Neurons, Neurotransmission & the Nervous System

Question 1

What are neurons?

Answer 1

Nerve cells
The basic building blocks of the nervous system

Question 2

What are the three main parts of a neuron?

Answer 2

Soma/cell body
Axon
Dendrites

Question 3

What is the soma responsible for?

Answer 3

Keeping the cell alive
Contains the nucleus and therefore genetic material

Question 4

What is the axon responsible for?

Answer 4

Conducts electrical impulses away from the soma to other neurons, muscles, or glands

Question 5

What are the dendrites responsible for?

Answer 5

Collects messages from neighbouring neurons and sends them to the soma

Question 6

What are the two things that neurons do?

Answer 6

Generate electricity that creates nerve impulses
Release chemicals to communicate with other neurons, muscles and glands

Question 7

What are the three stages of electrical activity in neurons?

Answer 7

Resting potential
Action potential
Return to resting potential

Question 8

Describe resting potential

Answer 8

Substances are able to pass through the cell membrane of the neuron via ion channels
The ions that remain within the axon of the neuron are more negatively charged than those that pass to the outside of the cell
This results in a net negative charge (polarisation)

Question 9

Describe action potential

Answer 9

The electrical shift that occurs when a neuron is stimulated
Positive sodium ions enter the neuron
This causes a brief depolarisation, which begins at one end of the axon and moves down along it

Question 10

Describe what happens after an action potential

Answer 10

There is a recovery period (the absolute refractory period) where the membrane is not excitable and cannot discharge another impulse

Question 11

What are the two benefits of the absolute refractory period?

Answer 11

It stops the charge from moving backwards along the axon
It limits how often a neuron can fire

Question 12

What is an “all or none event” ?

Answer 12

The idea that action potentials occur either at a uniform and maximum intensity, or not at all

Question 13

What is a graded potential?

Answer 13

A change in the negative resting potential that does not reach the action potential threshold

Question 14

What is special about graded potentials?

Answer 14

Multiple graded potentials may combine to trigger an action potential in certain circumstances

Question 15

What is the myelin sheath?

Answer 15

A layer of fatty insulation that surrounds the axon
It allows electrical conduction to take place at a higher speed (due to the nodes of Ranvier)

Question 16

Give an effect of damage to myelin sheath

Answer 16

Multiple sclerosis

Question 17

How do neurons communicate with each other?

Answer 17

Via synapses

Question 18

What is a synapse?

Answer 18

The conjunction of the axon terminal of one neuron and the membrane of another neuron

Question 19

What is the synaptic space?

Answer 19

The tiny gap between the axon terminal of one neuron and the next neuron

Question 20

What is a pre-synaptic neuron?

Answer 20

A neuron that sends messages

Question 21

What is a post-synaptic neuron?

Answer 21

A neuron that receives messages

Question 22

What are neurotransmitters?

Answer 22

Chemical substances that carry messages across the synaptic space

Question 23

What are the five steps of chemical communication?

Answer 23

Synthesis
Storage
Release
Binding
Deactivation

Question 24

Describe synthesis

Answer 24

The neurotransmitter molecules are formed

Question 25

Describe storage

Answer 25

The neurotransmitter molecules are stored in synaptic vesicles in the axon terminal

Question 26

Describe release

Answer 26

The action potential causes the neurotransmitter molecules to move out of the vesicles and across the synaptic space

Question 27

Describe binding

Answer 27

The neurotransmitter molecules bind themselves to receptor sites that are embedded in the post-synaptic neuron's cell membrane Neurotransmitters fit like a key in a lock and each is specifically complementary to its binding site

Question 28

Describe deactivation

Answer 28

The neurotransmitter molecules are broken down by other chemicals or undergo reuptake - where they are taken back into the pre-synaptic neuron's axon terminal

Question 29

What is an excitatory neurotransmitter?

Answer 29

A neurotransmitter that increases the likelihood of an action potential firing

Question 30

What is an inhibitory neurotransmitter?

Answer 30

A neurotransmitter that decreases the likelihood of an action potential firing

Question 31

What is summation?

Answer 31

The idea that the rate at which an axon fires is determined by the activity of the synapses - if the excitatory neurotransmitters are more active than the inhibitory ones, then an action potential will be caused and vice versa

Question 32

What is acetylcholine?

Answer 32

A neurotransmitter involved in muscle activity and memory

Question 33

What happens when acetylcholine is underproduced?

Answer 33

It can weaken the neural circuit that stores memories, leading to Alzheimer's

Question 34

What happens when acetylcholine is blocked by drugs?

Answer 34

When blocked by botulism paralysis can be caused, potentially even leading to death if the respiratory muscles are paralysed When blocked by botox wrinkles are removed by paralysing the muscles causing these wrinkles

Question 35

What happens when acetylcholine is overproduced?

Answer 35

Violent muscle contractions and convulsions can be caused, e.g. with black widow spider bites

Question 36

What are neuromodulators?

Answer 36

Chemicals that modulate the sensitivity of neurons to their specific neurotransmitters

Question 37

Give an example of a neuromodulator and what it does

Answer 37

Endorphins - they travel through the brain inhibiting pain transmission and enhancing pleasurable feelings

Question 38

What are the three types of neuron?

Answer 38

Sensory neurons Motor neurons Inter neurons

Question 39

What do sensory neurons do?

Answer 39

Carry input messages from the sense organs to the spinal cord and brain

Question 40

What do motor neurons do?

Answer 40

Transmit output impulses from the brain and spinal cord to the body's muscles and organs

Question 41

What do inter neurons do?

Answer 41

Perform connective or associative functions within the nervous system

Question 42

What are the two branches of the nervous system?

Answer 42

Central Nervous System Peripheral Nervous System

Question 43

What does the central nervous system consist of?

Answer 43

Brain Spinal Cord

Question 44

What is the spinal cord?

Answer 44

A densely packed bundle of nerve fibres that run along the spine and transmit messages from sensory and motor neurons

Question 45

What are the two branches of the peripheral nervous system?

Answer 45

Somatic Nervous System Autonomic Nervous System

Question 46

What is the somatic nervous system?

Answer 46

A system of sensory and motor neurons that allows us to sense and respond to our environment

Question 47

What is the autonomic nervous system?

Answer 47

A system that senses the body's internal functions and controls many glands and muscles - it is largely concerned with involuntary functions

Question 48

What are the two branches of the autonomic nervous system?

Answer 48

Sympathetic Nervous System Parasympathetic Nervous System

Question 49

What is the sympathetic nervous system?

Answer 49

Responsible for the activation or arousal function that occurs when facing stress (fight or flight)

Question 50

What is the parasympathetic nervous system?

Answer 50

Responsible for the slowing down of the body (one or two organs at a time)

Question 51

What is homeostasis and how does it relate to the sympathetic and parasympathetic nervous systems?

Answer 51

A delicately balanced and steady internal state These two systems work with each other to maintain this state, and they may also need to coordinate in order for certain functions to be performed, e.g. sex

Question 52

Describe a withdrawal reflex

Answer 52

A noxious stimulus (e.g. hot plate of food) produces a burst of action potentials in the sensory neurons The axons fire The neurotransmitter substance is released This causes the inter neurons to fire The inter neurons excite the motor neurons The motor neurons cause the muscles to release (e.g. withdraw the hand and drop the plate) But, a neuron in the brain excites an inhibitory inter neuron which decreases the rate of firing of the motor neuron (e.g. allowing you to put the plate down safely before dropping it)