Grey matter Flashcards
describe the function of a motor neuron
- transmitting electrical signals from CNS to effectors - glands and muscles.
Describe the structure and function of a sensory neuron
Cell body in the middle of the cell
transmits impulses from receptors to CNS
describe the structure and function of a relay neuron.
- located within the CNS, and transmit electrical impulses from sensory to motor neurons.
- lots of short dendrites and a long axon, with the cell body at the end of the neuron.
Describe the function of myelin sheath
- increases the speed of impulses by acting as an electrical insulator, allowing travel by saltatory conduction.
What factors affect transmission of an impulse?
- thickness of the neuron.
Describe the process in an axon that allows nerve impulses to be detected.
- potential difference across the axon changes from -70 to +40mV.
- voltage gated sodium channels open.
- causing sodium ions to move into axon.
- this causes potassium channels to open
- this causes repolarisation as potassium ions move out of the axon.
Describe the role of dendrites in a neuron.
- forms connection with other neurons
- receives impulses from other neurons
- initiate an action potential to the cell body/axon.
Describe the process of synaptic transmission
- on the arriving of action potential, the presynaptic neuron depolarises, and causes Ca2+ channels to open, and allow flow of Ca2+ ions into the neuron.
- This causes the fusion of synaptic vesicles filled with a certain neurotransmitter to the presynaptic neuron membrane into the synaptic cleft (the gap between)
- the neurotransmitter binds to receptors on the postsynaptic membrane, which stimulates Na+ ions to move in, causing another action potential (due to depolarisation)
- following the breakdown of the neurotransmitter, its taken up by the pre synaptic membrane and reused - this (presence of receptors on only one side) and the refractory period allows for travel in only one direction.
Name 3 processes Schwann cells are involved in.
- Phagocytosis
- electrical insulation
- nerve regeneration
Describe the role of the dendrites in a neurone.
- connect neurons to each other
- allow for receiving impulses from other neurons
- involved in summation
Describe the sequence of events that leads to the formation of an image.
- Light (stimulus) is received by the photoreceptor cells in the retina
- this causes impulses to travel up the CNS via the optic nerve
- info is passed on to the brain via a relay neuron
- info is processed
- Impulses sent down relay neuron to motor neuron
- Motor neuron impulses received by effector which carries out response (radial muscles and circular muscles)
Describe what happens to the radial and circular muscles when there is very little light
- pupil dialates
- because circular muscles relax
- radial muscles contract
Describe what happens to the radial and circular muscles when there is a lot of light
- pupil contracts
- circular muscles contract
- radial muscles relax.
describe saltatory conduction
- the idea of impulses ‘jumping’ from one node of Ranvier to another- which reduces the potential difference of the next node, causing the impulse to jump - initiating another action potential.
Excitatory neurons
- neurons that make the membrane more permeable to Na+ ions
- making it more likely that the threshold potential will be reached
- and more likely that the neuron will depolarise.
Inhibitory neurons
- make membrane more permeable to Cl- ions
- so less likely that the threshold potential will be reached
- so less likely the neuron will depolarise
Spatial summation
- when simultaneous impulses from multiple different neurons come along a pre-synaptic neuron to a post synaptic neuron
- number of these impulses coming determines response.
Temporal summation
- multiple impulses coming one after another in a short amount of time on one pre-synaptic neuron
- the time interval has to be short - only then can they summate and initiate an action potential.
what causes plant cells to elongate?
- auxins
Where are auxins released
- the darkest part of the shoot
what is a tropism
- growth in response to a stimulus
What are shoots in a seed showing?
- negatively gravitropic
Describe the role of photoreceptors
- name 2 types of photoreceptors in the eye.
- to detect light
- rods and cone
What do the rods and cones synapse with?
- bipolar neurons