Transcript Chapter 13 - tanabe homepage

Human Biology
Sylvia S. Mader
Michael Windelspecht
Chapter 13
Nervous
System
Lecture Outline
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Points to Ponder
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•
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 3 things protect the CNS?
What are the 4 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 2 parts of the peripheral nervous system?
Be able to explain the abuse of several drugs.
13.1 Overview of the nervous system
The nervous divisions
• 2 divisions:
– Central nervous
system (CNS): Brain
and spinal cord
– Peripheral nervous
system (PNS): Nerves
and ganglia (cell
bodies)
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brain
Central Nervous System (CNS)
cranial nerves
brain
spinal cord
spinal cord
spinal nerves
Peripheral Nervous System (PNS)
sensory (afferent) nerves —
carry sensory information
into brain and spinal cord
somatic sensory
nerves: signals
from skin,
muscles,
joints, special
senses
a.
b.
visceral sensory
nerves:
signals from
body organs
motor (efferent) nerves —
carry motor information
from CNS to effectors
somatic motor
nerves: signals
to skeletal
muscles,
voluntary
autonomic motor
nerves: signals
to smooth
muscle, cardiac
muscle, glands,
involuntary
sympathetic
division
“fight or flight”
parasympathetic
division
“rest and digest”
13.1 Overview of the nervous system
The nervous system
• Nervous system – Allows for
communication between cells through
sensory input, integration of data, and
motor output
• 2 cell types: neurons and neuroglia
13.1 Overview of the nervous system
Expanding on neurons
• 3 types of neurons:
• Sensory – takes impulses from sensory receptor to CNS
• Interneurons – receive information in the CNS and send it to a
motor neuron
• Motor – takes impulses from the CNS to an effector (i.e., gland
or muscle fiber)
• Neuron structure (Ch. 4 review):
• Cell body – main cell where organelles and nuclei reside
• Dendrite – many, short extensions that carry impulses to a cell
body
• Axon (nerve fiber) – single, long extension that carries impulses
away from the cell body
13.1 Overview of the nervous system
Types of neurons
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a. Sensory
neuron
sensory
receptor
cell body
axon
myelin
sheath
direction
of conduction
Schwann
cell
b. Interneuron
400 nm
axon
dendrite
c. Motorneuron
cell body
axon
node of Ranvier
2.7 μm
axon terminal
direction
of conduction
a(myelin): © M.B. Bunge/Biological Photo Service; c(cell body): © Manfred Kage/Peter Arnold/Photolibrary
13.1 Overview of the nervous system
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
13.1 Overview of the nervous system
Neuron structure
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a. Sensory
neuron
sensory
receptor
cell body
axon
myelin
sheath
direction
of conduction
Schwann
cell
b. Interneuron
400 nm
axon
dendrite
c. Motorneuron
cell body
axon
node of Ranvier
2.7 μm
axon terminal
direction
of conduction
a(myelin): © M.B. Bunge/Biological Photo Service; c(cell body): © Manfred Kage/Peter Arnold/Photolibrary
13.1 Overview of the nervous system
The nerve impulse: resting potential (RP)
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• Resting potential – when
the axon is not
conducting a nerve
impulse
recording
electrode
inside axon
+ + + + + + + + +
        
• More positive ions outside axonal
membrane

than inside the membrane
+
• There is a negative charge
inside axon
of -65mV inside the axon
• More Na+ outside than
inside
• More K+ inside than outside
outside axon
reference
electrode
outside axon
+

        
+ + + + + + + + +
K+
Na+
gated K+
channel
gated Na+
channel
Resting potential: Na+ outside the axon, K+ and large
anions inside the axon. Separation of charges polarizes
the cell and causes the resting potential.
13.1 Overview of the nervous system
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 (+40mV)
• Potassium gates open letting K+ out
• Repolarization occurs
• Interior of axon regains negative charge (-65mV)
• Wave of depolarization/repolarization travels down the axon
• Resting potential is restored by moving potassium inside and
sodium outside
13.1 Overview of the nervous system
The nerve impulse: stimulus causes the
axon to reach its threshold
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
+

+

+

+
     
+ + + + + +
direction of signal
+

+


+

+

+

+
   
+ + + +
open
Na+
channel
b. Stimulus causes the axon to reach its threshold;
the axon potential increases from -70 to -40.
The action potential has begun.
13.1 Overview of the nervous system
The nerve impulse: action potential
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+60



+
+
+
+
+
+
+
+

+
+
+
+
+
+
+
+
+
+
+








+
+
+
+
+
+
+
+
direction of signal
Voltage (mV)
+40

direction of signal
+
+
+
+











+
+
+
+
+
+
+
open
Na+
channel
c. Depolarization continues as Na+ gates
open and Na+ moves inside the axon.
 +
+
+
+
+
+
+
+








+
open K+
channel
d. Action potential ends: repolarization
occurs when K+ gates open and K+ moves
to outside the axon. The sodium—potassium
pump returns the ions to their
resting positions.
Na+ moves
to inside
axon.
+20
K+ moves
to outside
action
axon.
potential
0
20
40
threshold
60
resting
potential
0
1
2
3
4
5
Time (milli seconds)
6
e. An action potential can be visualized if
voltage changes are graphed over time.
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13.1 Overview of the nervous system
The synapse
• 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, and
serotonin)
• Neurotransmitters are stored in synaptic vesicles
in the axon terminals
13.1 Overview of the nervous system
How does transmission across the
synapse occur?
• Nerve impulse reaches the axon terminal
• Calcium ions enter the axon terminal that
stimulate the synaptic vesicles to fuse with
the presynaptic membrane
• Neurotransmitters are released and diffuse
across the synapse and bind with the
postsynaptic membrane to inhibit or excite
the neuron
13.1 Overview of the nervous system
A synapse and how it functions
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arriving action
potential
Sending neuron
Ca2+
axon of
sending
neuron
axon
terminal
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.
Synaptic vesicles
enclose neurotransmitter.
Synapse
receiving
neuron
Receiving neuron Synaptic
cleft
2. Neurotransmitter
molecules
are released
and bind to
receptors
on the
membrane of
the receiving
neuron.
Receiving neuron
neurotransmitter
neurotransmitter
receptor
Na+
Receiving
neuron
ion
channel
3. When an
excitatory
neurotransmitter
binds to a
receptor,
Na+ diffuses
into the
receiving
neuron, and
an action
potential
begins.
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13.1 Overview of the nervous system
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Synaptic integration
• Integration is the
summation of the
inhibitory and
excitatory signals
received by a
postsynaptic neuron
axon branches of
sending neurons
Cell body of the
receiving neuron
axon terminals
dendrite
inhibitory
synapse
excitatory
synapse
• This occurs because
a neuron receives
many signals
a.
+20
0
excitatory signal
integration
inhibitory signal
20
40
threshold
70
resting
potential
80
Time (milli seconds)
b.
Courtesy Dr. E.R. Lewis, University of California Berkeley
13.1 Overview of the nervous system
The nervous divisions
• 2 divisions:
– Central nervous
system (CNS): Brain
and spinal cord
– Peripheral nervous
system (PNS): Nerves
and ganglia (cell
bodies)
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brain
Central Nervous System (CNS)
cranial nerves
brain
spinal cord
spinal cord
spinal nerves
Peripheral Nervous System (PNS)
sensory (afferent) nerves —
carry sensory information
into brain and spinal cord
somatic sensory
nerves: signals
from skin,
muscles,
joints, special
senses
a.
b.
visceral sensory
nerves:
signals from
body organs
motor (efferent) nerves —
carry motor information
from CNS to effectors
somatic motor
nerves: signals
to skeletal
muscles,
voluntary
autonomic motor
nerves: signals
to smooth
muscle, cardiac
muscle, glands,
involuntary
sympathetic
division
“fight or flight”
parasympathetic
division
“rest and digest”
13.2 The central nervous system
The central nervous system
• 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
• Both made up of 2 types of nervous tissue:
• Gray matter – contains cell bodies and nonmyelinated fibers
• White matter – contains myelinated axons
13.2 The central nervous system
The CNS: Spinal cord
• Extends from the base of the brain and along the length
of the vertebral canal formed by the vertebrae
• Functions to provide communication between the brain
and most of the body
• Center for reflex arcs
• Gray matter in the center is a butterfly shape
• White matter surrounds the gray matter
13.2 The central nervous system
What does the spinal cord look like?
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white matter
gray matter
central canal
a.
gray matter
white matter
spinal cord
vertebra
dorsal root
dorsal root
ganglion
spinal
nerve
vertebra
ventral root
b.
central canal
dorsal root
dorsal root
ganglion
dorsal
dorsal root
branches
gray matter
white matter
dorsal root
ganglion
ventral
spinal
nerve
ventral root
cut vertebrae
meninges
c.
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
13.2 The central nervous system
The CNS: Brain
Four major parts:
1.
2.
3.
4.
Cerebrum
Diencephalon
Cerebellum
Brain stem
13.2 The central nervous system
The CNS: Overview of the brain
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lateral
third
ventricle ventricle
pineal
gland
Cerebrum
skull
meninges
corpus
callosum
Diencephalon
thalamus
(surrounds the
third ventricle)
hypothalamus
pituitary gland
Brain stem
midbrain
pons
medulla
oblongata
a. Parts of brain
Cerebellum
fourth ventricle
spinal cord
b. Cerebral hemispheres
13.2 The central nervous system
The brain: Cerebrum
• Cerebral hemisphere
• Cerebral cortex
• Primary motor and sensory areas of the
cortex
• Association areas
• Processing centers
• Central white matter
13.2 The central nervous system
1. The brain: Cerebrum – the lobes
• Cerebrum – largest portion of the brain
• Divided into 4 lobes/hemispheres:
• Frontal lobe: primary motor area and conscious
thought
• Temporal lobe: primary auditory, smell, and
speech area
• Parietal lobe: primary somatosensory and taste
area
• Occipital lobe – primary visual area
13.2 The central nervous system
1. The brain: Cerebrum – the cerebral
hemispheres
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central sulcus
Frontal lobe
Parietal lobe
primary somatosensory area
primary motor area
premotor area
leg
motor speech
(Broca’s) area
trunk
somatosensory
association area
primary taste area
arm
prefrontal
area
hand
general interpretation area
face
anterior
ventral
tongue
posterior
dorsal
Occipital lobe
primary
olfactory
area
lateral sulcus
Temporal lobe
auditory association area
primary auditory area
sensory speech (Wernicke’s) area
primary
visual area
visual
association
area
13.2 The central nervous system
1. The brain: Cerebrum – the cerebral
cortex
• Cerebral cortex – thin, outer layer of gray matter:
- Primary motor area – voluntary skeletal muscle
- Primary somatosensory area – 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
13.2 The central nervous system
1. The brain: Cerebrum – the cerebral
cortex
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arm
trunk
forearm
thumb, fingers,
and hand
swallowing
foot and
toes
a. Primary
motor area
hand, fingers,
and thumb
thigh
leg
facial
expression
salivation
vocalization
mastication
arm neck trunk pelvis
forearm
thigh
pelvis
longitudinal
fissure
leg
upper
face
foot and
toes
lips
teeth and
gums
tongue and
pharynx
genitals
b. Primary
somatosensory
area
longitudinal
fissure
13.2 The central nervous system
2. The brain: Diencephalon
• Includes the:
• Hypothalamus – helps maintain homeostasis
(hunger, sleep, thirst, body temperature, and
water balance) and controls pituitary gland
• Thalamus – 2 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
13.2 The central nervous system
2. The brain: Diencephalon
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lateral
third
ventricle ventricle
pineal
gland
Cerebrum
skull
meninges
corpus
callosum
Diencephalon
thalamus
(surrounds the
third ventricle)
hypothalamus
pituitary gland
Brain stem
midbrain
pons
medulla
oblongata
a. Parts of brain
Cerebellum
fourth ventricle
spinal cord
b. Cerebral hemispheres
13.2 The central nervous system
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)
13.2 The central nervous system
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;
regulate breathing rate; reflex center for head
movements
• Medulla oblongata – reflex centers for regulating
breathing, heartbeat, and blood pressure
• Reticular formation – major component of the reticular
activating system (RAS) that regulates alertness
13.2 The central nervous system
The reticular activating system
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RAS radiates
to cerebral
cortex.
thalamus
reticular
formation
ascending sensory
tracts (touch, pain,
temperature)
13.3 The limbic system and higher mental functions
The limbic system
• Joins primitive emotions (i.e., fear, pleasure)
with higher functions such as reasoning
• Can cause strong emotional reactions to
situations but conscious thought can override
and direct our behavior
• Includes:
• Amygdala – has emotional overtones
• Hippocampus – important to learning and memory
13.3 The limbic system and higher mental functions
The limbic system
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corpus
thalamus callosum
hypothalamus
olfactory bulb
olfactory tract
amygdala
hippocampus
13.3 The limbic system and higher mental functions
Higher mental functions
• 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
• Long-term memory – retention of information for more than a few
minutes and includes the following:
• Episodic memory – persons and events
• Semantic memory – number and words
• Skill memory – performing skilled motor activities (i.e., riding a bike)
• Language – depends on semantic memory
13.3 The limbic system and higher mental functions
What parts of the brain are active in
reading and speaking?
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primary auditory cortex
visual cortex
1. The word is seen in the
visual cortex.
Wernicke’s area
2. Information concerning the
word is interpreted in
Wernicke’s area.
primary motor cortex
Broca’s area
3. Information from Wernicke’s
area is transferred to Broca’s
area.
(all): © Marcus Raichle
4. Information is transferred from
Broca’s area to the primary motor
area.
13.4 The peripheral nervous system
The peripheral nervous system (PNS)
• Includes cranial (12 pr) and spinal nerves (31 pr)
and ganglia outside the CNS
- Spinal nerves conduct impulses to and from the
spinal cord
- Cranial nerves conduct impulses to and from the
brain
• Divided into 2 systems:
- Somatic
- Autonomic
13.4 The peripheral nervous system
The peripheral nervous system
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cranial
nerves
PNS
Spinal Cranial
Nerve
spinal
nerves
artery
and vein
Cranial Nerves
III
from olfactory
receptors
from retina of
eyes
to eye muscles
IV
to eye muscles
V
from mouth and
to jaw muscles
VI
to eye muscles
I
II
single nerve fiber
bundle of
nerve fibers
VII from taste buds
and to facial
muscles and
glands
VIII from inner ear
IX
blood vessels
SEM 200×
© Dr. Richard Kessel & Dr. Randy Kardon/Tissues & Organs/Visuals Unlimited
from pharynx
and to pharyngeal
muscles
XII to tongue
muscles
X from and to
internal organs
XI to neck and
back muscles
13.4 The peripheral nervous system
The PNS: Somatic division
• Serves the skin,
skeletal muscles
and tendons
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pin
central canal
dorsal root ganglion
white matter
sensory
receptor
(in skin)
Dorsal
gray matter
dorsal
horn
cell body of sensory neuron
• Automatic
responses are
called reflexes
axon of sensory neuron
cell body of interneuron
effector
(muscle)
axon of motor neuron
ventral root
cell body of
motor neuron
ventral horn
Ventral
13.4 The peripheral nervous system
The PNS: Autonomic division
• Regulates the activity of involuntary muscles
(cardiac and smooth) and glands
• Divided into 2 divisions:
– Sympathetic: coordinates the body for the “fight or
flight” response by speeding up metabolism, heart
rate, and breathing while slowing down and regulating
other functions
– Parasympathetic: counters the sympathetic system by
bringing up a relaxed state by slowing down
metabolism, heart rate, and breathing and returning
other functions to normal
13.4 The peripheral nervous system
The PNS: Autonomic division
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stimulates tears
constricts pupils
inhibits tears
dilates
pupils
Sympathetic Division
ganglion
Parasympathetic Division
inhibits salivation
stimulates
salivation
cranial
nerves
slows heart
speeds
heart
dilates air
passages
cervical
nerves
constricts
bronchioles
stimulates liver to
release glucose
stimulates gallbladder
to release bile
stimulates
adrenal
secretion
thoracic
nerves
vagus nerve
increases activity
of stomach and
pancreas
inhibits activity
of kidneys,
stomach, and
pancreas
increases
intestinal
activity
decreases
intestinal activity
lumbar
nerves
ganglion
inhibits
urination
causes
orgasmic
contractions
sympathetic ganglia
stimulates
urination
causes
erection
of genitals
sacral
nerves
Acetylcholine is neurotransmitter.
Norepinephrine is neurotransmitter.
13.5 Drug Therapy and Drug abuse
Drugs and drug abuse
Both pharmaceuticals and illegal drugs have several basic
modes of action:
• Promote the action of a neurotransmitter
• Interfere with or decrease the action of a neurotransmitter
• Replace or mimic a neurotransmitter or neuromodulator
13.5 Drug Therapy and Drug abuse
Drugs and drug abuse
• Most drug abusers take drugs that affect dopamine and
thus artificially affect this reward circuit to the point 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
13.5 Drug Therapy and Drug abuse
Drug abuse: Alcohol
• Alcohol – a depressant directly absorbed from the
stomach and small intestine
• Most socially accepted form of drug use
• About 80% of college-aged people drink
• Alcohol denatures proteins, 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
13.5 Drug Therapy and Drug abuse
Drug abuse: Nicotine and Cocaine
• Nicotine – stimulant derived from tobacco plant
– Causes neurons to release dopamine that helps lead to
dependence
– Adversely affects a developing embryo or fetus
– Increases heart rate and blood pressure
– Psychological and physiological dependency
• Cocaine – stimulant derived from a plant
– Results in a rush sensation (5-30 minutes) and an increased sex
drive
– Results in hyperactivity and little desire for food and sleep
– Extreme physical dependence with this drug
– “Crack” is a street name for cocaine that is processed to a free
base for smoking
13.5 Drug Therapy and Drug abuse
Drug abuse: methamphetamine
• Powder form is called speed and crystal form is called
meth or ice
• 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
• Causes psychological dependency and hallucinations
• “Ecstasy” is the street name for a drug that has the same
effects as meth without the hallucinations
13.5 Drug Therapy and Drug abuse
Drug abuse: Heroin
• Heroin: depressant from the sap of the opium poppy
plant
• Leads to a feeling of euphoria and no pain because it is
delivered to the brain and is converted into morphine
• Side effects are nausea, vomiting, and depression of the
respiratory and circulatory systems
• Can lead to HIV, hepatitis, and other infections due to
shared needles
• Extreme dependency
13.5 Drug Therapy and Drug abuse
Drug abuse and its use: Marijuana
• Marijuana: psychoactive drug derived from a hemp plant
called Cannabis
• Most often smoked as a “joint”
• Mild euphoria and brain damage
• 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
13.5 Drug Therapy and Drug abuse
Bioethical focus: Medical Marijuana
•
Banned in the US in 1937 but recently has
been legalized in a few states for medical use
in seriously ill patients.
– Should marijuana be available to more
patients? Why or why not?
– Should people in states where it is legal for
medical purposes be prosecuted?
– How should the use of medical marijuana be
regulated?