Nervous System Flashcards
What is depolarisation of membrane potential?
Decrease in potential which means the membrane is less negative
What is repolarisation of membrane potential?
Return to resting potential after depolarisation
What is hyperpolarisation of membrane potential?
Increase in potential which means the membrane is more negative
What are gated channels?
Channels which contain movable folds in the protein that can be open or closed
What are voltage gated ion channels?
Open/close in response to changes in membrane potential
What are chemically gated ion/ligand gated ion channels?
Change conformation in response to the binding of a specific chemical messenger
What are mechanically gated ion channels?
Respond to stretching or other mechanical deformation
What is the difference between graded potential and action potential?
- Graded potential - short distances, strength diminishes over distance
- Action potentials - long distance, strength does not diminish over ditance
What are five examples of graded potentials?
- Postsynaptic potentials
- Receptor potentials
- End-plate potentials
- Pacemaker potentials
- Slow wave potentials
What is a nerve?
A bundle of axons outside of the central nervous system
What is a fibre tract?
A bundle of axons inside the central nervous system
What is the axon hillock?
The first portion of the axon plus the region of the cell body from which the axon leaves
What are the two methods of propagation?
- Contiguous conduction
- Saltatory conduction
What is contiguous conduction?
The way an action potential travels along the axon of a neuron that is unmyelinated
What is saltatory conduction?
The way an action potential travels along the axon of a neuron that is myelinated
What is the refractory period?
Time period when a recently activated patch of membrane is unresponsive to further stimulation
What is the purpose of the refractory period?
Prevents an action potential from spreading backwards into the are through which it just passed
What are the two types of refractory periods?
- Absolute refractory period
- Relative refractory period
What is the absolute refractory period?
No new action potential no matter how strong the stimulus
What is the relative refractory period?
A second action potential can be initiated but it requires a stronger stimulus
What does a longer refractory period result in?
In a greater delay
What determines the strength of a stimulus?
The frequency of action potentials
What are the two things that influence speed of an action potential?
- Fibre myelination
- Fibre diameter
What are myelinated fibres?
Neuronal axons covered at regular intervals in myelin
What is the role of myelin coating on neural axons?
Acts as an insulator to prevent current leakage
What creates the myelination in the central nervous system?
Oligodendrocytes
What creates the myelination in the peripheral nervous system?
Schwann cells
What are nodes of ranvier?
short regions in the axonal membrane that are not insulated by myelin
How does saltatory conduction occur?
Action potential leaps over myelinated sections conducting the impulse 50x faster
What are electrical synapses?
Transfer of action potential waveforms through gap junction with negligible time delay
What response are electrical synapses used for?
Flight response
What are chemical synapses?
When nerves and target cells do not make direct contact converting action potentials into neurotransmitters
How are chemical synapses different to electrical synapses?
- Much slower than
- Operate in one direction
- Allow for various kinds of signalling events
What are the steps to an action potential traveling through a chemical synapse?
- Action potential reaches the terminal of presynaptic neuron
- Ca2+ enter the synaptic knob
- Neurotransmitter released by exocytosis into synaptic cleft
- Neurotransmitter binds to receptor sites on the postsynaptic neuron
- Specific ion channels open in the subsynaptic membrane
What are excitatory responses?
Occurs when neurotransmitters cause positive ions to enter the neuron making the inside less negative and increasing the likelihood of an action potential
What are inhibitory responses?
Occurs when neurotransmitters cause negative ions to enter or positive ions to leave the neuron making the inside more negative and decreasing the likelihood of an action potential
What are the three ways neurotransmitters are removes from the synaptic cleft?
- May diffuse away
- Is inactivated by specific enzymes
- Is taken back into the axon terminal
What is temporal summation?
Rapid repetitive excitation from a single persistent input
What is spatial summation?
Excitation occurring simultaneously from several different presynaptic inputs
Where does the action potential originate?
In the axon hillock
What is the axon hillock?
Where the axon originates from
What is in the central nervous system?
Brain and spinal cord organised into a continuous column of neuron cell bodies and bundle of axons
What is the peripheral nervous system?
Nerve fibres that carry information between CNS and other parts of the body subdivided into afferent and efferent divisions
What is the somatic nervous system?
Innervates skeletal muscles and controls voluntary actions
What is the autonomic nervous system?
Innervates the smooth muscle, cardiac muscle, glands and non-motor organs and controls involuntary actions
What are the two subdivisions of the autonomic nervous system?
- Sympathetic nervous system
- Parasympathetic nervous system
What is the sympathetic nervous system in charge of?
Fight or flight responses
What is the parasympathetic nervous system in charge of?
Rest and digest
What are glial cells?
Are non-neuronal cells in the nervous system that provide support and protection to neurons
What are the four types of glial cells in the central nervous system?
- Astrocytes
- Oligodendrocytes
- Ependymal cells
- Microglia
