Lecture 13- brain circuitry

Lecture 13- brain circuitry - Summary and into brain...

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Unformatted text preview: Summary and into brain ‘circuits’ Circuit• Circuit- assemblage of neurons and their synaptic interconnections that work together to achieve some function function • Very simple circuits • More complex circuits Knee Jerk Reflex Consists • Consists of a sensory neuron, a motor neuron, and a single synapse where the sensory neuron communicates with the motor neuron the Knee Jerk Reflex (page 81) Knee Jerk Reflex Tap • Tap on the tendon stimulates stretch receptors in quadriceps receptors Stretch • Stretch receptors are on sensory neurons Knee Jerk Reflex Stretch • Stretch depolarizes sensory neuron to threshold (many times)… many action potentials are fired (many EPSP Knee Jerk Reflex Sensory • Sensory neurons project through the dorsal root of the spinal cord and synapse onto motoneurons in the ventral horn Knee Jerk Reflex Sensory • Sensory neurons contain glutamate, so glutamate is • released onto motoneurons released Glutamate causes EPSPs on motoneuron and many Glutamate action potentials are fired action EPSP Knee Jerk Reflex Motoneuron • Motoneuron action potentials cause ACh release in the neuromuscular junction neuromuscular Ach causes action Ach potentials to fire in the muscle fibers and muscle contracts and the leg kicks the The leg begin to kick The just 40 ms after the initial tap. • • Cartoon doesn’t show the loop Cartoon doesn’t show the loop Integration at the motoneuron The • The firing patterns of motoneurons determine the onset, coordination, and termination of muscle activity coordination, Lordosis is more complex • Involves a more complex neural circuit Lordosis: from skin to spinal cord For • For the reflexive component of lordosis… pressure on the skin causes reflex pressure L1-L6 Lordosis: from skin to spinal cord Pressure • Pressure on the skin causes glutamate release onto interneurons in the spinal cord spinal Glutamate • Glutamate containing cell body is contained in the dorsal root ganglia (monopolar neurons) nterneurons • IInterneurons project to the motoneuron in the ventral horn ventral Motoneurons also modulated by brain Complex circuits • The ‘motive circuit’ Circuits for motivated behavior Motivated • Motivated behaviorbehavior that has approach, appetitive/procurement, and consummatory phases phases Circuits for motivated behavior Kalivas • Kalivas et al studied circuitry by measuring locomotor output locomotor Circuits for motivated behavior • 3 major processes 1) • 1) receive motivationally relevant information via limbic system system Circuits for motivated behavior • 3 major processes 1) • 1) receive • motivationally relevant information via limbic system system 2) Integration of this 2) information to determine the intensity of the behavioral output output Circuits for motivated behavior • 3 major processes 1) • 1) receive • motivationally relevant information via limbic system system 2) Integration of this 2) information to determine the intensity of the behavioral output output 3) initiation of the 3) motor response via projections to motor nuclei nuclei • Limbic portion of the motive circuit Kalivas • Kalivas et al refer to an ‘afferent limb’ of the motive circuit consisting of the VTA, nucleus accumbens shell, and ventromedial ventral pallidum shell, Motor portion of the motive circuit Kalivas • Kalivas et al refer to an ‘efferent limb’ of the motive circuit consisting of the substantial nigra, nucleus accumbens core, and dorsolateral ventral pallidum pallidum VTA SN Communication between limbic and motor Mediodorsal • Mediodorsal Thalamus and prefrontal cortex and Activation of Activation locomotor activity in rats by injection AMPA, dopamine, or DAMGO (a mu agonist) into the ventral pallidum pallidum 5 minutes prior these minutes manipulations, the medial dorsal thalamus was pharmacologically blocked blocked • • Circuits for motivated behavior Thalamus Visual input Visual input • Light flash increases firing of neurons in the tectum Bicuculine = GABA antagonist Visual input Light • Light flashes alter dopamine signaling in the striatum Visual input t • IIt takes 45 ms for visual input to travel to the thalamus to 10’s • 10’s of additional ms to get through the initial visual cortical areas areas t • IIt takes ~110 ms for the visual stimulus to be recognized (inferior temporal lobe important for this) Visual input And • And yet another ~35 ms for the signal to then travel to the prefrontal cortex prefrontal And • And another 30 ms and then another 40 ms to travel to premotor cortex and primary motor cortex respectively respectively Then • Then off to spinal cord for behavior to occur for ...
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