Summers

Neurobiology Spring 2000 click here for text only acronyms

text: Fundamental Neuroscience - Zigmond, et al.,: Read pages 863-909 for this lecture end

XXXI. Reflexes  			back to XXX. Neuromuscular Function


	A. a simple motor action, stereotyped and repeatable


		1. elicited by a sensory stimulus


			a. strength of motor action graded by stimulus intensity


		2. sensory stimuli travel to the spinal cord by afferent sensory
		   neurons (by way of the dorsal root)


	B. Interneurons determine the final form of a reflex motor pattern


		1. afferents terminate on homonymous (same muscle) and synergistic
		   motor neurons, and interneurons


			a. interneurons inhibit antagonist muscle motor neurons


		2. higher centers can affect expression of reflex behavior via
		   descending input to interneurons


			a. enhance or suppress specific reflex actions


		3. interneurons gate peripheral input to motor neurons		


			a. controls what input reaches a motor neuron


			b. via gating higher centers may preselect which of several
			   possible responses follows a stimulus


				i. gating may occur through presynaptic inhibition


				ii. allows quick responses without extra processing time


		4. reverberating circuits							        


			a. closed circuits of interneurons that re-excite themselves


				i. reflex may outlast the stimulus


		5. pattern generation							


			a. interneurons may have reciprocal inhibitory connections


				i. to create alternating flexor and extensor excitation


			b. temporal organization of reflexive behavior is controlled
			   by interneuronal connections


	C. Convergence


		1. motor neurons receive convergent input from afferents and interneurons


			a. motor activity reflects a summation of excitatory and
			   inhibitory postsynaptic potentials


				i. sensory, descending signals from supraspinal
				   regions, interneurons


	D. Withdrawal (leg)									


		1. afferent from nociceptor


		2. excitatory interneurons (4)


			a. 2 decussate


		3. ipsilateral connections to 2 more interneurons


			a. inhibitory interneuron to extensor muscle


			b. excitatory interneuron to flexor


				i. withdrawl of the leg


		4. contralateral excitatory and inhibatory interneurons are opposite


			c. extension of the contralateral leg for postural support

XXXII. Hypothalamus and Limbic System

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