1. Structure and Function
Nervous System
Structure and Function

2. Functions
Sensory input
Integration
Motor output

3. Classification Central Nervous System Peripheral Nervous System Brain
Cranial Nerves
Spinal Cord
Peripheral Nervous System
Spinal nerves
Sensory receptors

4. Divisions of Peripheral Nervous System
Sensory Division
Motor Division
muscles and glands
Divisions of the Motor
Somatic
Autonomic

5. Figure 11.2 Central nervous system (CNS)
Peripheral nervous system (PNS)
Brain and spinal cord
Cranial nerves and spinal nerves
Integrative and control centers
Communication lines between the
CNS and the rest of the body
Sensory (afferent) division
Motor (efferent) division
Somatic and visceral sensory
nerve fibers
Motor nerve fibers
Conducts impulses from the CNS
to effectors (muscles and glands)
Conducts impulses from
receptors to the CNS
Somatic sensory
fiber
Somatic nervous
system
Autonomic nervous
system (ANS)
Skin
Somatic motor
(voluntary)
Visceral motor
(involuntary)
Conducts impulses
from the CNS to
skeletal muscles
Conducts impulses
from the CNS to
cardiac muscles,
smooth muscles,
and glands
Visceral sensory fiber
Stomach
Skeletal
muscle
Motor fiber of somatic nervous system
Sympathetic division
Parasympathetic
division
Mobilizes body
systems during activity
Conserves energy
Promotes house-
keeping functions
during rest
Sympathetic motor fiber of ANS
Heart
Structure
Function
Sensory (afferent)
division of PNS
Parasympathetic motor fiber of ANS
Bladder
Motor (efferent)
division of PNS
Figure 11.2

6. How it works

7. Neurons = nerve cells Long lived, no mitosis,
Cell body- developed Golgi
Extensions outside the cell body
Dendrites
Axons
Axonal terminals contain vesicles with neurotransmitters
Axonal terminals are separated from other neurons or effectors (muscles or organs) by a gap called the synapse

9. Nerve Coverings
Myelin- Lipid/Protein
Schwann cells
Nodes of Ranvier

10. rotates around the axon, wrapping its plasma membrane loosely around
Schwann cell
plasma membrane
Schwann cell
cytoplasm
A Schwann cell
envelopes an axon. 1
Axon
Schwann cell
nucleus
The Schwann cell then
rotates around the axon,
wrapping its plasma
membrane loosely around
it in successive layers. 2
Neurilemma
The Schwann cell
cytoplasm is forced from
between the membranes.
The tight membrane
wrappings surrounding
the axon form the myelin
sheath. 3
Myelin sheath
(a) Myelination of a nerve fiber (axon)
Figure 11.5a

11. Classification of Neurons
Multipolar neurons
Bipolar
Unipolar

12. Classification Cont.. Sensory Neurons afferent Interneurons multipolar
most are unipolar
some are bipolar
Interneurons
multipolar
in CNS
Motor Neurons
efferent
carry impulses to effectors, muscle or gland

13. Table 11.1 (2 of 3)

15. Neuroglial Cells: Support Cells in CNS
Microglia
Phagocytes that engulf debris, necrotic tissue, invading viruses or bacteria
Astrocytes
Have many processes – look like stars
Perivascular feet wrap around and cover neurons and blood vessels
Form the blood-brain barrier which allows only certain substances to enter neurons from blood vessels

16. Ependyma Oligodendrocytes
Line the ventricles in the brain and central canal in spinal cord
Form cerebral spinal fluid
Oligodendrocytes
Support CNS cells
Have processes that form myelin sheaths around axons

17. Neuroglial Cells: Support Cells in PNS
Schwann Cells-PNS
Flattened cells, wrap around the axons
Form the myelin sheath around the axon
Satellite-PNS

19. Regeneration of Injury (if possible)

20. Principles of Electricity
Opposite charges attract each other
Energy is required to separate opposite charges across a membrane
Energy is liberated when the charges move toward one another
If opposite charges are separated, the system has potential energy

21. Definitions
Voltage (V): measure of potential energy generated by separated charge
Potential difference: voltage measured between two points
Current (I): the flow of electrical charge (ions) between two points

22. Definitions
Resistance (R): hindrance to charge flow (provided by the plasma membrane)
Insulator: substance with high electrical resistance
Conductor: substance with low electrical resistance

23. Role of Membrane Ion Channels
Leakage (nongated) channels—always open
Gated channels (three types):
Chemically gated (ligand-gated)
Voltage-gated channels
Mechanically gated channels

24. Generating a Nerve Impulse
polarized membrane: inside is negative relative to the outside under resting conditions
-70 mV

25. Voltmeter Plasma Ground electrode membrane outside cell Microelectrode
inside cell
Axon
Neuron
Figure 11.7

26. Action Potential (AP)
Brief reversal of membrane potential with a total amplitude of ~100 mV
Occurs in muscle cells and axons of neurons
Does not decrease in magnitude over distance
Principal means of long-distance neural communication

27. The big picture 1 2 3 3 4 2 1 1 4 Resting state Depolarization
Repolarization 3 4
Hyperpolarization
Membrane potential (mV) 2
Action
potential
Threshold 1 1 4
Time (ms)
Figure (1 of 5)

28. Generation of an Action Potential
Resting state
Only leakage channels for Na+ and K+ are open
All gated Na+ and K+ channels are closed

29. Depolarizing Phase Na+ influx causes more depolarization
At threshold (–55 to –50 mV) positive feedback leads to opening of all Na+ channels, and a reversal of membrane polarity to +30mV (spike of action potential)

30. Repolarizing Phase Repolarizing phase
Na+ channel slow inactivation gates close
Membrane permeability to Na+ declines to resting levels
Slow voltage-sensitive K+ gates open
K+ exits the cell and internal negativity is restored

31. Hyperpolarization Hyperpolarization
Some K+ channels remain open, allowing excessive K+ efflux
This causes after-hyperpolarization of the membrane (undershoot)

32. The AP is caused by permeability changes in the plasma membrane3
Action
potential
Membrane potential (mV)
Na+ permeability 2
Relative membrane permeability
K+ permeability 1 1 4
Time (ms)
Figure (2 of 5)

33. Peak of action potential Hyperpolarization
Voltage
at 0 ms
Recording
electrode
(a) Time = 0 ms. Action
potential has not yet
reached the recording
electrode.
Resting potential
Peak of action potential
Hyperpolarization
Figure 11.12a

34. potential peak is at the recording electrode.
Voltage
at 2 ms
(b) Time = 2 ms. Action
potential peak is at the
recording electrode.
Figure 11.12b

35. A&P Flix™: Propagation of an Action Potential
Voltage
at 4 ms
(c) Time = 4 ms. Action
potential peak is past
the recording electrode.
Membrane at the
recording electrode is
still hyperpolarized.
PLAY
A&P Flix™: Propagation of an Action Potential
Figure 11.12c

36. Impulse Conduction

37. Coding for Stimulus Intensity
All action potentials are alike and are independent of stimulus intensity
How does the CNS tell the difference between a weak stimulus and a strong one?
Strong stimuli can generate action potentials more often than weaker stimuli
The CNS determines stimulus intensity by the frequency of impulses

38. Saltatory Conduction Appear the jump from node to node.
Speed of impulses is much faster on myelinated nerves then unmyelinated ones. Speed also increases with increase in diameter. Ex.) 120m/s skeletal muscle .5m/s skin.

39. Conduction Velocity Conduction velocities of neurons vary widely
Effect of axon diameter
Effect of myelination
Myelin sheaths insulate and prevent leakage of charge
Saltatory conduction in myelinated axons is about 30 times faster

40. Nerve Fiber Classification
Group A fibers
Large diameter, myelinated somatic sensory and motor fibers
Group B fibers
Intermediate diameter, lightly myelinated ANS fibers
Group C fibers
Smallest diameter, unmyelinated ANS fibers

41. The Synapse Presynaptic neuron—conducts impulses toward the synapse
Postsynaptic neuron—transmits impulses away from the synapse
Axodendritic
Axosomatic
Some electrical, most chemical
Cleft = gap

42. Axodendritic synapses Dendrites Axosomatic synapses Cell body
Axoaxonic synapses
(a)
Axon
Axon
Axosomatic
synapses
Cell body (soma) of
postsynaptic neuron
(b)
Figure 11.16

43. Chemical synapses transmit signals from one neuron to another using neurotransmitters.
Presynaptic neuron
Presynaptic neuron
Postsynaptic neuron
Action potential arrives at axon terminal. 1
Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal. 2
Mitochondrion
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+ entry causes neurotransmitter- containing synaptic vesicles to release their contents by exocytosis. 3
Synaptic cleft
Axon terminal
Synaptic vesicles 4
Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane.
Postsynaptic neuron
Ion movement
Enzymatic degradation
Graded potential
Reuptake
Diffusion away from synapse 5
Binding of neurotransmitter opens ion channels, resulting in graded potentials. 6
Neurotransmitter effects are terminated by reuptake through transport proteins, enzymatic degradation, or diffusion away from the synapse.
Figure 11.17

44. postsynaptic membrane that brings the neuron closer to AP threshold.
An EPSP is a local
depolarization of the
postsynaptic membrane
that brings the neuron
closer to AP threshold.
Neurotransmitter binding
opens chemically gated
ion channels, allowing
the simultaneous pas-
sage of Na+ and K+.
Membrane potential (mV)
Threshold
Stimulus
Time (ms)
(a) Excitatory postsynaptic potential (EPSP)
Figure 11.18a

45. hyperpolarization of the postsynaptic membrane and drives the neuron
An IPSP is a local
hyperpolarization of the
postsynaptic membrane
and drives the neuron
away from AP threshold.
Neurotransmitter binding
opens K+ or Cl– channels.
Membrane potential (mV)
Threshold
Stimulus
Time (ms)
(b) Inhibitory postsynaptic potential (IPSP)
Figure 11.18b

46. Integration: Summation
A single EPSP cannot induce an action potential
EPSPs can summate to reach threshold
IPSPs can also summate with EPSPs, canceling each other out

47. Neurotransmitters
Most neurons make two or more neurotransmitters, which are released at different stimulation frequencies
50 or more neurotransmitters have been identified
Classified by chemical structure and by function
Some excite and some inhibit
Can be nucleotides, gas, protein, amino acid, lipoprotein

48. Neurotransmitters

49. (a) Channel-linked receptors open in response to binding
Ion flow blocked
Ions flow
Ligand
Closed ion channel
Open ion channel
(a) Channel-linked receptors open in response to binding
of ligand (ACh in this case).
Figure 11.20a

50. AMP in this case) that brings about the cell’s response.
Neurotransmitter
(1st messenger) binds
and activates receptor. 1
Closed ion
channel
Open ion
channel
Adenylate cyclase
Receptor
G protein
cAMP changes
membrane permeability
by opening or closing ion
channels. 5a
cAMP activates
specific genes. 5c
GDP 5b
cAMP activates
enzymes.
Receptor
activates G
protein. 2
G protein
activates
adenylate
cyclase. 3
Adenylate
cyclase converts
ATP to cAMP
(2nd messenger). 4
Nucleus
Active enzyme
(b) G-protein linked receptors cause formation of an intracellular second messenger (cyclic
AMP in this case) that brings about the cell’s response.
Figure 11.17b

51. Figure 11.22a

52. Figure 11.22b

53. Figure 11.22c, d

54. Clinical Application. Multiple Sclerosis Causes Symptoms
myelin destroyed in various parts of CNS
hard scars (scleroses) form
nerve impulses blocked
muscles do not receive innervation
may be related to a virus
Symptoms
blurred vision
numb legs or arms
can lead to paralysis
Treatments
no cure
bone marrow transplant
interferon (anti-viral drug)
hormones
10-29