CONTROL AND CO-ORDINATION

Nervous System

• Acts as the control center of the body in animals, including humans.
• Comprises neurons, nerves, and neural organs to link, coordinate, and control body activities.
• Receptors in sensory organs detect environmental information (e.g., taste via gustatory receptors in the tongue, smell via olfactory receptors in the nose).

Neuron or Nerve Cell

• Structural and functional unit of the nervous system.
• Nervous tissue consists of a network of neurons.
• Neurons are the longest cells in the human body (up to 90-100 cm).
• Specialized for transmitting information through electrical impulses.
• Detect information via the tips of nerve cells.

Structure of Neuron

• Dendrites: Protoplasmic projections that receive and transmit impulses.
• Cell Body (Cyton): Contains the nucleus, cytoplasm, and organelles.
• Axon: Long processes carrying impulses away from the cell body, often covered by a myelin sheath.
• Nerve Endings: Branch-like termination points.

Types of Neurons

• Sensory Neurons: Carry impulses from receptors to the brain or spinal cord.
• Motor Neurons: Carry impulses from the central nervous system to muscles or glands.
• Interneurons : Also known as relay neurons, they connect sensory neurons to motor neurons and are located in the brain and spinal cord.

Synapse

• A small gap between two adjacent neurons where impulses pass in one direction.

Transmission of a Nerve Impulse

• A nerve impulse is an electric signal similar to an electric current.

Pathway:

• Detected by receptors in sense organs and transferred to sensory neurons.
  • Information at dendrites causes a chemical reaction, producing an electrical impulse.
  • Impulse travels from dendrites to the cell body and along the axon.
  • At the axon end, neurotransmitters are released.
  • Neurotransmitters cross the synapse, triggering a similar impulse in the next neuron.
  • This process continues to muscles or glands (effectors).
• Neuromuscular Junction
• The connection point between a motor neuron and muscle fiber, allowing nerve impulses to stimulate muscle contraction.

Limitations of Electrical Impulse

• Only reaches cells connected by nervous tissue.
• Cells take time to reset before generating a new impulse.

Reflex Action

• An automatic, rapid response to stimuli (e.g., coughing, sneezing, blinking).
• Protects the body and doesn’t involve conscious thought.
• Message passes straight to the motor neuron via a relay neuron.
• Reflex actions are primarily controlled through the spinal cord, allowing quick response without involving the brain.

Reflex Arc

Definition: The pathway taken by nerve impulses in a reflex action is called a reflex arc

Reflex Arc

• Sense Organs: Receive the stimulus.
• Sensory Neuron: Conveys the stimulus to the spinal cord.
• Spinal Cord: Interprets the stimulus and sends commands to motor neurons.
• Motor Neuron: Conveys the command to effectors.
• Effectors/Muscles: Execute the response.

Importance:

• Provides immediate response to harmful stimuli. Reduces brain overload.

• Increases survival chances.

Divisions of Nervous System

The nervous system comprises two main parts:

• Central Nervous System (CNS): Includes the brain and spinal cord.
• Peripheral Nervous System (PNS).

Central Nervous System (CNS)

• Function: Acts as the center of control and coordination for all body activities.
• Components: Comprises the brain and spinal cord.
• Role: Receives and integrates information from all parts of the body.

Human Brain

• Role: Serves as the main coordinating center of the body, enabling thought and decision-making.
• Function: Interprets information from sense organs and sends instructions to muscles or other effectors.
• Complexity: Involves complex mechanisms and neural connections for processing information.

Human Brain Regions

Forebrain

Forebrain is comprised of Cerebrum, Olfactory lobes and Hypothalamus.

Cerebrum

Main thinking part, responsible for reasoning, speech, and intelligence.

Cerebrum consists of three functional areas.

• Sensory Areas: Receive sensory impulses.
• Association Areas: Interpret sensory information.
• Motor Areas: Control voluntary muscles.

Olfactory Lobes

• Description: Small, solid, club-shaped bodies that are widely separated.
• Function: Responsible for detecting smells from different receptors.
• Hypothalamus
• Function: Controls body temperature, and regulates the urge to eat and drink.

Midbrain

• Connects forebrain to hindbrain.

• Controls head, neck, and trunk movements.

• Involves in focusing and reflex movements of eyes.

Hindbrain

The parts of Hindbrain are Cerebellum, Pons and Medulla Oblongata.

• Cerebellum
  • Function: Controls and coordinates muscular actions.
  • Role: Maintains posture and equilibrium during activities like walking and riding a bicycle.
• Pons
  • Location: Above the medulla.
  • Function: Takes part in respiration and relays impulses within the brain.
• Medulla Oblongata
  • Location: Lowest part of the brain, continuing with the spinal cord.
  • Function: Controls involuntary actions such as breathing, blood pressure, salivation, and vomiting.

Functions of the Human Brain

• Coordination: Manages body activities and hormonal reactions to ensure they work together.
• Information Reception: Receives nerve impulses from all sensory organs.
• Stimulus Correlation: Processes stimuli from different senses to produce appropriate responses.
• Response to Impulses: Sends instructions to muscles and glands based on sensory input, enabling proper function.
• Information Storage: Stores information to modify behavior based on past experiences.

Spinal Cord

• Long bundle of nervous tissue.
• Controls reflex actions and transmits neural signals.

Brain Protection:

• Encased in a bony box called the cranium.

• Surrounded by a fluid-filled balloon for shock absorption.

Spinal Cord Protection:

• Protected by the vertebral column or backbone, which is a hard, bumpy structure at the back.

Mechanism of Nervous Tissue Action

• Nervous tissue receives information.
• Brain processes and makes decisions.
• Instructions conveyed to muscles.
• Proteins in muscles change shape, causing movement.

Peripheral Nervous System (PNS)

The Peripheral Nervous System facilitates communication between the central nervous system and the rest of the body. It includes:

• Cranial Nerves:
  • Emerge from the brain.
  • Spread throughout the head.
• Spinal Nerves:
  • Arise from the spinal cord.
  • Spread throughout the body, except the head.
• Visceral Nerves:
  • Special nerves arising mostly from the spinal cord.
  • Connect to internal organs of the body.

• Coordination in Plants

Plants don’t have a nervous system or muscles like animals, but they still respond to stimuli. Plant movements are classified into:

1. Immediate Response to Stimulus:
   1. These responses do not involve growth.
   1. Example: Leaves of the chui-mui (touch-me-not) plant fold when touched.
   1. Movement occurs at a different point from the touch.
   1. Plants use electrochemical means to convey information cell to cell, without specialized tissues like in animals.

• Plant Cell Response to Stimulus:

• Mechanism: Plant cells change shape by altering water content, causing swelling or shrinking.
• Example: The sensitive plant (Mimosa pudica) folds its leaves quickly when touched.
• Comparison: The response of sunflowers to light is slower, and growth-related movements are even slower.

Movement Due to Growth

• Tropic Movements: Directional movements in response to stimuli, which can be towards or away from the stimulus.

• Examples:
  • Plants like pea, pumpkin, and cucumber use tendrils to climb.
  • Tendrils are sensitive to touch; the part in contact grows slower, causing the tendril to encircle the object.

Types of Tropic Movements

Phototropic Movement (Stimulus—Light)

• Definition: Movement of plant parts in response to light.
• Phenomenon: Known as phototropism.

• Behavior:
  • Shoots grow towards light.
  • Roots grow away from light.

Geotropic Movement (Stimulus—Gravity)

• Definition: Movement of plant parts in response to gravity.
• Phenomenon: Known as geotropism.

Behavior:

• Roots: Exhibit positive geotropism by growing downward towards gravity.
• Shoots: Exhibit negative geotropism by growing upward, away from gravity.

Hydrotropic Movement (Stimulus—Water)

• Definition: Growth in response to water.
• Phenomenon: Hydrotropism.
• Example: Roots grow towards water sources.

Chemotropic Movement (Stimulus—Chemical)

• Definition: Growth in response to a chemical stimulus.
• Phenomenon: Chemotropism.
• Example: Pollen tube grows towards ovules during fertilization.

Chemical Communication

• Concept: Multicellular organisms use chemical communication instead of continuous electrical impulses.
• Hormones:
  • Chemicals released by cells.
  • Diffuse to other cells and are detected using special molecules.

Plant Hormones

• Definition: Naturally produced chemical substances in plants.
• Function: Synthesized away from the site of action and diffuse to where they are needed.

Major Classes of Plant Hormones

Auxins

• Synthesized at the tips of shoots.
• Promote cell growth and elongation.
• Cause bending towards light by diffusing to the shaded side.

Gibberellins

• Aid in the growth of stems and flowers.

Cytokinins

• Promote cell division.
• Concentrated in fruits and seeds, facilitating rapid division.

Abscisic Acid

• Acts as a growth inhibitor.
• Responsible for leaf wilting.

Animal Hormones

• Function: Regulate physiological processes in animals.
• Production: Secreted in small amounts by endocrine glands.
• Distribution: Released into the bloodstream and carried to specific organs via the circulatory system.

Human Endocrine Glands

• Characteristics: Ductless glands.
• Role: Secrete hormones that act on distant target organs or cells.

Major Hormones and Their Functions

Adrenaline

• Secreted by the adrenal glands.
• Increases heart rate to supply more oxygen to muscles.
• Reduces blood flow to the digestive system and skin, increasing it to skeletal muscles.
• Increases breathing rate for emergency response.

Thyroxine

• Secreted by the thyroid gland.
• Regulates metabolism of carbohydrates, proteins, and fats.
• Requires iodine for synthesis.

Growth Hormone

• Secreted by the pituitary gland.
• Regulates overall growth and development.

Testosterone and Oestrogen

• Responsible for changes during puberty.
• Testosterone in males, oestrogen in females.

Insulin

• Produced by the pancreas.
• Helps regulate blood sugar levels.

Hormonal Disorders

• Definition: Disorders caused by abnormal hormone secretion, either too little (hyposecretion) or too much (hypersecretion).
• Examples: Common hormonal disorders are discussed in the following sections.

Examples of Hormonal Disorders

Dwarfism

• Caused by hyposecretion of growth hormone.
• Leads to short stature, mainly in childhood.

Gigantism

• Caused by hypersecretion of growth hormone.
• Results in excessive growth.

Goitre

• Due to iodine deficiency.
• Characterized by a swollen neck.

Diabetes Mellitus

• Occurs when insufficient insulin is secreted by the pancreas.
• Leads to high blood sugar levels, requiring insulin treatment.

Feedback Mechanism

• Purpose: Regulates hormone secretion.
• Function: Controls the timing and amount of hormone release.
• Example: Increased blood sugar levels trigger pancreatic cells to produce more insulin.
• Flowchart: Typically illustrates the feedback mechanism for blood glucose regulation.