person who chronically takes cocaine, a drug that causes excess amounts of dopamine (DA) to collect in the synapse by inhibiting DA reuptake by the pre-synaptic neuron.
There would be an increase in DA receptors on the post-synaptic membrane.
There would be a decrease in DA receptors on the post-synaptic membrane
There would be an increase in the enzymes that breakdown DA
There would be a decrease in the enzymes that breakdown DA

59. Stimulus Quality How do we distinguish light from sound?
Different stimuli (e.g, light and sound) are recognized as qualitatively different because they are sent to different areas of the brain.

60. Stimulus Intensity How do we perceive different signal intensities?
Increased frequency of impulse signals increased intensity
The number of neurons that fire increases when strength of stimulus increases

61. Neurotransmitters Different neurotransmitters play different roles
Alzheimer’s disease - Acetylcholine
Depression – Serotonin, Dopamine, Norepineph
Parkinson’s disease - Dopamine

62. Alzheimer’s disease - Acetylcholine
FIGURE 7.9
Former President Ronald Reagan died in June 2004 at the age of 93. He had Alzheimer's disease since at least His wife, Nancy Reagan, described Alzheimer's disease as "the long good-bye" because it robs people of their memories long before it takes their lives.

63. Parkinson’s disease - Dopamine
FIGURE 7.10
Actor Michael J. Fox and former heavyweight champion Muhammad Ali have Parkinson's disease, a progressive debilitating disease characterized by slowed movements, tremors, and rigidity. The symptoms result from insufficient amounts of the neurotransmitter dopamine, caused by the death of dopamine-making nerve cells in a movement control center of the brain. The Michael J. Fox Foundation for Parkinson's Research ( funds research on the early diagnosis and treatment of Parkinson's disease.

64. Inhibitors that work at the post-synapse
Curare (plant bark)
Compet. Inhibitor of Ach for its receptor on muscle cell
Alpha-bungerotoxin (black mamba venom)
Similar mechanism to curare

65. Inhibitors that work at the pre-synapse
Tetnus toxin
Blocks inhibitory input to muscle; result is excess muscle contraction
BOTOX (Botulism toxin)
Blocks Ach neurotransmitter release (exocytosis) at neuromuscular synapse
Antidepressants (SSRIs)
Selective Serotonin Reuptake Inhibitors

66. Neurotransmitters Dopamine (DA)
Generally excitatory; emotional responses, euphoria
Re-uptake blocked by cocaine and amphetamines (see KO mouse)
Parkinson’s disease: degeneration of substantia nigra area of brain leads to  DA
Schizophrenia: Thorazine and clozapine are drugs that inhibit DA release from pre-synaptic terminal

67. Neurotransmitters (cont)
Serotonin
Involved in sleep and control of mood (eg, depression)
Antidepressants/SSRIs (eg, prozac) inhibit re-uptake from synaptic cleft.
LSD mimics serotonin

68. Neurotransmitters (cont)
Acetylcholine
Neurotransmitter in neuromuscular synapses
Blocked by curare; a-bungarotoxin (snake venom), BOTOX, and nerve gas
Norepinephrine (NE)
Neurotransmitter used in pathways involved in arousal, regulation of moods such as pleasure and feeling good
Cocaine augments the effects of NE

69. Neurotransmitters (cont)
Substance P
Signals perception of pain in sensory nerves
Endorphin
Binds to opiate receptor (same one that morphine binds to) & inhibits pain by inhibiting substance P release
Thought to be responsible for “runners high”?

70. Neurotransmitters (cont)
Gamma amino butyric acid (GABA)
Tends to inhibit or slow down other pathways
Target for anti-anxiety drugs such as Valium, which enhance the action of GABA

71. Action potentials are all-or-none
Action potentials are all-or-none. Which of the following statements summarizes this principle?
An action potential can vary in both strength and duration
If a threshold stimulus is reached the action potential will always be of the same strength
Several stimuli will cause a stronger response
The effects of several stimuli are combined until the neuron fires

72. Which of the following carry impulses toward the cell body?
axon
dendrite
glial cells
Schwann cells