Neural Control and Coordination — Biology Class 11 Notes (CBSE & HBSE)
Free NCERT Biology notes for Neural Control and Coordination (Class 11) on Siksha Sarovar, aligned to CBSE and Haryana Board (HBSE). This chapter is broken into 3 topics with clear explanations, formulas, solved examples and board-pattern practice — free to read, no sign-up required.
Board exam focus — Neural Control and Coordination (CBSE & HBSE)
This chapter studies how the nervous system coordinates and integrates the body's activities. It covers the structure and types of neurons, the generation and conduction of a nerve impulse through resting and action potentials, transmission across synapses, the organisation of the human neural system into central and peripheral parts, the major regions of the brain, the reflex action and reflex arc, and the structure and working of the sensory organs — the eye and the ear.
Neuron Structure, Nerve Impulse & Synapse
The Neural System
The neural system provides rapid coordination through electrical impulses, complementing the slower hormonal (endocrine) system. The neuron (nerve cell) is its structural and functional unit, and is excitable.
Structure of a Neuron
A neuron has three parts:
- Cell body (cyton): contains cytoplasm with Nissl's granules (rough ER), the nucleus and other organelles.
- Dendrites: short branched processes that receive impulses and carry them toward the cell body.
- Axon: a long process that carries impulses away from the cell body to a synapse; ends in synaptic knobs containing neurotransmitter vesicles.
Types of Neurons
| Basis | Types |
|---|---|
| Number of processes | Multipolar (cerebral cortex), Bipolar (retina), Unipolar (embryo) |
| Myelination | Myelinated (with Schwann sheath, nodes of Ranvier) and Non-myelinated |
- Myelinated fibres conduct impulses faster by saltatory conduction (jumping between nodes of Ranvier).
Resting Potential
In a resting (non-conducting) neuron the axonal membrane is polarised:
- The membrane is more permeable to K+ and nearly impermeable to Na+.
- The Na+/K+ pump pumps 3 Na+ out and 2 K+ in.
- The outer surface is positive (+) and the inner is negative (–): this potential difference is the resting potential.
Action Potential (Nerve Impulse)
When a stimulus is applied:
- Depolarisation: Na+ channels open, Na+ rushes in, making the inside positive at that point.
- The site of the membrane becomes reversed in polarity (outside –, inside +).
- Repolarisation: Na+ channels close and K+ channels open; K+ leaves, restoring the resting state.
- The impulse travels as a wave of depolarisation along the axon.
Synapse — Transmission of Impulse
A synapse is the junction between two neurons. Two types:
- Electrical synapse: membranes are very close; impulse passes directly and rapidly (like axonal conduction).
- Chemical synapse: separated by a synaptic cleft; impulse transmitted by neurotransmitters (e.g., acetylcholine). The arriving impulse causes Ca2+ entry, releasing neurotransmitter that binds receptors on the post-synaptic membrane and opens ion channels — generating a new potential. This is the more common type in humans.
Human Neural System, Brain & Reflex Action
Divisions of the Human Neural System
The human neural system is divided into:
- Central Nervous System (CNS) = brain + spinal cord (site of information processing and control).
- Peripheral Nervous System (PNS) = nerves connecting the CNS to the body. PNS nerve fibres are of two types:
- Afferent (sensory) fibres → carry impulses from tissues/organs to the CNS.
- Efferent (motor) fibres → carry impulses from the CNS to the effector organs.
The PNS is functionally divided into:
- Somatic neural system: relays impulses from CNS to skeletal muscles (voluntary).
- Autonomic neural system (ANS): relays impulses to smooth muscles and involuntary organs; further divided into sympathetic and parasympathetic (usually antagonistic).
The Human Brain
The brain is protected by the skull and three membranes (meninges) and is divided into three parts:
| Part | Major regions | Functions |
|---|---|---|
| Forebrain | Cerebrum, thalamus, hypothalamus | Thinking, memory, intelligence; relay (thalamus); temperature, hunger, thirst, emotions (hypothalamus) |
| Midbrain | Corpora quadrigemina | Visual and auditory reflexes |
| Hindbrain | Cerebellum, pons, medulla oblongata | Balance/coordination (cerebellum); control of respiration, heartbeat, BP (medulla) |
- The cerebrum is the largest part; its outer cortex (grey matter) has motor, sensory and association areas.
- The medulla oblongata connects to the spinal cord and controls vital involuntary functions.
Reflex Action and Reflex Arc
- A reflex action is a sudden, involuntary, automatic response to a stimulus that does not require conscious thought.
- The pathway is the reflex arc: Receptor → Afferent (sensory) neuron → CNS (spinal cord, with interneuron) → Efferent (motor) neuron → Effector (muscle/gland).
- Example: withdrawing the hand on touching a hot object (the knee-jerk reflex is another classic example).
NEET Tip: Most reflexes are processed at the spinal cord level, allowing a fast response before the brain even perceives the stimulus.
Sensory Reception — Eye and Ear
The Eye — Structure
The human eye is roughly spherical with three layers:
- Sclera (outer): tough, white; its transparent front part is the cornea.
- Choroid (middle): pigmented and vascular; thickens in front as the ciliary body, which continues as the iris (the coloured, visible part) surrounding the pupil.
- Retina (inner): contains photoreceptor cells.
Other parts:
- Lens: held by ligaments behind the pupil; focuses light onto the retina.
- Aqueous humour (between cornea and lens) and vitreous humour (behind the lens) maintain shape.
Photoreceptor cells of the retina:
| Cell | Pigment | Function |
|---|---|---|
| Rods | Rhodopsin (visual purple, has vitamin A) | Vision in dim light (twilight/scotopic) |
| Cones | Photopsins (3 types) | Colour vision and bright light (daylight/photopic) |
- The fovea (macula lutea) has only cones — the point of greatest visual acuity.
- The blind spot is where the optic nerve leaves; it has no photoreceptors.
- Light → photopigments dissociate → potential changes → impulse via optic nerve → visual cortex (occipital lobe).
The Ear — Structure and Working
The ear performs two functions: hearing and maintaining body balance (equilibrium). It has three regions:
1. Outer ear — pinna and external auditory canal, ending at the tympanic membrane (eardrum).
2. Middle ear — three ear ossicles: malleus, incus, stapes, which amplify and transmit vibrations to the oval window. Connected to the pharynx by the Eustachian tube (equalises pressure).
3. Inner ear (labyrinth) — fluid-filled, with:
- Cochlea (for hearing), containing the organ of Corti with hair cells.
- Vestibular apparatus (semicircular canals + otolith organs — utricle and saccule) for balance.
Mechanism of Hearing:
- Pinna collects sound; the eardrum vibrates.
- The ear ossicles amplify and transmit vibrations to the oval window.
- Vibrations create waves in the cochlear fluid, bending the hair cells of the organ of Corti.
- This generates nerve impulses sent via the auditory nerve to the auditory cortex of the brain, where sound is recognised.
Board Tip: Rods contain rhodopsin and need vitamin A — its deficiency causes night blindness (nyctalopia).
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