JAMB Biology Note- Co-ordination and control

Topics:

a. Nervous coordination:
i. the components, structure and functions of the central nervous system;
ii. The components and functions of the peripheral nervous systems;
iii. Mechanism of transmission of impulses;
iv. Reflex action
b. The sense organs
i. skin (tactile)
ii. nose (olfactory)
iii. tongue (taste)
iv. eye (sight)
v. ear (auditory)
c. Hormonal control
i. animal hormonal system
– Pituitary
– thyroid
– parathyroid
– adrenal gland
– pancreas
– gonads
ii. Plant hormones (phytohormones)
d. Homeostasis
i. Body temperature regulation
ii. Salt and water regulation

Table of Contents

• Topics:
  • A. Nervous Coordination
    • 1. The Central Nervous System (CNS)
    • 2. The Peripheral Nervous System (PNS)
    • 3. Mechanism of Transmission of Impulses
    • 4. Reflex Action
  • B. Reflex vs Voluntary Actions
    • C. Conditioned Reflexes
  • Additional Information on the Brain
  • Summary
  • C. The Sense Organs
    • i. Skin (Tactile)
    • ii. Nose (Olfactory)
    • iii. Tongue (Taste)
    • iv. Eye (Sight)
    • v. Ear (Auditory)
  • D. Hormonal Control
    • i. Animal Hormonal System
    • ii. Plant Hormones (Phytohormones)
  • Summary
  • E. Homeostasis
    • i. Body Temperature Regulation
    • ii. Salt and Water Regulation
  • Summary
  • Conclusion

A. Nervous Coordination

Nervous coordination involves the transmission of signals through the nervous system, allowing organisms to respond to stimuli and maintain homeostasis. This process involves the central and peripheral nervous systems.

1. The Central Nervous System (CNS)

• Components:
  • The brain and spinal cord.
• Structure:
  • Brain: The brain is the control center for the entire body and is divided into three main parts:
    • Cerebrum: The largest part of the brain, responsible for higher functions such as reasoning, emotions, memory, and voluntary muscle movements. It is divided into two hemispheres (left and right), each responsible for different functions, such as language (left) and spatial awareness (right).
    • Cerebellum: Located under the cerebrum, it controls balance, coordination, and fine motor skills. It is involved in maintaining posture and motor learning.
    • Medulla Oblongata: The brainstem connects the brain to the spinal cord and controls vital functions such as breathing, heart rate, and digestion.
  • Spinal Cord: A long, cylindrical structure that extends from the brainstem. It connects the brain to the peripheral nervous system and acts as a pathway for messages between the brain and the body.
• Functions:
  • Integration and processing of information: The brain integrates sensory inputs and produces responses. It is responsible for consciousness, thought processes, emotions, and memories.
  • Control of body functions: The brain controls essential bodily functions such as breathing, heartbeat, blood pressure, and digestion. The medulla oblongata controls autonomic functions such as heartbeat and respiration.
  • Coordination: Coordinates voluntary and involuntary actions through both the central nervous system and the peripheral nervous system.

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2. The Peripheral Nervous System (PNS)

• Components:
  • Sensory Neurons: Transmit sensory information from receptors (e.g., skin, eyes) to the CNS.
  • Motor Neurons: Carry signals from the CNS to muscles and glands to provoke a response.
• Functions:
  • Sensory function: Carries information from sensory organs (eyes, ears, skin, etc.) to the CNS.
  • Motor function: Transmits commands from the CNS to muscles and glands, causing movement or secretion.

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3. Mechanism of Transmission of Impulses

• Neurons: The basic units of the nervous system, responsible for transmitting electrical impulses.
  • Structure: Neurons consist of the cell body, dendrites (receive signals), and an axon (transmits signals).
• Transmission:
  • An impulse travels along the axon to the axon terminals, where it triggers the release of neurotransmitters.
  • Neurotransmitters cross the synapse (the gap between two neurons) and bind to receptors on the next neuron, continuing the transmission.
  • The transmission is both electrical (along the axon) and chemical (across the synapse).

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4. Reflex Action

• Definition: A reflex action is an automatic, rapid response to a stimulus that does not involve the conscious brain. Reflex actions help protect the body from harm.
• Example:
  • Blinking of the eyes when something approaches the face.
  • Knee jerk reflex when the patella is tapped.
• Process of Reflex Action:
  1. A sensory receptor detects a stimulus (e.g., touching something hot).
  2. The sensory neuron carries the impulse to the spinal cord.
  3. The spinal cord processes the information and sends a signal through the motor neuron to the muscle.
  4. The muscle contracts to remove the body part from the harmful stimulus.
• Reflexes are often faster than voluntary actions because they involve only the spinal cord, bypassing the brain.

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B. Reflex vs Voluntary Actions

• Reflex Actions:
  • Involuntary: Occur automatically without conscious thought.
  • Rapid: Fast response to protect the body.
  • Example: Blinking when something approaches the eyes, knee jerk.
• Voluntary Actions:
  • Controlled by the brain: Involve conscious thought and decision-making.
  • Slower than reflex actions: Because they involve processing by the brain.
  • Example: Writing, playing a musical instrument, speaking.

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C. Conditioned Reflexes

Conditioned reflexes are learned responses to stimuli based on experience or association.

• Example 1: Salivation: A person salivates when they smell food even if they have not seen it.
• Example 2: Riding a Bicycle: Once learned, the action of riding becomes a reflex action.
• Example 3: Swimming: After practice, swimming becomes almost automatic.

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Additional Information on the Brain

The brain is the most complex and vital organ of the nervous system. It is divided into several key regions, each responsible for different functions:

• Cerebrum: The largest part of the brain, responsible for thinking, decision-making, memory, and voluntary movement. It is divided into two hemispheres.
• Thalamus: Acts as a relay station, processing sensory and motor signals before sending them to the appropriate areas of the brain.
• Hypothalamus: Controls basic bodily functions such as hunger, thirst, temperature regulation, and hormone release. It maintains homeostasis in the body.
• Medulla Oblongata: Located at the base of the brain, it controls vital involuntary functions, such as heart rate, blood pressure, and breathing.
• Cerebellum: Controls balance, posture, and coordination. It fine-tunes movements and helps in motor learning.

The brainstem (which includes the medulla, pons, and midbrain) connects the brain to the spinal cord and manages critical functions such as respiration and heartbeat. It is also involved in reflex actions.

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Summary

• Central Nervous System (CNS) consists of the brain and spinal cord and is responsible for integrating and processing information.
• Peripheral Nervous System (PNS) includes sensory and motor neurons that transmit impulses between the CNS and the body.
• The transmission of impulses is both electrical and chemical and occurs through neurons and synapses.
• Reflex actions are automatic, involuntary responses to stimuli, providing rapid protection.
• Voluntary actions are conscious, slower actions controlled by the brain.
• Conditioned reflexes are learned behaviors that become automatic after repeated association with a stimulus.
• The brain plays a crucial role in regulating body functions and coordinating responses.

C. The Sense Organs

Sense organs are specialized organs that detect changes in the environment and transmit signals to the brain, where they are processed to form a perception.

i. Skin (Tactile)

• Structure: The skin contains receptors that detect pressure, temperature, and pain. These receptors are found in the dermis and epidermis layers.
• Function: The skin acts as the tactile sense organ, detecting stimuli such as heat, cold, pressure, and pain, which is transmitted to the brain via sensory neurons.
• Defects and Correction: Common skin defects include hypoesthesia (reduced sensation) and anesthesia (loss of sensation), which may be caused by nerve damage. Correction can involve medical treatment or therapy to restore nerve function.

ii. Nose (Olfactory)

• Structure: The nose contains olfactory receptors located in the olfactory epithelium inside the nasal cavity. These receptors detect odor molecules.
• Function: The nose detects smells (odorants) and sends signals to the olfactory bulb in the brain, which processes the information and helps identify odors.
• Defects and Correction: Anosmia (loss of smell) is a condition where a person cannot detect odors. This may be caused by injury or illness affecting the olfactory nerves. It can be corrected through treatment based on the underlying cause.

iii. Tongue (Taste)

• Structure: The tongue is covered with taste buds, located on papillae, which contain sensory cells for taste.
• Function: The tongue detects five basic tastes: sweet, salty, sour, bitter, and umami. The signals are sent to the gustatory cortex in the brain for processing.
• Defects and Correction: Ageusia (loss of taste) can occur due to nerve damage or illness. It can be corrected if the cause is treatable (e.g., infection or nerve damage repair).

iv. Eye (Sight)

• Structure: The eye consists of various components such as the cornea, lens, retina, and optic nerve. The retina contains photoreceptor cells (rods and cones) that detect light and color.
• Function: The eye detects light and images, focusing them onto the retina, where photoreceptor cells send visual signals to the visual cortex in the brain.
• Defects and Correction: Common defects include myopia (nearsightedness), hyperopia (farsightedness), astigmatism, and color blindness. Correction can be done through glasses, contact lenses, or surgery (e.g., LASIK).

v. Ear (Auditory)

• Structure: The ear consists of the outer ear (pinna), middle ear (ossicles), and inner ear (cochlea). The cochlea contains hair cells that detect sound vibrations.
• Function: The ear detects sound waves, which are converted into electrical signals by the hair cells in the cochlea and transmitted to the auditory cortex in the brain.
• Defects and Correction: Common defects include hearing loss, caused by damage to the ear structures or auditory nerve. It can be corrected with hearing aids or cochlear implants, depending on the severity of the defect.

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D. Hormonal Control

Hormonal control involves the release of hormones from endocrine glands that regulate body functions such as growth, metabolism, and reproduction.

i. Animal Hormonal System

The endocrine glands secrete hormones that act as chemical messengers in the body. These hormones regulate various physiological processes.

• Pituitary Gland:
  • Located at the base of the brain.
  • Known as the “master gland” because it controls other endocrine glands.
  • Produces hormones such as growth hormone (GH), thyroid-stimulating hormone (TSH), and adrenocorticotropic hormone (ACTH).
• Thyroid Gland:
  • Located in the neck.
  • Produces thyroxine and triiodothyronine, which regulate metabolism, growth, and development.
• Parathyroid Gland:
  • Located behind the thyroid.
  • Produces parathyroid hormone (PTH), which regulates calcium and phosphate levels in the blood.
• Adrenal Glands:
  • Located on top of the kidneys.
  • Produce hormones such as adrenaline (epinephrine), which prepare the body for fight-or-flight responses, and cortisol, which regulates stress and metabolism.
• Pancreas:
  • Located behind the stomach.
  • Produces insulin and glucagon, which regulate blood glucose levels.
• Gonads (Ovaries and Testes):
  • Ovaries produce estrogen and progesterone, which regulate female reproductive functions.
  • Testes produce testosterone, which regulates male reproductive functions and secondary sexual characteristics.

ii. Plant Hormones (Phytohormones)

Plant hormones, also known as phytohormones, regulate plant growth, development, and responses to environmental stimuli.

• Auxins:
  • Promote cell elongation, root growth, and tropic responses such as phototropism (growth towards light) and gravitropism (growth in response to gravity).
  • They also play a role in apical dominance, the inhibition of lateral bud growth by the apical bud.
• Gibberellins:
  • Promote stem elongation, seed germination, and flowering.
  • Used in agriculture to improve crop yields by promoting growth.
• Cytokinins:
  • Stimulate cell division and growth, especially in roots and shoots.
  • Promote the lateral branching of plants and delay leaf senescence (aging).
• Ethylene:
  • Regulates fruit ripening and leaf abscission (shedding).
  • Used commercially to ripen fruits like bananas and tomatoes.

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Summary

• The sense organs are specialized for detecting stimuli and sending signals to the brain for processing.
• The skin, nose, tongue, eyes, and ears each have unique functions for detecting environmental changes and protecting the body.
• The endocrine system regulates body functions through hormones secreted by various glands, including the pituitary, thyroid, adrenal glands, pancreas, and gonads.
• Phytohormones in plants regulate growth, development, and responses to stimuli, affecting processes like germination, flowering, and fruit ripening.

E. Homeostasis

Homeostasis refers to the process by which the body maintains a stable internal environment, despite changes in external conditions. It involves the regulation of factors like temperature, pH, glucose concentration, and the balance of water and salts.

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i. Body Temperature Regulation

The body must maintain a constant internal temperature for enzymes and biochemical reactions to function optimally. In humans, the normal body temperature is approximately 37°C (98.6°F). Deviations from this temperature can lead to harmful effects, so mechanisms have evolved to regulate it.

Mechanisms of Temperature Regulation:

• Thermoregulatory Center (Hypothalamus):
  The hypothalamus in the brain acts as the body’s thermostat. It monitors blood temperature and compares it to a set point (around 37°C). If the body’s temperature deviates from this point, the hypothalamus triggers appropriate responses.
• When the body is too hot:
  • Vasodilation: Blood vessels near the skin surface dilate, allowing more blood to flow near the skin, increasing heat loss.
  • Sweating: Sweat glands secrete sweat, which evaporates, cooling the skin.
  • Increased Respiration: Breathing rate increases to help release heat.
• When the body is too cold:
  • Vasoconstriction: Blood vessels near the skin surface constrict to reduce heat loss.
  • Shivering: Muscles rapidly contract to generate heat.
  • Reduced Sweating: Less sweat is produced to conserve heat.
  • Behavioral Responses: Seeking shelter, wearing warm clothing, or curling up to conserve body heat.

Hormonal Control in Temperature Regulation:

• The hormone thyroxine produced by the thyroid gland plays a role in regulating the metabolic rate, which impacts heat production. More thyroxine can increase metabolism and generate heat, especially in response to cold environments.

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ii. Salt and Water Regulation

The body must maintain a balanced concentration of water and salts (electrolytes) to ensure proper cell function and homeostasis. This balance is crucial for maintaining blood pressure, nerve function, and the overall fluid balance in cells.

Mechanisms of Salt and Water Regulation:

• Kidneys:
  The kidneys play a central role in regulating salt and water balance. They filter the blood and adjust the levels of water and salts in urine to maintain homeostasis. The amount of water reabsorbed by the kidneys can vary depending on the body’s needs.
• Antidiuretic Hormone (ADH):
  • Produced by the pituitary gland, ADH regulates water reabsorption in the kidneys.
  • When the body is dehydrated, the hypothalamus signals the release of ADH, which prompts the kidneys to conserve water by reabsorbing more from the urine.
  • When there is excess water, less ADH is released, and the kidneys excrete more water in the urine.
• Aldosterone:
  • Produced by the adrenal glands, aldosterone helps regulate salt balance by promoting the reabsorption of sodium ions in the kidneys. This reabsorption causes water to follow by osmosis, which helps maintain blood volume and pressure.
• Renin-Angiotensin System:
  • When blood pressure drops or there is a decrease in sodium concentration, the renin-angiotensin system is activated. Renin, released by the kidneys, converts angiotensinogen into angiotensin II, a hormone that constricts blood vessels and stimulates aldosterone release to help raise blood pressure and conserve water.

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Summary

• Body Temperature Regulation: The body maintains temperature homeostasis through mechanisms such as vasodilation, sweating, shivering, and hormonal control via thyroxine. The hypothalamus plays a crucial role in detecting temperature changes and initiating corrective actions.
• Salt and Water Regulation: The kidneys regulate the balance of water and salts. Hormones like ADH, aldosterone, and the renin-angiotensin system help maintain proper hydration levels and blood pressure by controlling water reabsorption and salt balance.

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Conclusion

Homeostasis is essential for maintaining the internal stability of the body, ensuring that physiological processes operate efficiently. The regulation of body temperature and the balance of salts and water are two crucial aspects of homeostasis, which are controlled by various organs and hormones to maintain health.