NEUROPHYS EXAM #1: neuron structure/formation of neuronal circuits (USE THIS ONE!)

dendrites

• receive incoming signals

• some have dendritic spines (small protrusions from dendrites; thought to be important for brain plasticity)

cell body of neuron

contains most organelles (nucleus, ER, golgi, etc)

axon

• carries signal to next cell

• chemical signals converted into electrical signals

Nodes of Ranvier

• gaps between myelin segments

• high concentration of voltage-gated ion channels

axon hillock

• cone-shaped base of an axon

• site of integration for incoming chemical signals

• decides whether to continue w/ electrical signal or not

synaptic terminal on the sending/presynaptic cell

• electrical signals converted into chemical signals (neurotransmitters) before passing across the synapse

axon growth cone

structure at the extending tip of a developing axon that determines direction of axon growth

sequence of formation of neuronal circuits (simple, 6 steps)

1. polarization (estab. of axon, rest become dendrites)

2. axon growth cone

3. axon guidance (chemoattraction/repulsion)

4. establishment of axonal polarity (stabilization of axon skeleton, maintenance, guided growth, local branching of dendrites)

5. dendritic tiling (dendrites from neighboring neurons start to spread)

6. Synapse formation

formation of neuronal circuits: polarization (step 1)

• establishment of axon

• after neurogenesis is complete, outgrowth begins w/ neurites (small projections)

• microtubules + actin redistribute among neurites —> creation of a single process (the axon); the rest of the protrusions become dendrites

formation of neuronal circuits: axon growth cone

• growth cone: specialized structure at the extending tip of the axon

• highly motile (to explore extracellular environment)

• movement through lameillipodium/filopodia branching from lamellipodium

• determines growth direction

• after growth cone reaches + recognizes appropriate target, it gradually transforms into either a presynaptic ending for an axon or a terminal domain of a dendrite

formation of neuronal circuits: what happens after the growth cone reaches + recognizes its appropriate target?

it transforms into either:

• presynaptic ending for an axon

• terminal domain of a dendrite

formation of neuronal circuits: axonal guidance

• post translational modification

• enzyme recruitment

• adhesion proteins regulate actin/tubulin polymerization/depolymerization

• chemoattraction + chemorepulsion help axons find appropriate target:

  • tropic molecules: help guide axon toward source

  • trophic molecules: support survival/growth of neurons + their processes after contact with target

formation of neuronal circuits: establishment of axonal polarity (step 4)

• identification of axon

• stabilization of axon cytoskeleton

• maintenance, guided growth + local branching of dendrites

formation of neuronal circuits: dendritic tiling

• neighboring neurons of same type spread out their dendrites

• developing dendrites are regulated to prevent growing toward dendrites from the same neuron; dendrites from different neurons repel each other —> ensures adequate coverage/no wasted space