General Biology2 Summers

Respiration and oxygen availability Heart and Circulation/Transport Nutrition, Digestion, Metabolism Excretion and Elimination

Chemical Messengers Sexual Reproduction Neuronal Structure & Signals Sensory Reception

text:Biological Science 5th Edition - Freeman ..: Read Chap 46 for this lecture Integration of Neural Function Neuromuscular Action - Behavior syllabus     Figures acronyms    end

XIII. Neural Structure 		

	A. Neuron (Single Unit - Consists of:)

		1. Dendrite(s)

			a. beginning

				i. where signal comes into neuron

				ii. usually short

		2. Cell Body (Soma)

			a. contains nucleus, ER, golgi, etc

				i. site of neurotransmitter production

		3. Axon

			a. takes message or signal where its going

				i. often very long

			b. Bouton

				i. widening of axonal ending

					1) facilitates transmission of signal

				ii. 1st 1/2 of synapse

					1) presynaptic

		4. Synapse (to clasp): 3 parts

			a. presynaptic side (1st part) connects to

				i. other neurons

					1) postsynaptic side (2nd part)

					2) with astrocytes

						a) side boundaries (3rd part)

						b) tripartite synapse

				ii. other cells  (e.g. muscles)

			b. site of delivery of neural signal

				i. electrically

				ii. chemically - neurotransmitters

	B. Nerve(s)

		1. collection of neuronal axons

	C. Ganglia / Nuclei

		1. collection of neural cell bodies

			a. ganglion - in the Peripheral NS

				i. bulbous

			b. nucleus - in the Central (Brain & Spinal cord) NS

XIV. Neural Function

	A. Neural Transmission (propagation, signal, depolarization, impulse,
	   conduction, action potential)

		1. Direction

			a. begins at dendrite

			b. travels (mostly) along axon

			c. moves from neuron to neuron (or to other cells) by synapses

				i. ensheathed by astrocyte network

		2. Mechanism

			a. ion balance

				i. Na+/K+ ATPase = active transport

				ii. Na+ pumped out,
				    therefore [Na+] higher outside the neuron

				iii. K+ pumped in, [K+] higher in

				iv. some K+ leaks out (pores)

					(1) + charge greater outside the cell

					(2) - charge greater inside the cell

						(a)  large proteins with a negative 
						     charge inside the cell

			b. signal transmission

				i. actual electricity - resting potential = -70mV

				ii. perturbation to cell membrane

					(1) Na+ rushes in K+ out 
						along [Na+] / [Na+] gradients

						(a) Na+ first,   K+  slightly later

					(2) depolarization

					(3) + / - charges move along electrical gradient

					(4) this movement of depolarization is the
					   action potential

					(5) Na+ rushes in as each new section of
					    axon becomes depolarized

						(a) depolarization  (a perturbation) opens the
						    gates to Na+ (= Na+ channels)

						(b) new Na+ rushing in reinforces
						    the depolarization/action potential

					(6) this is normal movement,
					    as when the signal begins at the dendrite

				iii. K+ rushes out, then Active transport
				     begins moving Na+ and K+ again

					(1) restores resting potential  

					(2) repolarization

				iv. depolarization spike

					1) measuring potential 
						as signal moves along the axon


					2) Na+ moving in lowers the negative
					    potential  (depolarization), then makes it positive

					3) K+ rushing out (slightly later) restores
					    negative potential, 

						a)  then overshoots -70mV (hyperpolarizes)

					4) Na+/K+ ATPase / repolarization
					    returns the cell to the resting potential

			c. Saltatory propagation

				i.  Oligodendrocytes & Schwann cells

					1) Glial cells associated with neurons

					2) includes myelin

						a) wrapped around axons

						b) fat

				ii. Node of Ranvier

					1) between Schwann cells

				iii. increased membrane resistance

					1) less time moving ions across the membrane

					2) current moves along its gradient more quickly

					3) depolarization reinforced at the node

			d. at the synapse

				i. neurotransmitters waiting in golgi vesicles

					   e.g.
					1) dopamine (DA), NE, Epi, acetylcholine (ACh),
					    serotonin (5-HT), GABA,  glutamate (Glu) ...

				ii. when the signal reaches the Bouton
				    neurotransmitter released by exocytosis

				iii. transmitter travels across synaptic cleft to receptors

					1) Astrocytes help keep tranmitter
					   in the synapse

					2) Astrocytes facilitate the signal

						a) Astrocytes can signal too

				iv. binding to receptors begins signal on next cell


				v. enzymes degrade transmitters in cleft,
				   or transmitter is taken back up by the original cell
				   and astrocytes to be reused


			e. electric synapses 

				i. Bouton membranes so closely apposed that gap junction
				   channels allow the electrical signal to
				   continue down the membrane of the new cell


		3. Excitatory and Inhibitory Synapses


			a. the effect of neurotransmitters may be stimulatory


				i. causing a new action potential in the following neuron
				   or stimulating a non-neural cell


				ii. neuromodulation


					(1) may enhance the probability of
					    another neuron having an action potential


			b. but it may be inhibitory: 


				i. inhibiting an action potential in another cell


			c. neurons may have excitatory and inhibtory neurons
			   impinging upon them