1. Chapter 10 Nervous System I
Cell Types of Neural Tissue
neurons
neuroglial cells

2. Composed of some blood vessels and connective tissue but mostly neural tissue
(2 cell types)
neurons
neuroglia
Neurons transmit information as nerve impulses along nerve fibers
Nerves are bundles of nerve fibers

3. Neuroglia surround, support, and nourish neurons and might even send and receive messages
Synapses are spaces between neurons
Neurotransmitters are biological messengers
Central nervous system (CNS) consists of the brain and spinal cord

4. Peripheral nervous system (PNS) consists of the peripheral nerves that connect the CNS to other body parts
CNS and PNS provide 3 general functions: sensory, integrative, and motor

5. Sensory receptors at the ends of peripheral neurons gather information:
Info  nerve impulse  CNS  integration  decision made  motor neurons  muscles or glands (effectors)

6. Divisions of the Nervous System
Central Nervous System
brain
spinal cord
Peripheral Nervous System
nerves
cranial nerves
spinal nerves

7. Divisions of Peripheral Nervous System
Sensory Division
picks up sensory information and delivers it to the CNS
Motor Division
carries information to muscles and glands
Divisions of the Motor Division
Somatic – carries information to skeletal muscle
Autonomic – carries information to smooth muscle, cardiac muscle, and glands

8. Divisions Nervous System

9. Functions of Nervous System
Sensory Function
sensory receptors gather information
information is carried to the CNS
Motor Function
decisions are acted upon
impulses are carried to effectors
Integrative Function
sensory information used to create
sensations
memory
thoughts
decisions

10. Neuron Structure

11. Mature neurons generally do not reproduce
All neurons have a cell body and nerve fibers
Cell body contains: granular cytoplasm, mitochondria, lysosomes, a Golgi apparatus, microtubules
Neurofibrils (fine threads) extends into and supports fibers

12. Chromatophilic substance (nissl bodies) made of rough endoplasmic reticulum is scattered in cytoplasm
Cytoplasmic inclusions include glycogen, lipids, and pigments
Large nucleus near the center with a nucleolus
Nerve fibers, dendrites and axons extend from the cell body

13. Dendrites are usually branched and communicate with other neurons
Axons carry nerve impulses away from the cell body
Axons also convey biochemicals produced in the cell body (axonal transport)
Schwann cells wind around axons in layers called myelin

14. Myelin has higher lipids than other surface membranes and forms a myelin sheath on the outside of axons
A neurilemmal sheath made of Schwann cells that have most of the cytoplasm and nuclei forms outside the myelin sheath
Nodes of Ranvier are gaps in myelin sheath between Schwann cells

15. Myelinated fibers appear white (white matter in brain and spinal cord)
Small axons don’t have myelin (unmyelinated) and appears gray (gray matter in brain and spinal cord)

16. Myelination of Axons White Matter contains myelinated axons
Gray Matter
contains unmyelinated structures
cell bodies, dendrites

18. Classification of Neurons – Structural Differences
Bipolar
two processes
eyes, ears, nose
Unipolar
one process
ganglia
Multipolar
many processes
most neurons of CNS

19. Neurons Vary in size and shape
May differ in length and size of axons and dendrites
Vary in the number of processes by which they communicate with other neurons
Vary in function

20. 3 types classified by structure: bipolar, unipolar, multipolar (Table 10.1)
3 types classified by function: sensory, interneuron, motor (Table 10.1)

21. Classification of Neurons – Functional Differences
Sensory Neurons
afferent
carry impulse to CNS
most are unipolar
some are bipolar
Interneurons
link neurons
multipolar
in CNS
Motor Neurons
multipolar
carry impulses away from CNS
carry impulses to effectors

23. Types of Neuroglial Cells in the PNS
Schwann Cells
produce myelin found on peripheral myelinated neurons
speed neurotransmission
Satellite Cells
support clusters of neuron cell bodies (ganglia)

24. Neuroglia
Guide neurons in the embryo to their positions and may stimulate them to specialize
Produce growth factors that nourish neurons
Remove ions and neurotransmitters that build up in between neurons, allowing continued information transmission

25. Some may communicate with neurons
Schwann cells are the neuroglia of the PNS
CNS neuroglia: astrocytes, oligodendrocytes, microglia, and ependyma

26. Neuroglia form more than half the volume of the brain
Most brain tumors are neuroglia that multiply too often

27. Types of Neuroglial Cells in the CNS
Astrocytes
CNS
scar tissue
mop up excess ions, etc
induce synapse formation
connect neurons to blood vessels
Microglia
CNS
phagocytic cell
Ependyma
CNS
ciliated
line central canal of spinal cord
line ventricles of brain
Oligodendrocytes
CNS
myelinating cell

28. Types of Neuroglial Cells

29. Regeneration of A Nerve Axon

30. Mature neurons do not reproduce
Injury to a neuron cell body usually kills it
Damaged axons in a peripheral nerve may regenerate (3-4mm /day), but may end up in the wrong place so full function often does not return

31. Neuroglial cells assist in regeneration (nerve growth factors)
Damaged axons in the CNS are unable to produce myelin and regeneration is unlikely

32. The Synapse
Nerve impulses pass from neuron to neuron at synapses

33. Synaptic Transmission
Neurotransmitters are released when impulse reaches synaptic knob

34. Cell Membrane Potential
A cell membrane is polarized (electrically charged) due to unequal distribution of ions. The inside is negative with respect to the outside.

35. Distribution of Ions
K+ are the major ions inside the cell (intracellular)
Na+ are the major extracellular ions
Channels in the membrane allow movement in and out
Chemical and electrical factors affect the opening and closing of these gatelike channels

36. Resting nerve cell is not being stimulated to send an impulse
K+ pass through resting cell membranes much easier than Na+
Ca2+ less able to cross a resting cell membrane than K+ or Na+

37. Resting Membrane Potential
inside is negative relative to the outside
polarized membrane
due to distribution of ions
Na+/K+ pump

38. Active transport keeps a greater concentration of K+ inside the cell and a greater concentration of Na+ outside the cell
Cytoplasm contains anions: (PO4-2), (SO4-2), and proteins that can’t diffuse through the cell membrane

39. Na+ and K+ follow the laws of diffusion (high to low)
more K+ diffuses out than Na+ can move in
more + charges leave the cell than enter
outside of the cell has a positive charge and the inside has a negative charge

40. Difference in electrical charge = potential difference (measured in volts)
Difference between inside and outside = -70 millivolts
Resting potential = separation of charge
Action potential = work it may do to send a nerve impulse

41. Local Potential Changes
caused by various stimuli
temperature changes
light
pressure
environmental changes affect the
membrane potential by opening a
gated ion channel

42. Local Potential Changes
if membrane potential becomes more negative, it has hyperpolarized
if membrane potential becomes less negative, it has depolarized
graded
summation can lead to threshold stimulus that starts an action potential

43. Local Potential Changes

44. Nerve cells can respond to changes in their surroundings
Changes affect the resting potential of the membrane
Hyperpolarized = membrane potential becomes more negative than resting potential

45. Depolarized = membrane potential becomes more positive than resting potential (Na+ move in)
Threshold potential = strong enough depolarization to conduct a nerve impulse (action potential

46. Action Potentials at rest membrane is polarized
threshold stimulus reached
sodium channels open and membrane depolarizes
potassium leaves cytoplasm and membrane repolarizes

47. Action Potentials Reached when the membrane potential becomes positive
When the threshold potential is reached Na+ move into the cell causing the membrane potential to become more positive (as high as +30 mV)  depolarization

48. At the same time K channels open and allow K+ to move out
causing the inside to become negative again  repolarization
Rapid sequence of depolarization and repolarization causes an electric current to move down the nerve fiber  nerve impulse

49. Action Potentials

50. Action Potentials

51. All-or None Response If a nerve fiber responds, it responds completely
All impulses are the same strength
Greater intensity of stimulation produces more impulses per second

52. Refractory Period
Short time after a nerve impulse that a threshold stimulus will not trigger another impulse
Limits the rate of nerve conduction
about one /millisecond

53. Impulse Conduction

54. Impulse conduction
Unmyelinated nerve fiber conducts an impulse over the entire surface
Myelinated fibers conduct impulses at only the nodes of ranvier
myelin insulates and prevents the flow of ions through the membrane

55. myelin made of lipids that are insoluble to water soluble substances
action potentials jump from node to node (saltatory conduction)
Myelinated axons conduct impulses much faster than unmyelinated axons

56. The larger the diameter of the fiber the faster the impulse is conducted
Ex: skeletal muscle motor fiber = 120m /s
unmyelinated sensory fiber = 0.5m/s

57. Saltatory Conduction

58. The Synapse Junction between two cells
Synaptic cleft is a space between two cells
Synaptic knobs are at the end of axons
contain vesicles that contain neurotransmitters
Neurotransmitters (NT) are released when a nerve impulse reaches the end of the axon – they diffuse across the synaptic cleft

59. Synaptic Potentials
Some NT depolarize membranes causing an action potential  excitatory postsynaptic potential (EPSP)
Some NT hyperpolarize membranes inhibiting an action potential  inhibitory postsynaptic potential (IPSP)
EPSPs and IPSPs are summed at the trigger zone (axon area close to cell body)  decision making part of the axon

60. Summation of EPSPs and IPSPs
EPSPs and IPSPs are added together in a process called summation
More EPSPs lead to greater probability of action potential

61. Neurotransmitters

62. Neurotransmitters

63. Neurotransmitters At least 30 different types
Neurons release 1-3 kinds
Synthesized in synaptic knobs and stored in synaptic vesicles

64. Ca2+ cause NT to be released
Enzymes decompose some NT to keep the impulse short
Reuptake transports some NT back into synaptic knobs
Removal of NT prevents continuous stimulation

65. Neuropeptides Act as NT or neuromodulators
Alter a neurons response to a NT or block its release
Enkephalins – bind to opiate receptors in brain and relieve pain
Beta endorphin – pain reliever

66. Substance P – transmits pain impulses into the spinal cord and then to the brain
enkephalins and endorphins may relieve pain by inhibiting the release of substance P

67. Impulse Processing Neuronal Pools Groups of neurons in the CNS
Each receive impulses from afferent nerve fibers
Each input fiber divides and branches
Impulses are conducted away from CNS on efferent output fibers

68. Facilitation
If incoming impulses do not reach threshold the neuron becomes more excitable to incoming stimulation

69. Convergence neuron receives input from several neurons
incoming impulses represent information from different types of sensory receptors
allows nervous system to collect, process, and respond to information
makes it possible for a neuron to sum impulses from different sources

70. Divergence one neuron sends impulses to several neurons
can amplify an impulse
impulse from a single neuron in CNS may be amplified to activate enough motor units needed for muscle contraction

71. Clinical Application Drug Addiction
occurs because of the complex interaction of neurons, drugs, and individual behaviors
understanding how neurotransmitters fit receptors can help explain the actions of certain drugs
drugs have different mechanisms of action
several questions remain about the biological effects of addiction, such as why some individuals become addicted and others do not