SlideShare una empresa de Scribd logo
1 de 34
Descargar para leer sin conexión
SYNAPTIC TRANSMISSION
SYNAPTIC TRANSMISSION
Study material for B.Sc (H) Physiology 2nd Sem
Dr Atanu Saha
REVIEW ~ SETTING THE STAGE
 Information is digitized at the axon hillock
 Information is digitized at the axon hillock
and a stream of action potentials carries the
output of a neuron down the axon to other
neurons
neurons.
 Neurons are the only class of cells that do not
touch neighboring cells.
 How is this output transferred to the next neuron
in the chain?
 The transfer of information from the end of
 The transfer of information from the end of
the axon of one neuron to the next neuron is
called synaptic transmission.
MOVING THE MESSAGE
MOVING THE MESSAGE
 Transmission of the signal between neurons
takes place across the synapse the space
takes place across the synapse, the space
between two neurons.
 In higher organisms this transmission is
chemical.
 Synaptic transmission then causes electrical
events in the next neuron
events in the next neuron.
 All the inputs coming into a particular
neuron are integrated to form the generator
potential at its a on hillock here a ne
potential at its axon hillock where a new
stream of action potentials is generated.
SYNAPTIC CONNECTIONS
 Neurons are the only cells that can
communicate with one another rapidly over
communicate with one another rapidly over
great distance
 Synaptic connections are specific.
 Underlie perception, emotion, behavior
 The average neuron makes 1000 synaptic connections
- receives more
 The human brain contains 1011 neurons & forms 1014
connections
 Neural processing occurs from the integration
 Neural processing occurs from the integration
of the various synaptic inputs on a neuron into
the generator potential of that neuron.
SPECIAL CHANNELS
SPECIAL CHANNELS
 Recall the 2 classes of channels for
signaling within cells:
 Resting channels that generate resting potential
Voltage gated channels that produce an action
 Voltage-gated channels that produce an action
potential
 Synaptic transmission uses 2 additional
l f h l
classes of channels:
 Gap-junction channels
 Ligand-gated channels
Ligand gated channels
COMPOSITION OF A SYNAPSE
COMPOSITION OF A SYNAPSE
 The s napse is made of 3
 The synapse is made of 3
elements:
 pre-synaptic terminal
 postsynaptic cell
 zone of apposition
TYPES OF SYNAPSES
TYPES OF SYNAPSES
 Synapses are divided into 2 groups based on
y p g p
zones of apposition:
 Electrical
 Chemical
 Fast Chemical
 Modulating (slow) Chemical
 Modulating (slow) Chemical
ELECTRICAL SYNAPSES
ELECTRICAL SYNAPSES
 Common in invertebrate neurons involved
ith i t t fl i it
with important reflex circuits.
 Less common in adult mammalian neurons,
but common in many other body tissues
but common in many other body tissues
such as heart muscle cells.
 Current generated by the action potential in
g y p
pre-synaptic neuron flows through the gap
junction channel into the next neuron
S d i l d l i i i l
 Send simple depolarizing signals
 May transmit metabolic signals between
cells
cells
PROPERTIES OF THE ELECTRICAL
SYNAPSE
 Two cell membranes are aligned parallel
g p
 The synaptic cleft is small ~3.5 nm
 Usually between large presynaptic neuron
y g p y p
& small postsynaptic neuron
 takes a lot of current to depolarize a cell
S i li d t i ll d
 Specialized proteins called connexons span
the pair of membranes to make a very
large pore (the Gap Junction Channel)
g p ( p )
 Signal can be bi-directional
GAP-JUNCTION CHANNELS
GAP JUNCTION CHANNELS
 Connect communicating cells at an electrical
synapse
synapse
 Consist of a pair of cylinders (connexons)
 one in presynaptic cell one in post
 one in presynaptic cell, one in post
 each cylinder made of 6 protein subunits
 cylinders meet in the gap between the two cell
b
membranes
 Always open
 All ions and many small organic molecules are free
 All ions and many small organic molecules are free
to pass through the pore
 Gap junctions serve to synchronize the activity
of a set of neurons
SYNCHRONIZING CELLS
SYNCHRONIZING CELLS
 Electrical transmission allows rapid,
synchronous firing of interconnected cells
 Can interconnect groups of neurons
 Very fast; virtually no delay
 Speed important for certain responses - defense
El i ll l d ll i
 Electrically coupled cells can trigger
explosive, all or none behavior
Ad ti d t ( ldfi h t il id
 Adaptive advantage (e.g. goldfish tail, squid
ink)
MODULATING CONDUCTANCE
MODULATING CONDUCTANCE
 Gap junctions close in response to lower
cytoplasmic pH or increased Ca+2
cytoplasmic pH or increased Ca
 Some act as rectifiers
 channels are sensitive to voltage
h f i i idi i l
 therefore transmission unidirectional
 Linkage to chemical synapses
 neurotransmitters released from nearby chemical
y
synapses can activate 2nd messenger dependent
enzymes that alter gating of gap junction channels
CHEMICAL SYNAPSES
CHEMICAL SYNAPSES
 Synaptic cleft is larger
 Synaptic cleft is larger
 There is no structural continuity between
presynaptic & postsynaptic cells
p y p p y p
 A chemical molecule, a
neurotransmitter, is released from the
presynaptic neuron
 diffuses across the synaptic cleft (20-50 nm)
 binds with a receptor on the postsynaptic
membrane.
CATEGORIES OF CHEMICAL
SYNAPSES
SYNAPSES
 Fast chemical synapses:
H t itt t d i h l
 Have transmitter-gated ion channels
 Fast, electrical response to arrival of presynaptic
action potential
 Use amino acids and amines as
neurotransmitters
 Slow modulatory chemical synapses:
 Slow, modulatory chemical synapses:
 Have G-protein-coupled ion channels
 Slow response to arrival of presynaptic action
p p y p
potential
 activate second messenger system; not always a
direct electrical effect
direct electrical effect
 May use amino acids, amines, or peptides
STRUCTURE OF THE CHEMICAL
SYNAPSE
 Presynaptic structures:
y p
 Vesicles - contain amino acids or amines,
released at synapse
S t l (d d i l )
 Secretory granules (dense-cored vesicles) -
contain peptides
 Presynaptic densities - serve to organize
vesicles and prepare them for release
 Postsynaptic structures:
 Postsynaptic densities loaded with receptors
 Postsynaptic densities - loaded with receptors
and ion channels, bind neurotransmitters and
establish ionic currents
WIRING PATTERNS OF CHEMICAL
SYNAPSES
 Axosomatic synapse - Axon terminal ends on a
y p
cell body
 Axodendritic synapse - Axon terminal ends on a
dendrite
dendrite
 Axoaxonic synapse - Axon terminal ends on
another axon
D d d d i i D d it k
 Dendrodendritic synapse - Dendrite makes
synapse with another dendrite
RELEASE OF
N
NEUROTRANSMITTERS
 Occurs in response to Ca+2 influx that
occurs with the action potential
 Change in membrane potential in
e a tic e o lead to elea e of
presynaptic neuron leads to release of
chemical transmitter from terminals
 transmitter diffuses across cleft
 binds to receptor molecules on the postsynaptic cell
membrane
 binding receptor causes ion channels to open or close,
g p p ,
altering potential
TRANSMITTER BINDING
TRANSMITTER BINDING
 Binding receptor is specific - lock & key
 Action determined by properties of receptor
 Action determined by properties of receptor,
not chemical properties of the transmitter
 receptor determines if response is excitatory or
i hibi
inhibitory
 All neurotransmitter receptors have 2
biochemical features in common:
biochemical features in common:
 they are membrane spanning proteins that
recognize & bind transmitter
 they carry out effector function with a target cell,
usually by influencing opening or closing of ion
channels
SYNAPTIC RELEASE
SYNAPTIC RELEASE
FAST CHEMICAL SYNAPSES
 Action potential invades axon terminal
 Action potential invades axon terminal
 Voltage-gated calcium channels pop open
 Calcium ions flood presynaptic terminal in region of
i l l
vesicle release
 Synaptic vesicles fuse with presynaptic membrane
– exocytosis
y
 Neurotransmitter molecules diffuse into and across
synaptic cleft
TRANSMITTER-GATED ION
CHANNELS
 Neurotransmitter molecules bind to the
receptor site on transmitter-gated ion channels
ecepto s te o t a s tte gated o c a e s
embedded in the postsynaptic membrane
 Ionic currents flow into or out of the
i ll
postsynaptic cell
 If Na+ ions are the carrier, the membrane
potential of the postsynaptic cell is depolarized
potential of the postsynaptic cell is depolarized
 EPSP -Excitatory Post-Synaptic Potential
 If Cl- ions or K+ ions are the carrier, the
C o s o o s a e e ca e , e
membrane potential of the postsynaptic cell is
hyperpolarized
IPSP I hibi P S i P i l
 IPSP - Inhibitory Post-Synaptic Potential
REMOVAL OF
NEUROTRANSMITTER
NEUROTRANSMITTER
 The neurotransmitter is inactivated or
 The neurotransmitter is inactivated or
removed from the synaptic cleft
 For acetylcholine, there is an enzyme,
y , y ,
acetylcholine esterase (AChE) that does
this
 For other amino acids and amines, the
presynaptic membrane actively sucks up
h i d i hb i li l ll
the transmitter and neighboring glial cells
may do likewise
SYNAPTIC RELEASE
NEUROMODULATORY SYNAPSES
 Action potential invades axon terminal
 Voltage-gated calcium channels pop open
 Calcium ions flood presynaptic terminal in
i f i l l
region of vesicle release
 Synaptic vesicles fuse with presynaptic
membrane exocytosis
membrane – exocytosis
 Neurotransmitter molecules diffuse into
and across synaptic cleft
y p
 Neurotransmitter molecules bind to
receptor proteins in the postsynaptic
b
membrane
G-PROTEIN-COUPLED RECEPTORS
 G-proteins in the membrane are activated and
p
move along inner face
 Activated G-proteins activate effector proteins
 May act directly or indirectly (2nd messenger)
 May act directly or indirectly (2nd messenger)
 The neurotransmitter is inactivated or removed
from the synaptic cleft
DIRECT RECEPTORS
DIRECT RECEPTORS
 Ionotropic
p
 Are membrane spanning
 Made of several peptide subunits
O bi di t itt d
 On binding neurotransmitter, undergo
conformational change that opens a G-protein
gated ion channel
 Example - acetylcholine receptor on muscle
INDIRECT RECEPTORS
 Are macromolecules that are separate from
the ion channels on which they act
2 f ilil
 2 famililes:
 Metabotropic
 membrane spanning proteins
 membrane spanning proteins
 a single polypeptide chain coupled to GTP-
binding proteins, which activate enzymes that
d 2 d h li AMP
produce 2nd messenger such as cyclic AMP
 2nd messenger either acts on channel directly or
thru enzyme
y
 Tyrosine kinase family
 add a phosphate group to tyrosine of substrate
t i d l ti h l
proteins, modulating channel
SYNAPTIC INTEGRATION:
FAST CHEMICAL SYNAPSES~ GATED ION
CHANNELS
 Synaptic transmitter release is quantal
 Each vesicle or secretory granule contains the
same number of neurotransmitter molecules
 The EPSP or IPSP that results is one of a set of
 The EPSP or IPSP that results is one of a set of
consistent sizes - one vesicle, two vesicles, three
vesicles, etc.
T i ll t l j ti 200
 Typically at a neuromuscular junction 200
vesicles are released from one action potential -
fail safe contraction of the muscle
 At a synapse in the CNS, typically only one
vesicle is released - input for processing in the
dendrite
 Not every synaptic release causes an action
potential in the postsynaptic neuron
SPATIAL SUMMATION
SPATIAL SUMMATION
 The dendrites of each neuron receive many
y
synaptic inputs from a variety of neurons.
 The combining of the EPSPs and IPSPs across
th d d it f th i lt i l f
the dendrite from the simultaneous arrival of
action potentials at various synapses is called
spatial summation
LENGTH CONSTANT
G CO S
 The measure of how effective a given synapse is
in contributing to spatial summation
 The length constant gives the distance (in µm)
that it take a EPSP o IPSP to dec ea e to
that it takes an EPSP or IPSP to decrease to
37% of its original value at the synapse:
 The length constant is directly proportional to
 The length constant is directly proportional to
the membrane resistance and inversely
proportional to the longitudinal resistance
f th t l
of the cytoplasm
 The leakier the membrane, the shorter the length
constant
 The narrower the dendrite, the shorter the length
constant
TEMPORAL SUMMATION
TEMPORAL SUMMATION
 The combining of EPSPs or IPSPs from repeated
action potentials arriving at a single synapse is
action potentials arriving at a single synapse is
called temporal summation
 The measure of how effective a given synapse is
 The measure of how effective a given synapse is
in contributing to temporal summation is the
time constant, t
 The time constant gives the time (in
milliseconds) that it takes an EPSP or IPSP to
decrease to 37% of its original value at the
decrease to 37% of its original value at the
synapse
 In most cases, the effects of spatial summation
and temporal summation must both be taken
into account
NEUROMODULATION
 With a G-protein-coupled receptor, a chain of events is
triggered that usually ends with the phosphorylation of a
protein.
protein.
 For example:
 When a receptor for norepinephrine is activated,
 a G-protein is activated.
 Adenyl cyclase (an enzyme) is activated, which
 uses ATP to produce cyclic AMP a second messenger
 uses ATP to produce cyclic AMP, a second messenger.
 cAMP activates a protein kinase.
 The protein kinase phosphorylates a potassium channel,
 Which causes it to close
 This increases l and t, thereby making synapses more
potent for a period of time
potent for a period of time
 hence the term modulation
W C T ?
WHY CHEMICAL TRANSMISSION?
 More flexible; produces more complex behaviors
; p p
 Plasticity
 Can amplify neuronal signals
Di tl t d ti l f t
 Directly gated are comparatively fast
 mediate behavior
 Indirect are slower
 important in memory, learning
F C T
FLEXIBILITY OF CHEMICAL TRANSMISSION
 Produces more complex behaviors
p
 Same neurotransmitter can have several
functions
 at one terminal can be released at the active zone &
 at one terminal can be released at the active zone &
serve as a direct transmitter, acting on neighboring
cells
 at another site can serve as a modulator
at another site can serve as a modulator
 at a third site released into bloodstream as
neurohormone
PLASTICITY OF CHEMICAL TRANSMISSION
 Chemical Transmission has plasticity plasticity
because it is multistep
I f & h hi h f i
 Important for memory & other higher functions
 Modifiability of chemical synapses is an important
mechanism in behavioral learning
mechanism in behavioral learning
AMPLIFYING NEURONAL
SIGNALS
SIGNALS
 Chemical transmission can amplify neuronal
signals
 A small nerve terminal can alter the potential of a
 A small nerve terminal can alter the potential of a
large postsynaptic cell
 The action of just one synaptic vesicle leads to
j y p
opening of thousands of ion channels

Más contenido relacionado

Similar a synaptictransmission-091111081952-phpapp02-Compatibility-Mode.pdf

Neurons& Synapses
Neurons& SynapsesNeurons& Synapses
Neurons& Synapsesraj kumar
 
Neurons& Synapses
Neurons& SynapsesNeurons& Synapses
Neurons& Synapsesraj kumar
 
Synaptic integration, Types of synapses, EPSP and IPSP
Synaptic integration, Types of synapses, EPSP and IPSPSynaptic integration, Types of synapses, EPSP and IPSP
Synaptic integration, Types of synapses, EPSP and IPSPGopu Hernandaz
 
synapticintegration-141202040428-conversion-gate01.pdf
synapticintegration-141202040428-conversion-gate01.pdfsynapticintegration-141202040428-conversion-gate01.pdf
synapticintegration-141202040428-conversion-gate01.pdfkeerthikrishna41
 
Synaptic transmission i
Synaptic transmission iSynaptic transmission i
Synaptic transmission ianju jha
 
Nerve Conduction and Synapse
Nerve Conduction and SynapseNerve Conduction and Synapse
Nerve Conduction and SynapseSado Anatomist
 
Classification and structure of synapses
Classification and structure of synapsesClassification and structure of synapses
Classification and structure of synapsesAlaaAlchyad
 
Presentation EXCITABLE TISSUES.pptx
Presentation EXCITABLE TISSUES.pptxPresentation EXCITABLE TISSUES.pptx
Presentation EXCITABLE TISSUES.pptxFranciKaySichu
 
Md (surg) part1 nmj 2011 student
Md (surg) part1 nmj 2011 studentMd (surg) part1 nmj 2011 student
Md (surg) part1 nmj 2011 studentvajira54
 
NERVE AND MUSCLE VETERINARY PHYSIOLOGY .pdf
NERVE AND MUSCLE VETERINARY PHYSIOLOGY .pdfNERVE AND MUSCLE VETERINARY PHYSIOLOGY .pdf
NERVE AND MUSCLE VETERINARY PHYSIOLOGY .pdfTatendaMageja
 
anatomyphysiologyofneuromuscularjunctionmonitoring-110201023707-phpapp02 2.pdf
anatomyphysiologyofneuromuscularjunctionmonitoring-110201023707-phpapp02 2.pdfanatomyphysiologyofneuromuscularjunctionmonitoring-110201023707-phpapp02 2.pdf
anatomyphysiologyofneuromuscularjunctionmonitoring-110201023707-phpapp02 2.pdfDrHardikDudhatra
 
synaptictransmission
synaptictransmissionsynaptictransmission
synaptictransmissionSania Tahir
 
Bio 201 chapter 12 lecture
Bio 201 chapter 12 lectureBio 201 chapter 12 lecture
Bio 201 chapter 12 lectureMatt
 

Similar a synaptictransmission-091111081952-phpapp02-Compatibility-Mode.pdf (20)

Neurons& Synapses
Neurons& SynapsesNeurons& Synapses
Neurons& Synapses
 
Neurons& Synapses
Neurons& SynapsesNeurons& Synapses
Neurons& Synapses
 
Synaptic integration, Types of synapses, EPSP and IPSP
Synaptic integration, Types of synapses, EPSP and IPSPSynaptic integration, Types of synapses, EPSP and IPSP
Synaptic integration, Types of synapses, EPSP and IPSP
 
Synaptic Transmission
Synaptic TransmissionSynaptic Transmission
Synaptic Transmission
 
synapticintegration-141202040428-conversion-gate01.pdf
synapticintegration-141202040428-conversion-gate01.pdfsynapticintegration-141202040428-conversion-gate01.pdf
synapticintegration-141202040428-conversion-gate01.pdf
 
Synaptic transmission i
Synaptic transmission iSynaptic transmission i
Synaptic transmission i
 
Nerve Conduction and Synapse
Nerve Conduction and SynapseNerve Conduction and Synapse
Nerve Conduction and Synapse
 
Neuro humoral transmission
Neuro humoral transmissionNeuro humoral transmission
Neuro humoral transmission
 
Classification and structure of synapses
Classification and structure of synapsesClassification and structure of synapses
Classification and structure of synapses
 
Epilepsy1
Epilepsy1Epilepsy1
Epilepsy1
 
Lect 4-synapse-8-
Lect 4-synapse-8-Lect 4-synapse-8-
Lect 4-synapse-8-
 
Presentation EXCITABLE TISSUES.pptx
Presentation EXCITABLE TISSUES.pptxPresentation EXCITABLE TISSUES.pptx
Presentation EXCITABLE TISSUES.pptx
 
Md (surg) part1 nmj 2011 student
Md (surg) part1 nmj 2011 studentMd (surg) part1 nmj 2011 student
Md (surg) part1 nmj 2011 student
 
Nerves
NervesNerves
Nerves
 
NERVE AND MUSCLE VETERINARY PHYSIOLOGY .pdf
NERVE AND MUSCLE VETERINARY PHYSIOLOGY .pdfNERVE AND MUSCLE VETERINARY PHYSIOLOGY .pdf
NERVE AND MUSCLE VETERINARY PHYSIOLOGY .pdf
 
Synapse
SynapseSynapse
Synapse
 
Neurons system
Neurons systemNeurons system
Neurons system
 
anatomyphysiologyofneuromuscularjunctionmonitoring-110201023707-phpapp02 2.pdf
anatomyphysiologyofneuromuscularjunctionmonitoring-110201023707-phpapp02 2.pdfanatomyphysiologyofneuromuscularjunctionmonitoring-110201023707-phpapp02 2.pdf
anatomyphysiologyofneuromuscularjunctionmonitoring-110201023707-phpapp02 2.pdf
 
synaptictransmission
synaptictransmissionsynaptictransmission
synaptictransmission
 
Bio 201 chapter 12 lecture
Bio 201 chapter 12 lectureBio 201 chapter 12 lecture
Bio 201 chapter 12 lecture
 

Último

IB Biology New syllabus B3.2 Transport.pptx
IB Biology New syllabus B3.2 Transport.pptxIB Biology New syllabus B3.2 Transport.pptx
IB Biology New syllabus B3.2 Transport.pptxUalikhanKalkhojayev1
 
Pests of cumbu_Identification, Binomics, Integrated ManagementDr.UPR.pdf
Pests of cumbu_Identification, Binomics, Integrated ManagementDr.UPR.pdfPests of cumbu_Identification, Binomics, Integrated ManagementDr.UPR.pdf
Pests of cumbu_Identification, Binomics, Integrated ManagementDr.UPR.pdfPirithiRaju
 
Legacy Analysis of Dark Matter Annihilation from the Milky Way Dwarf Spheroid...
Legacy Analysis of Dark Matter Annihilation from the Milky Way Dwarf Spheroid...Legacy Analysis of Dark Matter Annihilation from the Milky Way Dwarf Spheroid...
Legacy Analysis of Dark Matter Annihilation from the Milky Way Dwarf Spheroid...Sérgio Sacani
 
soft skills question paper set for bba ca
soft skills question paper set for bba casoft skills question paper set for bba ca
soft skills question paper set for bba caohsadfeeling
 
geometric quantization on coadjoint orbits
geometric quantization on coadjoint orbitsgeometric quantization on coadjoint orbits
geometric quantization on coadjoint orbitsHassan Jolany
 
Krishi Vigyan Kendras - कृषि विज्ञान केंद्र
Krishi Vigyan Kendras - कृषि विज्ञान केंद्रKrishi Vigyan Kendras - कृषि विज्ञान केंद्र
Krishi Vigyan Kendras - कृषि विज्ञान केंद्रKrashi Coaching
 
Principles & Formulation of Hair Care Products
Principles & Formulation of Hair Care  ProductsPrinciples & Formulation of Hair Care  Products
Principles & Formulation of Hair Care Productspurwaborkar@gmail.com
 
Lehninger_Chapter 17_Fatty acid Oxid.ppt
Lehninger_Chapter 17_Fatty acid Oxid.pptLehninger_Chapter 17_Fatty acid Oxid.ppt
Lehninger_Chapter 17_Fatty acid Oxid.pptSachin Teotia
 
RCPE terms and cycles scenarios as of March 2024
RCPE terms and cycles scenarios as of March 2024RCPE terms and cycles scenarios as of March 2024
RCPE terms and cycles scenarios as of March 2024suelcarter1
 
Role of Herbs in Cosmetics in Cosmetic Science.
Role of Herbs in Cosmetics in Cosmetic Science.Role of Herbs in Cosmetics in Cosmetic Science.
Role of Herbs in Cosmetics in Cosmetic Science.ShwetaHattimare
 
Q3W4part1-SSSSSSSSSSSSSSSSSSSSSSSSCI.pptx
Q3W4part1-SSSSSSSSSSSSSSSSSSSSSSSSCI.pptxQ3W4part1-SSSSSSSSSSSSSSSSSSSSSSSSCI.pptx
Q3W4part1-SSSSSSSSSSSSSSSSSSSSSSSSCI.pptxArdeniel
 
M.Pharm - Question Bank - Drug Delivery Systems
M.Pharm - Question Bank - Drug Delivery SystemsM.Pharm - Question Bank - Drug Delivery Systems
M.Pharm - Question Bank - Drug Delivery SystemsSumathi Arumugam
 
SUKDANAN DIAGNOSTIC TEST IN PHYSICAL SCIENCE ANSWER KEYY.pdf
SUKDANAN DIAGNOSTIC TEST IN PHYSICAL SCIENCE ANSWER KEYY.pdfSUKDANAN DIAGNOSTIC TEST IN PHYSICAL SCIENCE ANSWER KEYY.pdf
SUKDANAN DIAGNOSTIC TEST IN PHYSICAL SCIENCE ANSWER KEYY.pdfsantiagojoderickdoma
 
KeyBio pipeline for bioinformatics and data science
KeyBio pipeline for bioinformatics and data scienceKeyBio pipeline for bioinformatics and data science
KeyBio pipeline for bioinformatics and data scienceLayne Sadler
 
Controlling Parameters of Carbonate platform Environment
Controlling Parameters of Carbonate platform EnvironmentControlling Parameters of Carbonate platform Environment
Controlling Parameters of Carbonate platform EnvironmentRahulVishwakarma71547
 
Contracts with Interdependent Preferences (2)
Contracts with Interdependent Preferences (2)Contracts with Interdependent Preferences (2)
Contracts with Interdependent Preferences (2)GRAPE
 
MARSILEA notes in detail for II year Botany.ppt
MARSILEA  notes in detail for II year Botany.pptMARSILEA  notes in detail for II year Botany.ppt
MARSILEA notes in detail for II year Botany.pptaigil2
 
Pests of wheat_Identification, Bionomics, Damage symptoms, IPM_Dr.UPR.pdf
Pests of wheat_Identification, Bionomics, Damage symptoms, IPM_Dr.UPR.pdfPests of wheat_Identification, Bionomics, Damage symptoms, IPM_Dr.UPR.pdf
Pests of wheat_Identification, Bionomics, Damage symptoms, IPM_Dr.UPR.pdfPirithiRaju
 
Applied Biochemistry feedback_M Ahwad 2023.docx
Applied Biochemistry feedback_M Ahwad 2023.docxApplied Biochemistry feedback_M Ahwad 2023.docx
Applied Biochemistry feedback_M Ahwad 2023.docxmarwaahmad357
 

Último (20)

IB Biology New syllabus B3.2 Transport.pptx
IB Biology New syllabus B3.2 Transport.pptxIB Biology New syllabus B3.2 Transport.pptx
IB Biology New syllabus B3.2 Transport.pptx
 
Pests of cumbu_Identification, Binomics, Integrated ManagementDr.UPR.pdf
Pests of cumbu_Identification, Binomics, Integrated ManagementDr.UPR.pdfPests of cumbu_Identification, Binomics, Integrated ManagementDr.UPR.pdf
Pests of cumbu_Identification, Binomics, Integrated ManagementDr.UPR.pdf
 
Legacy Analysis of Dark Matter Annihilation from the Milky Way Dwarf Spheroid...
Legacy Analysis of Dark Matter Annihilation from the Milky Way Dwarf Spheroid...Legacy Analysis of Dark Matter Annihilation from the Milky Way Dwarf Spheroid...
Legacy Analysis of Dark Matter Annihilation from the Milky Way Dwarf Spheroid...
 
soft skills question paper set for bba ca
soft skills question paper set for bba casoft skills question paper set for bba ca
soft skills question paper set for bba ca
 
geometric quantization on coadjoint orbits
geometric quantization on coadjoint orbitsgeometric quantization on coadjoint orbits
geometric quantization on coadjoint orbits
 
Krishi Vigyan Kendras - कृषि विज्ञान केंद्र
Krishi Vigyan Kendras - कृषि विज्ञान केंद्रKrishi Vigyan Kendras - कृषि विज्ञान केंद्र
Krishi Vigyan Kendras - कृषि विज्ञान केंद्र
 
Principles & Formulation of Hair Care Products
Principles & Formulation of Hair Care  ProductsPrinciples & Formulation of Hair Care  Products
Principles & Formulation of Hair Care Products
 
Lehninger_Chapter 17_Fatty acid Oxid.ppt
Lehninger_Chapter 17_Fatty acid Oxid.pptLehninger_Chapter 17_Fatty acid Oxid.ppt
Lehninger_Chapter 17_Fatty acid Oxid.ppt
 
RCPE terms and cycles scenarios as of March 2024
RCPE terms and cycles scenarios as of March 2024RCPE terms and cycles scenarios as of March 2024
RCPE terms and cycles scenarios as of March 2024
 
Role of Herbs in Cosmetics in Cosmetic Science.
Role of Herbs in Cosmetics in Cosmetic Science.Role of Herbs in Cosmetics in Cosmetic Science.
Role of Herbs in Cosmetics in Cosmetic Science.
 
Q3W4part1-SSSSSSSSSSSSSSSSSSSSSSSSCI.pptx
Q3W4part1-SSSSSSSSSSSSSSSSSSSSSSSSCI.pptxQ3W4part1-SSSSSSSSSSSSSSSSSSSSSSSSCI.pptx
Q3W4part1-SSSSSSSSSSSSSSSSSSSSSSSSCI.pptx
 
M.Pharm - Question Bank - Drug Delivery Systems
M.Pharm - Question Bank - Drug Delivery SystemsM.Pharm - Question Bank - Drug Delivery Systems
M.Pharm - Question Bank - Drug Delivery Systems
 
SUKDANAN DIAGNOSTIC TEST IN PHYSICAL SCIENCE ANSWER KEYY.pdf
SUKDANAN DIAGNOSTIC TEST IN PHYSICAL SCIENCE ANSWER KEYY.pdfSUKDANAN DIAGNOSTIC TEST IN PHYSICAL SCIENCE ANSWER KEYY.pdf
SUKDANAN DIAGNOSTIC TEST IN PHYSICAL SCIENCE ANSWER KEYY.pdf
 
KeyBio pipeline for bioinformatics and data science
KeyBio pipeline for bioinformatics and data scienceKeyBio pipeline for bioinformatics and data science
KeyBio pipeline for bioinformatics and data science
 
Controlling Parameters of Carbonate platform Environment
Controlling Parameters of Carbonate platform EnvironmentControlling Parameters of Carbonate platform Environment
Controlling Parameters of Carbonate platform Environment
 
Contracts with Interdependent Preferences (2)
Contracts with Interdependent Preferences (2)Contracts with Interdependent Preferences (2)
Contracts with Interdependent Preferences (2)
 
Applying Cheminformatics to Develop a Structure Searchable Database of Analyt...
Applying Cheminformatics to Develop a Structure Searchable Database of Analyt...Applying Cheminformatics to Develop a Structure Searchable Database of Analyt...
Applying Cheminformatics to Develop a Structure Searchable Database of Analyt...
 
MARSILEA notes in detail for II year Botany.ppt
MARSILEA  notes in detail for II year Botany.pptMARSILEA  notes in detail for II year Botany.ppt
MARSILEA notes in detail for II year Botany.ppt
 
Pests of wheat_Identification, Bionomics, Damage symptoms, IPM_Dr.UPR.pdf
Pests of wheat_Identification, Bionomics, Damage symptoms, IPM_Dr.UPR.pdfPests of wheat_Identification, Bionomics, Damage symptoms, IPM_Dr.UPR.pdf
Pests of wheat_Identification, Bionomics, Damage symptoms, IPM_Dr.UPR.pdf
 
Applied Biochemistry feedback_M Ahwad 2023.docx
Applied Biochemistry feedback_M Ahwad 2023.docxApplied Biochemistry feedback_M Ahwad 2023.docx
Applied Biochemistry feedback_M Ahwad 2023.docx
 

synaptictransmission-091111081952-phpapp02-Compatibility-Mode.pdf

  • 1. SYNAPTIC TRANSMISSION SYNAPTIC TRANSMISSION Study material for B.Sc (H) Physiology 2nd Sem Dr Atanu Saha
  • 2. REVIEW ~ SETTING THE STAGE  Information is digitized at the axon hillock  Information is digitized at the axon hillock and a stream of action potentials carries the output of a neuron down the axon to other neurons neurons.  Neurons are the only class of cells that do not touch neighboring cells.  How is this output transferred to the next neuron in the chain?  The transfer of information from the end of  The transfer of information from the end of the axon of one neuron to the next neuron is called synaptic transmission.
  • 3. MOVING THE MESSAGE MOVING THE MESSAGE  Transmission of the signal between neurons takes place across the synapse the space takes place across the synapse, the space between two neurons.  In higher organisms this transmission is chemical.  Synaptic transmission then causes electrical events in the next neuron events in the next neuron.  All the inputs coming into a particular neuron are integrated to form the generator potential at its a on hillock here a ne potential at its axon hillock where a new stream of action potentials is generated.
  • 4. SYNAPTIC CONNECTIONS  Neurons are the only cells that can communicate with one another rapidly over communicate with one another rapidly over great distance  Synaptic connections are specific.  Underlie perception, emotion, behavior  The average neuron makes 1000 synaptic connections - receives more  The human brain contains 1011 neurons & forms 1014 connections  Neural processing occurs from the integration  Neural processing occurs from the integration of the various synaptic inputs on a neuron into the generator potential of that neuron.
  • 5. SPECIAL CHANNELS SPECIAL CHANNELS  Recall the 2 classes of channels for signaling within cells:  Resting channels that generate resting potential Voltage gated channels that produce an action  Voltage-gated channels that produce an action potential  Synaptic transmission uses 2 additional l f h l classes of channels:  Gap-junction channels  Ligand-gated channels Ligand gated channels
  • 6. COMPOSITION OF A SYNAPSE COMPOSITION OF A SYNAPSE  The s napse is made of 3  The synapse is made of 3 elements:  pre-synaptic terminal  postsynaptic cell  zone of apposition
  • 7. TYPES OF SYNAPSES TYPES OF SYNAPSES  Synapses are divided into 2 groups based on y p g p zones of apposition:  Electrical  Chemical  Fast Chemical  Modulating (slow) Chemical  Modulating (slow) Chemical
  • 8. ELECTRICAL SYNAPSES ELECTRICAL SYNAPSES  Common in invertebrate neurons involved ith i t t fl i it with important reflex circuits.  Less common in adult mammalian neurons, but common in many other body tissues but common in many other body tissues such as heart muscle cells.  Current generated by the action potential in g y p pre-synaptic neuron flows through the gap junction channel into the next neuron S d i l d l i i i l  Send simple depolarizing signals  May transmit metabolic signals between cells cells
  • 9. PROPERTIES OF THE ELECTRICAL SYNAPSE  Two cell membranes are aligned parallel g p  The synaptic cleft is small ~3.5 nm  Usually between large presynaptic neuron y g p y p & small postsynaptic neuron  takes a lot of current to depolarize a cell S i li d t i ll d  Specialized proteins called connexons span the pair of membranes to make a very large pore (the Gap Junction Channel) g p ( p )  Signal can be bi-directional
  • 10. GAP-JUNCTION CHANNELS GAP JUNCTION CHANNELS  Connect communicating cells at an electrical synapse synapse  Consist of a pair of cylinders (connexons)  one in presynaptic cell one in post  one in presynaptic cell, one in post  each cylinder made of 6 protein subunits  cylinders meet in the gap between the two cell b membranes  Always open  All ions and many small organic molecules are free  All ions and many small organic molecules are free to pass through the pore  Gap junctions serve to synchronize the activity of a set of neurons
  • 11. SYNCHRONIZING CELLS SYNCHRONIZING CELLS  Electrical transmission allows rapid, synchronous firing of interconnected cells  Can interconnect groups of neurons  Very fast; virtually no delay  Speed important for certain responses - defense El i ll l d ll i  Electrically coupled cells can trigger explosive, all or none behavior Ad ti d t ( ldfi h t il id  Adaptive advantage (e.g. goldfish tail, squid ink)
  • 12. MODULATING CONDUCTANCE MODULATING CONDUCTANCE  Gap junctions close in response to lower cytoplasmic pH or increased Ca+2 cytoplasmic pH or increased Ca  Some act as rectifiers  channels are sensitive to voltage h f i i idi i l  therefore transmission unidirectional  Linkage to chemical synapses  neurotransmitters released from nearby chemical y synapses can activate 2nd messenger dependent enzymes that alter gating of gap junction channels
  • 13. CHEMICAL SYNAPSES CHEMICAL SYNAPSES  Synaptic cleft is larger  Synaptic cleft is larger  There is no structural continuity between presynaptic & postsynaptic cells p y p p y p  A chemical molecule, a neurotransmitter, is released from the presynaptic neuron  diffuses across the synaptic cleft (20-50 nm)  binds with a receptor on the postsynaptic membrane.
  • 14. CATEGORIES OF CHEMICAL SYNAPSES SYNAPSES  Fast chemical synapses: H t itt t d i h l  Have transmitter-gated ion channels  Fast, electrical response to arrival of presynaptic action potential  Use amino acids and amines as neurotransmitters  Slow modulatory chemical synapses:  Slow, modulatory chemical synapses:  Have G-protein-coupled ion channels  Slow response to arrival of presynaptic action p p y p potential  activate second messenger system; not always a direct electrical effect direct electrical effect  May use amino acids, amines, or peptides
  • 15. STRUCTURE OF THE CHEMICAL SYNAPSE  Presynaptic structures: y p  Vesicles - contain amino acids or amines, released at synapse S t l (d d i l )  Secretory granules (dense-cored vesicles) - contain peptides  Presynaptic densities - serve to organize vesicles and prepare them for release  Postsynaptic structures:  Postsynaptic densities loaded with receptors  Postsynaptic densities - loaded with receptors and ion channels, bind neurotransmitters and establish ionic currents
  • 16. WIRING PATTERNS OF CHEMICAL SYNAPSES  Axosomatic synapse - Axon terminal ends on a y p cell body  Axodendritic synapse - Axon terminal ends on a dendrite dendrite  Axoaxonic synapse - Axon terminal ends on another axon D d d d i i D d it k  Dendrodendritic synapse - Dendrite makes synapse with another dendrite
  • 17. RELEASE OF N NEUROTRANSMITTERS  Occurs in response to Ca+2 influx that occurs with the action potential  Change in membrane potential in e a tic e o lead to elea e of presynaptic neuron leads to release of chemical transmitter from terminals  transmitter diffuses across cleft  binds to receptor molecules on the postsynaptic cell membrane  binding receptor causes ion channels to open or close, g p p , altering potential
  • 18. TRANSMITTER BINDING TRANSMITTER BINDING  Binding receptor is specific - lock & key  Action determined by properties of receptor  Action determined by properties of receptor, not chemical properties of the transmitter  receptor determines if response is excitatory or i hibi inhibitory  All neurotransmitter receptors have 2 biochemical features in common: biochemical features in common:  they are membrane spanning proteins that recognize & bind transmitter  they carry out effector function with a target cell, usually by influencing opening or closing of ion channels
  • 19. SYNAPTIC RELEASE SYNAPTIC RELEASE FAST CHEMICAL SYNAPSES  Action potential invades axon terminal  Action potential invades axon terminal  Voltage-gated calcium channels pop open  Calcium ions flood presynaptic terminal in region of i l l vesicle release  Synaptic vesicles fuse with presynaptic membrane – exocytosis y  Neurotransmitter molecules diffuse into and across synaptic cleft
  • 20. TRANSMITTER-GATED ION CHANNELS  Neurotransmitter molecules bind to the receptor site on transmitter-gated ion channels ecepto s te o t a s tte gated o c a e s embedded in the postsynaptic membrane  Ionic currents flow into or out of the i ll postsynaptic cell  If Na+ ions are the carrier, the membrane potential of the postsynaptic cell is depolarized potential of the postsynaptic cell is depolarized  EPSP -Excitatory Post-Synaptic Potential  If Cl- ions or K+ ions are the carrier, the C o s o o s a e e ca e , e membrane potential of the postsynaptic cell is hyperpolarized IPSP I hibi P S i P i l  IPSP - Inhibitory Post-Synaptic Potential
  • 21. REMOVAL OF NEUROTRANSMITTER NEUROTRANSMITTER  The neurotransmitter is inactivated or  The neurotransmitter is inactivated or removed from the synaptic cleft  For acetylcholine, there is an enzyme, y , y , acetylcholine esterase (AChE) that does this  For other amino acids and amines, the presynaptic membrane actively sucks up h i d i hb i li l ll the transmitter and neighboring glial cells may do likewise
  • 22. SYNAPTIC RELEASE NEUROMODULATORY SYNAPSES  Action potential invades axon terminal  Voltage-gated calcium channels pop open  Calcium ions flood presynaptic terminal in i f i l l region of vesicle release  Synaptic vesicles fuse with presynaptic membrane exocytosis membrane – exocytosis  Neurotransmitter molecules diffuse into and across synaptic cleft y p  Neurotransmitter molecules bind to receptor proteins in the postsynaptic b membrane
  • 23. G-PROTEIN-COUPLED RECEPTORS  G-proteins in the membrane are activated and p move along inner face  Activated G-proteins activate effector proteins  May act directly or indirectly (2nd messenger)  May act directly or indirectly (2nd messenger)  The neurotransmitter is inactivated or removed from the synaptic cleft
  • 24. DIRECT RECEPTORS DIRECT RECEPTORS  Ionotropic p  Are membrane spanning  Made of several peptide subunits O bi di t itt d  On binding neurotransmitter, undergo conformational change that opens a G-protein gated ion channel  Example - acetylcholine receptor on muscle
  • 25. INDIRECT RECEPTORS  Are macromolecules that are separate from the ion channels on which they act 2 f ilil  2 famililes:  Metabotropic  membrane spanning proteins  membrane spanning proteins  a single polypeptide chain coupled to GTP- binding proteins, which activate enzymes that d 2 d h li AMP produce 2nd messenger such as cyclic AMP  2nd messenger either acts on channel directly or thru enzyme y  Tyrosine kinase family  add a phosphate group to tyrosine of substrate t i d l ti h l proteins, modulating channel
  • 26. SYNAPTIC INTEGRATION: FAST CHEMICAL SYNAPSES~ GATED ION CHANNELS  Synaptic transmitter release is quantal  Each vesicle or secretory granule contains the same number of neurotransmitter molecules  The EPSP or IPSP that results is one of a set of  The EPSP or IPSP that results is one of a set of consistent sizes - one vesicle, two vesicles, three vesicles, etc. T i ll t l j ti 200  Typically at a neuromuscular junction 200 vesicles are released from one action potential - fail safe contraction of the muscle  At a synapse in the CNS, typically only one vesicle is released - input for processing in the dendrite  Not every synaptic release causes an action potential in the postsynaptic neuron
  • 27. SPATIAL SUMMATION SPATIAL SUMMATION  The dendrites of each neuron receive many y synaptic inputs from a variety of neurons.  The combining of the EPSPs and IPSPs across th d d it f th i lt i l f the dendrite from the simultaneous arrival of action potentials at various synapses is called spatial summation
  • 28. LENGTH CONSTANT G CO S  The measure of how effective a given synapse is in contributing to spatial summation  The length constant gives the distance (in µm) that it take a EPSP o IPSP to dec ea e to that it takes an EPSP or IPSP to decrease to 37% of its original value at the synapse:  The length constant is directly proportional to  The length constant is directly proportional to the membrane resistance and inversely proportional to the longitudinal resistance f th t l of the cytoplasm  The leakier the membrane, the shorter the length constant  The narrower the dendrite, the shorter the length constant
  • 29. TEMPORAL SUMMATION TEMPORAL SUMMATION  The combining of EPSPs or IPSPs from repeated action potentials arriving at a single synapse is action potentials arriving at a single synapse is called temporal summation  The measure of how effective a given synapse is  The measure of how effective a given synapse is in contributing to temporal summation is the time constant, t  The time constant gives the time (in milliseconds) that it takes an EPSP or IPSP to decrease to 37% of its original value at the decrease to 37% of its original value at the synapse  In most cases, the effects of spatial summation and temporal summation must both be taken into account
  • 30. NEUROMODULATION  With a G-protein-coupled receptor, a chain of events is triggered that usually ends with the phosphorylation of a protein. protein.  For example:  When a receptor for norepinephrine is activated,  a G-protein is activated.  Adenyl cyclase (an enzyme) is activated, which  uses ATP to produce cyclic AMP a second messenger  uses ATP to produce cyclic AMP, a second messenger.  cAMP activates a protein kinase.  The protein kinase phosphorylates a potassium channel,  Which causes it to close  This increases l and t, thereby making synapses more potent for a period of time potent for a period of time  hence the term modulation
  • 31. W C T ? WHY CHEMICAL TRANSMISSION?  More flexible; produces more complex behaviors ; p p  Plasticity  Can amplify neuronal signals Di tl t d ti l f t  Directly gated are comparatively fast  mediate behavior  Indirect are slower  important in memory, learning
  • 32. F C T FLEXIBILITY OF CHEMICAL TRANSMISSION  Produces more complex behaviors p  Same neurotransmitter can have several functions  at one terminal can be released at the active zone &  at one terminal can be released at the active zone & serve as a direct transmitter, acting on neighboring cells  at another site can serve as a modulator at another site can serve as a modulator  at a third site released into bloodstream as neurohormone
  • 33. PLASTICITY OF CHEMICAL TRANSMISSION  Chemical Transmission has plasticity plasticity because it is multistep I f & h hi h f i  Important for memory & other higher functions  Modifiability of chemical synapses is an important mechanism in behavioral learning mechanism in behavioral learning
  • 34. AMPLIFYING NEURONAL SIGNALS SIGNALS  Chemical transmission can amplify neuronal signals  A small nerve terminal can alter the potential of a  A small nerve terminal can alter the potential of a large postsynaptic cell  The action of just one synaptic vesicle leads to j y p opening of thousands of ion channels