This document discusses the physiology of neural transmission in the nervous system. It begins by defining neurons as the basic functional units that transmit electrical and chemical signals. It describes the basic structure of neurons including the cell body, dendrites, axon and synapses. It then explains how neurons generate and propagate electrical signals called action potentials down the axon. It discusses the processes involved in synaptic transmission including the release and binding of neurotransmitters and the generation of excitatory or inhibitory postsynaptic potentials. Finally, it lists some major neurotransmitters in the nervous system like acetylcholine, dopamine and GABA.

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.