📝 Chapter Notes & Revision

Neural Control and Coordination

🏫 MP BoardClass 11Biology

📐 Formula & Cheat Sheet (English)

Quick Revision Notes: Class 11 Biology

Chapter: Neural Control and Coordination (तंत्रिका नियंत्रण एवं समन्वय)

### Concept 1: Introduction to Neural System (तंत्रिका तंत्र)

  • Coordination (समन्वय): The process through which two or more organs interact and complement the functions of one another.
  • Neural System: Composed of highly specialized cells called neurons that can detect, receive, transmit, and respond to different kinds of stimuli.
  • Human Neural System: Divided into two main parts:
    1. Central Nervous System (CNS - केंद्रीय तंत्रिका तंत्र): Includes the Brain and the Spinal Cord. The site of information processing and control.
    2. Peripheral Nervous System (PNS - परिधीय तंत्रिका तंत्र): Includes all nerves of the body associated with CNS.
      • Afferent fibers: Transmit impulses from tissues/organs to the CNS.
      • Efferent fibers: Transmit regulatory signals from the CNS to the concerned peripheral tissues/organs.
  • PNS Division:
    • Somatic Neural System (कायिक तंत्रिका तंत्र): Relays impulses from CNS to skeletal muscles.
    • Autonomic Neural System (स्वायत्त तंत्रिका तंत्र): Transmits impulses from CNS to involuntary organs and smooth muscles. Further divided into Sympathetic and Parasympathetic neural systems.

### Concept 2: Structure of a Neuron (न्यूरॉन की संरचना)

A neuron is a microscopic structure composed of three major parts:

  1. Cell Body (Soma / साइटॉन): Contains cytoplasm, cell organelles, and Nissl's granules (granular bodies).
  2. Dendrites (दुमक्षिका): Short, branching fibres projecting out of the cell body that transmit impulses towards the cell body.
  3. Axon (तंत्रिकाक्ष): A long fiber that transmits nerve impulses away from the cell body to a synapse or to a neuro-muscular junction.
    • Synaptic Knob: The branched distal end of an axon containing synaptic vesicles filled with neurotransmitters.

  • Types of Neurons (Based on axon/dendrite number):

    • Unipolar: 1 axon + 0 dendrite (Embryonic stage).
    • Bipolar: 1 axon + 1 dendrite (Retina of eye).
    • Multipolar: 1 axon + 2 or more dendrites (Most common, e.g., Cerebral cortex).

  • Types of Axons:

    • Myelinated: Enveloped with Schwann cells which form a myelin sheath around the axon. Gaps between two myelin sheaths are called Nodes of Ranvier. (Found in spinal and cranial nerves).
    • Unmyelinated: Enclosed by a Schwann cell that does not form a myelin sheath (Found in autonomous and somatic neural systems).

### Concept 3: Generation and Conduction of Nerve Impulse (तंत्रिका आवेग की उत्पत्ति और चालन)

  • Polarized Membrane (Resting Potential):

    • When a neuron is not conducting any impulse (resting state), the axonal membrane is more permeable to potassium ions ($K^+$) and impermeable to sodium ions ($Na^+$).
    • The axoplasm inside contains high concentration of $K^+$ and negatively charged proteins, while outside fluid has high $Na^+$.
    • This creates a concentration gradient resulting in a negative charge on the inner side and a positive charge on the outer side.
    • Resting Potential value: Around -70 mV.

  • Depolarization (Action Potential):

    • When a stimulus is applied at a site, the membrane becomes freely permeable to $Na^+$.
    • Rapid influx of $Na^+$ reverses the polarity (outer side becomes negative, inner side becomes positive).
    • Action Potential / Nerve Impulse: The electrical potential difference across the plasma membrane at that site. Value reaches up to +30 mV to +45 mV.

  • Repolarization:

    • Immediately following depolarization, $Na^+$ permeability decreases, and $K^+$ permeability increases.
    • $K^+$ diffuses outside, restoring the resting potential of the membrane.

### Concept 4: Transmission of Impulses (Synapse) (तंत्रिका-प्रेषण / अंतर्ग्रथन)

  • Synapse: Formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, separated by a space called synaptic cleft.
  • Types of Synapses:
    1. Electrical Synapses: Membranes of pre- and post-synaptic neurons are in close proximity. Electric current flows directly. Impulse transmission is faster than chemical synapse.
    2. Chemical Synapses: Membranes are separated by a fluid-filled synaptic cleft. Uses chemicals called neurotransmitters (e.g., Acetylcholine).
  • Mechanism at Chemical Synapse:
    1. Action potential arrives at the axon terminal.
    2. Synaptic vesicles move towards the membrane and fuse, releasing neurotransmitters into the synaptic cleft.
    3. Neurotransmitters bind to specific receptors on the post-synaptic membrane.
    4. Opens ion channels, generating a new action potential.

### Concept 5: Central Nervous System - Human Brain (केंद्रीय तंत्रिका तंत्र - मानव मस्तिष्क)

The brain is protected by the skull (cranium) and covered by three cranial meninges:

  1. Dura mater (outer layer)
  2. Arachnoid (middle layer)
  3. Pia mater (inner layer, touching the brain)

The brain is divided into three major regions:

1. Forebrain (अग्र मस्तिष्क) - Main thinking part

  • Cerebrum (प्रमस्तिष्क):
    • Forms the major part of the human brain.
    • Divided longitudinally into two halves: Left and Right Cerebral Hemispheres, connected by a tract of nerve fibers called Corpus Callosum.
    • Outer layer is Cerebral Cortex (gray matter); inner part is white matter.
    • Associated with memory, communication, reasoning, and voluntary actions.
  • Thalamus: Sensory and motor relay center.
  • Hypothalamus: Lies at the base of thalamus. Controls body temperature, urge for eating/drinking, and secretes hypothalamic hormones.

2. Midbrain (मध्य मस्तिष्क)

  • Located between forebrain and hindbrain.
  • Contains four round lobes called Corpora quadrigemina.
  • Controls visual and auditory reflex centers.

3. Hindbrain (पश्च मस्तिष्क)

  • Pons: Consists of fiber tracts that interconnect different regions of the brain; contains pneumotaxic center.

  • Cerebellum (अनुमस्तिष्क): Has a convoluted surface to accommodate more neurons. Coordinates voluntary muscular movements and maintains body balance.

  • Medulla Oblongata: Connected to the spinal cord. Controls respiration, cardiovascular reflexes, and gastric secretions.

  • Brain Stem: Formed by Midbrain, Pons, and Medulla oblongata. Connects brain to the spinal cord.

### Concept 6: Reflex Action and Reflex Arc (प्रतिवर्ती क्रिया तथा प्रतिवर्ती चाप)

  • Reflex Action: A spontaneous, involuntary, and mechanical response to a peripheral nerve stimulation that occurs without conscious brain intervention.
  • Reflex Arc Pathway: $$\text{Receptor organ} \rightarrow \text{Afferent (Sensory) neuron} \rightarrow \text{CNS (Interneuron)} \rightarrow \text{Efferent (Motor) neuron} \rightarrow \text{Effector organ (Muscle/Gland)}$$ (Example: Knee-jerk reflex, withdrawal of hand on touching a hot object).

### Concept 7: Sensory Reception and Processing (संवेदी अभिग्रहण और प्रक्रमण)

A. The Eye (नेत्र)

  • Wall of the eyeball is composed of three layers:
    1. Sclera: External layer; dense connective tissue. Anterior transparent portion is called Cornea.
    2. Choroid: Middle layer; bluish in color, contains blood vessels. Forms the Ciliary body and Iris (colored visible portion) in front.
    3. Retina: Innermost layer. Contains three layers of neural cells (from inside to outside): Ganglion cells, Bipolar cells, and Photoreceptor cells.
  • Photoreceptor Cells:
    • Rods: Contain rhodopsin (visual purple). Sensitive to dim light (scotopic vision).
    • Cones: Contain iodopsin. Sensitive to bright light and color vision (photopic vision).
  • Blind Spot: Photoreceptor cells are absent here; optic nerve leaves the eye.
  • Fovea: Central point on the retina where only cones are densely packed. Point of greatest visual acuity.

B. The Ear (कान) - Functions in hearing and balancing

Divided into three major sections:

  1. Outer Ear: Pinna, external auditory meatus (ear canal), and tympanic membrane (eardrum).
  2. Middle Ear: Contains three tiny ear ossicles: Malleus, Incus, and Stapes (attached to the oval window). Eustachian tube connects middle ear to the pharynx (equalizes pressure).
  3. Inner Ear: Fluid-filled system called Labyrinth (bony and membranous labyrinth).
    • Cochlea: Coiled portion responsible for hearing. Contains the organ of Corti containing hair cells acting as auditory receptors.
    • Vestibular Apparatus: Composed of three semi-circular canals and otolith organs (saccule and utricle). Responsible for maintaining body balance and posture.