Sec 3 Neuron

Neuron Structure

• Dendrites

• Cell Body (Soma)

• Axon

• Myelin Sheath

• Axon Terminals (terminal buttons output)

• Glia

Dendrites

Tree like structure that receives signals from other neurons

Cell Body (Soma)

Contain neurons nucleus and most of its cytoplasm. needed for neuron maintainance.

Axon

Plays part of the road for electrical impulses away from Soma. Can be naked or covered with myelin sheath.

• neurotransmitters made here

Myelin Sheath

A fatty layer that wraps around the axon insulating it, speeds up the transmission of signal

Axon Terminal

Endpoint of axon where electrical signal is converted into chemical by the use of neurotransmitters

Glia

Support crew of neurons, helps w tissue repair, and myelin formation

What is the nervous system broken down into?

Central Nervous System (CNS) and Peripheral Nervous System (PNS)

Central Nervous System?

Brain + Spinal Cord

Peripheral Nervous System

Everything outside CNS

• Somatic Nervous System

  • Voluntary movement and muscle activity

• Autonomic Nervous System

  • Involuntary movement and organ activity

  • Sympathetic (Fight and flight)

  • Parasympathetic (Rest and digest)

Action Potential

When a stimulus occurs, rapid change of membrane potential occurs in 3 phases called action potential.

Resting membrane potential

Potential of dendrite cell membrane at rest. Inside is more negative contains K+ ions and negative large proteins, outside is positive with many Na+ ions. Around -70mV, difference of inside and out.

What are the phases of action potential?

Depolarization

Repolarization

Hyperpolarization

Depolarization

First phase: Stimulus comes in, Na+ channels open and Na+ rushes in. This increases membrane potential, making it closer to zero. K+ channels also open and K+ rushes out

Repolarization

Na+ Channels close up and K+ channels stay open and K+ keeps rushing out, making the membrane potential drop negative again

Hyperpolarization

K+ closes slowly, where the potential becomes even more negative than resting. Membrane potential then returns to resting.

Threshold Potential

Stimulus must bring membrane potential past threshold for action potential to be fired. This is all or nothing so it either fires completely if passed of not at all if it doesnt.

Rate Law

A stronger action potential doesnt spike differently than a “weaker one” it just happens more frequently. More will be fired.

Neural Communication

Action potentials trigger synthesis of neurotransmitters in axon terminal, placed into vesicles and released into the synaptic gap. This is where you go from electrical to chemical. These neurotransmitters bind to the next neuron dendrite

Different Neurotransmitters

Excitatory Neurotransmitter

• This binding makes it more likely for the next neuron to shoot an action potential

Inhibitory Neurotransmitter

• This binding makes it less likely for the next neuron to shoot an action potential

How to recycle neurotransmitters in the synapatic gap?

Reuptake (recycle) back to the neuron it came from via transporters

Degradation, degrade them via enzymes

SSRI Ex.

SSRI blocks the reuptake of seratonin so more is left in the synaptic gap