Slides on Nerve Cells and Nerve Impulses

1. Nerve Cells
and Nerve
Impulses

2. Cells and The Brain
• Information comes from the sensory
receptors.
• The brain transforms information into
perceptions and commands for movement.
• The complexity of brain results from the
number of the cells.
• The adult human brain contains
approximately 86 billion neurons, on average.
It varies from person to person.

3. Cells
• Fundamental units of Life
• Specialized based on functions
• Communicate via different
methods
• Hormones
• Local chemical signals
• Electrical impulses

4. Neurons
• Special category of cells that form the
Nervous System
• Four morphologically distinct regions:
1. Cell Body (Soma)- contains nucleus,
ribosome and mitochondria. Neurons
metabolic work occurs here.
2. Axon- thin fiber of constant diameter.
Carries impulses toward other neurons,
organs or muscles.
3. Dendrites- branching fibers that get
narrower near their ends, lined with
specialized synaptic receptors, it
receives information from other
neurons.
Courtesy: ThoughtCo.

5. Variation in Neurons: Neurons vary enormously in size, shape, and function.

6. Different Neuron Terms:
• Afferent Neurons: Brings information into a structure.
Sensory neurons are afferent to the rest of the nervous
system.
• Efferent Neurons: Carries information away from the
structure. Motor neurons are efferent from the nervous
system.
• Interneuron or Intrinsic Neurons: If a cell’s dendrites
and axon are entirely contained within a single
structure, they are called interneuron of that structure.

7. Glia – Supporting Cells
• Control Extracellular environment.
• Facilitate Neurotransmitter
Release
• Regulate ion concentrations
• Form Myelin Sheaths
• 1:1 ratio of Glia to Neurons (varies
from region to region)

8. Glia: Brain has several types of Glia.
• Astrocytes- Wrap around synapses and
protect the connection from chemicals
circulating in the surrounding, dilate
blood vessels, and help release
neurotransmitters and ions.
• Microglia- Act as part of the immune
system, removing viruses and fungi
from the brain.
• Radial glia- Guide the migration of
neurons and their axons and dendrites
during embryonic development.
• Oligodendrocytes in the brain and
spinal cord and Schwann cells in the
body’s periphery build the myelin
sheaths surrounding and insulating
certain vertebrate axons.

9. Nourishment of Brain and Blood-Brain-Barrier
• The Human brain exclusively uses Glucose as
fuel.
• The only nutrient that crosses the blood-brain-
barrier in large quantities.
• Endothelial cells, joined tightly to restrict entry.
• It keeps out useful as well as harmful chemicals.
• Small, uncharged molecules such as oxygen and
carbon dioxide that cross through cell walls
freely.
• Molecules that dissolve in the fats of the
membrane cross easily.
• Active Transport for other chemicals.

10. Resting Potential:
Resting potential is maintained to enable firing of action
potential whenever needed.
What is resting potential?
• At rest, the membrane maintains an electrical
• gradient, a difference in electrical charge between the inside
and outside of the cell.
• The potential inside the membrane is slightly negative, due to
negatively charged proteins inside the cell. The voltage
difference is called resting potential.
• Though magnitude varies, a typical resting potential is –70
millivolts (mV).
Sodium-Potassium Pumps
• Due to the sodium-potassium pump, sodium ions are more
than 10 times more concentrated outside the membrane
than inside.
• Potassium ions are more concentrated inside than outside.
• At rest, a balance between concentration and electrical
gradient is maintained of these two ions.

11. Action Potential:
Messages sent by axons are called axon potentials.
• Stimulation to the cells beyond the excitation
threshold produces a massive depolarization of the
membrane.
• When the potential reaches the threshold, the
membrane opens its sodium channels and lets sodium
ions flow into the cell.
• Neurons work in an All-or-None principal. Only if the
depolarization reaches the threshold, an action
potential would be generated. It’s independent of the
intensity of the stimuli.
The axon channels regulating sodium and potassium
are voltage-gated. Their permeability depends on the
voltage difference across the membrane.
At peak of action potential, sodium channel shut
allowing reverse polarity.

12. Local anesthetic drugs, such as Novocain and
Xylocaine, attach to the sodium channels of
the membrane, preventing sodium ions from
entering, which inhibits depolarization.

13. Myelin Sheath and Saltatory Conduction:
• In thinnest axons, action potentials travel at a
velocity of less than 1 meter/second.
Increasing the diameter brings conduction
velocity up to about 10 m/s.
• Myelinated axons are covered with layers of
fats and proteins. The sheath contains short
sections of axon called nodes of Ranvier
periodically, each one about 1 micrometer
wide.
• The action potential starts at first node of
Ranvier.
• The jumping of action potentials from node to
node is called saltatory conduction.

14. Action
Potentials
and
Behaviour of
Neurons

15. Synapses

16. Structure of
Synapse
• 1800s – Ramon y Cajal
demonstrated a narrow gap
between neurons.
• 1906 - Sherrington demonstrated
differences in communication
along a neuron vs between
neurons.
• Synapses are junctions between
axons and dendrites/cell body -
electrical/chemical in nature
• Transmission of nerve impulse
from neuron to neuron.
• Unidirectional Transmission.

17. Synapses in Behaviour
• Synaptic Plasticity
• Ability to form new connections
• Associated with learning, memory, motor activity, etc.
• Recovery from Stroke
• Neurodevelopment
• Ageing

18. Modes of Synaptic Transmission

19. Neurotransmitters
• Neurotransmitters are chemicals
released from the pre-synaptic terminals
of axons.
• >100 different molecules act as
neurotransmitters.
• Synthesized in Neurons
• Functionally distinct.

20. Role of Neurotransmitters in Behaviour
• Neurotransmitters play several important functions in modulating
behaviour
• GABA – regulation of anxiety.
• Glutamate – memory and learning, also plays a role in Alzheimer’s
disease and epilepsy.
• Oxytocin – social bonding and reproductive behaviours.
• Endorphins – feelings of Euphoria, e.g., runner’s high.
• Dopamine – rewards, motivations, and addiction.
• Serotonin – Regulates mood, anxiety, sleep, and appetite. Also
relevant in treatment of Depression.

21. 1. The neuron synthesizes neurotransmitters.
2. Action potential enables calcium to enter the cell
and releases neurotransmitters.
3. Released molecules diffuse and attach to
receptors, and alter the activity of the
postsynaptic neuron.
4. The neurotransmitter molecules separate from
their receptors.
5. Neurotransmitters molecules may be taken back
into the presynaptic neuron for recycling or they
may diffuse away.
6. Some postsynaptic cells send reverse messages
to control the further release of
neurotransmitter by presynaptic cells.
Steps of Synaptic
Transmission

22. Drugs and Neurotransmitters
• LSD – binds to serotonin receptors and causes prolonged activation.
• Nicotine – binds to nicotinic receptors and promotes release of
Dopamine causing reward sensation.
• Opiates – binds to receptors of endorphins
• Amphetamine and Cocaine – Block reuptake of Serotonin, Dopamine,
and Norepinephrine.
• Canabinoids – Blocks negative feedback at presynaptic terminal.

23. Types of Synapses
Structural:
• Electrical Synapses – direct
transmission – necessary for
fast transmission (ex –
octopuses)
• Chemical Synapses –
neurotransmitters facilitated
(ex – Dopamine, Serotonin,
GABA) – modulated response
Functional:
• Excitatory Synapses – produces
depolarization
• Inhibitory Synapses – produces
hyperpolarization

24. Neurons Connecting
at a Synapse
• Synaptic Plasticity
• Fundamental role in behaviour
• New synapses are fundamental to
cognitive processes such as learning,
recall, etc.

25. Effects on Post-synaptic Neurons
• Ionotropic – Glutamate (Excitatory – positive ions influx) and GABA
(Inhibitory – negative ions influx).
• Metabotropic Effects – Initiate a sequence of metabolic reactions
producing long lasting effects (smell, sound, taste)
• Neuropeptides – Behaviour modulation - slow acting (hunger, thirst,
etc.)

26. Properties of
Synapse
• Delays Transmission
• Graded Potentials allowing
Summation:
• Temporal Summation
• Spatial Summation
• Excitatory Postsynaptic Potential
(EPSP)
• Inhibitory Postsynaptic Potential
(IPSP)
• Why do we need IPSPs?
• Modulates spontaneous firing
rates
• Modulates Spatial/Temporal
Summation.

27. Hormones

28. Anatomy of Nervous
System

30. Functions of CNS and PNS
• Central Nervous System
• Integrates information across senses.
• Higher order processing of information
• Cognition, emotion, perception, etc.
• Peripheral Nervous System – carries information to and from CNS.
• Somatic Nervous System – Movement and control of voluntary muscles
• Autonomic Nervous System – Controls heart rate, breathing, etc.

31. Informal Divisions of Brain
• Forebrain
• Midbrain
• Hindbrain

32. Lobes of Cerebral Cortex
• Different lobes have specialized functions and damage to them can cause loss of functionality.
• Frontal - actions, working memory, certain aspects of emotion, and decision making.
• Parietal – body sensations
• Temporal – hearing vision, and information processing
• Occipital – vision

33. A representation of different
body parts according to their
neurological representations.

34. Binding of
Senses
The different sensory inputs are
bound to create a unified
experience.
Example – eating food combines
smell, texture, taste into a single
unified experience.
How do we bind sensory
information?