1. Nervous System: General Principles
Anatomy & Physiology 1
Tony Serino. Ph.D.
Biology Dept.
Misericordia University

2. Nervous System Lecture Outline:
Controls and/or modifies all other systems
Rapid response time
Usually short duration
Lecture Outline:
General anatomy and physiology of neurons
CNS (Central Nervous System)
PNS (Peripheral Nervous System)

3. Functional Areas

4. Divisions of the Nervous System

5. Nervous Tissue Non-excitable Tissue (Supportive cells)
Neuroglia –present in CNS
Schwann and Satellite cells –present in PNS
Neurons (excitable tissue)
Initiate and conduct electrical signals (action potentials)

6. Neuroglia (glial cells)
Phagocytic,protective
Form BBB
Regulate microenvironment
Pass on nutrients; get rid of waste

7. Neuroglia
Line cavities
Create CSF
Secrete myelin in CNS

8. PNS Supportive Cells Schwann cells –secrete myelin in PNS
Satellite cells –surround neuron cell bodies in PNS

9. Neuron Anatomy Axonal terminal Nerve ending Synaptic boutons
Synaptic knobs

10. Functional Zones of a Neuron
Receptor Zone
Initial segment of Axon (trigger zone)
Nerve endings
Axon

11. Internal Cell Body Structures

12. Myelination
In PNS, a Schwann cell wraps and individual segment of a single axon
In the CNS, an oligodendrocyte performs the same function but can attach to more than one axon

13. Node of Ranvier: gaps in myelin sheath

14. Types of Neurons Anatomical classification Functional Classification
Based on number of process projecting from cell body
Functional Classification
Based on location of neuron and direction of information flow

18. General Terms Ganglia vs. Nuclei Nerve vs. nerve fiber
Areas of densely packed nerve cell bodies
Ganglia are usually found in PNS
Nuclei are found in CNS
Nerve vs. nerve fiber
A nerve is a dissectible structure containing hundreds of axons
A nerve fiber is a single axon
CT sheaths covering peripheral nerves:

19. Nerve CT sheaths

20. Synapses Areas where neurons communicate with other cells
Can be chemical (with neurotransmitters) or electrical (gap junctions)

21. Anatomy of Synapse (chemical)
Neurotransmission ends when NT diffuses away,
re-absorbed by presynaptic neuron, or NT metabolized
(degraded) by enzymes in cleft

22. Neurotransmission: signal transduction

23. Neurotransmission
Electrical signal (action potential (AP)) descends axon to synaptic knob (nerve end)
Depolarization opens Ca++ channels to open in presynaptic membrane
Triggers a number of synaptic vesicles to fuse with outer membrane
Dumps neurotransmitter (NT) into synaptic cleft
NT diffuses across cleft and binds to receptor on postsynaptic membrane
This leads to channels opening on postsynaptic membrane changing the membrane’s potential

24. Types of Anatomical Synapses

26. Membrane Potentials
Produced by the unequal distribution of ions across a selectively permeable membrane
The inside of the cell is called negative by convention
The intensity of the ion difference is expressed as voltage (measured in millivolts (mV))

27. Measuring Membrane Potentials

28. Resting Membrane Potential
Parameters necessary to create a resting membrane potential:
A semi-permeable membrane
Distribution of ions across membrane
Presence of large non-diffusible anions in interior
Na-K pump (3 Na+ out for every 2 K+ in)

29. Gated Channel Proteins
Opening gate allows ions to travel into or out of the cell thereby changing the membrane potential
Can be controlled chemically or electrically

30. Chemically Gated Channel Protein

31. Voltage (electrically) Gated Channel Protein

32. Graded Potentials Transient Decremental
Most due to chemically gated channels opening
Can be summated
May be excitatory or inhibitory
Depolarization
Inside of cell becomes less negative
Will only trigger AP if the
threshold of the neuron is
reached.
Hyperpolarization
Inside of cell becomes more negative

33. Graded potentials magnitude vary with stimulus strength

34. Summation Temporal –a single axon fires repeatedly
Spatial –two or more axons fire simultaneously

35. Typical Receptor Zone Activity

36. Action Potentials Wave-like, massive depolarization
Propagated down entire length of axon or muscle cell membrane
All or none
No summation possible
Due to opening of voltage gated channels and corresponding positive feedback cycle established
1. Foot –graded potentials
2. Uplimb –fast depolarization
3. Downlimb –fast repolarization
4. After Hyperpolarization –overshoot due to ion distribution 2 3 1 4

37. Events in Membrane during the AP

38. Refractory Periods
Foot

39. AP propagation in unmyelinated axons
The depolarization event triggers depolarization in the next area of the axon membrane; followed by repolarization. In this way the AP appears to move in a wave-like fashion over an unmyelinated axon membrane.

40. AP propagation in myelinated axons
The AP appears to jump from node to node (saltatory conduction); the myelin sheath eliminates the need to depolarize the entire membrane.

41. Axonal Transport
Anterograde –towards synapse; flow of synaptic vesicles, mitochondria, etc.
Retrograde –towards CB; recycled membrane vesicles, neuromodulators, etc.

42. Regeneration of Nerve Fibers
Damage to nerve tissue is serious because mature neurons are post-mitotic cells
If the soma of a damaged nerve remains intact, damage may be repaired
Regeneration involves coordinated activity among Schwann cells, Neurons and WBCs or microglia:
remove debris
form regeneration tube and secrete growth factors
regenerate damaged part

43. Response to Injury
Anterograde degeneration with some retrograde; phagocytic cells (from Schwann cells, microglia or monocytes) remove fragments of axon and myelin sheath
Cell body swells, nucleus moves peripherally
Loss of Nissl substance (chromatolysis)
In the PNS, some Schwann cells remain and form a tubular structure distal to injury; if gap or scarring is not great axon regeneration may occur with growth down tube
In the CNS, glial scar tissue seems to prevent regeneration
If contact with tube is not established then no regeneration and a traumatic neuroma forms

44. Drug Intervention Possibilities
Increase leakage and breakdown of NT from vesicles
Agonize NT release
Block NT release
Inhibit NT synthesis
Block NT uptake
Block degradative enzymes in cleft
Bind to post-synaptic receptor
Stimulate or inhibit second messengers in post-synaptic cell