1. Chapter Nine The Nervous System

2. Introduction to the Nervous System
Section One
Introduction to the Nervous System

3. Functions of the Nervous System
Sensory input- information gathered by sensory receptors about internal and external changes
Integration- interpretation of sensory input
Motor output- activation of effector (muscles and glands) produces a response

4. Functions of the Nervous System

5. Divisions of the Nervous System
Central Nervous System (CNS)
Brain and spinal cord
Integration and command center
Peripheral nervous system (PNS)
Nerves outside brain & spinal cord
Paired spinal and cranial nerves carry messages to and from the CNS

6. Peripheral Nervous System Functional Classification
Sensory (afferent) division: Nerve fibers that carry information to the central nervous system
1 Somatic Afferent Fibers
voluntary
convey impulses from skin, skeletal muscles, and joints
2 Visceral Afferent Fibers
Involuntary
convey impulses from visceral organs

7. Motor (Efferent) Division
Transmits impulses AWAY from the CNS and takes it to the effector organs 2 Types: Somatic and Autonomic Nervous Systems
Somatic Nervous System
Voluntary
Conscious control of skeletal muscles
(Good pic on next slide)
Autonomic Nervous System
Involuntary
Visceral Nerve Fibers (for smooth muscle, cardiac, & glands)
2 types (continued……)

8. Functional Division of the Autonomic NS
Sympathetic
Fight or Flight
Parasympathetic
Rest and digest
Feed and breed

10. Section Two
Nervous System Cells

11. Histology of Nerve Cells

12. Neurons (Nerve Cells) excitable cells that transmit electrical signals
3 parts and accessory structures:
Cell Body
Dendrites
Axons

13. Cell Body Nucleus & metabolic center of the nerve cell Large Nucleolus
Associated structures:
Axon Hillock: Cone shaped area where the axon arises
Neurofibrils: Intermediate cytoskeleton that maintains cell shape
Clusters of cell bodies in the:
CNS: Nuclei PNS: Ganglia

14. Processes of the Cell Body
Dendrites: conduct impulses toward the cell body
Axons: conduct impulses away from the cell body
One long axon (“nerve fiber”) per cell body.
Axons end in axonal terminals
Axonal terminals contain vesicles with neurotransmitters
Axonal terminals are separated from the next neuron by a gap
Synaptic cleft – gap between adjacent neurons
Synapse – junction between nerves

15. The Nerve Cell and Associated Structures

16. Axon  Away from cell body
Dendrite  toward cell body

17. Axon in comparison to the rest of the nerve bundle

18. Nerve Fiber (long axons) Coverings
Schwann cells – produce myelin sheaths in jelly-roll like fashion
Nodes of Ranvier – gaps in myelin sheath along the axon

19. You need to know this structure!
Notice the difference?!

20. Neuron Cell Body Locations:
1. Most are found in the central nervous system
Gray matter – cell bodies and unmyelinated fibers
White matter – dense collection of myelinated fibers
Nuclei – clusters of cell bodies within the white matter of the central nervous system
2. Ganglia – collections of cell bodies outside the central nervous system

21. Functional Classification of Neurons
Sensory (afferent)- transmit impulses from sensory receptors toward the CNS
Interneurons (association neurons)- Connect sensory and motor neurons in the neural pathways of CNS
Motor (efferent)- carries impulses from the CNS to effectors

22. Neuron Classification

23. Structural Classification of Neurons
Multipolar neurons – many extensions from the cell body
Most common in vertebrates
Bipolar neurons – one axon and one dendrite
Eyes, nose, ears
Unipolar neurons – have a short single process leaving the cell body
Most common in invertebrates
Figure 7.8a

24. CNS Vs PNS Neuroglia (Support Cells)
This is not in your notes. It is for a reference.
There are 4 CNS support cells
Astrocytes
Microglia
Ependymal
Oligodendrocytes
There are 2 PNS support cells
Satellite Cells
Schwann Cells

25. Nervous Tissue: Support Cells (Neuroglia) (Glial Cells)
Astrocytes
MOST abundant, star-shaped cells
Support & Brace neurons
Form barrier between capillaries and neurons
Control the chemical environment of the brain
Microglia
Spider-like phagocytes (swallows invaders)
Dispose of debris
Figure 7.3a

26. Nervous Tissue: Support Cells
Ependymal cells
Line cavities of the brain and spinal cord
Circulate cerebrospinal fluid
Oligodendrocytes
Produce insulating myelin sheath around nerve fibers (axons) in the central nervous system
Nodes of Ranvier-myelin sheath gaps between Schwann cells, sites where axon collaterals can emerge
Figure 7.3b–c

27. Nervous Tissue: Support Cells
Satellite cells
Surround and protect neuron cell bodies in PNS
Schwann cells
Form myelin sheaths & surrounds the peripheral nerve fibers
Helps regeneration of damaged peripheral nerve fibers
Figure 7.3e

28. Chapter Nine Section 3: Delivering the Message
End of Day 1, Start of Day 2
Chapter Nine Section 3: Delivering the Message

29. Functional Properties of Neurons
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

30. Starting a Nerve Impulse
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
Figure 7.9a–c

31. The Action Potential
If the action potential (nerve impulse) starts, it is propagated over the entire axon
Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane
The sodium-potassium pump restores the original configuration
This action requires ATP

32. Nerve Impulse Propagation
The impulse continues to move toward the cell body
Impulses travel faster when fibers have a myelin sheath
Figure 7.9d–f

33. Continuation of the Nerve Impulse between Neurons
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

34. How Neurons Communicate at Synapses
Figure 7.10

35. Section 4: Developmental aspects of neurons
Cell death
About 2/3 of neurons die before birth
Death results in cells that fail to make functional synaptic contacts
Many cells also die due to apoptosis (programmed cell death) during development
(we have webbed fingers and toes in the womb!!!)

36. Multiple Sclerosis (MS)
An autoimmune disease that mainly affects young adults
Myelin sheaths in the CNS become nonfunctional scleroses
Shunting and short-circuiting of nerve impulses occurs, impulse condition slows and eventually ceases
Symptoms: visual disturbances, weakness, loss of muscular control, speech disturbances, and urinary incontinence.