Synapse

from ppt only

Charles Scott Sherrington

discovered that communication between one neuron and the next differs from the communication along axon

Charles Scott Sherrington

discovered that communication happens in the synapse

reflex arc

- Sherrington discovered that this is the circuit from sensory neuron to muscle response

synapse has 3 elements:

presynaptic membrane, postsynaptic membrane, synaptic cleft/gap

forms of synapse

- electrical and chemical

presynaptic membrane

formed by terminal button of an axon presynaptic neuron (promotes action)

postsynaptic membrane

composed of a segment of dendrite or cell body of postsynaptic neuron (taga tanggap ng action)

synaptic cleft

- space between these two neurons (gap)

electrical synapse

this form of synapse directly stimulates adjacent cells by sending ions across the gap through protein channels on the cell membrane that touch.

excitation

tells produce action potential

inhibition

tells not to produce action potential

electrical synapse

Gap junction: the membrane of one neuron comes into direct contact with the membrane of another - Have narrow synaptic gap (3.5 nm) making transmission instantaneous Requires large presynaptic neuron Has only one type of message: Excitatory

electrical synapse

• form of synapse that is frequently found in the circuits responsible for escape behaviors in invertebrates
  - Synchronize activity such as hormone release in response to activity in the hypothalamus

Chemical Synapse

- Neurons stimulate adjacent cells by sending chemical messengers or neurotransmitters, across the synaptic gap

Chemical Synapse

form of synapse that has a wider synaptic gap than electrical synapse
- Small presynaptic neurons can influence large postsynaptic neuron'
- Have more variety of message
-both Excitatory and Inhibitory

Neurotransmitters

chemicals released by a neuron to affect another neuron

Exocytosis

process in which the synaptic vesicles fuse with the membrane of the axon terminal and release neurotransmitter molecules to synaptic gap

Negative Feedback - Autroreceptors provide feedback to presynaptic neuron about its level of activity -> inhibit synthesis and release of neurotransmitter. Postsynaptic neurons respond to stimulation by releasing chemicals that travel back to the presynaptic terminal to inhibit further release of transmitter Ex. Nitric oxide

Autoreceptors

special protein structures in presynaptic membrane

Activating Postsynaptic Receptors - Exocytosis -> Neurotransmitter binds to postsynaptic receptors -> Ionotropic or Metabotropic

2 types of Receptors

ionotropic and metabotropic

Brain

this organ has different receptor types for each neurotransmitter

ionotropic Receptor

receptor protein in the postsynaptic membrane in which the recognition site is located in the same structure as the ligand-gated channel

Ionotropic Effect

very fast reaction to neurotransmitters Ligand-gated channel opens or closes immediately which induces an immediate postsynaptic potential

- Affects small, local part of the cell

Metabotropic Receptors

protein structure embedded in the postsynaptic membrane containing a recognition site and a G protein

G protein

this protein’s process:
it triggers synthesis of second-messenger -> diffuses and influence the activities of the neuron in a variety of ways

G protein

this protein’s process is:

- it attaches to ion channel -> charged ions get in the cell

G protein

protein coupled to guanosine triphosphate (GTP) an energy storing molecule found on the intracellular side of the metabotropic receptor

Second Messenger

chemical within the postsynaptic neuron that is indirectly activated by synaptic activity and interacts with different parts of the cell

Metabotropic Effect

Can last much longer than those produced by activation of iontropic receptors (maselan)

• Have wide ranging and multiple influences within the cell

Temporal Summation

repeated excitation from one active synapse evokes cumulative effect

• Summation over time

Spatial Summation

- repeated excitation from combined inputs from many synapses coverage evokes cumulative effect

• summation over space

Excitatory input -

mostly found in dendrites and dendrites spines

Inhibitory input

occurs at the synapse of the cell body

Diffusion

neurotransmitter diffuses away from areas of high concentration to areas of low concentration

Deactivating enzyme

neurotransmitter molecules are deactivated in the synapse by enzymes in the synaptic gap

reuptake -

presynaptic membrane uses its own set of receptors known as transporters to capture molecules of neurotransmitter substance and return them to the interior axon terminal

termination of chemical singals

- diffusion, deactivating enzyme, reuptake

inhibitory posynaptic potential (IPSP)

Neurotransmitter -> binds to receptors -> opens ion channels -> Cl - gets in, K+ gets out -> temporary hyperpolarization (graded hyperpolarization)

Excitatory Postsynaptic Potential (EPSP)

Neurotransmitter -> binds to receptors -> opens ion channels -> Na+ - gets in the cell -> slight depolarization (graded hyperpolarization)

excitatory input

mostly found in dendrites and dendrites spines

inhibitory input

- occurs at the synapse of cell body

autroreceptors

it provides feedback to presynaptic neuron about its level of activity -> inhibit synthesis and release of neurotransmitter (negative feedback)

release of neurotransmitter - Action Potential -> Ca2 + voltage-gated channel opens -> Ca2 + gets in the cell -> Exocytosis

Neurotransmitter

• can influence only those cells that have receptors for it

receptors

are protein structure embedded in neural membrane that responds to neurotransmitters