neuron cell biology lab Flashcards
what is hillock ?
The hillock is an expanded area of the soma marking the origin of the axon. Nerve impulses arise at the junction of the axon hillock and the axon itself.
what is myelin sheath and function ?
The myelin sheath is formed by specific glial cells that wrap themselves around the axon. Spaces between these cells are known as the nodes of Ranvier. The qualities of the glial cells cause the action potentials to jump from node to node, thus increasing the speed that information is transmitted.
what is terminal arborizations ?
The terminal arborizations, also known as telodondria, are branches of the axon.Their tips form expansions known as synaptic knobs that form synapses with other neurons, muscles, or glands. These synapses contain synaptic vesicles filled with neurotransmitters that are released in response to an action potential in order to stimulate an adjoining neuron.
what is axon and its function ?
An axon is a single process that arises from the hillock of the soma. It may be over 1 m in length in humans and carries information to other neurons, muscles, glands, or lymphatic tissue. It contains axoplasm, and is surrounded by a sheath known as an axolemma.
what is cell body and its function ?
The soma is the cell body of the neuron. It is the part of the cell that surrounds the nucleus, containing the major cytoplasmic organelles, and where the dendrites and an axon branch off. In addition to the nucleus, the soma contains
. nissl bodies
. cytoskeleton
what is nissl body ?
The Nissl bodies are formed by ribosomes and rough endoplasmic reticulum. They synthesize proteins and neurotransmitters.
what is dendrite and what is its function ?
The dendrites are short, cytoplasmic branches that radiate from the soma and can receive input from the axons of other neurons. In sensory neurons, dendrites can serve as receptors.
why do neurons not have centrioles ?
Because centrioles function in cell division, the fact that neurons lack these organelles is consistent with the amitotic nature of the cell.
neurons don’t divide
what is nodes of ranvier ?
These are the gaps formed between the myelin sheath where the axons are left uncovered.
what are ganglion ?
a collection of neuron cell bodies situated in the PNS
what are nerves ?
bundles of axons that extend out from the spinal cord as spinal nerves
what are tract ?
a bundle of axons ( nerve fibres ) within the CNS
explain the resting potential of a cell ?
All cells have a ‘resting potential’, meaning when at rest the overall charge of ions inside the cell are negative compared to the ions outside the cell in the extracellular fluid. The difference in charge across the cell membrane of a neuron creates a potential electrical difference of about -70mV. The cell membrane maintains this resting potential by selectively allowing some ions to pass into the cell via special channels or gates and by blocking the entry of other ions. Due to the electrochemical gradients Na+ slowly diffuses into the neuron and K+ slowly diffuses out of the neuron. Because of this natural diffusion the resting neuron must actively pump Na+ out of the cell and take K+ in to maintain its resting potential of -70 mV.
what happens when neuron becomes depolarised ?
When a neuron is stimulated it becomes depolarised by the exchange of ions across it. NA channels open allowing sodium ions to move inside the cell. The sodium ions are positively charged and are attracted into the cell by the negatively charged ions inside, as well as the lower sodium concentrations. The influx of positive ions reverses (depolarises) the resting potential and the inside of the neuron becomes more positively charged. When depolarisation reaches a certain level or threshold,, it triggers the opening of more sodium channels which in turn triggers the opening of sodium channels in the adjacent cell membrane. Thus, depolarisation is spread along the entire cell membrane in a wave; this is an action potential and conducts the nerve impulse along the axon. Once the action potential reaches the end of the axon the action potential is converted to a chemical signal by the release of a neurotransmitter. The inside of the cell continues to depolarise until the voltage peaks at about +35mV, at which point the cell membrane closes its sodium channels so that no more Na+ can enter, and opens its K+ channels to allow the positively charged K+ ions to leave the cell. This process reverses the depolarisation (repolarisation) and allows the neuron to return to its original resting potential of -70mV
what is speed at which action potential is propagated along a neuronal axon determined by ?
- Myelination of neuronal axons enables faster propagation of action potentials along the plasma membrane due to saltatory conduction.
- The larger the diameter of a nerve fiber axon, the larger the surface area for an action potential to travel along and therefore the faster the rate of propagation.
