Lecture8 nervous system

Nervous systemNervous system

Central nervous systemCentral nervous systemBrainBrainSpinal cordSpinal cord

Peripheral nervous systemPeripheral nervous systemNervesNervesGangliaGangliaNerve endingsNerve endings

Nervous tissueNervous tissueNervous tissueNervous tissue

supporting cellssupporting cellsGLIAL CELLSGLIAL CELLS

supporting cellssupporting cellsGLIAL CELLSGLIAL CELLS

nerve cellsnerve cellsNEURONSNEURONSnerve cellsnerve cellsNEURONSNEURONS

DendritesDendrites

Multiple processesMultiple processes Receptor processesReceptor processes Usually shortUsually short Branch profusely forming Branch profusely forming

a dendritic treea dendritic tree Become thinner as they subdivide Become thinner as they subdivide

into branchesinto branches

AxonsAxons

Single processesSingle processes Effector processesEffector processes Usually longUsually long Don’t branch profusely Don’t branch profusely Ends in terminal arborization – Ends in terminal arborization –

telodendrontelodendron Have constant diameterHave constant diameter

Types of neuronsTypes of neurons

Sensory (afferent)Sensory (afferent) Motor (efferent)Motor (efferent) InterneuronsInterneurons

Types of neuronsTypes of neurons

Bipolar neuronsBipolar neurons Retina Retina Olfactory mucosaOlfactory mucosa Cochlear and Cochlear and

vestibular gangliavestibular ganglia PPseudounipolar seudounipolar

neuronsneurons Sensory neuronsSensory neurons

MultiMultipolar neuronspolar neurons Motor Motor nneuronseurons InterneuronsInterneurons

Nuclei of glial cells Nuclei of glial cells

dendritedendrite Axon hillock Axon hillock

Nissl bodies Nissl bodies Nissl bodies Nissl bodies

rough endoplasmic reticulum rough endoplasmic reticulum cisternaes and free ribosomescisternaes and free ribosomesrough endoplasmic reticulum rough endoplasmic reticulum cisternaes and free ribosomescisternaes and free ribosomes

Types of synapsesTypes of synapses

AxosomaticAxosomaticAxodendriticAxodendriticAxoaxonicAxoaxonic

Types of synapsesTypes of synapses

ExcitatoryExcitatory InhibitoryInhibitory

Types of glial cellsTypes of glial cells

Central nervous systemCentral nervous system OligodendrocytesOligodendrocytes AstrocytesAstrocytes Ependymal cellsEpendymal cells MicrogliaMicroglia

Peripheral nervous systemPeripheral nervous system Schwann cellsSchwann cells Satellite cellsSatellite cells

AstrocytesAstrocytes Glial cells of central nervous systemGlial cells of central nervous system 2 types 2 types

ProtoplasmicProtoplasmic

FibrousFibrous

support neuronssupport neurons surround neurons, blood vessels, synapsessurround neurons, blood vessels, synapses form a layer on outer surface of the brain and spinal cordform a layer on outer surface of the brain and spinal cord control ionic and chemical environment of neuronscontrol ionic and chemical environment of neurons regulate neuronal activity and metabolismregulate neuronal activity and metabolism joined to one another by gap junctions forming joined to one another by gap junctions forming

a continous networka continous network

AstrocytesAstrocytes

Blood vesselBlood vessel

Microglial cells – MicrogliaMicroglial cells – Microglia

glial cells of central nervous glial cells of central nervous systemsystem

phagocytic cells – belong to phagocytic cells – belong to mononuclear phagocytic mononuclear phagocytic systemsystem

macrophages of CNSmacrophages of CNS derive from precursor cells in derive from precursor cells in

bone marrowbone marrow involved in inflammation involved in inflammation

processes in CNSprocesses in CNS phagocyte dead neurons and phagocyte dead neurons and

an excess of neurons during an excess of neurons during embryogenesisembryogenesis

Ependymal cellsEpendymal cells glial cells of CNSglial cells of CNS cuboidal cellscuboidal cells line the ventricles of the brain line the ventricles of the brain

and the central canal of the spinal cordand the central canal of the spinal cord

OligodendrocytesOligodendrocytes glial cells of CNSglial cells of CNS have only a few small processeshave only a few small processes myelin – forming cells in CNSmyelin – forming cells in CNS

Cells forming the myelin sheathCells forming the myelin sheathCells forming the myelin sheathCells forming the myelin sheath

CNSCNSOligodendrocytesOligodendrocytes

CNSCNSOligodendrocytesOligodendrocytes

PNSPNSSchwann cellsSchwann cells

PNSPNSSchwann cellsSchwann cells

Schwann cellSchwann cellInternodeInternode

Node of RanvierNode of Ranvier

Peripheral nervous systemPeripheral nervous systemPeripheral nervous systemPeripheral nervous system

Unmyelinated fibersUnmyelinated fibers

One Schwann cell→ several axonsOne Schwann cell→ several axons

Unmyelinated fibersUnmyelinated fibers

One Schwann cell→ several axonsOne Schwann cell→ several axons

Myelinated fibersMyelinated fibers

One Shwann cell→ one axonOne Shwann cell→ one axon

Myelinated fibersMyelinated fibers

One Shwann cell→ one axonOne Shwann cell→ one axon

Shwann cellShwann cell

Shwann cellShwann cell

AxonAxon

AxonsAxons

OligodendrocyteOligodendrocyte

Central nervous systemCentral nervous systemCentral nervous systemCentral nervous system

Unmyelinated fibersUnmyelinated fibers

Bare nerve fibers Bare nerve fibers – not imbedded in glial cells– not imbedded in glial cells

Unmyelinated fibersUnmyelinated fibers

Bare nerve fibers Bare nerve fibers – not imbedded in glial cells– not imbedded in glial cells

Myelinated fibersMyelinated fibers

OligodendrocytesOligodendrocytes

Myelinated fibersMyelinated fibers

OligodendrocytesOligodendrocytes

Peripheral nervous systemPeripheral nervous system

nervesnerves sensory nervessensory nerves motor nervesmotor nerves mixed nervesmixed nerves

gangliaganglia nerve endingsnerve endings

EpineuriumEpineurium

PerineuriumPerineurium

EndoneuriumEndoneurium

NerveNerve

EEndoneurium – loose connective tissuendoneurium – loose connective tissue PPerineurium – a few layers of flattened erineurium – a few layers of flattened

epithelium – like cellsepithelium – like cells EEpineurium – dense irregular connective pineurium – dense irregular connective

tissue containing blood vesselstissue containing blood vessels

Nucleus of nerve cellNucleus of nerve cell

Satelite cells Satelite cells NucleolusNucleolus

Sensory gangliaSensory ganglia

lie in dorsal roots of spinal cord, outside of CNSlie in dorsal roots of spinal cord, outside of CNS contain cell bodies of sensory neurons – contain cell bodies of sensory neurons –

pseudounipolar pseudounipolar 2 regions2 regions

central region – nerve fiberscentral region – nerve fibers peripheral region – cell bodiesperipheral region – cell bodies

cell bodies are covered by satellite cellscell bodies are covered by satellite cells satellite cells – a kind of glial cells of PNSsatellite cells – a kind of glial cells of PNS

Nervous systemNervous system

Somatic nervous system – voluntary Somatic nervous system – voluntary functions – functions – control skeletal musclescontrol skeletal muscles

Autonomic nervous system – Autonomic nervous system – involuntary functions – involuntary functions – control smooth control smooth muscle, secretion of some glands, modulation of muscle, secretion of some glands, modulation of cardiac rhythmcardiac rhythm

Autonomic nervous systemAutonomic nervous system

Sympathetic system – Sympathetic system – presynaptic presynaptic neurons are located in thoracic and lumbar neurons are located in thoracic and lumbar segments of spinal cordsegments of spinal cord

Parasympathetic system – Parasympathetic system – presynaptic presynaptic neurons have their nuclei in medulla, midbrain, neurons have their nuclei in medulla, midbrain, sacral portion of spinal cordsacral portion of spinal cord

Nerve endingsNerve endings

afferent – sensory receptorsafferent – sensory receptors efferentefferent

Sensory receptorsSensory receptors

exteroceptorsexteroceptors proprioceptorsproprioceptors interoceptorsinteroceptors

Sensory Sensory rereceptorsceptors

NonencapsulatedNonencapsulated Free nerve endingsFree nerve endings Merkel endingsMerkel endings

EncapsulatedEncapsulated Meissner corpuscleMeissner corpuscle Pacinian corpusclePacinian corpuscle Ruffini corpuscleRuffini corpuscle

Free nerve endingsFree nerve endings

Found in skin and Found in skin and corneal epitheliumcorneal epithelium

Terminate in Terminate in epidermisepidermis

Devoid of Schwann Devoid of Schwann cells and myelincells and myelin

Respond to touch, Respond to touch, heat, cold, painheat, cold, pain

Merkel endingMerkel ending

Nerve endings are Nerve endings are attached to Merkel attached to Merkel cellscells

Merkel cells – Merkel cells – modified epidermal modified epidermal cells located in skincells located in skin

Mechanoreceptors – Mechanoreceptors – sensitive to touchsensitive to touch

Pacinian corpusclesPacinian corpuscles Encapsulated receptorsEncapsulated receptors Ovoid structure resembling Ovoid structure resembling

a hemisected oniona hemisected onion Nerve ending is Nerve ending is

surrounded surrounded by concentric lamellae of by concentric lamellae of flattened cellsflattened cells

Found in hypodermis and Found in hypodermis and deed fascia tissuesdeed fascia tissues

Respond to vibrations and Respond to vibrations and deep pressuredeep pressure

Meissner’s corpusclesMeissner’s corpuscles

Encapsulated receptorsEncapsulated receptors Contain Schwann cells that Contain Schwann cells that

form irregular, tortuous form irregular, tortuous lamellaelamellae

Nerve fibers pass between Nerve fibers pass between lamellaelamellae

Found in the papillary layer Found in the papillary layer of hairless skin (lips, of hairless skin (lips, fingers, hands, foots)fingers, hands, foots)

Respond to touchRespond to touch

ProprioceptorsProprioceptors

Muscle spindlesMuscle spindles Golgi tendon organsGolgi tendon organs

Degeneration and regeneration of Degeneration and regeneration of peripheral nerve - stepsperipheral nerve - steps

1.1. Schwann cells proliferate and bridge the scar.Schwann cells proliferate and bridge the scar.

2.2. The axon degenerateThe axon degenerate Anterograde degeneration – (refers to distal segment) – comprise the Anterograde degeneration – (refers to distal segment) – comprise the

whole distal segment including axon and myelin sheathwhole distal segment including axon and myelin sheath Retrograde degeneration – (refers to proximal segment) –extends for a Retrograde degeneration – (refers to proximal segment) –extends for a

short distanceshort distance

3.3. Debris is phagocyted by macrophages.Debris is phagocyted by macrophages.

4.4. The cell body undergoes chromatolysis.The cell body undergoes chromatolysis.

5.5. The muscle fiber shows a denervation atrophy.The muscle fiber shows a denervation atrophy.

6.6. Shwann cell prolipherate within a connective tissue sleeve.Shwann cell prolipherate within a connective tissue sleeve.

7.7. The axon grows and penetrate the Schwann cell columns.The axon grows and penetrate the Schwann cell columns.

8.8. Schwann cells produce myelin sheath on the regenerated axon.Schwann cells produce myelin sheath on the regenerated axon.