Download Chapter 32 The Nervous System, Cells of the Nervous System

Chapter 32
The Nervous System,
Cells of the Nervous
System
D Detect
changes in body’s internal
and external environment
D Interpret meanings of those
changes
D Respond by sending appropriate
signals to the organs of the body
行為的基礎
生存的條件
Nervous
System of
Human
＊CNS中樞 Brain
Spinal cord
＊Peripheral 周圍
nervous system –
connects brain and
spinal cord to sense
organs, muscles
＊Protecting in is
called meninges 膜
Nervous System Cells
D
D
Neurons神經元 — carry information
Glial cells膠質細胞 — sustain neurons
Neurons 神經元
Nerve cells specialized to generate &
transmit nerve impulses神經衝動.
1. Anatomy
•
•
•
cell body - central portion; contains
organelles.
dendrites樹突 - short, branched
extensions; transmit impulses toward cell
body.
axon軸突 - long, unbranched extension;
transmits impulses away from cell body.
•
A nerve is composed of a bundle of axons
or dendrites.
2. Classification
•
sensory neuron - conducts information
inward, from sensory receptors to the
central nervous system (CNS).
•
•
motor neuron - conducts information
outward, from CNS to effectors 動器
(muscle or gland).
interneuron - conducts information
within the CNS; forms link between
sensory & motor neurons.
Nerve Impulses神經衝動
D Carried
by ions moving across cell
membranes
D Neurons have threshold閥值, lowest
stimulus that causes reaction
D Differences in intensity of stimulus
indicated by:
) Number of impulses per second
) Number of cells responding
1. Conditions in a “Resting” Neuron
•
(not conducting an impulse)
Cell membrane is polarized (charged).
Resting potential = -70 mV (millivolts)
Interior of neuron is
negative relative to
exterior because of
unequal distribution
of ions.
Resting Potential靜止電位
D Inside
of cell
contains fewer
sodium ions(鈉),
more
potassium(鉀)
Unequal
distribution
of ions is
due to:
•
selective permeability of membrane
•
•
•
Na+/K+ pump
•
D
more permeable to K+ than Na+
impermeable to negatively charged
proteins
pumps 3 Na+ out for every 2 K+ in
Sodium potassium pumps maintain uneven
distribution
What would happen to resting potential if...
• Na+ flooded into neuron?
• K+ flooded out of neuron?
• equal numbers of Na+ & K+ exchanged
places across membrane?
2. Generation & Conduction of an
Impulse (action potential)
•
Stimulus causes Na+ to leak into neuron;
membrane depolarizes去極化.
If membrane potential reaches -50 mV
[threshold potential ], Na+ gates pop open,
and Na+ rush into neuron.
Membrane
potential
increases
to +35 mV.
Action Potential動作電位
D Upon
stimulation, sodium channels open
D Inside of cell positively charged in
localized region
Action Potential 2
D Within
milliseconds, sodium channels
close, potassium channels open
D As potassium leaves, restores resting
potential
D Cell cannot
respond
for short
time —
refractory
period不反
應期
•
•
Na+ gates snap shut.
K+ gates pop open, and K+ rush out of
neuron; membrane repolarizes再極化.
Membrane potential
returns to negative
value; temporarily
drops below -70 mV
(hyperpolarized).
•
Na+/K+ pump reestablishes the resting
potential (-70 mV); returns Na+ to
outside & K+ to inside of neuron.
D Voltage電壓
is called potential
(potential energy difference)
D Resting potential — difference in
charge across membrane in resting
cell
D During nerve impulse, change in
voltage across membrane — action
potential — due to ion movement
D Impulse moves along axon as wave
(depolarization)去極化, repolarizes再
極化 as wave passes
Sodium-Potassium Pump
鈉鉀唧筒
D Maintains
resting potential
D Restores ion differences after
impulse
D Resting potential depends on
gradient of potassium ions
D Action potential depends on
gradient of sodium ions
Electrical changes occurring during an
action potential.
Na+ gates close &
K+ gates open
Na+ gates open
Stimulus
K+ gates close
Threshold
potential
Action potentials travel like waves along
a neuron, usually from dendrite -> cell
body -> axon.
Speed of conduction depends on:
• neuron diameter
• saltatory conduction跳躍式
朗氏結 200m/sec.
Myelin Sheath髓鞘
D Nodes
of Ranvier
D Speeds nerve
conduction 100X
) Action potential only
at nodes, saltatory
跳躍conduction
) Axons less leaky
D Multiple Sclerosis多發
性硬化症
Neurotransmitters神經傳導物質
Chemicals that relay information from a neuron
to a receptor cell (another neuron or an effector).
Transmitting neuron
(Presynaptic neuron)
Receiving neuron
(Postsynaptic neuron)
Axon
Synapse
Direction of action potential
Stored in synaptic vesicles of axon
terminals.
Synapses突觸
D Connections
between neurons
D Sending cell is presynaptic cell
D Receiving cell is postsynaptic cell
D Electrical synapse — cells have gap
junctions, ions diffuse through
D Chemical synapse — cells separated
by synaptic cleft裂隙,
neurotransmitter神經傳導物
molecules diffuse across for signal
Synapse
Kinds of Neurotransmitters
acetylcholine乙醯膽胺(Ach)
• adrenaline, noradrenaline, dopamine & serotonin
[amino acid derivatives]正腎上腺素(Ne)
• glycine, glutamic acid, aspartic acid & GABA
[amino acids]
Neurotransmitters send excitatory &/or inhibitory
messages to receptor cells.
Drugs can alter neurotransmitter levels.
Neurotransmitter imbalance can cause disease.
•
D Neurotransmitters
can have
different effects on different cells
D Acetylcholine
)Nicotinic尼古丁 receptors cause
contractions in skeletal muscles
)Muscarinic毒蕈鹼 receptors cause
inhibition in smooth muscle and
heart muscle
Inhibitory Neurotransmitters
D Open
+
-
channels that allow K or Cl
passage, increase negative
potential — hyperpolarize
D Negative voltage inhibits
formation of action potential
D GABA酒精 most common
inhibitory neurotransmitter
癲癇
Ending Signal
D Neurotransmitters
must be
cleared from the synaptic cleft
after impulse
)Diffusion
)Reuptake
)Enzymatic breakdown
Postsynaptic Cell
D Sodium
ion flows into
postsynaptic cell
D Depolarization triggers
contraction in muscle cell
D Single impulse may not reach
threshold; multiple neurons may
stimulate same cell
Postsynaptic cell receives input from
thousands of neurons.
Generation of an action potential depends
on sum of excitatory & inhibitory inputs.
Vertebrate
nervous system
Human Central Nervous System
Protected by bone (skull & vertebrae),
meninges (layers of connective tissue)膜 &
cerebrospinal fluid.
1. Spinal Cord
•
•
extends from brain
to just below last
rib (~17 inches).
composed of gray &
white matter.
•
•
conducts information to and from the
brain (ascending & descending tracts).
is a reflex center (allows body to respond
to stimuli without input from brain).
The reflex
arc
Paralysis
癱瘓
2. Brain - is subdivided into hindbrain,
midbrain & forebrain.
Forebrain–Vertebrate Brain
D Forebrain
— locus
of all conscious
activity
D Divisions:
) Cerebrum大
™ Cerebral
cortex
) Diencephalon間
™ Thalamus視丘
™ Hypothalamus下視丘
•
Cerebellum
•
•
•
coordinates muscular movements.
Hypothalamus
• regulates activity of pituitary gland.
• regulates body temperature & water
balance.
• contains hunger & thirst centers.
Thalamus
• major relay station for sensory input
going to cerebrum.
Midbrain-Vertebrate Brain
D Midbrain
relays
整合 sensory
information,
helps organize
movement and
regulates
attention
D Brain stem腦幹
Hindbrain-Vertebrate Brain
D Hindbrain
integrates and
processes both
sensory
information and
motor
instructions
D 3 parts: pons橋,
medulla
oblongata延,
cerebellum小
•
•
•
Brain Stem
Midbrain中腦
• contains visual & auditory reflex
centers.
Medulla oblongata延腦
• regulates heart rate, blood pressure
& breathing.
• contains reflex centers for vomiting,
swallowing, sneezing & hiccoughing.
Pons 橋腦
• helps regulate respiration.
•
Reticular formation 網狀構造
•
•
•
extends through the brainstem
and thalamus
screens and filters sensory
information going to the cerebrum
邊看電視邊讀書
sleep occurs when reticular
formation neurons are not active
due to inhibition by other neurons
Cerebrum大腦
Seat of intelligence, learning, emotion
& perception.
Taste
Smell
Frontal lobes contain額葉:
• olfactory cortex - interprets smell.
• primary motor cortex - controls
actions of voluntary muscles.
Parietal lobes contain頂葉:
• gustatory cortex - interprets taste.
• primary sensory cortex - receives
sensory input (pain, temperature, touch)
from the skin.
Temporal lobes contain顳葉:
• auditory cortex - interprets sound.
Occipital lobes contain枕葉:
• visual cortex - interprets sight.
In most individuals:
• Left hemisphere specializes in speech,
linguistic skills, mathematical ability &
reasoning.
• Right hemisphere specializes in spatial,
intuitive, musical & artistic abilities.
Organization of Peripheral周圍
Nervous System
D Connects
CNS to sense organs and
muscles
D Includes nerves of:
)Autonomic nervous system自主
™Carries
instructions to endocrine organs,
smooth and cardiac muscles
)Somatic
™Carries
nervous system體壁
information to voluntary muscles
Human Peripheral Nervous System
Consists of cranial nerves (12 pairs) &
spinal nerves (31 pairs).
Most cranial nerves & all spinal nerves
contain both sensory & motor pathways.
Autonomic Nervous System
Autonomic Nervous System
Enables internal organs to function
properly without conscious effort.
• Sympathetic division交感 (WAR) - most
active when body is under stress.
• Parasympathetic division 副交感(PEACE)
-most active in nonstressful situations.
Sympathetic & parasympathetic divisions
often stimulate the same organ, but
have opposite effects.
•
•
Nervous System protection
• bones
• meninges
• blood-brain barrier
• cerebrospinal fluid
Damage to the nervous system
• Mature neurons do not divide and
cannot be replaced
• Some damaged neurons can regrow
• Increasing age causes a loss of
efficiency in the nervous system
Limbic System邊緣系統
D Controls
memory
emotions and has role in
D Includes
-
Hypothalamus
-
Parts of the thalamus
- Amygdala杏仁核
- Hippocampus海馬體
How Do Humans Learn?
D Memories
form in stages, with shortterm memories including experiences
of the preceding few minutes and
long-term memories including
experience from many years before
D Hippocampus 海馬體plays a role in
long-term memories
D Amygdala杏仁核gives emotions.
•
Memory
•
•
Short term memories are circular
electrical impulses. As long as the
circuit continues stimulation, you
remember
Long term memories may involve
synaptic connection patterns and
frequent stimulation of neurons in
the hippocampus of the cerebral
cortex.
Slow wave sleep
REM
EEG
Drugs and Addiction癮
DA
drug is a substance introduced
into the body to provoke a
specific physiological response
D In
addiction, a drug assumes an
“essential” biochemical role in
the body
Invertebrate Nervous Systems
•
•
Cnidaria 水螅- nerve net
• loose organization of bi-directional
neurons
• no centralization
Flatworms渦蟲 - ladder
• 2 anterior ganglia (rudimentary brain) with
paired, longitudinal nerve cords
• paired sensory organs (eyespots)
•
•
•
Segmented worms環節 - advanced ladder
• prominent brain
• solid, fused, ventral nerve cord
• segmentally arranged ganglia
Arthropods節肢
• prominent brain
• solid, fused, ventral nerve cord
• extensive fusion of ganglia
• well-developed sensory organs
• exhibit complex behaviors
Mollusks軟體
• cephalopods have large diameter axons to
speed neural communication
• large brains
• are able to master complex tasks