1. Nervous System The body’s primary communication and control system
Divided according to structural and functional categories

2. Nervous System Structural Central Nervous System
Peripheral Nervous System
Functional
Sensory (Afferent) Division
Motor (Efferent) Division

3. Structural Organization
CNS
Brain
Spinal cord
PNS
Cranial nerves
Spinal nerves
Ganglia

4. Functional Organization

5. Functional Organization
Sensory (Afferent) Division – receives sensory information (input) from receptors and transmits this information to the CNS
Motor (Efferent) Division – transmits motor impulses (output) from the CNS to muscles or glands

6. Sensory Division
Somatic sensory components are the general somatic senses (touch, pain, pressure, vibration, temperature, proprioception)
Visceral sensory components transmit nerve impulses from blood vessels and viscera to the CNS (temperature, stretch of the organ wall)

7. Motor Division
Somatic motor component conducts nerve impulses from the CNS to skeletal muscles
Voluntary nervous system
Autonomic motor component (ANS) innervates internal organs, regulates smooth muscle, cardiac muscle, and glands
Visceral motor system or involuntary nervous system

8. Nervous Tissue
Specialized tissue responsible for excitability and conduction of impulses
Comprised of:
Neurons – nerve cells with processes
Neuroglia (glial cells) – cellular connective tissue of the NS

10. Neuron Structural and functional unit of nervous tissue
Excitable cells that initiate and transmit nerve impulses

11. Neuron Characteristics: High metabolic rate Extreme longevity
Typically non-mitotic

12. Neuron Size: varies from 4-20 um (motor neurons > sensory neurons)
Nucleus:
Large, pale vesicular, usually central
Large prominent nucleolus
“Fish eye” or “owl’s eye”

13. Neuron Cytoplasm (neuroplasm)
Basophilic, contains usual cell organelles (Golgi, mitochondria) and pigments (melanin, lipofuscin)
Centrosome – absent
Neurofibrils
Nissl granules

14. Nissl Granules Chromophilic bodies Give a granular appearance
Rough endoplasmic reticulum
Degenerate due to fatigue or injury to the neuron (chromatolysis)

16. Neurofibrils Thread-like structures
Form a plexiform pattern in the cell body
Arranged in parallel manner in both dendrites and axon
Functions: provide internal support, play role in intracellular transport of organelles and vesicles

17. Neurofibrils
Microtubules – thickest, contain a thin central filament with a hollow core
Neurofilaments – abundant in axon
Microfilaments – thinnest

19. Neuron Structure Vary in shape and size
Cell body (perikaryon, soma) + one or more cell processes
Enclosed by neurolemma

20. Neuron Structure
Cell body – serves as the neuron’s control center and is responsible for receiving, integrating, and sending nerve impulses
Cell processes
Axons
Dendrites

22. Cell Processes Axons Dendrites Only one axon is present in a neuron
May be absent, solitary, or numerous
Usually multiple in a neuron
Thin long process of uniform thickness and smooth surface
Short, multiple processes
Thickness diminishes as they divide repeatedly
Branches are studded with spiny projections

23. Cell Processes Axons Dendrites
Branches of axon are fewer and at right angles to the axon
Branch diffusely and are given off at acute angles
Contains neurofibrils and no Nissl granules
Contain both neurofibrils and Nissl granules
No Golgi complexes
Forms the efferent component of the impulse
Afferent component

24. Axon
a.k.a. axis cylinder
One long thin process that arises from a conical elevation on the perikaryon (axon hillock)
Cell membrane = axolemma
Carries impulse away from cell body
Axonal transport
Anterograde – perikaryon → axon terminal
Retrograde – axon terminal → perikaryon

25. Dendrites
Single or multiple processes containing the extension of cytoplasm of neurons with its cell organelles
Provide receptive surface for the neuron
Carry impulses towards the soma of the neuron

28. Types of Neurons Based on number of processes: Unipolar Pseudounipolar
Bipolar
Multipolar

29. Types of Neurons Description Location Unipolar Only 1 process (axon)
Embryo, rare in adults
Pseudounipolar
1 axon bifurcates
Dorsal root ganglia
Ganglia of some cranial nerves
Bipolar
Dendrite and axon arise at opposite poles of cell body
Olfactory epithelium
Vestibular and cochlear ganglia
Bipolar cells of retina
Multipolar
Numerous dendrites
Most common
Most neurons of cerebrum and cerebellum

31. Functional Classification
Types of Neurons
Functional Classification
Description
Sensory (Afferent)
Transmit impulses toward the CNS
Motor (Efferent)
Carry impulses toward the body surface
Interneurons (Association Neurons)
Any neurons between a sensory and a motor neuron

32. Neuroglia/Glial Cells
The cellular connective tissue of the nervous tissue
Functions:
1. Provide support and nutrition
2. Maintain homeostasis
3. Form myelin
4. Participate in signal transmission

33. Neuroglia Found in both the CNS and PNS Outnumber neurons
Smaller than neurons and capable of mitosis
Do not transmit nerve impulses

34. Neuroglia Astrocytes Oligodendrocytes Schwann cells Ependymal cells
Protoplasmic astrocytes
Fibrous astrocytes
Oligodendrocytes
Schwann cells
Ependymal cells
Microglia

35. Neuroglia Glial Cell Type Origin Location Function Astrocytes
Neural tube
CNS
Structural support, repair processes
Blood–brain barrier, metabolic exchanges
Oligodendrocytes
Myelin production, electric insulation
Schwann cells
PNS
Ependymal cells
Lining cavities of central nervous system
Microglia
Bone marrow
Macrophagic activity

37. Microglia Smallest glial cells
Small elongated cells with short irregular processes
Dense elongated nuclei (other glial cells: spherical nuclei)

38. Microglia
Function: phagocytic (represent the mononuclear phagocytic system in nerve tissue)

39. Astrocytes Largest, most numerous
Star-shaped cells with multiple radiating processes
Large vesicular nuclei
Only astrocytes exhibit vascular end-feet

40. Astrocytes Functions: Types: Form supporting network for neurons
Provide nourishment to the neurons
Types:
Protoplasmic
Fibrous

41. Protoplasmic Astrocyte
Thick processes
Abundant granular cytoplasm
Some processes attached to neighboring capillaries by perivascular sucker feet (vascular end-feet)
Found in grey matter

42. Fibrous Astrocyte
Have long and straight processes seen only in the white matter

43. Ependymal Cells Low columnar (cuboidal) epithelial cells
Lining the ventricles of the brain and central canal of the spinal cord

44. Ependymal Cells
Ciliated in some locations (facilitate movement of CSF)
Function:
Secrete CSF

45. Oligodendrocytes
Smaller than astrocytes, have fewer and shorter processes
Scanty cytoplasm
Nucleus usually ovoid or spherical and more deeply staining than astrocytes
Found mostly in white matter

46. Oligodendrocytes
Produce the myelin sheath (provides the electrical insulation of neurons in the CNS)
Processes wrap around axons (producing a myelin sheath)

47. Oligodendrocytes
Function: provides insulation to the axon that allows electrical signals to propagate more efficiently
1 oligodendrocyte can extend to up to 50 axons

49. Schwann Cells Nucleus: flattened Abundant cytoplasm
Function : same as oligodendrocytes but are located around axons in the PNS
Can only wrap around 1 axon