1. The Nervous System
Chapter 9

2. Objectives To identify the basic structure of a neuron.
To explain the main components of the nervous system.
To compare and contrast the central nervous system and the peripheral nervous system.
To differentiate between the somatic and autonomic nervous systems.

3. Functions of the Nervous System
Sensory input (gathering information): to monitor changes occurring inside and outside the body
Changes = stimuli
Integration: to process and interpret sensory input and decide if action is needed
Motor output: a response to integrated stimuli
The response activates muscles or glands

4. Functions of the Nervous System

5. Structure of a Neuron Neuron= Nerve Cell
Reacts to physical/chemical changes in surroundings
Transmit information through nerve impulses to other neurons and other cells.

7. Anatomy of a neuron video

8. Nervous Tissue Neuroglia
Definition: all support cells in the CNS (Central nervous system)
Function: to support, insulate, and protect neurons
Neurons
Function: transmit messages
Major regions of neurons
Cell body – nucleus and metabolic center of the cell
Processes – fibers that extend from the cell body
Dendrites – conduct impulses toward the cell body
Axons – conduct impulses away from the cell body

9. CNS vs. PNS CNS (Central Nervous System):
Brain
Spinal Cord
PNS (Peripheral Nervous System):
Cranial nerves
Spinal Nerves

10. PNS Contains a sensory division and a motor division.
Contains sensory receptors that convert info into a nerve impulse and transmit it back to the CNS to make sense of it.
Monitors environmental changes such as light and sound
Detects changes in homeostasis ( ex: temperature, oxygen level)

11. Motor Division
Utilize peripheral neurons to carry impulses from the CNS to an effector which will cause a response
Ex: muscle contraction, gland secretion, etc.

12. Motor Division Somatic Nervous System:
Controls skeletal muscle and voluntary movement.
Autonomic Nervous System:
Controls effectors that are involuntary
Ex: heart, smooth muscle, certain glands

13. Objectives
To identify and explain the 3 different structures of neurons.
To compare and contrast sensory, motor, and interneurons and explain a general pathway.
To determine the functions of the 5 types of neuroglia.

14. Types of Neurons Multipolar: Many processes stemming from cell body.
*most neurons in brain and spinal cord are multipolar

15. Types of Neurons Bipolar: Only two processes (one at each end.
*found in eyes, nose, ears..

16. Types of Neurons Unipolar:
One single process extending from cell body.
one side of axon is the peripheral process associated with body part, other side is the central process that enters brain or spinal cord.
Cell bodies create a tissue mass called ganglia.

17. Types of Neurons

18. Neuron Classification
Sensory Neurons (afferent):
Carry impulses from PNS to CNS
Contain “receptor ends” at the tips of dendrites
Changes outside the body stimulate receptor ends triggering an impulse
*Most are unipolar

19. Neuron Classification
Interneurons (association):
Completely in brain or spinal cord.
Link neurons together.
*multipolar

20. Neuron Classification
Motor Neurons (efferent):
carry impulses out of brain or spinal cord to the effector and stimulate response.

21. General Pathway

22. Neuroglial Cells
*More numerous than neurons, support neurons in different ways.
Microglial Cells:
Phagocytize bacterial cells and cellular debris
Oligodendrocytes:
Provide insulating layers of myelin
Astrocytes:
Provide structural support
join parts (ex: neuroncapillary)
help regulate concentrations of nutrients and ions
Form scar tissue in the CNS
Ependymal Cells:
Forms membrane that covers specialized brain parts and forms inner linings within the brain and spinal canal
Schwann cells:
Forms myelin sheath around axons.

23. Nervous Tissue: Support Cells

24. Nervous Tissue: Support Cells

25. Nervous Tissue: Support Cells

26. Nervous Tissue: Support Cells

27. Nervous Tissue: Support Cells

28. Neuroglial Cells

30. Myelin A lipid that sometimes coats axons
White matter = myelinated axons in CNS
Gray matter = cell bodies & unmyelinated axons in CNS
Produced by some neuroglial cells
Insulates neurons & increases efficiency of nerve impulses

31. Objectives To explain how a nerve impulse occurs.
To determine what types of stimuli elicit an action potential.
To explain different things that inhibit an action potential.
To understand components of a neuron that contribute to impulse velocity.

32. Cell Membrane Potential
The membrane is electrically charged, “polarized” due to Na+ and K+ ions
Greater concentration of sodium ions outside and potassium ions inside.
Potassium ions pass through more easily
Active transport (sodium/potassium pump) maintains balance
This is essential in the propagation of a nerve impulse.

33. Resting Potential
When a nerve cell membrane is undisturbed, the membrane remains polarized staying more negative on the inside and positive on the outside.

34. Threshold Potential
If the nerve cell detects a change in light/temp/pressure it effects the resting potential and the membrane begins depolarizing.
Sodium channels open and + ions flow in, making the inside less negative.
Change in potential is proportional to the intensity of the stimulation.
Stimulation + more stimulation before initial stimulation subsides is called summation.
Once the threshold is reached, an action potential occurs.

35. Action Potential
Definition: change in neuron membrane polarization and return to resting state
Nerve Impulse: chain of action potentials from neuron to neuron

36. Action Potential Depolarization: a decrease in membrane potential
Repolarization: increase in membrane potential, causes membrane to become negatively charged again
Action Potential
Stimuli (temperature, light, pressure, other neurons) decreases membrane potential
When threshold potential (~55 mV) is reached, stimulus is big enough to cause neuron to send a signal.

37. Action Potential Continued
3. Reaching threshold potential triggers Na+ and K+ channels (located in nodes of Ranvier) to open and equalize charges 3a. Na+ channels open faster, causing rapid depolarization. 3b. As K+ channels open slowly, membrane becomes more polarized, Na+ rushes out. 4. Further parts of axon are triggered and action potentials propagate down length of axon causing nerve impulse. 5. Results in neurotransmitters being released into synapse

38. Action Potential

39. Action potential video

40. Impulse Conduction
Unmyelinated nerve = impulse conducted over the entire surface.
Myelin insulates and prevents ion flow, would prevent conduction if it were continuous and didn’t have the nodes of ranvier.
Myelinated nerve= impulse jumps from node to node and creates a saltatory response and is much faster than unmyelinated.

42. All-or-None Nerve impulses create an “all or none response”.
Once the stimulus reaches threshold, it generates an action potential.

43. Objectives Identify the different components of a reflex arc.
Explain different autonomic reflexes found throughout the body.

44. Reflexes
Ordinarily, a receptor sends a signal to the brain where the brain coordinates a response.
What happens when you touch something hot?

45. Reflex Arcs
Reflex: a rapid, predictable, and involuntary response to a stimulus
Reflex Arc: Direct route from sensory neurons, to an interneuron, to an effector.
Interneuron: neuron between the primary sensory neuron and the final motor neuron.
A reflex is a rapid action that happens without thought and does not involve the brain.

46. Reflex Arc Receptor- sense organ in skin, muscle, or other organ
Sensory Neuron- carries impulse towards CNS from receptor
Interneuron- carries impulse within CNS
Motor Neuron- carries impulse away from CNS to effector
Effector- structure by which animal responds (muscle, gland, etc).

47. Steps in a Reflex Arc Stimulus: A receptor receives a stimulus
Afferent Pathway: Receptor sends message to integrating center (CNS) via a sensory neuron
Integration: CNS makes correct connection between sensory neuron and motor neuron; usually involves an interneuron
Efferent Pathway: Motor neuron carries message from CNS to effector
Response: Effector carries out appropriate response

48. Reflex Arc

49. Reflex arc video

50. Types of Reflexes Somatic reflexes: Activation of skeletal muscle
Example: when you move your hand away from a hot stove
Autonomic reflexes: Regulation of smooth muscle; regulation of cardiac muscle, regulation of glands
Example: Heart rate and blood pressure regulation; digestive system regulation; regulation of fluid balance

51. Neurotransmitters
Definition: chemicals that transmit signals from neurons to a target cell across a synapse
NTs can be either excitatory (excite) or inhibitory (inhibit)
Each neuron generally synthesizes and releases a single type of neurotransmitter

52. Neurotransmitter Role in the Body
Acetylcholine
Excitatory. Used by spinal cord neurons to control muscles; used by neurons in the brain to regulate memory. In most instances, acetylcholine is excitatory.
Dopamine
Inhibitory. Produces feelings of pleasure when released by the brain reward system.
GABA
(gamma-aminobutyric acid)
The major inhibitory neurotransmitter in the brain.
Glutamate
The most common excitatory neurotransmitter in the brain.
Glycine
Inhibitory. Used mainly by neurons in the spinal cord.
Norepinephrine
Mostly excitatory, can be inhibitory in a few brain areas. Acts as both neurotransmitter and hormone. In PNS, part of fight or flight response. it is part of the flight-or-flight response. In brain, regulates normal brain processes.
Serotonin
Inhibitory. Involved in many functions including mood, appetite, and sensory perception.

53. Drugs Interfere with Neurotransmission
Drugs can affect synapses at a variety of sites and in a variety of ways, including:
Increasing number of impulses (firing of nerves)
Release NT from vesicles with or without impulses
Block reuptake of neurotransmitters or block receptors
Produce more or less NT
Prevent vesicles from releasing NT

54. Three Drugs (of many) which affect Neurotransmission
Methamphetamine Nicotine Alcohol

55. Methamphetamine Meth alters Dopamine transmission in two ways:
Enters dopamine vesicles in axon terminal causing release of NT
Blocks dopamine transporters taking dopamine back into the transmitting neuron
Result: More dopamine in the synaptic cleft
This causes neurons to fire more often than normal resulting in a euphoric feeling.

56. Methamphetamine Problems…
After the drug wears off, dopamine levels drop, and the user “crashes”. The euphoric feeling will not return until the user takes more methamphetamine.
Long-term use of meth causes dopamine axons to wither and die.
Note that cocaine also blocks dopamine transporters, thus it works in a similar manner.

57. Nicotine
Similar to methamphetamine and cocaine, nicotine increases dopamine release in a synapse.
However, the mechanism is slightly different
Nicotine binds to receptors on the presynaptic neuron

58. Nicotine
Nicotine binds to the presynaptic receptors exciting the neuron to fire more action potentials causing an increase in dopamine release.
Nicotine also affects neurons by increasing the number of synaptic vesicles released.

59. Alcohol
Alcohol has multiple effects on neurons. It alters neuron membranes, ion channels, enzymes, and receptors.
It binds directly to receptors for acetylcholine, serotonin, and gamma aminobutyric acid (GABA), and gluatmate.

60. GABA and the GABA receptor
GABA is a neurotransmitter that has an inhibitory effect on neurons.
When GABA attaches to its receptor on the postsynaptic membrane, it allows Cl ions to pass into the neuron.
This hyperpolarizes the postsynaptic neuron to inhibit transmission of an impulse.

61. Alcohol and the GABA Receptor
When alcohol enters the brain, it binds to GABA receptors and amplifies the hyperpolarization effect of GABA.
The neuron activity is further diminished.
This accounts for some of the sedative affects of alcohol.

62. The Adolescent Brain and Alcohol
The brain goes through dynamic change during adolescence, and alcohol can can seriously damage long and short-term growth processes.
Frontal lobe development and the refinement of pathways and connections continue until age 16, and a high rate of energy is used as the brain matures until age 20.
Damage from alcohol at this time can be long-term and irreversible.

63. The Adolescent Brain and Alcohol
In addition, short-term or moderate drinking impairs learning and memory for more in youth than adults.
Adolescents need only drink half as much as adults to suffer the same negative effects.

64. Drugs that Influence Neurotransmitters
Change in Neurotransmission
Effect on Neurotransmitter release or availability
Drug that acts this way
increase the number of impulses
increased neurotransmitter release
nicotine, alcohol, opiates
release neurotransmitter from vesicles with or without impulses
increased neurotransmitter release
amphetamines
methamphetamines
release more neurotransmitter in response to an impulse
nicotine
block reuptake
more neurotransmitter present in synaptic cleft
cocaine
amphetamine
produce less neurotransmitter
less neurotransmitter in synaptic cleft
probably does not work this way
prevent vesicles from releasing neurotransmitter
less neurotransmitter released
No drug example
block receptor with another molecule
no change in the amount of neurotransmitter released, or neurotransmitter cannot bind to its receptor on postsynaptic neuron
LSD
caffeine

65. CNS (Brain Structure)

66. Regions of the Brain

67. Cerebral Hemispheres (Cerebrum)
Structure of cerebrum: Paired (left and right) superior parts of the brain
Function of cerebrum: Higher brain function (thought and action)

68. Regions of the Brain: Cerebrum

69. Four (Main) Lobes of the Cerebrum
Frontal lobe: problem solving, judgment, motor function (Primary Motor Area), speech (Broca’s Area)
Parietal lobe: sensation, handwriting, body position (Primary Somatic Sensory Area)
Occipital lobe: visual processing system
Temporal lobe: memory and hearing

70. Regions of the Brain: Cerebrum

71. Regions of the Brain: Diencephalon

72. Regions of the Brain: Diencephalon

73. Diencephalon
Structure: sits on top of brain stem; enclosed by cerebral hemispheres

74. Diencephalon Three parts Thalamus: relay station for sensory impulses
Hypothalamus: autonomic nervous system center; involved in emotion
Helps regulate body temperature
Controls water balance
Regulates metabolism
Epithalamus: houses the pineal gland (involved in sleep); forms CSF (Cerebrospinal fluid)

75. Regions of the Brain: Diencephalon

76. Brain Stem Structure: Attached to the spinal cord Midbrain Pons
Mostly composes of tracts of nerve fibers
Function: reflex center for vision and hearing
Pons
Structure: bulging center part of the brain stem
Function: control of breathing
Medulla Oblongata
Structure: most inferior part of the brain stem; merges into spinal cord
Functions: heart rate control, blood pressure regulation, breathing, swallowing, vomiting

77. Regions of the Brain: Brain Stem

78. Cerebellum
Structure: looks like a “little cerebrum”, sits inferior to cerebrum, posterior to brain stem
Function: provides involuntary coordination of body movements

79. Regions of the Brain: Cerebellum

80. Ventricles
Structure: four chambers within the brain filled with cerebrospinal fluid
Lateral Ventricles: within Cerebrum
Third Ventricle: in Diencephalon
Fourth Ventricle: between pons and cerebellum

81. Ventricles Functions Transport of waste and nutrients
Protects cerebrum from trauma
Contain signaling molecules that direct development and function

82. Spinal Cord Anatomy and PNS

83. Spinal Cord – General Info
Structure: extends from foramen magnum of skull to the first two lumbar vertebra

84. Spinal Cord Anatomy

85. Spinal Cord Anatomy
Internal gray matter – mostly cell bodies; surrounds central canal
Central canal is filled with cerebrospinal fluid
Exterior white matter - axons

86. Spinal Cord Anatomy

87. Peripheral Nervous System (PNS)
Definition: nerves and ganglia outside the central nervous system
Ganglia: mass of nerve cell bodies
Nerve: bundle of neuron fibers

88. PNS: Classification of Nerves
Mixed nerves: both sensory and motor fibers
Sensory (afferent) nerves: carry impulses toward the CNS
Motor (efferent) nerves: carry impulses away from the CNS

89. PNS: Cranial Nerves
Definition: 12 pairs of nerves that serve the head and neck

90. PNS: Cranial Nerves I Olfactory nerve – sensory for smell
II Optic nerve – sensory for vision
III Oculomotor nerve – motor fibers to eye muscles
IV Trochlear – motor fiber to eye muscles
V Trigeminal nerve – sensory for the face; motor fibers to chewing muscles
VI Abducens nerve – motor fibers to eye muscles
VII Facial nerve – sensory for taste; motor fibers to the face
VIII Vestibulococlear nerve – sensory for balance and hearing

91. PNS: Cranial Nerves
IX Glossopharyngeal nerve – sensory for taste; motor fibers to the pharynx
X Vagus nerves – sensory and motor fibers for pharynx, larynx, and viscera
XI Accessory nerve – motor fibers to neck and upper back
XII Hypoglossal nerve – motor fibers to tongue

92. Spinal Nerves
Structure: formed by the combination of the ventral and dorsal roots of the spinal cord
31 pairs of spinal nerves arise from the spinal cord
Cauda equina: collection of spinal nerves at the inferior end

93. Autonomic Nervous System
Definition: involuntary nervous system
Function: regulates activities of cardiac and smooth muscles and glands
Two subdivisions
Sympathetic divisions
Parasympathetic division

94. Sympathetic Division (E)
Sympathetic Function – “fight or flight”
Response to unusual stimulus
Takes over to increase activities
Remember the “E” division: Exercise, excitement, emergency, and embarrassment
Neurotransmitters
Norepinephrine
Epinephrine

95. Parasympathetic Division (D)
Parasympathetic function – “housekeeping” activities
Conserves energy
Maintains daily necessary body functions
Remember as the “D” division: digestion, defecation, and diuresis
Neurotransmitter
Acetylcholine

96. Difference between Somatic and Autonomic Nervous System
Nerves
Somatic: one motor neuron
Autonomic: preganglionic and postganglionic nerves
Effector organs
Somatic: skeletal muscle
Autonomic: smooth muscle, cardiac muscle, and glands
Neurotransmitters
Somatic: acetylcholine
Autonomic: acetylcholine, epinephrine, or norepinephrine

97. Review video (show on review day!!)