Download Central nervous system

Biology
Sylvia S. Mader
Michael Windelspecht
Chapter 37
Neurons and Nervous
Systems
Lecture Outline
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1
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Evolution of the Nervous System
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eyespot
auricle
ventral nerve
cord with ganglia
cerebral
ganglia
nerve
brain
nerve net
lateral
nerve
cords
transverse
nerves
a. Hydra
b. Planarian
c. Earthworm
2
Evolution of the Nervous System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
cerebrum
in forebrain
hindbrain
giant
nerve
fiber
spinal
cord
brain
eye
brain
thoracic
ganglion
d. Crab
tentacle
e. Squid
f. Cat
3
Evolution of the Nervous
System
• Division of Nervous System:
– The Central nervous system (CNS)
• Includes the brain and spinal cord
– The peripheral nervous system (PNS)
• Consists of all nerves that lie outside the CNS
– Somatic nervous system
» Sensory and motor functions that control skeletal
muscle
– Autonomic nervous system
» Controls smooth muscle, cardiac, muscle, and gland
» Divided into sympathetic and parasympathetic divisions
4
Organization of the Human Nervous System
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brain
cranial nerves
cervical nerves
thoracic
nerves
spinal cord
radial nerve
median nerve
ulnar nerve
lumbar
nerves
sacral
nerves
sciatic nerve
tibial nerve
common fibular
nerve
a.
5
37.2 Nervous Tissue
• Neurons (nerve cells)
– Cell body contains nucleus and organelles
– Dendrites receive signals from sensory
receptors or other neurons
– Axon conducts nerve impulses to another
neuron or to other cells
• Covered by myelin sheath
6
Nervous Tissue
• Types of Neurons
• Motor (efferent) neurons
– Accept nerve impulses from the CNS
– Transmit them to muscles or glands(away)
• Sensory (afferent) neurons
– Accept impulses from sensory receptors
– Transmit them to the CNS
• Interneurons
– Convey nerve impulses between various parts of the
CNS
7
Neuron Anatomy
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cell body
dendrite
direction
of conduction
myelin
sheath
axon
terminal
node of Ranvier
axon
a. Motor neuron (multipolar)
muscle
8
a: © M.B. Bunge/Biological Photo Service
Neuron Anatomy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
axon
cell body
direction of
conduction
sensory
receptor
axon
b. Sensory neuron (unipolar)
myelin sheath
skin
9
Neuron Anatomy
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axon
cell body
dendrite
c. Interneuron (multipolar)
c: © Manfred Kage/Peter Arnold, Inc.
10
Nervous Tissue
• Transmission of Nerve Impulses
– Resting Potential
• The membrane potential (voltage) when the axon
is not conducting an impulse
– The inside of a neuron is more negative than
the outside, around -70 mV
– Due in part to the activity of the sodiumpotassium pump
11
Nervous Tissue
• An action potential is a rapid change in
polarity across a portion of an axonal
membrane
• An action potential is generated only after a
stimulus larger than the threshold (-55mV)
– Gated channel proteins
• One channel protein suddenly allows sodium to
enter the cell
• Another channel protein allows potassium to leave
the cell
12
Resting and Action Potential of the Axonal
Membrane
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+60
+40
Na+ moves
to inside
axon
K+ moves
to outside
axon
action
potential
+20
Voltage (mV)
0
–20
–40
threshold
–60
resting
potential
0
1
2
3
4
5
6
Time (milliseconds)
d. An action potential can be visualized if voltage changes are
graphed over time.
13
Nervous Tissue
• Propagation of Action Potentials
– In nonmyelinated axons, the action potential travels
down an axon one small section at a time
– In myelinated fibers, an action potential at one node
causes an action potential at the next node
• Saltatory (jumping) Conduction
– Conduction of a nerve impulse is an all-or-nothing
event
• Intensity of signal is determined by how many impulses are
generated within a given time span
15
Nervous Tissue
• Transmission Across a Synapse
– A synapse is a region where neurons nearly touch
– Small gap between neurons is the synaptic cleft
– Transmission across a synapse is carried out by
neurotransmitters
• Sudden rise in calcium in the axon terminal of one neuron
• Calcium stimulates synaptic vesicles to merge with the
presynaptic membrane
• Neurotransmitter molecules are released into the synaptic
cleft
16
Nervous Tissue
• Synaptic Integration
– A single neuron is on the receiving end of
• Many excitatory signals, and
• Many inhibitory signals
– Integration
• The summing of excitatory and inhibitory signals
17
End of Nervous system Notes PT. 1
37.3 The Central Nervous
System
• The Central Nervous System
– Consists of the brain and spinal cord
– Three specific functions:
• Receives sensory input
• Performs integration
• Generates motor output
19
The Central Nervous System
• The Central Nervous System
– Consists of the brain and spinal cord
– Spinal cord and brain are wrapped in three
protective membranes called meninges
• Spaces between meninges are filled with
cerebrospinal fluid
• Fluid is continuous with that of central canal of
spinal cord and the ventricles of the brain
20
The Central Nervous System
• The Spinal Cord
– Two main functions
• Center for many reflex actions
• Means of communication between the brain and
spinal nerves
– Composed of grey matter and white matter
• Cell bodies and short unmyelinated fibers give the
gray mater its color
• Myelinated long fibers of interneurons running in
tracts give white mater its color
21
The Central Nervous System
• The Brain
– The cerebrum is the largest portion of the
brain in humans
• Communicates with, and coordinates the activities
of, the other parts of the brain
• Longitudinal fissure divides the cerebrum into left
and right cerebral hemispheres
22
The Human Brain
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Cerebrum
(telencephalon)
opening to lateral
ventricle
third ventricle
skull
meninges
corpus
callosum
pituitary gland
Diencephalon
thalamus
(surrounds the
third ventricle)
hypothalamus
pineal gland
fourth ventricle
Brain stem
midbrain
Cerebellum
pons
medulla
oblongata
a. Parts of brain
spinal cord
b. Cerebral hemispheres
23
The Lobes of a Cerebral
Hemisphere
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central sulcus
Frontal lobe
primary somatosensory area
primary motor area
premotor area
motor speech
(Broca’s) area
prefrontal
area
Parietal lobe
leg
trunk
arm
hand
somatosensory
association area
primary taste area
general interpretation area
face
tongue
Occipital lobe
primary
visual area
lateral sulcus
Temporal lobe
visual
association
area
auditory association area
primary auditory area
sensory speech (Wernicke’s) area
24
The Central Nervous System
• Cerebral Cortex
• A thin but highly convoluted outer layer of
gray matter
• Covers the cerebral hemispheres
• Contains motor areas and sensory areas as
well as association areas
– Primary motor area is in the frontal lobe, just
ventral to the central sulcus
– Primary somatosensory area is in the parietal lobe,
just dorsal to the central sulcus
25
The Central Nervous System
• Basal nuclei
– Integrate motor commands
– Ensures that the proper muscle groups are
either activated or inhibited
26
The Central Nervous System
• Other Parts of the Brain
• Diencephalon
• A region encircling the third ventricle
• Includes three structures
– Hypothalamus
• Forms the floor of the third ventricle
• Integrating center that maintains
homeostasis
• Controls the pituitary gland
27
The Central Nervous System
• Other Parts of the Brain
• Diencephalon (continued)
• Thalamus
• Consists of two masses of gray matter located in the
sides and roof of the third ventricle
• Receives all sensory input except smell
• Integrates sensory information and sends it to the
cerebrum
• Pineal gland
• Secretes melatonin
28
The Central Nervous System
• Other Parts of the Brain
• Cerebellum
• Separated from the brain stem by the fourth ventricle
• Largest portion of the brainstem
• Receives sensory input from the eyes, ears, joints, and
muscles
• Sends motor impulses out the brain stem to the skeletal
muscles
29
The Central Nervous System
• Other Parts of the Brain
• Brain Stem
• Contains the midbrain, pons, and the medulla
oblongata
• Midbrain
• Acts as a relay station for tracts passing between the
cerebrum and the spinal cord or cerebellum
• Pons
• Contains axons that form a bridge between the
cerebellum and the rest of the central nervous
system
• Medulla Oblongata
• Contains reflex centers for vomiting, coughing,
sneezing, hiccupping, and swallowing
30
The Central Nervous System
• The Reticular Activating System (RAS)
– A complex network of:
• Nuclei (masses of gray matter)
• Nerve fibers that extend the length of the brain
stem
– The reticular formation is a major component
of the RAS
– The RAS arouses the cerebrum via the
thalamus and causes a person to be alert
31
The Reticular Activating System
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radiations
to cerebral
cortex
thalamus
reticular
formation
ascending sensory
tracts (touch, pain,
temperature)
32
The Central Nervous System
• Limbic System
– Complex network of tracts and “nuclei”
– Incorporates
• Medial portions of the cerebral lobes,
• The basal nuclei, and
• The diencephalon
– Integrates higher mental functions and primitive emotions
– Important structures in the limbic system are
• The hippocampus and the amygdala
33
The Limbic System
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corpus callosum
thalamus
hypothalamus
hippocampus
olfactory bulb
amygdala
olfactory tract
34
The Central Nervous System
• Learning and Memory
– Memory
• The ability to hold a thought in mind or recall events from the
past
– Learning
• Takes place when we retain and use past memories
– Short term memory is associated with the prefrontal area
of the frontal lobe
– Long term memory is associated with the hippocampus
35
37.4 The Peripheral Nervous
System
• Somatic system
– Includes cranial nerves and spinal nerves
• Gather information from sensors and conduct decisions to effectors
• Controls the skeletal muscles
– Voluntary
• Autonomic system
–
–
–
–
Controls the smooth muscles, cardiac muscles, and glands
Innervates all internal organs
Usually involuntary
Divided into two divisions
• Sympathetic division
• Parasympathetic division
– Utilizes two neurons and one ganglion for each impulse
36
Cranial and Spinal Nerves
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spinal cord
gray matter
vertebra
white matter
frontal lobe
olfactory bulb
dorsal root
olfactory tract
dorsal root
ganglion
optic nerve
optic chiasma
spinal
nerve
ventral root
vertebra
b.
temporal lobe
central canal
cerebellum
gray matter
medulla
white matter
a.
c.
c: © Karl E. Deckart/Phototake
37
The Peripheral Nervous System
• Reflex Arc
• Sensory receptors generate a nerve impulse that moves along
sensory axons through a dorsal root ganglion toward the spinal
cord
• Sensory neurons pass signals on to many interneurons in the
gray matter of the spinal cord
• Nerve pulses travel along motor axons to an effector, which
brings about a response to the stimulus
38
A Reflex Arc Showing the
Path of a Spinal Reflex
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pin
dorsal root ganglion
sensory
receptor
(in skin)
axon of sensory neuron
central canal
white matter
dendrites
Dorsal
gray matter
dorsal
horn
cell body of
sensory neuron
interneuron
dendrites
axon of motor neuron
cell body of
motor neuron
effector
(muscle)
ventral root
ventral horn
Ventral
39
The Peripheral Nervous System
• Sympathetic division
– Especially important during fight or flight
responses
– Accelerates heartbeat and dilates bronchi
• Parasympathetic division
– Promotes all internal responses associated
with a relaxed state
– Promotes digestion and retards heartbeat
40
Autonomic System Structure and Function
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inhibits tears
stimulates tears
constricts pupils
dilates
pupils
ganglion
inhibits salivation
Sympathetic Division
Parasympathetic Division
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
stimulates
urination
causes
orgasmic
contractions
sympathetic ganglia
causes
erection
of genitals
sacral
nerves
Acetylcholine is neurotransmitter.
Norepinephrine is neurotransmitter.
41
Comparison of Somatic Motor
and Autonomic Motor Pathways
42
Drugs of Abuse
• Drug abuse - person takes a drug at a dose
level that increases the potential for a harmful
effect.
• Addiction - when more of the drug is needed
to get the same effect
• Withdrawal - when the user stops taking the
drug
• Alcohol, drugs, and tobacco can all adversely
affect the developing embryo, fetus, or
newborn.
43
Drug Use: Brain Activity Before and After
the Use of Cocaine
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brain activity
Before cocaine use,
brain is less active.
After cocaine use, brain is more active.
© Science VU/Visuals Unlimited
44
End Nervous system Notes PT. 2
Evolution of the Nervous
System
• Vertebrate Nervous-System
Organization
– Central nervous system
• Vertebrate brain is organized into three areas
– Hindbrain
– Midbrain
– Forebrain
46
37.1 Evolution of the Nervous
System
• Invertebrate Nervous System Organization
– Hydras
• Nerve net composed of neurons in contact with one
another
• Also in contact with contractile cells in the body wall
– Planarians
• Ladderlike nervous system
• Cephalization - a concentration of ganglia and
sensory receptors in the head
– Annelids, Arthropods and Molluscs
• Complex animals
• True nervous systems
47
Organization of the Human Nervous System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Central Nervous
System
brain and
spinal cord
Peripheral Nervous
System
somatic sensory
fibers (skin,
special senses)
visceral sensory
fibers (internal
organs)
somatic motor
fibers (to skeletal
muscles)
autonomic motor
fibers (to cardiac
and smooth
muscle, glands)
sympathetic
division
parasympathetic
division
48
b.
Resting and Action Potential of the Axonal
Membrane
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reference
electrode
outside axon
recording
electrode
inside axon
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
+
+
+
+
+
+
+
+
+
axonal
membrane
inside axon
K+
Na+
gated K+
channel
gated Na+
channel
outside axon
a. Resting potential: more Na+ outside the axon and more K+ inside
the axon causes polarization.
49
Resting and Action Potential of the Axonal
Membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
–
–
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
direction of impulse
+
+
–
–
–
–
–
–
–
–
–
–
+
+
+
+
+
+
+
+
open Na+
channel
b. Action potential begins: depolarization occurs when Na+ gates
open and Na+ moves to inside the axon.
50
Resting and Action Potential of the Axonal
Membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
+
+
–
–
–
–
–
–
–
–
–
–
+
+
+
+
+
+
+
+
direction of impulse
–
–
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
open K+
channel
c. Action potential ends: repolarization occurs when K+ gates open and
K+ moves to outside the axon.
51
Synapse Structure and Function
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
path of action potential
1. After an
action
potential
arrives at an
axon terminal,
Ca2+ enters,
and synaptic
vesicles fuse
with the
presynaptic
membrane.
Ca2+
axon
terminal
synaptic vesicles
enclose neurotransmitter
cell body of
postsynaptic
neuron
synaptic cleft
2. Neurotransmitter
molecules
are released
and bind to
receptors
on the
postsynaptic
membrane.
presynaptic
membrane
neurotransmitter
neurotransmitter
receptor
Na+
postsynaptic
neuron
postsynaptic
membrane
3. When an
excitatory
neurotransmitter
binds to a
receptor,
Na+ diffuses
into the
postsynaptic
neuron, and
an action
potential
begins.
52