Nervous Tissue. Nervous System CNS (brain and spinal cord) CNS (brain and spinal cord) PNS...

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Nervous TissueNervous Tissue

Nervous SystemNervous System

• CNS (brain and spinal cord)CNS (brain and spinal cord)

• PNS (peripheral nervous system)PNS (peripheral nervous system)

Types of CellsTypes of Cells

• Neurons – structural unitsNeurons – structural units

• Supporting cells – protect and Supporting cells – protect and myelinate neuronsmyelinate neurons

Structure of NeuronsStructure of Neurons

• Cell body – contains nucleus and Cell body – contains nucleus and cytoplasmcytoplasm

Structure of NeuronStructure of Neuron

• Dendrites – receptive regionsDendrites – receptive regions

• Axons – nerve impulse generatorsAxons – nerve impulse generators

• Axoplasm – cytoplasm of neuronAxoplasm – cytoplasm of neuron

• Axolema – plasma membraneAxolema – plasma membrane

• Collaterals – axon branchesCollaterals – axon branches

• Axon hillock – an enlarged cell body Axon hillock – an enlarged cell body structure, which is the beginning of structure, which is the beginning of the axonthe axon

• Axon terminals – The axon and its Axon terminals – The axon and its collaterals end divide into fine collaterals end divide into fine processesprocesses

• Synaptic end bulbs – tips of axon Synaptic end bulbs – tips of axon terminals that contain the synaptic terminals that contain the synaptic vessiclesvessicles

• Synaptic cleft – gap between two Synaptic cleft – gap between two neuronsneurons

• Supporting cells wrap themselves Supporting cells wrap themselves around the axons of some neurons around the axons of some neurons like a jelly rolelike a jelly role

• Myelin sheath – A tight core of Myelin sheath – A tight core of plasma membrane material around plasma membrane material around the axonthe axon

• Neurilemma – The peripheral part of Neurilemma – The peripheral part of the schwann cell and the exposed the schwann cell and the exposed plasma membraneplasma membrane

• Nodes of Ranvier – Since the myelin Nodes of Ranvier – Since the myelin sheath is composed of several sheath is composed of several schwann cells there are gaps or schwann cells there are gaps or indentations called nodes of ranierindentations called nodes of ranier

Classification by StructureClassification by Structure

1.1. UnipolarUnipolar

2.2. BipolarBipolar

3.3. MultipolarMultipolar

UnipolarUnipolar

• Have only one process that extends Have only one process that extends from the cell bodyfrom the cell body

UnipolarUnipolar

• Conduct impulses toward the CNSConduct impulses toward the CNS

BipolarBipolar

• Have two processes that extend from Have two processes that extend from the cell body (one axon and one the cell body (one axon and one dendrite)dendrite)

BipolarBipolar

• Found in the eye, ear, and olfactory Found in the eye, ear, and olfactory mucosamucosa

MultipolarMultipolar

• Have several processes that extend Have several processes that extend from the cell body (several dendrites from the cell body (several dendrites and one axon)and one axon)

MultipolarMultipolar

• Most neurons in CNS and neurons Most neurons in CNS and neurons that carry impulses away from the that carry impulses away from the CNSCNS

Classification by FunctionClassification by Function

1.1. SensorySensory

2.2. MotorMotor

Sensory or Afferent NeuronsSensory or Afferent Neurons

• Carry impulses away from sensory Carry impulses away from sensory receptors in the skin, skeletal receptors in the skin, skeletal muscle, and internal organs.muscle, and internal organs.

• Most are unipolarMost are unipolar

• Cell bodies lie outside the CNSCell bodies lie outside the CNS

Motor or Efferent NeuronsMotor or Efferent Neurons

• Carry impulses away from the CNSCarry impulses away from the CNS

• Most are multipolarMost are multipolar

• Cell bodies lie within the CNSCell bodies lie within the CNS

NeurogliaNeuroglia

• Supporting cellsSupporting cells

NeurogliaNeuroglia

• Half the volume in the CNSHalf the volume in the CNS

NeurogliaNeuroglia

• Smaller than neuronsSmaller than neurons

NeurogliaNeuroglia

• Five to fifty times more numerousFive to fifty times more numerous

NeurogliaNeuroglia

• Can divideCan divide

NeurogliaNeuroglia

• Do not generate or propogate action Do not generate or propogate action potentialspotentials

Brain TumorsBrain Tumors

• Derived from glia called gliomasDerived from glia called gliomas

• Highly malignant Highly malignant

• Grow fastGrow fast

Myelin sheathMyelin sheath

• Some axons are covered by a myelin Some axons are covered by a myelin sheath produced by neurogliasheath produced by neuroglia

Myelin sheathMyelin sheath

• Increases speed of nerve impulse Increases speed of nerve impulse productionproduction

NeurogliaNeuroglia

• Two types of neuroglia produce Two types of neuroglia produce myelin sheathmyelin sheath

1. Schwann cells (PNS) 1. Schwann cells (PNS)

2. Oligodendrocytes (CNS) 2. Oligodendrocytes (CNS)

Schwann CellsSchwann Cells

• Helps in regeneration of PNS axons Helps in regeneration of PNS axons

OligodendrocytesOligodendrocytes

• Inhibits axon regrowth after injuryInhibits axon regrowth after injury

Gray and White MatterGray and White Matter

• In the brain and spinal cord some In the brain and spinal cord some parts appear gray while other appear parts appear gray while other appear whitewhite

White MatterWhite Matter

• Contains the myelinated and Contains the myelinated and unmyelinated axons of neuronsunmyelinated axons of neurons

Gray MatterGray Matter

• Contains cell bodies, dendrites, and Contains cell bodies, dendrites, and unmyelinated axons of neuronsunmyelinated axons of neurons

• Also contains neurogliaAlso contains neuroglia

Organization of Nervous Organization of Nervous SystemSystem

1.1. CNSCNS

2.2. PNS PNS

Organization of Nervous Organization of Nervous SystemSystem

PNSPNS

• Somatic nervous systemSomatic nervous system

• Autonomic nervous systemAutonomic nervous system

Somatic Nervous SystemSomatic Nervous System

1.1. Sensory neurons convey Sensory neurons convey information from receptors in the information from receptors in the body wall, limbs, head, and special body wall, limbs, head, and special sensessenses

Somatic Nervous SystemSomatic Nervous System

2. Motor neurons conduct impulses to 2. Motor neurons conduct impulses to skeletal musclesskeletal muscles

Autonomic Nervous SystemAutonomic Nervous System

1.1. Sensory Neurons convey Sensory Neurons convey information from organs such as the information from organs such as the lungs and stomach to the CNSlungs and stomach to the CNS

2. Motor Neurons conduct impulses 2. Motor Neurons conduct impulses from the CNS to smooth muscle, from the CNS to smooth muscle, cardiac muscle, and glandscardiac muscle, and glands

• The motor part can be subdivided The motor part can be subdivided further into the further into the sympatheticsympathetic and and parasympatheticparasympathetic divisions divisions

SynapsesSynapses

• The functional junction between a The functional junction between a neuron and an effector or between neuron and an effector or between two neurons.two neurons.

SynapsesSynapses

• Presynaptic neuron – The neuron Presynaptic neuron – The neuron sending the signalsending the signal

SynapsesSynapses

• Postsynaptic neuron – the neuron Postsynaptic neuron – the neuron receiving the messagereceiving the message

Types of SynapsesTypes of Synapses

1.1. ElectricalElectrical

2.2. ChemicalChemical

Electrical SynapsesElectrical Synapses

• Action potentials or nerve impulses Action potentials or nerve impulses are conducted directly between are conducted directly between adjacent cells through gap junctions.adjacent cells through gap junctions.

Electrical SynapsesElectrical Synapses

• Ions flow from one cell to the next Ions flow from one cell to the next through the connexons thus the through the connexons thus the action potential is spread from one action potential is spread from one cell to the next.cell to the next.

Chemical SynapsesChemical Synapses

• Nerve impulses cannot be conducted Nerve impulses cannot be conducted across the synaptic cleftacross the synaptic cleft

Chemical Synapses - Chemical Synapses - SummarySummary

• The presynaptic neuron converts an The presynaptic neuron converts an electrical signal (nerve impulse) into electrical signal (nerve impulse) into a chemical signal (neurotransmitter a chemical signal (neurotransmitter release). release).

Chemical Synapses - Chemical Synapses - SummarySummary

• Then the postsynaptic neuron Then the postsynaptic neuron converts the chemical signal back converts the chemical signal back into an electrical signal (postsynaptic into an electrical signal (postsynaptic potential).potential).

Chemical Synapses – 7 Chemical Synapses – 7 StepsSteps

1. An action potential arrives at a 1. An action potential arrives at a synaptic end bulb of a presynaptic synaptic end bulb of a presynaptic neuronneuron

2. Voltage-gated calcium channels 2. Voltage-gated calcium channels open and calcium flows into the open and calcium flows into the synaptic end bulb of the presynaptic synaptic end bulb of the presynaptic neuronneuron

3. The increase in calcium 3. The increase in calcium concentration inside the synaptic end concentration inside the synaptic end bulb signals the synaptic vessicles to bulb signals the synaptic vessicles to release the neurotransmitters via release the neurotransmitters via exocytosis into the synaptic cleftexocytosis into the synaptic cleft

4. The neurotransmitters bind to 4. The neurotransmitters bind to receptors on the postynaptic neuronreceptors on the postynaptic neuron

5. Once the neurotransmitters bind to 5. Once the neurotransmitters bind to the receptors, ions flow across the the receptors, ions flow across the membranemembrane

6.6. As the ions flow across the As the ions flow across the membrane the voltage across the membrane the voltage across the membrane changes (postsynaptic membrane changes (postsynaptic potential)potential)

Chemical Synapses – 7 Chemical Synapses – 7 stepssteps

• If sodium flows across the membrane If sodium flows across the membrane it causes depolarizationit causes depolarization

• If chlorine flows across the If chlorine flows across the membrane it causes membrane it causes hyperpolarizationhyperpolarization

7. Once a depolarizing postsynaptic 7. Once a depolarizing postsynaptic potential reaches threshold, an potential reaches threshold, an action potential is triggeredaction potential is triggered

• Synaptic delay – The length of time Synaptic delay – The length of time between the arrival of the action between the arrival of the action potential at a presynaptic axon potential at a presynaptic axon terminal and the membrane potential terminal and the membrane potential change on the postsynaptic change on the postsynaptic membrane.membrane.

• Due to the synaptic delay electrical Due to the synaptic delay electrical synapses are faster than chemical synapses are faster than chemical synapsessynapses

Excitatory postsynaptic Excitatory postsynaptic potentialpotential

• Depolarizing postsynaptic potential Depolarizing postsynaptic potential caused by the influx of sodium, caused by the influx of sodium, potassium, and calciumpotassium, and calcium

Excitatory postsynaptic Excitatory postsynaptic potentialpotential

• Once it reaches threshold an action Once it reaches threshold an action potential is triggeredpotential is triggered

Inhibitory postsynaptic Inhibitory postsynaptic potentialpotential

• A hyperpolarizing postsynaptic A hyperpolarizing postsynaptic potential caused by the influx of potential caused by the influx of chlorine or efflux of potassiumchlorine or efflux of potassium

Inhibitory postsynaptic Inhibitory postsynaptic potentialpotential

• Makes it difficult for the generation of Makes it difficult for the generation of an action potentialan action potential

NeurotransmittersNeurotransmitters

1.1. Small-Molecule NeurotransmittersSmall-Molecule Neurotransmitters

2.2. NeuropeptidesNeuropeptides

Small-Molecule Small-Molecule NeurotransmittersNeurotransmitters

1.1. Acetylcholine Acetylcholine Released by PNS and CNS neuronsReleased by PNS and CNS neurons Can act as an excitatory Can act as an excitatory

(neuromuscular junction) or (neuromuscular junction) or inhibitory neuron (heart)inhibitory neuron (heart)

2.2. Amino acidAmino acid CNSCNS Glutamate has excitatory effects Glutamate has excitatory effects

(important for memory)(important for memory) Gamma aminobutyric (GABA) has Gamma aminobutyric (GABA) has

inhibitory effectsinhibitory effects

3.3. Biogenic aminesBiogenic amines Amino acids that are modified and Amino acids that are modified and

decarboxylateddecarboxylated Can be inhibitory or excitatory Can be inhibitory or excitatory

depending on the receptordepending on the receptor Norepinephrine, epinephrine, Norepinephrine, epinephrine,

dopamine, and serotonindopamine, and serotonin

3.3. Biogenic Amines continuedBiogenic Amines continued NE and Epinephrine play roles in NE and Epinephrine play roles in

arousal, dreaming, and regulating arousal, dreaming, and regulating moodmood

Small Molecule-Small Molecule-NeurotransmittersNeurotransmitters

3.3. Biogenic Amines continuedBiogenic Amines continued Dopamine are active during Dopamine are active during

emotional responses, addictive emotional responses, addictive behaviors, and pleasurable behaviors, and pleasurable experiencesexperiences

Small Molecule-Small Molecule-NeurotransmittersNeurotransmitters

3.3. Biogenic Amines continuedBiogenic Amines continued Serotonin involved in sensory Serotonin involved in sensory

reception, temperature regulation, reception, temperature regulation, control of mood, appetite, and the control of mood, appetite, and the induction of sleepinduction of sleep

Parkinson diseaseParkinson disease

• Due to degeneration of neurons that Due to degeneration of neurons that release dopaminerelease dopamine

SchizophreniaSchizophrenia

• Due to accumulation of excess Due to accumulation of excess dopaminedopamine

4.4. ATP and other PurinesATP and other Purines CNS and PNSCNS and PNS ExcitatoryExcitatory Usually released with another Usually released with another

neurotransmitterneurotransmitter

5.5. Nitric OxideNitric Oxide Simple gasSimple gas Plays a role in memory and learningPlays a role in memory and learning Causes vasodilationCauses vasodilation

ViagraViagra

• Enhances the effect of NOEnhances the effect of NO

NeuropeptidesNeuropeptides

• 3-40 amino acids linked by peptide 3-40 amino acids linked by peptide bondsbonds

• CNS and PNSCNS and PNS

• Excitatory and Inhibitory actionsExcitatory and Inhibitory actions

• Substance P enhances painSubstance P enhances pain

• Enkephalins and Endorphins inhibit Enkephalins and Endorphins inhibit pain (also morphine and heroin pain (also morphine and heroin receptors)receptors)

Nervous Tissue. Nervous System CNS (brain and spinal cord) CNS (brain and spinal cord) PNS...

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