Summers

Neurobiology Spring 2000 click here for text only acronyms

text: Fundamental Neuroscience - Zigmond, et al.,: Read pages 761-787, 855-891 for this lecture end

XXIX. Perception and Movement  			back to XXVIII. Autonomic Function

	A. Spinal cord provides sensory and motor innervation to trunk and limbs


		1. Gray matter  (shaped like a butterfly)


			a. cell bodies and dendrites of neurons + glia


			b. dorsal horn (sensory)


				i. relay sites for information entering the spinal cord


					(1) from axons of the dorsal root ganglion (also origin
					    of sensory axons innervating trunk and limbs,
						pseudo-unipolar/bipolar cell)


					(2) to ascending projection neurons transmitting sensory
					    informatin to brainstem and thalamus


						(a) ascending axons (myelinated) are in the white matter


							(i) arranged somatotopically


			c. ventral horn (motor)


				i. motor nuclei that innervate muscle via the ventral root


					(1) secrete ACh


					(2) ventral and dorsal root come together to make the
					   spinal nerve


			d. Interneurons


				i. from dorsal horn to motor neurons


				ii. or between motor neurons


			e. surrounds the central canal


		2. White matter	(surrounds the gray)


			a. 3 large bilaterally paired columns of longintudinally
			   arranged axons


				i. dorsal columns = 1o affernts carrying somatosensory
				   information to the brainstem


				ii. lateral columns = afferents that project to higher brain 


					(1) + efferents to motor neurons and interneurons


				iii. ventral columns: afferents carrying pain and
				     temperature information


					(1) efferent motor neurons (axial muscles and posture)


			b. ventral commissure: axons that cross from one side to the
			   other (decussation) (pain and posture)


	B. Thalamus relays sensory input to 1o sensory cortex


		1. composed (in part) of distinct sensory nuclei


			a. somatic sensation, vision, audition


			b. almost all thalamic nuclei project to and receive
			   information from the cerebral cortex


		2. relays information from cerebellum and basal ganglia to
		   1o motor cortex and higher motor areas


		3. Relay nuclei


			a. each posess single sensory modality or unique motor input


			b. projects to a specific local region of the cortex


			c. receives recurrent input from the region to which it projects


				i. allows cortex to modulate input according to ongoing activity


		4. Diffuse Projection Nuclei


			a. more widespread connections


			b. cortical and thalamic connections


				i. govern arousal


		5. Internal capsule = large axon fiber bundle carrying
		   thalamocortical connections


	C. 1o Motor Cortex is arranged somatotopically				


		1. 1o Motor Cortex neurons project directly to motor neurons
		 in spinal cord via the Corticospinal Tract (also somatotopic)  


			a. from layer 5 of cortex (cortex has 6 layers) ® white matter ® internal
                          capsule of thalamus ® basis pedunculi (fiber bundle in the base
                          of the midbrain)


			b. motor decussation - crosses to
			    the opposite side of the spinal cord


				i. afferent sensory fibers also cross over


				ii. each brain hemisphere controls the
				    contralateral motor function


			c. have synapses on motor neurons that
			    innervate specific muscles


				i. distal muscles for precised movement


					(1) brainstem mediates postural adjustments


			d. corticospinal pathway first appears in mammals


				i. somatotopic organization becomes
				    highly developed in primates


	D. Voluntary movements must be well timed and accurate


		1. require coordinated tactile, visual,
		    and proprioceptive information


		2. timing and trajectory of movements modulated by 2 structures
		   necessary for accurately aimed and smoothly executed movements


			a. Cerebellum (also somatotopically organized)			


				i. cerebellar cortex and 3 deep nuclei


				ii. initiation and timing of movement


			b. Basal Ganglia


				i. Corpus Striatum regulates speed of movements


		3. mediated by brainstem and thalamic motor nuclei

			a. Substantia Nigra (DA) in midbrain connects back to striatum,
			   globus pallidus and indirectly to thalamus


				i. not direct mediation (corticospinal tract is)


		4. hierarchical and parallel connections allows for coordination of
		   voluntary and rhythmic actions
		

			a. higher centers can give general commands without
			   details for motor action


			b. lower centers generate complex spatiotemporal patterns for
			   reflex and rhythmic movement 

XXX. Neuromuscular Function

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