1. Nervous Tissue

2. Nervous System Controls and integrates all body activities
Basic functions:
Sense change
Interpret and remember change
React to changes

3. Nervous vs Endocrine System
Nervous system
electrical
fast
local
Endocrine system
chemical
slow
general

4. CNS – brain/spinal cord
Nervous System
CNS – brain/spinal cord
Integration
Processing
input
output
Sensory
Motor
stimulus
PNS
response

5. Organization Central Nervous System – CNS brain spinal cord
Peripheral Nervous System - PNS
somatic (SNS)
sensory
motor
autonomic (ANS)
motor parasympathetic
sympathetic

6. Neurons Functional unit of the Nervous System
Dendrite
Cell
body
Nissl substance
Axon
hillock
Neurofibrils
Collateral
branch
One
Schwann cell
Node of
Ranvier
Schwann cells,
forming the myelin
sheath on axon
Nucleus
terminal
Mitochondrion
(a)
Transmit electrical impulses (action potentials)

7. Structural Classes of Neurons

8. Functional Classes of Neurons
Afferent

9. Functional Classes of Neurons
Efferent

10. Functional Classes of Neurons
Interneurons

11. Functional Classes of Neurons
Dendrites
Peripheral
process (axon)
Ganglion
Cell
body
Sensory
neuron
Central process (axon)
Spinal cord
(central nervous system)
Motor neuron
Interneuron
(association
neuron)
Afferent
transmission
nervous system
Receptors
To effectors
(muscles and glands)
Efferent transmission

12. Neuroglia

13. Schwann Cells
Schwann cell
cytoplasm
plasma membrane
nucleus
Axon
(b)
(a)
Neurilemma
Myelin
sheath
(c)
Myelin:
‘Insulates’ axon. Increases transmission of signal.
Node of Ranvier: Exposed axon between Schwann cells

14. Gray and White Matter

15. Overview of Nervous Function
Skeletal muscles
Brain
Right side of brain
Left side of brain
Cerebral cortex
Interneuron
Upper motor neuron
Thalamus
Spinal cord
Neuromuscular junction
Key:
Graded potential
Nerve action potential
Muscle action potential
Sensory
receptor
neuron
Lower motor neuron 1 2 3 8 7 4 6 5

16. Ion Channels Leakage Channel Ligand-gated channels
Mechanically gated channels
Voltage-gated channels
Ion Channels Animation

17. (b) Ligand-gated channel
Ion Channels
Extracellular fluid
Plasma membrane
Cytosol
K+ leak channel
closed
open K+
Channel randomly
opens and closes
(a) Leakage channel
Extracellular fluid
Plasma membrane
Cytosol
Ligand-gated
channel closed
Chemical stimulus
opens the channel
(b) Ligand-gated channel
channel open
Na+
Ca2+
Acetylcholine K+

18. Ion Channels Extracellular fluid Plasma membrane Cytosol
Mechanically gated channel closed
Mechanical stimulus
opens the channel
(c) Mechanically gated channel
Mechanically gated channel open
Na+
Ca2+
Extracellular fluid
Plasma membrane
Cytosol
Voltage-gated K+ channel closed
Change in
membrane potential
opens the channel
(d) Voltage-gated channel
Voltage-gated
K+ channel open K+
Voltage = –50 mV
Voltage = –70 mV

19. Ion Channels

20. Electrical Signals in Neurons
Like muscle fibers, neurons are electrically excitable. They communicate with one another using two types of electrical signals:
Graded potentials are used
for short-distance
communication only.
Action potentials allow
communication over long
distances within the body. 20

21. Resting Membrane Potential
Negative ions along inside of cell membrane & positive ions along outside
potential energy difference at rest is -70 mV
Resting potential exists because
concentration of ions different inside & outside
extracellular fluid rich in Na+ and Cl-
cytosol full of K+, organic phosphate & proteins
membrane permeability differs for Na+ and K+
50-100x’s greater permeability for K+
inward flow of Na+ can’t keep up with outward flow of K+
Na+/K+ pump removes Na+ as fast as it leaks in

22. Resting Membrane Potential
Extracellular fluid
Plasma membrane
Extracellular
fluid
(a) Distribution of charges that produce the resting membrane potential of a neuron
Cytosol
Equal numbers of + and – charges in most of ECF
Equal numbers of + and – charges in most of cytosol
Resting membrane potential
(an electrical potential difference across the plasma membrane)

23. Resting Membrane Potential

24. Graded Potential Typically on dendrites or cell body
Graded means that potential varies in amplitude.
Stronger the stimulus, greater the amplitude.
Stronger the stimulus the farther it will travel.
Decreases as it gets farther away from the stimulus point.
Graded Potentials Animation

25. Graded Potential

26. Binding of acetylcholine
Graded Potential
Extracellular fluid
Plasma membrane
Cytosol
Ligand-gated channel closed
(b) Depolarizing graded potential caused by the neurotransmitter acetylcholine, a ligand stimulus
Ligand-gated channel
open
Na+
Binding of acetylcholine
Depolarizing
graded
potential
Resting
membrane
Ca2+
Acetylcholine K+
Extracellular fluid
Plasma membrane
Cytosol
Ligand-gated channel closed
(c) Hyperpolarizing graded potential caused by the neurotransmitter glycine, a ligand stimulus
Ligand-gated channel
open
Binding of glycine
Hyperpolarizing
graded
potential
Resting
membrane
Cl–
Glycine

27. Graded Potential

28. Graded Potential

29. Action Potential

30. Action Potential Extracellular fluid Plasma membrane Cytosol Time K+
Inactivation
gate open
Na+
Na+ channel
K+ channel
Activation
gate closed mV
1. Resting state:
All voltage-gated Na+ and K+ channels are closed. Axon plasma membrane is at resting membrane potential: small buildup of negative charges along inside surface of membrane and equal buildup of positive charges along outside surface of membrane.

31. Action Potential 2. Depolarizing phase:
Time K+
Na+ mV
2. Depolarizing phase:
When membrane potential of axon reaches threshold, Na+ channel activation gates open. As Na+ ions move through these channels into neuron, buildup of positive charges forms along inside surface of membrane and membrane becomes depolarized.

32. Action Potential mV Time Na+ 3. Repolarizing phase begins:K+
Na+ mV
3. Repolarizing phase begins:
Na+ channel inactivation gates close and K+ channels open. Membrane starts to become repolarized as some K+ ions leave neuron and few negative charges begin to build up along inside surface of membrane.

33. Action Potential Na+ K+ 4. Repolarization phase continues:
Time
Na+ mV
4. Repolarization phase continues:
K+ outflow continues. As more K+ ions leave neuron, more negative charges build up along inside surface of membrane. K+ outflow eventually restores resting membrane potential. Na+ channel inactivation gates open. Return to resting state occurs when K+ gates close. K+

34. Action Potential

35. Comparison of Graded & Action Potentials

36. Continuous Conduction
Cell body
Na+
Leading edge of
action potential
(a) Continuous conduction
Current flow due to opening of Na+ channels
Trigger zone
Time 1
msec 5 10

37. (b) Saltatory conduction
Cell body
Na+
Leading edge of
action potential
(b) Saltatory conduction
Current flow due to opening of Na+ channels
Trigger zone
Time 1
msec 5 10
Nodes of Ranvier

38. Stimulus Intensity How do we differentiate a light touch from a firmer
frequency of impulses
firm pressure generates impulses at a higher frequency
number of sensory neurons activated
firm pressure stimulates more neurons than does a light touch

39. Signal Transmission at Synapses
2 Types of synapses
electrical
ionic current spreads to next cell through gap junctions
faster, two-way transmission & capable of synchronizing groups of neurons
chemical
one-way information transfer from a presynaptic neuron to a postsynaptic neuron
axodendritic -- from axon to dendrite
axosomatic -- from axon to cell body
axoaxonic -- from axon to axon

40. Chemical Synapse Presynaptic neuron Nerve impulse Ca2+
Postsynaptic neuron
Nerve impulse 1
Presynaptic neuron
Synaptic end bulb
Neurotransmitter
receptor
Ligand-gated
channel closed
Ca2+
Voltage-gated Ca2+ channel
Cytoplasm
channel open
Na+
Synaptic vesicles
Postsynaptic
potential
Synaptic cleft 2 3 4 5 6 7

41. Neurotransmitters ATP and Other Purines Acetylcholine Nitric oxide
Neuropeptides
endorphins
enkephalin
dynorphins
substance P
Acetylcholine
Amino Acids
glutamate and aspartate
GABA and glycine
Biogenic amines
norepinephrine
epinephrine
dopamine
serotonin

42. Neurotransmitters

43. Postsynaptic potentials
Excitatory postsynaptic potential (EPSP)
Na+ and K+ gates open at the same time, Na+ diffuses faster results in a depolarizing potential

44. Postsynaptic Potential
Inhibitory postsynaptic potential (IPSP)
Membrane made more permeable to K+ and Cl-, Na+ not affected results in a hyperpolarization

45. Removal of Neurotransmitter
Neurotransmitter must be removed from the synapse for
normal synaptic function.
- Diffusion
- Enzymatic degradation
- Uptake by cell
Events at the Synapse

46. Summation

47. Summation Presynaptic neuron 3 Cell body Dendrites
Trigger zone (net summation of EPSPs and IPSPs determines whether an action potential is generated here)
Excitatory
neurotransmitter
Postsynaptic neuron
Cell body
Dendrites
Axon
terminal
Inhibitory
Presynaptic neuron 5
Presynaptic neuron 4
Presynaptic neuron 3
Presynaptic neuron 2
Presynaptic neuron 1
EPSP
IPSP