1. Chapter 10 Nervous System

2. The Nervous System Components Responsible for Subdivisions
Brain, spinal cord, nerves, sensory receptors
Responsible for
Sensory perceptions, mental activities, stimulating muscle movements, secretions of many glands
Subdivisions
Central nervous system (CNS)
Peripheral nervous system (PNS)

3. Central Nervous System
Consists of
Brain
Spinal cord
Brain and spinal cord
Continuous with each other

4. Peripheral Nervous System
Two subcategories
Sensory or afferent
Motor or efferent
Divisions
Somatic nervous system
Autonomic nervous system (ANS)
Sympathetic
Parasympathetic
Enteric

5. Nervous System Organization

6. Cells of Nervous System
Neurons or nerve cells
Receive stimuli and transmit action potentials
Organization
Cell body or soma
Dendrites: Input
Axons: Output
Neuroglia or glial cells
Support and protect neurons

7. Section 1 General Function of Neuron and Neuroglia
I Neuron

8. Typical Neuron has 4 Regions
Structure and Function
Typical Neuron has 4 Regions
Cell Body
Dendrites
Axon
Presynaptic Terminals
Each region is specialized for its particular function
Information flows in a single direction

9. Neuron Cell Body Location
Most are found in the central nervous system
Gray matter – cell bodies and unmylenated fibers
Nuclei – clusters of cell bodies within the white matter of the central nervous system
Ganglia – collections of cell bodies outside the central nervous system

10. Functional Classification of Neurons
Sensory (afferent) neurons
Carry impulses from the sensory receptors
Cutaneous sense organs
Proprioceptors – detect stretch or tension
Motor (efferent) neurons
Carry impulses from the central nervous system

11. Functional Classification of Neurons
Interneurons (association neurons)
Found in neural pathways in the central nervous system
Connect sensory and motor neurons

12. By function (connections)
Sensory
Motor
Interneuron

13. Neuron Classification

14. Neuron Anatomy Extensions outside the cell body
Dendrites – conduct impulses toward the cell body
Axons – conduct impulses away from the cell body (only 1!)

15. Dendrites of Motor Neurons
Short, tapering, and diffusely branched processes
They are the receptive, or input, regions of the neuron
Electrical signals are conveyed as graded potentials (not action potentials)

16. Axons: Structure
Slender processes of uniform diameter arising from the hillock
Long axons are called nerve fibers
Usually there is only one unbranched axon per neuron
Rare branches, if present, are called axon collaterals
Axonal terminal – branched terminus of an axon

17. Axons: Function Generate and transmit action potentials
Secrete neurotransmitters from the axonal terminals

18. Whitish, fatty (protein-lipid), segmented sheath around most long axons
It functions in:
Protection of the axon
Electrically insulating fibers from one another
Increasing the speed of nerve impulse transmission
Myelin Sheath

19. Myelin
CNS: oligodendroglia
or oligodendrocytes
PNS: Schwann cells ~

20. Nodes of Ranvier
Gaps in the myelin sheath between adjacent Schwann cells
They are the sites where collaterals can emerge
Saltatory conduction

21. Myelin Sheath and Neurilemma: Formation
Formed by Schwann cells in the PNS
A Schwann cell:
Envelopes an axon in a trough
Encloses the axon with its plasma membrane
Concentric layers of membrane make up the myelin sheath
Neurilemma – remaining nucleus and cytoplasm of a Schwann cell

23. Myelin Sheath and Neurilemma: Formation
Figure 11.5a-d

25. Unmyelinated Axons
A Schwann cell surrounds nerve fibers but coiling does not take place
Schwann cells partially enclose 15 or more axons

26. Axons of the CNS Both myelinated and unmyelinated fibers are present
Myelin sheaths are formed by oligodendrocytes
Nodes of Ranvier are widely spaced
There is no neurilemma

27. 2. Classification and Function of Nerve Fibers
Function: conducting action potential
1)Characteristic
 physiological integration (anesthetic and tetrodotoxin, TTX)
 insulation,
 two direction
 no fatigue

28. 2). Conducting velocities of AP propagation:
0.5~120m/s.
The factors that influence the AP propagation:
~The diameter of NF: mm, The larger the diameter is , The faster A.P. propagates.
~ Myelin sheath:
~Temperature:

29. 3). The general classification of NF
 Electrical physiological classification (efferent nerve): A, A, A, A; B, C.
 Morphological classification (afferent nerve): I, II, III, IV.

30. 4) Axoplasmic transport
The concept: Various organelles and materials must be moved from the cell body, where they are made, to the axon and its terminals in order to maintain the structure and function of the cell axon.
 The mechanisms: Cytoskeletal filaments in the axon and cell body, which serve as the rails along which the transport occurs, are linked by proteins to the substances and organelles being moved.

31.  Anterograde axoplasmic transport
~ fast axoplasmic transport: 410mm/day, mitochondria, vesicles, secretory granule.
~ slow axoplasmic transport:1-12 mm/d, cytoskeletal elements & soluble proteins
 Retrograde axoplasmic transport：Axon transport of certain materials are from the axon terminals to the cell body. 205mm/d, NGF, tetanic toxin, horseradish peroxidase (HRP).

32. Fig. Axopasmic transport
Fig. The method of horseraidish peroxidase

33. 5) Trophic action of the nerve to the target
The motor nerve release some substance that has trophic action on the skeletal muscle
The denervated muscle does not receive nerve signals and due to this, muscle atrophy begins.
After two months, the muscle fibers degenerate and denervation atrophy follows.
Fibrous tissue replaces the muscle

34. II Supporting Cells: Neuroglia
Ependymal Cell
Microglia
Oligodendrocyte
Astrocyte
Martini, F. Fundamentals of Anatomy and Physiology, Fig 12-6.

35. Neuroglia of CNS Astrocytes Ependymal Cells
Regulate extracellular brain fluid composition
Promote tight junctions to form blood-brain barrier
Ependymal Cells
Line brain ventricles and spinal cord central canal
Help form choroid plexuses that secrete cerebrospinal fluid (CSF)

36. Neuroglia of CNS Microglia Specialized macrophages Oligodendrocytes
Form myelin sheaths if surround axon

37. Neuroglia of PNS Schwann cells or neurolemmocytes Satellite cells
Wrap around portion of only one axon to form myelin sheath
Satellite cells
Surround neuron cell bodies in ganglia, provide support and nutrients