Anatomy

1. Spinal Nerves
Cranial Nerves
A) NERVOUS SYSTEM GENERAL ANATOMY
NERVOUS SYSTEM CELLS 1
Brain
Spinal Cord
Central Nervous System Peripheral Nervous System

2. NERVOUS SYSTEM CELLS 2
B) NERVOUS TISSUE

3. NERVOUS SYSTEM CELLS 3
 Glial Cells (Neuroglia)
~ CNS glia:
1) ependymal cells: specialized epithelial cells lining the central
canal of the spinal cord and the ventricles of
the brain; cerebrospinal fluid (CSF)
2) astrocytes: help form the blood-brain barrier (BBB) with
pedicels (vascular feet); structural support/wound
repair (e.g., stroke); scavengers of
ions/neurotransmitters in IF
3) oligodendrocytes: myelination of CNS axons (myelin sheath);
one oligo can wrap around several different axons;
nodes of Ranvier
4) microglial cells: macrophages of the CNS; phagocytosis

4. NERVOUS SYSTEM CELLS 4
Gray matter
White matter
Gray matter
White matter

5. NERVOUS SYSTEM CELLS 5
~ PNS glia:
1) satellite cells: support cells; surround neuronal cell bodies within
ganglia; scavengers of ions/neurotransmitters in IF
2) Schwann cells: form myelinated coverings over axons; myelinate one
segment of one axon
Myelin sheath

6. NERVOUS SYSTEM CELLS 6

7. NERVOUS SYSTEM CELLS 7
 Nerve Cells (Neurons)
~ Classification of Neurons
√ Structural classes: bipolar, unipolar (pseudounipolar) and multipolar

8. NERVOUS SYSTEM CELLS 8
√ Functional classes: sensory (afferent), interneurons, motor (efferent)
99% of ALL
neurons!

9. NERVOUS SYSTEM CELLS 9
• Typical Motor Neuron

10. NERVOUS SYSTEM CELLS 10
~ Neural Communication
√ Synapse
- neuron/neuron junction (presynaptic cell – cleft – postsynaptic cell)
Synapse
Presynaptic
membrane
Postsynaptic
membrane
Synaptic
cleft

11. NERVOUS SYSTEM CELLS 11
√ Neuroeffector Junction
- neuron/non-neuron junction (e.g., neuromuscular junction)

12. NERVOUS SYSTEM CELLS 12
~ Properties of Neurons
√ Excitability
- resting membrane potential (RMP) of -70 mV
- can be “turned on,” or excited (depolarized) or “turned off,” or inhibited
(hyperpolarized)
√ Conductivity
- propagate changes in membrane potential (i.e., action potentials)
√ Secretion
- manufacture, store and secrete neurotransmitters
• Axonal Transport
- transport of vesicles containing neurotransmitters along axons
on microtubules (within the axoplasm) to synaptic knobs

13. NERVOUS SYSTEM CELLS 13
https://www.youtube.com/watch?v=B_zD3NxSsD8
Axonal Transport

14. NERVOUS SYSTEM CELLS 14

15. NERVOUS SYSTEM CELLS 15
C) GENERATION AND CONDUCTION OF ACTION POTENTIALS
Resting membrane potential
Graded (local) potential
Action potential

16. NERVOUS SYSTEM CELLS 16
 Membrane Potential
~ Equilibrium Potentials
- membrane potential at which a particular ion is at equilibrium across
the plasma membrane (i.e., between ICF and ECF)
Chemical
gradient
Electrical
gradient
+
Electrochemical
gradient

17. NERVOUS SYSTEM CELLS 17
1) K+ leak channels
2) Na+/K+ pump
3) anionic molecules
RMP “Generators”
Important ICF and IF
Solute Concentrations
Intracellular Interstitial Blood
Fluid Fluid Plasma
Na+ 15 mM 145 mM 142 mM
K+ 120 mM 4.5 mM 4.4 mM
Ca2+ 10-4 mM 1.2 mM 1.2 mM
Cl- 20 mM 116 mM 102 mM
HCO3
- 15 mM 25 mM 22 mM
Protein 4 mM 0 mM 1 mM
Glucose very low 5.6 mM 5.5 mM
Plasma 290 mOsm 290 mOsm 291 mOsm
~ Resting Membrane Potential (RMP)

18. NERVOUS SYSTEM CELLS 18
Na+/K+ Equilibrium Potentials and the RMP

19. NERVOUS SYSTEM CELLS 19
 Changes in Membrane Potential
- depolarization: positive deviation from the RMP
- repolarization: return of TMP to RMP after depolarization
- hyperpolarization: negative deviation from the RMP

20. ~ Graded (Local) Potential
- change in membrane potential in which the magnitude (or amplitude) of
the ∆Vm is variable and directly proportional to the size of the stimulus
Time (ms)
NERVOUS SYSTEM CELLS 20

21. NERVOUS SYSTEM CELLS 21
√ Generation of Graded Potentials
- generated by the opening of mechanically- or ligand-gated ion channels

22. NERVOUS SYSTEM CELLS 22
√ Distance-Dependence of Graded Potentials
- only affect small regions of the plasma membrane; hence the term local
Amplitude
of
∆V
m

23. NERVOUS SYSTEM CELLS 23
~ Action Potentials (APs)
- a very brief (all-or-none) membrane depolarization that is variable in
frequency, but not in magnitude (i.e., amplitude is fixed)
- generated by the opening of voltage-gated ion channels (e.g., Na+)
- series of action potentials in nodes of ranvier (e.g., along the axolemma
of an axon)

24. NERVOUS SYSTEM CELLS 24
Graded Potentials vs. Action Potentials
AM
Receiver
FM Transmitter

25. NERVOUS SYSTEM CELLS 25
~ Other Membrane Potentials
Generator
Potentials
Receptor
Potentials

26. NERVOUS SYSTEM CELLS 26
 Neural Integration
- a single neuron receives information across thousands of synapses
- mixture of excitatory and inhibitory presynaptic signals

27. Inhibitory Postsynaptic
Potentials (IPSPs)
- GABAergic synapses
- GABA
- ligand-gated Cl- channels
NERVOUS SYSTEM CELLS 27
Excitatory Postsynaptic
Potentials (EPSPs)
- glutamatergic synapses
- glutamate
- ligand-gated Na+ channels
~ The Axon Hillock
- net effect of integration on the axon hillock determines the cell’s response
RMP = -70 mV
TP = -60 mV
(voltage-gated
Na+ channels)
Action potential?

28. NERVOUS SYSTEM CELLS 28
The “Brain” of a Neuron
EPSP IPSP
Net effect on
axon hillock?
Net effect on
axon hillock?

29. NERVOUS SYSTEM CELLS 29
~ Initial Segment of Axon
- an action potential first arises at the initial segment of axon
Spike initiation zone
Local
Anesthesia/
”Nerve Block”
e.g., lidocaine
inhibits voltage-
gated Na+ channels

30. NERVOUS SYSTEM CELLS 30
4
5
1
2
3
 The Action Potential

31. NERVOUS SYSTEM CELLS 31
* 200-300 Hz (brain)
* 5-30 Hz (skeletal muscle)
* ~1-2 Hz (cardiac muscle)
~ The Refractory Period
- two components: absolute and relative refractory periods
- sets the maximum frequency of APs and determines direction of APs

32. NERVOUS SYSTEM CELLS 32
Types of Action Potentials

33. NERVOUS SYSTEM CELLS 33
~ Action Potential Propagation
- a series of successively regenerated action potentials linked by a
series of successively regenerated graded potentials

34. NERVOUS SYSTEM CELLS 34
√ Saltatory vs. Continuous Conduction
Saltatory Conduction
Continuous Conduction
Voltage-gated
Na+ channel
Voltage-gated
Na+ channel
Local current
Local current
K+

35. √ Action Potential Velocity
- factors affecting velocity: axon diameter and myelination
- effects of myelination: insulation and increased AP velocity
1 100
(m/sec)
NERVOUS SYSTEM CELLS 35

36. NERVOUS SYSTEM CELLS 36
Unmyelinated axon
(continuous conduction)
Myelinated axon (saltatory
conduction)
t = 1
t = 2
t = 3

37. NERVOUS SYSTEM CELLS 37
Demyelinating Disorders (e.g., Multiple Sclerosis)

38. NERVOUS SYSTEM CELLS 38
D) SYNAPTIC ACTIVITY
Resting membrane potential
Graded (local) potential
Action potential
Synaptic potential

39. NERVOUS SYSTEM CELLS 39

40. NERVOUS SYSTEM CELLS 40
 Presynaptic Neurotransmitter Release

41. NERVOUS SYSTEM CELLS 41
 Postsynaptic “Synaptic Potentials”
EPSP = excitatory postsynaptic potential
IPSP = inhibitory postsynaptic potential

42. NERVOUS SYSTEM CELLS 42
 Types of Synapses
~ Electrical Synapses
- presynaptic and postsynaptic membranes are coupled together via
gap junctions
- the presynaptic neuron always propagates its signal
(depolarization/hyperpolarization) to the postsynaptic neuron
- transmission is very quick (~0.2 ms) and occurs with 100% fidelity
~ Chemical Synapses
- presynaptic and postsynaptic membranes are not physically coupled
- presynaptic neuron may or may not propagate its signal to the
postsynaptic neuron; signal transmission can be influenced; pharm
- transmission is relatively* longer (~ 2.0 ms) than w/ electrical synapses
- contain excitatory or inhibitory chemicals (neurotransmitters)

43. NERVOUS SYSTEM CELLS 43

44. NERVOUS SYSTEM CELLS 44
√ Types of Chemical Synapses
• Cholinergic Synapses
- abundant in the brain and neuromuscular junctions (NMJs)
- contain the neurotransmitter acetylcholine (ACh)
- can be excitatory or inhibitory
- two types of ACh receptors:
1) nicotinic (Excitatory)– ionotropic; ACh and nicotine are agonists
2) muscarinic (Inhibitory)– metabotropic; ACh and muscarine are
agonists
ACh Nicotinic Receptor ACh Muscarinic Receptor

45. NERVOUS SYSTEM CELLS 45
Excitatory Cholinergic Synapse
Neuromuscular
junction (NMJ)

46. NERVOUS SYSTEM CELLS 46
Inhibitory Muscarinic Synapse
SA node
Pacemaker potential
ANS Regulation of Heart Rate

47. NERVOUS SYSTEM CELLS 47
• Adrenergic Synapses
- abundant in CNS and ANS
- contain catecholamines (norepinephrine and epinephrine (adrenaline))
- can be excitatory and inhibitory
- two subtypes of adrenergic receptors (α and β)
* all adrenergic receptors are G protein-coupled receptors (GPCRs)
α1-adrenergic
receptor
α2-adrenergic
receptor
β1-adrenergic
receptor
β2-adrenergic
receptor

48. NERVOUS SYSTEM CELLS 48
Excitatory Adrenergic Synapse

49. NERVOUS SYSTEM CELLS 49
• GABAergic Synapses
- synapses that contain the neurotransmitter γ-aminobutyric acid
- principal inhibitory neurotransmitter in the brain
- exclusively inhibitory

50. NERVOUS SYSTEM CELLS 50
• Glutamatergic Synapses
- synapses that contain the neurotransmitter glutamate
- principal excitatory neurotransmitter in the brain
- typically excitatory

51. NERVOUS SYSTEM CELLS 51
Common G Protein-Coupled Receptor Signaling Pathways

52. NERVOUS SYSTEM CELLS 52
E) CESSATION OF THE SIGNAL
1) cessation of firing of the presynaptic neuron
2) ligand-receptor binding is temporary (~1-2 msec)
3) neurotransmitter diffuses out of the synaptic cleft; peripheral glial cells
can absorb them and return them to neurons
4) neurotransmitter can be degraded in the synaptic cleft; e.g., the
enzyme acetylcholinesterase (AChE) degrades acetylcholine (ACh) to
acetate and choline
5) the presynaptic knob reabsorbs (reuptakes) neurotransmitters (e.g.,
serotonin) or their degraded constituents (e.g., choline from ACh);
antidepressants (e.g., selective serotonin reuptake inhibitor - SSRI)