what is nervous tissue

a quick visual understanding of what actually nervous tissue is made up of at cellular level its functions nerve cell types chemical synapse detailed structure of neuron

1. Nervous Tissue Nervous Tissue

2. Common course objectives:
1.1.Functions of the nervous systemFunctions of the nervous system
2.2.Organization of the nervous systemOrganization of the nervous system
3.3.Nerve tissue and nerve cell typesNerve tissue and nerve cell types
4.4.Structure of a typical neuronStructure of a typical neuron
5.5.Structure of a chemical synapseStructure of a chemical synapse

3. Nervous Tissue Histology
Composed of:
Neurons are true conducting cells in nervous tissue
Neuroglial (supporting) cells
-Astrocytes -Schwann cells
-Oligodendrocytes -Satellite cells
-Microglia
-Ependymal

4. The Nervous The Nervous SystemSystem
Defined: Defined: like the CPU of a computer, the nervous like the CPU of a computer, the nervous
system is the system is the master controlling systemmaster controlling system of the body. It is of the body. It is
designed to constantly and rapidly adjust and designed to constantly and rapidly adjust and
respond to stimuli the body receives. It includes the respond to stimuli the body receives. It includes the
brain, cranial nerves, spinal cord, and associated brain, cranial nerves, spinal cord, and associated
peripheral nerves. peripheral nerves.
Divisions of the nervous sytem:Divisions of the nervous sytem:
CNS = Brain + spinal cordCNS = Brain + spinal cord
PNS = Cranial nerves (12) + Spinal nerves (31 pairs)PNS = Cranial nerves (12) + Spinal nerves (31 pairs)
PNS = ANS, SS and SMSPNS = ANS, SS and SMS

5. Properties of NeuronsProperties of Neurons
1.1.ExcitabilityExcitability (irritability): ability to respond to environmental (irritability): ability to respond to environmental
changes or stimuli.changes or stimuli.
2.2.ConductivityConductivity: respond to stimuli by initiating electrical : respond to stimuli by initiating electrical
signals that travel quickly to other cells at distant locations.signals that travel quickly to other cells at distant locations.
3.3.SecretionSecretion: Upon arrival of the impulse at a distant location : Upon arrival of the impulse at a distant location
the neuron usually secretes a chemical neurotransmitter at a the neuron usually secretes a chemical neurotransmitter at a
synapse that crosses the synaptic gap and stimulates the next synapse that crosses the synaptic gap and stimulates the next
cell.cell.

6. NeuronsNeurons
Nerve cell proper:Nerve cell proper:
Cell body (soma)Cell body (soma)
Dendrites - TODendrites - TO
Axons -FROMAxons -FROM

7. Functional Classes of Neurons
Sensory (afferent) neuronsSensory (afferent) neurons – afferent neurons are – afferent neurons are
specialized to detect stimuli and transmit the information to specialized to detect stimuli and transmit the information to
CNS. They begin in any organ in the body, but end in the CNS. They begin in any organ in the body, but end in the
brain or spinal cord.brain or spinal cord.
Interneurons (association neurons):Interneurons (association neurons): lie entirely in the lie entirely in the
CNS. They receive signals from many different neurons and CNS. They receive signals from many different neurons and
perform an integrative function “decision making” to perform an integrative function “decision making” to
respond to the different stimuli. respond to the different stimuli.
Motor (efferent) neuronsMotor (efferent) neurons – – efferent neurons transmit the efferent neurons transmit the
appropriate response from the interneuron to an end organ appropriate response from the interneuron to an end organ
(muscle and gland cells) to carry out the body’s response to (muscle and gland cells) to carry out the body’s response to
the stimuli.the stimuli.

8. Functional Classification of NeuronsFunctional Classification of Neurons
Based on the direction of conductionBased on the direction of conduction
Sensory or afferent conduct toward the CNS ~ 100 millionSensory or afferent conduct toward the CNS ~ 100 million
Motor or efferent conduct away from the CNS ~ 500,000Motor or efferent conduct away from the CNS ~ 500,000
Interneuron interposed between sensory and motor ~ 500 Interneuron interposed between sensory and motor ~ 500
billionbillion

9. Organization of the Nervous System
Two main divisions:
The Central Nervous System (CNS)
- Consists of the brain and spinal cord with tracts and
nuclei
Nucleus = a collection of nerve cell bodies in the CNS.
Tract = bundle of nerve fibers within the CNS
The Peripheral Nervous System (PNS)
-Consists of ganglia, cranial nerves, spinal nerves and
peripheral receptors
Ganglia = a collection of nerve cell bodies in the PNS
Nerve = bundle of nerve fibers in the PNS

10. Organization of the Nervous System

11. Functional divisions of nervous system

12. CNSCNS = brain and = brain and
spinal cordspinal cord

13. Peripheral Nervous System (PNS)
Composed of cranial nerves and spinal nerves and Composed of cranial nerves and spinal nerves and
their branches, ganglia and sensory receptors. their branches, ganglia and sensory receptors.
PNS PNS is subdivided into sensory and motor divisions:is subdivided into sensory and motor divisions:
 somatic nervous system (SNS)somatic nervous system (SNS)
 autonomic nervous system (ANS) and theautonomic nervous system (ANS) and the
 enteric nervous system (ENS)enteric nervous system (ENS)

14. Sensory or Afferent Division
 Somatic sensory = = senses touch, pressure, pain, senses touch, pressure, pain,
temperature, vibration and proprioception in skin, temperature, vibration and proprioception in skin,
body wall and limbs.body wall and limbs.
 Visceral sensory = Autonomic sensory division- = Autonomic sensory division-
sensessenses stretch, pain, temperature, chemical changes stretch, pain, temperature, chemical changes
and irritation in viscera; nausea and hungerand irritation in viscera; nausea and hunger. .

15. Motor or Efferent Division
Somatic motor
--motor control to all skeletal muscles except pharyngeal motor control to all skeletal muscles except pharyngeal
muscles.muscles.
Visceral Motor = Autonomic Nervous System = Autonomic Nervous System
-Sensory receptors convey information from visceral organs -Sensory receptors convey information from visceral organs
(e.g. heart, lungs, intestines, etc.) to the CNS for integration (e.g. heart, lungs, intestines, etc.) to the CNS for integration
and interpretation. and interpretation.
-A motor response is initiated that conducts impulses from -A motor response is initiated that conducts impulses from
CNS to smooth muscle, cardiac muscle and/or glands for CNS to smooth muscle, cardiac muscle and/or glands for
appropriate responseappropriate response

16. Autonomic Nervous System
Two divisions of ANSTwo divisions of ANS
Sympathetic division – Fight or FlightSympathetic division – Fight or Flight
Parasympathetic division – Food or SexParasympathetic division – Food or Sex

17. CNS/PNS summary

18. Structural Classification of Neurons
Neurons may be: Multipolar, Bipolar or Unipolar
Determined by the number of processes attached to
the cell body

19. Neurons
Most (99%) neurons in the body are multipolar.
Bipolar neurons are rare and occur in special sense
organs of ear, nose and eye.
Unipolar neurons begin as bipolar but processes
fuse into one. They are primarily sensory neurons.
ex. dorsal root ganglion

20. Neuroglia cells
Found in CNS and PNS
Perform a supporting function for neurons
 CNS PNS
Oligodendrogliocytes Schwann cells
Astrocytes Satellite cells
Ependymal cells
Microglia

21. Neuroglia cells

22. Oligodendrogliocytes -CNS
Form myelin sheath in CNS
Fewer branches than astrocytes

23. Myelin
Insulating layer around a nerve
Formed by oligodendrocytes in CNS and Schwann
cells in PNS
Composed of a lipoprotein with phospholipids,
glycolipids and cholesterol.
Myelination is the process of myelin formation
Myelin allows nerve conduction to be 150 x faster
than nonmyelinated nerves. This occcurs by “Saltatory
conduction” and the impulse jumps from Node to
Node.

24. Microglia - CNS
Thorny bushes in appearance and the smallest glia
Phagocytic function in CNS
Originate from monocytes

25. Astrocytes - CNS
Star shapedStar shaped Most numerous Most numerous
Blood brain barrierBlood brain barrier

26. Ependymal cells - CNS
Epithelial cells that line ventricles and central cavities of brain Epithelial cells that line ventricles and central cavities of brain
and spinal cord-secrete CSFand spinal cord-secrete CSF
Ciliated to help circulate CSFCiliated to help circulate CSF

27. Schwann cells- PNS
Form myelin sheath around peripheral axonsForm myelin sheath around peripheral axons
Look like jelly roll with neurolemma coverLook like jelly roll with neurolemma cover
Node of Ranvier separates each Schwann cellNode of Ranvier separates each Schwann cell

29. Myelin and Unmyelinated fibers

30. Nerve conduction velocityNerve conduction velocity
Velocity is dependent on size and myelination.Velocity is dependent on size and myelination.

31. Satellite cells -PNS
Surround neuron cell bodies within gangliaSurround neuron cell bodies within ganglia
Provide nutrients, remove metabolites etc.Provide nutrients, remove metabolites etc.

32. Nerve structureNerve structure
Nerves are only in the peripheryNerves are only in the periphery
Cable-like organs in PNS = cranial and spinal nervesCable-like organs in PNS = cranial and spinal nerves
Consists of 100’s to 100,000’s of myelinated and Consists of 100’s to 100,000’s of myelinated and
unmyelinated axons (nerve fibers).unmyelinated axons (nerve fibers).
EndoneuriumEndoneurium surrounds each axon (nerve fiber). surrounds each axon (nerve fiber).
Axons are grouped into bundles of Axons are grouped into bundles of fasciclesfascicles
PerineuriumPerineurium surrounds each fascicle surrounds each fascicle
Epineurium Epineurium surrounds each nerve bundlesurrounds each nerve bundle
Conduction is saltatory (i.e. jumps node to node) in Conduction is saltatory (i.e. jumps node to node) in
myelinated nerves and continuous in nonmyelinated.myelinated nerves and continuous in nonmyelinated.

33. Nerve anatomyNerve anatomy

35. Synapse
The connection between 2 or more nerves and The connection between 2 or more nerves and
they are separated by a space or cleft. they are separated by a space or cleft.

36. Synaptic terminology
SynapseSynapse – site where two nerves communicate with – site where two nerves communicate with
each other.each other.
Presynaptic neuronPresynaptic neuron – neuron that is conducting – neuron that is conducting
information toward the next neuroninformation toward the next neuron
Postsynaptic neuronPostsynaptic neuron – transmits information away – transmits information away
from synapsefrom synapse
Most synaptic communication is via chemical Most synaptic communication is via chemical
messengersmessengers (e.g. acetylcholine, serotonin, (e.g. acetylcholine, serotonin,
norepinephrine, dopamine, endorphins, GABA, norepinephrine, dopamine, endorphins, GABA,
glycine, glutamic acid, etc.)glycine, glutamic acid, etc.)

37. Neurotransmission
Chemical (99%) Electrical (1%)

38. Types of synapses
Axodendritic = axon to dendriteAxodendritic = axon to dendrite
Axosomatic = axon to cell bodyAxosomatic = axon to cell body
Axoaxonic = axon to axonAxoaxonic = axon to axon

39. Types of synapses

40. Types of synapses

41. Types of Neuronal Integration
Neurons form many different types of connections Neurons form many different types of connections
and in so doing can result in finite control over the and in so doing can result in finite control over the
neuronal circuits. neuronal circuits.
Such pathways may create converging, diverging or Such pathways may create converging, diverging or
reverberating circuits as is shown in the next slide.reverberating circuits as is shown in the next slide.
Such circuits may produce EPSP’s or IPSP’s and help Such circuits may produce EPSP’s or IPSP’s and help
modulate the neuronal signals.modulate the neuronal signals.

42. Types of Neuronal Circuits

43. Axonal regeneration
Nerve tracts in the CNS are incapable of regeneration on their Nerve tracts in the CNS are incapable of regeneration on their
own and there may be hope for stem cells carrying out this own and there may be hope for stem cells carrying out this
process.process.
In the PNS, nerves can regenerate but vey slowly and under In the PNS, nerves can regenerate but vey slowly and under
only ideal conditions. Regeneration is dependent on 3 things: only ideal conditions. Regeneration is dependent on 3 things:
(a). Amount of damage, (b). Neurolemocyte secretion of nerve (a). Amount of damage, (b). Neurolemocyte secretion of nerve
growth factor and (c). The distance from the site of the growth factor and (c). The distance from the site of the
damage to the end organ being reinnervated.damage to the end organ being reinnervated.
Regeneration occurs at a rate of ~ 1 to 5 mm/day.Regeneration occurs at a rate of ~ 1 to 5 mm/day.

44. Neuronal regeneration in the PNS

46. WHAT IS NERVOUS SYSTEM?WHAT IS NERVOUS SYSTEM?

47. HOW’S THE CONTACT ?HOW’S THE CONTACT ?

48. HOW THUS THE SIGNALING HOW THUS THE SIGNALING
PROCESS IS DONE?PROCESS IS DONE?
THE INFORMATION IS CONDUCTED BY THE INFORMATION IS CONDUCTED BY
THE WORKING OF Na THE WORKING OF Na

52. Nervous Tissue: Support Cells Nervous Tissue: Support Cells
(Neuroglia = “Nerve Glue”)(Neuroglia = “Nerve Glue”)
Slide 7.5Slide 7.5
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
·Astrocytes
·Star-shaped cells
·Support neurons
·Form blood-brain
barrier
·Control the chemical
environment
Figure 7.3a

53. Nervous Tissue: Support CellsNervous Tissue: Support Cells
Slide 7.6Slide 7.6
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
·Microglia
·“little glue” cells
·Spider-like phagocytes
·Dispose of debris
Figure 7.3b, c

54. Nervous Tissue: Support CellsNervous Tissue: Support Cells
Slide 7.6Slide 7.6
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
·Ependymal cells
·Line cavities of the
brain and spinal
cord
·Circulate
cerebrospinal
fluid (CSF)
Figure 7.3b, c

55. Nervous Tissue: Support CellsNervous Tissue: Support Cells
Slide 7.7aSlide 7.7a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
·Oligodendrocytes
·“few branch” cells
·Produce myelin
sheath in the CNS
Figure 7.3d

56. Nervous Tissue: Support CellsNervous Tissue: Support Cells
Slide 7.7bSlide 7.7b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
·Schwann cells
·Form myelin sheath in the PNS
Figure 7.3e