1. The Nervous System

2. Functions of the Nervous System
Figure 7.1

3. Functions of the Nervous System
Sensory input — gathering information
To monitor changes occurring inside and outside the body
Changes = stimuli
Integration
To process and interpret sensory input and decide if action is needed

4. Functions of the Nervous System
Motor output
A response to integrated stimuli
The response activates muscles or glands

5. Crash Course: Part 1

6. Organization of the Nervous System
Figure 7.2

7. Structural Classification of the Nervous System
Central nervous system (CNS)
Brain
Spinal cord
Peripheral nervous system (PNS)
Nerves outside the brain and spinal cord
Spinal nerves
Cranial nerves

8. Functional Classification of the Peripheral Nervous System
Sensory (afferent) division
Nerve fibers that carry information to the central nervous system
Motor (efferent) division
Nerve fibers that carry impulses away from the central nervous system

9. Functional Classification of the Peripheral Nervous System
Motor (efferent) division (continued)
Two subdivisions
Somatic nervous system = voluntary
Autonomic nervous system = involuntary

10. Neuron Classification
Figure 7.6

11. Neurons
= nerve cells
Cells specialized to transmit messages

12. Figure 7.4

13. Nervous Tissue: Neurons
Figure 7.5

14. Nervous Tissue: Neurons
Cell body
Main functional unit of the neuron
Contains:
Nucleus
Large nucleolus
Processes outside the cell body
Dendrites—conduct impulses toward the cell body
Axons—conduct impulses away from the cell body

15. Dendrite - conduct impulses toward the cell body
Nissle substance (bodies) – rough ER
Neurofibrils – filaments that help maintain cell shape
Axon hillock – the beginning of the axon
Axon - conduct impulses away from the cell body
Schwann cells – cells that surround the axon
Nodes of Ranvier -- gaps in myelin sheath along the axon
Myelin sheath -- white, fatty material covering axons (insulates)
Axon terminals – ends of the axon

16. Nervous Tissue: Neurons
Axons end in axonal terminals
Most cells average about 10,000 axon terminals
Axon terminals contain vesicles with neurotransmitters (chemicals that excite or inhibit neurons or effector cells)
Axon terminals are separated from the next neuron by a gap
Synaptic cleft—gap between adjacent neurons
Synapse—junction between nerves

17. Neuron Cell Body Location
Most neuron cell bodies are found in the central nervous system
White matter – condensed areas of myelinated fibers
Gray matter — areas of unmyelinated fibers
Ganglia —collections of cell bodies outside the central nervous system

18. Structural Classification of Neurons
Multipolar neurons—many extensions from the cell body
Where found?
BRAIN
Figure 7.8a

19. Structural Classification of Neurons
Bipolar neurons—one axon and one dendrite
Where found?
SENSE ORGANS
Figure 7.8b

20. Structural Classification of Neurons
Unipolar neurons—have a short single process leaving the cell body
Where found?
SKIN
Figure 7.8c

21. Crash Course: Part 2

22. Nerve Impulse
The principle way neurons communicate is by generating and propagating ACTION POTENTIALS (AP).
Only cells with excitable membranes (like muscle cells and neurons) can generate APs.
An AP is a brief reversal of membrane potential.
In neurons, an AP is called a NERVE IMPULSE and only axons can generate one.
An AP involves the movement of Na+ and K+ ions moving in and out of the neuron, resulting in changes in POLARITY.

23. All or None Response
If the action potential (nerve impulse) starts, it is propagated over the entire axon
There are NO partial impulses.
The impulse happens completely or not at all.
Impulses travel faster when fibers have a myelin sheath.
saltatory conduction: impulse jumps from node to node

24. Action Potential
First, remember how DIFFUSION works… Bozeman

25. Nerve Impulses Resting neuron Depolarization
The plasma membrane at rest is polarized
Fewer positive ions are inside the cell than outside the cell
Depolarization
A stimulus depolarizes the neuron’s membrane
A depolarized membrane allows sodium (Na+) to flow inside the membrane
The exchange of ions initiates an action potential in the neuron

26. Nerve Impulses Repolarization
Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane
The sodium-potassium pump, using ATP, restores the original configuration

27. Action Potential video

28. Nerve Impulses
Figure 7.9a–b

29. Nerve Impulses
Figure 7.9c–d

30. Nerve Impulses
Figure 7.9e–f

31. Action Potential explained

36. Transmission of a Signal at Synapses
Impulses are able to cross the synapse to another nerve
Neurotransmitter is released from a nerve’s axon terminal
The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter
An action potential is started in the dendrite

37. Transmission of a Signal at Synapses
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Neurotrans- mitter binds to receptor on receiving neuron’s membrane
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
Receptor
Neurotransmitter
Na+
Neurotransmitter broken down and released
Ion channel opens
Ion channel closes
Transmission of a Signal at Synapses
Figure 7.10

38. Action potential arrives Axon of transmitting neuron
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Action potential arrives
Figure 7.10, step 1

39. 2. Vesicle fuses with plasma membrane
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Vesicle fuses with plasma membrane
Ion channels
Transmitting neuron
2. Vesicle fuses with plasma membrane
Figure 7.10, step 2

40. 3. Neurotransmitter is released into synaptic cleft
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
3. Neurotransmitter is released into synaptic cleft
Figure 7.10, step 3

41. 4. Neurotransmitter binds to receptor on receiving neuron’s membrane
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Neurotrans- mitter binds to receptor on receiving neuron’s membrane
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Neurotrans- mitter binds to receptor on receiving neuron’s membrane
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
4. Neurotransmitter binds to receptor on receiving neuron’s membrane
Figure 7.10, step 4

42. Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Neurotrans- mitter binds to receptor on receiving neuron’s membrane
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
Receptor
Neurotransmitter
Na+
Ion channel opens
REUPTAKE SYSTEM
Once neurotransmitters have stimulated the receiving neuron’s membrane, the excess neurotransmitters are recaptured by the transmitting neuron.
Figure 7.10, step 5

43. Transmission of a Signal at Synapses
Axon terminal
Vesicles
Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Neurotrans- mitter binds to receptor on receiving neuron’s membrane
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
Receptor
Neurotransmitter
Na+
Neurotransmitter broken down and released
Ion channel opens
Ion channel closes
Transmission of a Signal at Synapses
Figure 7.10, step 6

44. Figure 7.10, step 7 Axon terminal Vesicles Synaptic cleft
Action potential arrives
Synapse
Axon of transmitting neuron
Receiving neuron
Neurotrans- mitter is re- leased into synaptic cleft
Neurotrans- mitter binds to receptor on receiving neuron’s membrane
Vesicle fuses with plasma membrane
Neurotransmitter molecules
Ion channels
Transmitting neuron
Receptor
Neurotransmitter
Na+
Neurotransmitter broken down and released
Ion channel opens
Ion channel closes
Figure 7.10, step 7

45. Distribution in the Central Nervous System
Neurotransmitter
Distribution in the Central Nervous System
Functions Affected
Drugs That Affect It
Dopamine
Midbrain, Ventral tegmental area (VTA), Cerebral cortex, Hypothalamus
Pleasure and reward Movement, Attention, Memory
Cocaine, Methamphetamine, Amphetamine. In addition, virtually all drugs of abuse directly or indirectly augment dopamine in the reward pathway
Serotonin
Midbrain, VTA, Cerebral cortex, Hypothalamus
Mood, Sleep, Sexual desire, Appetite
MDMA (ecstasy), LSD, Cocaine
Norepinephrine
Sensory processing, Movement, Sleep, Mood, Memory, Anxiety
Cocaine, Methamphetamine, Amphetamine
Endogenous opioids (endorphin and enkephalin)
Widely distributed in brain but regions vary in type of receptors, Spinal cord
Analgesia, Sedation, Rate of bodily functions, Mood
Heroin, Morphine, Prescription painkillers (Oxycodone)
Acetylcholine
Hippocampus, Cerebral cortex, Thalamus, Basal ganglia, Cerebellum
Memory, Arousal, Attention, Mood
Nicotine
Endogenous cannabinoids (anandamide)
Cerebral cortex, Hippocampus, Thalamus, Basal ganglia
Movement, Cognition and memory
Marijuana
Glutamate
Widely distributed in brain
Neuron activity (increased rate), Learning, Cognition, Memory
Ketamine, Phencyclidine, Alcohol
Gamma-aminobutyric acid (GABA)
Neuron activity (slowed), Anxiety, Memory, Anesthesia
Sedatives, Tranquilizers, Alcohol

46. Impact of Drugs on Neurotransmission