The document provides an overview of the nervous system, including:
1. It describes the organization and main components of the nervous system, including neurons, neuroglia, nerves, and the central and peripheral nervous systems.
2. It explains the functions of the nervous system in sensation, motor control, and higher cognitive processes. It also describes the types of sensory receptors and motor responses.
3. It provides details on the structure and function of neurons, neurotransmission, and the generation and propagation of nerve impulses through neurons.
Nervous system 3; Synapses and NeurotransmittersJames H. Workman
Lecture notes and diagrams for Anatomy and Physiology students describing / showing the connections between nerve cells (synapses) and how neurotransmitters work. Video of animation that shows how drugs affect neurotransmitters is included, although it will not show in slideshare.
Define what is neuron .
Describe the anatomy of neuron .
Enumerate the constituents of neuron.
Enlist the types of neuron .
Describe the function of neuron .
Nervous system 3; Synapses and NeurotransmittersJames H. Workman
Lecture notes and diagrams for Anatomy and Physiology students describing / showing the connections between nerve cells (synapses) and how neurotransmitters work. Video of animation that shows how drugs affect neurotransmitters is included, although it will not show in slideshare.
Define what is neuron .
Describe the anatomy of neuron .
Enumerate the constituents of neuron.
Enlist the types of neuron .
Describe the function of neuron .
Lecture notes and diagrams to help high school anatomy and physiology students learn the general functions of the nervous system and types of glial support nerve cells, types of neurons and anatomy of typical neurons.
Lecture notes and diagrams to help high school anatomy and physiology students learn the general functions of the nervous system and types of glial support nerve cells, types of neurons and anatomy of typical neurons.
Structures of Axon Terminals and Presynaptic Membrane
Presynaptic axon terminal has a definite intact membrane known as presynaptic
membrane.
Axon terminal has two important structures:
i. Mitochondria, which help in the synthesis of neurotransmitter substance
ii. Synaptic vesicles, which store neurotransmitter substanceMain function of the synapse is to transmit the
impulses, i.e. action potential from one neuron to
Another
1. Excitatory synapses
2. Inhibitory synapses,
Nervous system ( anatomy and physiology)Ravish Yadav
the topic contain function of nervous system, classification of nervous system, neurons anatomy, structural classification of neurons, functional classification of neurons, nerve impulse
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
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Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
2. Contents
Introduction
Organization of nervous system
Neuron and its classification
Neuroglia
Properties of nerve fibre
Electrophysiology, nerve impulse, action
potential
Receptors
Synapse
Neurotransmitters
3. Nervous System
(Introduction)
• Nervous system is the most important
organization which control and integrates the
different body functions and maintains the
consistency of internal environment.
• A network of billions of nerve cells linked
together in a highly organized fashion to form
the rapid control center of the body
4. Functions of Nervous System
Depending on the type of nerve impulse and its interpretation,
functions of the nervous system may be of three types:
1. Sensory functions: These may be either conscious or
unconscious. When conscious they are called „sensations‟. In
the autonomic nervous system, they are usually unconscious.
2. Motor functions: These may be of two types:
▫ Reflex or involuntary and
▫ Voluntary: In the autonomic nervous system, all motor
effects are reflex. In the central nervous system, motor
effects are both reflex and voluntary.
3. Associated functions: For instance, idea, memory,
intelligence, etc. These are carried out mainly by the
cerebrum.
5. NERVES
• A nerve consists of numerous neurones collected
into bundles (bundles of nerve fibers in the CNS
known as tract). Each bundle has several coverings
of connective tissue:
1. Endonerium- surrounding the individual fiber.
2. Perineurium- smooth connective tissue
surrounding each bundle of fibers.
3. Epineurium- is the fibrous tissue which
surrounds and encloses a number of bundles of
nerve fibers .
6.
7. Sensory or afferent nerves
• Sensory nerves carry information from the body to
the spinal cord.
• And then information pass to brain or to connector
neuron of reflex arc in the spinal cord.
8.
9. Sensory receptors
• Specialized endings respond to different stimuli inside
and outside the body
1. Somatic, cutaneous or common senses- these
originate in the skin, they are pain, touch, heat and
cold , sensory nerve ending in the skin are fine
branching filaments without myelin sheaths. When
stimulated an impulse is generated and transmitted by
the sensory nerves to the brain where sensation is
perceived.
10. Sensory receptors
2. Proprioceptor senses- these originates in the
muscles and joints and contribute to the maintenance
of balance and posture.
3. Special senses- These are sight, hearing, balance,
smell and taste.
4. Autonomic afferent nerves- These originates in
the internal organs, glands, and tissues e.g.-
baroreceptors involved in control of blood pressure.,
chemoreceptors involved in control of respiration .
11. Motor or efferent nerves
• Motor nerves originates in the brain, spinal cord and
autonomic ganglia.
• They transmit impulses to the effector organs ; muscles
and glands there are two types
1. Somatic nerve- Involved in involuntary and reflex
skeletal muscle contraction.
2. Autonomic nerves-(Sympathetic or
parasympathetic) involved in cardiac and smooth
muscle contraction and glandular secretions.
12. MIXED NERVES
• In the spinal cord, sensory and motor nerves are
arranged in separate groups or tracts.
• Outside the spinal cord, when sensory and motor nerves
are enclosed within same sheath of connective tissue
they are called mixed nerves.
18. Nerve Tissue
Nerve Tissue Consists of two types of cells:
1. Neurons/Nerve cells: Structural and functional
unit of nervous system that generates and
transmit nerve impulse.
2. Neuroglia/Glial cells: Supporting cells
19.
20.
21. Neuron
Cell body/soma:
• The following structures are found in the cell body:
a) nucleus: large, spherical
b) neuroplasm: a cytoplasmic matrix containing nissl
bodies(participate in conduction of nerve impulses)
and neurofibrils (fine filaments).
c) mitochondria, golgi apparatus, ribosome,
endoplasmic reticulum, etc.
• Cell body forms the grey matter, in periphery of
brain, in centre of spinal cord.
22.
23. Neuron
Axon:
• It is a process arises from cell body that carries impulse
away from it.
• The term nerve fiber usually refers to the axons.
• It arises from axon hillock of the cell body.
• It is generally long with few branches (axon terminals).
• Axon is single but constant. If a neuron has only one
process, it will be the axon.
Axolemma Axon hillock
Myelin
sheath
Nodes of
Ranvier
Schwann
cells
24.
25. Myelinated neuron
• Large axon & those of peripheral nerves are surrounded
by a myelin sheath.
• This consists of series of Schwann cells arranged along
with the length of axon.
• Each one is wrapped around the axon so that it is
covered by number of concentric layers of Schwann cells
plasma membrane.
• Between these layers of plasma membrane there is a
small amount of fatty substance called myelin.
27. Myelinated neuron
• The outermost layer of Schwann cell plasma
membrane is the neurilemma.
• There are tiny areas of exposed axolemma between
adjacent Schwann cells, nodes of Ranvier, which
assist the rapid transmission of nerve impulses in
Myelinated neurons.
28. Non- Myelinated neurons
• Postganglionic fibers and some small fibers in the
CNS are non-Myelinated.
• In this type a number of axons are embedded in
Schwann cells are in close association and there is no
exposed axolemma.
• The speed of transmission of nerve impulses is slower.
29. Neuron
Dendrites:
• It is the process that carries impulse towards the
cell body.
• It collects impulses from other neurons and
carries them towards the cell body.
• It is generally short with many branches.
• Number varies from nil to numerous.
• They are the part of receptor membrane of the
neuron.
33. Neuroglia/Glial
cells
• These are the non-excitable supporting
connective tissues present in nervous system,
called neuroglia or glial cells.
• There are two major types of glial cells in the
vertebrate nervous system: -
▫ Microglia
▫ Macroglia
34. Neuroglia/Glial cells
• Macroglia: There are 3 types of macroglia:
1. Astrocytes
2. Oligodendrocytes
3. Schwann cells
• Microglia: Specialized immune cells that act as
the macrophages of the CNS
35. Macroglia:
1. Astrocytes
• Main supporting tissue of CNS.
• Star shaped with fine branching .
• At the free end of some of the processes are small swellings
called foot processes.
• Found in large number adjacent to blood vessels with their
foot processes forming a sleeve around them.
• This means blood is separated from the neurones by the
capillary wall and a layer of foot processes together
constitute the blood brain barrier.
• Fibrous astrocytes, which contain many intermediate
filaments, are found primarily in white matter.
• Protoplasmic astrocytes are found in gray matter and have
a granular cytoplasm.
Astrocytes in cerebral cortex
36. Functions
• Supporting network in brain.
• Form the blood brain barrier (BBB).
• Maintain chemical environment of extra cellular fluid.
• Recycles neurotransmitters.
Blood brain barrier
A. Longitudinal section
B. Transverse section
37. Blood brain barrier
• That protect the brain from potentially harmful
toxic substances and chemical variations in the
blood e.g. after a meal.
38. • These cells are smaller than astrocytes and
• Found in clusters round nerve cell bodies in grey matter,
where they are thought to have a supportive function.
• They are found adjacent to, and along the length of,
myelinated nerve fibres.
• They form and maintain myelin.
Macroglia:
2. Oligodendrocytes
39. • Schwann cells are involved in myelin formation
around axons in the peripheral nervous system.
Macroglia:
3. Schwann cells
40. Microglia
• The smallest and least numerous glial cells.
• Derived from monocytes that migrate from the blood
into the nervous system before birth.
• They are found mainly in the area of blood vessels.
• They enlarge and become phagocytic, removing
microbes and damaged tissue, in areas of inflammation
and cell destruction.
41. Ependymal cells
• These cells form the epithelial lining of the ventricles of
the brain and the central canal of the spinal cord.
• Those cells that form the choroid plexusess (a network
of blood vessels that secret CSF in ventricles) of the
ventricles secrete cerebrospinal fluid.
42. Satellite Cells
• Satellite cells are flat cells that surround the cell bodies of
neurons in the PNS.
• They appear to enclose and support the cell bodies, and
have intertwined processes that link them with other
parts of the neuron, other satellite cells, and also
neighboring Schwann cells.
43. Nerve fibers
• A nerve fiber is a threadlike extension of a
nerve cell and consists of an axon
(microfilament + microtubule) and myelin
sheath (if present) in the nervous system.
44. Properties of nerve fibers
1. Excitability: the nerve can be stimulated by a
suitable stimulus, which may be: -
mechanical
thermal
chemical
electrical
• After excitation, nerve impulse is generated through
depolarisation, repolarisation and hyperpolarisation.
• Excitability depends upon the following factors:
a) Strength of stimulus
b) Duration of stimulus
c) Direction of the current
d) Frequency of stimulus Injury
45. Properties of nerve fibers
2. Conductivity:
Impulse is propagated along a nerve in both directions [but under
normal conditions the nerve impulse travels in one direction only;
in the motor nerve towards the responding organ, in sensory nerve
toward the center].
The nerve impulse is propagated with a definite speed. The
conduction velocity depends upon the diameter of the nerve fibers,
the thicker fibers showing higher velocity. The velocity also depends
on the myelination and on temperature.
3. All-or-none law:
▫ If the stimulus be adequate, a single nerve will always give a
maximum response.
▫ If the strength or duration of the stimulus be further increased,
no alteration in the response will take place.
46. Properties of nerve fibers
4. Refractory period:
When the nerve fiber is once excited, it will not respond to
a second stimulus for a brief period. This period is called
refractory period.
4. Summation:
In a nerve fiber summation of two submaximal stimuli is
possible.
4. Adaptation:
The nerve fiber quickly adapts itself. Due to this adaptation
there is no excitation during the passage of a constant
current.
Only when the strength of the current is suddenly altered
or the current is made or broken excitation takes place.
47. Properties of nerve fibers
7. Accommodation: -
If a stimulus even in stronger strength is applied very
slowly to a nerve, then there may have no response
only due to lack of attaining the threshold strength.
This phenomenon is called accommodation.
8. Indefatigability: -
In the nerve muscle preparation, if the nerve is
stimulated repeatedly, then after a certain period the
muscle fails to give any response but nerve is not
fatigued.
48. NERVE PHYSIOLOGY AND THE NERVE
IMPULSES (ACTION POTENTIAL)
The nerve cells are excitable cells.
There is a different electrical charge on each side of the
membrane, which is known as membrane potential.
Any stimulus will change the membrane potential and
cause an action potential to generate.
The synchronized opening and closing of Na+ and K+
gates result in the movement of electrical charges that
generates a nerve impulse or action potential.
Action potentials reach the end of each neuron where
these electrical signals are either transmitted directly to
the next cell in the sequence via gap junctions, or are
responsible for activating the release of specialized
neurotransmitter chemicals.
49. THE NERVE IMPULSES (ACTION
POTENTIAL)
• Impulses is initiated by stimulation of sensory nerve
ending or by passage of an impulse from another nerve.
• Transmission of impulse or action potential is due to
movement of ion across the nerve cell membrane.
• In resulting state nerve cell membrane is polarised due
to difference in concentration of ions across plasma
membrane.
• This is called RESTING MEMBRANE POTENTIAL.
• Na+ main extracellular cation.
• K+ main intracellular cation.
50. THE NERVE IMPULSE (ACTION
POTENTIAL)
When stimulated
the permeability of
nerve cell
membrane
Na+ floods into
neurone from
extracellular fluid
causing
depolarisation
Creation of nerve
impulse or action
potential
Conduction of
nerve impulse in
one direction only
K+ flood out of
neurone
Return of
membrane
potential to
resting state
Action of sodium
potassium pump
expels Na+ from
cell in exchange
for k+
51.
52. Steps involved
1. Closed Sodium and Potassium channels (Resting
potential)
2. Membrane depolarization and sodium channel
activation (Depolarization)
3. Sodium channel inactivation (Repolarization)
4. Potassium channel activation (Hyperpolarization)
5. Return to normal permeability (Resting potential)
53.
54.
55. 2. DEPOLARIZATION
• Na+ floods into neuron from the extracellular fluid to
intracellular fluids causing depolarization, creating a
nerve impulse or action potential.
• It is very rapid enabling the conduction of a nerve
impulse along the entire length of a neuron in a few
milliseconds.
• It passes from area of stimulation to resting potential, it
takes time for repolarization to occur.
56. 3. Repolarization
• As the membrane potential approaches +50 mV,
voltage gated potassium channels open and positively
charged potassium ions begin to flow out of the cell.
• This begins to repolarise, the cell by reducing the excess
internal positive charge and moving the membrane
potential closer to the resting potential.
• At this point the cell is basically impermeable to sodium
and very permeable to potassium which rapidly flows
out of the cell.
57. 4. Hyperpolarization
• Potassium efflux (exiting) continues past the resting
potential of -70 mV due to the slow closing voltage gated
potassium channels.
• This causes a hyperpolarisation known as undershoot
which takes the membrane potential to around -75mV.
5. Return to normal permeability/resting
state (Resting potential)
• Soon afterward the cell returns to resting potential via
the standard membrane proteins.
58.
59.
60. • Refractory periods prevent the backward movement of
action potentials and limit the rate of firing.
63. Saltatory conduction
• An action potential at one node of Ranvier causes
inwards currents that move down the action,
depolarizing the membrane and stimulating a new action
potential at the next node of Ranvier.
64. Saltatory conduction
• Myelin sheath reduces membrane capacitance and
increases membrane resistance in the inter-node
intervals, thus allowing a fast, saltatory movement of
action potentials from node to node.
• Myelin prevents ions from entering or leaving the axon
along myelinated segments.
• As a general rule, myelination increases the conduction
velocity of action potentials and makes them more
energy-efficient.
65.
66.
67.
68.
69.
70. Receptors (According to the type of
binding with neurotransmitter)
• Nearly all neurotransmitters induce postsynaptic
potentials by binding to their receptors in the
postsynaptic membrane.
• The type of receptor to which a neurotransmitter binds
determines the postsynaptic response.
• Two types of neurotransmitter receptors have been
identified:
1. Ionotropic receptors
2. Metabotropic receptors
71. 1. Ionotropic receptors
• Are simply receptors that are part of ligand-gated ion
channels.
• They are called ionotropic because they directly
control the movement of ions into or out of the neuron
when bound by a neurotransmitter.
• Neurotransmitters that bind ionotropic receptors have
very rapid but short-lived effects on the membrane
potential of the postsynaptic neuron.
72. 2. Metabotropic receptors
• Are receptors within the plasma membrane that are
connected to a separate ion channel.
• They are called metabotropic because they are directly
connected to metabolic processes that begin when they
are bound by neurotransmitters.
• Most are connected through a group of intracellular
enzymes called G-proteins.
73. 2. Metabotropic receptors
When the
neurotransmitter
molecule (“first
messenger”) binds
to the receptor
activates one or
more G-proteins
followed by
enzyme-
catalyzed
reactions
formation of a
second
messenger
inside the
postsynaptic
neuron
The second messenger
(Eg; cyclic adenosine
monophosphate (or
cAMP)opens or closes
an ion channel
Causes slow changes in
the membrane potential
of the postsynaptic
neuron, but are
typically longer-lasting.
74. THE SYNAPSE
• There is always more than one neuron is involved in the
transmission of a nerve impulses from its origin to its
destination, whether its sensory or motor.
• No physical contact between these neurones.
• Synapse is the region where communication occurs
between 2 neurons or between a neuron and a target
cell.
75. THE SYNAPSE
• At its free ends the axon of the presynaptic neurone breaks up
into minute branches that terminate into small swellings
called synaptic knobs or terminal buttons.
• These are in close proximity to the dendrites and the cell body
of postsynaptic neuron.
• These chemicals are synthesized by nerve cells, actively
transported along the axons and stored in vesicles.
• They are released by exocytosis in response to action potential
and diffuse across the synaptic cleft.
• They act on the specific receptor site on the postsynaptic
membrane. There action is short lived as they act on effector
organ or neurone, or taken up by synaptic knob.
76.
77. THE SYNAPSE
• Synapse has the following elements:
• Presynaptic terminal: It contains synaptic vesicles encapsulated
around the neurotransmitter substance.
• Synaptic cleft: It refers to the 20 nm wide synaptic gap, which
separates the two adjacent neurons.
• Postsynaptic terminal: It possesses receptor sites for the
binding of neurotransmitters, which can either inhibit or promote
the passage of nerve signal from one cell to the next.