Download The Nervous System

The Nervous System
CH 28
Nervous system
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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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Cinepak decompressor
are needed to see this picture.
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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are needed to see this picture.
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
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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 open
Green - Na closed, K open
Gray- 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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are needed to see this picture.
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