1. The Nervous System and the Brain

2. The master controlling and communicating system of the body
Nervous System
The master controlling and communicating system of the body
Functions
Sensory input – monitoring stimuli
Integration – interpretation of sensory input
Motor output – response to stimuli

3. Nervous System
Figure 11.1

4. Organization 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
Carries messages to and from the spinal cord and brain

5. Peripheral Nervous System (PNS): Two Functional Divisions
Sensory (afferent) division
Sensory afferent fibers – carry impulses from skin, skeletal muscles, and joints to the brain
Visceral afferent fibers – transmit impulses from visceral organs to the brain
Motor (efferent) division
Transmits impulses from the CNS to effector organs

6. Motor Division: Two Main Parts
Somatic nervous system
Conscious control of skeletal muscles
Autonomic nervous system (ANS)
Regulates smooth muscle, cardiac muscle, and glands
Divisions – sympathetic and parasympathetic

7. Concept Check
What is the difference between peripheral and central nervous systems?
Explain the difference between somatic and autonomic nervous systems…
What are the two divisions of the PNS?

8. Central Nervous System
Brain
Spinal Cord
Peripheral Nervous System
Sensory (afferent)
Motor (efferent)
Autonomic
Somatic
Sympathetic
Parasympathetic

9. Autonomic Nervous System
Split into two parts
Parasympathetic
Sympathetic
Responsible for our bodies ability to respond to stress, and recover from that stressful response
Controls involuntary and visceral functions
Respiration, digestion, cardiovascular, urinary, reproduction

10. Sympathetic
The section that allows our body to respond to stressful environments or situations
“Fight or Flight”
Sometimes we can get stuck in this response, which causes long term health issues
Physical Reaction
Long-Term Impact
Blood Pressure Rises
Heart Disease
Stress hormones Rise
Anxiety, insomnia, addiction, weight gain
Slowing of Digestion
Gastro Intestinal Problems
Growth and sex hormone levels decrease
Premature aging, infertility
Immune system weakens
Cancer and infections
Sticky blood platelets increase
Plaque build up – heart attackts

11. Parasympathetic
Controls our ‘vegetative’ functions
Constantly opposing the sympathetic system
Restores body to homeostasis

13. Concept Check
What are some of the consequences of being at a high stress level for a sustained period of time?
What are the major functions of the sympathetic system?
What are the main functions of the parasympathetic system?

14. Neurons
See How I work

15. Histology of Nerve Tissue
The two principal cell types of the nervous system are:
Neurons – excitable cells that transmit electrical signals
Supporting cells – cells that surround and wrap neurons

16. Microglia and Ependymal Cells
Microglia – small, ovoid cells with spiny processes
Phagocytes that monitor the health of neurons
Ependymal cells – range in shape from squamous to columnar
They line the central cavities of the brain and spinal column

17. Microglia and Ependymal Cells
Figure 11.3b, c

18. Oligodendrocytes, Schwann Cells, and Satellite Cells
Oligodendrocytes – branched cells that wrap CNS nerve fibers
Schwann cells (neurolemmocytes) – surround fibers of the PNS
Satellite cells surround neuron cell bodies with ganglia

19. Oligodendrocytes, Schwann Cells, and Satellite Cells
Figure 11.3d, e

20. Concept Check
What is the difference between Schwann Cells and Oligodendrocytes?

21. Structural units of the nervous system
Neurons (Nerve Cells)
Structural units of the nervous system
Composed of a body, axon, and dendrites
Long-lived, amitotic, and have a high metabolic rate
Their plasma membrane function in:
Electrical signaling
Cell-to-cell signaling during development

22. Neurons (Nerve Cells)
Figure 11.4b

23. Dendrites of Motor Neurons
Short, tapering, branched arms of the nerve
They are the receptive, or input, regions of the neuron
Electrical signals are conveyed as graded potentials (not action potentials)

24. Cell Body of the Nerve
Factory of the neuron
Produces the proteins for the neuron to function
Connects the dendrites to the axon

25. Axons: Function Generate and transmit action potentials
Secrete neurotransmitters from the axonal terminals
Get information from the dendrites and pass it along to another nerve
Movement along axons occurs in two ways
Anterograde — toward axonal terminal (Normal)
Retrograde — away from axonal terminal (abnormal)

26. Myelin Sheath
Whitish, fatty (protein-lipoid), segmented sheath around most long axons
It functions to:
Protect the axon
Electrically insulate fibers from one another
Increase the speed of nerve impulse transmission

27. Nodes of Ranvier (Neurofibral Nodes)
Gaps in the myelin sheath between adjacent Schwann cells
They are the sites where axon collaterals can emerge

28. Unmyelinated vs Myelinated Axons
Unmyelinated axons
A Schwann cell surrounds nerve fibers but coiling does not take place
Schwann cells partially enclose 15 or more axons
Impulse must travel the entire length of the axon, slowing transmission
Myelinated Axons
Much faster
Impulse can ‘jump’

29. Axons of the CNS
Both myelinated and unmyelinated fibers are present
Myelin sheaths are formed by oligodendrocytes
Nodes of Ranvier are widely spaced
There is no neurilemma

30. Regions of the Brain and Spinal Cord
White matter – dense collections of myelinated fibers
Gray matter – mostly soma (body) and unmyelinated fibers

31. Concept Check
Why are myelin sheaths helpful to a neuron?
What are the parts of the neuron? What are their functions?

32. How are Neurons work

33. Neuron Classification
Functional:
Sensory (afferent) — transmit impulses toward the CNS
Motor (efferent) — carry impulses away from the CNS
Interneurons (association neurons) — shuttle signals through CNS pathways

34. Neurons are highly irritable
Neurophysiology
Neurons are highly irritable
Action potentials, or nerve impulses, are:
Electrical impulses carried along the length of axons
Always the same regardless of stimulus
The underlying functional feature of the nervous system – this is what makes everything work
Chemical Synapse

35. Definitions
Synapse = the small space between the axon terminal of one neuron and the dendrites of others
Neurotransmitter = chemical messages that allow neurons to communicate with other neurons across the synapse
Receptor cites = areas on a neuron that connect and respond to neurotransmitters
Acetylcholine = most common neurotransmitter
Used in movement of peripheral NS and related to atterion and memory in the brain
Neuropeptides = special class of neurotransmitters that regulate activity of neurons and systems in the brain
Presynaptic terminal = site where the neurotransmitters are released
Postsynaptic terminal = site that receives neurotransmitters

37. How does it work
Our cells have proteins embedded in their plasma membranes
These proteins create channels for ions (charged particles) to flow in and out of the cell
Some require energy to open while others do not

38. Describes our membranes ‘electric charge’
Membrane Potential
Describes our membranes ‘electric charge’
At rest, the inside of our cell is negative in comparison to the outside
At rest
Activation gates of Na+ are closed
Inactivation gates of Na+ are open
Voltage-gated K+ channels are closed
Nerve Impulse

39. Types of plasma membrane ion channels:
Role of Ion Channels
Types of plasma membrane ion channels:
Passive, or leakage, channels – always open
Chemically gated channels – open with binding of a specific neurotransmitter
Voltage-gated channels – open and close in response to membrane potential (change in charge)
Mechanically gated channels – open and close in response to physical deformation of receptors

40. Operation of Sodium-Potassium Pump
Chemical-gated channel – only works when the right Neurotransmitters bind to its receptor sites
Active transport
Moves the ions against their concentration gradient
Steps – Na+ is inside and K+ is outside
3 Na+ and 1 ATP bind to the carrier protein inside the cell
Protein changes shape and releases Na+ outside of the cell
2 K+ ions bind to the protein out of the cell
Protein changes back to its original configuration and releases K+ into the cell
Sodium-Potassium Pump

41. Operation of a Gated Channel
Figure 11.6a

42. Operation of a Voltage-Gated Channel
Example: Na+ channel
Require a stimulus to open the channels
Steps
Nerve receives stimulus – opens sodium activation gates
Sodium diffuses into cell causing depolarization
Potassium channels open allowing potassium to diffuse out of the cell
Depolarization
Sodium is entering the cell faster than potassium can leave
Voltage-Gated Channel

43. Operation of a Voltage-Gated Channel
Figure 11.6b

44. Changes in Membrane Potential
Changes are caused by three events
Depolarization – the inside of the membrane becomes less negative
Repolarization – the membrane returns to its resting membrane potential
Hyperpolarization – the inside of the membrane becomes more negative than the resting potential

45. Check for understanding
What is the job of the sodium potassium pump
How does a synapse work
What is the difference between and chemical channel and a voltage channel