1. Biology 30 NERVOUS SYSTEM
1.    Nervous System Overview
2.    The Neuron
3.    Reflex Arc
4.    The Action Potential
5.    The Synapse / Neurotransmitters
6.    Nervous System Diseases
7.    Drugs
8.    PNS
9.    CNS
10. The Brain

2. General Functions 4. Transmission Reception 2. Conduction
3. Interpretation and Organization
4.  Transmission
The nervous systems main function is to maintain homeostasis: a maintenance of the internal environment i.e. pH, body temp, glucose levels, BP, water levels, etc

3. Nervous System Organization

4. The Neuron- The functional unit of the nervous system, it conducts nerve impulses
There are 3 kinds of neurons:
1) sensory neurons (afferent)- take impulses from the body receptors to the CNS
2) motor neurons (efferent)-take impulse away from the CNS and to the muscles and glands
3) interneurons- are actually in the CNS (in the brain and spinal cord)
***Neuroglia (glial cells)- supportive cells that aid the interneurons of the brain. Nourish neurons, removes waste from neurons, and protect neurons.

6. The Neuron has 3 basic Basic parts:
1) cell body- nucleus and cytoplasm
2) Dendrites-finger-like projections of cytoplasm of cell body. They receive information
3) Axon-extension of cytoplasm. Transmit impulse away from the body

8. Some neurons contain the following additional parts:
Myelin Sheath-a white fatty covering that insulates the axon. Schwann cells produce the myelin sheath
Schwann cells- a special kind of glial cell that produces a myelin sheath that wraps around the axons as insulation
On top of protection, the myelin sheath allows for faster conduction of impulses and greater power of regeneration
The myelin sheath is NOT continuous but rather forms intermitted gaps called the Nodes of Ranvier. Impulses will now ‘jump’ from Node to Node rather then slowly moving through the entire length of the axon. (faster impulses)

10. All nerves of the PNS, as well as all motor and sensory neurons are myelinated, only some of the nerves in the CNS are myelinated
Non- Myelinated neurons in the brain= grey matter
Myelinated nerves in the brain are called white matter

11. Neuron structure

13. Nerves
Individual neurons are organized into tissues called nerves.

14. Repairing Damaged Nerves
Nerves in the PNS are surrounded by a thin membrane called the neurilemma which helps to regenerate damaged axons
Nerves in CNS lack neurilemmas and cannot be repaired
Area of research: stem cells, brain band-aid

15. Reflex Arc
automatic, quick, involuntary responses to internal or external stimuli.
does not immediately involve the brain.
allows quicker reaction times to a potentially harmful stimulus

16. Stretch Reflex
Stretch Reflex

17. 5 Components of a Reflex Arc:
1. Sensory receptor -senses something
2. Sensory neuron -sends signal to the CNS
3. Interneuron- registers signal
4. Motor neuron -sends response back
5. Effector- caries out the action

18. Action Potential A nerve impulse is an action potential
An action potential is an electrochemical event with a rapid change in polarity (relative electrical potential) down a nerve cell that results in the conduction of a nerve impulse.

19. Steps of a Nerve Impulse (Action Potential 1. Resting Potential
Polarization: voltage difference of -70mV across a nerve cell membrane
caused by the sodium potassium pump (gate): more sodium is pumped out than potassium is pumped in, resulting in a negative charge inside the axon of the neuron

20. also potassium moves out by diffusion more easily than sodium moves in
Result: excess positive charge outside the membrane and negative charge inside the membrane

21. 2. Stimulation / Depolarization
A threshold stimulus must be applied (a change in pH, pressure, or an electrical stimulus) This causes the sodium potassium pump to cause Na+ gates to open and tons of Na+ rush into the cell, and small amounts of K+ to move out
membrane becomes depolarized (+ 40 mV)

22. 3. Re-polarization
After the wave of impulse has move through Na+ gates close to stop inflow
change in electrical potential causes K+ channels to open and K+ ions rush out of the cell

23. Restores the polarized state but now is hyperpolarized – more positively charged on the outside than the resting state (over-shoot)
(also the ion concentrations are reversed from the resting state )

24. 4. Refractory period
resting potential (-70mv) must be restored before the neuron can fire again
Na+ are pumped out and K+ are pumped back into the cell using ATP energy.
The

25. The Action Potential

26. The Action Potential in Action
Neuron Action Potential
Propagation

27. Saltatory Action
the speed of the nerve impulse is increased by jumping from node of Ranvier to node of Ranvier (gated channels are found only at the nodes)
Propagation of the Action Potential

28. Threshold level – minimum depolarization that must be reached (usually around +30mV) before sufficient Na+ gates open to continue the action potential
All or None Response – if the threshold level is not reached, the action potential will not occur at all. If the threshold is reached or exceeded a full action potential will result.
The wave of depolarization is self propagating, meaning that it will continue without any aid until its passed on to the next neuron

29. How do we differentiate intensity? Ex hot vs warm?

30. Intensity is determined by:
1. the number of neurons that fire simultaneously
2. the frequency at which the neurons fire
3. the threshold level of different neurons (lower threshold neurons are more likely to fire, and are found in more “sensitive” areas)

31. The Synapse and Neurotransmitters
Neurons are NOT physically attached to each other, but are separated by a gap (synaptic cleft), the electrical impulse cannot just simply cross the gap to the next dendrite, something is needed
Neurotransmitters are stored in synaptic vesicles of the axon and are released to carry the information across this synaptic gap

32. The Synapse
Terminal Axon

33. Structures in the Synapse
Pre-synaptic membrane – membrane found at the synaptic ending of the neuron sending information
Post-synaptic membrane- membrane found at the dendrite of the neuron receiving information
Synaptic cleft – space between the pre and post synaptic membranes.

34. Neurotransmitters continue the impulse across the synaptic cleft
Crossing the impulse across the gap is a chemical reaction
1) The end of pre-synaptic axon contains vesicles that have specialized neurotransmitters (NTs), as the impulse gets to the end of the axon the NTs are released in to the gap
2) The NTs diffuse across the gap and attached to specialized receptors found on the post synaptic dendrite.
3) The wave of depolarization continues on the through the next neuron

35. Neurotransmitters
excitatory neurotransmitters – cause the opening of Na+ channels to cause depolarization

36. -inhibits action potentials
2. inhibitory neurotransmitters –block Na+ channels and open K+ channels ions which causes hyper-polarization
-inhibits action potentials

37. Summation – at any given time there are many neurons acting and releasing NTs into the synaptic cleft, the net effect of excitatory and inhibitory neurotransmitters is called summation
ONLY if there is adequate excitation to reach the threshold, the neuron will fire.

38. -may require more than one neuron to release neurotransmitters

39. A response may involve both excitatory and inhibitory neurotransmitters
Ex) Throwing a ball: Triceps contracts and bicep relaxes

40. Integration – the degree of sensation felt or the degree of response created by the brain depends on the number of neurons that fire

41. There are 9 universally recognized neurotransmitters: aspartate, glycine, GABA, glutamate, dopamine, nor-epinephrine, epinephrine, seratonin, and acetylcholine.

42. Some of the more common neurotransmitters (and their enzymes) include:
Function of Neurotransmitter
Acetylcholine
Cholinesterase
Involved with muscle contraction of the skeletal muscles
Dopamine
Monoamine oxidase enzyme
Responsible for voluntary movement and emotions of pleasure
Serotonin
Regulates temperature, sensory perception, sleep and involved in mood stabilization and control
Nor-epinephrine
Regulates the stress “fight or flight” response
GABA
Inhibitory action of motor behavior

43. Removing Neurotransmitters
To be effective, the NTs must NOT linger around in the gap, other wise successive impulses will occur. NTs are removed from the gap by:
1. Degradation by enzymes in the synaptic cleft
2. Re-uptake by the pre-synaptic membrane
3. Diffusion out of the synaptic cleft
4. Inability to bind due to competitive inhibitors

44. The Effects of Drugs
Drug – anything that is not food that alters the normal bio-chemistry of the body in some way.

45. Stimulant – mimics neurotransmitter, decreases rate of breakdown of neurotransmitter or increases release of neurotransmitter
Depressant – blocks receptor site, decreases production of neurotransmitter, or increases the breakdown of neurotransmitter

46. Alcohol: - depressant -seems to enhance GABA
-leads to lack of coordinated response, and loss of normal social inhibitions.
-may also weaken the effect of glutamine, an excitatory neurotransmitter, leading to sluggishness and lack of co-ordination.
Close to Home Animation: Alcohol

47. Marijuana:
- a depressant and hallucinogen
-acts on the canniboid receptors of the brain that affect concentration, perception and movement.
-may have an impact on the activity of seratonin, GABA and norepinephrine in the brain
not physically addicting, however this is a gateway drug and may be psychologically addicting

48. Cocaine:
-a stimulant
-blocks the re-uptake of dopamine, causing an adrenaline like effect from the dopamine
-as dopamine levels increase in the synapse, the body produces less, thus making cocaine very physically addicting
Close to Home Animation: Cocaine

49. Crystal meth:
-a stimulant
-passes directly through neuron membranes and causes excessive release of dopamine
-leads to feelings of euphoria, psychosis, delusions and extreme aggressiveness.

50. Ecstasy:
- a stimulant and hallucinogen
-affects neurons in the brain by causing an over-production of serotonin.
-creates shorter feelings of pleasure, however use can result in brain damage, and cardiac arrest.

51. The venom of the black widow spider is called “latrotoxin”
The venom of the black widow spider is called “latrotoxin”. This toxin results in a massive release of the neurotransmitter acetylcholine from the neuromuscular junctions of victims and may cause muscle spasms, pain, increased blood pressure, nausea and vomiting.

52. Diseases of the Nervous System
Parkinson’s Disease: wide-eyed, unblinking expression, involuntary tremor, muscle rigidity, shuffling gait. Ex. Muhammad Ali
-dopamine deficiency caused by the degeneration of dopamine producing cells in the brain -

53. -caffeine may offer protection against Parkinson’s disease as it prevents loss of dopamine

54. Alzheimer’s Disease: characterized by loss of memory, senility, deterioration of cells in the basal nuclei, presence of tangles and plaques
-possibly due to a malfunction of acetylcholine
- seems to be linked to a gene located on chromosome #21

55. Schizophrenia: delusions, random thoughts, disjointed thoughts, sensory hallucinations
- may be the result of excessive activity of brain neurotransmitters such as dopamine

56. Huntington’s Disease: progressive deterioration of the nervous system that leads to writhing movements, insanity and eventually death
- seems to be caused by the malfunction of the inhibitory neurotransmitter GABA

57. Depression: low affect, feeling blue, lack of or excessive sleep and eating patterns
- seems to be linked to malfunctions in dopamine and seratonin, perhaps caused by an excess of monoamine oxidase enzymes

58. Stroke: caused by interruption of blood flow to the brain which causes brain cells to perish.

59. Epilepsy: is a seizure disorder where there is a sudden, un-explained surge of electrical activity through the brain with no specific known cause.
Epilepsy.com

60. Chemical Warfare
1) Nerve Gas: inhibit acetylcholinesterase (enzyme that removed acetylcholine from the synaptic gap). Causes spastic paralysis which is continues muscle spasms
2) Strychnine: similar to nerve gas, causes convulsions and spastic paralysis

61. Central Nervous System (CNS)
Is primarily responsible for the processing and organization of information.
The CNS consists of two major structures:
1. The Brain
2. The Spinal Cord

62. Spinal Cord
Made of 31 segments
Protected by the vertebrae

63. Spinal Cord Central Cavity – contains cerebrospinal fluid
White Matter – contains myelinated nerve cells
Grey Matter – contains un-myelinated nerve cells

64. Spinal Cord
Dorsal Root Ganglion – entry of sensory neurons to spinal cord and CNS, ganglion is the collection of cell bodies
Ventral Root – exit of motor neurons from the spinal cord

65. Meninges – 3 protective membranes surrounding the spinal cord and brain (dura mater, arachnoid, pia mater)
Meningitis is an infection of the meninges (A spinal tap is a needle that is inserted between 2 vertebrates into the meninges to check for meningitis)

66. Cerebrospinal Fluid – circulates between the inner and middle membranes of the brain and spinal cord.
Provides protection, nutrient / waste exchange, etc.

67. Spinal Cord

68. Spinal Cord Functions center for reflex action
provides a pathway for communication between the brain and peripheral nerves

69. The Brain

70. Hindbrain - The Unconscious Brain
– important for autonomic functions required for survival
Cerebellum – responsible for muscle co-ordination, posture, coordinated muscle movement and balance

71. Medulla oblongata – controls heartbeat, respiration, blood pressure, reflex center for vomiting, sneezing, hiccupping, coughing and swallowing
Pons – connects the cerebrum to other parts of the brain, regulates breathing rate

73. Midbrain – reflex center for head movements in response to visual stimuli, connects cerebrum to other parts of the brain

74. Forebrain – responsible for conscious and unconscious actions
Thalamus – central relay station
- directs incoming sensory information to the cerebrum

75. Hypothalamus – contains cells that produce some hormones, controls thirst, hunger, and controls many of the pituitary hormones
Also aids in sleep regulation, sexual arousal, emotions (anger, fear, pain, pleasure)

76. Cerebrum – largest part of the brain (80% of brain mass), left and right hemispheres.
responsible for intellect, memory, consciousness and language.

77. Lobes of the Cerebral Cortex
Frontal Lobe –voluntary motor muscle movement, higher intellectual processes, personality/behavior, language

78. Temporal Lobe – hearing

79. Parietal Lobe –perceptions of touch, temperature, pressure, pain, etc from the skin

80. Occipital Lobe –vision
Olfactory Lobe –smell

81. Other parts of the brain
Limbic System –emotions, associated with hypothalamus

82. Pituitary Gland- Master Gland
attaches to hypothalamus

83. Corpus Callosum
Bundle of nerves that connects the two halves of the brain
allows for integrated thoughts and coordinated responses

84. Left brain – verbal, linguistic dominant
Right brain – spatial, artistic, visual dominant

85. Radioactive chemicals are injected into the bloodstream
PET – Positron Emission Tomography
Radioactive chemicals are injected into the bloodstream
data is used to produce 2D or 3D images of the distribution of the chemicals throughout the brain and body.

86. SPECT-Single Photon Emission Computed Tomography
radioactive tracers and a scanner record data
computer constructs 2D or 3D images of the active brain regions.

87. MRI-Magnetic Resonance Imaging
- magnetic fields and radio waves produce high-quality 2D or 3D images of brain structures without injecting radioactive tracers.

88. EEG-Electroencephalography
- electrodes placed on the scalp detect and measure patterns of electrical activity from the brain.

89. CT-Computed Tomography Scan
- a series of X-ray beams passed through the head.
-images are then developed on sensitive film.
-creates cross-sectional images of the brain

90. Peripheral Nervous System (PNS)
Cranial nerves – 12 pairs of sensory, motor and mixed nerves that control the face, neck and shoulders
Spinal Nerves – 31 pairs of nerves that emerge from the spinal cord by two roots (one pair for each segment)

91. Dorsal root nerves – contain sensory neurons and ganglia
Ventral root nerves – contain motor neurons
All other nerves not part of the CNS

92. Spinal Cord Injuries

93. The PNS is subdivided into two major parts:
The Somatic Nervous System
-contains all the nerves that serve the muscular-skeletal system and the sensory organs.
-conscious and deliberate.

94. -non-voluntary actions
The Autonomic Nervous System
-non-voluntary actions
-contains all the nerves that serve the internal organs.
-unconscious and automatic.
-made of two parts:

95. Sympathetic nervous system
-responsible for the 4 Fs: fight, flight, fright, or having sex response
-ex) dilation of the pupils, increased heart rate, increased breathing rate, slowed digestion, enhanced performance, increase in blood sugar

96. - brings the body back to normal levels
Parasympathetic nervous system – responsible for the relaxation response (after fight, flight, fright, having sex)
- brings the body back to normal levels

97. Fig 2 p 434