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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