1. HISTOLOGY OF THE NERVOUS SYSTEM
LAB EXERCISE 9
HISTOLOGY OF THE NERVOUS SYSTEM

2. The Nervous System ** The Central Nervous System
The brain and spinal cord
** The Peripheral Nervous System
>Thirty-one pairs of spinal
nerves that connect
to the spinal cord.
> Twelve pairs of cranial
nerves attaching to the
brain.

3. Nervous System

4. Sensory & Motor Neurons
Sensory Neurons (afferent)
“Pick up” the stimulus
Carry information to the spinal cord
Spinal cord carries the information to the brain
Exception:
Reflexes stay within the spinal cord
*Will discuss later
Motor Neurons (efferent)
Carry information away from the CNS
Bring the information from the brain, via the spinal cord, to the effector

5. Functional Divisions of the Nervous System
Receptors (Sensory division)(Afferent)
Detect changes or respond to stimuli
Somatic sensory receptors
Position, Touch, pressure, temperature & pain
Visceral sensory receptors
Monitor internal organs
Special sensory receptors
Sensory organs
vision, hearing, balance , taste & smell

6. The Nervous System Motor Fibers The Peripheral Nervous System
Effectors(Efferent)
Respond to efferent signals
Cells and organs
Somatic system
> Carry signals
for the movement
of head, trunk and
limbs.
> Voluntary
2. Autonomic System >Carry
signals for smooth muscle,
heart, Muscles and glands
> Involuntary
Somatic Nerves In green
Autonomic nerves in red

7. Two Types of Autonomic Nerves
Sympathetic nerves
Promote responses that prepare the body for stress or physical activity (fight-or-flight response)
Parasympathetic nerves
Promote housekeeping responses, such as digestion.
Associated with a relaxed state

8. ANS Divisions -“Fight or flight” Sympathetic Thoracolumbar
-Axons emerge from thoracic and superior lumbar segments of spinal cord
-Innervate ganglia relatively close to spinal cord
-“Kicks in” only during periods of exertion, stress, or emergency
-“Fight or flight”

9. ANS Divisions Parasympathetic Craniosacral
-Axons emerge from brain stem and sacral spinal segments
-Innervate ganglia very close (or within) target organs
Most often, effects are opposite to sympathetic
“Rest and digest”

10. Both Systems Are Usually Active
Most organs are continually receiving both sympathetic and parasympathetic stimulation
For example, sympathetic nerves signal heart to speed up and parasympathetic stimulate it to slow down
Which dominates depends on situation

11. The Nervous System

12. An Introduction to the Nervous System
Learning Outcomes
Describe the anatomical and functional
divisions of the nervous system.
Sketch and label the structure of a
typical neuron, describe the functions
of each component, and classify
neurons on the basis of their structure
and function.
Describe the locations and functions of
the various types of neuroglia.

13. NERVOUS & ENDOCRINE SYSTEMS
HOMEOSTASIS
Is a condition of equilibrium in the body’s internal environment produced by the ceaseless interplay of all the body’s regulatory processes.
Regulated by nervous and endocrine systems
NERVOUS & ENDOCRINE SYSTEMS

14. Histology of Nervous Tissue
Made up of two types of cells
Neuroglia
Preserve physical and biochemical structure of neural tissue
Neuroglia are essential to survival and function of neurons
Support Cells
Neurons perform:
All communication, information processing, and control functions of the nervous system
Excitable cells that relay transmission

15. Histology of Nervous Tissue
Neuroglia (Glial cells)
Support and nourish neurons.
Make up more than half the volume of the vertebrate nervous system
Neuroglia in CNS
1. Microglia-
Astrocytes- (Star Cells)
Oligodendrites-
Ependymal cells
Neurolglia in the PNS
Swann cells (Neurolemma)
2. Satellitte Cells

16. CNS Neuroglia Ependymal Cells
Line central canal of spinal cord and ventricles of brain
Secrete cerebrospinal fluid (CSF)
Have cilia or microvilli that circulate CSF
Transports dissolved gases, nutrients and wastes
Contain stem cells for repair

17. CNS Neuroglia Astrocytes Maintain blood–brain barrier (isolates CNS)
Isolates CNS from chemicals and hormones in the blood
Regulate ion, nutrient, and dissolved gas concentrations in interstitial fluid
Absorb & recycle neurotransmitters
Repair damaged neural tissue
Guide neuron development

18. CNS Neuroglia Microglia Migrate through neural tissue
Persist as mobile phagocytic cells
Clean up cellular debris, waste products, and pathogens

19. CNS Neuroglia Provide CNS framework by stabilizing axons
Oligodendrocytes (oligo-, few)
Provide CNS framework by stabilizing axons
Produce myelin
Coats axons and increases speed of neural impulse transmission
One oligodendrocyte wraps axonal segments of many neurons
but the myelin sheath is incomplete
Myelin-wrapped areas = internodes
Gaps between internodes = nodes

20. CNS Neuroglia Spinal Cord Oligodendrocytes Myelinated Unmyelinated
Axons that have myelin sheath
Appear white due to lipid content
Constitute white matter of the CNS
Tracts within the CNS
Unmyelinated
Axons that lack myelin sheath
Contribute to gray matter of the CNS
Along with neuron cell bodies and dendrites
Spinal Cord

21. Figure 12-4 An Introduction to Neuroglia
are found in
Central Nervous System
contains
Ependymal cells
Astrocytes
Oligodendrocytes
Microglia
Line ventricles
(brain) and central
canal (spinal cord);
assist in
producing,
circulating, and
monitoring
cerebrospinal fluid
Maintain blood–brain
barrier; provide structural
support; regulate ion,
nutrient, and dissolved-
gas concentrations;
absorb and recycle
neurotransmitters; form
scar tissue after injury
Myelinate CNS
axons; provide
structural
framework
Remove cell
debris,
wastes, and
pathogens by
phagocytosis 21

22. PNS Neuroglia Much like astrocytes Remember
Ganglia are the neuron cell bodies of the PNS
PNS neuroglia
Schwann cells
Form sheath around peripheral axons
Outer surface of Schwann cell is called neurilemma
Participate in repair after injury
Satellite cells
Surround neuron cell bodies in ganglia
Regulate intercellular environment
Much like astrocytes

23. 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

24. Neurons Basic units of communication in nearly all nervous systems
Monitor information in and around the body and issue commands for responsive actions
Neurons are excitable cells
Electric charge changes across plasma membrane – action potential
Integration of excitatory and inhibitory signals which act upon neurons

25. Neurons Nerve cell with the following characteristics:
Extreme longevity –
You maintain the same neurons throughout most of your life
Amitotic –
Most CNS neurons CANNOT REGENERATE
Exception
Hippocampus (Limbic System)- Memory
Olfactory receptors
Retina of eye
High Metabolic Rate
Need a constant supply of oxygen and glucose

26. Histology of Nervous Tissue
Neurons – Transmit signals
Cell body
contains nucleus and other organelles.
Within the CNS they are called nuclei
Outside the CNS they are called ganglia
Dendrites
receive signals from sensory receptors or other neurons.
Axon ( Nerve fiber)
conducts nerve impulses usually from the cell body to the synapse
CNS – tracts of white matter
PNS – periphereral nerves

27. Neurons Nerve cell with the following characteristics:
Extreme longevity –
You maintain the same neurons throughout most of your life
Amitotic –
Most CNS neurons CANNOT REGENERATE
Exception
Hippocampus (Limbic System)- Memory
Olfactory receptors
Retina of eye
High Metabolic Rate
Need a constant supply of oxygen and glucose

28. Cell Body (Soma) Single nucleus with prominent nucleolus
Perikaron (Nucleoplasm)
Cytoplasm of neuron
Mitochondria
Produce energy
Nissl bodies
Rough ER & free ribosomes
for protein synthesis
Cytoskeleton
Neurofilaments & nurofibrils
Give cell shape and support
Neurotubules
Move material inside cell

29. Dendrites
Conducts impulses towards the cell body
Surfaces specialized for contact with other neurons
Typically short, highly branched & unmyelinated
Short distance signals – Graded Potential
Contains
Mitochondria
ATP
Neurofibrils
Support
Nissl bodies
Contain clusters of ribosomes and rough ER for protein synthesis

30. Axons -Trigger Zone * Axon hillock Thick section of cell body
**Long, thin cylindrical process of cell That are mylenated
**Conduct impulses away from cell body (action potential)
Axoplasm
Cytoplasm of axon
Contains neurofibrils, neurotubules, enzymes, organelles
No ER therefore no protein synthesis
Axolemma
Specialized cell membrane
Covers the axoplasm
-Trigger Zone
* Axon hillock
Thick section of cell body
Attaches to initial segment
*Initial segment
Attaches to axon hillock
Collaterals
Side branches of a single axon
Telodendria
Fine extensions of distal axon
Synaptic terminals
Swollen tips of telodendria where synapses occur.

31. Axoplasmic Transport Slow Stream – travel a few mm a day
Materials travel the axon using neurotubules
Slow Stream – travel a few mm a day
Fast Stream – travel 5-10mm per hour
Move in two directions:
Anterograde
Toward axonal terminal by kinesin
Examples: mitochondria, membrane components, enzymes
Retrograde
Toward the cell body by dynein
Examples: organelles to be degraded, signal molecules, viruses, and bacterial toxins

32. The Synapse Presynaptic cell Postsynaptic cell The synaptic cleft
Neuron that sends message
The synaptic bulb is enlarged end of the telodendria
The presynaptic membrane contains synaptic vesicles that carry neurotransmitters to the postsynaptic cell.
Postsynaptic cell
Cell that receives message
Contains a postsynaptic membrane which bear receptors for neurotransmitters
The synaptic cleft
The small gap that separates the presynaptic membrane and the postsynaptic membrane

33. Synapses with another neuron
The type of synapses
Synapses with another neuron
Synapses with
another neuron
Neuron 1
Neuron 2
Collateral
branch
Dendrites
Axolemma
Neuromuscular junctions
Neuromuscular
junctions
Collateral
branch
Neuron
Skeletal
muscle
fibers
Telodendria
Synaptic terminals
Figure Neurons are nerve cells specialized for intercellular communication
Neuroglandular synapses
Neuroglandular
synapses
Neuron
Gland
cells
Figure 33

34. Synapses of a neuron with another neuron
Axodendritic synapse
Synapse between an axon of one
neuron to a dendrite of another axon.
Axosomatic synapse
body and the cell body of another
Axoaxonic Synapse
Synapses between axons
Dendrodendritic
Synapses between dendrites
Dendrosomatic
Synapse between dendrites and cell bodies
Axodendritic
synapses
Axosomatic
synapses
Axoaxonic
synapses

35. NEURON FUNCTION
Neurons are classified according to structure or function.
FUNCTIONALLY
Sensory neurons- (Afferent)
Interneurons (Association)
Motor neurons

36. Functional Classification of Neurons
Functions of Sensory Neurons
Monitor internal environment (visceral sensory neurons)
Monitor effects of external environment (somatic sensory neurons)
Structures of Sensory Neurons
Unipolar (Functional)
Cell bodies grouped in sensory ganglia
Processes (afferent fibers) extend from sensory receptors to CNS

37. Functional Classification of Neurons
Three Types of Sensory Receptors
Interoceptors
Monitor internal systems (digestive, respiratory, cardiovascular, urinary, reproductive)
Internal senses (taste, deep pressure, pain)
Exteroceptors
External senses (touch, temperature, pressure)
Distance senses (sight, smell, hearing)
Proprioceptors
Monitor position and movement (skeletal muscles and joints)

38. Functional Classification of Neurons
Motor Neurons
Carry instructions from CNS to peripheral effectors
Via efferent fibers (axons)
Two major efferent systems
Somatic nervous system (SNS)
Includes all somatic motor neurons that innervate skeletal muscles
Autonomic (visceral) nervous system (ANS)
Visceral motor neurons innervate all other peripheral effectors
Smooth muscle, cardiac muscle, glands, adipose tissue

39. Comparison of Somatic and Autonomic Systems
Figure 14.2

40. Functional Classification of Neurons
Interneurons
Most are located in brain, spinal cord, and autonomic ganglia
Between sensory and motor neurons
Are responsible for:
Distribution of sensory information
Coordination of motor activity
Are involved in higher functions
Memory, planning, learning

41. Structural Classification of Neurons
Anaxonic neuron
Bipolar neuron
Unipolar neuron
Multipolar neuron
Dendrites
Dendrites
Initial
segment
Cell
body
Dendritic
branches
Axon
Dendrite
Cell body
Cell
body
Axon
Axon
Cell
body
Synaptic
terminals
Axon
Synaptic
terminals
Synaptic
terminals
Anaxonic neurons
have more than two
processes, but axons
cannot be
distinguished from
dendrites.
Bipolar neurons
have two
processes
separated by the
cell body.
Unipolar neurons
have a single
elongate process,
with the cell body
situated off to the
side.
Multipolar neurons
have more than two
processes; there is a
single axon and
multiple dendrites
Most common in the CNS
Include all skeletal
muscle motor neurons
Found in special
sensory organs
Sight, smell & hearing
Found in brain & sense organs
Found in sensory neurons of PNS 41

42. Table 11.1 (3 of 3)

44. CONNECTIVE TISSUE WRAPPINGS
*Endoneurium =
Wrapping of each
nerve fibers
around an axon.
Not myelin sheath
*Perineurium =
Surrounds group
of nerve fibers
forming a fascicle
*Epineurium =
Covering of entire
nerve dura mater blends
into it at intervertebral
foramen

45. PERIPHERAL NERVE HISTOLOGY