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CHAPTER 6:Nervous & Hormonal
Communication
Siti Noorfahana Mohd Idris, CFS UiTM
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Learning Objectives
i. Identify four different types of hormone classesii. Compare the mechanism of action of hormones
iii. Identify the endocrine glands and describe the
actions of their hormones
iv. Describe the processes involved in neural signaling
v. Describe the structure of neuron
vi. Explain how a neuron transmit impulse
vii. Describe several types ofnervous system in animals
viii. Identify the organization of a human nervous system
ix. Compare endocrine with nervous system function
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Overview: The Bodys Long-
Distance Regulators
Animal hormones are
chemical signals that are
secreted into the circulatory
system and communicateregulatory messages within the
body
Hormones reach all parts of the
body, but only target cells havereceptors for that hormone
Insect metamorphosis is
regulated by hormones
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Overview: The Bodys Long-
Distance Regulators
Two systems coordinate communicationthroughout the body: the endocrine system andthe nervous system
The endocrine system secretes hormones thatcoordinate slower but longer-acting responsesincluding reproduction, development, energymetabolism, growth, and behavior
The nervous system conveys high-speedelectrical signals along specialized cells calledneurons; these signals regulate other cells
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Hormone classes
i) Fatty acid derivatives Prostaglandins and juvenile
hormones of insects
Synthesized from arachidonic acid (a
20 carbon fatty acids)
ii) Steroids
The natural steroid hormones are
generally synthesized from cholesterol
in the gonads (sex hormones) andadrenal cortex (mineralcortisoids and
glucocortisoids).
These forms of hormones are lipids.
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Hormone classes
iii) Amino acid derivatives
Synthesized from amino acids
Adrenaline, noradrenalline
(cathecolamnies) and thyroxine are
derived from the amino acid
thyrosine.
iv) Peptides and proteins
Peptide hormones shorter in length
Protein hormones are one or morepolypeptide.
Synthesized in ER Golgi
Packed in vesicles store/release
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Hormone classes
Peptide hormones oxytoxin, calcitonin, parathyroid
hormone (PTH), Antidiuretic hormone
Protein hormones - Insulin, glucagon, growth hormone
(GH), FSH, LH, prolactin
Lipid-soluble hormones (steroid hormones) pass easily
through cell membranes, while water-soluble hormones
(polypeptides and amines) do not.
The solubility of a hormone correlates with the location of
receptors inside or on the surface of target cells.
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Mechanism of action
Hormones are released by endocrine glands
into blood
Transported by blood, they will arrive at the
target cells where they shows differentmechanism of action
The mechanism can be divided into steroid and
non steroid hormones
Steroid hormones are lipid soluble
Non steroid hormones are water soluble
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Mechanism of action
Water and lipid soluble hormones differ in theirpaths through a body
Water-soluble hormones are secreted by
exocytosis, travel freely in the bloodstream,and bind to cell-surface receptors
Lipid-soluble hormones diffuse across cellmembranes, travel in the bloodstream bound to
transport proteins, and diffuse through themembrane of target cells
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Water-soluble Vs Lipid-soluble
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Water-soluble Vs Lipid-soluble
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Mechanism of action Steroid
(Lipid-soluble)
Lipid soluble hormones are able to enter cells.
This is because the lipid portion of the plasma
membrane does not act as a barrier to entry of
lipophilic regulators. Steroid hormones are lipid themselves and thus
they are lipophilic.
Because these hormones are NOT watersoluble, they are not able to dissolve in the
plasma portion of the blood (need transport
protein in blood)
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Mechanism of action -
Steroid
Therefore, they are carried in the
blood attached to a protein carrier.
When the hormones arrive at their
target cells, they dissociate from
their carriers and pass through the
plasma membrane of the cell.
Some steroid hormones (steroids,
thyroid hormones, and the hormonal
form of vitamin D) will combine with
receptors within the target cell
cytoplasm and then move as a
hormone receptor complex to the
nucleus.
Others travel into the nucleus to
encounter their receptor protein.
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Mechanism of action -
Steroid
The hormone-receptor complex that is
activated may able to bind to specific
regions in the DNA.
This may activate or repress
transcription of gene regions into
messenger RNA.
Translation of the mRNA transcripts
that happens outside the cell results in
enzymes and other proteins that are
able to carry out a response to the
hormonal signal.
* Protein alter the activity of cell.
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Mechanism of action - Steroid
For example, estrogen is a
steroid hormone necessary
for female.
In female birds and eggs,
estradiol (a form of estrogen)
has specific receptor on liver
cells.
Binding of this hormone to
the receptor activates
transcription of the gene for
protein vitellogenin.
Vitellogenin is secreted and
transported to the blood,
where it is used to produce
egg yolk.
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Mechanism of action- Peptide
hormones (Water-soluble)
Peptide hormones are hydrophilic.
Therefore, a peptide hormone cannot cross the
target cell's plasma membrane that is lipid
soluble (consist of dwilayer lipid membrane) The hormones include all the peptide and
glycoprotein hormones.
Because these hormones are not able to entercells, they will bind to receptor proteins located
on the surface of the plasma membrane.
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Mechanism of action-
Peptide hormones
(Water-soluble)
Once the hormone has bound to its
receptor, a cascade of events will occur
producing secondary messenger
molecules that will allow the cell to
properly respond to the hormones
message. Binding of a peptide hormone (first
messenger) caused formation of a
second messenger, the cyclic AMP
(cAMP).
These cascade of reactions are
enzyme mediated and results in aresponse of the cell to the hormonal
action.
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Mechanism of action- Peptide
hormones (Water-soluble)
The hormone epinephrine has multiple effects
in mediating the bodys response to short-term
stress
Epinephrine binds to receptors on the plasmamembrane of liver cells
This triggers the release of messenger
molecules that activate enzymes and result in
the release of glucose into the bloodstream
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Mechanism of action- Peptide
hormones (Water-soluble)
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Multiple Effects of Hormones
The same hormone may have different effects
on target cells that have
Different receptors for the hormone
Different signal transduction pathways
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Endocrine Tissues and Organs
In some tissues, endocrine cells are grouped
together in ductless organs called endocrine
glands.
Endocrine glands secrete hormones directly into
surrounding fluid.
These contrast with exocrine glands, which have
ducts and which secrete substances onto body
surfaces or into cavities
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Endocrine Vs Exocrine
Exocrine glands have ducts to carry hormones, while endocrineglands are ductless.
Examples of exocrine glands are sweat, saliva and mammary
glands, as well as oil and enzymes. There are glands which function
as both endocrine and exocrine glands.
Exocrine hormones are released into the external environment, oroutside of the body. Endocrine hormones are released into the
internal environment, or inside of the body.
Endocrine response is slower because hormones travel through the
blood.
The duration in endocrine transmission is prolonged becausekidneys have to filter the blood
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Glands in the endocrine system
Vertebrate hormones regulate growth and
development, reproduction, salt and fluid
balance, many aspects of metabolism and fluid
behavior. Homeostasis depends on normal concentrations
of hormones.
Over or under-secretion of hormones will result
in endocrine disorders.
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Pituitary gland
Most endocrine activity is controlled either directly or indirectly bythe hypothalamus.
The pituitary glands hang by a stalk from the hypothalamus.
The pituitary gland activity is
regulated by the integration of
the nervous and endocrine system
(neuroendocrine gland)
Because it controls the activity of
several other endocrine glands,
pituitary gland is said to be the
master gland of the body.
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Pituitary gland
The pituitary gland can
be divided into two
parts, the anteriorand
posterior lobes.
The posterior lobe ofthe pituitary gland
develops from brain
tissue; therefore it
contains axons thatoriginate in cell bodies
within the
hypothalamus.
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Pituitary gland
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Posterior Pituitary gland
This neuroendocrine gland secretes two peptide
hormones, oxytoxin and antidiuretic hormone
(ADH).
These hormones are enclosed within vesicles. They are transported down the axons into the
posterior lobe of the pituitary gland.
The vesicles are stored in the axon terminalsuntil the neuron is stimulated.
Once it is stimulated, the axon content will
diffuse into the surrounding capillaries.
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Posterior Pituitary gland
Oxytoxin stimulates
contraction
of the uterus and
stimulates ejection of
milk by the mammaryglands.
ADH stimulates
reabsorption of water
by the kidney tubules.
The posterior pituitary
stores and secretes
hormones that are made in
the hypothalamus
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Anterior Pituitary gland
Compared to the posterior lobe,
the anterior lobe develops from
epithelial cell rather than
neural cell.
The anterior lobe receivessignal and releases its hormone
into the blood vessels.
The anterior pituitary makes
and releases hormones underregulation of the hypothalamus
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Anterior Pituitary gland
The anterior lobe of the pituitary gland secretes growthhormone, prolactin and several tropic hormones
(hormones produced at the anterior gland but stimulates
other endocrine glands).
The other tropic hormones are ACTH, TSH, FSH and
LH.
Prolactin stimulates the mammary glands to produce
milk.
Melanocyte-stimulating hormone (MSH) regulates
skin color in amphibians, fish, and reptiles by controlling
pigment distribution in melanocytes.
In mammals, MSH plays additional roles in hunger and
metabolism in addition to coloration.
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Anterior Pituitary gland
Growth hormone (GH/somatotropin) is a hormone that
promotes tissue growth by promoting protein synthesis.
GH stimulates the liver to produce insulin-like growth
factors (IGFs), which promotes skeletal and tissue
growth. An excess of GH can cause gigantism, while a lack of
GH can cause dwarfism
ACTH and TSH control the secretions from the adrenal
glands and thyroid glands respectively. FSH and LH have essential roles in gamete formation
and hormonal secretions required in sexual reproduction
of animals.
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Thyroid gland
The thyroid gland is located in the neck region,
in front of the trachea and below the larynx (Adams
apple).
The thyroid gland secretes thyroid hormones, thyroxine
(T4) = four iodine atoms and triiodothyronine (T3) =three iodine atoms.
In vertebrates, thyroid hormones
are essential for normal growth
and development because they
stimulate the rate of metabolism.
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Thyroid gland
Regulation of thyroid
secretion depends mainly
on the secretion of the TSH
(thyroid secreting hormone)
from the anterior lobe ofthe pituitary gland.
When the concentration of
the thyroid hormones in the
blood rises above normal,the anterior pituitary
secretes less thyroid-
stimulating hormone (TSH).
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Di d f Th id F ti
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Disorders of Thyroid Function
and Regulation
Hypothyroidism, too little thyroid function, can
produce symptoms such as
Weight gain, lethargy, cold intolerance
Hyperthyroidism, excessive production of thyroid
hormone, can lead to
High temperature, sweating, weight loss,
irritability and high blood pressure Malnutrition can alter thyroid function
Di d f Th id F ti
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Disorders of Thyroid Function
and Regulation
Graves disease, a form of hyperthyroidism
caused by autoimmunity, is typified by protruding
eyes
Insufficient dietary iodine leads to an enlarged
thyroid gland, called a goiter
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Thyroid gland: Control of Blood
Calcium
The thyroid gland also secretes calcitonin, a
peptide hormone that maintains a proper level
of calcium in the blood.
When blood calcium levels rises, calcitonin is
released to cause calcium to be deposited in
the bones.
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Thyroid gland: Control of Blood
Calcium
The parathyroid gland is
located on the surface of the
thyroid gland.
It secretes parathyroid
hormone (PTH), which
regulates the calcium
concentration by
stimulating calciumrelease from bones and
increasing calcium
reabsorption in the
intestine.
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Th id l d C t l f Bl d
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Thyroid gland: Control of Blood
Calcium
PTH increases the level of blood Ca2+
It releases Ca2+ from bone and stimulates
reabsorption of Ca2+ in the kidneys
It also has an indirect effect, stimulating thekidneys to activate vitamin D, which promotes
intestinal uptake of Ca2+ from food
Calcitonin decreases the level of blood Ca2+
It stimulates Ca2+ deposition in bones andsecretion by kidneys
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Adrenal gland
The paired adrenal
glands are small,
yellow masses of
tissue that lie incontact with the upper
ends of the kidneys.
Each gland consists of
a central portion, theadrenal medulla, and
the outer section, the
adrenal cortex.
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Adrenal gland
Adrenal medulla is a neuroendocrine gland that is
controlled by the sympathetic nervous system.
- The adrenal medulla secretes epinephrine and
norepinephrine, the hormones help the body cope
with stress.
- Epinephrine and norepinephrine help the body to
respond to danger by increasing the heart rate,
metabolic rate and the strength of muscle
contraction. These hormones reroute blood toorgans needed for fight or flight.
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Adrenal gland
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Adrenal gland
Adrenal cortex
The hypothalamus controls the activity in the
adrenal cortex by means of the ACTH (from the
anterior lobe of the pituitary gland). Two other hormones secreted by the adrenal
cortex are
i. mineralcortisoids such as aldosterone
iii. glucocortisoids such as cortisol
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Adrenal gland
Aldosterone maintains a proper balance of
sodium and potassium ions in the kidney
tubules.
Cortisol promotes gluconeogenesis in liver
cells resulting in the conversion of amino
acids increasing level of glucose in the blood.
Thus during stress, the adrenal cortex ensures
adequate fuel supplies for the cells.
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Pancreas- An endocrine system In addition to secreting
digestive enzymes, thepancreas is an important
endocrine gland.
Its hormones, insulin and
glucagon, are secreted bycells that occur in little
clusters called the islets of
Langerhans.
The islets consist mainlyofbeta cells, which
secrete insulin, and
alpha cells, which
secrete glucagon.
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Pancreas- An endocrine system
Glucagon raises blood glucose (glycogenolysis) while
insulin lowers the concentration of glucose in the blood.
Insulin reduces blood glucose levels by
Promoting the cellular uptake of glucose
Slowing glycogen breakdown in the liver
Promoting fat storage, not breakdown
Glucagon increases blood glucose levels by
Stimulating conversion of glycogen to glucose in theliver
Stimulating breakdown of fat and protein into
glucose
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Diabetes Mellitus
Diabetes mellitus is perhaps the best-
known endocrine disorder
It is caused by a deficiency of insulin or a
decreased response to insulin in targettissues
It is marked by elevated blood glucose
levels
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Diabetes Mellitus
Type I diabetes mellitus (insulin-dependent) is an
autoimmune disorder in which the immune system
destroys pancreatic beta cells
Type II diabetes mellitus (non-insulin-dependent)
involves insulin deficiency or reduced response of targetcells due to change in insulin receptors
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Testes and ovaries
Testes produce testosterone and ovaries
produce estrogen and progesterone.
Hypothalamus controls the secretion of these
hormones by means of the LH and FSHhormone.
Testosterone allows secondary growth in male
during puberty.
Estrogen is necessary for egg development and
maturation and together with progesterone they
are responsible for the menstruation cycle.
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Thymus
Thymus gland is located beneath the sternum. It secretes thymosin that is responsible forlymphocyte
(white blood cells) maturation.
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Pineal gland
Melatonin secreted by the pineal gland, which is
located in the brain that influence the onset of
sexual maturity and our biological clock.
We feel sleepy at night and awake in the daytime.
This 24 hour cycle is called the circadian
rhythm that is controlled by melatonin.
It also helps regulate sexual development.
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Hormones from other tissue
Atrial natriuretic factor(ANF), which is
secreted by the atrium of the heart, promotes
sodium reabsorption thus lowering blood
pressure. Gastrin is secreted by the stomach that
stimulates release of gastric juice and
somastostatin inhibits secretion of gastric juice.
Secretin and cholecystokinin increase outputof pancreatic juice. The latter also stimulates
ejection of bile salts from the gallbladder.
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Review
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Molting and metamorphosis in
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Molting and metamorphosis in
insect
In invertebrates, hormones are secreted by
neuron rather than the endocrine glands.
These hormones regulate
i. Regeneration in hydras, flatworms andannelids
ii. Color changes in crustaceans
iii. Growth and developmentiv. Metabolic rate
v. Gamete production and reproduction
Molting and metamorphosis in
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Molting and metamorphosis in
insect
As insects grow, their hardened exoskeleton cannot fitthem anymore.
Therefore, insects undergo a series of molting process
where they shed their old exoskeleton in a process
called molting. In an immature insect, paired endocrine glands called
the corpora allata secretejuvenile hormone (JH).
This hormone suppresses metamorphosis at each larval
molt in order to ensure the larvae increase in size butremains in the larval (immature) state.
Molting and metamorphosis in
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Molting and metamorphosis in
insect
When the concentration of JH decreases,metamorphosis occurs and the larvae transformed into
pupae.
Prior to molting, neuroendocrine cells in the insect brain
secrete brain hormone (BH). BH stimulates theproduction of the ecdysone from the prothoracic glands,
which stimulates growth and molting.
Therefore, metamorphosis in adult form occurs when
molting hormone acts in the absence of juvenilehormone.
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Overview: Lines of Communication
The cone snail kills preywith venom that disablesneurons.
Neurons are nerve cellsthat transfer informationwithin the body
Neurons use two types ofsignals to communicate:electrical signals (long-distance) and chemicalsignals (short-distance)
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Neural signaling
Sensors Sensory receptors at the end of peripheral
nerves pick up information about the body's
internal and external environment.
These receptors also detect changes that
occur. For example, when you feel pain when
touching a hot object, a sensory receptor is
picking up that information. All sensory information is picked up in the
peripheral nervous system and sent to the
central nervous system.
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Neural signaling
Integration
The integrative function takes place in the brain
or spinal cord.
These organs receive sensory informationand make decisions regarding the
information.
The decision making is the integrative function.
For example, if you feel pain your brain might
decide you need to move away from the painful
stimulus.
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Neural signaling
Effectors
Once the CNS makes a decision, it then carries
out a motor function.
The motor function is the stimulation of a muscle(skeletal, smooth or cardiac muscle) or a gland.
When a motor function is carried out, neurons in
the CNS carry an impulse along a peripheral
nerve to either a muscle or a gland; these are
called effectors.
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Nervous tissue consists of nerve cells orneurons.
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Neurons are functional units of the nervous system which are
specialized to receive and send information in a form of electrical
signals called nerve impulses.
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Neuron
The largest/enlarged portion of the neuron is the cellbody. It contains the nucleus, the bulk of cytoplasm and
most of the organelles.
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Neuron
There are two types of cytoplasmic extensions which project fromthe cell body:
i. Dendrites
Typically short and highly branched. Numerous of them extend
from the cell body.
They functions in receiving stimuli and sending signals to the
cell body. Can be found at one end of the cell body.
ii. Axon
Conducts nerve impulses away from the cell
body to another neuron, a muscle or a gland. Eachneuron has a single axon leaving its cell body.
The cone-shaped base of an axon is called the axon hillock.
Information is transmitted from a
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Information is transmitted from a
presynaptic cell (a neuron) to a
postsynaptic cell (a neuron, muscle, or
gland cell)
Most neurons are nourished or
insulated by cells called glia.
In vertebrates the axons of many neurons are
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In vertebrates, the axons of many neurons are
surrounded by a myelin sheath that is made of
Schwann cells. The nucleus of the Schwann cells can
clearly be seen at the myelin sheath. The gap between Schwann cells is known as the node
of Ranvier.At this point, the axon is not insulated by
myelin.
They serve as points along the neuron forgenerating asignal.
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Neuron
Neurons are supported structurally and functionally by supportingcells called neuroglia.
The neuroglia supplies the neurons with nutrients; removes waste
and also provide immune function.
Two of the most important kinds of neuroglia in invertebrates are
Schwann cells and oligodendrocytes that produce myelinsheath.
Schwann cells produce myelin sheath in the Peripheral Nervous
System (PNS) whereas the oligodendrocytes produce myelin sheath
for the Central Nervous System (CNS).
N
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Neuron
There are three types of neurons
i. Sensory neurons typically have a long dendrite and
short axon, and carry messages from sensory
receptors to the central nervous system.
ii. Motor neurons have a long axon and short dendrites
and transmit messages from the central nervous
system to the muscles (or to glands).
iii. Interneurons are found only in the central nervous
system where they connect neuron to neuron.
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Neuron
N t i i f i l
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Neuron transmission of impulse
Every cell has a voltage (difference in electricalcharge) across its plasma membrane called a
membrane potential
The resting potential is the membrane potential
of a neuron not sending signals
Changes in membrane potential act as signals,
transmitting and processing information
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Neuron transmission of impulse
The plasma membrane of neurons always hadan unequal distribution of electrical charges
between the two sides of the membrane.
(Electrical Gradient).
This electrical gradient is called potential
difference that exists at every cells plasma
membrane.
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Neuron transmission of impulse
Biologists can measure the potential across themembrane by placing one electrode inside the cell and a
second electrode outside the cell, and connecting
through a very sensitive voltmeter oroscilloscope.
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Neuron transmission of impulse
The fluid outside of the membrane has a positivecharge while the cytoplasm inside has a
negative charge.
Opposite charges are usually attracted to eachother, the membrane stores energy by holding
opposite charges apart.
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Neuron transmission of impulse
There are three factors that results in differences ofcharges between the extracelullar fluid and inside the
neurons.
i) These differences are due to ionic concentrations.Molecules such as proteins, carbohydrates, and
nucleic acids that carry net negative charge are
more abundant inside the cell. This is because they
are too large to diffuse out. These molecules are calledfixed anions.
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Neuron transmission of impulse
ii) The sodium-potassium pumps (Na+ / K+) activelypumps in two K+ ions for every three Na+ ions that it
pumps out. These helps in maintaining a concentration
gradient where there is high K+ ion and low Na+ ion
inside the cell whereas high Na+
ion and low K+ ionoutside the cell.
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Neuron transmission of impulse
iii) Ion leak channels are membrane proteins that are morenumerous for K+ than Na+. This channels functions in allowing little
(Na+) to diffuse in but allows more (K+) to diffuse out, leaving an
excess of negative charge (from ions like Cl-) inside the
membrane.
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Neuron transmission of impulse
This charge difference is called membrane potential and ismeasured in millivolts.
When a cell at rest (resting membrane potential) where it does not
transmit any impulse, the voltage potential is - 65 to -70mV. The
negative sign indicates that the inside of the cell is negative
compared to the outside.
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Neuron transmission of impulse
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Neuron transmission of impulse
The cell membrane of aneuron will respond to stimuli
such as heat, pressure, and
chemicals by changing the
amount of polarization across
its membrane.
As a stimulus is applied,
within 2-3 msec, the voltage
will rise to a voltage at about-50mV, which is called the
threshold potential.
Ne ron transmission of imp lse
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Neuron transmission of impulse
The stimulus triggers the opening of the Na+ channel.Once the threshold is reached, the increasing positive
charge inside the membrane triggers the opening of
more and more of Na+ channels.
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Neuron transmission of impulse
As more and more Na+ moves in, the voltage will soar to its peak toat about +35mV.
The peak voltage triggers the closing of the Na+ channels while
the K+ channels opens to allow rapid diffusion of K+ ions out of
the membrane.
Neuron transmission of impulse
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Neuron transmission of impulse
The first region shows the flow of Na+ into the neuronsmembrane creating the action potential.
The action potentials regenerate itself along the neuron.
The three parts shown in the figure below show movements of
stimulus along the neuron.
As the action potential moves to the next region, K+ will diffuse
out of the neuron. At this time Na+ channels are closed (Almost
like domino effect).
Action potential are propagated in only one direction along the axon
due to the fact that action potential cannot be regenerated in the
regions where K+ leaving the axon.
The regeneration of action potential will carry the stimulus to our
central nervous system (spinal cord and the brain).
Neuron transmission
of impulse
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of impulse
At the site where the action
potential is generated, usually theaxon hillock, an electrical currentdepolarizes the neighboring regionof the axon membrane
Action potentials travel in only
one direction: toward the synapticterminals
Inactivated Na+ channels behindthe zone of depolarization preventthe action potential from travelingbackwards
Neuron transmission of impulse
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Neuron transmission of impulse
Action potentials are conducted without decrement,thus, the last action potential at the end of the axon is
just as large as the first action potential.
Myelinated axons conduct impulses more rapidly than
nonmyelinated axons because the action potentials innonmyelinated axons are only produced at the nodes of
Ranvier.
The process that impulses jump from node to node in
myelinated axons is called salutatory conduction. An action potential is all or none event, each threshold
depolarization produces either a full action potential due
to the complete opening of gated channels or none at all.
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Neuron transmission of impulse
Neuron transmission of impulse
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Neuron transmission of impulse
Neuron transmission of impulse
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Neuron transmission of impulse
Hyperpolarization
Some stimuli causes the
inside of the membrane
became more negative by
the opening of gated K+
channels.
Usually did not generate
an action potential
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Neuron transmission of impulse
Depolarization astimulation that
causes the inside of
the membrane to
become less negative
If it reached threshold
it might cause an
action potential
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Neuron
transmission of
impulse
Generation of Action
Potentials:
A Closer Look
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A Closer Look
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During the refractory period after anaction potential, a second action potential
cannot be initiated
The refractory period is a result of a
temporary inactivation of the Na+ channels
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Neuron transmission of impulse:
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Synapse
Wheneveraction potentials arrive at the endof a neurons axon, the information will be
passed to a receiving cell across the synapse.
The neuron whose axon transmits action
potentials to the synapse is the presynaptic
neuron, while the cell receiving the signal on the
other cell is the postsynaptic neuron.
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Synapse
Synapses can be eitherelectricalorchemical.
In an electrical synapse, action
potentials possibly passed from
one neuron to the other where the
receiving neuron is stimulated
quickly and at the same level. Thisis because it involves cytoplasmic
connections formed by the pre and
postsynaptic neuron.
In human, electrical synapses are
common in the heart and thedigestive system because the
nerve signals need to maintain
steady and rhythmic muscle
contractions.
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Synapse
Chemical synapses have a narrow gap called thesynaptic cleft that separates the sending neuron
(presynaptic) from the receiving neuron (postsynaptic).
The end of a presynaptic neuron is swollen and filled
with numerous synaptic vesicles that are packed withneurotransmitters.
Arriving at a synaptic cleft, the action potential (an
electrical signal) will stimulate the opening of gated
Ca++ channels. These will lead to rapid entrance ofCa++ via diffusion.
This serves as a stimulus for the fusion of presynaptic
neurons vesicle with its own outer membrane cell.
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Synapse
Therefore, the contents of the vesicles which are in aform ofneurotransmitter will be released by
exocytosis to the synaptic cleft.
The released neurotransmitter molecules will diffuseacross the cleft and bind to receptors protein on the
receiving postsynaptic neurons plasma membrane.
The binding opens chemical sensitive ion channelscausing ions to diffuse to the receiving cells
membrane and trigger new action potentials.
1. An action potentialarrives, depolarizing the
presynaptic membrane.
2. The depolarization opens
voltage-gated channels,
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g g ,
triggering an influx of
Ca++.
3. The elevated Ca++
concentration causes
synaptic vesicles to fusewith the presynaptic
membrane, releasing
neurotransmitter into the
synaptic cleft.
4. The neurotransmitter
binds to ligand-gated ion
channels in the
postsynaptic membrane.
In this example, bindingtriggers opening, allowing
Na+ and K+ to diffuse
through.
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Synapse
After release, the neurotransmitter May diffuse out of the synaptic cleft
May be taken up by surrounding cells
May be degraded by enzymes
Neurotransmitters are very important in homeostasis
because their precise signaling among neurons enables
the nervous system to coordinate the activities at all part
of the body.
Neurotransmitter
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Neurotransmitter
Neurotransmitters can be divided into two,i. Excitatory-They open Na+ channels, thus triggering
the action potentials in the receiving cells. Excitatory
neurotransmitters promote depolarization.
ii. Inhibitory- Open membrane channels for ions like
Cl- that decreases the receiving cells tendency to
develop action potentials. This promotes
hyperpolarization because the membrane inside thereceiving neuron becomes more negatively charged.
Neurotransmitter
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Neurotransmitter
Neurotransmitters tend to be small molecules, some areeven hormones. The time for neurotransmitter action is
between 0.5 and 1 millisecond.
Neurotransmitters are either destroyed by specific
enzymes in the synaptic cleft, diffuse out of the cleft, orare reabsorbed by the cell.
More than 30 organic molecules are thought to act as
neurotransmitters.
There are five groups: acetylcholine, biogenic amines,amino acids, neuropeptides, and gases
Neurotransmitter
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Neurotransmitter
Neurotransmitter: Acetylcholine
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Neurotransmitter: Acetylcholine
Acetylcholine is an example of a neurotransmitter. AcHcrosses the synapse between a motor neuron and a
skeletal muscle.
AcH causes Na+ to diffuse inside the cell causing the
postsynaptic membrane to become depolarized. Because the postsynaptic cell is a skeletal muscle cell,
the action potential stimulates muscle contraction.
To stop muscle contraction, an enzyme in the
postsynaptic membrane called acetylcholinesterasecleaves AcH into an inactive fragment.
Neurotransmitter: Amino Acids
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Neurotransmitter: Amino Acids
Amino acid neurotransmitters are active in the CNS andPNS
Known to function in the CNS are
Glutamate
Gamma-aminobutyric acid (GABA)
Glycine
Glycine and GABA are inhibitory neurotransmitters
that produce hyperpolarization at the postsynaptic
membrane.
Neurotransmitter: Biogenic Amines
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Neurotransmitter: Biogenic Amines
Biogenic amines include Epinephrine
Norepinephrine
Dopamine Serotonin
Dopamine and serotonin affect sleep, mood,
attention and learning.
They are active in the CNS and PNS
Neurotransmitter: Neuropeptides
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Neurotransmitter: Neuropeptides
Several neuropeptides, relatively short chainsof amino acids, also function asneurotransmitters
Neuropeptides include substance P and
endorphins, which both affect our perception ofpain
Opiates bind to the same receptors asendorphins and can be used as painkillers
Neurotransmitter: Gases
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Neurotransmitter: Gases
Gases such as nitric oxide and carbon monoxideare local regulators in the PNS
For example, during sexual arousal, certain
neurons in human male releases NO into the
erectile tissue of the penis.
This causes the blood vessel to dilate and fill the
spongy erectile tissue with blood.
How Drugs Affect
N t itt ?
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Neurotransmitter?
Drugs can interfere with just about every step in the work ofneurotransmitters.
More specifically, drugs can:
- Stop the chemical reactions that create neurotransmitters.
- Empty neurotransmitters from the vesicles where they're normally stored
and protected from breakdown by enzymes.
- Block neurotransmitters from entering or leaving vesicles.
- Bind to receptors in place of neurotransmitters.
- Prevent neurotransmitters from returning to their sending neuron (the
reuptake system).
- Interfere with second messengers, the chemical and electrical changes
that take place in a receiving neuron.
Nervous system in animals
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Nervous system in animals
Some animals lack a nervous system; such as thesponges that do not have any cell specialized for
generating and transmitting nervous signals.
Nervous system in animals
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Nervous system in animals
Hydra is an animal that has the simplest typeof nervous system. Their nervous system is
what we referred as a nerve net.
The nerve net is a web-like system of
neurons that extends throughout the body.
This adaptation is adequate for the hydrabecause they are headless and have a
radial symmetry. Besides, their activity is
limited where they are usually stationary,
attached to submerged plant stems or rocks.
Their nerve net is responsive to signalsabout food or danger.
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e ous sys e a a s
Another animal with radial symmetry, theechinoderms have radial nerves that extend
through each arm from a central nerve ring.
Nervous system in animals
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y
Radially symmetrical nervous systems areuncentralized unlike the bilaterally symmetrical
animals. These animals have a head and a tail and
have a tendency to move head-first through the
environment.
Nervous system in animals
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y
Two evolutionary hallmarks ofbilateralsymmetrical:
i. Cephalization Concentration of the
nervous system at the head end.
ii. Centralization The presence of a central
nervous system (CNS) distinct from the
peripheral nervous system (PNS)
The flatworm has a small brain composed of
ganglia (masses of nerve cell bodies) and two
parallel nerve cords (bundles of
axons and dendrites).
These elements are the worms CNS while thesmaller nerves are the PNS.
The high degree of cephalization and
centralization in the squids nervous system
give them a degree of intelligence.
Nervous system in animals
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y
Annelids and arthropods have segmentallyarranged clusters of neurons called ganglia.
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Organization of the nervous system
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g y
In vertebrates The CNS is composed of the brain and spinal cord
The per ipheral nervous system(PNS) is
composed ofnerves and ganglia
Central Nervous System
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y
The spinal cord conveys information from and to the brain The spinal cord also produces reflexes independently of the brain
A reflex is the bodys automatic response to a stimulus
For example, a doctor uses a mallet to trigger a knee-jerk
reflex
Central Nervous System
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y
Invertebrates usuallyhave a ventral nerve
cord while vertebrates
have a dorsal spinal
cord
The spinal cord and
brain develop from the
embryonic nerve cord
The nerve cord givesrise to the central canal
and ventricles of the
brain
Central Nervous System
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y
Central Nervous System
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y
The central canal of the spinal cord and the ventricles ofthe brain are hollow and filled with cerebrospinal fluid
The cerebrospinal fluid is filtered from blood and
functions to cushion the brain and spinal cord as well as
to provide nutrients and remove wastes The brain and spinal cord contain
Gray matter, which consists of neuron cell bodies,
dendrites, and unmyelinated axons
White matter, which consists of bundles ofmyelinated axons
Central Nervous System
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y
Central Nervous System
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y
Glia are present throughout the vertebrate brain and spinal cord. Glia have numerous functions to nourish, support, and regulate
neurons:
i. To surround neurons and hold them in place,
ii.To supply nutrients and oxygen to neurons,
iii.To insulate one neuron from another,
iv.To destroy pathogens and remove dead neurons.
Embryonic radial glia form tracks along which newly formed
neurons migrate. Astrocytes induce cells lining capilaries in the CNS to form tight
junctions, resulting in a blood-brain barrier and restricting the entry
of most substances into the brain
Astrocytes: Enable the
neurons to obtain oxygen
and glucose more quickly.
Central Nervous System
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Ependymal cells line the
ventricles and have cilia that
promote circulation of the
cerebrospinal fluid.
Microglial: Immune
cells that protect
against pathogens.
Peripheral Nervous System
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y
The PNS transmits information to and from theCNS and regulates movement and the internal
environment
The PNS can be divided into two subdivision,
sensory (afferent) and motor (efferent)
pathways.
Afferent neurons transmit information to the
CNS and efferent neurons transmit informationaway from the CNS
Peripheral Nervous System
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Sensory divisions are nerve fibers that carryinformation from sensory receptors all over
the body to the CNS.
Sensory division keeps the CNS constantly
informed of events going on both inside and
outside the body.
Peripheral Nervous System
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The motor(efferent)division carries impulses from
the CNS to effector organs,
the muscles and the glands
that responses to the stimulussensed by the sensory division.
The motor division can be
further subdivided into two
subdivisions, the autonomicand somatic systems.
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Peripheral Nervous System
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The somatic nervous system (Motor System) primarilyallows us to control and coordinate, usually voluntarily
the skeletal muscles, so it is most involved with
physical activity.
The autonomic nervous system control eventsinvoluntarily the blood vessels, glands and internal
organs.
Peripheral Nervous System
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Autonomic nervous system is divided into two parts theparasympathetic nervous system which slows body
functions, thus conserving energy (rest and digest) and
the sympathetic nervous system which speeds body
functions, thus increasing energy use (fight-or-flight
response).
These two divisions has opposing effect, when one
stimulate, the other inhibits.
The enteric division controls activity of the digestive
tract, pancreas, and gallbladder
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Nervous system disorders
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Disorders of the nervous system includeschizophrenia, depression, drug addiction,
Alzheimers disease, and Parkinsons disease
Genetic and environmental factors contribute to
diseases of the nervous system
Schizophrenia
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About 1% of the worlds population suffers fromschizophrenia
Schizophrenia is characterized by hallucinations,
delusions, and other symptoms
Available treatments focus on brain pathways
that use dopamine as a neurotransmitter
Depression
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Two broad forms of depressive illness areknown: major depressive disorder and bipolar
disorder
In major depressive disorder, patients have a
persistent lack of interest or pleasure in most
activities
Bipolar disorderis characterized by manic
(high-mood) and depressive (low-mood) phases Treatments for these types of depression include
drugs such as Prozac
Alzheimers Disease
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Alzheimers disease is a mental deterioration
characterized by confusion and memory loss Alzheimers disease is caused by the formation of
neurofibrillary tangles and amyloid plaques in the brain
There is no cure for this disease though some drugs are
effective at relieving symptoms
Parkinsons Disease
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Parkinsons disease is a motor disordercaused by death of dopamine-secreting
neurons in the midbrain
It is characterized by muscle tremors,flexed posture, and a shuffling gait
There is no cure, although drugs and
various other approaches are used tomanage symptoms
Endocrine vs Nervous
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Both are systems of internal communication and alsoregulation
However the nature of the messages in the endocrine
system are in a form ofchemical signal whereas themessages in the nervous system are electrical signal.
The speed of message in the endocrine system is quite
slow because it needs to be transported by blood tospecific target sites whereas in the nervous system the
speed is really fast due to salutatory conduction
Endocrine vs Nervous
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Even though message can arrive really fast to targetsites in the nervous system, the duration of effect is very
short and prompt as compared to the duration of effect
in the endocrine system
The speed of response in the nervous system is rapid
whereas the speed of response in the endocrine system
is slower
The accuracy of message in the nervous system is
precise but the accuracy of message in the endocrine
system is more diffused
Endocrine vs Nervous
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THE END