CHAPTER 13CHAPTER 13Nervous TissueNervous Tissue

COMMON COURSE OBJECTIVES:COMMON COURSE OBJECTIVES:

1.1. Functions of the nervous systemFunctions of the nervous system

2.2. Organization of the nervous Organization of the nervous systemsystem

3.3. Nerve tissue and nerve cell typesNerve tissue and nerve cell types

4.4. Structure of a typical neuronStructure of a typical neuron

5.5. Structure of a chemical synapseStructure of a chemical synapse

Nervous Tissue HistologyNervous Tissue Histology

Composed of:Composed of: Neurons true conducting cells in nervous Neurons true conducting cells in nervous

tissuetissue

Neuroglial (supporting) cellsNeuroglial (supporting) cells-Astrocytes-Astrocytes -Schwann cells-Schwann cells

-Oligodendrocytes-Oligodendrocytes -Satellite cells-Satellite cells

-Microglia-Microglia

-Ependymal-Ependymal

The NERVOUS The NERVOUS SYSTEMSYSTEM

Defined: Defined: like the CPU of a computer, like the CPU of a computer, the nervous system is the the nervous system is the master master controlling systemcontrolling system of the body. It is of the body. It is designed to constantly and rapidly designed to constantly and rapidly adjust and respond to stimuli the body adjust and respond to stimuli the body receives. It includes the brain, cranial receives. It includes the brain, cranial nerves, spinal cord, and associated nerves, spinal cord, and associated peripheral nerves. peripheral nerves.

Properties of NeuronsProperties of Neurons

1.1. Excitability (irritability): ability to respond to Excitability (irritability): ability to respond to environmental changes or stimuli.environmental changes or stimuli.

2.2. Conductivity: respond to stimuli by initiating Conductivity: respond to stimuli by initiating electrical signals that travel quickly to other electrical signals that travel quickly to other cells at distant locations.cells at distant locations.

3.3. Secretion: Upon arrival of the impulse at a Secretion: Upon arrival of the impulse at a distant location the neuron usually secretes a distant location the neuron usually secretes a chemical neurotransmitter at a synapse that chemical neurotransmitter at a synapse that crosses the synaptic gap and stimulates the next crosses the synaptic gap and stimulates the next cell.cell.

Functional Classes of Neurons Functional Classes of Neurons

Sensory (afferent) neuronsSensory (afferent) neurons – afferent neurons – afferent neurons are specialized to detect stimuli and transmit the are specialized to detect stimuli and transmit the information to CNS. They begin in any organ in information to CNS. They begin in any organ in the body, but end in the brain or spinal cord.the body, but end in the brain or spinal cord.

Interneuron (association neurons): Interneuron (association neurons): lie entirely lie entirely in the CNS. They receive signals from many in the CNS. They receive signals from many different neurons and perform an integrative different neurons and perform an integrative function “decision making” to respond to the function “decision making” to respond to the different stimuli. different stimuli.

Motor (efferent) neurons – Motor (efferent) neurons – efferent neurons efferent neurons transmit the appropriate response from the transmit the appropriate response from the interneuron to an end organ (muscle and gland interneuron to an end organ (muscle and gland cells) to carry out the body’s response to the cells) to carry out the body’s response to the stimuli.stimuli.

Functional Classification of Functional Classification of NeuronsNeurons

Based on the direction of conductionBased on the direction of conduction Sensory or afferent conduct toward the CNSSensory or afferent conduct toward the CNS Motor or efferent conduct away from the Motor or efferent conduct away from the

CNSCNS Interneuron interposed between sensory and Interneuron interposed between sensory and

motormotor

Organization of the Nervous Organization of the Nervous

SystemSystem Two main divisionsTwo main divisions::

The Central Nervous System (CNS)The Central Nervous System (CNS)- - Consists of the brain and spinal cord with Consists of the brain and spinal cord with tracts and nucleitracts and nucleiNucleus = a collection of nerve cell bodies in the Nucleus = a collection of nerve cell bodies in the CNS.CNS.Tract = bundle of nerve fibers within the CNSTract = bundle of nerve fibers within the CNS

The Peripheral Nervous System (PNS)The Peripheral Nervous System (PNS) -Consists of ganglia, cranial nerves, spinal -Consists of ganglia, cranial nerves, spinal nerves and peripheral receptorsnerves and peripheral receptorsGanglia = a collection of nerve cell bodies in the Ganglia = a collection of nerve cell bodies in the PNSPNSNerve = bundle of nerve fibers in the PNSNerve = bundle of nerve fibers in the PNS

CNSCNS = brain = brain + spinal cord+ spinal cord

Peripheral Nervous System Peripheral Nervous System (PNS)(PNS)

Composed of cranial nerves and spinal Composed of cranial nerves and spinal nerves and their branches, ganglia and nerves and their branches, ganglia and sensory receptors. sensory receptors.

PNS PNS is subdivided into sensory and is subdivided into sensory and motor divisions:motor divisions: somatic nervous system (SNS)somatic nervous system (SNS) autonomic nervous system (ANS) and autonomic nervous system (ANS) and

thethe enteric nervous system (ENS)enteric nervous system (ENS)

Sensory or Afferent Division Sensory or Afferent Division

Somatic sensorySomatic sensory = = senses touch, senses touch, pressure, pain, temperature, vibration pressure, pain, temperature, vibration and proprioception in skin, body wall and proprioception in skin, body wall and limbs.and limbs.

Visceral sensoryVisceral sensory = = Autonomic Autonomic sensory division-sensory division- sensessenses stretch, pain, stretch, pain, temperature, chemical changes and temperature, chemical changes and irritation in viscera; nausea and hungerirritation in viscera; nausea and hunger. .

Motor or Efferent DivisionMotor or Efferent Division Somatic motorSomatic motor

--motor control to all skeletal muscles except motor control to all skeletal muscles except pharyngeal muscles.pharyngeal muscles.

Visceral MotorVisceral Motor = Autonomic Nervous System – = Autonomic Nervous System – Four “F’s”Four “F’s”

-Sensory receptors convey information from -Sensory receptors convey information from visceral organs (e.g. heart, lungs, intestines, visceral organs (e.g. heart, lungs, intestines, etc.) to the CNS for integration and etc.) to the CNS for integration and interpretation. A motor response is initiated interpretation. A motor response is initiated that conducts impulses from CNS to smooth that conducts impulses from CNS to smooth muscle, cardiac muscle and/or glands for muscle, cardiac muscle and/or glands for appropriate responseappropriate response

Autonomic Nervous SystemAutonomic Nervous System

Two divisions of ANS (4 “F’s”)Two divisions of ANS (4 “F’s”) Sympathetic divisionSympathetic division – Fight or – Fight or

FlightFlight

Parasympathetic divisionParasympathetic division – Food or – Food or SexSex

CNS/PNS summaryCNS/PNS summary

NeuronsNeurons

Nerve cell properNerve cell proper

Cell body (soma)Cell body (soma)

Dendrites - TODendrites - TO

Axons -FROMAxons -FROM

Structural Classification of Structural Classification of NeuronsNeurons

Neurons may be: Neurons may be: Multipolar, Bipolar or Multipolar, Bipolar or UnipolarUnipolar

Determined by the number of processes Determined by the number of processes attached to the cell bodyattached to the cell body

NeuronsNeurons

Most (99%) neurons in the body are Most (99%) neurons in the body are multipolar.multipolar.

Bipolar neurons are rare and occur in Bipolar neurons are rare and occur in special sense organs of ear, nose and special sense organs of ear, nose and eye.eye.

Unipolar neurons begin as bipolar but Unipolar neurons begin as bipolar but processes fuse into one. They are processes fuse into one. They are primarily sensory neurons.primarily sensory neurons.

Neuroglia cellsNeuroglia cells

Found in CNS and PNSFound in CNS and PNS Perform a supporting function for Perform a supporting function for

neurons neurons CNSCNS PNSPNS

Oligodendroglialcytes Oligodendroglialcytes Schwann cellsSchwann cells Astrocytes Astrocytes Satellite cellsSatellite cells Ependymal cellsEpendymal cells MicrogliaMicroglia

Oligodendrogliocytes -Oligodendrogliocytes -CNSCNS

Form myelin sheath in CNS Form myelin sheath in CNS Fewer branches than astrocytesFewer branches than astrocytes

MyelinMyelin

Insulating layer around a nerveInsulating layer around a nerve Formed by oligodendrocytes in CNS Formed by oligodendrocytes in CNS

and Schwann cells in PNSand Schwann cells in PNS Composed of a lipoprotein with Composed of a lipoprotein with

phospholipids, glycolipids and phospholipids, glycolipids and cholesterol.cholesterol.

Myelination is process of myelin Myelination is process of myelin formationformation

Astrocytes - CNSAstrocytes - CNS

Star shapedStar shaped

Blood brain barrierBlood brain barrier

Most numerous Most numerous

Ependymal cells - CNSEpendymal cells - CNS Epithelial cells that line ventricles and central Epithelial cells that line ventricles and central

cavities of brain and spinal cord-secrete CSFcavities of brain and spinal cord-secrete CSF Ciliated to circulate CSFCiliated to circulate CSF

Microglia - CNSMicroglia - CNS

Thorny bushes in appearance and the smallest Thorny bushes in appearance and the smallest gliaglia

Phagocytic function in CNSPhagocytic function in CNS Originate from monocytesOriginate from monocytes

Schwann cells- PNSSchwann cells- PNS Form myelin sheath around peripheral Form myelin sheath around peripheral

axonsaxons Look like jelly roll with neurolemma Look like jelly roll with neurolemma

covercover Node of Ranvier separate each Schwann Node of Ranvier separate each Schwann

cellcell

Myelin and Unmyelinated Myelin and Unmyelinated fibersfibers

Satellite cells -PNSSatellite cells -PNS Surround neuron cell bodies within Surround neuron cell bodies within

gangliaganglia

Synaptic endingSynaptic ending

SynapseSynapse – site where two nerves – site where two nerves communicate with each other.communicate with each other.

Presynaptic neuronPresynaptic neuron – neuron that is – neuron that is conducting information toward the next conducting information toward the next neuronneuron

Postsynaptic neuronPostsynaptic neuron – transmits information – transmits information away from synapseaway from synapse

Most synaptic communication is via Most synaptic communication is via chemical messengerschemical messengers (e.g. acetylcholine, (e.g. acetylcholine, serotonin, norepinephrine, dopamine, serotonin, norepinephrine, dopamine, endorphins, GABA, glycine, glutamic acid, endorphins, GABA, glycine, glutamic acid, etc.)etc.)

Synaptic terminalsSynaptic terminals

Types of synapsesTypes of synapses

Axodendritic = axon to dendriteAxodendritic = axon to dendrite Axosomatic = axon to cell bodyAxosomatic = axon to cell body Axoaxonic = axon to axonAxoaxonic = axon to axon Dendrodendritic = dendrite to Dendrodendritic = dendrite to

dendritedendrite Dendrosomatic = dendrite to cell Dendrosomatic = dendrite to cell

bodybody

Types of Neuronal Types of Neuronal CircuitsCircuits