Signal Transduction Mechanisms (I)
• The Nervous System
• Understanding Membrane Potential
• Electrical Excitability
• The Action Potential
• Synaptic Transmission
• Integration and Processing of Nerve Signals
The Nervous System
• Three functions:
–
Collects information
–
Processes that information
–
Elicits responses（引起反應）
• Nervous system:
–
Central nervous system （中樞神經系統）
• Brain and spinal cord- sensory and motor cells
–
Peripheral nervous system（周邊神經係統）
• Somatic（軀體）nervous system
– Control the skeleton muscle
• Autonomic（自主）nervous system
– Control the cardiac muscle and smooth muscle
1. 在造成壓力的緊急的狀況下，我們還
得去選擇「迎戰」或「潰退」(逃跑)
2. 在處於「休息」和 「消化」非緊急
的狀態下。
交感神經系統
• 是一個陽光普照，舒爽的日子，你悠哉地在公園
散步。突然，一隻發怒的熊出現在前面。你會蓄
勢放手一搏，還是轉身逃走？這就是「搏鬥」或
是「逃跑」的反應。在這種情況下，你的交感神
經活化－血壓上升，心跳加快，消化作用減慢，
因而得以應付能量之消耗。
• 交感神經系統的另外兩個特點：交感神經系統的
神經節突觸係以乙醯膽鹼（acetylcholine）來當神
經傳導素；投射至目標器官上的節後神經元突觸
則利用腎上腺素（norepinephrine）為神經傳導素。
副交感神經系統
• 舒適，晴朗的一天....你在公園悠哉地散步。
此時，不管怎樣，你決定要坐在自己帶的椅子
裡放輕鬆。這就是所謂的「休息和消化」狀態。
此時副交感神經開始運作－血壓降低，心跳減
緩，啟動消化作用－而得以儲存能量。
• 來自延腦或脊髓的節前神經纖維會投射到非常
靠近標的器官的神經節並形成突觸。這個突觸
所使用的神經傳導素為乙醯膽鹼
（acetylcholine）。而節後神經元則由這種神
經節投射到標的器官並在末端釋出乙醯膽鹼
（acetylcholine）。
The Nervous System
– Neurons（神經元）- divided into three types
• Sensory neurons(感覺）: vision, smell, touch
• Motor（運動） neurons: transmit the signals
from CNS to the muscles or gland
• Interneurons（中間神經原）: process signals
received from other neurons
– Glial cells (神經膠質細胞) ：the most abundant
types of cell in the CNS
• Microglia (小神經膠質細胞) : phagocytic cellsfight for infection and remove the debris
• Oligodendrocytes (少突神經膠質細胞): form
insulating the myelin sheath around neurons of the
CNS and peripheral nerves
• Astrocytes (星狀膠細胞): 圍繞在腦部微血管外
圍，形成血腦屏障(blood-brain barrier)，可限制
大部分的物質進入腦部
• Schwann cells (神經鞘細胞): form insulating the
myelin sheath (髓鞘) around neurons of the CNS
and peripheral nerves
The functions of glial cells
• Repair and maintenance. Glial cells attempt to keep neurons
heathly. They produce new myelin(髓磷酯) when it become
damaged (oligodendroctyes) and lay down scar tissue
(astroctyes).
• Physical support. Glial cells have hairlike filaments which
hold the neurons in place and allow the central nervous system
to retain its structural integrity (astrocytes).
• Central Nervous System development. Glial cells provide an
important function in the early and continuing development of
the brain.
The functions of glial cells
• Chemical regulation. Glial cells supply chemicals
such as potassium and calcium and regulate
neurotransmitter levels (astrocytes).
• Cleaning. Glial cells remove dead cells and other
debris from the CNS (astrocytes and microglia).
• Isolation of the CNS. It used to be thought that glial
cells were important to the Blood Brain Barrier (BBB)
which shields the brain from invasion by pathogens
and other unwanted cells. This function is now
disputed and many neurologists now believe it is
performed by the endothelial cells.
Neurons are specially adapted for the
transmission of electrical signals
Signal Transduction Mechanisms (I)
• The Nervous System

• Understanding Membrane Potential
• Electrical Excitability
• The Action Potential
• Synaptic Transmission
• Integration and Processing of Nerve Signals
• Resting membrane potential (靜止膜電位)
– Cells at rest normally have an excess of
negative charge inside and an excess of
positive charge outside the cell; the resulting
electrical poteintial is called resting
membrane potential.
• Negative resting membrane potential
– Comparing the ratio of negative to positive
charge inside the cell and outside the cell,
the inside of a cell typically has an excess
negative charge.
– -60 mV for the squid giant axon（軸索）
• How a Cell Maintains a Membrane Potential.
– Cations.
• K+ the principal intracellular cation: (potassium ion gradient)
• Na+ is the principal extracellular cation.
– Anions.
• Proteins, amino acids, sulfate, and phosphate are the
principal intracellular anions.
• Cl– is principal extracellular anion.
Signal Transduction Mechanisms (I)
• The Nervous System
• Understanding Membrane Potential

• Electrical Excitability
• The Action Potential
• Synaptic Transmission
• Integration and Processing of Nerve Signals
• Excitable cells (興奮細胞) have the ability to
generate large changes in their membrane
potentials.
– Gated ion channels (閘門離子通道) open or
close in response to stimuli.
• The subsequent diffusion of ions leads to a
change in the membrane potential.
Chemical or electrical communication
between cells occurs at synapses (突觸)
• Electrical Synapses. （電性突觸）
– Action potentials travels directly from the presynaptic
to the postsynaptic cells via gap junctions.
• Chemical Synapses （化學性突觸）.
– More common than electrical synapses.
– Postsynaptic chemically-gated channels exist for ions
such as Na+, K+, and Cl-.
• Depending on which gates open the postsynaptic neuron
can depolarize or hyper polarize.
Neurotransmitter
• Acetylcholine(乙醯膽鹼).
– Excitatory to skeletal muscle.
– Inhibitory to cardiac muscle.
– Secreted by the CNS, PNS.
• Catecholamines (兒茶酚胺).
– Epinephrine(腎上腺素), norepinephrine(正腎上
腺素) and Dopamine(多巴胺).
• Can have excitatory or inhibitory effects.
• Secreted by the CNS and PNS.
• Serotonin(血清張力素).
– Generally inhibitory.
• Widespread in the brain.
• Affects sleep, mood, attention, and learning
– Secreted by the CNS.
• Amino Acids
– Gamma aminobutyric acid (GABA) 氨基丁
酸.
• Inhibitory.
• Secreted by the CNS and at invertebrate
neuromuscular junctions.
• Glycine (甘胺酸).
– Inhibitory.
– Secreted by the CNS.
• Glutamate(麥酸酐鹽).
– Excitatory.
– Secreted by the CNS and at invertebrate
neuromuscular junctions.
• Aspartate(天門冬氨酸).
– Excitatory.
– Secreted by the CNS.
• Neuropeptides(神經肽類).
– Substance P.
• Excitatory.
• Secreted by the CNS and PNS.
• Endorphin內啡肽.
– Generally inhibitory.
– Secreted by the CNS.
• Gases that act as local regulators.
– Nitric oxide.
– Carbon monoxide.