2. The Nervous System

3. Functions of the Nervous System
Nervous System – master controlling and communicating system of the body.
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
Nervous system does not act alone to maintain homeostasis. The endocrine system and hormones are a slower method.

5. Structural Classification of the Nervous System
Central nervous system (CNS) – includes the brain and spinal cord.
Peripheral nervous system (PNS) – all the nerves outside the brain and spinal cord

6. Functional Classification of the Peripheral Nervous System
Sensory (afferent) division - Nerve fibers that carry information to the central nervous system
Figure 7.1
p. 223

7. Functional Classification of the Peripheral Nervous System
Motor (efferent) division - Nerve fibers that carry impulses away from the central nervous system
Two subdivisions
Somatic nervous system = voluntary; skeletal muscles
Autonomic nervous system = involuntary; smooth muscles, cardiac muscle, hormones
Figure 7.1
p. 223

8. Organization of the Nervous System
Figure 7.2
p. 224

9. Nervous Tissue: Support Cells (Neuroglia)
Neuroglia – supporting cells in the CNS; means “nerve glue”
Astrocytes - Abundant, star-shaped cells; make up half of all nerve tissue.
Brace and anchor neurons to capillaries
Form a living barrier between capillaries and neurons and play a role in exchange
Control the chemical environment of the brain picking up excess ions and recapturing neurotransmitters
Figure 7.3a
p. 225

10. Nervous Tissue: Support Cells (CNS)
Microglia - Spider-like phagocytes Dispose of debris such as dead brain cells and bacteria
Ependymal cells - line cavities of the brain and spinal cord and Circulate cerebrospinal fluid with Cilia
Figure 7.3b–c
p. 225

11. Nervous Tissue: Support Cells (CNS)
Oligodendrocytes - produce myelin sheath around nerve fibers in the central nervous system
Figure 7.3d
p. 225

12. Nervous Tissue: Support Cells (PNS)
Satellite cells - Protect neuron cell bodies
Schwann cells - Form myelin sheath in the peripheral nervous system
Figure 7.3e
p. 225

13. Nervous Tissue: Support Cells
Neuroglia cells CAN NOT transmit nerve impulses
Neuroglia cells never lose their ability to divide (mitosis) Neurons DO lose the ability to divide (paralyisis)

14. Nervous Tissue: Neurons
Neurons = nerve cells. Cells highly specialized to transmit nerve impulses (messages) from one part of the body to another.
Major regions of neurons
Cell body – nucleus and
metabolic center of the cell
Processes – fibers that extend
away from the body
Axon Hillock – cone-like region
that leads to the axon
Fig. 7-4 a / b p. 227

15. Neuron Anatomy Processes -(Extensions) outside the cell body
(up to 3 ft)
Dendrites – conduct impulses toward the cell body (one or more)
Axons – conducts impulses away from the cell body (usually only one)
Figure 7.4a
p. 227

16. Axons and Nerve Impulses
Axons end in axon terminals (many times in two or more branches)
Axon terminals contain vesicles (tiny sacs) with neurotransmitters
Axon terminals are separated from the next neuron by a gap (they never touch)
Synaptic cleft – gap between adjacent neurons
Synapse – junction between nerves
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17. Schwann cells – produce myelin sheaths in jelly-roll like fashion
Nerve Fiber Coverings
Schwann cells – produce myelin sheaths in jelly-roll like fashion
Nodes of Ranvier – gaps in myelin sheath along the axon
You Tube clip later showing this
Figure 7.5
p. 228

18. Neuron Cell Body Location
Most are found in the central nervous system
Gray matter – cell bodies and unmylenated fibers
White matter – mylenated fibers; clusters of cell bodies within the central nervous system
Ganglia – collections of cell bodies outside the central nervous system in the PNS

19. Functional Classification of Neurons
Neurons are classified by the direction of the nerve impulse relative to the CNS
Sensory (afferent) neurons - Carry impulses from the sensory receptors TO the CNS
Cutaneous sense organs such as pain receptors (heat, cold, pressure as pain)
Proprioceptors – detect stretch or tension
Motor (efferent) neurons - Carry impulses FROM the CNS to the muscles, organs or glands to respond to the stimuli

20. Functional Classification of Neurons
Interneurons (association neurons) - Found in neural pathways in the central nervous system
Connect sensory and motor neurons
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21. Neuron Classification
Figure 7.6
p. 229

22. Structural Classification of Neurons
Multipolar neurons – many extensions from the cell body; most common type of neuron
Figure 7.8a
p. 231

23. Structural Classification of Neurons
Bipolar neurons – one axon and one dendrite
Figure 7.8b
p. 231

24. Structural Classification of Neurons
Unipolar neurons – have a short single process leaving the cell body
Figure 7.8c
p. 231

25. Neuron Physiology (function)
Irritability – ability to respond to stimuli
Conductivity – ability to transmit an impulse
The plasma membrane at rest is polarized
Fewer positive ions are inside the cell than outside the cell (outside of cell is slightly + and inside of cell is slightly - )

26. Starting a Nerve Impulse
Depolarization – a stimulus depolarizes the neuron’s membrane
A deploarized membrane allows sodium (Na+) to flow inside the membrane causing it to become more positive
The exchange of ions initiates an action potential in the neuron
Figure 7.9a–c
p. 232

27. The Action Potential
If the action potential (nerve impulse) starts, it is propagated over the entire axon (all or nothing; firing a gun)
Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane (becomes more negative again; K is also a positive ion)
The sodium-potassium pump, using ATP, restores the original configuration (3 na+ out and 2 k+ in)

28. Nerve Impulse Propagation
The impulse continues to move away from the cell body
Impulses travel faster when fibers have a myelin sheath
The impulse will “jump” from one node of Ranvier to the next avoiding the mylinated area this is called Saltatory conduction
(also talks about schwann cells making myelin sheath)
Figure 7.9d–f
p. 232

29. Continuation of the Nerve Impulse between Neurons
Impulses are able to cross the synapse to another nerve
An Action Potential arriving at the axon terminal signals the vesicles to release Neurotransmitter
Neurotransmitter vesicles fuse with the plasma membrane and are released into the synaptic cleft by Exocytosis.
The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter
An action potential is started in the dendrite. Na+ moves in briefly.

30. How Neurons Communicate at Synapses
Figure 7.10
p. 233

31. Homeostatic Imbalnce
Multiple Sclerosis (MS) - Myelin sheaths around nerve fibers are gradually destroyed and become hard. The current becomes short-circuited, and the person loses the ability to control their muscles. This is an autoimmune disease which means the body is destroying itself.
Cold and Continuous pressure hinder impulse conduction because they interrupt blood circulation to neurons. Holding ice causes numbness or pressure caused the foot to “fall asleep”. When you return circulation of blood the impulses begin working again and it gives the unpleasant prickly feeling … thought you might want to know!