13.2 Neurons

Question 1

define stimulus

Answer 1

a detectable change in external or internal environment of an organism

Question 2

define neuron

Answer 2

specialised cell which transmits impulses in the form of action potentials

Question 3

describe the cell body

Answer 3

• contains the nucleus
• surrounded by cytoplasm
• large amounts of endoplasmic reticulum and mitochondria which produce neurotransmitters

Question 4

define neurotransmitter

Answer 4

chemicals which are used to pass signals from one neuron to the next

Question 5

describe dendrons

Answer 5

• short extensions which come from the cell body
• divide into smaller branches called dendrites
• transmit electrical impulses towards the cell body

Question 6

describe the axon

Answer 6

• singular, elongated nerve fibres that transmit impulses away from the cell body
• fibre is cylindrical consisting of a very narrow range of cytoplasm surrounded by a plasma membrane

Question 7

describe sensory neurons

Answer 7

• transmit impulses from a sensory receptor –> relay/motor neuron or the brain
• have one dendron (carries impulse to cell body)
• have one axon (carry impulse away from the cell body)

Question 8

describe relay neurons

Answer 8

• transmit impulses between neurons

- short axons and dendrons

Question 9

describe motor neurons

Answer 9

• transmit impulses from a relay/sensory neuron –> effector
• one long axon
• many short dendrites

Question 10

what pathway do electrical impulses follow

Answer 10

receptor – > sensory neuron –> relay neuron –> motor neuron –> effectors

Question 11

describe the myelin sheath

Answer 11

• cover axons of some neurons
• made up of Schwann cells (produce layers of membrane by growing around the axon - each time they grow, a double layer of phospholipid bilayer is laid down)
• acts as an insulating layer
• can conduct electrical impulses faster

Question 12

how fast can myelinated neurons conduct impulses compared to non-myelinated neurons

Answer 12

myelinated = 100m per sec

non-myelinated = 1m per sec

Question 13

what is the node of Ranvier and what does it do

Answer 13

• small gap between each adjacent Schwann cell
• occur every 1-3mm in humans
• electrical impulse jumps from one node to the next allowing the impulse to be transmitted faster