Neurons structure and function Flashcards
What is a neuron?
A specialised cell that is electrically and chemically excitable
A basic cellular unit of nerves and brains
Responsible for transmitting information to other nerve cells, gland cells and muscles
Describe the structure of a presynaptic cell
Has a cell body that contains the nucleus and other organelles
Has dendrites to receive information from other neurons
Describe the structure of a postsynaptic cell
Has a cell body that contains the nucleus and other organelles
Receives information from the axon terminals
How are ion channels opened and closed?
By specific triggers;
Ligands
Voltage conditions
Association with structural elements
What is a graded potential?
A potential at the cell body
A change from the resting potential that is proportional to the magnitude of the stimulus
A means of integrating stimuli because the membrane can respond with proportional amounts of depolarisation or hyperpolarisation
What is conduction with decrement?
A graded potential ‘s signal will decrease with distance
Describe how conduction with decrement occurs?
Neurotransmitter binds to a ligand gated Na+ channel
The Na+ enters through the open channel
The current will spread through the cell
The signal strength will then decrease with distance
What is spatial summation?
Where signals arriving from dendrites will be summed over a certain space at the axon hillock
What is temporal summation?
Signals arriving at the axon hillock from dendrites will be summed over time
What are the activation and inactivation gates in Na+ channels?
The activation gate opens and allows ions to pass through
The inactivation gate plugs the pore preventing ion passage
What is the resting potential?
-70mV
What is the threshold potential?
-55mV
What is the potential at which the membrane will begin to repolarise?
+30mV
Explain how Na+ channels are activated
At resting potential the inactivation gate plugs the pore preventing Na+ entry
A suprathreshold depolarising graded potential causes the activation gate to open allowing Na+ to enter the cell
Positive feedback loop causes more Na+ channels to open and more Na+ enters the cell
The inactivation gate closes as membrane approaches +30mV preventing Na+ entry and the K+ channels open
K+ leaves the cell which repolarises the membrane
ATPase is Na+/K+ pump
Overshoots-hyperpolartisation then equilibrium
What is the all-or-nothing principle?
When it comes to an action potential, the threshold value of around -55mV is needed to produce an action potential, anything less than this will not result in the production of an action potential
Describe the features of a graded potential
Vary in magnitude Vary in duration Decay with distance Occur in dendrites and the cell body Caused by the opening/closing of many kinds of ion channels
Describe the features of an action potential
Always the same size and shape Always the same duration Don't decay with distance Occur in axons Caused by the opening/closing of voltage gated ion channels
Describe how action potentials move across synapses?
Action potential arrives at axon terminal
Voltage gated Ca2+ channels open and Ca2+ enters the cell and signal to the vesicles
The vesicles move to the plasma membrane
Docked vesicles release neurotransmitter by exocytosis
The neurotransmitter diffuses across the synaptic cleft to the postsynaptic cleft
The neurotransmitter binds to receptors on the post synaptic cell
Explain how acetylcholine moves from the presynaptic cell to the postsynaptic cell
Acetyl CoA is made in the mitochondria
Choline acetyl transferase catalyses the conversion of acetyl CoA and choline into acetylcholine
Acetylcholine is packaged into synaptic vesicles
Acetylcholine is released into synapses
Acetylcholine binds to receptors on the postsynaptic cell
Acetylcholinesterase breaks down the acetylcholine into acetate and choline thus terminating the signal in the postsynaptic cell
The presynaptic cell takes up and recycles the choline and the acetate diffuses out of the cell
What are Glial cells?
A group of different cells surrounding neurons to provide support and insulation
What do astrocytes do?
Maintain homeostasis
What do microglial cells do?
Remove damaged neurons and tackle infections
What do oligodendrocytes do?
Wrap around neurons for insulation
What are Schwann cells?
Oligodendrocytes of the periphery
What do Schwann cells do?
Produce the myelin sheath
What is the myelin sheath?
An extended and modified plasma membrane that is wrapped around the axon in a spiral
How fast are action potentials in myelinated axons?
Up to 100m/s
Are axons myelinated in invertebrates?
No
