NEURONAL TRANSMISSION IN HUMANS

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.