1. Chapter 11 Fundamentals of the Nervous System and Nervous Tissue
Anatomy and Physiology I(2)
Mr. Scott

2. Functions of the Nervous System
Sensory input
Information gathered by sensory receptors about internal and external changes
Integration
Interpretation of sensory input
Motor output
Activation of effector organs (muscles and glands) produces a response
Motor output is the response generated from the information

3. Functions of the Nervous System
Each muscle in the body is supplied by a particular level or segment of the spinal cord and by its corresponding spinal nerve. The muscle, and its nerve make up a myotome. This is approximately the same for every person and are as follows:
C3,4 and 5 supply the diaphragm (the large muscle between the chest and the belly that we use to breath).
C5 also supplies the shoulder muscles and the muscle that we use to bend our elbow .
C6 is for bending the wrist back.
C7 is for straightening the elbow.
C8 bends the fingers.
T1 spreads the fingers.
T1 –T12 supplies the chest wall & abdominal muscles.
L2 bends the hip.
L3 straightens the knee.
L4 pulls the foot up.
L5 wiggles the toes.
S1 pulls the foot down.
S3,4 and 5 supply the bladder. bowel and sex organs and the anal and other pelvic muscles.

4. Divisions of the Nervous System
Central nervous system (CNS)
Brain and spinal cord
Integration and command center
Peripheral nervous system (PNS)
Paired spinal and cranial nerves carry messages to and from the CNS

5. Peripheral Nervous System (PNS)
Two functional divisions
Sensory (afferent) division
Somatic afferent fibers—convey impulses from skin, skeletal muscles, and joints
Visceral afferent fibers—convey impulses from visceral organs
Motor (efferent) division
Transmits impulses from the CNS to effector organs
Afferent (Sensory) = arriving; Efferent (Motor) = exiting
Location of afferent versus efferent branches from spinal cord demonstrates evolution

6. Motor Division of PNS Somatic (voluntary) nervous system
Conscious control of skeletal muscles
Autonomic (involuntary) nervous system (ANS)
Visceral motor nerve fibers
Regulates smooth muscle, cardiac muscle, and glands
Two functional subdivisions
Sympathetic
Parasympathetic
Sympathetic Nervous System (Pushing)
Heart rate increased and force increased, bronchial muscles relaxed, Eye pupil dialation, intestinal motility reduced, bladder sphincter closed, decrease kidney output
Parasympathetic Nervous System (PNS) 
Increases: digestion intestinal motility, fuel storage (increases insulin activity), resistance to infection, rest and recuperation, circulation to nonvital organs, (skin, extremities...), endorphins, the "feel good" hormones 
Decreases: heart rate blood pressure temperature, kidney output, urine secretion, digestion, pupil constriction,

7. Histology of Nervous Tissue
Two principal cell types
Neurons—excitable cells that transmit electrical signals

8. Histology of Nervous Tissue
Neuroglia (glial cells)—supporting cells:
Astrocytes (CNS)
Microglia (CNS)
Ependymal cells (CNS)
Oligodendrocytes (CNS)
Satellite cells (PNS)
Schwann cells (PNS)

9. Astrocytes Capillary Neuron Astrocyte
Most abundant, versatile, and highly branched glial cells
Cling to neurons, synaptic endings, and capillaries
Support and brace neurons
Neuron
Help determine capillary permeability
Guide migration of young neurons
Control the chemical environment
Participate in information processing in the brain
Help with exchanges between capillaries and nuerons
Help with cleanup of potassium and neurotransmitters from neurons
Astrocyte

10. Small, ovoid cells with thorny processes
Microglia
Small, ovoid cells with thorny processes
Migrate toward injured neurons
Phagocytize microorganisms and neuronal debris
Help with monitoring health of neurons
Help remove diseased or damage neurons by becoming phagocytes
Important because cells of the immune system are not allowed in the central nervous system

11. Range in shape from squamous to columnar May be ciliated
Ependymal Cells
Range in shape from squamous to columnar
May be ciliated
Line the central cavities of the brain and spinal column
Separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities
Cilia helps to circulate cerebrospinal fluid

12. (c) Ependymal cells line cerebrospinal fluid-filled cavities.
Fluid-filled cavity
Ependymal
cells
Brain or
spinal cord
tissue
(c) Ependymal cells line cerebrospinal fluid-filled cavities.
Figure 11.3c

13. Oligodendrocytes Branched cells
Processes wrap CNS nerve fibers, forming insulating myelin sheaths

14. Satellite Cells and Schwann Cells
Surround neuron cell bodies in the PNS
Schwann cells (neurolemmocytes)
Surround peripheral nerve fibers and form myelin sheaths
Vital to regeneration of damaged peripheral nerve fibers
Both of these are neuroglia of the peripheral nervous system
Satellite cells – similar in function to the astrocytes
Schwann cells – similar to oligodendrocytes

15. Special characteristics:
Neurons (Nerve Cells)
Special characteristics:
Long-lived ( 100 years or more)
Amitotic—with few exceptions
High metabolic rate—depends on continuous supply of oxygen and glucose
Plasma membrane functions in:
Electrical signaling
Cell-to-cell interactions during development
Amitotic = no divide
Important in signaling cells during development to form

16. Cell Body (Perikaryon or Soma)
Spherical nucleus with nucleolus
Well-developed Golgi apparatus
Rough ER called Nissl bodies (chromatophilic substance)
Cell body is also called the Perikaryon or soma
Endoplasmic reticulum of the neurons is probably the most well developed and active of any cells in the body
Lots of Golgi bodies

17. Cell Body (Perikaryon or Soma)
Network of neurofibrils (neurofilaments)
Axon hillock—cone-shaped area from which axon arises
Clusters of cell bodies are called nuclei in the CNS, ganglia in the PNS
Bundles of processes are called
Tracts in the CNS
Nerves in the PNS

18. Dendrites
Short, tapering, and diffusely branched
Receptive (input) region of a neuron
Convey electrical signals toward the cell body as graded potentials

19. The Axon One axon per cell arising from the axon hillock
Long axons (nerve fibers)
Occasional branches (axon collaterals)
Numerous terminal branches (telodendria)
Knoblike axon terminals (synaptic knobs or boutons)
Secretory region of neuron
Release neurotransmitters to excite or inhibit other cells
Telodendria
Axon terminals

20. Axons: Function Conducting region of a neuron
Generates and transmits nerve impulses (action potentials) away from the cell body
Molecules and organelles are moved along axons by motor molecules in two directions:
Anterograde—toward axonal terminal
Examples: mitochondria, membrane components, enzymes
Retrograde—toward the cell body
Examples: organelles to be degraded, signal molecules, viruses, and bacterial toxins

21. and conducting region)
Dendrites
(receptive regions)
Cell body
(biosynthetic center
and receptive region)
Nucleolus
Axon
(impulse generating
and conducting region)
Impulse
direction
Nucleus
Node of Ranvier
Nissl bodies
Axon
terminals
(secretory
region)
Axon hillock
Schwann cell
(one inter-
node)
Neurilemma
(b)
Terminal
branches
Figure 11.4b

22. Segmented sheath around most long or large-diameter axons
Myelin Sheath
Segmented sheath around most long or large-diameter axons
It functions to:
Protect and electrically insulate the axon
Increase speed of nerve impulse transmission
Myelin in PNS
Schwann cells wraps many times around the axon
Myelin sheath—concentric layers of Schwann cell membrane
Neurilemma—peripheral bulge of Schwann cell cytoplasm
Nodes of Ranvier
Myelin sheath gaps between adjacent Schwann cells
Sites where axon collaterals can emerge

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. Unmyelinated Axons Thin nerve fibers are unmyelinated
One Schwann cell may incompletely enclose 15 or more unmyelinated axons

25. Myelin Sheaths in the CNS
Formed by processes of oligodendrocytes, not the whole cells
Nodes of Ranvier are present
No neurilemma
Thinnest fibers are unmyelinated

26. White Matter and Gray Matter
Dense collections of myelinated fibers
Gray matter
Mostly neuron cell bodies and unmyelinated fibers

27. Functional Classification of Neurons
Three types:
Sensory (afferent)
Transmit impulses from sensory receptors toward the CNS
Motor (efferent)
Carry impulses from the CNS to effectors
Interneurons (association neurons)
Shuttle signals through CNS pathways; most are entirely within the CNS
Except for a few all sensory neurons are unipolar
Impulses from great toe travel a meter before they reach a cell body in a ganglion close to the spinal cord.
Efferent = exiting
Most motor neurons are multipolar
Multipolar—1 axon and several dendrites
Most abundant
Motor neurons and interneurons
Bipolar—1 axon and 1 dendrite
Rare, e.g., retinal neurons
Unipolar (pseudounipolar)—single, short process that has two branches:
Peripheral process—more distal branch, often associated with a sensory receptor
Central process—branch entering the CNS

28. Resting Membrane Potential
Differences in ionic makeup
Inside the neuron has lower concentration of Na+ and Cl– than outside
Inside has higher concentration of K+ and negatively charged proteins (A–) than outside

29. Resting Membrane Potential
Negative interior of the cell is due to much greater diffusion of K+ out of the cell than Na+ diffusion into the cell
Sodium-potassium pump stabilizes the resting membrane potential by maintaining the concentration gradients for Na+ and K+
Because K+ is always leaking out and Na+ is always leaking in – you would think the concentrations would eventually even out BUT the Na-K pump transports Na out and K in to maintain concentration differences.

30. Membrane Potentials That Act as Signals
Membrane potential changes when:
Ion concentrations on two sides change
Permeability of membrane to ions changes
Changes in membrane potential are signals used to receive, integrate and send information

31. Changes in Membrane Potential
Depolarization
A reduction in membrane potential (toward zero)
Inside of the membrane becomes less negative than the resting potential
Increases the probability of producing a nerve impulse
Hyperpolarization
An increase in membrane potential (away from zero)
Inside of the membrane becomes more negative than the resting potential
Reduces the probability of producing a nerve impulse
Remember we start at -70 mV

32. Membrane Potentials That Act as Signals
Two types of signals
Graded potentials
Incoming short-distance signals
Action potentials
Long-distance signals of axons

33. Occur when a stimulus causes gated ion channels to open
Graded Potentials
Occur when a stimulus causes gated ion channels to open
E.g., receptor potentials, generator potentials, postsynaptic potentials
Magnitude varies directly (graded) with stimulus strength
Decrease in magnitude with distance as ions flow and diffuse through leakage channels
Short-distance signals
Current dies within a few millimeters of its origin

34. Action Potential (AP)
Brief reversal of membrane potential with a total amplitude of ~100 mV
Occurs in muscle cells and axons of neurons
Does NOT decrease in magnitude over distance
Principal means of long-distance neural communication

35. Graded Potentials vs. Action Potentials
Chemically gated ion channels
Stimulus is related to the strength
Die out with increasing distance
Due to leakage of the charge
Short distance travel
Voltage gated ion channels
Stimulus is consistent
Do not decrease with distance
Long distance travel
Graded Potentials can cause Action Potentials

36. The big picture 1 2 3 3 4 2 1 1 4 Resting state Depolarization
Repolarization 3 4
Hyperpolarization
Membrane potential (mV) 2
Action
potential
Depolorization is caused by Na+ flowing into cell
Repolorization is caused by K+ flowing out
Hyperpolorization (threshold) caused by continual K+ flowing out
Threshold 1 1 4
Time (ms)
Figure (1 of 5)

37. Threshold At threshold:
Membrane is depolarized by 15 to 20 mV
Na+ permeability increases
Na influx exceeds K+ efflux
The positive feedback cycle begins
Subthreshold stimulus—weak local depolarization that does not reach threshold
Threshold stimulus—strong enough to push the membrane potential toward and beyond threshold
AP is an all-or-none phenomenon—action potentials either happen completely, or not at all

38. Coding for Stimulus Intensity
Action potentials do not vary and are independent of stimulus intensity
How does the CNS tell the difference between a weak stimulus and a strong one?
Strong stimuli can generate action potentials more often than weaker stimuli
CNS determines stimulus intensity by the frequency of impulses
Action
potentials
Stimulus
The more impulses, the greater the intensity of the stimulus

39. Conduction velocities of neurons vary widely Effect of axon diameter
Conduction Velocity
Conduction velocities of neurons vary widely
Effect of axon diameter
Larger diameter fibers = less resistance to local current flow = faster impulse conduction
Effect of myelination
Continuous conduction in unmyelinated axons is slower than saltatory (jumping) conduction in myelinated axons

40. Effects of myelination
Conduction Velocity
Effects of myelination
Myelin sheaths insulate and prevent leakage of charge
Saltatory conduction in myelinated axons is about 30 times faster
Voltage-gated Na+ channels are located at the nodes
APs appear to jump rapidly from node to node
Multiple Sclerosis (MS)
An autoimmune disease that mainly affects young adults
Symptoms: visual disturbances, weakness, loss of muscular control, speech disturbances, and urinary incontinence
Myelin sheaths in the CNS become nonfunctional scleroses
Shunting and short-circuiting of nerve impulses occurs
Impulse conduction slows and eventually ceases
Some immune system–modifying drugs, including interferons and Copazone:
Hold symptoms at bay
Reduce complications
Reduce disability

41. Nerve Fiber Classification
Group A fibers
Large diameter, myelinated somatic sensory and motor fibers
Group B fibers
Intermediate diameter, lightly myelinated ANS fibers
Group C fibers
Smallest diameter, unmyelinated ANS fibers
Nerve fibers are classified according to:
Diameter
Degree of myelination
Speed of conduction

42. A junction that mediates information transfer from one neuron:
The Synapse
A junction that mediates information transfer from one neuron:
To another neuron, or
To an effector cell
Presynaptic neuron—conducts impulses toward the synapse
Postsynaptic neuron—transmits impulses away from the synapse

43. Types of Synapses Axodendritic Axosomatic
Between the axon of one neuron and the dendrite of another
Axosomatic
Between the axon of one neuron and the soma of another

44. Less common than chemical synapses
Electrical Synapses
Less common than chemical synapses
Neurons are electrically coupled (joined by gap junctions)
Communication is very rapid, and may be unidirectional or bidirectional
Are important in:
Embryonic nervous tissue
Some brain regions
In embryos they guide early neuronal development
In brain responsible for normal jerky movements of the eyes and also the hippocampus which is associated with learning

45. Chemical Synapses
Specialized for the release and reception of neurotransmitters
Typically composed of two parts
Axon terminal of the presynaptic neuron
Receptor region on the postsynaptic neuron

46. Synaptic Cleft
Fluid-filled space separating the presynaptic and postsynaptic neurons
Prevents nerve impulses from directly passing from one neuron to the next

47. Transmission across the synaptic cleft:
Is a chemical event (as opposed to an electrical one)
Involves release, diffusion, and binding of neurotransmitters
Ensures unidirectional communication between neurons

48. Termination of Neurotransmitter Effects
Within a few milliseconds, the neurotransmitter effect is terminated
Degradation by enzymes
Reuptake by astrocytes or axon terminal
Diffusion away from the synaptic cleft

49. Synaptic Delay
Neurotransmitter must be released, diffuse across the synapse, and bind to receptors
Synaptic delay—time needed to do this (0.3–5.0 ms)
Synaptic delay is the rate-limiting step of neural transmission

50. Postsynaptic Potentials
Graded potentials
Strength determined by:
Amount of neurotransmitter released
Time the neurotransmitter is in the area
Types of postsynaptic potentials
EPSP—excitatory postsynaptic potentials
IPSP—inhibitory postsynaptic potentials

51. Excitatory Synapses and EPSPs
Neurotransmitter binds to and opens chemically gated channels that allow simultaneous flow of Na+ and K+ in opposite directions
Short distance signaling
Moves the polarity towards AP

52. Inhibitory Synapses and IPSPs
Neurotransmitter binds to and opens channels for K+ or Cl–
Causes a hyperpolarization (the inner surface of membrane becomes more negative)
Reduces the postsynaptic neuron’s ability to produce an AP

53. Neurotransmitters
Most neurons make two or more neurotransmitters, which are released at different stimulation frequencies
50 or more neurotransmitters have been identified
Classified by chemical structure and by function

54. Chemical Classes of Neurotransmitters
Acetylcholine (Ach)
Released at neuromuscular junctions and some ANS neurons
Synthesized by enzyme choline acetyltransferase
Degraded by the enzyme acetylcholinesterase (AChE)

55. Chemical Classes of Neurotransmitters
Biogenic amines include:
Catecholamines
Dopamine, norepinephrine (NE), and epinephrine
Indolamines
Serotonin (sleep) and histamine (wakeful, appetite, inflammation)
Broadly distributed in the brain
Play roles in emotional behaviors and the biological clock
Dopamine – Happy neurotransmitter
Drugs like crystal meth flood the brain with pleasure so it does not produce its own
Cocaine on the other hand blocks the reabsorption of dopamine so dopamine continues to stimulate over and over-after repeated stimulation the body makes less dopamine
Another effect of the drug abuse is the release of glutamate (reponsible for learning)-this NT can be responsible for “jonesing”

56. Functional Classification of Neurotransmitters
Neurotransmitter effects may be excitatory (depolarizing) and/or inhibitory (hyperpolarizing)
Determined by the receptor type of the postsynaptic neuron
GABA and glycine are usually inhibitory
Glutamate is usually excitatory
Acetylcholine
Excitatory at neuromuscular junctions in skeletal muscle
Inhibitory in cardiac muscle