1. Chapter 10 Nervous System I

2. Divisions of the Nervous System
Central Nervous System
Brain and spinal cord
All sensations have to be relayed here to be acted on
Muscle & gland stimulation
Control center for the entire system

3. Divisions of the Nervous System
Peripheral Nervous System
Connection between and CNS & receptors, muscles, and glands
Nerves
Cranial nerves
Spinal nerves

4. Divisions of Peripheral Nervous System
Sensory Division
Afferent System
Picks up sensory information and delivers it to the CNS
Motor Division
Efferent System
Carries information to muscles and glands

5. Divisions of Peripheral Nervous System
Divisions of the Motor Division
Somatic (SNS)
Carries information to skeletal muscle
Voluntary
Autonomic (ANS)
Carries information to smooth muscle, cardiac muscle, and glands
Involuntary

6. Divisions Nervous System

7. Functions of Nervous System
Sensory Function
sensory receptors gather information
information is carried to the CNS
Motor Function
decisions are acted upon
impulses are carried to effectors
Integrative Function
sensory information used to create
sensations
memory
thoughts
decisions
Most rapid means of maintaining homeostasis in your body

8. Nervous System Cytology
Two Types of Cells
Neurons
Conduct nerve impulses from one part of the body to another
Information Processing Units
Neuroglial cells

9. Neuron Structure

10. Neuron Structure Dendrites Cell Body
Large nucleus surrounded by granular cytoplasm
Dendrites
Thick branched divisions of cell body
Bring nerve impulses toward the cell body

11. Neuron Structure
Axon
Usually a single, longer process that conducts nerve impulses from the cell body
Terminates at another neuron, muscle or gland
May be up to a meter

12. Neuron Structure Axon Axon terminal
End of an axon with many branching fibers
End expands to form synaptic end bulb
Nerve Fiber
Common name for an axon and its myelin sheath

13. Myelination of Axons Myelin sheath Formed by neuroglial cell
Phospholipid segment that wraps around axon
Provides protection for axon
Increases speed of impulse along axon

14. Myelination of Axons Myelin sheath Schwann cells Form myelin sheath
Found ONLY in peripheral nervous system
Assist in repair of damaged axons, provides tube for axon or dendrite to grow

15. Myelination of Axons Myelin sheath
Production begins during 1st year of life
Amount increases from birth to maturity
This is why adults react quicker to certain stimuli

16. Myelination of Axons Myelin sheath Nodes of Ranvier
Segments on axon that are not myelinated
Gaps in sheath

17. Myelination of Axons White Matter contains myelinated axons
Gray Matter
contains unmyelinated structures
cell bodies, dendrites

18. Classification of Neurons – Structural Differences
Bipolar
Two processes
One axon, one dendrite
Eyes, ears, nose
Unipolar
One process that branches in two
Ganglia
Specialized masses of nerve tissue outside brain & spinal cord

19. Classification of Neurons – Structural Differences
Multipolar
Many processes
Only one axon
Most neurons of CNS

20. Classification of Neurons – Functional Differences
Sensory Neurons
Afferent
Carry impulse to CNS
Dendrites act as sensory receptors
Most are unipolar
Some are bipolar
Motor Neurons
multipolar
carry impulses away from CNS
Carry impulses to effectors (muscles or glands)
Interneurons
Link neurons
Multipolar
In CNS

21. Classification of Neurons – Functional Differences

22. Types of Neuroglial Cells in the PNS
Schwann Cells
Produce myelin found on peripheral myelinated neurons
Speed neurotransmission
Satellite Cells
Support ganglia in PNS

23. Types of Neuroglial Cells in the CNS
Astrocytes
CNS
Scar tissue in CNS
Regulate ion concentrations (K+)
Induce synapse formation
Connect neurons to blood vessels
Oligodendrocytes
Form myelin in CNS
Myelinating cell

24. Types of Neuroglial Cells in the CNS
Microglia
CNS
Phagocytic cell
Proliferate w/ CNS injury
Ependyma
CNS
Cuboidal or columnar
Ciliated
Line central canal of spinal cord
Line ventricles of brain

25. The Synapse Junction between two neurons Also called synaptic clefts
Essential in homeostasis because of the ability to transmit some impulses while inhibiting others
Brain disease & many psychiatric disorders result from bad synaptic communication

26. The Synapse 2 Types Electrical & Chemical Most in CNS are chemical
Function
Neuron secretes neurotransmitters across synaptic cleft
Post-synaptic neuron has receptors to match transmitter
When they match, impulse continues

27. Resting Membrane Potential
Inside is negative relative to the outside
Polarized membrane
Due to distribution of ions
Unequal distribution of Na+ and K+ ions
K+ 28x greater inside
Na+ 14x greater outside
Na+/K+ pump

28. Sodium/Potassium Pump
Fights osmosis
Transports 3 Na+ out & 2 K+ into a resting neuron
Active Process

29. Local Potential Changes
Caused by various stimuli
Temperature changes
Light
Pressure
Environmental changes affect the membrane potential by opening a
gated ion channel
Allows Na+ to diffuse in & K+ to diffuse out

30. Local Potential Changes
If membrane potential becomes more negative, it has hyperpolarized
If membrane potential becomes less negative, it has depolarized
Summation can lead to threshold stimulus that starts an action potential
Multiple impulses often needed to reach threshold stimulus

31. Local Potential Changes

32. Action Potentials At rest membrane is polarized
Threshold stimulus reached
Na+ channels open and membrane depolarizes
Na+ enters cell
K+ leaves cytoplasm and membrane repolarizes

33. Action Potentials

34. Action Potentials

35. All-or-None Response
If a neuron responds at all, it responds completely
A nerve impulse is conducted whenever a stimulus of threshold intensity or above is applied to an axon
All impulses carried on an axon are the same strength

36. Refractory Period Absolute
– Time when threshold stimulus does not start another action potential
Relative
– Time when stronger threshold stimulus can start another action potential
Under normal conditions each fiber may conduct impulses per second
Larger neurons conduct up to 2500 per second

37. Impulse Conduction
Nerve cell membrane maintains resting potential by diffusion of Na+ and K+ down their concentration gradients as the cell pumps them up the gradients
Neurons receive stimulation, causing local potentials, which may sum to reach threshold
Sodium channels in a local region of the membrane open
Sodium ions diffuse inward, depolarizing the membrane

38. Impulse Conduction Potassium channels in the membrane open
Potassium ions diffuse outward, repolarizing the membrane
The resulting action potential causes an electric current that stimulates adjacent portions of the membrane
Series of action potentials occurs sequentially along the length of the axon as a nerve impulse

39. Saltatory Conduction

40. Saltatory Conduction Impulse along myelinated fiber
Sheath inhibits movement of ions
Nodes of Ranvier allow generation of action potentials and conduction
Ionic current flows through extra-cellular fluid & triggers impulse at next node
Impulse mechanism is the same, BUT impulse skips from one node to the next.

41. Saltatory Conduction Valuable to Homeostasis
Speed of impulse greatly increased
Low ATP expenditure by Na-K pump due to little exposed membrane

42. Clinical Application Drug Addiction
Occurs because of the complex interaction of neurons, drugs, and individual behaviors
Understanding how neurotransmitters fit receptors can help explain the actions of certain drugs
Drugs have different mechanisms of action
Several questions remain about the biological effects of addiction, such as why some individuals become addicted and others do not