Chapter 14 Lecture Outline · 2017. 1. 20. · 4 The nervous divisions •Two divisions –Central nervous system (CNS): Brain and spinal cord –Peripheral nervous system (PNS):

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Chapter 14

Lecture Outline

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Nervous System

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Points to ponder • What are the three types of neurons?

• What are neuroglia?

• What is the structure of a neuron?

• What is the myelin sheath? Saltatory conduction? Schwann cell? Node of Ranvier?

• Explain the resting and action potential as they relate to a nerve impulse.

• How does the nerve impulse traverse the synapse?

• What are the two parts of the nervous system?

• What three things protect the CNS?

• What are the four parts of the brain and their functions?

• What is the reticular activating system and the limbic system?

• What are some higher mental functions of the brain?

• What are the two parts of the peripheral nervous system?

• How do abused drugs work?

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The nervous divisions

• Two divisions

– Central nervous system (CNS): Brain

and spinal cord

– Peripheral nervous system (PNS):

Nerves and ganglia (collections of cell

bodies)

14.1 Overview of the Nervous System

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The nervous divisions


Figure 14.1 The two divisions of the nervous system.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

somatic motor

nerves: signals

to skeletal

muscles,

voluntary

autonomic motor

nerves: signals

to smooth

muscle, cardiac

muscle, glands,

involuntary

somatic sensory

nerves: signals

from skin,

muscles,

joints, special

senses

visceral sensory

nerves:

signals from

body organs

parasympathetic

division

“rest and digest”

sympathetic

division

“fight or flight”

sensory (afferent) nerves —

carry sensory information

into brain and spinal cord

motor (efferent) nerves —

carry motor information

from CNS to effectors

brain

cranial nerves

spinal nerves

spinal cord

Central Nervous System (CNS)

brain spinal cord

Peripheral Nervous System (PNS)

b. a.

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The nervous system

• The nervous system allows for

communication between cells through

sensory input, integration of data, and

motor output.

• Two cell types: neurons and neuroglia


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Expanding on neurons

• Three types of neurons • Sensory – takes impulses from sensory

receptor to CNS

• Interneuron – receives information in the CNS and sends it to a motor neuron

• Motor – takes impulses from the CNS to an effector (i.e., gland or muscle fiber)


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Expanding on neurons

• Neuron structure (Ch. 4 review) • Cell body – main cell where nucleus and

most organelles reside

• Dendrites – many short extensions that carry impulses to a cell body

• Axon (nerve fiber) – single, long extension that carries impulses away from the cell body


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Types of neurons

Figure 14.2 The structure

of sensory neurons,

interneurons, and motor

neurons.


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The myelin sheath • A lipid covering on long axons that acts to

increase the speed of nerve impulse conduction, insulation, and regeneration in the PNS

• Schwann cells – neuroglia that make up the myelin sheath in the PNS

• Nodes of Ranvier – gaps between myelination on the axons

• Saltatory conduction – conduction of the nerve impulse from node to node


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Neuron structure

Figure 14.2 The structure

of sensory neurons,

interneurons, and motor

neurons.


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The nerve impulse: Resting potential (RP)

• Resting potential – when the axon is not conducting a nerve impulse

• More positive ions outside than inside the membrane

• Negative charge of -70 mV inside the axon

• More Na+ outside than inside

• More K+ inside than outside


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The nerve impulse: Resting potential (RP)

Figure 14.3a Generation of an action potential.


+ + + + + + + + + +

+ + + + + + + + + +

K+

recording electrode

inside axon

reference electrode

outside axon

axonal membrane

inside axon

outside axon

Na+

gated Na+

channel

gated K+

channel

a. Resting potential: Na+ outside the axon, K+ and large

anions inside the axon. Separation of charges polarizes the cell and causes the resting potential.


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The nerve impulse: Action potential

• Action potential – rapid change in the axon membrane that allows a nerve impulse to occur

• Sodium gates open, letting Na+ in. • Depolarization occurs.

• Interior of axon loses negative charge (-55 mV, then +35 mV).


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• Potassium gates open, letting K+ out. • Repolarization occurs.

• Interior of axon regains negative charge (-70 mV).

• Wave of depolarization/repolarization travels down the axon.

• Resting potential is restored by moving potassium inside and sodium outside.



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The nerve impulse: Stimulus causes

the axon to reach its threshold

Figure 14.3b Generation of

an action potential.



− −

+ +

− −

+ + + + + + + +

+ +

+ + + + + + + +

direction of signal

open

Na+

channel

b. Stimulus causes the axon to reach its threshold;

the axon potential increases from −70 to −55.

The action potential has begun.

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Figure 14.3c Generation of an action potential.


+ + + +

+ + + +

+ +

+ + + + + +

+ + + +

c. Depolarization continues as Na+ gates open

and Na+ moves inside the axon.

direction of signal

open

Na+

channel


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The synapse

• The synapse is a small gap between the sending neuron (presynaptic membrane) and the receiving neuron (postsynaptic membrane).

• Transmission is accomplished across this gap by a neurotransmitter (e.g., ACh, dopamine, or serotonin).

• Neurotransmitters are stored in synaptic vesicles in the axon terminals.


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How does transmission across

the synapse occur?

• Nerve impulse reaches the axon terminal.

• Calcium ions enter the axon terminal and stimulate the synaptic vesicles to fuse with the presynaptic membrane.

• Neurotransmitters are released and diffuse across the synapse, where they bind with the postsynaptic membrane to inhibit or excite the neuron.


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A synapse and how it functions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1. After an action

potential arrives

at an axon

terminal (arrow),

Ca2+ enters,

and synaptic

vesicles fuse

with the plasma

membrane of

the sending

neuron.

2. Neuro-

transmitter

molecules

are released

and bind to

receptors

on the

membrane of

the receiving

neuron.

3. When an

excitatory

neuro-

transmitter

binds to a

receptor,

Na+ diffuses

into the

receiving

neuron, and

an action

potential

begins.

Sending neuron

axon of sending neuron

axon terminal

receiving neuron

Receiving neuron Synaptic cleft

arriving action potential

Ca2+

Synaptic vesicles enclose neurotransmitter.

Synapse

Receiving neuron

neurotransmitter

neurotransmitter

Receiving neuron

ion channel Na+

receptor

Figure 14.4 Signal transmission at

the synapse.


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Synaptic integration

• Integration is the summation of the inhibitory

and excitatory signals received by a

postsynaptic neuron.

• This occurs because a neuron receives many

signals.


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Synaptic integration

Figure 14.5 Integration of excitatory and inhibitory signals at the synapse.


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The central nervous system • The CNS consists of the brain and spinal cord.

• Both are protected by

• Bones – skull and vertebral column

• Meninges – 3 protective membranes that wrap

around CNS

• Cerebral spinal fluid (CSF) – space between

meninges is filled with this fluid that cushions and

protects the CNS

14.2 The Central Nervous System

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The central nervous system • Both the brain and spinal cord are made up of two

types of nervous tissue.

• Gray matter – contains cell bodies and

nonmyelinated fibers

• White matter – contains myelinated axons


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The CNS: Spinal cord

• It extends from the base of the brain and along the length of the vertebral canal formed by the vertebrae.

• The spinal cord functions to provide communication between the brain and most of the body.

• It is the center for reflex arcs.

• Gray matter in the center is a butterfly shape.

• White matter surrounds the gray matter.


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What does the spinal cord look like? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

dorsal root

dorsal root

ventral root

ventral root

vertebra

spinal cord

white matter

central canal

gray matter

gray matter

white matter

gray matter

meninges

ventral

dorsal white matter

central canal

vertebra

b.

a.

c.

dorsal root

ganglion

spinal

nerve

dorsal root

ganglion

spinal

nerve

dorsal root

branches

dorsal root

ganglion

cut vertebrae

d. Dorsal view of spinal cord and dorsal roots of spinal nerves.


a: © Karl E. Deckart/Phototake; d: © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer and Don Kincaid, dissections

Figure 14.7 The organization of white and gray matter in

the spinal cord and the spinal nerves.


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The CNS: Brain

Four major parts

1. Cerebrum

2. Diencephalon

3. Cerebellum

4. Brain stem


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The CNS: Overview of the brain 14.2 The Central Nervous System


skull

meninges

pituitary gland

fourth ventricle

spinal cord

Cerebrum

Diencephalon

Cerebellum

hypothalamus

midbrain

pons

Brain stem

a. Parts of brain b. Cerebral hemispheres

lateral

ventricle

third

ventricle

pineal

gland

corpus

callosum

thalamus

(surrounds the

third ventricle)

medulla

oblongata

Figure 14.8 The human brain.

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The brain: Cerebrum

• Cerebral hemispheres

• Cerebral cortex

• Primary motor and sensory areas of

the cortex

• Association areas

• Processing centers

• Central white matter


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1. The brain: Cerebrum –

The lobes • Cerebrum – largest portion of the brain

• Divided into four lobes

1. Frontal lobe: primary motor area and conscious thought

2. Temporal lobe: primary auditory, smell, and speech area

3. Parietal lobe: primary somatosensory and taste area

4. Occipital lobe : primary visual area


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The cerebral lobes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Frontal lobe

Occipital lobe

Parietal lobe

auditory association area

primary auditory area

primary somatosensory area

primary taste area

general interpretation area

primary motor area

premotor area

lateral sulcus

central sulcus

trunk

arm

hand

face

tongue

leg

motor speech (Broca’s) area

prefrontal area

anterior ventral

primary

olfactory area

sensory speech (Wernicke’s) area

Temporal lobe

somatosensory

association area

posterior dorsal

primary visual area

visual association

area

Figure 14.9 The lobes of the cerebral hemispheres.


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The cerebral cortex • Cerebral cortex – thin, outer layer of gray matter

• Primary motor area – voluntary control of skeletal muscle

• Primary somatosensory area – for sensory information from skeletal muscle and skin

• Association areas – integration occurs here

• Processing centers – perform higher level analytical functions including Wernicke’s and Broca’s areas, both involved in speech


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The cerebral cortex Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

salivation

vocalization

mastication longitudinal

fissure

facial

expression

swallowing

thumb, fingers,

and hand

forearm arm trunk

pelvis

thigh

leg

foot and

toes lips

upper

face

tongue and

pharynx

hand, fingers,

and thumb

forearm

arm neck trunk pelvis

thigh

leg

foot and

toes

genitals

teeth and

gums longitudinal

fissure b. Primary

somatosensory

area

a. Primary

motor area

Figure 14.10 The primary motor and primary somatosensory areas of the brain.


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2. The brain: Diencephalon

• Includes the • Hypothalamus – helps maintain homeostasis

(hunger, sleep, thirst, body temperature, and water balance) and controls pituitary gland

• Thalamus – Two masses of gray matter that receive all sensory input except smell; involved in memory and emotions

• Pineal gland – secretes melatonin that controls our daily rhythms


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2. The brain: Diencephalon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

skull

meninges

pituitary gland

fourth ventricle

spinal cord

Cerebrum

Diencephalon

Cerebellum

hypothalamus

midbrain

pons

Brain stem

a. Parts of brain b. Cerebral hemispheres

lateral

ventricle

third

ventricle

pineal

gland

corpus

callosum

thalamus

(surrounds the

third ventricle)

medulla

oblongata

Figure 14.8 The human brain.


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3. The brain: Cerebellum

• Receives and integrates sensory input from the

eyes, ears, joints, and muscles about the current

position of the body

• Functions

• Maintains posture

• Coordinates voluntary movement

• Allows learning of new motor skills (i.e., playing

the piano or hitting a baseball)


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4. The brain: The brain stem • Includes

• Midbrain – relay station between the cerebrum and spinal cord or cerebellum; reflex center

• Pons – a bridge between cerebellum and the CNS; regulates breathing rate; reflex center for head movements

• Medulla oblongata – contains reflex centers for regulating breathing, heartbeat, and blood pressure

• Reticular formation – major component of the reticular activating system (RAS) that regulates alertness


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The reticular formation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

RAS radiates

to cerebral

cortex.

thalamus

reticular

formation

ascending sensory

tracts (touch, pain,

temperature)

Figure 14.11 The reticular formation of the brain.


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The limbic system

• It joins primitive emotions (i.e., fear, pleasure) with higher functions such as reasoning.

• The limbic system can cause strong emotional reactions to situations but conscious thought can override and direct our behavior.

• Includes

• Amygdala – imparts emotional overtones

• Hippocampus – important to learning and memory

14.3 The Limbic System and Higher Mental Functions

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The limbic system Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

amygdala

hippocampus

olfactory bulb

olfactory tract

hypothalamus

corpus

callosum thalamus

Figure 14.12 The regions of the brain

associated with the limbic system.


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• Learning – what happens when we recall and use past memories

• Memory – ability to hold a thought or to recall past events

• Short-term memory – retention of information for only a few minutes


Higher mental functions

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Higher mental functions

• Long-term memory – retention of information for more than a few minutes and includes the following • Episodic memory – people and events

• Semantic memory – numbers and words

• Skill memory – performing skilled motor activities (i.e., riding a bike)

• Language – depends on semantic memory


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What parts of the brain are

active in reading and speaking? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

primary auditory cortex

visual cortex

primary motor cortex

1. The word is seen in the

visual cortex.

2. Information concerning the

word is interpreted in

Wernicke’s area.

Wernicke’s area

3. Information from Wernicke’s

area is transferred to Broca’s

area.

Broca’s area

4. Information is transferred from

Broca’s area to the primary motor

area.

(all): © Marcus Raichle

Figure 14.13 The areas of the brain involved in reading.


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The peripheral nervous system (PNS)

• It includes cranial nerves (12 pairs), spinal nerves (31 pairs), and ganglia outside the CNS.

- Spinal nerves conduct impulses to and from the spinal cord.

- Cranial nerves conduct impulses to and from the brain.

• The PNS is divided into two systems.

- Somatic division

- Autonomic division

14.4 The Peripheral Nervous System

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The peripheral nervous system

Figure 14.14 The structure of a nerve.


46 Figure 14.15 The cranial nerves.


The peripheral nervous system Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

I

II

III

IV

VI

VII

V

VIII

IX

X

XI

XII

Cranial Nerves

to eye muscles

to eye muscles

to eye muscles

from inner ear

from olfactory

receptors

from retina of

eyes

from mouth and

to jaw muscles

from taste buds

and to facial

muscles and

glands

from pharynx

and to pharyngeal

muscles

to tongue

muscles

from and to

internal organs

to neck and

back muscles

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The PNS: Somatic division

• The somatic system serves the skin,

skeletal muscles and tendons.

• Automatic responses are called reflexes.


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The PNS: Somatic division

Figure 14.16 The events in a spinal reflex.



white matter

ventral root

axon of motor neuron

dendrite of sensory neuron

cell body of sensory neuron

pin

dorsal root ganglion

interneuron

Dorsal gray matter

central canal

ventral horn

sensory receptor (in skin)

effector (muscle)

cell body of motor neuron

Ventral

dorsal horn

dendrites

dendrites

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The PNS: Autonomic division

• The autonomic system regulates the

activity of involuntary muscles (cardiac and

smooth) and glands.


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The PNS: Autonomic division

• Two divisions 1. Sympathetic division: coordinates the body

for the “fight or flight” response by speeding up metabolism, heart rate, and breathing while slowing down and regulating other functions.

2. Parasympathetic division: counters the sympathetic system by bringing up a relaxed state by slowing down metabolism, heart rate, and breathing, and returning other functions to normal.


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The PNS: Autonomic division Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

ganglion

inhibits tears

inhibits salivation

stimulates tears

constricts pupils

slows heart

ganglion

sympathetic ganglia

vagus nerve

Sympathetic Division Parasympathetic Division

dilates

pupils

stimulates

salivation cranial

nerves

speeds

heart

cervical

nerves

dilates air

passages

stimulates liver to

release glucose

constricts

bronchioles

stimulates gallbladder

to release bile stimulates

adrenal

secretion increases activity

of stomach and

pancreas

increases

intestinal

activity

inhibits activity

of kidneys,

stomach, and

pancreas

decreases

intestinal activity

stimulates

urination

inhibits

urination sacral

nerves

causes

orgasmic

contractions causes

erection

of genitals

lumbar

nerves

thoracic

nerves

Acetylcholine is neurotransmitter. Norepinephrine is neurotransmitter.

Figure 14.17 The two

divisions of the

autonomic nervous

system.


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Drugs and drug abuse

• Both legal pharmaceuticals and illegal drugs of abuse have certain basic modes of action.

They: – promote the action of a neurotransmitter.

– interfere with or decrease the action of a neurotransmitter.

– replace or mimic a neurotransmitter or neuromodulator.

14.5 Drug Therapy and Drug Abuse

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Drugs and drug abuse

• Most drug abusers take drugs that affect dopamine and thus artificially affect this reward circuit to the point that they ignore basic physical needs in favor of the drug.

• Drug abusers tend to show a physiological and psychological effect.

• Once a person is physically dependent, they usually need more of the drug for the same effect because their body has become tolerant.


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Drug abuse: Alcohol

• Alcohol – a depressant directly absorbed from the stomach and small intestine

• Alcohol is the most socially accepted form of drug use.

• About 80% of college-aged people drink.

• Alcohol denatures proteins and causes damage to tissues such as the brain and liver; chronic consumption can damage the frontal lobe.

• High blood alcohol levels can lead to poor judgment, loss of coordination, or even coma and death.


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Drug abuse: Nicotine

• Nicotine – stimulant derived from tobacco plant

• Nicotine stimulates neurons to release dopamine that reinforces dependence on the drug.

• It adversely affects a developing embryo or fetus.

• Smoking increases heart rate and blood pressure.

• Nicotine causes psychological and physiological dependency.


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Drug abuse: Cocaine • Cocaine – stimulant derived from a shrub

• Cocaine causes a rush sensation that lasts from 5-30 minutes.

• A cocaine binge occurs when a user takes the drug at ever-higher doses, resulting in hyperactivity, little desire for food and sleep, and an increased sex drive.

• There is extreme physical dependence with this drug.

• “Crack” is the street name for cocaine that is processed to a free-base form for smoking.


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Drug abuse: Methamphetamine

• Powder form is called speed and crystal form is called meth or ice.

• It is a stimulant that reverses the effects of fatigue and is a mood elevator.

• High agitation is common after the rush and can lead to violent behavior.

• Methamphetamine causes psychological dependency and hallucinations.

• “Ecstasy” is the street name for a drug that has the same effects as meth without the hallucinations.


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Drug abuse: Heroin • Heroin – depressant from the sap of the opium poppy

plant

• It leads to a feeling of euphoria and no pain because it is delivered to the brain and converted into morphine.

• Side effects are nausea, vomiting, and depression of the respiratory and circulatory systems.

• Heroin use can lead to HIV, hepatitis, and other infections due to shared needles.

• Extreme dependency is common.


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Drug abuse: Marijuana • Marijuana – psychoactive drug derived from a hemp plant

called Cannabis

• It is most often smoked as a “joint.”

• Occasional users experience mild euphoria, alterations to vision and judgment, as well as impaired motor coordination with slurred speech.

• Heavy users may experience depression, anxiety, hallucinations, paranoia, and psychotic symptoms.

• Long term use may lead to brain damage.

• K2 (“Spice”) is a synthetic drug with higher potency than the active chemical in marijuana.


Documents

Chapter 14 Lecture Outline · 2017. 1. 20. · 4 The nervous divisions •Two divisions –Central nervous system (CNS): Brain and spinal cord –Peripheral nervous system (PNS):