1. The Nervous System

2. The Nervous System
The master controlling and communicating system of the body.
Vital in maintaining homeostasis
Two divisions:
Central Nervous System (CNS) = brain and spinal cord
Peripheral Nervous System (PNS) = nerves that extend from CNS

3. PNS Structures
Sensory / Afferent Division – Nerves that convey impulses to the CNS from sensory receptors in the body.
Motor / Efferent Division – Nerves that convey impulses from the CNS to organs, muscles, and glands.
Two divisions of motor / efferent nerves:
Somatic nervous system – voluntary control
Ex: skeletal muscle contraction
Autonomic nervous system (ANS) – automatic or involuntary regulation
Ex: cardiac muscles

4. Basic Divisions of the Nervous System
Figure 12.2

5. THREE BASIC FUNCTIONS OF THE NERVOUS SYSTEM
Sensory -  gathers info
Integrative - information is brought together
Motor - responds to signals, homeostasis

6. Neurons

7. Neurons – nerve cells
Parts:
Cell body – metabolic center
Dendrites – convey signals toward the cell body
Axons – convey signals away from the cell body
Myelin sheath – enclose axon, increase transmission rate
Nodes of Ranvier – gaps between myelin

8. White vs Grey Matter
Myelinated (white matter) – myelinated axons
Unmyelinated (grey matter) - unmyelinated

9. Types of Nerves
Sensory Neurons - conduct impulses into the brain or spinal cord
Motor Neurons - carry impulses to muscles of glands
Interneurons- contain both sensory and motor nerves

10. Neurons Classified by Function: Sensory vs. Motor Neurons
Figure 12.11

11. Neuroglial Cells – “nerve glue”
 - support cells for the neurons
1.  Microglial Cells: scattered throughout, digest debris or bacteria
Microglial cells respond to immunological alarms

12. Neuroglial Cells 2. Oligodendrocytes:
Produce Myelin sheath around axons of neurons in CNS

13. 3. Astrocytes: connect blood vessels to neurons
Neuroglial Cells 
3. Astrocytes:  connect blood vessels to neurons
I connect to blood vessels

14. Neuroglial Cells 
4.  Ependymal Cells:  form a protective membrane (Blood-brain barrier), allow diffusion

15. Practice with neuroglia coloring!
5.  Schwann cells:  form the insulating myelin sheath around neurons in PNS
       
Practice with neuroglia coloring!

16. Supporting Cells - NEUROGLIA

17. Supporting Cells- NEUROGLIA

18. Label

19. Cell Membrane Potential

21. Membrane of a resting, or inactive, neuron is polarized – meaning it is internally more negative (less positive ions) and there are more positive ions outside.

22. During stimulation, often by a neurotransmitter, the sodium channel will open, allowing sodium ions to flow into the cell.
This will change the polarity of the neuron locally, an event called depolarization. Locally the inside is now more positive and the outside less positive. This is called a graded potential.

23. If stimulus is strong enough (threshold reached; threshold = minimum stimulus needed for response) and enough Na+ ions enter cell, the graded potential activates the neuron to begin a long-distance signal called an action potential (or nerve impulse)

24. Action potential propagates along the entire length of the axon, making it an All-or-none response.

25. After the sodium influx, the membrane becomes impermeable to sodium and permeable to potassium, causing K+ ions to diffuse into cell.
This loss of positive ions leads to the membrane becoming polarized, at rest, in a process called repolarization.
Until repolarization, cell cannot conduct another impulse (this time is called the refractory period)

26. After repolarization, the neuron’s initial concentrations of ions are restored by the sodium-potassium pump.

27. Nerve Impulses Animations of Nerve Impulses
view0/chapter14/animation __the_nerve_impulse.html
animations/actionpotential.swf

28. The Synapse Junction between two communicating neurons
Neurons do not touch– synapse
To complete a signal, a neurotransmitter is released across synaptic cleft to reach next neuron

30. Structure of a Synapses

32. Events at the Synapse
Arriving action potential depolarizes the synaptic knob and presynaptic membrane
Calcium ions enter cytoplasm of knob
Neurotransmitter released through diffusion and exocytosis of neurotransmitter vesicles
Neurotransmitter goes across synapse and binds to receptors on post-synaptic membrane
Sodium channels open on new neurons
Neurotransmitter is broken down
This ends depolarization

33. Neurotransmitters
Excitatory - increase membrane permeability, increases chance for threshold to be achieved
Inhibitory - decrease membrane permeability, decrease chance for threshold to be achieved

34. Examples of Neurotransmitters
Acetylcholine - stimulates muscle contraction
Catecholamines – Epinephrine and Norepinephrine (fight-or-flight response) & Dopamine (sense of feeling good, low levels = depression)
Serotonin (happiness, sleepiness, metabolism)
GABA (gamma-Aminobutyric acid) – chief inhibitor

35. Common Neurotransmitter Disorders
Alzheimer’s
Depression
Epilepsy
Huntington’s
Insomnia
Mania
Parkinson’s
Schizophrenia
SIDS
Deficient ACh
Def serotonin/norepinephrine
Excess GABA
Deficient GABA
Deficient serotonin
Excess norepinephrine
Deficient dopamine
Def. GABA / excess dopamine
Excess dopamine

36. Reflexes
Reflexes – rapid, predictable, involuntary responses to stimuli
Reflex arc – neural pathways that involve both CNS and PNS on which reflexes occur
Somatic reflexes – stimulate skeletal muscles (hot pan)
Autonomic reflexes – regulate smooth muscles, heart, glands (secretion of saliva, dilation of pupils)

37. AUTONOMIC NERVOUS SYSTEM
Two divisions:
Sympathetic (fight or flight – rage, fear)
Utilizes norepinephrine primarily
Parasympathetic (resting – digestion, etc.)
Utilizes acetylcholine primarily