1. Human Physiology Chapter 6 The Mechanisms of Body Function
Vander’s
Human Physiology
The Mechanisms of Body Function
Tenth Edition by
Widmaier • Raff • Strang
© The McGraw-Hill Companies, Inc.
Figures and tables from the book, with additional comments by:
John J. Lepri, Ph. D.,
The University of North Carolina at Greensboro

2. Chapter 6 Neuronal Signaling and the Structure of the Nervous System
Communication by neurons is based on changes in the
membrane’s permeability to ions. Two types of membrane
potentials are of major functional significance: graded potentials
and action potentials.
A typical neuron has a dendritic region and an axonal region.
The dendritic region is specialized to receive information whereas
the axonal region is specialized to deliver information.

3. Chapter 6 Neuronal Signaling and the Structure of the Nervous System (cont.)
The two major divisions in the nervous system are the central
nervous system (CNS) and the peripheral nervous system (PNS).
Within the PNS, major divisions are the somatic nervous system
and the autonomic nervous system, which has two branches:
the parasympathetic and the sympathetic branches.

4. Axons: undergo action potentials to deliver information,
Dendrites: receive information, typically neurotransmitters, then undergo graded potentials.
Figure 6-1
Axons: undergo action potentials to deliver information,
typically neurotransmitters, from the axon terminals.

5. Among all types of neurons, myelinated neurons
Schwann cells form myelin on peripheral neuronal axons.
Oligodendrocytes form myelin
on central neuronal axons.
Figure 6-2
Among all types of neurons, myelinated neurons
conduct action potentials most rapidly.

6. CNS PNS Figure 6-4 PNS = afferent neurons (their activity
“affects” what will happen
next) into the CNS +
efferent neurons (“effecting” change:
movement, secretion, etc.)
projecting out of the CNS.
CNS = brain
+ spinal cord;
all parts of interneurons
are in the CNS.

8. COMMUNICATION: Figure 6-5 A single neuron postsynaptic
to one cell can be presynaptic
to another cell.
Figure 6-5

9. Fig
06.06.jpg

10. Glial Cells
Astroglia : help regulate CNS extracellualr fluid composition by removing K and neurotransmitters Surround the neurons, axons, and dentrities as a physical support.
Microglia : macrophage-like cells, perform immune function in the CNS.

11. Figure 6-7
Opposite charges attract each other and
will move toward each other if not separated
by some barrier.

12. Figure 6-8

13. Figure 6-9
Only a very thin shell of charge difference
is needed to establish a membrane potential.

15. Figure 6-10 Begin: K+ in Compartment 2, Na+ in Compartment 1;
BUT only K+ can move.
Ion movement:
K+ crosses into
Compartment 1;
Na+ stays in
Compartment 1.
Figure 6-10
buildup of positive charge in Compartment 1 produces an electrical potential that exactly offsets the K+ chemical concentration gradient.
At the potassium
equilibrium potential:

16. Begin:
K+ in Compartment 2,
Na+ in Compartment 1;
BUT only Na+ can move.
Ion movement:
Na+ crosses into
Compartment 2;
but K+ stays in
Compartment 2.
buildup of positive charge in Compartment 2
produces an electrical potential that exactly
offsets the Na+ chemical concentration gradient.
At the sodium
equilibrium potential:

17. The Nernst Equation The equilibrium potential of a given ion
E = 60 log C0/Ci
Ci intracellular concentration of the ion
Co extracellular concentration of the ion

18. Fig. 06.12 At resting membrane potential of -70 mV, both the conc. and
06.12.jpg
At resting membrane potential
of -70 mV, both the conc. and
elec, gradient favor inward move
of Na, but K is in opposite.

19. Figure 6-13
Establishment of resting membrane potential:
Na+/K+ pump establishes concentration gradient
generating a small negative potential; pump
uses up to 40% of the ATP produced by that cell!

20. Figure 6-14
Overshoot refers to
the development of
a charge reversal.
A cell is
“polarized”
because
its interior
is more
negative
than its
exterior.
Repolarization is
movement back
toward the
resting potential.
Depolarization
occurs
when ion
movement
reduces the
charge
imbalance.
Hyperpolarization is
the development of
even more negative
charge inside the cell.

22. Figure 6-15
The size of a
graded potential
(here, graded
depolarizations)
is proportionate
to the intensity
of the stimulus.

23. Figure 6-16
Graded potentials can be: EXCITATORY or INHIBITORY (action potential (action potential
is more likely) is less likely)
The size of a graded potential is proportional to the size of the stimulus.
Graded potentials decay as they move over distance.

24. Graded potentials decay as they move over distance.
Figure 6-17
Graded potentials decay as they move over distance.

25. Figure 6-19 An action potential is an “all-or-none”
sequence of changes
in membrane potential.
The rapid opening of
voltage-gated Na+ channels
allows rapid entry of Na+,
moving membrane potential
closer to the sodium
equilibrium potential (+60 mv)
Action potentials result
from an all-or-none
sequence of changes
in ion permeability
due to the operation
of voltage-gated
Na+ and K + channels.
The slower opening of
voltage-gated K+ channels
allows K+ exit,
moving membrane potential
closer to the potassium
equilibrium potential (-90 mv)
Figure 6-19

26. The rapid opening of voltage-gated Na+ channels
explains the rapid-depolarization phase at the
beginning of the action potential.
The slower opening of voltage-gated K+ channels
explains the repolarization and after hyperpolarization
phases that complete the action potential.

27. Fig
06.18.jpg

28. Fig a
06.19a.jpg

29. Fig b
06.19b.jpg

30. Fig a
06.20a.jpg

31. Fig b
06.20b.jpg

32. Figure 6-21 Four action potentials, each the result
of a stimulus strong enough to cause
deloplarization,are shown in the right
half of the figure.
Figure 6-21

33. Action of local anesthetics
Lidocaine (xylocaine) and procaine (novocaine) block voltage-gated sodium channels, preventing their opening in response to depolarization stimuli.
Without action potential, signals generated in the periphery in response to injury cannot reach the brain.

34. Fig ab
06.22ab.jpg

35. Refractory periods
Absolute refractory period: occurred during the period when the voltage-gated Na channels are either already open or are in the inactivated state during the first action potential.
Relative refractory period: it lasted for 1 to 15 mSec and coincides roughly with the period of afterhyperpolarization.

36. Saltatorial Conduction: Action potentials jump from one node to the
next as they propagate along a myelinated axon.
Figure 6-23

37. Types of potentials
Receptor potential: In afferent neurons,the initial depolarization is achieved by a graded potential,the receptor potential
Synaptic potential: In all other neurons, the depolarization to threshold is due either to a graded potential generated by the synaptic input (synaptic potential ), or to a spontaneous change in the neurons membrane potential ( pacemaker potential ).

38. Type of synapses
Electrical synapses : through gap junctions, commom in smooth muscle and cardiac muscle.
Chemical synapses : through neurotransmitters.

39. Figure 6-24 Four primary neurons communicate to one secondary neuron.
One primary neuron
communicates to four
secondary neurons.
Figure 6-24

40. Figure 6-25 The synapse is the point of communication
between two neurons
that operate sequentially.
Figure 6-25

41. Figure 6-27

42. Activation of the postsynaptic cell
Ionotropic receptors : the receptors activated by the neurotansmitters are themselves ion channels.
Metabotropic receptors : the receptors act indirectly on separate ion channels through
G proteins.

43. An excitatory postsynaptic potential (EPSP) is a graded depolarization that moves the membrane potential closer to the threshold for firing an action potential (excitement).
Figure 6-28

44. An inhibitory postsynaptic potential (IPSP) is a graded hyperpolarization that moves the membrane potential further from the threshold for firing an action potential (inhibition).
Figure 6-29

45. The membrane potential of a real neuron typically undergoes many EPSPs (A) and IPSPs (B), since it constantly receives excitatory and inhibitory input from the axons terminals that reach it.
Figure 6-30

46. Panel 1: Two distinct, non-overlapping, graded depolarizations.
Panel 2: Two overlapping graded depolarizations demonstrate temporal summation.
Panel 3: Distinct actions of stimulating neurons A and B demonstrate spatial summation.
Panel 4: A and B are stimulated enough to cause a suprathreshold graded depolarization, so an action potential results.
Panel 5: Neuron C causes a graded hyperpolarization; A and C effects add, cancel each other out.
Figure 6-31

47. Real neurons
receive as
many as
200,000
terminals.

48. Figure 6-32

49. Figure 6-33 Axo-axonal communication (here, between A & B)
can modify classical synaptic communication
(here, between B & C); this can result in
presynaptic inhibition or presynaptic facilitation.
Note: the Terminal B must have receptors for the signal released from A.
Figure 6-33

50. Figure 6-34 Possible drug effects on synaptic effectiveness:
A. release and degradation of the neurotransmitter inside the axon terminal.
B. increased neurotransmitter release into the synapse.
C. prevention of neurotransmitter release into the synapse.
D. inhibition of synthesis of the neurotransmitter.
E. reduced reuptake of the neurotransmitter from the synapse.
F. reduced degradation of the neurotransmitter in the synapse.
G. agonists (evoke same response as neurotransmitter) or antagonists (block response to neurotransmitter) can occupy the receptors.
H. reduced biochemical response inside the dendrite.
Figure 6-34

51. Tetanus toxin (Clostridium tetani)
A protease that destroys SNARE proteins in the presynaptic terminal, thus preventing movement of vesicles to the membrane.
Presynaptic neurotransmitter release is inhibited.
Neurons that are affected are the inhibitory, tetanus is characterized by an increase in muscle contraction.

52. Clostridium botulinum
Its toxin causes muscle paralysis by inhibiting the release of excitatory neurotransmitters at neuromuscular junctions, through interfering SNARE system.
Botox is used to ease wrinkles for the cosmetic purpose.

54. Acetylcholine receptors
Ach is a major neurotransmitter in the PNS at the neuromuscular junctions and in the brain.
Nicotinic receptor: is a ligand gated Na/K channel. Present in neurumuscular junctions.
Muscarinic receptor: G-protein couple receptor, present in neural junctions that innervate many smooth muscles and cardiac muscle.

55. Nicotinic-acetylcholine receptors
These receptors mediate:
Catecholamine release from adrenal medulla.
Release dopamine in the brain’s ”rewarding” pathway.
Tobacco smoking produce an euphoric sensation that strongly reinforces the desire to smoke. The desensetization of the N-AchRs drives the users to smoke more to regain the pleasurable sensation.

56. Figure 6-35 The catecholamines are formed from the amino acid
tyrosine and share the same two initial steps in their
biosynthetic pathway.
Figure 6-35

57. Catecholamines
After release,are actively transported back into the axon terminal by membrane transporters, they are also degraded by MONOAMINE OXIDASE (MAO).
MAO inhibitors increase dopamine and norepinephrine in a synapse, they are used in the treatment of depression and anxiety.

58. Receptor Signaling Adrenergic receptors:
β AR—metabotropic, acts by initiating metabolic processes that affect cell function.
α AR—ionotropic postsynaptically( K and or Ca )
GABA receptor– ionotropic, ,increases Cl- ion flux into the cell resulting in the hyperpolarization of the postsynaptic membrane.

59. Gamma-aminobutyric acid (GABA)
GABA is the major inhibitory neurotransmitter in the brain.
Binding of GABA to its ionotropic receptor increases Cl flux into the cell, resulting in hyperpolarization.
This receptor also binds barbiturates, ethanol, and benzodiazepines (valium), they also induce Cl influx and reduce anxiety, induce sleep, and guard against seizures.

60. Glycine
Glycine is the major neurotransmitter released from inhibitory interneurons in the spinal cord and brainstem.
Glycine binds to ionotropic receptors on postsynaptic cells that allow Cl to enter causing hyperpolarization or stabilization of the resting membrane potential.
Normal function of glycinergic interneurons is essential for the balance of excitation and inhibition in spinal cord integrating centers that regulate skeletal muscle contraction.

61. long-term potentiation (LTP)
A mechanism coupling frequent activity across a synapse with lasting changes in the strength of signalings across the synapse
A cellular process underlying learning and memory.

62. Fig
06.36.jpg

63. NMDA receptor and excitotoxicity
When glutamate containing cells die and rupture, the flood of glutamate excessively stimulated AMPA and NMDA receptors on the nearby neurons. The excessive stimulation causes calcium accumulation to a toxic level, which in turn kills those neurons and causes them to rupture, and the wave of damage progressively spreads.

64. Fig
06.37.jpg

65. Figure 6-38
Major landmarks of the Central Nervous System

66. Forebrain: 4 major parts
Cerebral hemisphere : perception, reasoning, learning, memory and skilled movement.
Thalamus : skeletal muscle coordination.
Hypothalamus : regulates pituitary function, water balance, eating and drinking behavior,body temperature,circadian rhythm, reproductive system. Generation of emotional behavior.
Limbic system : generation of emotions and emotional behavior,essential for all kinds of learning.

67. Cerebellum and Brainstem
Cerebellum : Does not initiate voluntary movement but is the center for coordinating movements and controlling posture and balance. Participates in some learning processes.
Brainstem : Integrating centers for cardiovascular and respiratory functions. Contains nuclei for cranial nerves III to XII.

68. Diencephalon
The diencephalon contains 2 parts : thalamus and hypothalamus.
Nerve fibers entering the cerebral cortex predominantly from the diencephalon, from a region known as the thalamus, and areas of brainstem.
Hypothalamus is the command center for neural and endocrine coordination.

69. Figure 6-39
Organization of neurons in the cerebral cortex reveals six layers.

70. Figure 6-40 Functions of the limbic system: learning emotion
appetite (visceral function)
sex
endocrine integration
Figure 6-40

71. Figure 6-41 Anterior view of one vertebra and the
nearby section of the spinal cord.
Figure 6-41

72. Spinal Cord
Gray matter: Composes of interneurons, cell bodies and dendrities of the efferent neurons, axons of the afferent neurons and glial cells.
White matter: Consists of decending and ascending myelinated axons.

75. Figure 6-43 M o t o r n e u r o n Preganglionic neuron
Postganglionic neuron
Figure 6-43

76. Sympathetic: “emergency responses” Parasympathetic: “rest and digest”
Figure 6-44

77. The sympathetic trunks are chains of sympathetic ganglia that are parallel to either side of the spinal cord; the trunk interacts closely with the associated spinal nerves.
Figure 6-45

79. Figure 6-46 M o t o r n e u r o n Skeletal muscle Voluntary
contraction
Voluntary
command:
Move!
M o t o r n e u r o n
Heart,
smooth
muscle,
glands,
many
“involuntary”
targets.
Involuntary
command:
Rest & digest.
Involuntary
command:
Emergency!
Heart,
smooth
muscle,
glands,
many
“involuntary”
targets.
Figure 6-46

80. Thanks for your attention !