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NERVOUS SYSTEM
Your Getting on My Nerves!
NERVOUS SYSTEM• Interpreting, processing and transferring
information
Across Species• Lets look at some different organisms and
how their nervous system is oriented.
• Try to focus on structure and function… What the organism looks like, where/how it lives
Simple Organism only a few cells thick
Sessile NO need for complex skeletal
movements
Centralized Gastrovascular cavity. No complex method to deliver ions for nervous system
Simple Organism…Simple nervous system
Ganglia: Group of
nervous tissueCephalization
Eyespots to sense light and detect
specific chemicals
Can learn to change responses Due to stimuli
Slightly more complex organism… with a slightly more
complex Nervous system
Larger more complex organism
than the Planarian… More complex system
Multiple Ganglia
throughout body for more
complex responses and coordination
Primitive Brain
Larger more complex
organism…Larger more
complex system
LARGE Axons extending from
brain tissue
Developed sensory organs
Must have a more developed
system to process information
Molecular Components of Neural Communication
NEURON: a cell of the nervous system
PARTS OF A NEURON
• Cell Body : Nucleus and Organelles of the neuron… if it dies the neuron dies… FOREVER
• Axon: The SENDING end of a neuron– Axon hillock: Signal generation site of an axon– Synaptic Terminals: Where neurotransmitters are
stored and expelled into the synapse• Dendrites: The RECEIVING end of a neuron• Synapse: The space between communicating
neurons
Details of a Nervous Signal• Nervous system connects all body systems
and functions with ion exchanges and neurotransmitters to make its point
• A membrane potential is a localized electrical gradient across membrane.– Anions are more concentrated within a cell.– Cations are more concentrated in the extracellular
fluid.
Every cell has a voltage, or membrane potential, across its
plasma membrane
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
CELL
AT
REST
• How a Cell Maintains a Membrane Potential.– Cations.• K+ is the principal intracellular cation.• Na+ is the principal extracellular cation.
– Anions.• Proteins, amino acids, sulfate, and phosphate are the
principal intracellular anions.• Cl– is the principal extracellular anion.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
CELLS HAVE TO BE NEGATIVE…
DUH… DNA IS NEGATIVE!CELLS HAVE DNA!!
• Ungated ion channels allow ions to diffuse across the plasma membrane.– These channels are always open.
• This diffusion does not achieve an equilibrium since the sodium-potassium pump transports these ions against their concentration gradients.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.7
Sodium-Potassium pump- A protein pump
found mainly in the nervous system that
ACTIVELY pumps K+ INTO a cell and Na+ OUT
• Hyperpolarization.– Gated K+ channels open
K+ diffuses out of the cell the membrane potential becomes more negative.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.8a
More K+ INSIDE the cellWhen the gates open K+ Rushes OUTWARD
Because of the concentration Losing the + makes the
Inside more -
Can lead to INHIBITION NOT wanting the neuron to
FIREOr reach
POTENTIAL
• Depolarization.– Gated Na+ channels open
Na+ diffuses into the cell the membrane potential becomes less negative.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.8b
Again due to concentration
Differences… Na+ rushes INWARD causing theCell to become more
POSITIVE
• The Action Potential: All or Nothing Depolarization.– If graded potentials sum
to -55mV a threshold potential is achieved.• This triggers an action
potential.– Axons only.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.8c
Once enough Positive ions change the membrane
potential Enough… the Axon will
FIRESending a cascading ionic
Electrical current…ACTION POTENTIAL
• Step 1: Resting State.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.9
• Step 2: Threshold.
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Fig. 48.9
• Step 3: Depolarization phase of the action potential.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.9
• Step 4: Repolarizing phase of the action potential.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.9
• Step 5: Undershoot.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.9
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.10
Click on image to play video
• Schwann cells are found within the PNS.– Form a myelin sheath by insulating axons.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.5
• Saltatory conduction.– In myelinated neurons only unmyelinated regions of
the axon depolarize.• Thus, the impulse moves faster than in unmyelinated
neurons.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.11
• Electrical Synapses.– Action potentials travels directly from the presynaptic
to the postsynaptic cells via gap junctions.• Chemical Synapses.– 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 hyperpolarize.
Chemical or electrical communication between cells occurs
at synapses
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.12
• Excitatory postsynaptic potentials (EPSP) depolarize the postsynaptic neuron.– The binding of neurotransmitter to postsynaptic
receptors opens gated channels that allow Na+ to diffuse into and K+ to diffuse out of the cell.
• Inhibitory postsynaptic potential (IPSP) hyperpolarizes the postsynaptic neuron.– The binding of neurotransmitter to postsynaptic
receptors open gated channels that allow K+ to diffuse out of the cell and/or Cl- to diffuse into the cell.
Neural integration occurs at the cellular level
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Summation: graded potentials (EPSPs and IPSPs) are summed to either depolarize or hyperpolarize a postsynaptic neuron.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 48.14
NEUROTRANSMITTERS
• Acetylcholine: Most studied in the muscular response, but also in Memory formation and learning. Causes an excitatory response in muscle cell.
• Acetyl cholinesterase hydrolyzes Acetylcholine terminating the excitatory response.
Released by the PRESYNAPTIC cell to cause an affect on the POSTSYNAPTIC cell
Homeostasis… feedback
Otherwise your muscles would Contact out of control!!!
QUESTION
• If I told you BOTOX was a neurotoxin that disrupted the function of Acetylcholine…
WHAT DOES THAT MEAN???
Botox is a neurotoxin that prevents vesicles containing acetylcholine
from being released into the synapse. The vesicles are unable to
connect to the cell membrane to release their contents
Ach cannot cause a contraction of The muscle.
Muscles relax and wrinkles fade.And EYEBROWS do not move for 3-4
months!
DOPAMINE and SEROTONIN• Made from amino Acids• Affect sleep, mood, attention and learning
• Treat depression by inhibiting the reabsorption of Serotonin allowing it to remain in the synapse longer… PROZAC more serotonin to react, more HAPPY
• Lack of Dopamine in the brain is associated with Parkinson’s disease… a degenerative nerve disease associated with a lack of muscle control
LSD & L-dopa (derivative) can doc with the dopamine receptors
VIDEO ATTACHED!
PAIN Neurotransmitters
• Substance P (a neuropeptide)- “P FOR PAIN!” This neurotransmitter allows you to feel PAIN!
Nocieptors- dendrites that receive noxious thermal, mechanical or chemical PAIN information.• Endorphins – This neurotransmitter diminishes pain.– Opiate, Morphine and heroin mimic Endorphins… Similar
shape, can doc with the endorphin receptor to cause euphoria. They also increase urine output.
Click boy
THINKING IT THROUGH• You have now had several examples of
different neurotransmitters and their function in the body.
• Take a moment to discuss how some medicines are made. Be sure to document your answer in your notes
NERVOUS SYSTEM organization
1. Central nervous systema. Brain : Processing centerb. Spinal cord : sending and receiving
2. Peripheral nervous systema. Somatic (Motor) : voluntary (except
REFLEX)b. Autonomic : involuntary
AUTONOMIC NS• The Autonomic nervous system is further
divided into Sympathetic and Parasympathetic
What do you notice about the
relationship between the 2
divisions?
Which one would be activated when
you are being chased by the Boogie man
How is this regulation Efficient?
AUTONOMIC NS
• The 3rd division: Enteric– Control of smooth muscles (digestion), Cardiac
muscles and glands
HOW is a reflex efficient?HOW is it protective?
OUCH!Nociceptor Sensory neuron
Synapse
Cross Section of Spinal cord
Interneuron
Motor Neuron Muscle contraction
WHY THIS DIAGRAM IS MISLEADING
1. Interneuron are primarily INHIBITORY
They inhibit the antagonistic muscle group.
2. The sensory neuron ALSO sends a message
to the brain… It just takes longer… which is
why there is a second or two that your burn
doesn’t hurt
Take a moment to describe what happens in a reflex in
your notes
EFFICENT REGULATION! One
stimulus… 2 responses… the SAME
sensory nerve can stimulate one muscle while inhibiting the
other!
Interneurons typically release the neurotransmitter GABA… which is
inhibitory