1. Chapter 7: The Nervous System
The Communication System of the Body

2. Nervous System
Master controlling and communicating system of the body

3. The Nervous System : communication
A.  Neurons = masses of nerve cells that transmit information
Two processes:
1. Dendrites – shorter, more numerous, receive information
2. Axons - send information

4. Central Nervous System (CNS): brain and spinal cord.
Peripheral Nervous System (PNS): nerves of the body
        
 -- Includes 31 pairs of spinal nerves
 -- And  12 pairs of cranial nerves

6. Three Basic Functions of Nervous System
Sensory function: gathers info
Integrative function: bring the info together
Motor function: responds to signals

9. Neuroglial cells (neuroglia) – supportive tissue of the nervous system (more numerous than neurons)
5 Types of Cells:
Microglial cells
Oligodendrocytes
Astrocytes
Ependymal cells
Schwann cells

10. Microglial cell – digest debris or bacteria
Respond to immunological alarms

11. Oligodendrocytes – makes the myelin sheath that provides insulation to the axon

12. Astrocytes – connect blood vessels to neuron

13. Ependymal cell- forms a membrane

14. Schwaan cells – forms the insulating myelin sheath around a neuron

16. Neuron (nerve cell) structure:
Axon – long section, transmits impulses
Dendrite – extend from the cell body; receive information
Neurofibril – fibers within the impulse
Chromatophilic substance (rough ER) – transport system
Myelin – insulation surrounding axons
Nodes of Ranvier – gaps in the insulation

18. *Myelinated vs. Unmyelinated
Myelinated (white matter) – myelinated axons Unmyelinated (grey matter) - unmyelinated

19. Facts about Neurons Longevity: can live and function for a lifetime
Do not divide: fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception
High metabolic rate: require abundant amounts of oxygen and glucose

20. Classification of Neurons
Functional
Sensory – receives information from senses
Motor – sends information to muscles, glands, organs
Interneuron – relays information
Structural
Bipolar
Unipolar
Multipolar

21. Cell Membrane Potential
Resting Potential / Threshold Potential / Action Potential
Nerve Impulse = weak electric current

22. 2. Threshold stimulus is received 3. Sodium channels open
1. Neuron membrane maintains resting potential
2. Threshold stimulus is received
3. Sodium channels open
4. Sodium ions diffuse inward, depolarizing the membrane
5. Potassium channels open
6. Potassium ions diffuse outward, repolarizing the membrane
7. The resulting action potential causes a local bioelectric current that stimulates adjacent portions of the membrane.
8. Wave of action potentials travel the length of the axon as a nerve impulse

24. Nerve Impulse
Speed of an impulse is proportionate to the DIAMETER of the AXON.
Greater diameter = faster speed
**Myelinated Axons conduct faster than unmyelinated ones**

25. The Synapse A: Neuron (axon) B: Neuron (dendrite) Mitochondria Vesicle
Receptor
Synapse
Calcium Channel
Releases neurotransmitter
Re-uptake

26. Synapse - junction between two communicating neurons
Nerve pathway - nerve impulse travels from neuron to neuron
Dendrite → cell body → along axon -> synapse (gap) → dendrite

27. To complete the signal, a NEUROTRANSMITTER is released in the gap to signal the next neuron. They can be two types:
Excitatory:
increase membrane permeability, increases chance for threshold to be achieved
Inhibitory:
decrease membrane permeability, decrease chance for threshold to be achieved

28. Types of neurotransmitters in Humans
Acetylcholine - stimulates muscle contraction Monoamines - Norepinephrine & Dopamine (sense of feeling good, low levels = depression) Serotonin (sleepiness) and mood Endorphins = reduction of pain, good mood

29. Nerves – bundles of axons common to a section of the body
Types of Nerves:
Sensory: conduct impulses into the brain and spinal cord
Motor: carry impulses to muscles or gland
Mixed: contains both sensory and motor

30. Nerve Pathways
Reflex Arc: simple pathway, only includes a few neurons (involuntary, instantaneous)
Reflex behavior
Knee-jerk reflex: maintains uprightness
Withdrawal reflex: avoids painful stimuli