Coordination and Control

14.1 Mammalian Nervous System

1. Role of the Nervous System

● Function: The nervous system coordinates and regulates body functions by transmitting
electrical impulses throughout the body.
● Components: It includes the brain, spinal cord, and nerves.

2. Overview of the Nervous System

(a) Central Nervous System (CNS):

● Components: Consists of the brain and the spinal cord.

● Function:
○ The brain is responsible for processing sensory information, coordinating
voluntary and involuntary responses, and cognitive functions such as thinking
and memory.
○ The spinal cord transmits signals between the brain and the rest of the body and
coordinates reflexes.

(b) Peripheral Nervous System (PNS):

● Components: Consists of all nerves outside the brain and spinal cord.
● Function:
○ Sensory Nerves: Carry information from sensory receptors to the CNS.
○ Motor Nerves: Transmit commands from the CNS to muscles and glands.

3. Types of Neurones

● Sensory Neurones:
○ Function: Transmit impulses from sensory receptors (e.g., skin, eyes) to the
CNS.
○ Structure: Long dendrites and short axons.
● Relay Neurones:
○ Function: Interconnect sensory neurones with motor neurones within the CNS.
○ Structure: Short axons and dendrites.
● Motor Neurones:
○ Function: Transmit impulses from the CNS to effectors (muscles or glands).
○ Structure: Long axons and short dendrites.
4. Electrical Impulses

● Nature of Impulses: Electrical impulses, also known as action potentials, travel along
neurones to transmit information.
● Mechanism: Impulses are generated by changes in the electrical potential across the
neuron's membrane, propagating along the axon.

5. Simple Reflex Arcs

● Components of Reflex Arc:

○ Receptor: Detects the stimulus (e.g., pain receptors in the skin).
○ Sensory Neurone: Carries the impulse from the receptor to the CNS.
○ Relay Neurone: Processes the impulse in the CNS and connects to the motor
neurone.
○ Motor Neurone: Carries the impulse from the CNS to the effector.
○ Effector: Executes the response (e.g., muscles contracting).
 ● Example: Touching a hot object results in a reflex action where the hand is quickly
pulled away.

6. Reflex Action

● Definition: A reflex action is a rapid, automatic response to a stimulus.

● Characteristics: It does not require conscious thought and is designed to protect the
body from harm.

7. Synapse

● Definition: A synapse is a junction between two neurones.

● Function: It allows the transfer of electrical impulses from one neurone to another,
facilitating communication within the nervous system.

8. Structure of a Synapse

● Components:
○ Synaptic Knob: Contains vesicles filled with neurotransmitter molecules.
○ Synaptic Gap (Cleft): The small space between the pre-synaptic neurone and
the post-synaptic neurone.
○ Receptor Proteins: Located on the membrane of the post-synaptic neurone;
bind with neurotransmitters to propagate the impulse.

9. Events at a Synapse

(a) Release of Neurotransmitters:

● An electrical impulse arriving at the synaptic knob stimulates the release of

neurotransmitter molecules from vesicles into the synaptic gap.

(b) Diffusion and Binding:

 ● Neurotransmitter molecules diffuse across the synaptic gap and bind with receptor
proteins on the post-synaptic neurone.

(c) Stimulation of Next Neurone:

● The binding of neurotransmitters to receptors generates a new electrical impulse in the

post-synaptic neurone, continuing the signal transmission.

10. Direction of Impulse Travel

● Unidirectional Flow:
○ Synapses ensure that electrical impulses travel in one direction only—from the
pre-synaptic neurone to the post-synaptic neurone. This prevents the backflow of
impulses and maintains the directionality of signal transmission.

14.2 Mammalian Sense Organs

1. Sense Organs
 ● Definition: Sense organs are specialized structures that contain groups of receptor cells
designed to respond to specific types of stimuli. They include the eyes, ears, skin,
tongue, and nose.
● Types of Stimuli and Receptors:
○ Light: Detected by photoreceptors in the eyes.
○ Sound: Detected by mechanoreceptors in the ears.
○ Touch: Detected by mechanoreceptors in the skin.
○ Temperature: Detected by thermoreceptors in the skin.
○ Chemicals: Detected by chemoreceptors in the nose (olfaction) and on the
tongue (taste).

2. Structures of the Eye

● Cornea: The transparent, dome-shaped front part of the eye that refracts (bends) light.
● Iris: The colored part of the eye that controls the size of the pupil and thus the amount of
light entering the eye.
● Pupil: The black opening in the center of the iris through which light enters the eye.
● Lens: A transparent, flexible structure behind the iris that focuses light onto the retina.
● Ciliary Muscles: Muscles attached to the lens that control its shape for focusing.
● Suspensory Ligaments: Fibers connecting the ciliary muscles to the lens, helping to
adjust the lens shape.
● Retina: The inner layer at the back of the eye containing photoreceptors (rods and
cones) that detect light and color.
● Fovea: The central part of the retina with the highest concentration of light receptors,
responsible for sharp, central vision.
● Optic Nerve: The nerve that carries visual information from the retina to the brain.
● Blind Spot: The area on the retina where the optic nerve exits the eye, lacking
photoreceptors and therefore insensitive to light.
3. Functions of Each Part of the Eye

(a) Cornea:

● Function: Refracts light rays entering the eye, helping to focus them onto the retina.
● Characteristics: Provides the majority of the eye’s refractive power.

(b) Iris:

● Function: Regulates the amount of light that enters the eye by adjusting the size of the
pupil.
● Mechanism: Contains circular and radial muscles that constrict or dilate the pupil.

(c) Lens:

● Function: Focuses light rays onto the retina by changing its shape, allowing for clear
vision at various distances.
● Characteristics: Works together with the cornea to focus light.

(d) Ciliary Muscles and Suspensory Ligaments:

● Function: Adjust the shape of the lens for focusing on near or distant objects.
● Mechanism: Ciliary muscles contract or relax, altering tension in the suspensory
ligaments, which changes the lens shape.
(e) Retina:

● Function: Contains photoreceptors (rods and cones) that convert light into electrical
impulses.
● Characteristics: Rods are sensitive to low light and do not detect color, while cones are
responsible for color vision and function best in bright light.

(f) Fovea:

● Function: Provides the sharpest vision due to its high density of cones.
● Characteristics: Essential for activities requiring fine detail, such as reading or
recognizing faces.

(g) Optic Nerve:

● Function: Transmits visual information from the retina to the brain, where it is processed
into an image.
● Characteristics: Composed of axons from ganglion cells in the retina.

4. Pupil Reflex

● Definition: The pupil reflex is the automatic response of the pupil to changes in light
intensity.
● Mechanism:
○ Light Intensity: In bright light, the pupil constricts to limit light entry; in dim light,
it dilates to allow more light in.
○ Antagonistic Action:
■ Circular Muscles: Contract to constrict the pupil (reduce size).
■ Radial Muscles: Contract to dilate the pupil (increase size).
○ Coordination: These muscles work in opposition to regulate the amount of light
entering the eye.

5. Accommodation

● Definition: Accommodation is the process by which the eye adjusts its focus to see
objects at different distances.
● Mechanism:
○ Viewing Distant Objects:
■ Ciliary Muscles: Relax.
■ Suspensory Ligaments: Tense.
■ Lens: Becomes thinner and less convex.
■ Light Refraction: Less bending required, lens focuses light onto the
retina from distant objects.
○ Viewing Near Objects:
■ Ciliary Muscles: Contract.
■ Suspensory Ligaments: Loosen.
 ■ Lens: Becomes thicker and more convex.
■ Light Refraction: More bending required, lens focuses light onto the
retina from near objects.

Mammalian Hormones

1. Definition of a Hormone

● Hormones are chemical substances produced by specialized glands known as

endocrine glands.
● They are released into the bloodstream and carried throughout the body.
● Hormones affect the activity of specific target organs, meaning they only impact
organs or tissues that have receptors for that specific hormone.
● Hormones can either stimulate or inhibit the functions of these organs, helping to
regulate various bodily functions such as growth, metabolism, and reproduction.

Key points:

● Hormones are produced in glands.

● They travel through the blood.
● They target specific organs and influence their activity.

2. Endocrine Glands and the Hormones They Produce

The human body has several major endocrine glands, each responsible for producing different
hormones. Here's a summary of the key endocrine glands, their locations, and the hormones
they produce:

(a) Adrenal Glands

● Location: On top of each kidney.

● Hormone produced: Adrenaline (also known as epinephrine).
● Function: Adrenaline prepares the body for 'fight or flight' responses by increasing heart
rate, blood glucose levels, and other physiological changes.

(b) Pancreas

● Location: Behind the stomach.

● Hormones produced:
○ Insulin: Lowers blood glucose levels by promoting the uptake of glucose into
cells.
○ Glucagon: Increases blood glucose levels by promoting the breakdown of
glycogen into glucose in the liver.

(c) Pituitary Gland

 ● Location: Base of the brain.
● Hormones produced:
○ Follicle-stimulating hormone (FSH): Stimulates the development of eggs in the
ovaries and sperm in the testes.
○ Luteinising hormone (LH): Triggers ovulation in females and stimulates
testosterone production in males.

(d) Testes

● Location: In the scrotum (males).

● Hormone produced: Testosterone.
● Function: Promotes the development of male secondary sexual characteristics and the
production of sperm.

(e) Ovaries

● Location: In the pelvic region (females).

● Hormones produced:
○ Oestrogen: Stimulates the development of female secondary sexual
characteristics and regulates the menstrual cycle.
○ Progesterone: Prepares the uterus for pregnancy and maintains pregnancy by
preventing uterine contractions.
3. The Role of Adrenaline
 ● Adrenaline, produced by the adrenal glands, is released in response to stress,
excitement, or danger. It is part of the body's 'fight or flight' mechanism.
● Key effects of adrenaline:
○ Increases heart rate: This allows more blood to be pumped to muscles and vital
organs, preparing the body for physical action.
○ Increases blood glucose concentration: This provides more energy (in the
form of glucose) to cells, particularly muscle cells.

Situations where adrenaline release is triggered:

● Stressful situations such as public speaking or exams.

● Dangerous situations such as being chased by a predator or facing a sudden
emergency.
● Physical exertion, like during intense exercise or sports.

These physiological changes prepare the body to either fight the threat or flee from it,
enhancing physical performance.

4. Comparison Between Nervous and Hormonal Control

There are two main ways the body controls and coordinates activities: the nervous system and
the endocrine (hormonal) system. Here's how they differ:

Aspect Nervous Control Hormonal Control

Speed of Action Very fast (milliseconds) Slower (seconds to hours)

Mode of Electrical impulses via neurons Chemical signals (hormones) via

Transmission the blood

Duration of Effect Short-lived (until the stimulus Longer-lasting effects

stops)

Target Specificity Highly specific (specific Can target multiple organs or

neurons) tissues

Homeostasis

1. Definition of Homeostasis
 ● Homeostasis is the process by which living organisms maintain a constant internal
environment, despite changes in the external environment.
● The internal environment refers to conditions such as temperature, pH, water balance,
and glucose concentration in the blood.
● Homeostasis ensures that the body’s cells can function optimally, as large fluctuations in
these internal conditions could impair enzyme activity, metabolic processes, and overall
physiological functions.

Key Points:

● Internal environment must remain constant for proper cell function.

● Homeostasis is essential for maintaining conditions like temperature and glucose levels
within narrow, optimal ranges.

Examples of internal conditions maintained by homeostasis:

● Body temperature: Remains around 37°C in humans.

● Blood glucose concentration: Usually maintained around 90 mg/dL.
● Water balance: Prevents dehydration or overhydration.
● pH levels: Maintained around pH 7.4 in blood.

2. Negative Feedback and the Concept of Control

Negative Feedback Mechanism

● Negative feedback is a regulatory mechanism in homeostasis where any deviation from

a set point (the ideal value) triggers a response that counteracts the change, bringing
the condition back to normal.
● It acts to reverse the direction of change, keeping internal conditions stable.

Set Point

● The set point is the ideal value or range for a specific physiological condition. For
example:
○ Temperature: The set point for human body temperature is around 37°C.
○ Blood glucose: The set point for blood glucose concentration is around 90
mg/dL.

When the internal environment deviates from this set point, the body uses negative feedback
to bring it back to the desired level.

How Negative Feedback Works:

1. Deviation from the set point: A stimulus causes a change in the internal environment
(e.g., an increase in body temperature or a rise in blood glucose levels).
2. Receptors detect the change: Specialized cells detect this deviation from the set point.
 3. Corrective action is triggered: An appropriate response is initiated to reverse the
change (e.g., sweating to lower body temperature or the release of insulin to lower blood
glucose).
4. Return to set point: The internal condition returns to its normal state, and the corrective
action stops.

Example of Negative Feedback: Body Temperature Regulation

● Set point: 37°C.

● If body temperature rises (e.g., during exercise):
○ Receptors in the skin and hypothalamus detect the increase in temperature.
○ Effectors (sweat glands) are activated to release sweat, which cools the body as
it evaporates.
○ As body temperature returns to the set point, sweating stops.

If body temperature drops (e.g., in a cold environment):

● Receptors detect the fall in temperature.

● Effectors (muscles) initiate shivering, which generates heat to raise the body
temperature.
● As the temperature returns to normal, shivering stops.

Example of Negative Feedback: Blood Glucose Regulation

● Set point: 90 mg/dL.

● If blood glucose levels rise after eating:
○ Receptors in the pancreas detect the increase in glucose levels.
○ The pancreas releases insulin, which promotes the uptake of glucose by cells
and the conversion of excess glucose into glycogen in the liver.
○ As glucose levels fall back to the set point, insulin secretion decreases.

If blood glucose levels drop:

● Receptors detect the low glucose concentration.

● The pancreas releases glucagon, which stimulates the conversion of glycogen back
into glucose in the liver.
● As glucose levels rise to the set point, glucagon secretion decreases.

Temperature Control

1. Structure of the Skin

The skin plays a crucial role in regulating body temperature. Below are the key structures
involved in this process:

● Hairs: Trap a layer of air close to the skin, providing insulation.

 ● Hair erector muscles: Contract to raise hairs, trapping more air to retain heat, or relax
to lower hairs, allowing heat loss.
● Sweat glands: Produce sweat, which evaporates to cool the body.
● Receptors: Detect changes in temperature and send signals to the brain.
● Sensory neurones: Transmit information about temperature changes from the
receptors to the brain.
● Blood vessels (arterioles and capillaries): Carry blood to and from the skin, and can
constrict or dilate to regulate heat loss.
● Fatty tissue: Provides insulation and reduces heat loss by trapping heat inside the
body.

Diagram of the Skin

● You should be able to identify the following structures on a diagram:

○ Hairs
○ Hair erector muscles
○ Sweat glands
○ Receptors
○ Sensory neurones
○ Blood vessels
○ Fatty tissue (adipose tissue)

2. Role of Insulation in Temperature Control

● Insulation helps maintain a constant internal body temperature by reducing the loss
of heat from the body.
● In mammals, insulation comes from fatty tissue under the skin and hair or fur on the
body’s surface.
● Fatty tissue provides a layer that reduces the loss of heat by conduction and radiation.
● Hair or fur traps a layer of air close to the skin, which acts as an insulating layer to
reduce heat loss.

3. Role of the Hypothalamus and Skin Receptors

● The hypothalamus in the brain is the control center for regulating body temperature. It
maintains a constant internal temperature by receiving information from temperature
receptors and then triggering appropriate responses.
● Temperature receptors in the skin detect external temperature changes. They send
signals to the hypothalamus about the body’s external environment (whether it’s too hot
or too cold).
● The hypothalamus also monitors the internal body temperature by detecting the
temperature of the blood.

If the body’s temperature deviates from the normal range, the hypothalamus triggers
corrective mechanisms (like sweating or shivering) to bring it back to normal.
4. Processes Involved in Maintaining Constant Internal Temperature

(a) Sweating

● When the body temperature rises, the sweat glands in the skin produce sweat.
● As sweat evaporates from the skin surface, it cools the body by removing heat.
● This process is essential for preventing overheating in hot environments or during
exercise.

(b) Shivering

● When the body temperature falls below normal, the muscles contract rapidly in a
process called shivering.
● This muscle activity generates heat to help raise the body’s temperature.
● Shivering is a short-term mechanism to prevent the body from becoming too cold.

(c) Contraction of Hair Erector Muscles

● In cold conditions, the hair erector muscles contract, causing the hairs on the skin to
stand upright.
● This traps a layer of warm air close to the skin, providing insulation and reducing heat
loss.
● In hot conditions, the hair erector muscles relax, allowing the hairs to lie flat, so less air
is trapped, and heat is lost more easily.

(d) Vasodilation and Vasoconstriction

● Vasodilation: When the body is too hot, the arterioles leading to the skin surface dilate
(widen), allowing more blood to flow close to the skin’s surface. This enables more heat
to be lost by radiation, cooling the body.
● Vasoconstriction: When the body is too cold, the arterioles constrict (narrow),
reducing blood flow to the skin surface. This reduces heat loss and helps conserve heat.

O Level Biology 5090 – Blood Glucose Control

1. The Need to Control Blood Glucose Concentration

● Blood glucose levels must be regulated to ensure that cells have a constant supply of
glucose for respiration, which is essential for producing energy.
● If blood glucose levels are too high, it can damage cells and tissues, leading to
conditions like diabetes.
● If blood glucose levels are too low, cells, especially those in the brain, will not get
enough energy, leading to fainting, confusion, or even death.
Maintaining blood glucose levels within a narrow range ensures that the body has enough
energy while preventing damage to cells and organs.

2. Control of Blood Glucose Concentration by the Liver and Pancreas

● The pancreas and liver work together to regulate blood glucose concentration through
the hormones insulin and glucagon.

Role of Insulin

● Insulin is produced by the beta cells of the pancreas when blood glucose levels are high
(e.g., after eating).
● Insulin promotes:
○ The uptake of glucose by cells, especially in muscles and the liver.
○ The conversion of glucose into glycogen (storage form) in the liver, reducing
blood glucose levels.

Role of Glucagon

● Glucagon is produced by the alpha cells of the pancreas when blood glucose levels are
too low.
● Glucagon promotes:
○ The breakdown of glycogen into glucose in the liver.
○ The release of glucose into the bloodstream, increasing blood glucose levels.

The combined action of insulin and glucagon ensures that blood glucose levels remain within
a narrow, optimal range.

3. Signs of Type 1 Diabetes and Its Treatment

Signs of Type 1 Diabetes

● Type 1 diabetes occurs when the pancreas produces little or no insulin, resulting in
high blood glucose concentrations.
● Key signs:
○ Increased blood glucose concentration.
○ Presence of glucose in urine (since the kidneys cannot reabsorb the excess
glucose from the blood).

Treatment of Type 1 Diabetes

● Administration of insulin: People with Type 1 diabetes need regular injections of

insulin to control their blood glucose levels.
● Insulin allows cells to take in glucose from the blood and helps regulate the blood
glucose concentration, preventing damage to cells and tissues.