The nervous system is composed of the central nervous system (CNS) and peripheral nervous system (PNS). The CNS contains the brain and spinal cord while the PNS contains nerves, ganglia and sensory receptors. Neurons are the basic functional units that transmit electrochemical signals. The neuron has a cell body, dendrites, axon and synapse. Neuroglia provide support and protection to neurons. The nervous system uses electrical and chemical signals for communication. Neurotransmitters are released at synapses to transmit signals between neurons. While the nervous system has limited regeneration, neurogenesis allows new neurons to form.

1. NERVOUS TISSUE
CHAPTER12
Aubrey Vale G. Sagun

2. OVERVIEW OF THE
NERVOUS SYSTEM

3. The Nervous System
•The network of nerve cells
and fibers that transmits
nerve impulses between parts
of the body.

4. Components of Nervous System
Nerve cells /
Neurons
Brain Spinal cord

5. The Brain - Part of the CNS that is located in the skull.
- Contains about 100 billion neurons

6. The Spinal
Cord
• The Spinal cord is connected to the brain
through the foramen magnum and is
encircled by the bones of the vertebral
column.
• It contains about 100 million neurons.

7. Nerve cell /
Neuron
- also known as nerve cells,
communicate within the body by
transmitting electrochemical signals

8. Two Divisions of Nervous System
Peripheral
Nervous
System
(PNS)
Central
Nervous
System
(CNS)

9. The Central Nervous System
Consists of:
-Brain
-Spinal Cord

10. The Peripheral Nervous System
Consists of:
-All nervous tissue outside CNS
- nerves
- ganglia
- enteric plexuses
- sensory receptors

11. Ganglia - Are small masses of nervous
tissue, consisting primarily of
neuron cell bodies, that are
located outside of the brain and
spinal chord.

12. Enteric
Plexus
- Are extensive networks of
neurons located in the walls of
organs of the Gastrointestinal
tract.
- The neurons of these plexuses
help regulate the digestive
system.

13. Sensory
Receptors
- Refers to a structure of the
nervous system that monitors
changes in the external and
internal environment.

14. Three Divisions of Peripheral Nervous
System
Autonomic
Nervous
System
(ANS)
Enteric
Nervous
System
(ENS)
Somatic
Nervous
System
(SNS)

15. Somatic Nervous System (SNS)
Consists of :
1. Sensory neurons that convey
information from somatic
receptors in the head, body wall,
and limbs and from receptors for
the special senses of vision,
hearing, taste and smell to the
to the CNS.
2. Motor Neurons that
conduct impulses from the
CNS to skeletal muscles only.

16. Autonomic Nervous System (ANS)
1. Sensory neurons that convey
information from autonomic
sensory receptors.
2. Motor neurons that conduct
nerve impulses from the CNS to
smooth muscle, cardiac muscle
and glands.
Consists of :

17. Two branches of the motor part of the ANS
Parasympathetic division
Is responsible for stimulation of
“rest and digest” or “feed and
breed”
.
Sympathetic division
Is responsible for stimulation of
“fight or flight”

18. Enteric Nervous System (ENS)
•The ENS is the subdivision of the Autonomic Nervous
System that directly control the Gastrointestinal
system.

19. Three basic Functions of Nervous System
•Sensory Function
•Integrative Function
•Motor Function

20. Sensory Function
• monitors internal & external environment through presence of
receptors

21. Integrative Function
 interpretation of sensory information (information processing);
complex (higher order) functions

22. Motor Function
 response to information processed through stimulation of
effectors
 muscle contraction
 glandular secretion

23. HISTOLOGY OF
NERVOUS
TISSUE

24. Nervous
Tissues
Comprises two types of cells.
- Neurons
- Neuroglia

25. • For processing, transfer, and storage of
information
• are specialized to carry "messages" through
an electrochemical process
• is a basic unit of nervous system
• Properties of neuron:
- Excitability
- Conductivity
Neuron

26. Parts of a
Neuron

27. Cell body
(perikaryon /soma)
- Contains the nucleus &
mitochondria, ribosomes, and
other organelles.
Axon
- Propagates nerve impulses
toward another neuron, a
muscle fibre or a gland cell.
Dendrites
- Are the receiving or input
portions of a neuron.
Three Main parts of a Neuron

28. Other parts of a Neuron
Neurofibrils
• Composed of
bundles of
intermediate
filaments that
provide the cell
shape and
support
Microtubules
• Assist in moving
materials between
the cell body and
axon
Nerve fibre
• Is a general term
for any neural
process that
emerges from the
cell body of a
neuron
Nissl bodies
• Group of
ribosomes used for
protein synthesis

29. • Synapse
– the site of
communication between
two neurons or between
a neuron and an effector
cell.
• Neurotransmitter
A molecule released
from a synaptic vesicle
that excites or inhibits
another neuron,
muscle fibre or gland
cell
• Synaptic end bulb
Contains synaptic
vesicles which are
filled with a
neurotransmitter
substance
• Synaptic vesicles
Store various
neurotransmitters
that are released at
the synapse
• Node of Ranvier
Periodic gaps in the
myelin sheath

30. Classification of Neurons
•Multipolar neuron
•Bipolar neuron
•Unipolar neuron

31. • Bipolar – have one
main dendrite and one
axon.
• Multipolar– have
several dendrites and
one axon.

32. • Unipolar – have
dendrites and one
axon.

33. Functional Classification of Neurons
• Sensory (afferent) neurons –
• transmit sensory information from receptors of PNS towards the CNS
• most sensory neurons are unipolar, a few are bipolar
• Motor (efferent) neurons –
• transmit motor information from the CNS to effectors (muscles/glands/adipose tissue) in
the periphery of the body
• all are multipolar
• Association (interneurons) –
• transmit information between neurons within the CNS; analyze inputs, coordinate
outputs
• are the most common type of neuron (20 billion)
• are all multipolar
Functional classification based on type of information & direction of information transmission:

34. • For support, regulation and protection
of neurons.
• Held nervous tissue together
Neuroglia

35. Neuroglia of the CNS
• Oligoendrocytes
•create myelin sheath
around axons of
neurons in the CNS.
Myelinated axons
transmit impulses
faster than
unmyelinated axons
• Microglia
•brain
Macrophages
• phagocytize
cellular wastes &
pathogens
• Ependymal cells
•line ventricles of
brain & central canal
of spinal cord
• produce, monitor &
help circulate CSF
(cerebrospinal fluid)
• Astrocytes
•create supportive
framework for neurons
•create “blood-brain
barrier”
•monitor & regulate
interstitial fluid
surrounding neurons

36. Neuroglia of the PNS
•Satellite Cells
•support groups of
cell bodies of neurons
within ganglia of the
PNS
•surround all axons of neurons
in the PNS creating a
neurilemma around them.
•Neurilemma allows for
potential regeneration of
damaged axons
• creates myelin sheath
around most axons of PNS
• Schwann Cells

37. Myelination
• Increases the speed
of nerve impulse
conduction.

38. UnmyelinatedMyelinated

39. Gray and White Matter
CNS Two kinds of
tissue
Gray Matter contains the cell
bodies, dendrites and axon
terminals of neurons
White Matter is made of axons
connecting different parts of grey
matter to each other.

40. ELECTRICAL
SIGNALS IN
NEURONS

41. Ion Channels
• A protein that acts as a pore in a cell membrane and permits
the passage of selective ions.
• Controls the flow of ions

42. Ion channels in Neurons

43. Resting Membrane Potential
• Is the voltage (charge) difference across the cell
membrane when the cell is at rest.

44. Two types of Electric signals
•Action
Potentials
Allow communication
over long distances
•Graded
Potentials
Used in short distance
communication

45. Graded Potentials - is a small deviation from
the membrane potential
that makes the membrane
either more polarized or
less polarized.

46. Generation of
Action Potentials
Is the process by which a neuron rapidly
depolarizes from a negative resting potential to
a more positive potential, and is achieved by
influx of cations through ion channels.

47. After-hyperpolarizing Phase
Describes the
hyperpolarizing phase
of a neuron’s action
potential where the
cell’s membrane falls
below the normal
resting potential
Refractory Period
A period immediately
following stimulation
during which a nerve or
muscle is unresponsive
to further stimulation.
Depolarizing Phase
Is when the membrane
potential becomes
more negative at a
particular spot on the
neuron’s membrane
Repolarizing Phase
Typically results from
the movement of
positively charged ions
out of the cell

48. Propagation of
Action Potentials

49. Two types of Propagation
Saltatory
conduction
Continuous
conduction

50. SIGNAL
TRANSMISSION
AT SYNAPSES

51. Synapse
• It is the site of communication of neurons which consists of:
A. Presynaptic Neuron
A. Postsynaptic Neuron
Sends the Signal
Receives the message

52. Two types of Synapses
• Chemical Synapse • Electrical Synapse

53. Electrical Synapse
•Transmission is DIRECT because of gap junctions.
Action potentials
(impulses) conduct
directly between
adjacent cells through
GAP JUNCTIONS

55. Electrical Synapse
Two main advantages of Electrical synapse
1. Faster
Communication
2. Synchronization

56. Transmission of
Signal in an Electrical
Synapse

58. Chemical Synapse
•Transmission is INDIRECT because of synaptic cleft.
Membranes are close but
do not touch with the
presence of
SYNAPTIC CLEFT

59. Three types of Chemical Synapse
Axodendritic
Axon to dendrite
Axosomatic
Axon to soma
Axoaxonic
Axon to axon

60. Transmission of
Signal in a Chemical
Synapse

62. 1
2
3 4
The synapse carries a signal from cell to cell

63. Excitatory and Inhibitory Postsynaptic
Potentials
• A neurotransmitter causes either an excitatory or an inhibitory graded
potential.
A neurotransmitter : Messenger of the Brain - is a
chemical messenger that transmits signals from a
neuron to a target cell across a synapse.
•A graded potential depolarization is called excitatory
postsynaptic potential (EPSP).
• A graded potential hyperpolarization is called an inhibitory
postsynaptic potentials (IPSP).

64. Two Classes of Neurotransmitter based on
size.
1. Small-molecule
neurotransmitter
2. Neuropeptides
Acetyl choline, Amino acids,
Biogenic amines, ATP and
other Purines, Nitric Oxide
and Carbon Monoxide
Composed of 3-40 amino
acids

65. ACETYL CHOLINE
AMINO ACIDS
ATP AND OTHER PURINES
NITRIC OXIDE
CARBON MONOXIDE
1. Small-molecule
neurotransmitter

66. NEUROPEPTIDES
Are relatively large transmitter
molecules composed of 3-36
amino acids.

67. INHIBITORY
POSTSYNAPTIC
POTENTIAL
INHIBITORY: IF THE
NEUROTRANSMITTER
DEPOLARIZES THE
POSTSYNAPTIC MEMBRANE

68. EXCITATORY
POSTSYNAPTIC
POTENTIAL
EXCITATORY: IF THE
NEUROTRANSMITTER
CAUSES
HYPERPOLARIZATION OF
OF THE POSTSYNAPTIC
MEMBRANE

69. NEUROTRANSMITTER RECEPTOR
•Is a membrane receptor protein that is activated by a
neurotransmitter

70. Types of Neurotransmitter Receptor
•Ionotropic
Receptor
•Metabotropic
Receptor

71. Ionotropic Receptor
• a type of neurotransmitter
receptor that contains a
neurotransmitter binding
site and an ion channel.

72. Metabotropic
Receptor
• a type of neurotransmitter
receptor that contains a
neurotransmitter binding site
but lacks an ion channel as
part of its structure.

73. Summation of Postsynaptic Potentials
TWO TYPES
SPATIAL
SUMMATION
TEMPORAL
SUMMATION
Results from build-up of
neurotransmitter released
simultaneously by SEVERAL
presynaptic end bulb.
Results from build-up of
neurotransmitter released
by a SINGLE presynaptic
end bulb two or more times
in rapid succession.

74. NEURAL
CIRCUITS

75. NEURAL CIRCUITS
• Neurons in the central nervous system are organized into
networks called NEURAL CIRCUITS.

76. TYPES OF
NEURAL CIRCUIT

77. DIVERGING CIRCUIT
REVERBERATING
CIRCUIT
4 TYPES
OF A
NEURAL
CIRCUIT
PARALLEL AFTER
DISCHARGE CIRCUIT
CONVERGING CIRCUIT
A mechanism for spreading stimulation
to multiple neurons or neuronal pools
in the CNS
A mechanism for providing input to a
single neuron from multiple sources
A positive feedback mechanism
A combination of
Converging circuit
and Diverging
circuit

78. REGENRATION AND REPAIR OF NERVOUS
TISSUE
• The Nervous system exhibits plasticity but it has very limited powers
of regeneration.

79. NEUROGENESIS
The birth of new neurons from undifferentiated stem
cells – occurs regularly in some animal cells.