Grey Matter Flashcards
Which direction do dendrites travel?
Towards the cell body.
Which direction do axons travel?
Away from the cell body.
Describe a reflex arc.
Receptors detect a stimulus. Sensory neurons conduct a nerve impulse to the CNS which enters the spinal cord through the dorsal route. A synapse is formed with a relay neuron and then a motor neuron via the ventral route. The motor neuron transmits the impulse to an effector.
Describe the pupil reflex.
Light strikes photoreceptors in the retina. Sensory neurons pass nerve impulses along the optic nerve to the CNS. These impulses are sent along parasympathetic motor neurons. Circular muscles contract and radial muscles relax. The pupil constricts, reducing the amount of light entering the eye.
Describe the resting potential.
-70mV.
The inside of the axon is more negative than the outside and hence the membrane is polarised.
Na+/K+ pump creates a concentration gradient. K+ diffuses out of the cell, down a concentration gradient, the membrane becomes polarised. The potential difference pulls K+ back inside the cell. There is no net movement of K+.
Describe an action potential (depolarisation, repolarisation and hyperpolarisation).
Depolarisation occurs when voltage-dependent gated Na+ channels open, causing a flow of Na+ ions. All-or-nothing. Potential difference of +40mV. There is a refractory period to ensure that impulses only travel one way.
Repolarisation occurs when Na+ channels close but K+ channels open. K+ ions leave the axon down an electrochemical gradient, repolarising the membrane.
Hyperpolarisation happens when more ions move out of the cell than usual. K+ channels close and K+ diffuses back into the axon.
What does the size of a stimulus affect?
Frequency of impulses.
Number of neurons in a nerve conducting impulses.
Define saltatory conduction.
An impulse jumps from one node to the next due to an electrical current inducing an action potential.
Describe speed of conduction.
Determined by the diameter of an axon. Speed is quicker for normal squid but slower for a giant squid.
The myelin sheath acts as an electrical insulator and the depolarisation occurs in the nodes of Ranvier.
Describe the process of neurotransmission.
An action potential arrives at the pre-synapse. The membrane depolarised and Ca2+ channels open. Synaptic vesicles fuse with the pre-synapse membrane. The neurotransmitter is released into the synaptic cleft and binds with receptors on the post-synaptic membrane. Cation channels open and Na+ ions flow through. The membrane depolarises and causes an action potential. Neurotransmitter is taken up by the pre-synapse membrane.
What are synapses used for?
Control of nerve pathways.
Integration of information from different neurons.
Describe excitatory synapses.
Post-synaptic membrane is more permeable to Na+ ions.
Define spatial summation.
Different synapses, different neurons.
Define temporal summation.
Several impulses from a single neuron.
Describe inhibitory synapses.
Less likely for there to be an action potential. Cl- and K+ channels are opened. Greater potential difference leads to hyperpolarisation.
What are the differences between nervous and hormonal control?
Nerves transmit signals electrically, hormones transmit signals chemically.
Nerves are fast acting, hormones are slow acting.
Nerves create short-term changes, hormones create long-term changes.
Nerves are transmitted in action potentials, hormones are transported in blood.
Nerves have a local response, hormones have a widespread response.
How does auxin work?
Stimulates growth in response to cell elongation.
Increased concentration on shaded side increases cell elongation, reduced concentration on illuminated side inhibits cell elongation.
What other factors are plants sensitive to?
Gravity.
Touch.
Mechanical stress.
Describe rod cells in the dark.
Na+ ions flow through non-specific cation channels and move down a concentration gradient. Depolarises the cell. Glutamate is released and binds to bipolar cells.
Describe rod cells in the light.
Light falls on rhodopsin which breaks down into retinal and opsin. Opsin stimulates hydrolysis of nucleotides, closing cation channels, the inside of the cell is hyperpolarised. Glutamate is inhibited. The bipolar cell is depolarised, an action potential is induced.
