Download Chapter 24 Nervous Systems

Chapter 24 Nervous Systems
Nervous System
Structure and Function
Nerve Signals and
Their Transmission
Neurons receive and process inputs
and communicate responses.
Nerve signals are electrical messages generated
by the movement of ions across membranes.
An Overview of Animal
Nervous Systems
The vertebrate nervous system can be understood
as a structural and functional hierarchy.
The Human Brain
Modern research techniques are illuminating how
the interplay of brain regions controls our actions
and behavior.
Nervous systems receive sensory input, interpret it,
and send out appropriate commands
Sensory input
Integration
感受器
Sensory receptor
Motor output
Brain and spinal cord
作用細胞
Effector cells
Muscle
Gland cells
Peripheral nervous
system (PNS)
周邊神經系統
Central nervous
system (CNS)
中樞神經系統
Organization of a nervous system
Analysis
Interpretation
Nervous systems
12 pairs
31 pairs
神經元
星狀神經膠細胞
寡突膠細胞
Nerve & Ganglia in the PNS
神經節
Ganglia (ganglion):
clusters of neuron cell bodies.
神經
Nerve: a bundle of neurons
tightly wrapped in
connective tissue.
Sensory neurons 感覺神經元
- convey signals from sensory receptors to the CNS.
Interneurons 連絡神經元
- are located entirely in the CNS.
- integrate information, and send it to
other interneurons/motor neurons.
Motor neurons 運動神經元
- convey signals to effector cells.
The knee-jerk reflex 膝躍反射
1
Sensory
receptor
2
Sensory
neuron
Brain
Ganglion
Motor
neuron
Spinal
cord
3
Quadriceps
muscles
4
Interneuron
Nerve
Flexor
muscles
PNS
CNS
Neurons are the functional units of nervous systems
神經元
 Neurons are
- cells specialized for carrying signals.
- the functional units of the nervous system.
 A neuron consists of
- a cell body. 細胞本體
- two types of extensions (fibers) that conduct signals:
- numerous dendrites. 樹突
- single axon. 軸突
 Myelin sheaths
髓鞘
- enclose axons.
- form a cellular insulation.
- speed up signal
transmission.
Structure of a myelinated motor neuron
Signal direction
Cell body
Nucleus
蘭氏結
Signal
pathway
Node of Ranvier
Layers of
myelin
Nodes of
Ranvier
Myelin
sheath
Dendrites
Cell
body
許旺細胞
突觸末(端)稍
Schwann
cell
Synaptic
terminals
Nucleus
Axon
突觸
Schwann
cell
Transmission of the action potential 動作電位
150 m/sec
Glia cells 神經膠細胞
Glia supporting cells:
(1) noruish neoruns
(2) insulate the axons of neurons
(3) maintain homeostasis of the extracellular fluid surrounding neurons.
微膠細胞
星狀神經膠細胞
寡突膠細胞
管膜細胞
Multiple sclerosis (MS) 多發性硬化症
Autoimmune disease
by Tc cells
Nerve function depends on charge differences
across neuron membranes
 At rest, a neuron’s
plasma membrane has potential energy,
膜電位
the membrane potential: exists as an electrical charge difference
across the neuron’s plasma membrance.
in which
- just inside the cell is slightly negative.
- just outside the cell is slightly positive.
靜止電位
 The resting potential is the voltage
across the plasma membrane of
a resting neuron. (about -70 mV).
 The membrane potential can change
from its resting value if the
membrane’s permeability to
particular ion changes.
How the resting potential is generated
Neuron
Axon
Plasma
membrane
Outside of neuron
Na
Na
Na
Na
K
K
Na
channel
Na
Na
Na
Na
K
Na
Na
Na
Na-K
pump
K
K
Plasma
membrane
Na
Na
Na
Na
Na
Na+ is high
k+ is low
ATP
K channel
K
Na
K
K
Na
Na
K
K
Inside of neuron
K
K
K
K
K
K
K
K+ is high
Na+ is low
How stimuli trigger signals in a living neuron?
A nerve signal begins as a change
in the membrane potential
 A stimulus is any factor that causes a nerve signal to be generated.
A stimulus
- alters the permeability of a portion of the membrane.
- allows ions to pass through.
- changes the membrane’s voltage.
動作電位
 A nerve signal, called an action potential, is
-a change in the membrane voltage.
動作電位
-from the resting potential to a maximum level.
-back to the resting potential.
Hyperpolarization
過極化
The action potential
Na
Na
Na
Na
K
Additional Na channels
open, K channels are
closed; interior of cell
becomes more positive.
Na
50
Membrane potential
(mV)
3
Na
K
2
Na
Sodium Potassium
channel channel
Action
potential
3
0
閥值
4
Na channels close
and inactivate; K
channels open, and
K rushes out;
interior of cell is more
negative than outside.
5
The K channels
close relatively
slowly, causing a
brief undershoot.
4
2
50 Threshold
1
100
Resting potential
5
1
Time (msec)
A stimulus opens some Na
channels; if threshold is reached,
an action potential is triggered.
Na
K
Outside
of neuron
Na
Na
Plasma membrane
K
1
Resting state: Voltage-gated Na
and K channels are closed;
resting potential is maintained by
ungated channels (not shown).
K
Inside of neuron
1
Return to resting
state.
Action potentials are all-or-none events
全有全無律
絕對不反應期
相對不反應期
去極化
再極化
過極化
The action potential propagates itself along the axon
 Action potentials are
- self-propagated in a one-way chain reaction along a neuron.
- all-or-none events.
 The frequency of action potentials (but not their strength)
changes with the strength of the stimulus.
Propagation of the action potential along the axon
Axon
Na
Plasma
membrane
Action
potential
Axon
segment
1
Na
Action potential
Na
K
2
K
Na
Action potential
Na
K
3
K
Na
Neurons communicate at synapses
突觸
 Synapses are junctions where signals are transmitted between
two neurons or between neurons and effector cells.
電位突觸
 Electrical signals pass between cells at electrical synapses.
化學突觸
 At chemical synapses
- the ending (presynaptic) cell secretes a chemical signal,
a neurotransmitter. 神經傳遞物質
- the neurotransmitter crosses the synaptic cleft. 突觸間隙
- the neurotransmitter binds to a specific receptor on the surface
of the receiving (postsynaptic) cell.
Electrical synapses
Two types of synapses
Chemical synapses
Neuron communication at a typical chemical synapse (1)
1
Sending cell
Axon of
sending
cell
Synaptic
terminal
of sending
cell
Action
potential
arrives
Synaptic
vesicles
Synaptic
terminal
2
Vesicle fuses
with plasma
membrane
Dendrite
of receiving
cell
3
Neurotransmitter
is released into
synaptic cleft
Synaptic
cleft
4
Receiving
cell
Neurotransmitter
binds to receptor
Ion channels
Neurotransmitter
molecules
Neuron communication at a typical chemical synapse (2)
Neurotransmitter
Receptor
Neurotransmitter broken
down and released
Ions
5
Ion channel opens
6
Ion channel closes
Chemical synapses enable complex information
to be processed
 Some neurotransmitters excite a receiving cell, and others
inhibit a receiving cell’s activity by decreasing its ability to
develop action potentials.
 A receiving neuron’s membrane may receive signals
- that are both excitatory and inhibitory.
- from many different sending neurons.
 The summation of excitation and inhibition determines if a neuron
will transmit a nerve signal.
A neuron’s multiple synaptic inputs
Synaptic terminals
Dendrites
Inhibitory
Excitatory
Myelin
sheath
Receiving
cell body
Axon
Hillock
Synaptic
terminals
Synaptic intergration
Na+ channels (in)
Excitatory postsynaptic potential
興奮性突觸後電位
抑制性突觸後電位
Inhibitory postsynaptic potential
K+ channels (out)
Cl- channels (in)
A variety of small molecules function
as neurotransmitters
乙醯膽鹼
 Acetylcholine is a neurotransmitter in the brain and at synapses
between motor neurons and muscle cells.
(Excitatory in skeletal muscles contraction; inhibitory in cardiac muscles contraction)
谷氨酸
-丁氨基酪酸(Gama-aminobutyric acid)
甘氨酸
 Amino
acids
glutamate
(+),
glycine
(-),
and
GABA
(-)
in
CNS.
生物胺
 Biogenic amines - norepinephrine, serotonin,
and dopamine
in
血清素
多巴胺
正腎上腺素
CNS. Serotonin and dopamine affect sleep, mood, attention, and
learning.
(Lack of dopamine  Parkinson’s disease; Lack of serotonin and noerpinephrine  depression)
神經胜肽
 Many neuropeptides - consist of relatively short chains of amino
acids important in the CNS and include 腦內啡
endorphins, decreasing
our perception of pain.
 Nitric oxide is a dissolved gas and triggers erections during
sexual arousal in men. The erectile dysfunction drug Viagra
promotes release NO into blood vessels in the erectile tissue of
the penis.
Classes of neurotransmitters
兒茶酚胺激素
吲哚胺
Botulinum toxin inhibits the release of ACh
肉毒桿菌素
Many drugs act at chemical synapses
 Many psychoactive drugs act at synapses
and affect neurotransmitter action.
- Caffeine counters the effect of inhibitory neurotransmitters.
- Nicotine acts as a stimulant by binding to acetylcholine receptors.
- Alcohol is a depressant.
(increase the inhibitory effects of the neurotransmitter GABA)
Selective serotonin reuptake inhibitors (SSRIs)
選擇性血清素回收抑制劑
Tranquilizers activate the receptors for GABA
鎮靜劑
Benzodiazepine increasing GABA’s effect at inhibitory synapses
安眠藥：苯重氮基鹽
Adderall = “study drug”
Block the reuptake of dopamine and norepinephrine,
which can increase alertness.
Illegal drugs
Opiates
Stimulants
Amphetamines, cocaine
Bind to endorphin receptors
Reducing pain
&
Producing euphoria
Increase the
release and availability
of norepinephrine and
dopamine at synapses
The evolution of animal nervous systems
reflects changes in body symmetry
輻射對稱
 Radially symmetrical animals have a nervous system arranged in a
diffuse, weblike system of neurons called a nerve net.
兩側對稱
 Most bilaterally symmetrical animals evolved
- cephalization, the concentration of the nervous system
at the head end (sense organs, brain). 頭部集中(專)化
- centralization, the presence of a central nervous system distinct
from a peripheral nervous system. 集中管理
Invertebrate nervous systems
Eyespot
Brain
Nerve
cord
Nerve
net
Transverse
nerve
Neuron
Hydra (cnidarian)
Brain
Ventral
nerve
cord
Segmental
ganglion
Leech (annelid)
Flatworm (planarian)
Brain
Ventral
nerve
cord
Brain
Giant
axon
Ganglia
Insect (arthropod)
Squid (mollusc)
Vertebrate nervous systems are highly centralized
 In the vertebrates, the central nervous system (CNS)
- consists of the brain and spinal cord.
腦脊液
- includes spaces filled with cerebrospinal fluid.
- forming ventricles of the brain.
腦室
中央管
- forming the central canal of the spinal cord.
- surrounding the brain.
 The vertebrate peripheral nervous system (PNS) consists of
- cranial nerves (12 pairs).
- spinal nerves (31 pairs).
- ganglia.
A vertebrate nervous system
Central
nervous
system
(CNS)
Brain
Spinal
cord
Cranial
nerves
Ganglia
outside
CNS
Spinal
nerves
Peripheral
nervous
system
(PNS)
Fluid-filled spaces of the vertebrate CNS
(nerve cell bodies & dendrites)
Gray matter
Brain
Cerebrospinal fluid
Meninges
(axons)
White
matter
Central canal
Ventricles
Central canal
of spinal cord
Spinal cord
背根神經結
Dorsal root
ganglion
(part of PNS)
Spinal nerve
(part of PNS)
Spinal cord
(cross section)
Blood-brain barrier (BBB)
血腦障壁
The peripheral nervous system of vertebrates
is a functional hierarchy
 The PNS can be divided into two functional components:
- the motor system, mostly voluntary.
- the autonomic nervous system, mostly involuntary.
自主神經系統
 The motor nervous system
- carries signals to and from skeletal muscles.
- mainly responds to external stimuli.
 The autonomic nervous system
- regulates the internal environment.
- controls smooth and cardiac muscle and organs and glands of
the digestive, cardiovascular, excretory, and endocrine systems.
The autonomic nervous system
is composed of three divisions
“rest and digest”
1. The parasympathetic division primes the body for activities
that gain and conserve energy for the body.
交感神經系“fight-or-flight”
2. The sympathetic division prepares the body for intense,
energy-consuming activities.
副交感神經系
腸道神經系
3. The enteric division consists of networks of neurons in the
digestive tract, pancreas, and gallbladder that control
secretion and peristalsis.
Cooperate to maintain homeostasis.
Functional divisions of the vertebrate PNS
Brain
Peripheral nervous system
(to and from the central
nervous system)
Motor system
(voluntary and
involuntary; to and from
skeletal muscles)
Autonomic nervous system
(involuntary; smooth and
cardiac muscles, various glands)
Spinal cord
Parasympathetic
division
(“Rest and digest”)
Sympathetic
division
(“Fight and flight”)
Enteric division
(muscles and glands
of the digestive system)
Antagonistic opposite effects
Sympathetic division
Parasympathetic division
norepinephrine
acetylcholine
Brain
Eye
Dilates pupil
Constricts pupil
Salivary
glands
Stimulates
saliva
secretion
Inhibits
saliva
secretion
Lung
Relaxes
bronchi
Constricts
bronchi
Slows
heart
Accelerates
heart
Heart
Adrenal
gland
Spinal
cord
Liver
Stomach
Stimulates
stomach,
pancreas,
and intestines
Pancreas
Stimulates
epinephrine
and norepinephrine release
Stimulates
glucose release
Inhibits
stomach,
pancreas,
and intestines
Intestines
Bladder
Stimulates
urination
Inhibits
urination
Promotes
erection of
genitalia
Promotes ejaculation and vaginal
contractions
Genitalia
Cooperation
The vertebrate brain develops from
three anterior bulges of the neural tube
大腦
Cerebrum
Midbrain
Hindbrain
Diencephalon 間腦
Midbrain 中腦
Pons 橋腦
Cerebellum 小腦
Medulla 延腦
oblongata
Forebrain
Embryo (1 month old)
Spinal cord 脊髓
Fetus (3 months old)
In the course of vertebrate evolution, the forebrain and hindbrain
gradually become subdivided both structurally and functionally.
Embryonic development of the human brain
Embryonic
Brain Regions
Brain Structures
Present in Adult
Cerebrum (cerebral hemispheres; includes
cerebral cortex, white matter, basal ganglia)
Forebrain
Diencephalon (thalamus, hypothalamus,
posterior pituitary, pineal gland)
Midbrain
Midbrain (part of brainstem)
Pons (part of brainstem), cerebellum
Hindbrain
Medulla oblongata (part of brainstem)
The main parts of the human brain
Cerebral cortex
(outer region
of cerebrum)
Cerebrum
Forebrain
Thalamus
Hypothalamus
pituitary gland
body temperature
blood pressure
hunger
thirst
sex drive
fight-or-flight responses
emotions
Pituitary gland
Midbrain
Hindbrain
Brainstem
Pons
Medulla
oblongata
Cerebellum
Spinal
cord
The rear view of the brain
- the largest and most complex part of the brain.
- most of the cerebrum’s integrative power resides in the
cerebral cortex of the two cerebral hemispheres.
each responsible for the opposite side of the body
Left cerebral
hemisphere
Right cerebral
hemisphere
Thalamus
Cerebrum
contains most of the cell bodies of
neurons that relay information to
the cerebral cortex
Cerebellum
a planning center fir body movement
facilitates communication
between the hemispheres
Corpus
callosum
胼胝體
Basal
nuclei
基底核 motor coordination
Medulla
(Parkinson’s disease )
oblongata
Major structures of the human brain
The cerebral cortex is a mosaic of
specialized, interactive regions
 The cerebral cortex
- is less than 5 mm thick.
- accounts for 80% of the total human brain mass.
 Specialized integrative regions of the cerebral cortex include
the somatosensory cortex and centers for vision, hearing, taste,
and smell. 體感覺皮質區
 The motor cortex directs responses.
運動皮質區
 Association areas 聯合區
make up most of the cerebrum and are concerned
with higher mental activities such as reasoning and language.
偏側化
 In a phenomenon known as lateralization, right and left
cerebral hemispheres tend to specialize in different mental tasks.
Functional areas on the left cerebral hemisphere
頂葉
額葉
Frontal lobe
Parietal lobe
Frontal
association
area
Speech
Somatosensory
association
area
Reading
Speech
Hearing
Smell
Auditory
association
area
Visual
association
area
Vision
顳葉
Temporal lobe
Occipital lobe
枕葉
Einstein’s Brain
Injuries and brain operations provide insight
into brain function
Broken brains
Computer model of Phineas Gage’s injury
X-ray of hemispherectomy patient after surgery
fMRI scans provide insight into
brain structure and function
功能性核磁造影
Functional magnetic resonance imaging (fMRI) is
- a scanning and imaging technology used to study brain functions.
- used on conscious patients,
- monitors changes in blood oxygen usage in the brain.
- correlates to regions of intense brain function.
Comparative human fMRI images showing regions of brain activity
in healthy veterans (left) and veterans with Gulf War syndrome (right)
when performing the same task
Several parts of the brain regulate sleep and arousal
 Sleep and arousal involve activity by the
- hypothalamus.
- medulla oblongata.
- pons.
- neurons of the reticular formation.
EEG (electroencephalogram)
 Sleep
- is essential for survival.
- is an active state (REM sleep).rapid eye movement
- may be involved in consolidating learning and memory.
The reticular system
網狀結構
The reticular formation is a diffuse network of neurons containing over
90 separate clusters of cell bodies, that is present in the brainstem.
Acting as a sensory filter.
邊緣系統 The limbic system is involved in
emotions, memory, and learning
下視丘
視丘
Thalamus
Hypothalamus
Cerebrum
Prefrontal
cortex
Smell
Olfactory
bulb
Amygdala
杏仁核
Hippocampus
海馬迴
The limbic system (shown in shades of gold)
Memory
Changes in brain physiology can produce
neurological disorders - Schizophrenia
精神分裂症
Schizophrenia is (1% of the population)
- a severe mental disturbance.
- characterized by psychotic episodes in which patients lose the
ability to distinguish reality.
妄想症
幻覺
語無倫次
緊張性情神分裂症
情感平淡
Mechanism unknown.
Strong genetic component.
Changes in brain physiology can produce
neurological disorders - Depression憂鬱症
(2/3 are women)
 Two broad forms of depressive illness have been identified:
重鬱症- major depression.
躁鬱症
(1% of the population)
雙相障礙- bipolar disorder (manic-depressive disorder).
 Treatments may include selective serotonin reuptake inhibitors
(SSRIs), which increase the amount of time serotonin is available
to stimulate certain neurons in the brain.
PET scans showing brain activity in a
depressed person (top)
and healthy person (bottom).
SSRI prescriptions in the United States.
Changes in brain physiology can produce
neurological disorders - Alzheimer’s Disease
阿茲海默症(老年痴呆症)
Alzheimer’s disease is
- characterized by confusion, memory loss, and personality change.
- difficult to diagnose.
- neurons die in huge areas of the brain, and brain tissue often
shrinks.
- 10% at age 65 to about 35% at age 85.
Two features 神經纖維糾結
- neurofibrillary tangles (NFTs) are bundles of a protein called tau.
- senile plaques are aggregates of beta-amyloid, an insoluble
老化斑塊
peptide of 40 to 42 amino acids. 類澱粉胜肽
Changes in brain physiology can produce
neurological disorders - Parkinson’s Disease
帕金森氏症
Parkinson’s disease is
- a motor disorder.
- 1% at age 65 to about 5% at age 85.
- characterized by
(1) difficulty in initiating movements.
(2) slowness of movement.
(3) rigidity.
- death of neuron (dopamine release)
in the basal nuclei (substantia
nigra).
- environmental and genetic factors.