Neurons, Neurotransmission & the Nervous System Flashcards
What are neurons?
Nerve cells
The basic building blocks of the nervous system
What are the three main parts of a neuron?
Soma/cell body
Axon
Dendrites
What is the soma responsible for?
Keeping the cell alive
Contains the nucleus and therefore genetic material
What is the axon responsible for?
Conducts electrical impulses away from the soma to other neurons, muscles, or glands
What are the dendrites responsible for?
Collects messages from neighbouring neurons and sends them to the soma
What are the two things that neurons do?
Generate electricity that creates nerve impulses
Release chemicals to communicate with other neurons, muscles and glands
What are the three stages of electrical activity in neurons?
Resting potential
Action potential
Return to resting potential
Describe resting potential
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)
Describe action potential
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
Describe what happens after an action potential
There is a recovery period (the absolute refractory period) where the membrane is not excitable and cannot discharge another impulse
What are the two benefits of the absolute refractory period?
It stops the charge from moving backwards along the axon
It limits how often a neuron can fire
What is an “all or none event” ?
The idea that action potentials occur either at a uniform and maximum intensity, or not at all
What is a graded potential?
A change in the negative resting potential that does not reach the action potential threshold
What is special about graded potentials?
Multiple graded potentials may combine to trigger an action potential in certain circumstances
What is the myelin sheath?
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)
Give an effect of damage to myelin sheath
Multiple sclerosis
How do neurons communicate with each other?
Via synapses
What is a synapse?
The conjunction of the axon terminal of one neuron and the membrane of another neuron
What is the synaptic space?
The tiny gap between the axon terminal of one neuron and the next neuron
What is a pre-synaptic neuron?
A neuron that sends messages
What is a post-synaptic neuron?
A neuron that receives messages
What are neurotransmitters?
Chemical substances that carry messages across the synaptic space
What are the five steps of chemical communication?
Synthesis
Storage
Release
Binding
Deactivation
Describe synthesis
The neurotransmitter molecules are formed
Describe storage
The neurotransmitter molecules are stored in synaptic vesicles in the axon terminal
Describe release
The action potential causes the neurotransmitter molecules to move out of the vesicles and across the synaptic space
Describe binding
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
Describe deactivation
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
What is an excitatory neurotransmitter?
A neurotransmitter that increases the likelihood of an action potential firing
What is an inhibitory neurotransmitter?
A neurotransmitter that decreases the likelihood of an action potential firing
What is summation?
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
What is acetylcholine?
A neurotransmitter involved in muscle activity and memory
What happens when acetylcholine is underproduced?
It can weaken the neural circuit that stores memories, leading to Alzheimer’s
What happens when acetylcholine is blocked by drugs?
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
What happens when acetylcholine is overproduced?
Violent muscle contractions and convulsions can be caused, e.g. with black widow spider bites
What are neuromodulators?
Chemicals that modulate the sensitivity of neurons to their specific neurotransmitters
Give an example of a neuromodulator and what it does
Endorphins - they travel through the brain inhibiting pain transmission and enhancing pleasurable feelings
What are the three types of neuron?
Sensory neurons
Motor neurons
Inter neurons
What do sensory neurons do?
Carry input messages from the sense organs to the spinal cord and brain
What do motor neurons do?
Transmit output impulses from the brain and spinal cord to the body’s muscles and organs
What do inter neurons do?
Perform connective or associative functions within the nervous system
What are the two branches of the nervous system?
Central Nervous System
Peripheral Nervous System
What does the central nervous system consist of?
Brain
Spinal Cord
What is the spinal cord?
A densely packed bundle of nerve fibres that run along the spine and transmit messages from sensory and motor neurons
What are the two branches of the peripheral nervous system?
Somatic Nervous System
Autonomic Nervous System
What is the somatic nervous system?
A system of sensory and motor neurons that allows us to sense and respond to our environment
What is the autonomic nervous system?
A system that senses the body’s internal functions and controls many glands and muscles - it is largely concerned with involuntary functions
What are the two branches of the autonomic nervous system?
Sympathetic Nervous System
Parasympathetic Nervous System
What is the sympathetic nervous system?
Responsible for the activation or arousal function that occurs when facing stress (fight or flight)
What is the parasympathetic nervous system?
Responsible for the slowing down of the body (one or two organs at a time)
What is homeostasis and how does it relate to the sympathetic and parasympathetic nervous systems?
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
Describe a withdrawal reflex
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)
