1. Central nervous system (CNS)
The Nervous System 11/14
Divisions
Central nervous system (CNS)
Brain and spinal cord (dorsal body cavity)
Integration and command center
Interprets sensory input and dictates motor output
Peripheral nervous system (PNS)
Portion of nervous system outside CNS; brings information from body
Consists mainly of nerves that extend from brain and spinal cord
Spinal nerves to and from spinal cord
Cranial nerves to and from brain
Lab 8B-BIO 105

2. Peripheral Nervous System (PNS)
Two functional divisions
Sensory (afferent) division
Somatic sensory fibers—convey impulses from skin, skeletal muscles, and joints to CNS
Visceral sensory fibers—convey impulses from visceral organs to CNS
Motor (efferent) division
Transmits impulses from CNS to effector organs
Muscles and glands
Two divisions
Somatic or Voluntary nervous system
Autonomic nervous system

3. Motor Division of PNS: Somatic Nervous System
Voluntary nervous system
Conscious control of skeletal muscles
Conducts impulses from CNS to skeletal muscle

4. Motor Division of PNS: Autonomic Nervous System
Involuntary nervous system
Regulates smooth muscle, cardiac muscle, and glands
Visceral motor nerve fibers
Two functional subdivisions which work in opposition to each other
Sympathetic
Parasympathetic

5. Histology of Nervous Tissue
Two principal cell types
Neurons (nerve cells)—excitable cells that transmit electrical signals
Neuroglia or Glia – small cells that surround, wrap, and generally support neurons

6. Neuroglial cells: Provide a supportive scaffolding for neurons
Insulate neurons
Guide young neurons so they can make proper connections
Promote health and growth

7. Neuroglia
Astrocytes (CNS)
Microglial cells (CNS)
Ependymal cells (CNS)
Oligodendrocytes (CNS)
Satellite cells (PNS)
Schwann cells (PNS)

8. Most abundant, highly branched cell
Astrocytes
Most abundant, highly branched cell
Cling to neurons, synaptic endings, and covers capillaries
Functions include
Support neurons and help maintain position
Play role in exchanges between capillaries and neurons; help with nutrient supply
Control chemical environment around neurons

9. Microglial Cells
Small cells with processes that monitor neurons
Migrate toward injured neurons
Can transform to phagocytize microorganisms and neuronal debris

10. Ependymal Cells
May be ciliated
Cilia help CerebroSpinalFluid circulate throughout CNS
Line central cavities of brain and spinal column

11. Myelin Sheath
Whitish, protein-lipoid segmented sheath around most long or large-diameter axons
Myelinated fibers
Function of myelin
Protects and electrically insulates axon
Increases speed of nerve impulse transmission
Nonmyelinated fibers conduct impulses more slowly

12. Oligodendrocytes
Branched cells that wrap CNS nerve fibers and form insulating myelin sheaths
Can wrap up to 60 axons at once
Have Nodes of Ranvier (gaps in myelin)
No neurilemma

13. Satellite Cells and Schwann Cells: in PNS Schwann cells
Surround all peripheral nerve fibers and form myelin sheaths
Wrap around axon in jelly roll fashion
One cell forms one segment of myelin sheath
Similar function as oligodendrocytes
Vital to regeneration of damaged peripheral nerve fibers

14. Neurilemma
Outermost layer of Schwann cell containing nucleus and most of cytoplasm
Essential for axon healing and repair
Nodes of Ranvier
Myelin sheath gaps between adjacent Schwann cells

15. Plasma membrane functions in:
Neurons
Structural units of nervous system--form gray matter of CNS
Highly specialized cells that conduct impulses
Extreme longevity
High metabolic rate—requires continuous supply of oxygen and glucose
All have cell body, axon and one or more dendrites
Plasma membrane functions in:
Electrical signaling

16. Neuron Cell Body (Perikaryon or Soma) Contains nucleus and nucleolus
Major biosynthetic center
Synthesizes proteins, membranes, and other chemicals
Rough ER is very active; also called nissl bodies
Synthesizes neurotransmitters
Plasma membrane receives information from other neurons

17. Receptive (input) region of neuron
Dendrites
short, tapering, diffusely branched processes
Increase surface area of cell so can receive messages
Receptive (input) region of neuron
Convey incoming electrical signals toward cell body as graded potentials (short distance signals) not action potentials

18. Carries on many conversations with different neurons at same time
The Axon
Generates and transmits nerve impulses along axolemma (neuron cell membrane) to axon terminal
Neurotransmitters released into extracellular space
Either excite or inhibit neurons with which axons are in close contact
Carries on many conversations with different neurons at same time

19. Structural Classification of Neurons Grouped by number of processes
Three types
Multipolar – 3 or more processes
1 axon, other processes dendrites
Most common; major neuron in CNS
Bipolar – 2 processes
Rare, e.g., Retina and olfactory mucosa
Unipolar – 1 short process
One process –sensory or afferent receptor
Other process – motor or efferent branch

20. Functional Classification of Neurons
Grouped by the direction in which impulse travels in relation to CNS
Sensory or afferent
Transmit impulses from sensory receptors toward CNS
Almost all are Unipolar
Motor or efferent
Carry impulses away from CNS to effectors
Multipolar
Interneurons (association neurons)
Lie between motor and sensory neurons
Shuttle signals through CNS pathways; most are entirely within CNS

21. Structure of a Nerve
Bundle of myelinated and non-myelinated axons enclosed by connective tissue
Cell bodies lie in CNS or in ganglia near CNS
Connective tissue coverings include
Endoneurium—loose connective tissue that encloses axons and their myelin sheaths
Perineurium—coarse connective tissue that bundles fibers into fascicles
Epineurium—tough fibrous sheath around a nerve

22. LABWORK
Explain organization of nervous system.
2. Describe neuroglia and process of myelin formation.
3. Describe and identify parts of a neuron and the different classifications of neurons on models and microscope slides.
4. Describe and identify structure of a nerve (microscope slides and models).