Mod. 5 Neuronal communication

Question 1

sensory neuron

Answer 1

• cell body comes off of the axon, contains the nucleus
• responds to stimuli and passes on an action potential to the relay neuron.
• charge of -70μv
• myelinated sheath with nodes of Ranvier
• conducts impulses towards the cell body

Question 2

relay neuron

Answer 2

• located in grey matter of the CNS
• charge of -70μv
• lots of dendrons leading to cell body located at the end where the action potentials originate from. (head of the cell)
• intermediary neuron between sensory and motor neurons.
• no myelinated sheath

Question 3

motor neuron

Answer 3

• cell body at head of cell (end where action potentials originate from)
• head of cell is located in grey matter of CNS
• myelinated sheath with nodes of Ranvier
• charge of -70μv
• terminal branches in the muscles

Question 4

dendrites

Answer 4

• conducts impulse towards cell body
• very thin
• also can have receptor endings

Question 5

axon

Answer 5

• contains axoplasm
• negative charge of -70μv
• conducts impulses away from the cell body
• contains branches which end in swellings/synaptic bulbs
• contains organelles such as mitochondria in the synaptic bulbs.

Question 6

dendrons

Answer 6

• most apparent in sensory neurons

- conduct impulses towards cell body

Question 7

what are the properties of a neuron’s cell body?

Answer 7

• contains the nucleus
• cytoplasm has many organelles; many ribosomes, rough e.r. and mitochondria because it needs lots of ATP.
• the cell body is the metabolically active part of the cell

Question 8

Myelin sheath

Answer 8

• fatty layer
• made of the plasma membrane of schwann cells
• protects the axon, charged ions cannot pass through
• not present on all neurons (i.e. relay neurons)
• presence of the myelin sheath speeds up the conduction of an action potential
• electrically insulating

Question 9

Schwann cells

Answer 9

• cells that wrap around the axon that are electrically insulating
• make the myelin sheath

Question 10

nodes of Ranvier

Answer 10

• gaps between Schwann cells
• in humans they are 2μm
• contains ion channels allowing action potentials to occur.
• action potentials jump between nodes on myelinated axons.

Question 11

Who were Huxley and Hodgekin and what was their scientific discovery?

Answer 11

• scientists that worked with giant squids.
• giant squids have giant axons 1μm in diameter.
• they recorded the potential difference across the membrane, -70μv is the resting potential, this is negative compared to the potential outside the cell.

Question 12

What causes resting potential?

Answer 12

• active transport of ions across the membrane. sodium potassium pumps remove 3Na+ ions for every 2K+ pumped in. process requires ATP (hence large number of mitochondria)
• there is a differential permeability in the membrane, it is more permeable to Na+ than K+. K+ diffuse out of the axon by facilitated diffusion
• some anions like Cl- stay inside the axon.

Question 13

What is action potential?

Answer 13

• a stimulus causes a change in charge on the membrane, causing the charges in the axon to be reversed temporarily.
• the change in charge has to reach -50μv to become an action potential.
• the voltage gated Na+ channels are opened, so Na+ ions enter channel down their electrochemical gradient. The inside becomes less negatively charged.
• when the potential difference is +40μv, the Na+ channels close, and the K+ channels open.
• the K+ ions leave the axon, making it negative in comparison to the outside. It becomes more negative than the resting potential, so the K+ ions close.

Question 14

What are the stages of the transmission of an action potential?

Answer 14

1. resting potential at -60μv. Na+/K+ pumps are active.

2. action potential increase to +40μv