Nervous TissueNervous TissueA. Nervous system divisionsA. Nervous system divisions

B. Functional anatomy of B. Functional anatomy of nervous tissuenervous tissue

1. Neuroglia1. Neuroglia a. Types of neurogliaa. Types of neuroglia b. Myelinationb. Myelination 2. Neurons2. Neurons a. Parts of a neurona. Parts of a neuron b. Classification of b. Classification of neuronsneurons 3. Gray and white matter3. Gray and white matter

C. NeurophysiologyC. Neurophysiology 1. Resting membrane potential1. Resting membrane potential 2. Ion channels2. Ion channels 3. Action potential (impulse)3. Action potential (impulse) a. Depolarizationa. Depolarization b. Repolarizationb. Repolarization c. Refractory periodc. Refractory period d. Propagation (conduction) of d. Propagation (conduction) of action potentialsaction potentials e. The all-or-none principlee. The all-or-none principle f. Saltatory conductionf. Saltatory conduction 4. Transmission at synapses4. Transmission at synapses a. Chemical synapsesa. Chemical synapses b. Excitatory and inhibitory b. Excitatory and inhibitory

postsynaptic potentialspostsynaptic potentials c. Spatial and temporal c. Spatial and temporal summation of PSPssummation of PSPs d. Removal of neurotransmitterd. Removal of neurotransmitter 5. Neuronal circuits5. Neuronal circuits

The nervous system is the body's control The nervous system is the body's control center and communicates network.center and communicates network.

It serves three broad functions:It serves three broad functions:

1. senses changes in the environment1. senses changes in the environment

2. integrates and interprets2. integrates and interprets

3. responds3. responds

Nervous Systems DivisionsNervous Systems Divisions

1. central nervous 1. central nervous systemsystem

a. braina. brain

b. spinal cordb. spinal cord

2. peripheral nervous 2. peripheral nervous systemsystem

a. somatic divisiona. somatic division

b. autonomic divisionb. autonomic division

(1) sympathetic (1) sympathetic vsvs

(2) parasympathetic(2) parasympathetic

NeurogliaNeuroglia

1. astrocytes1. astrocytes

2. oligodendrocytes2. oligodendrocytes

3. microglia3. microglia

4. ependyma4. ependyma

5. neurolemmocytes5. neurolemmocytes

(Schwann cells)(Schwann cells)

6. satellite cells6. satellite cells

NeuronNeuron

1. cell body1. cell body a. nucleusa. nucleus b. nucleolusb. nucleolus c. Nissl substancec. Nissl substance

2. dendrite2. dendrite3. axon3. axon

a. axon hillocka. axon hillock b. trigger zoneb. trigger zone c. axon collateralsc. axon collaterals d. telodendriond. telodendrion e. end bulbse. end bulbs

MyelinationMyelination

1. PNS = neurolemmocytes1. PNS = neurolemmocytes

CNS = oligodendrocytesCNS = oligodendrocytes

2. process2. process

3. myelin sheath3. myelin sheath

4. neurolemma4. neurolemma

5. nodes of Ranvier5. nodes of Ranvier

Structural Classification of NeuronsStructural Classification of Neurons

1. multipolar neuron1. multipolar neuron

2. bipolar neuron2. bipolar neuron

3. unipolar neuron3. unipolar neuron

a. central processa. central process

b. receptorb. receptor

Functional Classification of Functional Classification of NeuronsNeurons

1. sensory (afferent) neurons1. sensory (afferent) neurons

2. association neurons (interneurons)2. association neurons (interneurons)

3. motor (efferent) neurons3. motor (efferent) neurons

Some TerminologySome Terminology

1. nerve fiber 1. nerve fiber

2. nerve vs. tract2. nerve vs. tract

3. tract3. tract

4. ganglion vs. nucleus (center)4. ganglion vs. nucleus (center)

5. gray matter5. gray matter

6. white matter6. white matter Gray matter

White matter

NeurophysiologyNeurophysiology

Communication by neurons depends upon Communication by neurons depends upon two two basic properties of their cell membranes:basic properties of their cell membranes:

1. There is an electrical voltage, called the 1. There is an electrical voltage, called the resting membrane potential, across the cell resting membrane potential, across the cell membrane.membrane.

2. Their cell membranes contain a variety of 2. Their cell membranes contain a variety of ion channels (pores) that may be open or ion channels (pores) that may be open or closed.closed.

Resting Membrane PotentialResting Membrane Potential

1. build-up of ions1. build-up of ions

2. separation of charges =2. separation of charges =

potential energy (mV)potential energy (mV)

3. membrane potential = -70 mV3. membrane potential = -70 mV

4. polarized membrane4. polarized membrane +++++

---------

+++++

--------

Two Main Factors Contribute to Two Main Factors Contribute to the RMPthe RMP

1. distribution of ions across the cell membrane.1. distribution of ions across the cell membrane. a. extracellular fluid is rich in Na+ and Cl-a. extracellular fluid is rich in Na+ and Cl- b. intracellular fluid is rich in K+ and anions b. intracellular fluid is rich in K+ and anions such as organophosphates and proteinssuch as organophosphates and proteins

2. relative permeability of the cell membrane to 2. relative permeability of the cell membrane to Na+ and K+Na+ and K+ a. moderately permeable to K+ and Cl-a. moderately permeable to K+ and Cl- b. slightly permeable to Na+b. slightly permeable to Na+ c. impermeable to the intracellular anionsc. impermeable to the intracellular anions

Ion Channels(Pores)Ion Channels(Pores)

1. non-gated (leakage)1. non-gated (leakage)

2. gated (regulated)2. gated (regulated)

a. open in response to stimulus a. open in response to stimulus

(chemical, voltage change, light, mechanical)(chemical, voltage change, light, mechanical)

b. excitable cells have themb. excitable cells have them

c. found in trigger zonesc. found in trigger zones

How do chemically gated ion How do chemically gated ion channels open?channels open?

intracellular fluid

extracellular fluid

+++++++ +++++++++++++

- - - - - - - - - - - - - - - - - - --

cell membrane

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+ACh

CHEMICALLY-GATED Na+ CHANNELclosed

intracellular fluid

extracellular fluid

+++++++ +++++++++++++

- - - - - - - - - - - - - - - - - - --

cell membrane

Na+

Na+

Na+

Na+Na+

Na+

Na+

Na+

Na+

AC

h

CHEMICALLY-GATED Na+ CHANNELopen

Chemically gated channelChemically gated channel

How do voltage-gated channels open?

intracellular fluid

extracellular fluid

+++++++ +++++++++++++

- - - - - - - - - - - - - - - - - - --

cell membrane

Na+

Na+

Na+

Na+Na+

Na+

Na+

Na+

Na+

VOLTAGE GATED Na+ CHANNELopen

intracellular fluid

extracellular fluid

+++++++ +++++++++++++

- - - - - - - - - - - - - - - - - - --

cell membrane

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

VOLTAGE-GATED Na+ CHANNELclosed

Voltage

3. Mechanically-gated channels, light-gated channels

An Action PotentialAn Action Potential

Action Potential-DepolarizationAction Potential-Depolarization1. threshold stimulus1. threshold stimulus

2. voltage-gated Na+ channels open2. voltage-gated Na+ channels open

3. Na+ influx (-70 ---> +30 mV)3. Na+ influx (-70 ---> +30 mV)

__________________________________________________________

4. positive feedback4. positive feedback

Action Potential-RepolarizationAction Potential-Repolarization1. voltage-gated K+ channels open1. voltage-gated K+ channels open

2. K+ efflux (-90 <--- +30 mV)2. K+ efflux (-90 <--- +30 mV)

3. hyperpolarization3. hyperpolarization

4. Na-K pumps restore ions4. Na-K pumps restore ions

Action Potential SummaryAction Potential Summary

Refractory PeriodRefractory Period1. absolute1. absolute

2. relative2. relative

POSITIVE FEEDBACK OF AN ACTION POTENTIAL

CONTROLLED CONDITION

A stimulus or stress disrupts membrane homeostasis by causing a threshold

depolarization

RECEPTORThe receptors in this case are

voltage-gated Na+ channels in their resting state

CONTROL CENTERThe shape of the voltage-gated Na+

channel depends on membrane voltage change

EFFECTORSVoltage-gated Na+ channels are also effectors. Threshold depolarization

causes shape changes in the channel

NO RETURN TO HOMEOSTASISOpening of the voltage-gated Na+ channels causes depolarization in adjacent membrane, opening more

voltage-gated Na+ channels

All of None PrincipleAll of None Principle

Each time an action potential is formed, it has a constant and maximum strength for the existing conditions.

Continuous ConductionContinuous Conduction

1. trigger zone to synapse1. trigger zone to synapse

2. propagation2. propagation

3. one direction only3. one direction only

Saltatory ConductionSaltatory Conduction

1. myelin sheath1. myelin sheath

2. nodes of Ranvier2. nodes of Ranvier

3. "jumping" impulse3. "jumping" impulse

4. 0.5 vs 130 m/sec4. 0.5 vs 130 m/sec

5. energy conservation5. energy conservation

Transmission at SynapsesTransmission at Synapses

1. "synapsis" means connection1. "synapsis" means connection

2. synapses integrate and filter information2. synapses integrate and filter information

3. signals are transmitted or inhibited3. signals are transmitted or inhibited

4. presynaptic vs postsynaptic neurons4. presynaptic vs postsynaptic neurons

Chemical SynapsesChemical Synapses

1. arrival of action potential1. arrival of action potential

2. Ca++ influx2. Ca++ influx

3. synaptic vesicle rupture3. synaptic vesicle rupture

4. NT release4. NT release

5. NT diffusion5. NT diffusion

6. NT/receptor interaction6. NT/receptor interaction

7. postsynaptic potential7. postsynaptic potential

Postsynaptic Potentials can be Postsynaptic Potentials can be excitatory or inhibitoryexcitatory or inhibitory

1. excitatory (EPSP)1. excitatory (EPSP)

a. facilitationa. facilitation

b. summationb. summation

(1) spatial(1) spatial

(2) temporal(2) temporal

2. inhibitory (IPSP)2. inhibitory (IPSP)

a. hyperpolarizationa. hyperpolarization

Postsynaptic PotentialsPostsynaptic Potentials

Facilitation and SummationFacilitation and Summation1. spatial1. spatial2. temporal2. temporal

______________________net effectsnet effects

1. facilitation1. facilitation2. summation (impulses)2. summation (impulses)3. inhibition (hyperpolarization)3. inhibition (hyperpolarization)

EXAMPLE OF SYNAPTIC INTEGRATION

postsynaptic neuron inhibitory presynaptic neuronexcitatory presynaptic neuron

Threshold = +3

TYPES OF NEUROTRANSMITTERS

AcetylcholineMost common neurotransmitter; In a class by itself chemically; Mostly excitatory, depending on location and function; Brain, spinal cord, neuromuscular and neuroglandular synapses of the periphery

Excitatory amino acidsGlutamate – 75% of excitatory synapses in

brainAsparate – spinal cord

Inhibitory amino acidsGlycine – most common in spinal cordGABA (gamma amino butyric acid) – most common in

brainMonoamines (biogenic amines)

Catecholamines – norepinephrine, epinephrine, dopamineOther amines – serotonin, histamineNeuropeptides – substance P, enkephalines and endorphins, cholecystokinin

Removal of Neurotransmitter from Removal of Neurotransmitter from Synaptic CleftSynaptic Cleft

1. diffusion1. diffusion

2. enzymatic degradation2. enzymatic degradation

3. uptake into the cell3. uptake into the cell

Neuronal CircuitsNeuronal Circuits1. simple series1. simple series

2. diverging2. diverging

3. converging3. converging

4. reverberating4. reverberating

5. parallel after-discharge5. parallel after-discharge