NEURAL TRANSMISSION ppt
- 1. PHYSIOLOGICAL PSYCHOLOGY NEURAL TRANSMISSION PRESENTED BY NIVEDITA MENON. C 24/02/2021
- 2. NEURONES The neuron is the basic working unit of the brain. It’s a specialized cell designed to transmit information to other nerve cells, muscle, or gland cells. Neurons are cells within the nervous system that transmit information to other nerve cells, muscle, or gland cells.
- 3. BASIC STRUCTURE OF A NEURON Most neurons have a • cell body • an axon • dendrites
- 4. The cell body contains the nucleus and cytoplasm. The axon extends from the cell body and often gives rise to many smaller branches before ending at nerve terminals. Dendrites extend from the neuron cell body and receive messages from other neurons. Synapses are the contact points where one neuron communicates with another. The dendrites are covered with synapses formed by the ends of axons from other neurons.
- 5. When neurons receive or send messages, they transmit electrical impulses along their axons, which can range in length from a tiny fraction of an inch (or centimeter) to three feet (about one meter) or more. Many axons are covered with a layered myelin sheath, which accelerates the transmission of electrical signals along the axon. This sheath is made by specialized cells called glia. In the brain, the glia that make the sheath are called oligodendrocytes, and in the peripheral nervous system, they are known as Schwann cells.
- 6. NEURAL TRANSMISSION The function of a neuron is to transmit information within the nervous system. Neural transmission occurs when a neuron is activated, or fired (sends out an electrical impulse). IMPORTANT TERMS 1. Potential • the term potential refers to a difference in electrical charges. • Neurons have two types of potentials- • a resting potential • an action potential
- 7. 2. Resting potential • The resting potential of neurons is about -70 mV. • At resting potential concentration of ions is kept constant through Na+/K+ pumps. • When the threshold is reached, the Na+ gated channel are opened. 3. Action potential: • An action potential is defined as a sudden, fast, transitory, and propagating change of the resting membrane potential. • Only neurons and muscle cells are capable of generating an action potential; that property is called the excitability • The action potential has three main stages: depolarization, repolarization, and hyperpolarization.
- 8. • Polarization is the existence of opposite electrical charges on either side of a cell membrane (difference in inside a cell versus the outside of the cell • Depolarization is the state which the cell membrane change from positive to negative charged outside the cell and from negative to positive charge inside the cell. • Repolarization refers to the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential which has changed the membrane potential to a positive value. • Hyperpolarization is the movement of a cell's membrane potential to a more negative value i.e., movement further away from zero. When a neuron is hyperpolarized, it is less likely to fire an action potential.
- 9. 4. Refractory period • It is a period of time during which a cell is incapable of repeating an action potential. • In terms of action potentials, it refers to the amount of time it takes for an excitable membrane to be ready to respond to a second stimulus once it returns to a resting state. 5. Absolute refractory period • This is a short period where even when a greater stimulation occurs, the neuron will not fire again. 6. Relative refractory period • is the interval of time during which a second action potential can be initiated, but initiation will require a greater stimulus than before.
- 10. 7. Neural threshold • is the level of stimulation below which the cell does not fire. 8. All Or None Principle • Henry P. Bowditch (1871) • The all-or-none law is a principle that states that the strength of a response of a nerve cell or muscle fiber is not dependent upon the strength of the stimulus. • If a stimulus is above a certain threshold, a nerve or muscle fiber will fire. 9. Activation (firing) • Firing of the neuron takes place when the neuron is stimulated by pressure, heat, light, or chemical information from other cells.
- 11. SYNAPTIC TRANSMISSION Synaptic transmission is the process by which one neuron communicates with another. The synapse is the name given the junction between neurons where information is exchanged. Information is passed down the axon of the neuron as an electrical impulse known as action potential. Once the action potential reaches the end of the axon it needs to be transferred to another neuron or tissue. It must cross over the synaptic gap between the presynaptic neuron and post-synaptic neuron. The axon of the presynaptic neuron does not actually touch the dendrites of the postsynaptic neuron and is separated from them by a space called the synaptic cleft.
- 12. At the end of the neuron (in the axon terminal) are the synaptic vesicles, which contain chemical messengers, known as neurotransmitters. When the electrical impulse (action potential) reaches these synaptic vesicles, they release their contents of neurotransmitters. Neurotransmitters then carry the signal across the synaptic gap. They bind to receptor sites on the post-synaptic cell, thereby completing the process of synaptic transmission. Molecules of the neurotransmitter that do not bind to receptors in the postsynaptic neuron are taken up again by the presynaptic neuron, a process called reuptake. The combination of the neurotransmitter molecules to receptor cell molecules in the postsynaptic cell membrane produces a change of potential in the postsynaptic cell membrane called the postsynaptic potential (PSP).
- 13. The PSP allows ions to enter or leave the cell membrane of the postsynaptic neuron. The ionic movements increase or decrease the probability of a neural impulse occurring in the postsynaptic neuron. There are two types of PSPs • excitatory (EPSPs) • inhibitory (IPSPs) EPSPs increase and IPSPs decrease the likelihood that the postsynaptic neuron will fire a neural impulse. The rate of firing of a neuron at a particular time depends upon the relative number of EPSPs and IPSPs.
- 14. NEUROTRANSMITTERS. Neurotransmitters are chemical messengers that transmit a signal from a neuron across the synapse to a target cell, which can be a different neuron, muscle cell, or gland cell. Neurotransmitters are chemical substances made by the neuron specifically to transmit a message. Neurotransmitters are mainly divided into 6 types: 1. Acetylcholine • Occurs throughout the nervous system • Is the only neurotransmitter found in synapses between motor neurons and voluntary muscle cells. • Degeneration of cells producing acetylcholine is associated with Alzheimer's disease.
- 15. 2. Biogenic amines • Include three neurotransmitters: norepinephrine, dopamine, and serotonin. • Parkinson's disease is believed to be related to a deficiency of dopamine • Certain types of depression are associated with low levels of norepinephrine • Levels of serotonin increase with the use of the recreational drug LSD (lysergic acid diethylamide). 3. GABA (gamma aminobutyric acid) • appears to produce only inhibitory PSPs. • Many tranquilizers work by increasing the inhibitory actions of GABA.
- 16. 4. Glycine • is an inhibitory neurotransmitter found in the lower brainstem, spinal cord, and retina. 5. Endorphins • modulate the activity of other neurotransmitters and are called neuromodulators. • They seem to function in the same way as opiates such as morphine; “runner's high” is produced by an increase in endorphins. 6. Substance P • is a neurotransmitter in many neural circuits involving pain.
Editor's Notes
- #5: Nucleus has the genetic material embedded in it. Cytoplasm has all the organelles like mitochondria, ribosomes, … The info. from one neuron’s axon is passes to the next neuron’s dendrite through the synapse.
- #6: Glial cells are of 5 types- astro, oligo, ependymal, micro and schwann.
- #9: Inside cell it is -ve and outside it is +ve.