1. Fundamentals of the Nervous System and Nervous Tissue11
P A R T A
Fundamentals of the Nervous System and Nervous Tissue

2. Doh!!
The Nervous System

3. The master controlling and communicating system of the body
Nervous System
The master controlling and communicating system of the body
Functions can be divided into three themes:
Sensory input – gathering information about the internal and external environments, monitoring stimuli
Integration – interpretation of sensory input, analysis of information, memory, decision making…
Motor output – response to stimuli, taking action (sometimes automatic, sometimes voluntary)

4. Nervous System
Figure 11.1

5. Organization of the Nervous System
The nervous system includes two anatomical divisions
Central nervous system (CNS)
Brain and spinal cord
Integration and command center
Peripheral nervous system (PNS)
31 pairs of spinal nerves (enter or exit the spinal cord between vertebrae, such as the femoral nerve)
12 pairs of cranial nerves (enter or exit the brain, such as the optic nerve)
Carries sensory messages from the body to the CNS, and motor outputs from the CNS to the body

6. Spinal Nerves
CNS vs. PNS
Cranial Nerves

7. Peripheral Nervous System (PNS): Two Functional Divisions
Sensory (afferent) division
Sensory afferent fibers – carry impulses from sense organs, skin, skeletal muscles, and joints to the brain
Visceral afferent fibers – transmit impulses from visceral organs to the brain
Motor (efferent) division
Transmits impulses from the CNS to effector organs (muscles and glands)

8. Motor Division: Two Main Parts
Somatic nervous system
Conscious control of skeletal muscles
Autonomic nervous system (ANS)
Regulates smooth muscle, cardiac muscle, and glands
Divisions – sympathetic (“fight or flight”) and parasympathetic (“chillax, dude!”)

9. Autonomic Nervous System

10. Autonomic Nervous System
Organ
Sympathetic Action
Parasympathetic Action
Summary of Action
Eye
Salivary Gland
Heart
Lungs
Stomach, Pancreas, Intestines
Liver & Gall Bladder
Adrenal Glands
Bladder
Blood Vessels to Muscles
Blood Vessels to Visceral Organs
Fight or Flight
Chillax
Dilates Pupil
Constricts Pupil
Slows Relase of Saliva
Secretes Saliva
Tachycardia
Bradycardia
Dilates Bronchi
Constricts Bronchi
Slows Movement & Secretion
Speeds Movement & Secretion
Slows Secretion of Bile
Speeds Secretion of Bile
Release adrenaline (epinephrine)
Store adrenaline
Inhibits Constriction
Constricts
Arterioles Dilate
Arterioles Constrict
Constrict
Dilate

11. Regions of the Brain and Spinal Cord
White matter – dense collections of myelinated fibers (myelin is a pale fatty substance produced by glial cells, which wraps around some axons to speed action potentials) – function is to transmit messages
Gray matter – mostly neuron cell bodies and unmyelinated fibers – function is to analyze information and make decisions

12. Grey Matter vs. White Matter
ganglion
white matter
spinal nerve
grey matter

13. Histology of Nerve Tissue
The two principal cell types of the nervous system are:
Neurons – excitable cells that transmit electrical signals
Glial cells – cells that surround and wrap neurons, providing structural and functional support to neurons

14. Supporting Cells: Neuroglia
The supporting cells (neuroglia or glial cells):
Provide a supportive scaffolding for neurons
Segregate and insulate neurons
Guide young neurons to the proper connections
Promote health and growth
Speed action potentials
May have some influence on neuronal communication (recent research suggests this)

15. Astrocytes
Most abundant, versatile, and highly branched glial cells
They cling to neurons and their synaptic endings, and cover capillaries

16. Astrocytes Functionally, they: Support and brace neurons
Anchor neurons to their nutrient supplies
Guide migration of young neurons
Control the chemical environment by forming the “Blood-Brain Barrier”

17. Astrocytes
Figure 11.3a

18. Microglia and Ependymal Cells
Microglia – small, ovoid cells with spiny processes
Phagocytes that monitor the health of neurons
Ependymal cells – range in shape from squamous to columnar
They line the central cavities (the ventricles) of the brain and spinal column – this structure is called the choroid plexus
Produce cerebrospinal fluid (CSF)

19. Microglia and Ependymal Cells
(ventricle)
Figure 11.3b, c

20. Oligodendrocytes, Schwann Cells, and Satellite Cells
Oligodendrocytes – branched cells that wrap CNS nerve fibers, fill up with myelin to speed action potentials in brain and spinal cord
Schwann cells (neurolemmocytes) – surround fibers of the PNS, fill up with myelin to speed action potentials in peripheral sensory and motor neurons
Satellite cells surround neuron cell bodies within ganglia of the PNS (clusters of neurons outside the brain & spinal cord)

21. Oligodendrocytes, Schwann Cells, and Satellite Cells
Figure 11.3d, e

22. Structural units of the nervous system
Neurons (Nerve Cells)
Structural units of the nervous system
Composed of a body, axon, and dendrites
Long-lived, amitotic, and have a high metabolic rate
Their plasma membranes function in:
Electrical signaling (action potentials / nerve impulses)
Chemical communication (synaptic transmission)
Cell-to-cell signaling during development
PLAY
InterActive Physiology ®:
Nervous System I, Anatomy Review, page 4

23. Neuron Classification
Functional:
Sensory (afferent) — gather information about the environment and transmit impulses toward the CNS
Motor (efferent) — carry impulses away from the CNS with commands for musclar contractions and glandular secretions
Interneurons (association neurons) — shuttle signals through CNS pathways, process information, combine information, make decisions, store and access memories….

24. Neuron Classification
Structural:
Multipolar — three or more processes
Bipolar — two processes (axon and dendrite)
Unipolar — single, short process

25. Comparison of Structural Classes of Neurons
Table

26. Comparison of Structural Classes of Neurons
Table

27. Comparison of Structural Classes of Neurons
Table

28. Neurons (Nerve Cells)
Figure 11.4b 2 1 3 4 5 6 7 8 9 10 11 12

29. Neurons (Nerve Cells)
Figure 11.4b

30. Nerve Cell Body (Perikaryon or Soma)
Contains the nucleus and a nucleolus
Is the major biosynthetic center
Is the focal point for the outgrowth of neuronal processes
Has no centrioles (hence its amitotic nature)
Has well-developed Nissl bodies (rough ER)
Contains an axon hillock – cone-shaped area from which axons arise

31. Processes
Armlike extensions from the soma
Called tracts in the CNS and nerves in the PNS
There are two types: axons and dendrites

32. Dendrites of Motor Neurons
Short, tapering, and diffusely branched processes
They are the receptive, or input, regions of the neuron
Electrical signals are conveyed as graded potentials (not action potentials)

33. Axons: Structure
Slender processes of uniform diameter arising from the hillock
Long axons are called nerve fibers
Usually there is only one unbranched axon per neuron
Rare branches, if present, are called axon collaterals
Axonal terminal – branched terminus of an axon

34. Generate and transmit action potentials
Axons: Function
Generate and transmit action potentials
Secrete neurotransmitters from the axonal terminals
Movement along axons occurs in two ways
Anterograde — toward axonal terminal
Retrograde — away from axonal terminal

35. The Myelin Sheath
Whitish, fatty (protein-lipoid), segmented sheath around most long axons
It functions to:
Protect the axon
Electrically insulate fibers from one another
Increase the speed of nerve impulse transmission using “saltatory conduction” (jumping)
Animation of Saltatory Conduction

36. Saltatory Conduction

37. Myelin Sheath and Neurilemma: Formation
Formed by Schwann cells in the PNS
Steps in myelin formation:
A Schwann cell envelopes an axon in a trough
It encloses the axon with its plasma membrane
It wraps around and around the axon forming concentric layers of membrane that make up the myelin sheath
Neurilemma – remaining nucleus and cytoplasm of a Schwann cell

38. Myelin Sheath and Neurilemma: Formation
PLAY
InterActive Physiology ®:
Nervous System I, Anatomy Review, page 10
Figure 11.5a–c

39. Nodes of Ranvier (Neurofibral Nodes)
Gaps in the myelin sheath between adjacent Schwann cells
The action potential jumps from node to node across the myelin sheath – much faster than continuous conduction
The nodes have voltage gates that conduct the a.p. like the normal membrane
Nodes are also the sites where axon collaterals can emerge

40. Unmyelinated Axons
A Schwann cell surrounds nerve fibers but coiling does not take place
Schwann cells partially enclose 15 or more axons

41. Axons of the CNS
Both myelinated and unmyelinated fibers are present
Myelin sheaths are formed by oligodendrocytes
Nodes of Ranvier are widely spaced
There is no neurilemma