the nervous system - fayetteville state universityfaculty.uncfsu.edu/ssalek/biol130/ch 28.pdf ·...
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The Nervous System
CH 28
Nervous system
• Structure and function• Nerve signals and their transmission• Nervous systems• The human brain
Giant Squid!
Artituthus can be 30 ft+
The Giant Squid Nervous System• Nervous system- coordinates an appropriate
response to internal and external stimuli• Squid - coordinates, balance, eyesight,
movement, feeding, predator defense, color change
• Large brain and sensory nerves• Large cells with thick, giant fibers• Easily manipulated and used for nervous
system research
Fig 28.1
Structure and Function
• Sensory input– Conduction of signals from sensory receptors– Recall the eye, ear, tongue, etc
• Intergration– Interpretation of signals and formation of a
response• Motor output
– Conduction of signals from integration center to effector cells i.e. muscle cells
Structure and Function
• Divisions of the nervous system• Central nervous system (CNS)
– Brain and spinal cord• Peripheral nervous system (PNS)
– Carries information from sensory receptors to CNS and motor information to effector cells
Structure and Function
• Neuron - the functional unit of the nervous system
• Nerves are made of bundles of neurons– Sensory neurons, motor neurons, interneurons
• Clusters of neurons– CNS - nuclei; PNS - ganglia
• Reflex, see fig 21.8B
Fig 28.2
Neurons• Cell body
– nucleus and organelles
• Dendrites– Numerous short projections that convey signals to the cell body
• Axons– Long and convey signals away from the cell body
• Synaptic knob– Relays signal to effector cell
• Supporting cells (six types)– Glial cells/Schwann cells– Myelin sheaths (fast conduction of nerve impulses 150 m/s) – Nodes of ranvier
• MS
Fig 28.3
Resting potential
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Fig 28.3
Transmission of nerve signals
• Neurons contain potential energy ( battery)• Excitable cells!
– Charge across membrane , -70 mV, neg on inside positive on the outside
– This is called resting potential• Determined by
– Large organic molecules, K and Na– Na/K pump
Action Potential
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Fig 28.4
Nerve signal• Begins as a local change in membrane potential• The change results from some type of stimulus• The change in membrane potential spread as and action
potential• Stages
– Rp resting phase (-70 mv)– Rising phase ( -70 to +35) Na rushes into the cell: (Threshold)– Falling phase (+35 to -70) K diffuses out– Undershoot; K channels close
• Depolarization - membrane charge becomes more positive• Hyperpolarization - membrane charge becomes more
negative
Blue - Na channels openGreen - Na closed, K openGray- No AP ( NA/K pump)
Fig 28.5
Regeneration of AP’s
• Spread of charge along the axon is caused by Na influx
• Na influx triggers more Na influx further on down the axon
• Changes are unidirectional, K moving out blocks the AP in the reverse direction
• All or none- Ap’s don’t change in magnitude, but do change in frequency
Synapse
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Fig 28.6
Information processing:Chemical synapses
• Synapse - relay between two neurons or between a neuron and an effector cell– Electrical or chemical
• Electrical signals are converted to chemical signals here, neurotransmitters transmit chemical information across the synapse - space prevents electrical signals from spreading
• Synaptic knobs - store NT’s in vesicles; Ca influx triggers the release
Fig 28.7
Information processing
• Neurotransmitters open ion channels on the receiving cell’s membrane
• NT’s– Excitatory open Na channels and start a new Ap– Inhibitory open Cl channels and decrease tendency of
cell to start an AP
• Cells receive multiple inputs! They are integrated!
Neurotransmitters• Excitatory of inhibitory - depending on the receptor on the
receiving cell• Small N containing molecules, Acetylcholine• Some come from amino acids:
– Epinepherine, norepinepherine, - change heart rate– serotonin, dopamine- sleep., mood, attention, learning
• Stimulants and depressants affect chemical synapses– Cocaine, amphetamines, caffiene– Valium, Librium, alcohol– Serotinin reuptake inhibitors, Prozac, Zoloft