1. Nervous System part i

2. What is the nervous system?

3. The nervous system
The master controlling and communicating system of the body
Every thought, action, and emotion shows the nervous system’s activity

4. How does the nervous system Work?

5. How does the nervous system Work?
Electrical signals are how the brain communicates with the nerves
Do you think these signals are fast or slow?

6. Organization of the Nervous system

7. Organization
The nervous system can be broken down into structural and functional classification

8. Structural Classification (What’s it made up of)
2 subdivisions:
CNS
PNS

9. 1. CNS Central nervous system made of the brain and spinal cord
Interprets information and responds

10. 2. PNS
Peripheral nervous system is made up of the nerves outside the CNS
Links all parts of the body together through electrical impulses

11. Functional Classification (What does it do)
Only deals with PNS structures (nerves)
2 major divisions:
Sensory division (afferent)
Motor division (efferent)

12. Sensory division (afferent)
Convey information TOWARD the CNS from sensory receptors

13. Motor division (Efferent)
Carry impulses AWAY from the CNS to muscles for movement and glands for hormone secretion
There are 2 types of motor nerves:

14. 2 types of motor nerves Somatic: VOLUNTARY impulses
Ex) Skeletal muscles
Autonomic: INVOLUNTARY impulses
Ex) Cardiac and smooth muscle
Ex) Glands
2 types of autonomic nerves

15. 2 types of autonomic responses
Sympathetic: “fight or flight”
Parasympathetic “rest and digest”

16. The 3 steps to Normal activity
1. Sensory input
2. Integration
3. Motor output

17. 1. Sensory input
The nerves contain sensory receptors to monitor changes in and out of the body (stimuli) to send to the CNS
The gathered information is called sensory input

18. 2. Integration
The brain/spinal cord processes the sensory input and makes a decision about what must be done.
This decision is called integration

19. 3. Motor output
A response is then created by activating muscles or glands (away from CNS)
The response is called motor output

20. Reflex Arc

21. Nervous Tissue
Complex nervous tissue can be separated into two overall types of cells:
Supporting cells
Neurons

22. Supporting cells in the CNS
Called neuroglial cells, or simply called glia
Each type of glial cell has a unique shape and function

23. 1. Astrocytes Star-shaped (hence the name)
Account for nearly half of neural tissue
Attached to blood capillaries and neurons

24. Functions of astrocytes:
1. Protect neurons from harmful substances in blood (BBB)
2. Help control chemicals in the brain (Na+, K+, CO2)
Creating a 3-d framework for the CNS
Performing repairs in damaged neural tissue
Guiding neuron development
Controlling the interstitial environment

25. 2. Microglia Look like spiders
Function to dispose of debris in the brain
Start off as phagocytic white blood cells that have migrated across capillary walls in the neural tissue of the CNS

26. 3. Ependymal cells
Thin coat with cilia line cavities of CNS tissue and move fluid around brain and spinal cord
Forms a protective cushion around the CNS
Distributes dissolved gases, nutrients and wastes
Cuboidal columnar
Cilia or microvili
Some can secrete CSF

27. 4. Oligodendrocytes Made up mostly of myelin
Wrap tightly around nerve fibers to produce myelin sheaths

28. Supporting cells of the PNS
2 types:
1. Schwann cells that help form the myelin sheaths around nerve fibers
2. Satellite cells that act as protective cushioning around cell bodies

29. Neurons AKA nerve cells
Transmit messages sent as electrical signals (nerve impulses)

30. General neuron

31. Cell Body (soma)
Contains the nucleus; is the metabolic center of the cell

32. Dendrites
Conduct electrical currents TOWARD the cell body, and to RECEIVE information
This is where sensory input occurs
Highly branched
Fine processes called dendritic spines

33. Axons Generate nerve impulses and send them AWAY from the cell body
Axon hillock- where the axon attaches to the soma

34. Collateral branch A branch of the same axon
Allow a single neuron to communicate with several other cells

35. Schwann cell (PNS only)
Form the myelin sheath

36. Myelin Sheath
Fatty, protective coating around the axon

37. Nodes of Ranvier Gaps or indentations in between Schwann cells
Occur at regular intervals

38. Axon terminals
Branching ends of axons

39. Synapse
End of the axon terminal releases the neurotransmitter

40. Synaptic cleft
Where an axon terminal interacts with another neuron

41. General Neuron

42. Organization of the nervous system
PNS: nerves
CNS:
Brain and spinal cord
Motor/efferent
Sensory/afferent
Somatic
Autonomic
Sympathetic
Parasympathetic

43. Classification of Neurons
2 ways to classify neurons:
Function
Structure

44. Functional Classification
Groups neurons based on what direction the electrical impulse is travelling related to the CNS
3 general types

45. 1. Afferent Neurons AKA sensory neurons
Carry impulses from the sensory receptors to the CNS
Sensory neurons keep us informed about what is happening inside and outside the body

46. 2. Efferent neurons AKA motor neurons
Carry impulses from the CNS to muscles and glands
The cell bodies of these neurons are always located in the CNS

47. 3. Interneurons
Connect the motor and sensory neurons in neural pathways
Cell bodies are always located in the CNS

49. Structural classification
In structural classification, neurons are classified based on the number and type of projections off the cell body

50. 1. Anaxonic
Small, have no anatomical clues to distinguish dendrites from axons
Found in special sense organs

51. 2. Multipolar Most common type 1 axon Many dendrites
CNS & motor neurons

52. 3. Bipolar Most rare type 2 processes 1 axon 1 dendrite
Sight, smell, & hearing

53. 4. Unipolar (pseudounipolar)
The dendritic and axonal processes are continuous, cell body lies off to the side Common in sensory neurons

54. Nerve impulses Neurons have 2 major functional properties:
Irritability
Conductivity

55. Irritability
Ability to respond to a stimulus and convert it to a nerve impulse
So in order to function, the neuron must first receive a stimulus, then be able to send the message out
Let’s then take a look at possible stimuli, then observe how an impulse is sent out

56. Stimuli
Most neurons are stimulated by neurotransmitters (found in the synaptic cleft)
However, different types of neurons are stimulated by different stimuli
Ex) light excites eye receptors
Ex) pressure excites cutaneous receptors

57. Electrical impulses (How it works)
The following 4 steps are going to explain exactly how an electrical signal is created in the neurons
This process is similar to the process in muscles and follows the same concept

58. Step 1: Resting state (resting potential)
At rest, the neuron has a negative charge inside (where K+ ions are) the neuron and a positive charge outside (where there are more Na+ ions)
-70v

59. Step 2. Generation of action potential
The nerve is stimulated , which opens up “sodium gates” to allow Na+ into the neuron
This “charges” up the neuron, generating electricity (action potential)
The charge inside the cell is now more positive because both K+ ions and Na+ ions are both inside
+30v

60. Step 3. Propagation of action potential
When the neuron is fully charged, the charge is released
This sends an electrical impulse through the neuron

61. Step 4: Repolarization
Once the charge is released, K+ leaves the neuron, returning the neuron to a negative charge
Until repolarization is finished, a neuron cannot conduct another impulse

63. Action potential video

64. Conductivity
The ability to transmit an impulse to other neurons, muscles, or glands

65. reflexes
When conductivity occurs across a muscle or gland, it is called a reflex
A series of reflexes across many neurons is called a reflex arc

66. Autonomic reflexes Involuntary reflexes
Stimulate smooth muscles, heart, and glands

67. Somatic reflexes
Voluntary reflexes
Stimulate skeletal muscles

68. Nerve fiber classification
Just like neurons, nerves are classified the same way

69. Nerve Fiber Classification
Mixed nerves carry BOTH sensory and motor fibers
Sensory nerves carry information TOWARD the CNS
Motor nerves carry information AWAY from the CNS to muscles and glands etc

70. Somatic nervous system
Voluntary impulses
Effects skeletal muscles

71. 1. Sympathetic division
Often referred to as the “fight or flight” system
Signs of activity of this division are:
Pounding heartbeat
Rapid breathing
Cold, sweaty skin
Dilated eye pupils
Increased adrenaline

72. How long do these signs last?
Effects usually last several minutes, until the liver dissolves released hormones

73. 2. Para-sympathetic division
Most active when the body is at rest
Promotes normal digestion, elimination of urine and feces, and conserving body energy (especially concerning the cardiovascular system)

74. Lack of oxygen
Since the nervous system has the highest metabolic rate in the body, lack of oxygen for even just a few minutes leads to death of neurons

75. Older age
Neurons cannot reproduce themselves, so we lose neurons as we age, but cannot replace them
Loss of neurons and lack of oxygen lead to senility; symptoms:
Forgetfulness
Irritability
Difficulty concentrating