Download Nervous System - Gordon State College

Module 3
The Nervous System
Nerve Tissue
◦ Nerve tissue throughout the body is
composed of two types of cells:
 Neurons
 Supporting glial cells
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.
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.
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
Structure of a Neuron
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
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
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).
Structure and Operation
of the Neuron
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.
Synaptic Transmission
Synaptic Transmission—Reuptake
Synaptic Transmission— Enzyme
Deactivation
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.
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.
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
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
Agonists and Antagonists
Neurotransmitter
molecule
Receptor site on
receiving neuron
Receiving cell
membrane
Agonist mimics
neurotransmitter
Antagonist
blocks
neurotransmitte
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.
Effects of Cocaine on Neurotransmitters
Drugs and Consciousness

Drug rebound
◦ Returning to a “higher” or “lower” state than normal
following the use of a drug
Drug Tolerance

Drug
effect
Tolerance
◦ diminishing effect with
regular use of the same
dose of a drug
Response to
first exposure

After repeated
exposure, more
drug is needed
to produce
same effect
Drug dose
Withdrawal
◦ discomfort and distress
that follow discontinued
use of an addictive drug
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
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
Psychoactive Drugs
 Depressants
◦ Opiates
 Stimulants
 Psychedelics/hallucinogens
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
Stimulants

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
Hallucinogens

psychoactive drugs that distort perception
and generate sensory images without any
external stimulation
◦
◦
◦
◦
◦
LSD
PCP
Mescaline
Psilocybin
marijuana
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.
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.
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.
Psychoactive Drugs
Drug
Type
Pleasurable Effects
Adverse Effects
Alcohol
Depressant
Initial high followed by
relaxation and disinhibition
Depression, memory loss, organ
damage, impaired reactions
Heroin
Depressant
Rush of euphoria, relief from
pain
Depressed physiology,
agonizing withdrawal
Caffeine
Stimulant
Increased alertness and
wakefulness
Anxiety, restlessness, and
insomnia in high doses;
uncomfortable withdrawal
Metham- Stimulant
phetamine
Euphoria, alertness, energy
Irritability, insomnia,
hypertension, seizures
Cocaine
Stimulant
Rush of euphoria, confidence,
energy
crash
Cardiovascular stress,
suspiciousness, depressive
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
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
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
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
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
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.
Reflex: a simple, automatic, inborn
response
Brain
Sensory neuron
(incoming information)
Muscle
Interneuron
Spinal cord
Neural and Hormonal
Systems
Nervous
system
Central
(brain and
spinal cord)
Peripheral
Autonomic (controls
self-regulated action of
internal organs and glands)
Skeletal (controls
voluntary movements of
skeletal muscles)
Sympathetic
(arousing)
Parasympathetic
(calming)
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.