Chap 19 nervous system

THE NERVOUS SYSTEM ,[object Object]

[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object]

[object Object],[object Object],[object Object],Brain Spinal cord (dorsal nerve cord) Sensory ganglion (h) Salamander (chordate)

Information Processing ,[object Object],[object Object],Sensor Effector Motor output Integration Sensory input Peripheral nervous system (PNS) Central nervous system (CNS)

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],Sensory neurons from the quadriceps also communicate with intermediate neurons in the spinal cord. The interneurons inhibit motor neurons that supply the hamstring (flexor) muscle. This inhibition prevents the hamstring from contracting, which would resist the action of the quadriceps. The sensory neurons communicate with motor neurons that supply the quadriceps. The motor neurons convey signals to the quadriceps, causing it to contract and jerking the lower leg forward. 4 5 6 The reflex is initiated by tapping the tendon connected to the quadriceps (extensor) muscle. 1 Sensors detect a sudden stretch in the quadriceps. 2 Sensory neurons convey the information to the spinal cord. 3 Quadriceps muscle Hamstring muscle Spinal cord (cross section) Gray matter White matter Cell body of sensory neuron in dorsal root ganglion Sensory neuron Motor neuron Intermediate neuron (interneuron)

Neuron Structure ,[object Object],[object Object],Dendrites Cell body Nucleus Axon Signal direction Synapse Myelin sheath Synaptic terminals Presynaptic cell Postsynaptic cell

[object Object],[object Object],Figure 48.6a–c Axon Cell body Dendrites (a) Sensory neuron (b) Interneurons (c) Motor neuron

Supporting Cells (Glia) ,[object Object],[object Object]

[object Object],[object Object],Myelin sheath Nodes of Ranvier Schwann cell Schwann cell Nucleus of Schwann cell Axon Layers of myelin Node of Ranvier 0.1 µm Axon Figure 48.8

Transmission of Nerve Impulses ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],APPLICATION Electrophysiologists use intracellular recording to measure the membrane potential of neurons and other cells. TECHNIQUE A microelectrode is made from a glass capillary tube filled with an electrically conductive salt solution. One end of the tube tapers to an extremely fine tip (diameter < 1 µm). While looking through a microscope, the experimenter uses a micropositioner to insert the tip of the microelectrode into a cell. A voltage recorder (usually an oscilloscope or a computer-based system) measures the voltage between the microelectrode tip inside the cell and a reference electrode placed in the solution outside the cell. Microelectrode Reference electrode Voltage recorder – 65 mV

The Resting Potential ,[object Object],[object Object]

[object Object],[object Object],CYTOSOL EXTRACELLULAR FLUID [Na + ] 15 m M [K + ] 150 m M [Cl – ] 10 m M [A – ] 100 m M [Na + ] 150 m M [K + ] 5 m M [Cl – ] 120 m M – – – – – + + + + + Plasma membrane

[object Object],[object Object],+50 0 – 50 – 100 Time (msec) 0 1 2 3 4 5 Threshold Resting potential Depolarizations Membrane potential (mV) Stimuli (b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na+. The larger stimulus produces a larger depolarization.

[object Object],[object Object],- 40 mV +50 0 – 50 – 100 Time (msec) 0 1 2 3 4 5 6 Threshold Resting potential Membrane potential (mV) Stronger depolarizing stimulus Action potential (c) Action potential triggered by a depolarization that reaches the threshold.

[object Object],[object Object],[object Object]

[object Object],– – – – – – – – + + + + + + + + + + + + – – – – Na + Na + K + Na + Na + K + Na + Na + K + Na + K + K + Na + Na + Rising phase of the action potential Undershoot Sodium channel Action potential Resting potential Time Threshold Membrane potential (mV) +50 0 – 50 – 100 Threshold Cytosol Depolarization opens the activation gates on most Na + channels, while the K + channels’ activation gates remain closed. Na + influx makes the inside of the membrane positive with respect to the outside. The inactivation gates on most Na + channels close, blocking Na + influx. The activation gates on most K + channels open, permitting K + efflux which again makes the inside of the cell negative. A stimulus opens the activation gates on some Na + channels. Na + influx through those channels depolarizes the membrane. If the depolarization reaches the threshold, it triggers an action potential. The activation gates on the Na + and K + channels are closed, and the membrane’s resting potential is maintained. Both gates of the Na + channels are closed, but the activation gates on some K + channels are still open. As these gates close on most K + channels, and the inactivation gates open on Na + channels, the membrane returns to its resting state. + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – + + – – – – + + – – + + – – + + – – + + 5 1 Resting state 2 Depolarization 3 4 Falling phase of the action potential 1 2 3 4 5 1 Plasma membrane Extracellular fluid Activation gates Potassium channel Inactivation gate

Conduction of Action Potentials ,[object Object],[object Object]

[object Object],[object Object],– + – + + + + + – + – + + + + + + – + – + + + + + – + – + + + + + – + – – – – – + – + – – – – – – – – – – – – – – – – – + + + + + + + + – – – – + + + + – – – – – – – – + + + + – – – – + + + + Na + Na + Na + Action potential Action potential Action potential K + K + K + Axon An action potential is generated as Na + flows inward across the membrane at one location. 1 2 The depolarization of the action potential spreads to the neighboring region of the membrane, re-initiating the action potential there. To the left of this region, the membrane is repolarizing as K + flows outward. 3 The depolarization-repolarization process is repeated in the next region of the membrane. In this way, local currents of ions across the plasma membrane cause the action potential to be propagated along the length of the axon. K +

Conduction Speed ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],Cell body Schwann cell Myelin sheath Axon Depolarized region (node of Ranvier) + + + + + + + + + + + – – – – – – – – – – – –

[object Object],[object Object],Postsynaptic neuron Synaptic terminal of presynaptic neurons 5 µm

[object Object],[object Object],Presynaptic cell Postsynaptic cell Synaptic vesicles containing neurotransmitter Presynaptic membrane Postsynaptic membrane Voltage-gated Ca 2+ channel Synaptic cleft Ligand-gated ion channels Na + K + Ligand- gated ion channel Postsynaptic membrane Neuro- transmitter 1 Ca 2+ 2 3 4 5 6

Direct Synaptic Transmission ,[object Object],[object Object]

Summation of Postsynaptic Potentials ,[object Object],[object Object]

[object Object],[object Object],Figure 48.18a E 1 E 1 Resting potential Threshold of axon of postsynaptic neuron (a) Subthreshold, no summation Terminal branch of presynaptic neuron Postsynaptic neuron E 1 0 – 70 Membrane potential (mV)

[object Object],[object Object],Figure 48.18b E 1 E 1 Action potential (b) Temporal summation E 1 Axon hillock

[object Object],[object Object],Figure 48.18c E 1 + E 2 Action potential (c) Spatial summation E 1 E 2

[object Object],[object Object],Figure 48.18d E 1 E 1 + I I (d) Spatial summation of EPSP and IPSP E 1 I

Indirect Synaptic Transmission ,[object Object],[object Object],[object Object],[object Object]

Neurotransmitters ,[object Object],[object Object]

Acetylcholine ,[object Object],[object Object],[object Object]

Biogenic Amines ,[object Object],[object Object],[object Object]

Amino Acids and Peptides ,[object Object],[object Object]

Gases ,[object Object],[object Object]

Chap 19 nervous system

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Chap 19 nervous system