BILD 12 Lecture Notes - Lecture 3: Neural Ensemble, Sodium Channel, Excitatory Synapse
19 Jan 2017
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BILD 12 Lecture 3 18 Jan 2017: Neurobiology and Behavior
● 100,000,000,000 neurons in the human brain
● The brain is a complex circuit of Neurons
● Components of neural circuits:
○ Sensory neurons
○ Interneurons
○ Motor Neurons
○ Excitatory Neurons
○ Inhibitory Neurons
● Information flow
○ Must be reliable and rapid within neurons and across neurons
● Three players, two forces
○ Ions
○ Membrane
○ Membrane Proteins
○ Diffusion
○ Electricity
● Resting Membrane Potential
○ K+ concentrated inside
the cell
○ Neuronal Membrane at
rest is selectively permeable to K+
○ K flows out until the electric force counteracts the diffusion force
■ The Equilibrium potential.
○ Typically about -65 mV
■ At rest - negatively charged.
■ Polarized
● Voltage Gated Sodium channel
○ Selectively permeable to sodium (Na+)
○ Sensitive to membrane potential
■ Closed at resting potential (-65 mV)
■ Opens briefly (~1ms) upon
depolarization above threshold (~-40 mV)
■ And then closes back again
● Action Potential generation
○ A small depolarization (ex: stimulation by
other neurons) leads to a breif (1ms) opening of voltage gated
sodium channels, leading Na+
to enter the neuron. Membrane potential goes up.
find more resources at oneclass.com
find more resources at oneclass.com
○ Sodium channels quickly close. Membrane potential goes back to
the resting potential as K+leave the cell.
○ Action potential is a molecularly regulated brief depolarization of the
membrane.
● A transient depolarization away from the resting potential and back to it.
● An action potential rapidly travels down the axon.
● Active propagation: reproduced at each site. No attenuation. (People
passing a message across a room)
● Imaging neural ensemble activity
○ Introduced a sensor that changes it’s brightness based on
neural activity.
■ The more AP’s a neuron fires, the brighter the
neuron becomes
● Synapse
○ Specialized sites of contact between two neurons
○ The junction between the axon of the presynaptic neuron
and the dendrites of a postsynaptic neuron.
● Are neurons electrically coupled?
● Electrical coupling
○ Electrical synapses (aka gap junctions): electrical coupling of two
neurons.
■ Bidirectional
■ Ion non-selective
■ More common in invertebrate animals
■ Almost never in humans
● Chemical synapses
○ The presynaptic neuron releases special chemicals to
communicate with the postsynaptic neuron!
○ Neurotransmitters
○ Main way of communication
● Information flow
○ Action potential reaches the axon terminal
○ This electrical signal is translated to a chemical signal (release of
neurotransmitters)
○ How does it translate this back and forth??
● Otto Loewi’s famous experiment
○ Loewi took out a frog’s heart. He discover a nerve (bundle of
axons) attached to the heart neurons. Heart continues to beat for a
few hours. Loewi stimulated the heart and found a decrease in
beats
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Bild 12 lecture 3 18 jan 2017: neurobiology and behavior. The brain is a complex circuit of neurons. Must be reliable and rapid within neurons and across neurons. K flows out until the electric force counteracts the diffusion force the cell. Neuronal membrane at rest is selectively permeable to k+ Opens briefly (~1ms) upon depolarization above threshold (~-40 mv) A small depolarization (ex: stimulation by other neurons) leads to a breif (1ms) opening of voltage gated sodium channels, leading na+ to enter the neuron. Membrane potential goes back to the resting potential as k+leave the cell. Action potential is a molecularly regulated brief depolarization of the membrane. A transient depolarization away from the resting potential and back to it. An action potential rapidly travels down the axon. No attenuation. (people passing a message across a room) Introduced a sensor that changes it"s brightness based on neural activity. The more ap"s a neuron fires, the brighter the neuron becomes.
