Neurons

Question 1

Neuron parts

Answer 1

• Cell body
• Axon
• Dendrites
• Myelin sheath
• Nodes of Ranvier
• Synaptic terminal

Question 2

Cell body

Answer 2

• Nucleus
• Cytoplasm
• Organelles
  □ Mitochondria
  □ Endoplasmic reticulum
  □ Ribosomes
  □ Golgi apparatus
• Carries out the essential cell processes that keep the cell alive

Question 3

Dendrites

Answer 3

○ Short branched extensions from the cell body
○ Consists of the cytoplasm surrounded by the cell membrane
○ Receives impulses from other neurons and receptors
○ Conduct impulses towards the cell body

Question 4

Axon

Answer 4

○ Single (usually) long cylindrical process extending from the cell body
○ Transmits nerve impulses away from the cell body towards other neurons
○ Ends by dividing into synaptic terminals

Question 5

Myelin sheath

Answer 5

○ Made of fate (myelin) and gives axons a white appearance
○ Insulates the axon
○ Protects from damage
○ Increases speed of transmission and impulses

Question 6

Nodes of Ranvier

Answer 6

Gaps in the myelin sheath

Question 7

Types of neurons

Answer 7

○ Classified according to their function - the ‘direction’ they carry their impulses
- Sensory (receptor) neurons
- Connector neurons
- Motor (effector) neurons

Question 8

Sensory neurons

Answer 8

○ Begin with receptors that detect stimuli
- E.g.
□ Internal stimuli (temperature, pH)
□ External stimuli (sounds, tastes)
○ Carry impulses toward central nervous system (brain and spinal cord)
○ Can be identified by the location of their cell body which is on the side of the axon

Question 9

Connector/interneuron

Answer 9

○ Found in the brain and spinal cord
○ Link sensory and motor neurons
○ Transport impulses in both directions
○ Cell body is located centrally

Question 10

Motor neurons

Answer 10

○ Receives impulses from the central nervous system
○ Transmit impulse to muscle cells to achieve a response
○ Cell body is found on the end of the axon

Question 11

Synapses

Answer 11

○ Junction between two or more neurons
○ The very small gap (synaptic cleft) between the neurons (they do not physically touch)
○ Most synapses are between the axon terminal of one neuron and the dendrite of another
○ When an impulse reaches the end of the axon, it causes the release of neurotransmitters (chemicals) from the synaptic terminal
○ The neurotransmitters diffuse across the small space (synaptic cleft) between the two neurons
○ Here is no physical contact between the two nerve cells
○ These neurotransmitters start a new impulse in the next neuron
○ The main neurotransmitters are acetylcholine (memory and muscle contractions), adrenaline, dopamine and histamine

Question 12

Effects of chemicals on the transmission of nerve impulse

Answer 12

○ There are natural chemicals (e.g. venom and synthetic, organophosphates) that influence the transmission of nerve impulses
○ Most of these act at the neuromuscular junction blocking neurotransmitters releasers or receptors causing paralysis
○ Stimulants (e.g. caffeine and benzedrine) stimulate or speed up transmission at the synapse
○ Depressants (e.g. anesthetics or hypnotics) slow down or depress the transmission
○ Botulinum blocks the release of acetylcholine from motor neurons - paralysis