Topic 8: Nervous System Flashcards
What are neurons?
nerve cells that transfer information within the body
What are the two types of signals neurons use to communicate?
electrical signals (long-distance) and chemical signals (short-distance)
Where are most of a neuron’s organelles?
the cell body
What are dendrites?
highly branched extensions that receives signals from other neurons
What is an axon?
a much longer extension that transmits signals to other cells at synapses
What is the axon hillock?
the cone-shaped base of an axon
What are neurotransmitters?
chemical messengers that pass information from the synaptic terminal of one axon across the synapse
What is a synapse?
a junction between an axon and another cell
Where do information transmit from and to?
from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell)
What cells are neuron cells supported by?
glia or glia cells
What are the three stages of the nervous system?
- sensory input
- integration
- motor output
What happens during sensory input?
sensors detect external stimuli and internal conditions and transmit information along sensory neurons
What happens during integration?
sensory information is sent to the brain or ganglia, where interneurons integrate the information
What happens during motor output?
motor output leaves the brain or ganglia via motor neurons, which trigger muscle or gland activity
What are three classes of neurons?
- sensory neuron
- interneuron
- motor neuron
What is the central nervous system?
(CNS) where integration takes place; this includes the brain and a nerve cord
What is the peripheral nervous system?
(PNS) which carries information into and out of the CNS
What forms nerves?
bundles of PNS neurons
What establishes the resting potential of a neuron?
ion pumps and ion channels
What is a membrane potential?
a voltage (difference in electrical charge) across its plasma membrane
What is the resting potential?
the membrane potential of a neuron not sending signals
What is the resting potential in mammalian neurons (concentrations)?
the concentration of K+ is the highest inside, while the concentration of Na+ is highest outside the cell
What are the sodium-potassium pumps?
use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane
What is the function of the opening of ion channels?
converts the chemical potential to electrical potential
What is the resting potential in mammalian neurons (channels)?
many open K+ channels and fewer open Na+ channels
What is the major source of membrane potential?
the resulting buildup of negative charge within the neuron
What are action potentials?
signals conducted by axons
Why do changes in membrane potential occur?
neurons contain gated ion channels that open or close in response to stimuli
What are graded potentials?
changes in polarization where the magnitude of the change varies with the strength of the stimulus
What causes an action potential?
a sufficient depolarization results in a non-linear change in membrane voltage
What are the characteristics of action potentials?
have a constant magnitude, are all-or-none, and transmit signals over long distances
What happens during resting potential?
most voltage-gated sodium (Na+) and potassium (K+) channels are closed
What happens during depolarization?
voltage-gated Na+ channels open first and Na+ flows into the cell
What happens during the rising phase of the action potential?
the threshold is crossed, and the membrane potential become positive
What happens during the falling phase of the action potential?
voltage-gated Na+ channels become inactivated; voltage gated K+ channels open, and K+ flows out of the cell
What happens during undershoot?
membrane permeability to K+ is at first higher than at rest, then voltage-gated K+ channels close and resting potential is restored
What is the refractory period?
after an action potential, a second action potential cannot be initiated
How is the speed of action potential propagation limited in unmyelinated axons?
the time it takes to move along every section of the membrane
What is the function of the refractory channels?
- prohibits the action potential from going backwards
- limit the frequency of firing a second one cannot follow two closely after
What is the relationship between action potential and diameter?
the speed of an action potential increases with the axon’s diameter
What is the speed difference between myelinated and non-myelinated axons?
the speed of action potential propagation is 15x faster (150 m/sec or 335 mph) than with non-myelinated axons (with no increase in axon diameter)
What is saltatory conduction?
myelin sheath allows the action potential to jump from node to node; can only be generated at the nodes
What is the function of refractory periods (2)?
- prevents backward propagation
- sets an upper limit on frequency of firing
What are the mechanisms for electrical synapse (3)?
- coordinates adjacent cells
- rapid synaptic transmission
- bidirectional
What are the mechanisms for chemical synapse (3)?
- amplifies signals
- diversity of postsynaptic responses
- plasticity allows for flexibility
What does direct synaptic transmission involve?
binding of neurotransmitters to ligand-gated ion channels in postsynaptic cell causing ion channels to either open or close, generating a postsynaptic potential
What is excitatory postsynaptic potentials (EPSPs)
depolarizations that bring the membrane potential toward threshold
What is inhibitory postsynaptic potentials (IPSPs)
hyperpolarizations that move the membrane potential farther from threshold
When do receptor activation and postsynaptic response cease?
when neurotransmitters are cleared from the synaptic cleft
How are neurotransmitters removed?
by simple diffusion, inactivation by enzymes, or recapture into the presynaptic neuron
What happens in neural plasticity?
- connections between neuron are strengthened or weakened in response to activity
- if two synapses are often active at the same time, the strength of the postsynaptic response may increase at both synapses
What is long-term potentiation (LTP)?
- an increase in the strength of synaptic transmission
- involves glutamate receptors
What happens when presynaptic and postsynaptic neurons are stimulated at the same time?
the set of receptors present on the postsynaptic membranes changes
What is the gyrus?
a small protrusion or bump formed by the folding of the cerebral cortex
What is the sulcus?
a groove in brain matter, often found in the neocortex or cerebellum
What is the fissure?
a very deep sulcus
What is the function of cerebrospinal fluid?
fills the central canal of the spinal cord and the ventricles of the brain, which supplies the CNS with nutrients and hormones and carries away wastes
What is gray matter?
neuron cell bodies, dendrites, and unmyelinated axons
What is white matter?
bundles of myelinated axons
What is the function of the peripheral nervous system?
transmits information to and from the CNS and regulates movement and the internal environment
What is the function of afferent neurons?
transmit information to the CNS
What is the function of efferent neurons?
transmit information away from the CNS
What is the sympathetic division?
regulates arousal and energy generation (“fight-or-flight” response)
What is the parasympathetic division?
antagonistic effects on target organs and promotes calming and a return to “rest and digest” functions
