1. Module 3
The Nervous System

2. Nerve Tissue
Nerve tissue throughout the body is composed of two types of cells:
Neurons
Supporting glial cells

3. The Neuron
Neurons are specialized cells in the nervous system that send and receive information throughout the body.
Neurons are the nervous system’s building blocks.

4. The Neuron
The nervous system contains 90 to 180 billion neurons (98.8 percent in the brain and 1.2 percent in the spinal cord).
Each neuron transmits information to about a thousand other neurons; there are trillions of different neural connections in the brain.

5. The Neuron: Three Basic Parts
Soma: central part of neuron (Latin word for “body”)
Dendrites: branchlike extensions attached to the soma that receive information from other neurons
Axon: a tubelike extension of the soma that sends information in the form of an electrochemical impulse

6. Structure of a Neuron

7. Three Basic Types of Neurons
Sensory neurons: send information from sensory receptors to the brain
Motor neurons: send commands from the brain to glands, muscles, and organs
Interneurons: connect other neurons to one another

8. Neural Communication Action Potential
a neural impulse; a brief electrical charge that travels down an axon
generated by the movement of positively charged atoms in and out of channels in the axon’s membrane

9. Neural Communication Threshold
the level of stimulation required to trigger a neural impulse
Firing is all or none
Neurons differ in their potential speed of firing (2 – 270 mph).

10. Structure and Operation of the Neuron

11. Synapses: Points of Chemical Transmission between Neurons
Axon terminal buttons contain round sacs called synaptic vesicles.
When an action potential arrives, it causes these vesicles to release chemical messengers, called neurotransmitters, which travel across the synaptic cleft.
These neurotransmitters fit into the receiving dendrites’ receptor sites, like keys fit into locks.

12. Synaptic Transmission

13. Synaptic Transmission—Reuptake

14. Synaptic Transmission— Enzyme Deactivation

15. Synapses: Chemical Transmission between Neurons
After locking into receptor sites, neurotransmitters either excite or inhibit firing of the receiving neuron. Excitatory messages increase the probability of an action potential. Inhibitory messages reduce the likelihood of neural firing. Whether the neuron fires will depend on which type of message is in greater abundance.

16. After neurotransmitters deliver their messages they are either:
Synapses:
Chemical Transmission between Neurons
After neurotransmitters deliver their messages they are either:
Repackaged into new synaptic vesicles in a process known as reuptake or
Broken down by enzymes and removed from the synaptic cleft in a process called enzyme deactivation.

17. Chemical Neurotransmitters
About 75 neurotransmitters have been identified, including:
Acetylcholine (ACh): involved in muscle contraction, cognition, and memory formation
Dopamine (DA): controls large muscle movements; influences pleasure and motivation

18. Chemical Neurotransmitters
About 75 neurotransmitters have been identified, including:
Endorphins: important in the experience of pleasure and control of pain
Serotonin: involved in regulating emotional states such as depression, sleep cycles and dreaming, aggression, and appetite

19. Agonists and Antagonists
Neurotransmitter
molecule
Receiving cell
membrane
Receptor site on
receiving neuron
Agonist mimics
neurotransmitter
Antagonist
blocks

20. Psychoactive Drug Use Psychoactive drugs:
chemicals that modify mental processes, behavior, mood, and/or perception)
are often used to deliberately alter consciousness
work at synapses to block or stimulate neural activity.

21. Effects of Cocaine on Neurotransmitters

22. Drugs and Consciousness
Drug rebound
Returning to a “higher” or “lower” state than normal following the use of a drug

23. Drug Tolerance Tolerance Withdrawal
diminishing effect with regular use of the same dose of a drug
Withdrawal
discomfort and distress that follow discontinued use of an addictive drug
After repeated
exposure, more
drug is needed
to produce
same effect
Drug dose
Drug
effect
Response to
first exposure

24. Drugs and Consciousness
Physical Dependence
a physiological need for a drug
marked by unpleasant withdrawal symptoms
Psychological Dependence
a psychological need to use a drug
for example, to relieve negative emotions

25. Psychoactive Drug Use Common Drug Effects
rebound: returning to a state different from normal when the drug has “worn off”
tolerance: requiring greater amounts of a drug to produce the same effect
withdrawal: unpleasant to life-threatening physical reactions to the absence of a drug in the body
addiction: felt physical and/or psychological need to continue use of a drug

26. Psychoactive Drugs Depressants Stimulants Psychedelics/hallucinogens
Opiates
Stimulants
Psychedelics/hallucinogens

27. Depressants
a class of psychoactive drugs that slow down—or depress—the nervous system and decrease mental and physical activity
Alcohol: the most widely consumed and abused depressant
Sedatives/ tranquilizers: Mild doses produce relaxation, mild euphoria, and reduced inhibitions.
The opiates (narcotics): include opium, morphine, and heroin; reduce pain

28. Stimulants Caffeine and nicotine Cocaine and amphetamines
Psychoactive drugs that speed up—or stimulate—the nervous system and increase mental and physical activity.
Caffeine and nicotine
Cocaine and amphetamines
Cocaine activates the sympathetic nervous system
Amphetamines: activate the sympathetic nervous system; increase dopamine and norepinephrine activity.
Ecstasy and Ritalin
Ecstasy or MDMA: affects the brain cells that produce serotonin
Ritalin: decreases distractibility and improves concentration

29. Hallucinogens
psychoactive drugs that distort perception and generate sensory images without any external stimulation
LSD
PCP
Mescaline
Psilocybin
marijuana

30. Hallucinogens LSD (lysergic acid diethylamide): Synthesized
Chemically similar to serotonin
Binds with serotonin brain receptors (agonist) associated with dreaming
Principal effects involve hallucinations & perceptual distortions
Causes users to experience a dreamlike state of mind while they are awake.

31. Hallucinogens Users of LSD may also experience:
Synesthesia: a blending of sensory experiences
Subjective time alteration
Flashbacks:
recurrences of the drug’s effects without the drug (occur in more than 15 percent of LSD users and can persist for months following the drug experience)
There is no way to predict how a person will react to the drug.

32. Marijuana From the hemp, or Cannabis, plant
The major psychoactive ingredient is THC, organic molecule delta-9 tetrahydrocannabinol.
Users often experience:
An increased sense of well-being/relaxation,
Spontaneous laughter,
A heightened sensitivity to various stimuli,
A distortion of time, and
A disconnected flow of ideas.
Consistent high quantity use of marijuana may have negative effects on motivation and interpersonal skills.

33. Psychoactive Drugs Drug Type Pleasurable Effects Adverse Effects
Alcohol Depressant Initial high followed by Depression, memory loss, organ
relaxation and disinhibition damage, impaired reactions
Heroin Depressant Rush of euphoria, relief from Depressed physiology,
pain agonizing withdrawal
Caffeine Stimulant Increased alertness and Anxiety, restlessness, and
wakefulness insomnia in high doses;
uncomfortable withdrawal
Metham- Stimulant Euphoria, alertness, energy Irritability, insomnia,
phetamine hypertension, seizures
Cocaine Stimulant Rush of euphoria, confidence, Cardiovascular stress,
energy suspiciousness, depressive crash
Nicotine Stimulant Arousal and relaxation, sense Heart disease, cancer (from of well-being tars)
Marijuana Mild Enhanced sensation, pain relief Lowered sex hormones, hallucinogen disrupted memory, distortion of lung damage from smoke
time, relaxation

34. Neural and Hormonal Systems
The nervous system is the body’s primary information system and is divided into two major portions:
Central nervous system
Peripheral nervous system

35. Neural and Hormonal Systems
Nerves
neural “cables” containing many axons
part of the peripheral nervous system
connect the central nervous system with muscles, glands, and sense organs

36. Nervous System Central Nervous System (CNS) the brain and spinal cord
Peripheral Nervous System (PNS)
the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body

37. The Peripheral Nervous System
Peripheral nervous system: All the nerves located outside the brain and spinal cord.
Its function—to connect the brain and spinal cord with the organs and tissues of the body.
The peripheral nervous system is composed of two major divisions:
The somatic/skeletal nervous system
The autonomic nervous system
Sympathetic nervous system
Parasympathetic nervous system

38. Spinal Cord: Connects the Peripheral Nervous System to the Brain
Central nervous system (CNS): brain and spinal cord
Spinal cord: slender, tube-shaped part of the (CNS) that connects the brain to the body via the peripheral nervous system
The spinal cord transmits information from sensory neurons to the brain, and from the brain to motor neurons that initiate movement.
The upper segments of the spinal cord control the upper parts of the body, while the lower segments control the lower body.
The spinal cord also controls some automatic, involuntary responses to sensory stimuli called reflexes.

39. Reflex: a simple, automatic, inborn response
Brain
Sensory neuron
(incoming information)
Interneuron
Skin
receptors
Muscle
Spinal cord

40. Neural and Hormonal Systems
Central
(brain and
spinal cord)
Nervous
system
Autonomic (controls
self-regulated action of
internal organs and glands)
Skeletal (controls
voluntary movements of
skeletal muscles)
Sympathetic
(arousing)
Parasympathetic
(calming)
Peripheral

41. The Endocrine System Communicates by Secreting Hormones
The endocrine system is interconnected with—but not part of—the nervous system.
consists of a network of glands that make and secrete hormones - chemical messengers.
The pituitary gland, in the base of the brain, releases about 10 different hormones and is controlled by the hypothalamus.
Other endocrine glands include the thyroid gland, the adrenal glands, and the gonads.