ANA 305 Intro To Nervous System

Question 1

What is axonal transport

Answer 1

Axoplasmic transport (axonal transport) is a cellular process responsible for movement of mitochondria, lipids, synaptic vesicles, proteins and other cell parts (i.e organelles) to and from a neuron’s cell body, through the cytoplasm of its axon (axoplasm).
• Axonal transport is also responsible for moving molecules destined for degradation from the axon back to the cell body, where they are broken down by lysosomes.
• Axonal transport can be fast or slow and anterograde or retrograde.

Question 2

Types of axonal transport

Answer 2

Retrograde and Anterograde

Question 3

Retrograde transport

Answer 3

RetrogradeTransport
• Movement of molecules/organelles inward, away from the synapse or plasma membrane towards the cell body or Soma is called retrograde transport.
• Retrograde transport is mediated by dynein and is used for example to send chemical messages and endocytosis products headed to endolysosomes from the axon back to the cell.
• Fast retrograde transport can cover 100-200mm per day.

Question 4

Anterograde Transport

Answer 4

• Movement of molecules /organelles outward, from the cell body to the synapse or cell membrane is called anterograde transport.
• Fast and Slow components along microtubules mediated by KINESIN
• Two classes of slow anterograde transport:
• Slow component a (Sca) that carries mainly microtubules
and neurofilaments at 0.1-1mm/day.
• Slow component b (SCb) that carries over 200 diverse proteins and actin at a rate of up to 6mm/day.
• Actin are transported at a rate of 2-3mm/day in retinal cell axons

Question 5

What is Wallerian degeneration

Answer 5

Wallerian degeneration is a process that results when a nerve fiber is cut or crushed, in which the part of the axon separated from the neuron’s cell body degenerates distal to the injury.
• This is also known as Anterograde or orthograde degeneration.
• It is also a degeneration of a nerve that has been separated from its nutritive center by injury.
• Wallerian degeneration occurs after axonal injury in both the peripheral nervous system (PNS) and central nervous system (CNS).
• It occurs in the axon stump distal to a site of injury and usually begins within 24-36 hours of a lesion.

• Prior to degeneration, distal axon tends to remain electrically excitable.
• After injury, the axonal skeleton disintegrates and the axonal membrane breaks apart.
• The axonal degeneration is followed by degeneration of the myelin sheath and infiltration by macrophages which result in atrophy and destruction of the axon.