C2.2 (Neural signalling) Flashcards
(45 cards)
What is in the body of a neuron?
Cytoplasm + nucleus
What are axons?
long elongated nerve fibres responsible for transmitting signals away from the cell body
What are dendrites?
short branched nerve fibres that receives signals from other neurons and transmits them toward the cell body
What are the 2 body systems for internal communication?
Nervous system
Endocrine system
What is the membrane potential?
the difference in electric potential (voltage) between the interior and the exterior of a cell
What is the resting membrane potential
The voltage across the neuron’s membrane when it is not transmitting signals (at rest) at -70mV
Because there is a potential difference across the cell membrane, the membrane is said to be
Polarized
Pumps
integral membrane proteins that use active transport
What are two factors contributing to resting potential?
- Na+ and K+ ions leaking back to membrane by diffusion
- Negatively charged ions inside of the neuron
Sodium-potassium pump found in many cell membranes, powered by
ATP which moves NA+ and K+ ions in opposite directions against their concentration gradient (low to high)
The sodium-potassium pump has binding sites for…
3 Na+ ions, 2 K+ ions and an inorganic phosphate group (from ATP)
nerve impulse is electrical because
it involves movement of positively charged ions
Threshold potential is…
the level to which a membrane potential must be depolarized to initiate an action potential.
Action potential, also known as…
Nerve impulse
When a signal reaches the dendrite, the neuron will
fire by sending an electrical impulse called an action potential down the length of its axon
Action potential involves 3 stages:
- Depolarization
- Repolarization
- Refractory period (hyperpolarization)
What happens during depolarization?
- Na+ ions diffuse into membrane and run down the concentration gradient
- Potential typically rises from -70mV to +40mV
- An electrical change within a neuron from a (relatively) negative charge to a positive charge
What happens during repolarization?
- DUe to Sodium channels closing and opening of Potassium channels
- Potassium ions diffuse out of neuron down concentration gradient
- electrical change within a neuron from a (relatively) positive charge to a negative charge
What happens during Refectory Period/ Hyperpolarization/ Rebuilding gradients?
- Period in which neuron is unresponsive to stimulation
- Re establishes Na+ and K+ concentration gradients
What is the Nerve Fibre Structure?
-Circular in cross-section with a plasma membrane enclosing cytoplasm
-Diameter is ~1µm
-Nerve impulses are about 1 m/s on a nerve fibre
Nerve fibre structure diameter
- increasing the diameter reduces resistance → impulses transmit faster
- less leakage of ions from wide diameter axons, results in faster generation of axon potential
- Axons of smaller diameter, the ions face lots of resistance from other molecules (such as proteins)
Structure of Myelin Sheath
- Insulating layer forms around nerves
- Increases the speed of nerve impulses
-Schwann cell: cell that surrounds neurons
-Nodes of Ranvier: gaps between the myelin sheath
-Allows nerve impulses to jump from one node to the next → speeds of transmission (by as much as 100 m/s!)
Why is resting potential negative?
Pums are pumping more sodium out than potassium in
What are synapses?
-a junction between 2 cells in the nervous system
-Signals can only pass in one direction of a synapse
