Chapter 3 LF

8/17/2019 Chapter 3 LF

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Chapter Three

Cells of the

Nervous System


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CHAPTER 3CELLS OF THE NERVOUS SYSTEM


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Neurons and Glia

• The Structure of neurons – Neuron membranes separate

intracellular uid from extracellular uid

– The neural cytoskeleton providesstructural support that maintains theshape of the neuron


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Figure 3. The Neural !embrane


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Figure 3.3 Three Fiber Types "omposethe "ytoskeleton of Neurons


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Neurons and Glia

• Structural Features of Neurons – "ell body 'soma( contains nucleus and

other organelles

– &endrites ) branches that serve aslocations at *hich information fromother neurons is received

– +xons are responsible for carryingneural messages to other neurons

• ,ary in diameter and length

• !any covered by myelin


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Figure 3.- The Neural "ell ody


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Figure 3./ +xons and &endrites


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Structural ,ariations in Neurons

• 0nipolar – Single branch extending from the cell body

• ipolar – T*o branches extending from the neural cell

body1 one axon and one dendrite

• !ultipolar

– !any branches extending from the cell body2usually one axon and many dendrites


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Functional ,ariations in Neurons

• Sensory Neurons – Speciali5ed to receive information from the

outside *orld

• !otor Neurons – Transmit commands from the "NS directly to

muscles and glands

• 6nterneurons – +ct as bridges bet*een the sensory and motor

systems


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Glia

• !acroglia1 %argest of the glial cells

– +strocytes

– 7ligodendrocytes

– Sch*ann cells

• !icroglia1 Smallest of the glial cells


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Table 3.8 Types of Glia


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Figure 3.9 +strocytes


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Figure 3.8: 7ligodendrocytes andSch*ann "ells


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The Generation of the +ction $otential

• 6onic "omposition of the 6ntracellularand ;xtracellular Fluids – The di


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Figure 3.8 The "omposition of6ntracellular and ;xtracellular Fluids


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Figure 3.83 !easuring the =esting$otential

of Neurons


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• The !ovement of 6ons – &iually *ithin a medium

– ;lectrical force is an important cause ofmovement

• %ike electrical charges repel

• 7pposite electrical charges attract


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Figure 3.8# &i


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• The =esting $otential – !embrane allo*s potassium to cross freely

– !easures about ?@:m,

– 6f potassium levels in extracellular uidincreaseA resting potential is *iped out


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The +ction $otential

• Threshold – Bhen recording reaches about ?/-m,

• "hannels open C close during action

potential – Sodium o*s into neuron A potassium o*s out

around the peak of the action potential

• =efractory period – =ecording returns to resting potential

– +bsolute versus relative refractory periods

• The action potential is all?or?none


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Figure 3.8- The +ction $otential


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The $ropagation of the +ction $otential

• $ropagation – Signal reproduces itself do*n the length of the

neuron

– 6nuenced by myelination• $assive conduction D propagation in unmyelinated

axon

• Saltatory conduction D propagation in myelinatedaxon


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Figure 3.8/ +ction $otentials $ropagate&o*n the %ength of the +xon


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Figure 3.8@ $ropagation in0nmyelinated and !yelinated +xons


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The Synapse

• ;lectrical synapses – &irectly stimulate adEacent cells by sending ions

across the gap through channels that actually touch

• "hemical synapses – Stimulate adEacent cells by sending chemical

messengers• Neurotransmitter release

• Neurotransmitters bind to postsynaptic receptor sites

• Termination of the chemical signal

• $ostsynaptic potentials

• Neural 6ntegration


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Table 3. + "omparison of ;lectricaland "hemical Synapses


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Figure 3.89 The ;lectrical Synapse


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Figure 3.8 ;xocytosis =esults in the=elease of Neurotransmitters


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Figure 3. 6onotropic and!etabotropic =eceptors


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Figure 3.3 !ethods for &eactivatingNeurotransmitters

Fi 3 # N l 6 t ti


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Figure 3.# Neural 6ntegration"ombines ;xcitatory and 6nhibitory

6nput

T bl 3 3 + " i f th


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Table 3.3 + "omparison of the"haracteristics of +ction $otentialsA

;$S$s and 6$S$s


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Neuromodulation

• Synapses bet*een an axon terminaland another axon 4ber – +xo?axonic synapses have modulating e


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Figure 3./ Synapses et*een T*o+xons !odulate the +mount of

Neurotransmitter =eleased

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