Nervous system

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.


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.


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.


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.


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.


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.


Fig. 48.9

• Step 2: Threshold.


Fig. 48.9

• Step 3: Depolarization phase of the action potential.


Fig. 48.9

• Step 4: Repolarizing phase of the action potential.


Fig. 48.9

• Step 5: Undershoot.


Fig. 48.9


Fig. 48.10

Click on image to play video

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

• Schwann cells are found within the PNS.– Form a myelin sheath by insulating axons.


Fig. 48.5

• Saltatory conduction.– In myelinated neurons only unmyelinated regions of

the axon depolarize.• Thus, the impulse moves faster than in unmyelinated

neurons.


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


CLICK ME!

http://www.youtube.com/watch?v=HXx9qlJetSU

http://www.youtube.com/watch?v=HXx9qlJetSU


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


• Summation: graded potentials (EPSPs and IPSPs) are summed to either depolarize or hyperpolarize a postsynaptic neuron.


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!

http://www.youtube.com/watch?v=xIueQPhBawg

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

http://www.youtube.com/watch?v=PMZdkac4YLk&feature=related

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?

http://www.youtube.com/watch?v=YFYRosjcVuU

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

Nervous system

Technology

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