Nervous System

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Nervous System
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Why do animals need a nervous system?

• What characteristics do animals need in a
  nervous system?
• fast
• accurate
• reset quickly

Rememberthink aboutthe bunny
Poor bunny!
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Nervous system cells

• Neuron
• a nerve cell

signal direction
dendrites

• Structure fits function
• many entry points for signal
• one path out
• transmits signal

cell body
axon
signal direction
synaptic terminal
myelin sheath
dendrite ? cell body ? axon
synapse
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Fun facts about neurons

• Most specialized cell in animals
• Longest cell
• blue whale neuron
• 10-30 meters
• giraffe axon
• 5 meters
• human neuron
• 1-2 meters

Nervous system allows for 1 millisecond response
time
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Transmission of a signal

• Think dominoes!
• start the signal
• knock down line of dominoes by tipping 1st one
• ? trigger the signal
• propagate the signal
• do dominoes move down the line?
• ? no, just a wave through them!
• re-set the system
• before you can do it again, have to set up
  dominoes again
• ? reset the axon

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Transmission of a nerve signal

• Neuron has similar system
• protein channels are set up
• 1 channel open, the rest open in succession
• all or nothing response
• a wave action travels along neuron
• have to re-set channels so neuron can react again

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Simile time! (or do I mean analogy?)

• Think of an analogy for a firing neurone. What
  can you think of that happens in the same way
  every time, and needs to be reset after it has
  operated?

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Cells surrounded by charged ions

• Cells live in a sea of charged ions
• anions (negative)
• more concentrated within the cell
• Cl-, charged amino acids (aa-)
• cations (positive)
• more concentrated in the extracellular fluid
• Na

channel leaks K
K


K
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Cells have voltage!

• Opposite charges on opposite sides of cell
  membrane
• membrane is polarized
• negative inside positive outside
• charge gradient
• stored energy (like a battery)

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Measuring cell voltage
unstimulated neuron resting potential of -70mV
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How does a nerve impulse travel?

• Stimulus nerve is stimulated
• reaches threshold potential
• open Na channels in cell membrane
• Na ions diffuse into cell
• charges reverse at that point on neuron
• positive inside negative outside
• cell becomes depolarized

The 1stdomino goesdown!
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How does a nerve impulse travel?

• Wave nerve impulse travels down neuron
• change in charge opens next Na gates down the
  line
• voltage-gated channels
• Na ions continue to diffuse into cell
• wave moves down neuron action potential

The restof thedominoes fall!
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How does a nerve impulse travel?

• Re-set 2nd wave travels down neuron
• K channels open
• K channels open up more slowly than Na channels
• K ions diffuse out of cell
• charges reverse back at that point
• negative inside positive outside

Setdominoesback upquickly!
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How does a nerve impulse travel?

• nerve impulse action potential
• Combined waves travel down neuron
• wave of opening ion channels moves down neuron
• signal moves in one direction ? ? ? ? ?
• Refractory period stops activation of wave in
  wrong direction

Readyfornext time!
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Voltage-gated channels

• Ion channels open close in response to changes
  in charge across membrane
• Na channels open quickly in response to
  depolarization close slowly
• K channels open slowly in response to
  depolarization close slowly

Structure function!
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How does the nerve re-set itself?

• After firing a neuron has to re-set itself
• Na needs to move back out
• K needs to move back in
• both are moving against concentration gradients
• need a pump!!

A lot ofwork todo here!
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How does the nerve re-set itself?

• Sodium-Potassium pump
• active transport protein in membrane
• requires ATP
• 3 Na pumped out
• 2 K pumped in
• re-sets chargeacross membrane

ATP
Thats a lot of ATP ! Feed me somesugar quick!
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Neuron is ready to fire again
resting potential
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Action potential graph

1. Resting potential
2. Stimulus reaches threshold potential
3. Depolarization Na channels open K channels
   closed
4. Na channels close K channels open
5. Repolarizationreset charge gradient
6. UndershootK channels close slowly

40 mV
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30 mV
20 mV
Depolarization Na flows in
Repolarization K flows out
10 mV
0 mV
10 mV
3
5
Membrane potential
20 mV
30 mV
40 mV
Hyperpolarization (undershoot)
Threshold
50 mV
60 mV
2
70 mV
1
Resting
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Resting potential
80 mV
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Stimulus strength Membrane potential (mv)
0 -70
5 -70
10 10
15 10
20 10
What do you know from this table?
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Stimulus strength Membrane potential (mv)

• What do you know from this table?
• The stimulus strength that hits threshold is
  between 5 and 10
• Notice that the size of the action potential does
  not change regardless of how intense the stimulus
  is. (ALL OR NONE PRINCIPLE)

0 -70
5 -70
10 10
15 10
20 10
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Stimulus strength frequency of impulses
(/s)
0 0
5 10
10 20
15 30
20 40
What does this table tell you?
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Stimulus strength frequency of impulses
(/s)
0 0
5 0
10 10
15 20
20 30

• A stimulus strength of between 5 and 10 hits the
  threshold of this neuron.
• The frequency of impulses increases with the
  stimulus strength

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Myelin sheath

• Axon coated with Schwann cells
• insulates axon
• speeds signal
• signal hops from node to node
• saltatory conduction
• 150 m/sec vs. 5 m/sec(330 mph vs. 11 mph)

signal direction
myelin sheath
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action potential
saltatory conduction
Na
myelin


axon





Na

• Multiple Sclerosis
• immune system (T cells) attack myelin sheath
• loss of signal

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Synapse
What happens at the end of the axon?

• Impulse has to jump the synapse!
• junction between neurons
• has to jump quickly from one cell to next

How does the wavejump the gap?
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Chemical synapse

• Events at synapse
• action potential depolarizes membrane
• opens Ca channels
• neurotransmitter vesicles fuse with membrane
• release neurotransmitter to synapse ? diffusion
• neurotransmitter binds with protein receptor
• ion-gated channels open
• neurotransmitter degraded or reabsorbed

axon terminal
action potential
synaptic vesicles
synapse
Ca
neurotransmitteracetylcholine (ACh)
receptor protein
muscle cell (fiber)
We switched from an electrical signal to a
chemical signal
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Nerve impulse in next neuron

• Post-synaptic neuron
• triggers nerve impulse in next nerve cell
• chemical signal opens ion-gated channels
• Na diffuses into cell
• K diffuses out of cell
• switch back to voltage-gated channel

Here wego again!
K
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Neurotransmitters

• Acetylcholine
• transmit signal to skeletal muscle
• Epinephrine (adrenaline) norepinephrine
• fight-or-flight response
• Dopamine
• widespread in brain
• affects sleep, mood, attention learning
• lack of dopamine in brain associated with
  Parkinsons disease
• excessive dopamine linked to schizophrenia
• Serotonin
• widespread in brain
• affects sleep, mood, attention learning

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Neurotransmitters

• Weak point of nervous system
• any substance that affects neurotransmitters or
  mimics them affects nerve function
• gases nitrous oxide, carbon monoxide
• mood altering drugs
• stimulants
• amphetamines, caffeine, nicotine
• depressants
• quaaludes, barbiturates
• hallucinogenic drugs LSD, peyote
• SSRIs Prozac, Zoloft, Paxil
• poisons

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Acetylcholinesterase

• Enzyme which breaks downacetylcholine
  neurotransmitter
• acetylcholinesterase inhibitors neurotoxins
• snake venom, sarin, insecticides

neurotoxin in green
active site in red
snake toxin blockingacetylcholinesterase active
site
acetylcholinesterase
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Ponder thisAny Questions??
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Remember as many of the following words as
possible.

• read, pages, letters, school, study, reading,
  stories, sheets, cover, pen, pencil, magazine,
  paper, words

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How many of these words were on the first list?

• house, pencil, apple, shoe, book, flag, rock,
  train, ocean, hill, music, water, glass, school

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Brain is divided into forebrain, midbrain,
hindbrain
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You have 3 brains!
Lizard Brain
Mammal Brain
Human Brain
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Midbrain and Hindbrain (Pons, medulla oblongota,
cerebullum)

• Bodys housekeeping.homeostasis
• Breathing, heart rate, sleeping, waking, etc.

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Limbic System

• Control of the four Fs
• Fighting, feeding, fleeing and..reproduction
• Composed of
• Amygdala emotions
• Hippocampus storage of memories
• H.M.

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Lobes of cerebrum
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Sensory and motor cortexes mapped
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Lobes of the Cerebrum 1. Frontal lobe
a)Prefrontal area (behind forehead)
personality b)Motor Cortex voluntary
movement 2. Parietal Lobe Sensory cortex
conscious sensation
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3. Occipital Lobe Visual cortex - seeing 4.
Temporal lobe auditory cortex - hearing
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Song time

• http//www.youtube.com/watch?vLi5nMsXg1Lk

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Listen first, when Im done, write as many down
as you can

• cat apple ball tree square head house door box
  car king hammer milk fish book tape arrow flower
  key shoe

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How does a nerve impulse travel?

• Action potential propagates
• wave nerve impulse, or action potential
• brain ? finger tips in milliseconds!

In theblink ofan eye!
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See how many of these objects you can remember.
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Your brain is plastic
http//www.youtube.com/watch?vTSu9HGnlMV0