Chapter 48: Nervous Systems
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Chapter 48: Nervous Systems March 12, 2008
•
Often cooperate with endocrine and immune.
•
Survival, reproduction depends on fast response to environment.
•
Nucleus here means mass of neurons.
Contents
1 An Overview of the Nervous Systems 1.1
Nervous systems perform three overlapping functions of sensory
1.2
Networks of neurons with intricate connections form nervous sys-
input, integration, and motor output. . . . . . . . . . . . . . . . .
2.2
2
tems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
1.2.1
Neuron Structure and Synapses . . . . . . . . . . . . . . .
3
1.2.2
A Simple Nerve Circuitthe Re ex Arc . . . . . . . . . .
3
1.2.3
Types of Nerve Circuits
. . . . . . . . . . . . . . . . . . .
3
1.2.4
Supporting Cells (Glia)
. . . . . . . . . . . . . . . . . . .
4
2 The Nature of Nerve Signals 2.1
2
Every cell has a voltage, or membrane potential, across its plasma
4
membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
2.1.1
Measuring Membrane Potentials
4
2.1.2
How a Cell Maintains a Membrane Potential
. . . . . . . . . . . . . . . . . . . . .
4
Changes in the membrane potential of a neuron give rise to nerve impulses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2.2.1
Graded Potentials: Hyperpolarization adn Depolarization
5
2.2.2
The Action Potential: All or Nothing Depolarization . . .
2.3
Nerve impulses propagate themselves along an axon
. . . . . . .
2.4
Chemical or electrical communication between cells occur at synapses
5 5 6
2.4.1
Electrical Synpases . . . . . . . . . . . . . . . . . . . . . .
6
2.4.2
Chemical Synapses . . . . . . . . . . . . . . . . . . . . . .
6
2.5
Neural integration occurs at the cellular level
. . . . . . . . . . .
2.6
The same neurotransmitter can produce dierent eects on dif-
6
ferent types of cells . . . . . . . . . . . . . . . . . . . . . . . . . .
7
2.6.1
7
Acetylcholine
. . . . . . . . . . . . . . . . . . . . . . . . .
1
2.6.2
Biogenic Amines
. . . . . . . . . . . . . . . . . . . . . . .
7
2.6.3
Other Chemical Neurotransmitters . . . . . . . . . . . . .
8
2.6.4
Gaseous Signals of the Nervous System
8
3 Evolution and Diversity of Nervous Systems
. . . . . . . . . .
The ability of cells to respond to the environment has evolved . . . . . . . . . . . . . . . . . . . . . . . . .
8
3.2
Nervous systems show diverse patterns of organization . . . . . .
8
4.1
Vertebrate nervous system have central and peripheral components
4.2
The division of the peripheral nervous system interact in main-
4.3
Embryonic development of the vertebrate brain re ects its evo-
4.4
Evolutionarily older structures of the vertebrate brain regulate
over billions of years
4 Vertebrate Nervous Systems
taining homeostasis . . . . . . . . . . . . . . . . . . . . . . . . . . lution from three anterior bulges of the neural tube . . . . . . . . essential autonomic and integrative functions
9 9
9 10
. . . . . . . . . . .
10
. . . . . . . . . . . . . . . . . . . . . . . .
10
4.4.1
The Brainstem
4.4.2
The Reticular System, Arousal, and Sleep . . . . . . . . .
11
4.4.3
The Cerebellum
11
4.4.4
The Thalamus and Hypothalamus
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
4.5
The cerebrum is the most highly evolved structure of the mam. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
4.6
Regions of the cerebrum are specialized for dierent functions . .
12
malian brain
4.7
4.6.1
Integrative Function of the Association Areas . . . . . . .
12
4.6.2
Lateralization of Brain Function
. . . . . . . . . . . . . .
13
4.6.3
Language and Speech
. . . . . . . . . . . . . . . . . . . .
13
4.6.4
Emotions
. . . . . . . . . . . . . . . . . . . . . . . . . . .
13
4.6.5
Memory and Learning . . . . . . . . . . . . . . . . . . . .
13
4.6.6
Human Consciousness
14
. . . . . . . . . . . . . . . . . . . .
Research on neuron development and neural stem cells may lead to new approaches for treating CNS injuries and diseases
1
8
3.1
. . . .
14
4.7.1
Nerve Cell Development . . . . . . . . . . . . . . . . . . .
14
4.7.2
Neural Stem Cells
14
. . . . . . . . . . . . . . . . . . . . . .
An Overview of the Nervous Systems
1.1 Nervous systems perform three overlapping functions of sensory input, integration, and motor output. 1. Detect outside and inside signals. 2. Integration: interpret, respond. Continuous. (a)
Central nervous system
brain, spinal cord.
2
3.
Motor output
nervous system.
CNS
→
eector cells
(muscles, glands).
Peripheral
1.2 Networks of neurons with intricate connections form nervous systems
1.2.1 Neuron Structure and Synapses Cell body Dendrites receive. Axons send. 1.
nucleus and organelles.
2.
short, branched,
3.
long,
Only one.
(a) Some > 1m (spinal cord
→
foot).
Axon hillock Synaptic terminals neurotransmitter. Synapse Presynaptic postsynaptic 1.2.2 A Simple Nerve Circuitthe Re ex Arc (b)
joins cell body; cone.
(c)
relay via
(d)
contact other cell.
4.
: transmitter;
: receiver.
1. Automatic response. 2. 3.
Sensory neuron → motor neuron → eector cell. Interneurons
inhibit motor neurons to ensure re ex success.
(a) Decision: can resist re ex. 4. Gray matter: body. White matter: motor/sensory axons. 5.
Ganglion
cell bodies, similar in function. Called
lular!) in brains.
1.2.3 Types of Nerve Circuits 1. Signal diverges. 2. Signals converge: identify object: see, touch, hear. 3. Circular ow: memory.
3
nuclei
(not intracel-
1.2.4 Supporting Cells (Glia) 1. Gk.
glue.
2. Embryo: radial glia form tracks for neuron to grow. 3.
Astrocytes
structural, metabolic support.
(a) Blood-brain barrier.
4.
Oligodendrocytes
(central)/
Schwann cells
(peripheral) myelin sheath.
(a) Separate cells wrap axons. (b) Lipid
2
→
insulate.
The Nature of Nerve Signals 1. Galvani: frog muscles electric; 2. Hermann von Helmholtz: electricity between nerves carry signals.
2.1 Every cell has a voltage, or membrane potential, across its plasma membrane
2.1.1 Measuring Membrane Potentials Resting potential −70 1.
unstimulated;
mV.
2. Invertebrates have huge neurons (squid). Research.
2.1.2 How a Cell Maintains a Membrane Potential 1. Inside: K
+
and A
+
2. Outside: Na , Cl 3. More K
+
−
−
2−
(proteins, AAs, SO4
3−
, PO4
.
channels.
− 4. A cannot diuse. 5.
[K+ ] gradient competes with electrochemical.
librium.
+
(a) K
(b) Cell
wants to exit
−→
+
→
Cell
Membrane potential is equi-
−.
+
K enters.
(c) Simplest case, 6. Na
).
−85mV
equilibrium.
favored to enter cell (both
[]
and electro.).
+
(a) K exit because charge too high (−75
+ + (b) Na /K pump prevent.
4
mV
).
2.2 Changes in the membrane potential of a neuron give rise to nerve impulses
Excitable cells ∆ Gated ion channels Chemically-gated voltage-gated. 2.2.1 Graded Potentials: Hyperpolarization adn Depolarization Hyperpolarization Depolarization 1.
generate large
2.
. (Neuron, muscle).
open/close o stimuli. One channel, one stim., one
ion.
3.
or
1.
+ voltage. Open K
2.
+
reduce voltage: open Na
channel; exit; more neg.
+
channel.
3. Graded because magnitude depend on stimulus.
2.2.2 The Action Potential: All or Nothing Depolarization Threshold potential action potential. 1.
activates
Only axon.
(a) 50-55 mV. Only depolarize. Hyperpolarized inhibit. 2. Triggered by graded depolarization in dendrite/body. Spreads along membrane.
+
3. K : one gate opens during depolarization
+
slowly
slowly.
4. Na : fast activation gate during after depolarization; open inactivation gate closes 5. K
+
during depolarization.
+
trickle out; Na
(a) After spike, K
+
gush
in.
+
gush out (gates opened) and Na
back to pre-spike
permeability. (b) (c)
Hyperpolarize
because K
Refractory period:
+
gates slow.
+ Na activation gate remains closed (slow).
Can't respond. (d) Intensity
→
frequency.
2.3 Nerve impulses propagate themselves along an axon 1. Action potential regenerated like graded depolarization. 2. Na
+
in ux meets threshold
→
new action potential.
3. One way due to refractory period: axon behind is recovering. 4. Rate factors:
5
(a) Larger diameter
→
faster transmission. Electrical resistance.
(b) Channels concentrated in (c)
nodes of Ranvier
Saltatory conduction saltare
tential at nodes. +
(d) Na
(L.
leap).
.
Fasteronly action po-
current ows inside to nodes.
2.4 Chemical or electrical communication between cells occur at synapses 1. Neuron
→
→
neuron; sense receptor
sense neuron; neurons
→
gland.
2.4.1 Electrical Synpases 1. Spread action potential. 2. Gap junction
fast.
3. Crustaceans, sh.
2.4.2 Chemical Synapses Synaptic cleft Synaptic vesicles neurotransmitters. Presynaptic membrane 1.
narrow gap.
2.
contain
3.
2+
when depolarized causes Ca
to enter neuron
(voltage-gated channels).
4. Stimulates synaptic vesicles to fuse with membrane; spill. 5.
Postsynaptic membrane
has receptor speci c to transmitter, ion.
6. Depolarize or hyperpolarize. 7. Removed: enzymatic breakdown or takeup into adjacent cells. 8.
Guaranteed one-way.
2.5 Neural integration occurs at the cellular level 1.
Excitatory postsynaptic potential (EPSP) Inhibitory postsynaptic potential (IPSP)
electrical charge caused
by neurotransmitter binding. 2.
chemicals
tion.
−
(a) Can in ow Cl
−
or out ow K
3. Both graded.
6
.
→ depolariza-
4. One EPSP insu cient. 5.
Summation:
additive eect of PSPs.
(a) Temporal: PSPs very close together; one arrives before membrane rests. (b) Spatial: PSPs simultaneous. (c) Both E/IPSP. Counterbalance too. 6. Axon hillock integration center. Average of polarization and depolarization. 7.
Action potentials depend on quantitative information.
2.6 The same neurotransmitter can produce dierent effects on dierent types of cells 1. Some shortmillisecs. 2. Others long because use signal-transduction pathways in postsynaptic cell. 3. Some in brain active enough to spread to many synapses.
2.6.1 Acetylcholine Most common; (in)vertebrates. 1. Vert. central: both excit./inhib. 2. Neuromuscular: motor neuron
→
depolarize muscle.
+
3. Heart: inhibit adenyl cyclase + open K action potential
→
in muscle
→ less able to generate
reduce strength/rate of pulse.
2.6.2 Biogenic Amines From amino acids. 1. Catecholamines from 2.
tyrosine epinephrine, norepinephrine, dopamine.
Tryptophan → serotonin.
:
3. Usually central. (a) Norepinephrine autonomic.
7
2.6.3 Other Chemical Neurotransmitters GABA, glycine, glutamate, aspartate. Neuropeptides Substance P Endorphins 1. Amino acids:
GABA most
common inhibitor.
2.
short AA chains. Use signal-transduction.
(a)
pain.
(b)
analgesics.
Decrease urine, depress respiration, eu-
phoria.
3. Overlap between nervous and endocrine.
2.6.4 Gaseous Signals of the Nervous System 1. Sexual arousal: NOin penis 2. NO relaxes muscle
→
→
erection.
dialate blood vessel.
3. Synthesized on demand.
3
Evolution and Diversity of Nervous Systems
3.1 The ability of cells to respond to the environment has evolved over billions of years 1. Prokaryote sense improve survival/reproduction. 2. Cambrian explosion, nervous nearly modern.
3.2 Nervous systems show diverse patterns of organization 1. Neurons same; network dier. 2. Porifera lack nerves. 3. Cnidarians have
nerve net
around radial gastrovascular.
(a) Component of complex nervous systems.
4.
Cephalization Nerve cord
cluster sensory neurons, interneurons near anterior (brain)
in bilateral.
5.
longitudinal. First CNS.
6. Advanced: ventral nerve cord with ganglia, complex brain. 7. Chordate: nerve cord dorsal. 8. Correspond with role: sessile little cephalization and sense. Motile (squid) very responsive, smart.
8
4
Vertebrate Nervous Systems
4.1 Vertebrate nervous system have central and peripheral components 1. Spinal cord re ex. 2. CNS from hollow nerve cord of embryo. 3.
Central canal ventricles and
of brains lled with
cerebrospinal uid.
(a) Formed in brain: ltered blood. (b) Shock absorber for brain. (c) Meningesconnective tissue to protect brain, spinal.
4.
Gray matter
; dendrites, bodies.
4.2 The division of the peripheral nervous system interact in maintaining homeostasis 1. 2.
Cranial nerves Spinal nerves
orginiate in brain. Organs in head.
in spinal. Rest of body.
3. Most sensory and motor neurons. 4. Sensory (aerent): (a) External (b) Internal 5. Motor (eerent): (a) Autonomic: involuntary internal control i. Parasympathetic: claming (paralyze). Acetylcholine. ii. Sympathetic: exciting. Norepinephrine. (b) Somatic: voluntary skeletal muscles; external. 6. Cooperate for homeostasis:
autonomic constrict blood vessel; somatic
shiver.
9
4.3 Embryonic development of the vertebrate brain re ects its evolution from three anterior bulges of the neural tube 1. Forebrain
Cerebrum Cereberal cortex
(a) Telencephalon i.
fanciest.
convulted gray matter.
(b) Diencephalonthalamus, hypothalamus, epithalamus i. Earliest vertebrate evolution. 2. Midbrain (a) Mesencephalonpart of brainstem. 3. Hindbrain (mostly brainstem) (a) Metencephalonpons,
cerebellum.
(b) Myelencophalonmedulla oblongata.
4.4 Evolutionarily older structures of the vertebrate brain regulate essential autonomic and integrative functions
4.4.1 The Brainstem
Homeostasis, coordinate movement, conduct to higher brain.
The Medulla and Pons. 1. Axons to cereberal cortex, cerebellum. 2.
Medulla pons visceral f (n) and
3. Higher sensory
pass through.
: breathe, cardiovascular, digestive.
4. Right/left brain crossover here.
The Midbrain. 1. Receive, integrate sense. 2. Relay sensory to speci c forebrain regions. 3. Inferior cullicoli: hearing; 4. Superior cullicoli: vision. Only vision center in nonmammals; re exes in mammal.
10
4.4.2 The Reticular System, Arousal, and Sleep 1. 2.
Arousal
awareness. Cmp.
Reticular formation
sleep
.
90 nuclei in core.
(a) Reticular activating system (RAS) (b) More input
→
lters input
more aroused.
(c) Can lter speci c noise (like Herman talking (
3.
Electroencephalogram EEG (
(a) Less activity (b) Fast
β
→
to cerebral cortex.
probably not really
) record electrical brain activity.
more synchronous waves (α).
for thinking.
(c)
θ
early sleep (irregular).
(d)
δ
deep sleep synchronized waves.
4.4.3 The Cerebellum 1. Coordination, error-checking during motor, perception, cognition. 2. Learn, remember motor sequence (muscle memory). 3. Hand-eye coordination example.
4.4.4 The Thalamus and Hypothalamus Epithalamus pineal gland Thalamus 1.
capillaries for cerebrospinal uid.
(a) Endocrine
2.
.
I/O for cerebrum.
(a) Specialized neurons for senses. (b) Sent to appropriate higher-brain center. (c) Emotion and arousal input.
3.
Thalamus homeostasis
.
(a) Posterior pituitary
→
anterior pituitary.
(b) Thermostat, hunger, thirst, survival instincts. (c) Sexual behavior, ight-or- ight, pleasure. (d) Pure pleasures (even at expense of eating and drinking)
11
. . . )).
The Hypothalamus and Circadian Rhythms. biological clock. Suprachiasmatic nuclei (SCN) 1. Strongly internal 2.
produce proteins in response to light/dark
cycle.
3. Light important: calibrate internal to external. Biological not quite 24hrs.
4.5 The cerebrum is the most highly evolved structure of the mammalian brain 1. 2. 3.
Cereberal hemispheres Basal nuclei Neocortex
covered with gray matter; cortex white.
deep in white matter.
mammalian-unique.
Outer layer of neurons tangential to
brain surface.
4. Convulations increase S.A. 5.
Corpus callosum
band of bers (white matter) communicate between
two hemispheres. 6.
Cognition:
process of knowing, awareness and judgment. No deep meta-
physical discussion in this book, darn.
4.6 Regions of the cerebrum are specialized for dierent functions Lobes: 1. Frontalsmell after going through primitive. (a) Motor cortexcommand skeleton. 2. Temporalhearing. (a) Somatosensory cortextouch. Proportion of motor/soma. devoted to part of body correlated with relative importance. 3. Occipitalvision. 4. Parietaltaste inside.
4.6.1 Integrative Function of the Association Areas 1. From thalamus
→
appropriate sensory area within lobe.
2. Association regions in frontal lobe 3.
Early
damage
→
→
response plan
functions shift elsewhere.
12
→
move skeletal.
4.6.2 Lateralization of Brain Function 1. Competing 2. Left:
f (n)
detailed
segregate into hemispheres.
perception; speed, linear.
3. Right: perception of
relationships/context.
4.6.3 Language and Speech
1. Frontal (Broca's area): generate. 2. Posterior temporal (Wernicke's area) comprehend. 3.
New stimuli use lots of resources and brain activity. Familiar → less brain activity.
4.6.4 Emotions → limbic system.
1. Hippocampus + olfactory cortex + some lobes + parts of (hypo)thalamus
2. Feeling to survival instinct. 3. Foundation for later development. 4. Primates born with caretaker emotionsrecognize face, express fear, anger, distress. . . (a) Learn what works to get food. (b) Distinguish morality (from external cues?)
tional memory.
5. Amygdalanucleus in temporal lobe recognize emotion in
face
and
emo-
(a) Emotional memory earlier than explicit. (b) Emotions integrated with neocortex. Emotional responses learned.
4.6.5 Memory and Learning Short-term Long-term memory 1.
in frontal.
2.
require hippocampus.
3. Memory accession
enhanced by:
(a) Reheasal (practice
→
perfect);
(b) Emotional state; (c) Association of new data with old.
13
4. Memorization of facts: rapid change in strength on existing nerve connection. 5. Learning of skills:
grow new connections.
(a) Skill memories not consciously recalled. 6. Di cult to unlearn. 7. 8.
Long-term depression Long-term potentiation
decreased response in postsynaptic cell. increased . . .
(a) Bombarded with actin potentials depolarized. (b)
New
action potential much
→ postsynaptic membrane strongly
greater eect.
9. This is what happens where learning?
4.6.6 Human Consciousness 1. Consciousness is emergent property that recruits cortex activity. 2. Scanning mechanisms unite into uni ed consciousness. . .
4.7 Research on neuron development and neural stem cells may lead to new approaches for treating CNS injuries and diseases CNS cannot repair.
4.7.1 Nerve Cell Development 1. How neurons grow w/o tangling? 2. Axons follow molecular signposts. 3.
Growth cone
responsive region at growing edge of axon.
(a) Repond attract or repel signal molecules. (b) Cell adhesion molecules bond to complements on surrounding cells.
4.7.2 Neural Stem Cells 1. Produced in hippocampus. 2. Must be from stem b/c mature cells can't divide. 3. Hey, I wrote a paper on the rest of this crap!
14
•
Often cooperate with endocrine and immune.
•
Survival, reproduction depends on fast response to environment.
•
Nucleus here means mass of neurons.
Contents
1 An Overview of the Nervous Systems 1.1
Nervous systems perform three overlapping functions of sensory
1.2
Networks of neurons with intricate connections form nervous sys-
input, integration, and motor output. . . . . . . . . . . . . . . . .
2.2
2
tems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
1.2.1
Neuron Structure and Synapses . . . . . . . . . . . . . . .
3
1.2.2
A Simple Nerve Circuitthe Re ex Arc . . . . . . . . . .
3
1.2.3
Types of Nerve Circuits
. . . . . . . . . . . . . . . . . . .
3
1.2.4
Supporting Cells (Glia)
. . . . . . . . . . . . . . . . . . .
4
2 The Nature of Nerve Signals 2.1
2
Every cell has a voltage, or membrane potential, across its plasma
4
membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
2.1.1
Measuring Membrane Potentials
4
2.1.2
How a Cell Maintains a Membrane Potential
. . . . . . . . . . . . . . . . . . . . .
4
Changes in the membrane potential of a neuron give rise to nerve impulses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2.2.1
Graded Potentials: Hyperpolarization adn Depolarization
5
2.2.2
The Action Potential: All or Nothing Depolarization . . .
2.3
Nerve impulses propagate themselves along an axon
. . . . . . .
2.4
Chemical or electrical communication between cells occur at synapses
5 5 6
2.4.1
Electrical Synpases . . . . . . . . . . . . . . . . . . . . . .
6
2.4.2
Chemical Synapses . . . . . . . . . . . . . . . . . . . . . .
6
2.5
Neural integration occurs at the cellular level
. . . . . . . . . . .
2.6
The same neurotransmitter can produce dierent eects on dif-
6
ferent types of cells . . . . . . . . . . . . . . . . . . . . . . . . . .
7
2.6.1
7
Acetylcholine
. . . . . . . . . . . . . . . . . . . . . . . . .
1
2.6.2
Biogenic Amines
. . . . . . . . . . . . . . . . . . . . . . .
7
2.6.3
Other Chemical Neurotransmitters . . . . . . . . . . . . .
8
2.6.4
Gaseous Signals of the Nervous System
8
3 Evolution and Diversity of Nervous Systems
. . . . . . . . . .
The ability of cells to respond to the environment has evolved . . . . . . . . . . . . . . . . . . . . . . . . .
8
3.2
Nervous systems show diverse patterns of organization . . . . . .
8
4.1
Vertebrate nervous system have central and peripheral components
4.2
The division of the peripheral nervous system interact in main-
4.3
Embryonic development of the vertebrate brain re ects its evo-
4.4
Evolutionarily older structures of the vertebrate brain regulate
over billions of years
4 Vertebrate Nervous Systems
taining homeostasis . . . . . . . . . . . . . . . . . . . . . . . . . . lution from three anterior bulges of the neural tube . . . . . . . . essential autonomic and integrative functions
9 9
9 10
. . . . . . . . . . .
10
. . . . . . . . . . . . . . . . . . . . . . . .
10
4.4.1
The Brainstem
4.4.2
The Reticular System, Arousal, and Sleep . . . . . . . . .
11
4.4.3
The Cerebellum
11
4.4.4
The Thalamus and Hypothalamus
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
4.5
The cerebrum is the most highly evolved structure of the mam. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
4.6
Regions of the cerebrum are specialized for dierent functions . .
12
malian brain
4.7
4.6.1
Integrative Function of the Association Areas . . . . . . .
12
4.6.2
Lateralization of Brain Function
. . . . . . . . . . . . . .
13
4.6.3
Language and Speech
. . . . . . . . . . . . . . . . . . . .
13
4.6.4
Emotions
. . . . . . . . . . . . . . . . . . . . . . . . . . .
13
4.6.5
Memory and Learning . . . . . . . . . . . . . . . . . . . .
13
4.6.6
Human Consciousness
14
. . . . . . . . . . . . . . . . . . . .
Research on neuron development and neural stem cells may lead to new approaches for treating CNS injuries and diseases
1
8
3.1
. . . .
14
4.7.1
Nerve Cell Development . . . . . . . . . . . . . . . . . . .
14
4.7.2
Neural Stem Cells
14
. . . . . . . . . . . . . . . . . . . . . .
An Overview of the Nervous Systems
1.1 Nervous systems perform three overlapping functions of sensory input, integration, and motor output. 1. Detect outside and inside signals. 2. Integration: interpret, respond. Continuous. (a)
Central nervous system
brain, spinal cord.
2
3.
Motor output
nervous system.
CNS
→
eector cells
(muscles, glands).
Peripheral
1.2 Networks of neurons with intricate connections form nervous systems
1.2.1 Neuron Structure and Synapses Cell body Dendrites receive. Axons send. 1.
nucleus and organelles.
2.
short, branched,
3.
long,
Only one.
(a) Some > 1m (spinal cord
→
foot).
Axon hillock Synaptic terminals neurotransmitter. Synapse Presynaptic postsynaptic 1.2.2 A Simple Nerve Circuitthe Re ex Arc (b)
joins cell body; cone.
(c)
relay via
(d)
contact other cell.
4.
: transmitter;
: receiver.
1. Automatic response. 2. 3.
Sensory neuron → motor neuron → eector cell. Interneurons
inhibit motor neurons to ensure re ex success.
(a) Decision: can resist re ex. 4. Gray matter: body. White matter: motor/sensory axons. 5.
Ganglion
cell bodies, similar in function. Called
lular!) in brains.
1.2.3 Types of Nerve Circuits 1. Signal diverges. 2. Signals converge: identify object: see, touch, hear. 3. Circular ow: memory.
3
nuclei
(not intracel-
1.2.4 Supporting Cells (Glia) 1. Gk.
glue.
2. Embryo: radial glia form tracks for neuron to grow. 3.
Astrocytes
structural, metabolic support.
(a) Blood-brain barrier.
4.
Oligodendrocytes
(central)/
Schwann cells
(peripheral) myelin sheath.
(a) Separate cells wrap axons. (b) Lipid
2
→
insulate.
The Nature of Nerve Signals 1. Galvani: frog muscles electric; 2. Hermann von Helmholtz: electricity between nerves carry signals.
2.1 Every cell has a voltage, or membrane potential, across its plasma membrane
2.1.1 Measuring Membrane Potentials Resting potential −70 1.
unstimulated;
mV.
2. Invertebrates have huge neurons (squid). Research.
2.1.2 How a Cell Maintains a Membrane Potential 1. Inside: K
+
and A
+
2. Outside: Na , Cl 3. More K
+
−
−
2−
(proteins, AAs, SO4
3−
, PO4
.
channels.
− 4. A cannot diuse. 5.
[K+ ] gradient competes with electrochemical.
librium.
+
(a) K
(b) Cell
wants to exit
−→
+
→
Cell
Membrane potential is equi-
−.
+
K enters.
(c) Simplest case, 6. Na
).
−85mV
equilibrium.
favored to enter cell (both
[]
and electro.).
+
(a) K exit because charge too high (−75
+ + (b) Na /K pump prevent.
4
mV
).
2.2 Changes in the membrane potential of a neuron give rise to nerve impulses
Excitable cells ∆ Gated ion channels Chemically-gated voltage-gated. 2.2.1 Graded Potentials: Hyperpolarization adn Depolarization Hyperpolarization Depolarization 1.
generate large
2.
. (Neuron, muscle).
open/close o stimuli. One channel, one stim., one
ion.
3.
or
1.
+ voltage. Open K
2.
+
reduce voltage: open Na
channel; exit; more neg.
+
channel.
3. Graded because magnitude depend on stimulus.
2.2.2 The Action Potential: All or Nothing Depolarization Threshold potential action potential. 1.
activates
Only axon.
(a) 50-55 mV. Only depolarize. Hyperpolarized inhibit. 2. Triggered by graded depolarization in dendrite/body. Spreads along membrane.
+
3. K : one gate opens during depolarization
+
slowly
slowly.
4. Na : fast activation gate during after depolarization; open inactivation gate closes 5. K
+
during depolarization.
+
trickle out; Na
(a) After spike, K
+
gush
in.
+
gush out (gates opened) and Na
back to pre-spike
permeability. (b) (c)
Hyperpolarize
because K
Refractory period:
+
gates slow.
+ Na activation gate remains closed (slow).
Can't respond. (d) Intensity
→
frequency.
2.3 Nerve impulses propagate themselves along an axon 1. Action potential regenerated like graded depolarization. 2. Na
+
in ux meets threshold
→
new action potential.
3. One way due to refractory period: axon behind is recovering. 4. Rate factors:
5
(a) Larger diameter
→
faster transmission. Electrical resistance.
(b) Channels concentrated in (c)
nodes of Ranvier
Saltatory conduction saltare
tential at nodes. +
(d) Na
(L.
leap).
.
Fasteronly action po-
current ows inside to nodes.
2.4 Chemical or electrical communication between cells occur at synapses 1. Neuron
→
→
neuron; sense receptor
sense neuron; neurons
→
gland.
2.4.1 Electrical Synpases 1. Spread action potential. 2. Gap junction
fast.
3. Crustaceans, sh.
2.4.2 Chemical Synapses Synaptic cleft Synaptic vesicles neurotransmitters. Presynaptic membrane 1.
narrow gap.
2.
contain
3.
2+
when depolarized causes Ca
to enter neuron
(voltage-gated channels).
4. Stimulates synaptic vesicles to fuse with membrane; spill. 5.
Postsynaptic membrane
has receptor speci c to transmitter, ion.
6. Depolarize or hyperpolarize. 7. Removed: enzymatic breakdown or takeup into adjacent cells. 8.
Guaranteed one-way.
2.5 Neural integration occurs at the cellular level 1.
Excitatory postsynaptic potential (EPSP) Inhibitory postsynaptic potential (IPSP)
electrical charge caused
by neurotransmitter binding. 2.
chemicals
tion.
−
(a) Can in ow Cl
−
or out ow K
3. Both graded.
6
.
→ depolariza-
4. One EPSP insu cient. 5.
Summation:
additive eect of PSPs.
(a) Temporal: PSPs very close together; one arrives before membrane rests. (b) Spatial: PSPs simultaneous. (c) Both E/IPSP. Counterbalance too. 6. Axon hillock integration center. Average of polarization and depolarization. 7.
Action potentials depend on quantitative information.
2.6 The same neurotransmitter can produce dierent effects on dierent types of cells 1. Some shortmillisecs. 2. Others long because use signal-transduction pathways in postsynaptic cell. 3. Some in brain active enough to spread to many synapses.
2.6.1 Acetylcholine Most common; (in)vertebrates. 1. Vert. central: both excit./inhib. 2. Neuromuscular: motor neuron
→
depolarize muscle.
+
3. Heart: inhibit adenyl cyclase + open K action potential
→
in muscle
→ less able to generate
reduce strength/rate of pulse.
2.6.2 Biogenic Amines From amino acids. 1. Catecholamines from 2.
tyrosine epinephrine, norepinephrine, dopamine.
Tryptophan → serotonin.
:
3. Usually central. (a) Norepinephrine autonomic.
7
2.6.3 Other Chemical Neurotransmitters GABA, glycine, glutamate, aspartate. Neuropeptides Substance P Endorphins 1. Amino acids:
GABA most
common inhibitor.
2.
short AA chains. Use signal-transduction.
(a)
pain.
(b)
analgesics.
Decrease urine, depress respiration, eu-
phoria.
3. Overlap between nervous and endocrine.
2.6.4 Gaseous Signals of the Nervous System 1. Sexual arousal: NOin penis 2. NO relaxes muscle
→
→
erection.
dialate blood vessel.
3. Synthesized on demand.
3
Evolution and Diversity of Nervous Systems
3.1 The ability of cells to respond to the environment has evolved over billions of years 1. Prokaryote sense improve survival/reproduction. 2. Cambrian explosion, nervous nearly modern.
3.2 Nervous systems show diverse patterns of organization 1. Neurons same; network dier. 2. Porifera lack nerves. 3. Cnidarians have
nerve net
around radial gastrovascular.
(a) Component of complex nervous systems.
4.
Cephalization Nerve cord
cluster sensory neurons, interneurons near anterior (brain)
in bilateral.
5.
longitudinal. First CNS.
6. Advanced: ventral nerve cord with ganglia, complex brain. 7. Chordate: nerve cord dorsal. 8. Correspond with role: sessile little cephalization and sense. Motile (squid) very responsive, smart.
8
4
Vertebrate Nervous Systems
4.1 Vertebrate nervous system have central and peripheral components 1. Spinal cord re ex. 2. CNS from hollow nerve cord of embryo. 3.
Central canal ventricles and
of brains lled with
cerebrospinal uid.
(a) Formed in brain: ltered blood. (b) Shock absorber for brain. (c) Meningesconnective tissue to protect brain, spinal.
4.
Gray matter
; dendrites, bodies.
4.2 The division of the peripheral nervous system interact in maintaining homeostasis 1. 2.
Cranial nerves Spinal nerves
orginiate in brain. Organs in head.
in spinal. Rest of body.
3. Most sensory and motor neurons. 4. Sensory (aerent): (a) External (b) Internal 5. Motor (eerent): (a) Autonomic: involuntary internal control i. Parasympathetic: claming (paralyze). Acetylcholine. ii. Sympathetic: exciting. Norepinephrine. (b) Somatic: voluntary skeletal muscles; external. 6. Cooperate for homeostasis:
autonomic constrict blood vessel; somatic
shiver.
9
4.3 Embryonic development of the vertebrate brain re ects its evolution from three anterior bulges of the neural tube 1. Forebrain
Cerebrum Cereberal cortex
(a) Telencephalon i.
fanciest.
convulted gray matter.
(b) Diencephalonthalamus, hypothalamus, epithalamus i. Earliest vertebrate evolution. 2. Midbrain (a) Mesencephalonpart of brainstem. 3. Hindbrain (mostly brainstem) (a) Metencephalonpons,
cerebellum.
(b) Myelencophalonmedulla oblongata.
4.4 Evolutionarily older structures of the vertebrate brain regulate essential autonomic and integrative functions
4.4.1 The Brainstem
Homeostasis, coordinate movement, conduct to higher brain.
The Medulla and Pons. 1. Axons to cereberal cortex, cerebellum. 2.
Medulla pons visceral f (n) and
3. Higher sensory
pass through.
: breathe, cardiovascular, digestive.
4. Right/left brain crossover here.
The Midbrain. 1. Receive, integrate sense. 2. Relay sensory to speci c forebrain regions. 3. Inferior cullicoli: hearing; 4. Superior cullicoli: vision. Only vision center in nonmammals; re exes in mammal.
10
4.4.2 The Reticular System, Arousal, and Sleep 1. 2.
Arousal
awareness. Cmp.
Reticular formation
sleep
.
90 nuclei in core.
(a) Reticular activating system (RAS) (b) More input
→
lters input
more aroused.
(c) Can lter speci c noise (like Herman talking (
3.
Electroencephalogram EEG (
(a) Less activity (b) Fast
β
→
to cerebral cortex.
probably not really
) record electrical brain activity.
more synchronous waves (α).
for thinking.
(c)
θ
early sleep (irregular).
(d)
δ
deep sleep synchronized waves.
4.4.3 The Cerebellum 1. Coordination, error-checking during motor, perception, cognition. 2. Learn, remember motor sequence (muscle memory). 3. Hand-eye coordination example.
4.4.4 The Thalamus and Hypothalamus Epithalamus pineal gland Thalamus 1.
capillaries for cerebrospinal uid.
(a) Endocrine
2.
.
I/O for cerebrum.
(a) Specialized neurons for senses. (b) Sent to appropriate higher-brain center. (c) Emotion and arousal input.
3.
Thalamus homeostasis
.
(a) Posterior pituitary
→
anterior pituitary.
(b) Thermostat, hunger, thirst, survival instincts. (c) Sexual behavior, ight-or- ight, pleasure. (d) Pure pleasures (even at expense of eating and drinking)
11
. . . )).
The Hypothalamus and Circadian Rhythms. biological clock. Suprachiasmatic nuclei (SCN) 1. Strongly internal 2.
produce proteins in response to light/dark
cycle.
3. Light important: calibrate internal to external. Biological not quite 24hrs.
4.5 The cerebrum is the most highly evolved structure of the mammalian brain 1. 2. 3.
Cereberal hemispheres Basal nuclei Neocortex
covered with gray matter; cortex white.
deep in white matter.
mammalian-unique.
Outer layer of neurons tangential to
brain surface.
4. Convulations increase S.A. 5.
Corpus callosum
band of bers (white matter) communicate between
two hemispheres. 6.
Cognition:
process of knowing, awareness and judgment. No deep meta-
physical discussion in this book, darn.
4.6 Regions of the cerebrum are specialized for dierent functions Lobes: 1. Frontalsmell after going through primitive. (a) Motor cortexcommand skeleton. 2. Temporalhearing. (a) Somatosensory cortextouch. Proportion of motor/soma. devoted to part of body correlated with relative importance. 3. Occipitalvision. 4. Parietaltaste inside.
4.6.1 Integrative Function of the Association Areas 1. From thalamus
→
appropriate sensory area within lobe.
2. Association regions in frontal lobe 3.
Early
damage
→
→
response plan
functions shift elsewhere.
12
→
move skeletal.
4.6.2 Lateralization of Brain Function 1. Competing 2. Left:
f (n)
detailed
segregate into hemispheres.
perception; speed, linear.
3. Right: perception of
relationships/context.
4.6.3 Language and Speech
1. Frontal (Broca's area): generate. 2. Posterior temporal (Wernicke's area) comprehend. 3.
New stimuli use lots of resources and brain activity. Familiar → less brain activity.
4.6.4 Emotions → limbic system.
1. Hippocampus + olfactory cortex + some lobes + parts of (hypo)thalamus
2. Feeling to survival instinct. 3. Foundation for later development. 4. Primates born with caretaker emotionsrecognize face, express fear, anger, distress. . . (a) Learn what works to get food. (b) Distinguish morality (from external cues?)
tional memory.
5. Amygdalanucleus in temporal lobe recognize emotion in
face
and
emo-
(a) Emotional memory earlier than explicit. (b) Emotions integrated with neocortex. Emotional responses learned.
4.6.5 Memory and Learning Short-term Long-term memory 1.
in frontal.
2.
require hippocampus.
3. Memory accession
enhanced by:
(a) Reheasal (practice
→
perfect);
(b) Emotional state; (c) Association of new data with old.
13
4. Memorization of facts: rapid change in strength on existing nerve connection. 5. Learning of skills:
grow new connections.
(a) Skill memories not consciously recalled. 6. Di cult to unlearn. 7. 8.
Long-term depression Long-term potentiation
decreased response in postsynaptic cell. increased . . .
(a) Bombarded with actin potentials depolarized. (b)
New
action potential much
→ postsynaptic membrane strongly
greater eect.
9. This is what happens where learning?
4.6.6 Human Consciousness 1. Consciousness is emergent property that recruits cortex activity. 2. Scanning mechanisms unite into uni ed consciousness. . .
4.7 Research on neuron development and neural stem cells may lead to new approaches for treating CNS injuries and diseases CNS cannot repair.
4.7.1 Nerve Cell Development 1. How neurons grow w/o tangling? 2. Axons follow molecular signposts. 3.
Growth cone
responsive region at growing edge of axon.
(a) Repond attract or repel signal molecules. (b) Cell adhesion molecules bond to complements on surrounding cells.
4.7.2 Neural Stem Cells 1. Produced in hippocampus. 2. Must be from stem b/c mature cells can't divide. 3. Hey, I wrote a paper on the rest of this crap!
14
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