Basic Principles of Sensory Physiology Flashcards
What is neural processing?
- the interaction of the signals of many neurons
What makes up a neuron?
- cell body
- dendrites
- axon/nerve fiber
What is the cell body?
- contains mechanisms to keep the cell alive
What are dendrites?
- branch out from the cell body to receive electrical signals from other neurons
What is the axon/nerve fiber?
- filled with fluid that conducts electrical signals
What are sensory receptors?
- specialized neurons that respond to specific kinds of energy
- neurons specialized to respond to environmental stimuli
How many neurons are there?
- hundreds of millions
How do we record electrical signals in neurons?
- Small electrodes are used to record from single neurons - recording electrode
- Recording electrode is inside the nerve fiber
- Reference electrode is outside the fiber, some distance away so it is not affected by the electrical signals
- connected to a meter that records the difference in charge between the tips of the two electrodes
What is the resting potential?
- When the axon, or nerve fiber, is at rest, the difference in the electrical potential between the tips of the two electrodes is –70 millivolts
- negative charge of the neuron relative to its surroundings (more negative inside than outside)
What is the action potential?
- As the signal passes the recording electrode, the charge inside the axon rises to +40 mV compared to the outside
- the charge inside the fiber reverses course and starts becoming negative again
- until it returns to the resting level
- lasts about 1 millisecond
- hen neurons are “firing,” the neuron has action potential
What are the basic properties of action potentials?
- Show propagated response
- Remain the same size regardless of stimulus intensity
- Changing the stimulus intensity does not affect the size of the action potentials but does affect the rate of firing
- there is an upper limit to the number of nerve impulses per second that can be conducted down an axon: upper firing rate is 500 to 800 impulses per second
- refractory period
- Show spontaneous activity that occurs without stimulation
What is a propagated response?
- once the response is triggered, it travels all the way down the axon without decreasing in size
What is the refractory period?
- the interval between the time one nerve impulse occurs and the next one can be generated in the axon
- 1 ms
What is the chemical basis of action potentials?
- Neurons are surrounded by a solution containing ions
- The solution outside the axon of a neuron is rich in positively charged sodium (Na+) ions
- the solution inside the axon is rich in positively charged potassium (K+) ions
- channels in the membrane that are selective to Na+ have opened, which allow Na+ to flow across the membrane and into the neuron
- increase in the membrane’s selective permeability to sodium
- once the charge in- side the neuron reaches +40 mV, the sodium channels close and potassium channels open
- positively charged potassium rushes out of the axon when the channels open, causing the charge inside the axon to become more negative
- sodium potassium pump
What are ions?
- carry an electrical charge
- created when molecules gain or lose electrons
What is depolarization?
- An increase in positive charge inside the neuron
- rising phase of the action potential
What is hyperpolarization?
- An increase in negative charge inside the neuron
- falling phase of the action potential
What is the sodium potassium pump?
- the sodium-in, potassium-out flow that occurs during the action potential doesn’t cause sodium to build up inside the axon and potassium to build up outside
- keeps this buildup from happening by continuously pumping sodium out and potassium into the fiber
What is a synapse?
- small space between neurons
What are neurotransmitters?
- stored in synaptic vesicles at the end of the sending neuron
- flow into the synapse to small areas on the receiving neuron called receptor sites that are sensitive to specific neurotransmitters
- When a neurotransmitter makes contact with a receptor site matching its shape, it activates the receptor site and triggers a voltage change in the receiving neuron
- when an electrical signal reaches the synapse, it triggers a chemical process that causes a new electrical signal in the receiving neuron
Neurotransmitters are:
- Released by the presynaptic neuron from vesicles
- Received by the postsynaptic neuron on receptor sites
- Matched, like a key to a lock, into specific receptor sites
- Used as triggers for voltage change in the postsynaptic neuron
What is the excitatory response?
- depolarization
- inside of neuron becomes more positive
- smaller than depolarization during action potential
- Increases the likelihood of an action potential, it might take more than one excitatory response
- If the resulting depolarization is large enough, an action potential is triggered
- increasing rates of nerve firing
What is an inhibitory response?
- hyperpolarization
- inside of neuron becomes more negative
- Decreases the likelihood of an action potential
- lowering rates of nerve firing
What is the sensory code?
- how neurons represent various characteristics of the environment