Nerve transmission

1. Nerve Transmission

2. Neurons
• Basic units of the nervous system
• Receive, integrate, and transmit
information
• Operate through electrical impulses
• Communicate with other neurons
through chemical signals

3. Structure of neuron
Main functions of Neurons : Reception, Conduction, Transmission
1.3.
2.

5. Nerve transmission

6. Mechanism of nerve transmission
• Axonal transmission: Voltage gated cation
channels generate action potentials in
electrically excitable cells.
• Synaptic transmission: Transmitter gated ion
channels convert chemical signals into
electrical ones at chemical synapses.

7. Axonal transmission
• A nerve impulse can be initiated by mechanical,
chemical, thermal or electrical stimulation.
• When the axon is stimulated the resting potential
changes.
• It changes from -70mV inside the membrane to
+40mV.
• For a very brief period the inside of the axon
becomes positive and the outside negative.
• This change in potential is called action potential
and lasts about 3 milliseconds.

8. Cont…
• Cell membrane permeability must be changed
for a nerve impulse to travel down a neuron.
• Na⁺- K⁺ ATPase pumps K⁺ into and Na⁺ out of the
neuron.
a) A cell is normally polarized when a neuron is at rest – called
it resting potential

9. b) A portion of the neuron becomes depolarized
–
Na⁺ moves into the cell
c) Cell repolarization - K⁺ moves out of the cell.

10. Action potential

11. Cont…

12. Cont…
• The axon may be myelinated or non-myelinated
Saltatory conduction: It is the word used to
describe the “jumping” of the action potential
from node to node.
- Provides rapid conduction of impulses
- conserves energy for the cell
Multiple sclerosis is the disease in which the
myelin sheath is destroyed and associated with
poor muscle coordination.

13. Myelinated axon transmission

14. Synaptic transmission
• Neuronal signals are transmitted from cell to cell at
specialized site known as synapses.
• It may be of 2 types:
a) Electrical synapse: synaptic cleft gap is 20Å and
direct action potential
b) Chemical synapse: synaptic cleft gap is >200Å and
action potential is by neurotransmitters.
• A change in electric potential in the pre-synaptic cell
triggers it to release small signal molecules known as
Neurotransmitters, which are stored in synaptic
vesicles and released by exocytosis.

15. Neurotransmitters
– Chemical messengers that traverse the synaptic
gaps between neurons
– When released by the sending neuron,
neurotransmitters travel across the synapse and
bind to receptor sites on the receiving neuron,
thereby influencing whether it will generate a
neural impulse

16. Types of neurotransmitters
• Excitatory (EPSP)
– usually when receptor channels admit sodium
Ex: Acetyl choline, glutamate, adrenaline
• Inhibitory (IPSP)
– usually when receptor channels admit
chloride/potassium
Ex: Dopamine, glycine, GABA

18. Acetylcholine
• 1st substance identified as NT
• Links motor neurons and
muscles (contract or relax)
• Also involved in memory,
learning, sleep, dreaming.
• It is called as cholinergic
synapse, it has 2 receptors:
a) Nicotinic receptor
b) Muscarinic receptor
• It is a ligand gated cation
channel & degraded by
acetylcholineesterase.

19. Neuromuscular transmission by
acetylcholine
It involves the sequential activation of gated ion channels
1. Arrival of an action potential at the terminus of a pre-synaptic
motor neuron induces opening of voltage gated Ca²⁺
channel
2. Subsequent release of acetylcholine, which triggers opening of
ligand gated acetylcholine receptors in the muscle plasma
membrane
3. The resulting influx of Na⁺ produces a localized depolarization
of the membrane leading to opening voltage gated Na⁺
channels and generation of an action potential

20. Cont…
4. When the spreading depolarization reaches the T tubules, it is
sensed by voltage gated Ca²⁺ channels in the plasma
membrane. This leads to opening of Ca²⁺ release channels in
the sarcoplasmic reticulum membrane releasing stored Ca²⁺
into the cytosol.
The resulting rise in cytosolic Ca²⁺ causes the muscle
contraction.

21. Synaptic Transmission