Neuroscience quiz 1 Domina Petric, MD

What kind of neuronal circuits are present in human brain?

the genesis of neuronal rhythmicity Brain circuits NANOCIRCUITS (networks within neurons) constitute the underlying biochemical machinery for mediating key neuronal properties such as: learning and memory the genesis of neuronal rhythmicity John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

processing sensory information generating locomotion Brain circuits MICROCIRCUITS (few interconnected neurons) can perform sophisticated tasks: mediating reflexes processing sensory information generating locomotion mediating learning and memory  John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Brain circuits MACROCIRCUITS (more complex networks) consist of multiple imbedded microcircuits and mediate higher brain functions such as: object recognition cognition John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Why are neurons different than most other cells in the human body? John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Neurons Neurons are polarized and have distinct morphological regions with specific functions.  John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

What is resting potential? John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Resting potential Resting potential (about -60 millivolts inside negative with respect to the outside) is constant for indefinite periods of time in the absence of any stimulation.  Neurons and muscle cells are capable of changing their resting potential.  Nerve cells change resting potential for integrating information and transmitting information. Muscle cells change resting potential for producing muscle contractions.  John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

What is action potential? John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

The peak is followed by an equally rapid repolarization phase. Action potential The action potential is associated with a very rapid depolarization to achieve a peak value (about +40 mV in just 0.5 milliseconds). The peak is followed by an equally rapid repolarization phase. John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

What is treshold? John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Treshold The voltage at which the depolarization becomes sufficient to trigger an action potential is called TRESHOLD. Action potentials are elicited in an all-or-nothing fashion and are also propagated in an all-or-nothing fashion. The nervous system encodes information in terms of the changes in the frequency of action potentials.  Greater the stimulus, grater the FREQUENCY of the action potentials, amplitude is always the same. John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

What kinds of microcircuit patterns exist in the human brain? John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Microcircuit patterns are: feedforward excitation feedforward inhibition convergence/divergence lateral inhibition feedback/reccurent inhibition feedback/reccurent excitation John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Feedforward excitation Allows one neuron to relay information to its neighbor.  Long chains of these feedforward excitatory connections propagate information through the nervous system. John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Neuron A Neuron B John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Feedforward inhibition A presynaptic cell excites an inhibitory interneuron. Interneuron is a neuron interposed between two neurons. Inhibitory interneuron then inhibits the next neuron. Shutting down or limiting excitation in a downstream neuron. John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Inhibitory interneuron Neuron B Neuron A Inhibitory interneuron John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Image source: PINTEREST https://i.pinimg.com Image source: PINTEREST

Convergence/divergence One postsynaptic cell receives convergent input from a number of different presynaptic cells which allows a neuron to recieve input from many neurons in a network. An individual neuron can make divergent connections to many different postsynaptic cells which allows one neuron to communicate with many other neurons in a network.   John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Convergence Neuron B Neuron C Neuron A Neuron D

Divergence Neuron B Neuron A Neuron C Neuron D

Convergence and divergence A single sensory neuron has multiple branches that diverge and make synaptic connections with many individual motor neurons. When the muscle contracts as a result of the stimulus, multiple muscle fibers are activated simultaneously by multiple motor neurons.   When the muscle is stretched, multiple sensory neurons are activated and project into the spinal cord where they converge onto the extensor motor neurons. The stretch reflex is due to the combined effects of the activation of multiple sensory neurons and extensor motor neurons. John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Lateral inhibition A presynaptic cell excites inhibitory interneurons and they inhibit neighboring cells in the network.  This type of circuit can be found in sensory systems to provide edge enhancement.  John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Light intensity (light intensity units) 5 5 5 10 10 10 RECEPTORS Excitation strenght between receptors and second order neurons is +1. Inhibition strenght of interneurons in lateral inhibition is -1 for those neurons illuminated with 5 light intensity units and -2 for those cells illuminated with 10 LIU. One cell recieves two inhibitory interneurons. Second order neurons outputs are: 3 3 2 7 6 6 Edge enhancement is mediated by lateral inhibition in the retina.

Feedback reccurent excitation Recurrent excitation in nanocircuits and microcircuits is critical for learning and memory processes.  Learning involves changes in the biophysical properties of neurons and changes in synaptic strength.  John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Feedback reccurent excitation CA3 region of the hippocampus! John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Feedback reccurent inhibition example Nanocircuit for the gene regulation that underlies circadian rhythms:  per gene leads to the production of per messenger RNA per mRNA leaves the nucleus and enters the cytoplasm where it leads to the synthesis of PER protein  PER protein diffuses or is transported back into the nucleus where it represses the further transcription of the per gene John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston

Literature John H. Byrne, Ph.D., Department of Neurobiology and Anatomy, The UT Medical School at Houston https://i.pinimg.com