3.4 The Cells of the Nervous System and Neurotransmitters at Synapses Flashcards
Describe the structure of a neuron.
Neuron structure involves dendrites, cell body and axon.
Dendrites
These are the parts of a neuron that receive a stimulus and conduct an electrical impulse to the cell body.
Cell body
This is the part of a neuron that contains the nucleus. The cell body connects the dendrites which receive information and the axon which sends information to other neurons / muscles/glands.
Axon
This is a long projection known as a nerve fibre which transmits information in the form of an electrical impulse to another neuron / muscle / gland.
Identify the myelin sheath on a neuron and state its function
Axons are surrounded by a myelin sheath. The myelin sheath insulates the axon and increases the speed of transmission / conduction of an electrical impulse.
Identify the cells that support neurons and produce the myelin sheath.
Glial cells support neurons and produce the myelin sheath – sleeves of fatty tissue that are wrapped around the axon.
Describe the process of myelination during maturation.
Myelination is a process that occurs from birth to adolescence leading to the creation of myelin sheaths around the axons of neurons. This myelination develops over time allowing the nerve impulses to be conducted more rapidly and leading to increasing co-ordination and more rapid responses to stimuli during the first two years of life.
Explain the impact of a disease which destroys the myelin sheath.
Diseases that attack and destroy the myelin sheath reduce the ability of neurons to conduct electrical impulses leading to a loss of co-ordination e.g. multiple sclerosis
Describe the transmission of an electrical impulse across a synapse. (1)
Neurons are connected to other neurons / muscle / glands by synaptic clefts.
Describe the transmission of an electrical impulse across a synapse (2)
A synaptic cleft is a physical gap across which neurotransmitters will diffuse to relay an electrical impulse across the synaptic cleft.
Describe the transmission of an electrical impulse across a synapse (3)
When an electrical impulse travels through the pre-synaptic neuron and reaches the axon ending, this triggers the release of neurotransmitters which are stored in vesicles.
Describe the transmission of an electrical impulse across a synapse (4)
The neurotransmitters are released into the synaptic cleft and diffuse across the gap where they bind to receptors in the post-synaptic neuron
Describe the transmission of an electrical impulse across a synapse (5)
When enough neurotransmitter molecules have bound to receptors, this triggers an electrical impulse in the post-synaptic membrane or causes a muscle contraction or a gland secretion.
Explain what is meant by the term ‘threshold level’
A minimum number of neurotransmitter molecules must attach to the receptors in the post-synaptic membrane in order to trigger an impulse to fire in the post-synaptic neuron. This minimum number of neurotransmitter molecules is referred to as the threshold level.
State what is meant by ‘summation’.
Summation is the term used to describe the adding together of weak stimuli either from multiple presynaptic neurons or from a series of stimuli in order to reach the threshold level required to trigger a nerve impulse to fire in the postsynaptic neuron. Summation occurs in a converging neural pathway such as the rods of the retina in dim light.
