Coordination and Control

Definition: Coordination means to integrate different parts of the body and to respond to stimuli in order to keep harmony with the environment.

Importance: Coordination helps to keep harmony with the environment.

There are two types of coordination:

• Nervous Coordination: Brought about by the nervous system using electrical signals (nerve impulses). Responses are quick but short-lived.
• Chemical Coordination: Brought about by the endocrine system using chemicals called hormones. Responses are usually slow but long-lasting.

Note: Animals have both systems, while plants show only chemical coordination.

A coordinated action has five components:

1. Stimulus: Any factor in the external or internal environment which can initiate a response in the body (e.g., heat, light, sound).
2. Receptor: The organ, tissue, or cell which receives stimuli (e.g., ears, eyes, nose).
3. Coordinator: Organs that receive messages from receptors and send messages to effectors.
   • Nervous Coordination: Brain and Spinal Cord.
   • Chemical Coordination: Endocrine Glands.
4. Effector: Special parts of the body that receive messages from coordinators and produce a response (e.g., muscles, glands).
5. Response: The action performed by effectors (e.g., pulling hand away from heat).

The nervous system of humans consists of two major components:

1. Central Nervous System (CNS): Consists of coordinators (Brain and Spinal Cord).
2. Peripheral Nervous System (PNS): Consists of nerves that arise from brain and spinal cord and spread in different parts of body.

Definition: Functional unit of the nervous system specialized to conduct messages in the form of nerve impulses.

Structure:

• Cell Body: Contains nucleus, organelles, and cytoplasm.
• Dendrites: Small branches projecting from cell body. Transmit impulses towards cell body.
• Axon: Long branch from cell body. Transmits impulses away from cell body.

Myelin Sheath: Insulating covering produced by Schwann cells over some axons. Gaps in sheath are called Nodes of Ranvier, allowing impulses to jump (Saltatory Conduction).

• Sensory Neurons: Transmit impulses from receptors to CNS.
• Inter-neurons: Present in CNS. Receive impulses from sensory neurons and transmit to motor neurons.
• Motor Neurons: Transmit impulses from CNS to effectors (muscles/glands).

Definition: A nerve is a collection of axons enveloped by a covering.

• Sensory Nerves: Contain axons of sensory neurons only.
• Motor Nerves: Contain axons of motor neurons only.
• Mixed Nerves: Contain axons of both sensory and motor neurons.

Location: Present inside cranium (skull). Covered by three layers of meninges (protect from damage). Fluid filled ventricles contain Cerebrospinal Fluid (CSF).

Divisions of Brain:

• Forebrain: Largest area.
  • Cerebrum: Controls skeletal muscles, thinking, intelligence, emotions. Divided into two hemispheres. Outer layer is Cortex (Grey Matter).
    • Frontal Lobe: Motor control, speech.
    • Parietal Lobe: Sensory information.
    • Temporal Lobe: Hearing, smell.
    • Occipital Lobe: Vision.
  • Thalamus: Relay center between spinal cord and cerebrum. Involved in pain perception.
  • Hypothalamus: Controls body temperature, hunger, thirst, and pituitary gland secretions.
• Midbrain: Bridge between forebrain and hindbrain. Controls reflexes (visual/auditory).
• Hindbrain:
  • Cerebellum: Coordinates muscle movements and balance.
  • Pons: Connects cerebellum and spinal cord. Controls sleep/wake.
  • Medulla Oblongata: Controls autonomic functions (heartbeat, breathing, digestion).

Structure: Tubular bundle of nerves extending from brain stem to lower back. Protected by vertebral column.

• Outer Region: White matter (myelinated axons).
• Inner Region: Butterfly-shaped Grey matter (cell bodies).

Spinal Nerves: 31 pairs arise from spinal cord. All are mixed nerves.

Function: Transmits impulses between body and brain. Controls simple reflexes.

Definition: Quick, involuntary response to a stimulus (e.g., pulling hand from hot object).

Reflex Arc: The pathway of nerve impulses in a reflex action.

1. Receptor detects stimulus.
2. Sensory neuron carries message to Spinal Cord.
3. Inter-neuron processes message.
4. Motor neuron carries command to Effector.
5. Effector produces response.

Structure: Wall of eye has three layers:

• Sclera (Outer): White, dense connective tissue. Anterior transparent part is Cornea.
• Choroid (Middle): Vascular layer. Forms Ciliary Body and Iris (colored part). Pupil is the aperture in Iris controlled by muscles (constricts in bright light, dilates in dim light). Lens is transparent and held by ligaments.
• Retina (Inner): Contains photoreceptors.
  • Rods: Sensitive to dim light (contain Rhodopsin, vitamin A dependent). Deficiency causes Night Blindness.
  • Cones: Sensitive to bright light and colors (contain Iodopsin).
  • Fovea: Spot with high cone density (sharpest vision).
  • Blind Spot: No photoreceptors where optic nerve leaves.

• Myopia (Short-sightedness): Eyeball elongated. Image formed in front of retina. Cannot see distant objects. Treated with Concave Lens.
• Hypermetropia (Long-sightedness): Eyeball shortened. Image formed behind retina. Cannot see near objects. Treated with Convex Lens.

Functions: Hearing and Balance.

Structure:

• Outer Ear: Pinna, Auditory Canal, Ear Drum (Tympanum). Wax/hairs protect from germs/dust.
• Middle Ear: Ossicles (Malleus, Incus, Stapes). Eustachian tube equalizes pressure.
• Inner Ear:
  • Cochlea: Coiled tube containing receptors for hearing (Organ of Corti).
  • Semicircular Canals: Maintain body balance.

Mechanism of Hearing: Sound waves -> Pinna -> Ear Drum -> Ossicles -> Oval Window -> Cochlea (Fluid) -> Organ of Corti -> Auditory Nerve -> Brain.

Definition: System of ductless glands that secrete hormones regulating growth, reproduction, and glucose levels.

Major Glands:

• Pituitary Gland (Master Gland):
  • Anterior Lobe: Secretes Growth Hormone (GH) and Thyroid Stimulating Hormone (TSH). Disorders: Gigantism/Dwarfism.
  • Posterior Lobe: Stores Oxytocin and ADH (Vasopressin). ADH regulates water reabsorption.
• Thyroid Gland: Secretes Thyroxine (Iodine dependent). Deficiency causes Goiter. Regulates cellular metabolism. Also secretes Calcitonin (lowers blood calcium).
• Parathyroid Gland: Secretes Parathormone (increases blood calcium).
• Adrenal Gland:
  • Medulla: Secretes Epinephrine (Adrenaline) for 'Fight of Flight' response.
  • Cortex: Secretes Corticosteroids (Cortisol, Aldosterone).
• Pancreas: Islets of Langerhans secrete:
  • Insulin: Lowers blood glucose. Deficiency causes Diabetes Mellitus.
  • Glucagon: Raises blood glucose.
• Gonads:
  • Testes: Secrete Testosterone (Male characteristics).
  • Ovaries: Secrete Estrogen/Progesterone (Female characteristics).

Definition: Regulation of a process by the output of the process.

• Negative Feedback: Output of process slows down/stops process (e.g., Blood glucose regulation by Insulin/Glucagon).
• Positive Feedback: Output accelerates the process (e.g., Sucking reflex/Milk production).