5.1.3 - Neuronal Communication Flashcards
What is a stimulus?
A change in the internal or external environment
What are the main 3 key features of a neurone?
Cell body, dendrons, axons
What is the cell body?
Contains the nucleus surrounded by cytoplasm. Cytoplasm contains large amounts of endoplasmic reticulum and mitochondria which are involved in neurotransmitter production
What are dendrons?
Short extensions which come from the cell body. They divide into smaller and smaller branches called dendrites. They are responsible for transmitting electrical impulses towards the cell body
What are axons?
Elongated nerve fibres that transmit impulses away from the cell body
What are the three types of neurones?
Sensory, relay, and motor
Describe sensory neurones
Neurones that transmit impulses from a sensory receptor to a relay neurone, motor neurone, or the brain. They have one dendron, which carries the impulse to the cell body, and one axon, which carries the impulse away from the cell body
Describe relay neurones
Neurones that transmit impulses between neurones
Describe motor neurones
Neurones that transmit impulses from a relay neurone or sensory neurone to an effector. They have one long axon and many short dendrites
What covers the axons of some neurones?
Myelin sheath, made of many layers of plasma membrane. They are produced by Schwann cells
What is a mechanoreceptor?
A receptor that responds to pressure and movement
What is a chemoreceptor?
A receptor that responds to chemicals
What is a thermoreceptor?
A receptor that responds to heat
What is a photoreceptor?
A receptor that responds to light
How do receptors act as transducers?
They detect a range of different stimuli, before converting the stimulus into a nervous impulse, called a generator potential
Describe the processes taking place at resting potential
Sodium-potassium pump is active, 3 Na+ pumped out for every 2 K+ pumped in. Most gated Na+ channels are closed, so few Na+ ions diffuse back into the axon, while many K+ channels are open, so lots of K+ ions diffuse out.
What is depolarisation?
A change in potential difference from negative to positive
What happens when a stimulus is detected?
Energy from stimulus triggers some Na+ ion channels to open, making membrane more permeable to Na+ ions. Na+ ions diffuse in, increasing the membrane potential
What does the increase in charge cause?
More Na+ ion channels to open. This is positive feedback
What happens when the potential difference reaches +40 mV?
Na+ ion channels close and K+ ion channels open.
What happens once the K+ ion channels open?
K+ ions diffuse out of the axon, decreasing membrane potential. It becomes more negative than its resting state, which is known as hyperpolarisation
What happens after hyperpolarisation?
K+ ion channels close. Sodium potassium pump is still active. Axon returns to membrane potential.
What is meant by the all or nothing principle?
Nerve impulses are said to be all-or-nothing responses. A certain level of stimulus, a threshold value, always triggers a response.
What are the two types of neurotransmitter?
Excitatory, which causes depolarisation of the postsynaptic neurone, and inhibitory, which causes hyperpolarisation of the postsynaptic neurone
What happens during synaptic transmission?
Action potential reaches end of presynaptic neurone. Depolarisation of presynaptic neurone causes Ca+2 ion channels to open, so Ca+2 enters, causing secretory vesicles containing neurotransmitters to fuse with the presynaptic membrane. Exocytosis takes place. Neurotransmitters diffuse across the cleft, and bind with the receptor. This causes Na+ ion channels to open, so Na+ ions move into the postsynaptic neurone, so action potential starts
What happens after the neurotransmitter has triggered an action potential in the postsynaptic neurone?
It is broken down and removed.
What is spatial summation?
When a number of presynaptic neurones connect to one postsynaptic neurone. Each releases neurotransmitters which builds up to a high enough level in the synapse to trigger an action potential in the single postsynaptic neurone
What is temporal summation?
When a single presynaptic neurone releases neurotransmitters as a result of an action potential several times over a short period. This builds up in the synapse until the quantity is sufficient to trigger an action potential
What are the roles of synapses?
They ensure impulses are unidirectional, they allow one stimulus to cause many responses, and they can allow many stimuli to cause one response
