NERVOUS SYSTEM AND THE ENDOCRINE SYSTEM

Endocrine System
Introduction

 A system of glands and chemicals called hormones which is produced by the glands is known as
the endocrine system.
 A gland is an organ that produces hormones.
 Hormones are chemical messengers.
 The hormones released by the glands travel in the bloodstream.

Hormonal Control

 Hormones use chemical signals to transmit information.

 They transmit information through the bloodstream.
 The effectors are target cells in particular tissues.
 The speed of response is slow.
 The duration of response is long.
 The response ends when the hormone breaks down completely.

Different Glands and their function

Gland Hormone Location Function

Thyroid Thyroxine Neck Regulates Metabolism
Pituitary Many glands which Brain Regulates gland
control other glands function
Adrenal Adrenaline On top of kidneys Regulates flight or fight
reaction
Pineal Melatonin Brain Controls the sleep
cycle.
Testes Testosterone Testes Male characteristics
Ovaries Estrogen, Progesterone Ovaries Female Characteristics
and maintains
pregnancy
Pancreas Insulin, Glucagon Pancreas Insulin reduces sugar,
glucagon increases
sugar

Homeostasis

 Homeostasis is the tendency of an organism to maintain a stable internal state.

 Hypothalamus is a region of the brain producing hormones
 The hormones released by hypothalamus controls heart rate, hunger and mood.
 To do so, hypothalamus receives impulses from thermoreceptors in the skin on surface
temperatures.
 The thermoreceptors in hypothalamus are sensitive to blood temperature.
 The hypothalamus responds to the information by sending nerve impulses to the effectors, such
as the skin.
 This returns the body temperature back to normal.
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Negative Feedback

 A negative feedback mechanism is a type of control that is used in homeostasis.

 It responds when conditions change from the ideal or set point and returns the conditions back
to set point.
 The events in a negative feedback take place in a continuous cycle of events.

General Stages in a negative feedback

 If the level of something rises, the control system reduces the level.
 If the level of something falls, the control system increases the level.
 Conditions in a system change from the set point.
 The change is detected.
 Corrective mechanisms in the control system are activated.
 Conditions are returned to the set point.
 The corrective mechanisms are turned off.
 The cycle then continues.

Example 1 – Body Temperature

 If the body gets too hot, it begins to sweat to reduce the body temperature.
 If the body gets too cold, it shivers to increase the body temperature.

Example 2 – Blood Sugar Levels

 We have consumed sugary food.

 High blood sugar is detected.
 Beta cells in the pancreas release insulin.
 Glucose is taken in by the cells or stored as glycogen.
 This decreases the blood sugar levels and brings it back to normal.
 Over-time, we have not exercised or have not consumed enough food.
 This leads to a detection of low blood sugar.
 Glucagon is released by alpha cells in the pancreas.
 Glycogen is converted to glucose in the liver and is released back into the bloodstream.

Example 3 – Thyroxine Levels

 Low thyroxine levels are detected.

 Hypothalamus releases TRH (Thyrotropin-releasing hormone).
 The TRH signals the pituitary gland to release TSH (Thyroid-stimulating hormone).
 The thyroid then releases thyroxine.
 This brings thyroxine levels back to normal.
 Over-time, the thyroxine levels have increased.
 This leads to the detection of high thyroxine levels.
 The anterior pituitary restrains the release of TRH.
 This restricts the release of TSH from the pituitary.
 The release of thyroxine has stopped.
 This brings the thyroxine levels back to the optimal level.
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Flight or Fight Response

 The flight or fight response is an automatic physiological reaction.

 This is triggered to a certain event that is thought to be stressful.
 The perception of threat triggers the sympathetic nervous system.
 This system triggers an acute stress response, which prepares the body to fight or flee.
 The hormones released during this response is adrenaline and noradrenaline.
 These hormones are controlled through negative feedback.
 Cortisol and catecholamine are chemicals energizing our fight or flight response.
 When cortisol levels in the blood are high, the sensory-receptors in the brain trigger a shutting-
off response.
 The fight or flight response is useful in reacting quickly to life-threatening situations.
 If this response is frequent, it is not useful because it can cause physical and mental health
issues.

Nervous System
Introduction

 An electrical wiring that coordinates and controls all of the functions in our body is known as the
nervous system.
 It is used to detect changes in the environment, scientifically known as stimuli, by receptors.
 There are two types of nervous systems, central nervous system (CNS), and peripheral nervous
system (PNS).

Central Nervous System

 It is made up of the brain and the spinal cord.

 The brain is the control centre of our body.
 It receives and analyses information from the senses. Our actions and reactions are controlled
by the brain.
 The spinal cord relays information from the base of the brain to the lower back.
 It is made up of nerves.

Peripheral Nervous System

 It is a system of nerves from the spinal cord to the rest of the body.
 The somatic nervous system controls voluntary muscles.
 The autonomic nervous system controls internal organs and glands.

Neurons

 Neurons are nerve cells that are adapted to carry impulses from one place to another.
 A bundle of neurons is called a nerve.
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Structure of a Neuron

 Dendrites transfer the received information to the soma, or the cell body of the neuron. They
receive data or signals from another neuron.
 The axon acts as cables to send signals over long distances. The axons are covered by myelin
sheath, a sheath which is fatty and insulates the axons. They are long so that they can carry
messages up and down the body.
 The cell body controls and processes all of the functions of the neurons.

Three different Neurons

 Sensory Neurons
 Motor Neurons
 Relay Neurons

Sensory Neurons

 Consist of a cell body, nucleus, dendrites and an axon.

 They have long dendrites but a short axon.
 Action potentials are involved in signal transmissions.
 The sensory neurons send impulses to the CNS.
 Involved with the PNS.
 Myelin Sheath is present.
 Fast Impulse Transmission.
 Long in size.
 One end attached to a receptor.

Motor Neurons

 They also consist of a cell body, nucleus, dendrites and an axon.

 NERVOUS SYSTEM AND THE ENDOCRINE SYSTEM
 They have short dendrites and a long axon.
 Action potentials are also involved in signal transmission.
 They send impulses from the CNS to the effector.
 Involved with the PNS.
 Myelin Sheath is present.
 Fast Impulse Transmission.
 Long in Size.
 One end attached to effector. This could be a gland or a muscle.

Relay Neurons

 They are involved in the CNS.

 Myelin Sheath is absent.
 Slow impulse transmission.
 They are short in size.
 Both of the sends connect to other neurons.

Reflex Arc

 The reflex arc is the pathway that an impulse travel from the receptor to an effector in order to
respond to a stimulus.
 A reflex is an automatic response to a stimulus.
 The receptor identifies the stimulus.
 It then goes to the sensory neuron which picks up the impulse from the receptor in the PNS.
 The relay neuron passes the impulse to the brain and motor neuron in the CNS.
 The motor neuron passes the impulse to the effector in the PNS.
 The effector is the gland or muscle where the action is done.

Synapses

 Synapses are spaces between neurons.

 The impulse first arrives at the terminal button in the presynaptic neuron.
 This causes vesicles containing neurotransmitters, which are chemical messengers, to empty
into the synapse.
 Neurotransmitters are picked up in the postsynaptic neuron.
 The impulse continues in the postsynaptic neuron.

Nervous System Vs Endocrine System

Characteristic Nervous System Endocrine System
Made up of? Brain, Spinal Cord, Neurons, Hormones and Glands
Nerve, Receptors, Effectors
How is message transmitted Stimulus is detected by the The signal is detected by the
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receptors. They then transfer hypothalamus, which signals
the signal to the relay neurons the pituitary gland to release
and then to the motor neurons the respective hormone. This
through synapses. The motor hormone signals the respective
neuron then transfers the gland to release their hormone.
information to the effectors. This is done through chemical
impulses.
Speed of Response Fast Slow
Duration of Effect Few Minutes to Few Hours Longer effects
Type of Control Autonomous control Feedback Loop

How do methods of transfer differ?

 The nervous system uses electrical impulses to transfer messages.

 The endocrine system uses hormones as chemical transporters to transfer signals.
 The impulses in the nervous system travel through synapses from neurons to neurons.
 The chemicals in the endocrine system travel through the bloodstream to the respective organ.

Why is the response time of nervous system much faster than the endocrine system?

 The signal transmission in the nervous system is quick because the neurons are close to each
other.
 They travel through synapses.
 The myelin sheath in the neurons are wrapped along the axon in a loop which increases the
speed of the electrical impulse.
 On the other end, the endocrine system relies on slow blood circulation to transfer chemical
signals, and is therefore slow.

When will the body require nervous system and not the endocrine system?

 The body may use the nervous system for quick automatic responses to a stimulus.
 They would need a reflex action to save life.
 An example is touching a hot plate.
 If the endocrine system is used, our hand would burn because the endocrine system is slow.

When will the body require the endocrine system and not the nervous system?

 The body may use the endocrine system in internal regulation.

 This is because the endocrine system uses chemical coordination.
 This chemical coordination covers a large part of the body.
 The effects also last longer than the nervous system.
 An example is insulin production, which needs to last longer so as to sustain life.

Glands

 A gland is an organ that produces hormones for a specific function in the body.
 An example of a gland is ovaries.
 Ovaries produces Estrogen and Progesterone.
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 This hormone is only in females and it maintains pregnancy.

How do the nervous and endocrine system work together?

 An example of the nervous and endocrine system working together is the fight or flight
response.
 The brain detects a stressful situation, usually detected by the amygdala.
 The hypothalamus then activates the sympathetic nervous system.
 They do this by sending signals through the autonomic nerves to the adrenal glands.
 These glands produce the hormone adrenaline into the bloodstream.
 The heart then beats faster than normal.
 The breathing rate also increases.
 To supply energy to all parts of the body immediately, adrenaline instructs temporary storage
sites to release glucose in the body.