Coordination and Response

13.1 Human Nervous System

• Electrical Impulses:

  • Travel along neurones to facilitate rapid communication within the body.

  • Important for reflex actions and immediate responses.

  • Involved in transmitting sensory information and motor commands.

• Nervous System Components:

  • Central Nervous System (CNS):

  • Comprises the brain and spinal cord.

  • Responsible for processing information.

  • Coordinates higher brain functions like thought and memory.

  • Peripheral Nervous System (PNS):

  • Comprises nerves that extend outside the CNS.

  • Divided into somatic (voluntary) and autonomic (involuntary) systems.

  • Connects the CNS to limbs and organs.

• Function of the Nervous System:

  • Coordinates and regulates body functions.

  • Relays information through electrical impulses between the body and the brain.

  • Ensures homeostasis by responding to internal and external changes effectively.

• Neurones:

  • Specialized cells designed for rapid transmission of electrical signals.

  • Have unique structures including dendrites and axons.

  • Continuously regenerate signals for effective communication.

• Types of Neurones:

  Type	Function	Location
  Sensory Neurones	Relay information from sense receptors to the CNS.	Periphery
  Relay Neurones	Connect sensory and motor neurones in the CNS.	CNS
  Motor Neurones	Send signals from the CNS to effectors (muscles/glands)	CNS to body

• Reflex Arc Components:

  Component	Description	Example
  Receptor	Detects the stimulus (e.g. pain receptors).	Skin
  Sensory Neurone	Transmits impulse to CNS.	Dorsal root
  Relay Neurone	Processes the impulse in the CNS.	Spinal cord
  Motor Neurone	Transmits impulse from CNS to effector.	Efferent path
  Effector	Carries out the response (muscle/gland).	Muscle

• Examples of Reflex Actions:

  • Knee Jerk Reflex:

  • A sharp tap below the knee stimulates a receptor.

  • Impulses sent through a reflex arc result in muscle contraction and leg movement.

  • Hot Plate Reaction:

  • Stimulus: Hand touches a hot plate.

  • Receptor: Pain receptors in the skin.

  • Motor Response: Pull hand away swiftly to avoid injury.

13.2 Sense Organs

• Definition: Group of receptor cells responding to specific stimuli (light, sound, touch, temperature, chemicals).

• Human Sense Organs:

  Organ	Function	Receptors Involved
  Skin	Touch (pressure, pain, temperature).	Mechanoreceptors
  Tongue	Taste (chemicals).	Taste buds
  Nose	Smell (chemicals).	Olfactory receptors
  Eyes	Sight (light).	Photoreceptors
  Ears	Hearing and balance (movement/position of head).	Hair cells

• Eye Structure and Function:

  Structure	Function	Disorders
  Cornea	Bends light rays for focus.	Corneal abrasion, astigmatism
  Lens	Adjusts shape for focusing on near/far objects (accommodation).	Cataracts
  Retina	Contains rod and cone cells; sends impulses to the brain.	Retinal detachment
  - Rods	Sensitive to dim light, respond to black and white.	Night blindness
  - Cones	Sensitive to bright light, respond to color (red, green, blue).	Color blindness

• Pupil Reflex:

  • Iris Adjustment: Controls pupil size; wider in dim light, narrower in bright light (antagonistic muscle actions).

  • Adjusts to regulate the amount of light entering the eye for optimal vision.

13.3 Hormones

• Definition: Chemical substances produced by glands that travel in the bloodstream to regulate specific target organs.

• Key Hormones and Their Functions:

  Hormone	Function	Gland Type
  Adrenaline	Secreted during stress, increases heart rate, blood flow, and energy availability (fight or flight response).	Adrenal glands
  Insulin	Manages blood glucose levels.	Pancreas
  Oestrogen	Regulates sexual development and menstrual cycle.	Ovaries
  Testosterone	Regulates sexual development and male characteristics.	Testes

• Nervous vs. Hormonal Control:
  

• 13.4 Tropic Responses in Plants

  • Tropism: Growth responses by plants towards stimuli (light, gravity).

  • Types of Tropisms:

    Type	Description	Example
    Phototropism	Growth towards light.	Plant bending towards the sun
    Gravitropism	Growth direction influenced by gravity.	Roots growing downwards

  • Auxin in Plant Growth:

    • Auxin: A plant hormone that affects growth direction.

    • Accumulates on the side of the plant opposite to light, leading to elongation of that side and a bend towards light.

    • In the absence of light, auxin accumulates on the lower side when a shoot is oriented upward, leading to downward growth in roots.

  • Tropic Responses:

    • Auxins play a key role in phototropism and gravitropism, leveraging the plant's ability to adjust based on environmental stimuli.

  • Growth Responses in Other Directions:

    • Certain plants may exhibit negative tropism (growth away from stimuli).

    • Example: Roots growing away from light is a negative phototropism.

  • Nastic Movements vs. Tropisms:

    • Nastic movements are non-directional responses that are not growth-based.

      | Type | Description | Example |
      |-------------|--------------------------------------------------|-------------------------------|
      | Nastic Movements | Non-directional responses to stimuli. | Closing of a Venus flytrap when prey is detected. |

  • Environmental Factors Influencing Tropisms:

    Factor	Impact on Plant Growth
    Light	Influences phototropism, driving direction of growth towards light sources.
    Gravity	Influences gravitropism, causing roots to grow downward and shoots to grow upward.
    Water	Water accessibility can dictate root growth patterns.
    Touch	Thigmotropism (response to touch) seen in vines wrapping around supports.

  • Practical Applications of Understanding Tropisms:

    • Agriculture:

    • Using knowledge of tropisms to tailor plant growth for better yields (e.g. pruning to optimize light exposure).

    • Horticulture:

    • Designing gardens that utilize natural plant behaviors for health and aesthetics, such as encouraging flower or fruit growth.

  • Homeostasis:

    • The process by which organisms maintain a stable internal environment despite changes in external conditions.

    • Critical for optimal functioning of cells.

    • Involves multiple systems working in coordination.

  • Mechanisms of Homeostasis:

    Mechanism	Description	Example
    Feedback Loops	Systems that regulate output based on input.	Blood glucose regulation via insulin and glucagon.
    Hormonal Control	Use of hormones to regulate physiological functions.	Thyroid hormones regulate metabolism.
    Nervous Control	Use of electrical impulses for rapid response.	Reflex actions in response to stimuli.

  • Examples of Homeostasis in Humans:

    • Temperature Regulation:

    • Hypothalamus detects changes in body temperature; triggers mechanisms to maintain 37°C.

    • Physiological Responses:

      • Sweating when overheating to cool down.

      • Shivering when cold to generate heat.

    • Blood Glucose Regulation:

    • Insulin lowers blood glucose levels after meals.

    • Glucagon raises levels between meals.

  • Importance of Homeostasis:

    • Essential for survival: keeps biochemical processes running efficiently.

    • Disruptions can lead to disease; examples include diabetes and hyperthyroidism.

  • Interactions Between Systems:

    • The nervous and endocrine systems communicate and coordinate to maintain homeostasis.

    • Stress can initiate a cascade of hormonal responses, activating the fight-or-flight response.

    • Involves the adrenal gland releasing adrenaline.

  • Plant Responses to Environmental Changes:

    • Adjustments made to optimize survival amid environmental challenges (e.g., drought, flooding).

    • Photoperiodism:

      • The response to the duration of day and night; influences flowering in plants.

      • Key in determining the timing of reproductive events.
        | Type | Description | Example |
        |--------------|--------------------------------------------------------|------------------------------------|
        | Short-day | Flowering in response to short daylight hours. | Chrysanthemums. |
        | Long-day | Flowering in response to long daylight hours. | Spinach and certain grasses. |
        | Day-neutral | Flowering not affected by day length. | Dandelions and tomatoes. |

  • Conclusion:

    • Understanding homeostasis is vital in both plants and animals.

    • Knowledge of these mechanisms is crucial for fields like medicine and agriculture, aiding in the improvement of health