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
What are the types of sensory coding?
- specificity coding
- sparse coding
- population coding
What is specificity coding?
- a specialized neuron that responds to only one concept or stimulus
- one neuron represents one perceptual experience
- grandmother cell
- a “grandmother cell” for every face, stimulus, and concept that you’ve ever encountered
What is sparse coding?
- Sparse coding occurs when a particular stimulus is represented by a pattern of firing of only a small group of neurons
-Most neurons remain silent - a particular neuron can respond to more than one stimulus
- a pattern of activity across a relatively small number of neurons
What is population coding?
- our experiences are represented by the pattern of firing across a large number of neurons
- A large number of stimuli can be represented, because large groups of neurons can create a huge number of different patterns
- good evidence for population coding in each of the senses, and for other cognitive functions as well
What is phrenology?
- mental faculties: correlation between the shape of a person’s skull and their abilities and traits
- about 35 different mental faculties that could be mapped onto different brain areas based on the bumps and contours on the person’s skull
- phrenology has now been debunked as a method
What is modularity?
- The idea that specific brain areas are specialized to respond to specific types of stimuli or functions
- each specific area called a module
- evidence supporting modularity of function came from case studies of humans with brain damage
- modularity can be studied by recording brain responses in neurologically normal humans using brain imaging, making it possible to create pictures of the location of the brain’s activity
- neuropsychology
- Broca’s and Wernicke’s areas provided early evidence for modularity
What is Broca’s area?
- speech production area
- left frontal lobe
What is Wernicke’s area?
- involved in understanding speech
- temporal lobe
What is brain imaging?
magnetic resonance imaging (MRI):
- made it possible to create images of structures within the brain
- detecting tumors and other brain abnormalities
- doesn’t indicate neural activity
functional magnetic resonance imaging (fMRI):
- has enabled researchers to deter- mine how various types of cognitions, or functions activate different areas of the brain
- takes advantage of the fact that blood flow increases in areas of the brain that are activated
- Areas of the brain that are more active consume more oxygen, so the hemoglobin molecules lose some of the oxygen they are transporting, which makes them more magnetic and increases their response to the magnetic field
- can’t record activity from individual neurons
- activity in subdivisions of the brain called voxels
- each voxel contains many neurons
- Red and yellow indicate increases in brain activity
- blue and green indicate decreases
What is the voice area?
- area in the temporal lobe—the superior temporal sulcus (STS)
- was activated significantly more in response to vocal sounds than non-vocal sounds
What is distributed representation?
- The idea that the brain represents information in patterns distributed across the cortex, not just one brain area
- focuses on the activity in multiple brain areas and the connections between those areas
- a single stimulus can cause widespread activity
What is structural connectivity?
- the “road map” of fibers connecting different areas of the brain
What is functional connectivity?
- the neural activity associated with a particular function that is flowing through this structural network
- measuring functional connectivity involves us- ing fMRI to measure resting state activity of the brain - resting state fMRI
What is the theory of connections between brain areas?
- Research has shown that connections between brain areas may be just as important for perception as the activity in each of those areas alone
- Structural connectivity
- Functional connectivity
How is the resting state method of measuring functional activity measured?
- Use task-related fMRI to determine a brain location associated with carrying out a specific task
- Measure the resting-state fMRI at the seed location. The rest- ing-state fMRI of the seed location is called a time-series response because it indicates how the response changes over time
- Measure the resting-state fMRI at another location - test location
- Calculate the correlation between the seed and test location responses
- high correlation indicates high functional connectivity
- poor match between these two responses results in a low corre- lation, which indicates poor or no functional connectivity
What is the mind-body problem?
- How do physical processes like nerve impulses (the body part of the problem) become transformed into the richness of perceptual experience (the mind part of the problem)?
- It asks how physiological processes cause our experience
