Coordination and Response

1. The Nervous System

• Function: Detects and responds to changes in the environment (stimuli) to maintain homeostasis.

Key Components

• Central Nervous System (CNS):

  • Brain and spinal cord.

  • Processes information and coordinates a response.

• Peripheral Nervous System (PNS):

  • Nerves that connect the CNS to the body.

Neurons

• Sensory Neurons: Carry impulses from receptors to the CNS.

• Relay Neurons: Connect sensory and motor neurons in the CNS.

• Motor Neurons: Carry impulses from the CNS to effectors (muscles or glands).

Reflex Arc

• A quick, automatic response to a stimulus (e.g., withdrawing a hand from a hot object).

  • Stimulus → Receptor → Sensory Neuron → Relay Neuron → Motor Neuron → Effector → Response.

    

2. Hormonal System

• Works alongside the nervous system but uses chemical messengers (hormones) transported in the blood.

Key Hormones

3. The Eye

Structure and Function

Accommodation (Focusing):

• Near Object:

  • Ciliary muscles contract.

  • Suspensory ligaments loosen.

  • Lens becomes thicker.

• Distant Object:

  • Ciliary muscles relax.

  • Suspensory ligaments tighten.

  • Lens becomes thinner.

Pupil Reflex:

• Bright Light: Pupil constricts (circular muscles contract).

• Dim Light: Pupil dilates (radial muscles contract).

  

4. Coordination in Plants

• Tropisms: Growth responses to stimuli.

  • Phototropism: Growth towards light (shoots).

  • Gravitropism (Geotropism): Growth towards gravity (roots).

Role of Auxins:

• Plant hormones that regulate growth.

• Uneven distribution causes cells to grow at different rates:

  • In shoots: Auxins promote cell elongation (towards light).

  • In roots: Auxins inhibit cell elongation (towards gravity).

    

5. Homeostasis

• Maintaining a constant internal environment (e.g., temperature, water balance).

Thermoregulation:

• Controlled by the hypothalamus.

• Too Hot:

  • Sweat glands produce sweat.

  • Vasodilation: Blood vessels widen to increase heat loss.

• Too Cold:

  • Shivering generates heat.

  • Vasoconstriction: Blood vessels narrow to reduce heat loss.

Osmoregulation:

• Controlled by the kidneys.

• ADH (Antidiuretic Hormone):

  • Regulates water reabsorption in the kidneys.