Nervous System
Two Regulatory Systems
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Nervous System
Fast!
Short duration effect
Electric (ionic) signals
…but also chemicals
(neurotransmitters)
• Affects nearby cells
(local)
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Endocrine System
Slower to start
Longer duration effect
Chemical signals
(hormones)
• Affects any cell (long
distance)
NS & ES are Related
1. Neurosecretory Cells
– In brain, but secrete hormones
– Ex: epinephrine as hormone & neurotransmitter
2. Each system affects outcome of other
– Ex: suckling…neurons…oxytocin…more milk
– Ex: chemoreceptors detect glucose in
blood…pancreas secretes insulin/glucagon
NS & ES are Related
3. Feedback Mechanisms
– Positive
• Ex: suckling/oxytocin
– Negative
• Ex: calcium levels/
PTH/calcitonin
Nervous System
The Cellular Level
Intro Video - Signaling
Neuron = Nerve Cell
• How does its structure fit its function?
Gated Ion Channels
open or close in response to 3 kinds of stimuli
• Stretch–gated - in cells that sense stretch; open
when membrane mechanically deformed
• Ligand–gated - at synapses; open/close when
specific neurotransmitter binds to channel
• Voltage–gated - in axons; open/close when
membrane potential changes
• Gated ion channels are responsible for generating
the signals of the nervous system
Membrane Potential
the outside of the cell is
more positive
the difference in charge
while it is not “firing” is
called the “resting
potential”
Action Potential Cartoon –Self-Guided
Action Potential Video
Voltage-Gated Ion Channels
• Resting state…more (+) outside than inside
Voltage-Gated Ion Channels
• Stimulus causes Na channels to open
Voltage-Gated Ion Channels
• Once enough Na+ moves in, membrane is
“depolarized”
Voltage-Gated Ion Channels
• Next, K+ gates open to allow them to move
out…just as Na+ gates close… ”repolarization”
Voltage-Gated Ion Channels
Propagation of the Action Potential
• How related to neuron?
• As Na+ ions move in, the
potential “flip-flops” triggering
K+ gates to open
• Meanwhile the Na+ ions diffuse
over to next area causing the
“flip-flop” in charge
• And it goes on and on…
Propagation of the Action Potential
Saltatory Conduction
• Action potentials can only be generated at
nodes of Ranvier (myelin sheath blocks
membrane)…message hops quickly
How do the Na/K concentrations return to resting state?
…the Na-K Pump!
~ More Na+ outside…more K+ inside (salty banana)
~ K tends to leak out…leaving negative ions in
~ Na-K pump maintains this difference
Video - Sodium-Potassium Pump
Na-K Pump (Active Transport)
More Na+ outside…more K+ inside
ATP allows movement of 3 Na out (uses 1 ATP)
Then 2 K pulled in
Video - Sodium-Potassium Pump
A Chemical Synapse
Video - Synapse
A Chemical Synapse
• Depolarization triggers Ca-channels to let Ca ions
enter
• Synaptic vesicles (w/ neurotransmitters) fuse with
presynaptic membrane
• Receptors on post-synaptic membrane bind
neurotransmitter
• Depolarization of gates carries message along
Integration of Multiple Synaptic Inputs
• Each neuron makes connections with
many other neurons
Nervous System
The Organs & their Functions
Overview of the Vertebrate
Nervous System
Overview of the Vertebrate
Nervous System
• “Sensory receptor” – may be “special senses”
• - light (vision), chemicals (taste & smell),
movement (hearing)
• Or…
Overview of Vertebrate
Nervous System
• “Sensory receptor” – may be general senses
• - pressure, movement, temperature,
chemicals, pain, location in space
Overview of Vertebrate
Nervous System
Effector = skeletal, smooth, or cardiac muscle or glands
Diversity in Nervous Systems
• Don’t need to memorize…just compare
Structural Divisions of the NS
• CNS
– Brain
– Spinal cord
• PNS
– Nerves
Functional Divisions of the PNS
Sense
Move
Automatic
Choice
Rest & digest
Rev you up!
Parasympathetic & Sympathetic
Embryonic Brain Development
• Don’t memorize…notice the pattern
Human Brain
Human Brain
Cerebrum – “thinking”; conscious actions; all the fancy stuff
Cerebellum – coordinates voluntary muscle movements
Brainstem – basic life functions (involuntary stuff)
Hypothalamus – homeostasis (hunger, thirst, etc)
Cerebrum – Functional Areas
• The brain integrates most functions but
there is some centralization…
Primary Motor/Somatosensory
Areas of Cortex
• Which motor areas get
the most attention?
• Why does that make
sense?
Primary Motor/Somatosensory
Areas of Cortex
• Which sensory areas
get the most attention?
• Does that make
sense?
• Is this the same as for
the motor cortex?
The Limbic System
• Memory – emotion - …
• Note the association with the special senses
Reflexes
• Purpose – quickly respond to danger
– What selection pressure for this to develop?
The
Reflex Arc
• Components
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Stimulus - signal detected by sensory neuron
Sensory neuron carries msg to spinal cord
Decision made …U-turn at the interneuron
Motor neuron sends back reposnse
Effector – completes response; muscle or gland
The End