1. Chapter 9 Nervous Tissue
Copyright 2010, John Wiley & Sons, Inc.

2. Copyright 2010, John Wiley & Sons, Inc.
End of Chapter 9
Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.
Copyright 2010, John Wiley & Sons, Inc.

3. Structures of the Nervous System
Brain: neurons enclosed within skull
Spinal cord: connects to brain and enclosed within spinal cavity
Nerves: bundles of many axons of neurons
Cranial nerves (12 pairs) emerge from brain
Spinal nerves (31 pairs) emerge from spinal cord
Ganglia: groups of neuron cell bodies located outside of brain and spinal cord
Enteric plexuses: networks in digestive tract
Sensory receptors: monitor changes in internal or external environments
Copyright 2010, John Wiley & Sons, Inc.

4. Structures of the Nervous System
Copyright 2010, John Wiley & Sons, Inc.

5. Functions of the Nervous System
Sensory receptors and sensory nerves
Carry information into brain and spinal cord
Integration: information processing
Perception = awareness of sensory input
Analyzing and storing information to help lead to appropriate responses
Motor activity: efferent nerves
Signals to muscles and glands (effectors)
Copyright 2010, John Wiley & Sons, Inc.

6. Organization of the Nervous System
Central Nervous System (CNS)
Brain and spinal cord
Peripheral Nervous System (PNS)
All nervous system structures outside of the CNS
Copyright 2010, John Wiley & Sons, Inc.

7. Histology of the Nervous System
Neurons
Can respond to stimuli and convert stimuli to electrical signals (nerve impulses) that travel along neurons
Neuroglia cells: support, nourish and protect neurons
Neuroglia critical for homeostasis of interstitial fluid around neurons
Copyright 2010, John Wiley & Sons, Inc.

8. Copyright 2010, John Wiley & Sons, Inc.
Neuronal Structure
Cell body: nucleus, cytoplasm with typical organelles
Dendrites: highly branched structures that carry impulses to the cell body
Axon: conducts away from cell body toward another neuron, muscle or gland
Emerges at cone-shaped axon hillock
Axon terminals: contain synaptic vesicles that can release neurotransmitters
Copyright 2010, John Wiley & Sons, Inc.

9. Copyright 2010, John Wiley & Sons, Inc.
Neuronal Structure
Copyright 2010, John Wiley & Sons, Inc.

10. Structural Classes of Neurons
Multipolar
Have several or many dendrites and one axon
Most common type in brain and spinal cord
Bipolar
Have one dendrite and one axon
Example: in retina of eye and inner ear
Unipolar
Have fused dendrite and axon
Sensory neurons of spinal nerves
Copyright 2010, John Wiley & Sons, Inc.

11. Functional Classes of Neurons
Sensory (afferent)
Convey impulses into CAN (brain or spinal cord)
Motor (efferent)
Convey impulses from brain or spinal cord out through the PNS to effectors (muscles or glands)
Interneurons (association neurons)
Most are within the CNS
Transmit impulses between neurons, such as between sensory and motor neurons
Copyright 2010, John Wiley & Sons, Inc.

12. Copyright 2010, John Wiley & Sons, Inc.
Neuroglia
Cells smaller but much more numerous than neurons
Can multiply and divide and fill in brain areas
Gliomas: brain tumors derived from neuroglia
Functions
Do not conduct nerve impulses
Do support, nourish and protect neurons
Copyright 2010, John Wiley & Sons, Inc.

13. Copyright 2010, John Wiley & Sons, Inc.
Neuroglia
Astrocytes: help form blood brain barrier
Oligodendrocytes: produce myelin in CNS
Microglia: protect CNS cells from disease
Ependymal cells: form CSF in ventricles
Schwann: produce myelin around PNS neurons; help to regenerate PNS axons
Satellite cells: support neurons in PNS ganglia
Copyright 2010, John Wiley & Sons, Inc.

14. Copyright 2010, John Wiley & Sons, Inc.
Myelination
Axons covered with a myelin sheath
Many layers of lipid and protein: insulates neurons
Increases speed of nerve conduction
Appears white (in white matter)
Nodes of Ranvier: gaps in the myelin
Nodes are important for rapid signal conduction
Some diseases destroy myelin:
Multiple sclerosis
Tay-Sachs
Copyright 2010, John Wiley & Sons, Inc.

15. Collections of Nervous Tissue
Clusters of neuron cell bodies
Ganglion: cluster of cell bodies in PNS
Nucleus: cluster of cell bodies in CNS
Bundles of axons
Nerve: bundle of axons in PNS
Tract: bundle to axons in CNS
Copyright 2010, John Wiley & Sons, Inc.

16. Copyright 2010, John Wiley & Sons, Inc.
Gray and White Matter
White matter: primarily myelinated axons
Gray matter: cell bodies, dendrites, unmyelinated axons, axon terminals, neuroglia
Locations of gray and white matter
Spinal cord: white matter (tracts) surround centrally located gray matter “H” of “butterfly”
Brain: gray matter in thin cortex surrounds white matter (tracts)
Copyright 2010, John Wiley & Sons, Inc.

17. Copyright 2010, John Wiley & Sons, Inc.
Neuron Regeneration
Regeneration of PNS neurons
Axons and dendrite in the PNS can be repaired if cell body is intact and Schwann cells functional. These form a regeneration tube and grow axons or dendrites if scar tissue does not fill the tube
Regeneration of CNS neurons
Very limited even if cell body is intact
Inhibited by neuroglia and by lack of fetal growth-stimulators
Copyright 2010, John Wiley & Sons, Inc.

18. Organization of the Nervous System
Central nervous system (CNS) structures:
Brain
Spinal cord
Peripheral nervous system (PNS) structures:
Cranial nerves and branches
Spinal nerves and branches
Ganglia
Sensory receptors
Copyright 2010, John Wiley & Sons, Inc.

19. Organization of the Nervous System
Copyright 2010, John Wiley & Sons, Inc.

20. Organization of the Nervous System
Peripheral nervous system (PNS) divisions
Somatic (SNS)
Sensory neurons from head, body wall, limbs, special sense organs
Motor neurons to skeletal muscle: voluntary
Autonomic (ANS) nervous systems
Sensory neurons from viscera
Motor neurons to viscera (cardiac muscle, smooth muscle, glands): involuntary
Sympathetic: “fight-or-flight”
Parasympathetic: “rest-and-digest”
Enteric nervous system (ENS): “brain of the gut”
Copyright 2010, John Wiley & Sons, Inc.

21. Organization of the Nervous System
Peripheral nervous system (PNS),
Enteric nervous system (ENS): “brain of the gut”
Sensory neurons monitor chemical changes and stretching of GI wall
Motor neurons regulate contractions, secretions and endocrine secretions (involuntary)
Copyright 2010, John Wiley & Sons, Inc.

22. Structure and Function of the Nervous System Interactions Animation
Introduction to Structure and Function of the Nervous System
You must be connected to the internet to run this animation.
Copyright 2010, John Wiley & Sons, Inc.

23. Copyright 2010, John Wiley & Sons, Inc.
Action Potentials
Action potentials = nerve impulses
Require
A membrane potential: a charge difference across cell membrane (polarization)
Ion channels: allow ions to move by diffusion from high to low concentration
Leakage channels: allow ions to leak through membrane; there are more for K+ than for Na+
Gated channels
Open and close on command
Respond to changes in membrane so can generate and conduct action potentials
Copyright 2010, John Wiley & Sons, Inc.

24. Resting Membrane Potential
Typically –70 mV
Inside of membrane more negative than outside
Caused by presence of ions:
Inside (more negative) because cytosol has:
Many negative ions (too large to leak out): amino acids (in cellular proteins) and phosphates (as in ATP)
K+ that easily leaks out through many K+ channels
Outside (more positive) because interstitial fluid has:
Few negative ions
Na+ that does not leak out of cell: few Na+ channels
Membrane “pumps” that quickly pump out Na+ that does leak (diffuse) into cell
Copyright 2010, John Wiley & Sons, Inc.

25. Resting Membrane Potential
Copyright 2010, John Wiley & Sons, Inc.

26. Copyright 2010, John Wiley & Sons, Inc.
Action Potential
Series of events that activate cell membrane in neuron or muscle fiber
An initial event (stimulus) is required
Triggers resting membrane to become more permeable to Na+
Causes enough Na+ to enter cell so that cell membrane reaches threshold (~ –55 mv)
If so, the following events occur: action potential which spreads along neuron or muscle fiber
Copyright 2010, John Wiley & Sons, Inc.

27. Copyright 2010, John Wiley & Sons, Inc.
Action Potential
Depolarizing phase
Na+ channels open  as more Na+ enters cell, membrane potential rises and becomes positive (–70  0  + 30 mv)
Repolarizing phase
K+ channels open  as more K+ leave cell, membrane potential is returned to resting value (+ 30  0  –70 mv)
May overshoot: hyperpolarizing phase
Typically depolarization and repolarization take place in about 1 millisecond (1/1000 sec)
Copyright 2010, John Wiley & Sons, Inc.

28. Copyright 2010, John Wiley & Sons, Inc.
Action Potential
Copyright 2010, John Wiley & Sons, Inc.

29. Copyright 2010, John Wiley & Sons, Inc.
Action Potential
Recovery
Levels of ions back to normal by action of Na+/K+ pump
Refractory period (brief): even with adequate stimulus, cell cannot be activated
All-or-none principle
If a stimulus is strong enough to cause depolarization to threshold level, the impulse will travel the entire length of the neuron at a constant and maximum strength.
Copyright 2010, John Wiley & Sons, Inc.

30. Membrane Potentials Interactions Animations
You must be connected to the internet to run this animation.
Copyright 2010, John Wiley & Sons, Inc.

31. Conduction of Nerve Impulses
Nerve impulse conduction (propagation)
Each section triggers the next locally as even more Na+ channels are opened (like row of dominos)
Types of conduction
Continuous conduction
In unmyelinated fibers; slower form of conduction
Saltatory conduction
In myelinated fibers; faster as impulses “leap” between nodes of Ranvier
Factors that increase rate of conduction
Myelin, large diameter and warm nerve fibers
Copyright 2010, John Wiley & Sons, Inc.

32. Conduction of Nerve Impulses
Copyright 2010, John Wiley & Sons, Inc.

33. Conduction of Nerve Impulses
Copyright 2010, John Wiley & Sons, Inc.

34. Synaptic Transmission
Similar sequence of events occurs at
Synapse (neuron-neuron)
Neuromuscular junction (neuron-muscle fiber: chapter 8)
Neuroglandular junction (neuron-gland)
Triggered by action potential (nerve impulse)
Components of synapse:
Sending neuron: presynaptic neuron (releases neurotransmitter)
Space between neurons: synaptic cleft
Receiving neuron: postsynaptic neuron
Copyright 2010, John Wiley & Sons, Inc.

35. Synaptic Transmission
Action potential arrives at presynaptic neuron’s end bulb
Opens voltage gated Ca2+ channels  Ca2+ flows into presynaptic cytosol
Increased Ca2+ concentration  exocytosis of synaptic vesicles
Neurotransmitter (NT) released into cleft
NT diffuses across cleft and binds to receptors in postsynaptic cell membrane
Copyright 2010, John Wiley & Sons, Inc.

36. Synaptic Transmission
NT serves as chemical trigger (stimulus) of ion channels
Postsynaptic cell membrane may be depolarized or hyperpolarized
Depends on type of NT and type of postsynaptic cell
1000+ neurons converge on synapse; the sum of all of their NTs determines effect
If threshold reached, then postsynaptic cell action potential results
Copyright 2010, John Wiley & Sons, Inc.

37. Synaptic Transmission
One-way transmission only because
Only presynaptic cells release NT
Only postsynaptic cells have receptors for NT binding
Finally, NT must be removed from the cleft. Three possible mechanisms
Diffusion out of cleft
Destruction by enzymes (such as ACh-ase) in cleft
Transport back (recycling) into presynaptic cell
Copyright 2010, John Wiley & Sons, Inc.

38. Signal Transmission at the Chemical Synapse
Copyright 2009 John Wiley & Sons, Inc.
Copyright 2010, John Wiley & Sons, Inc. 38

39. Copyright 2010, John Wiley & Sons, Inc.
Neurotransmitters
Acetylcholine (ACh): common in PNS
Stimulatory (on skeletal muscles)
Inhibitory (on cardiac muscle)
Amino acids
Glutamate, aspartate, gamma aminobutyric acid (GABA), glycine
Modified amino acids
Norepinephrine (NE), dopamine (DA), serotonin
Neuropeptides such as endorphins
Nitric oxide (NO)
Copyright 2010, John Wiley & Sons, Inc.

40. Copyright 2010, John Wiley & Sons, Inc.
End of Chapter 9
Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.
Copyright 2010, John Wiley & Sons, Inc.