CBSE Class 11 Biology Revision Notes Chapter 21

CBSE Class 11 Biology Revision Notes Chapter 21 – Neural Control and Coordination

Chapter 21 of Class 11 Biology introduces students to the systems of Neural Control and Coordination within the human body. Our nervous system permits our mind and body to connect with one another, which assists in detecting and responding to a variety of stimuli. This chapter covers the entire nervous system and more.

To help students tackle the many technical terminologies and concepts covered in this chapter, Extramarks offers clear and concise Revision Notes, which can be accessed for free. These notes summarise all the important concepts that students need to know from an exam perspective, which makes it easier for them to prepare and revise for this chapter.

Access Class 11 Biology Chapter 21- Neural Control and Coordination

Some of the core concepts covered in this chapter and the revision notes provided by Extramarks have been summarised below for students’ reference.

Neural Control and Coordination

Coordination is defined as the interaction of two or more organs to complement each other’s functions.

Neural System

Neurons are the structural and functional components of the nervous system. They are capable of detecting, receiving and transmitting impulses.

Human Nervous System

The nervous system is classified into two parts:

1. CNS(central nervous system): The brain and spinal cord comprise the central nervous system.
2. PNS(peripheral nervous system): All of the brain and spinal cord nerves are part of the peripheral nervous system. There are two types of nerve fibres in the PNS:

• Sensory nerve fibres or afferent nerve fibres: Afferent nerve fibres transport impulses from organs and tissues to the CNS.
• Efferent nerve fibres or motor nerve fibres: Efferent nerve fibres carry impulses from the central nervous system to the target tissue/organ.

PNS is divided into two groups:

• Somatic nervous system 

The somatic nervous system transmits impulses from the CNS to skeletal muscles. 

• Autonomic nervous system 

The autonomic nervous system innervates the cardiac and smooth muscles of the glands, which convey impulses from the CNS to the involuntary part of the body. The autonomic nervous system is classified into two categories:

• The sympathetic nervous system 
• Parasympathetic nervous system

Structure and the Function of the Neuron

The nervous system is divided into three sections:

1. Axon 
2. Cell body
3. Dendrites 

The cytoplasm of the cell body contains Nissl’s granules, which are granular bodies. Dendrites are short finger-like projections that emerge from the cell body. Dendrites carry nerve impulses towards or into the cell body. 

An axon is a long, unitary structure with a branching distal end. Each axon terminates in a synaptic knob, a bulb-like structure that stores neurotransmitters. Schwann cells are axon cells that produce and cover the myelin sheath. The Nodes of Ranvier are the junctions between two neighbouring myelin sheaths.

Types of Neurons

• Multipolar neurons: 

Multiple processes originate in multipolar neurons with one axon and several dendrites (in the cerebral cortex) for example.

• Bipolar neurons: 

Bipolar neurons are those that have just one axon and one dendrite. Consider the retina.

• Unipolar neurons: 

Unipolar neurons have just two fibres that emerge close together, one axon and no dendrite. Consider the embryonic stage.

Generation and Conduction of Nerve Impulses

Neurons are cells that may be activated electrically. When activated, the neurons’ membranes become polarised. The membrane comprises ion channels and is selectively permeable to various ions. When no nerve impulse is sent, the membrane becomes more permeable to potassium ions and less permeable to sodium ions. As a result, there is a far higher concentration of potassium ions in the membrane than sodium ions.

Outside, however, the situation changes, with a higher potassium content than sodium. The difference in concentration of these ions causes a concentration gradient to form. The sodium-potassium pump helps to keep this gradient in place by transferring three sodium ions outside and two potassium ions within the neuronal membrane. As a result, the outer surface of the axonal membrane becomes positively charged, while the interior surface becomes negatively charged. It causes depolarisation of the membrane. When a stimulus reaches a neuronal membrane, sodium ions can pass through. As a result, sodium ions enter the neuronal membrane. The interior of the membrane gets positively charged because of this polarity, while the outside becomes negatively charged. An electrical potential differential produces an action potential. With time, sodium ion permeability decreases, whereas potassium ion permeability rises. An outflow of sodium ions polarisation occurs from the inside to the outside of the axonal membrane. The polarity is flipped once more. This series of events is repeated along the whole axon, which aids in nerve impulse conduction.

Transmission of Impulses

Synapses are the connections that allow a nerve impulse to go from one neuron to the next. A synapse is formed when a synaptic cleft separates the membranes of presynaptic and postsynaptic neurons.

There are two types of synapses:

1. Electrical synapses 
2. Chemical synapse 

Pre- and postsynaptic neurons are close together in an electrical synapse. Direct transmission of electric current from one neuron to another is possible. The chemical synapse is slower than this mechanism of nerve impulse transmission.

Pre- and postsynaptic neurons are separated by a fluid-filled area called the synaptic cleft in chemical synapses. These synapses are made up of neurotransmitters. There are axon terminals present, which contain neurotransmitter-filled vesicles. Synaptic vesicles begin to move towards the membrane and merge with it when the impulse reaches the axon terminal. The neurotransmitters are discharged from the synaptic cleft as a result of this. The neurotransmitters now bind to receptors on the postsynaptic neuron. Ion channels are opened as a result, and fuse nerve impulses are sent.

Central Nervous System

The brain is a command and control system that governs and coordinates all body processes. Inside the skull, the human brain is protected. The meninges are the three layers that cover the brain. The names of the three meninges are given below:-

• outermost dura mater, 
• middle arachnoid, 
• innermost pia mater. 

The brain is divided into three sections:

1. the forebrain
2. the midbrain
3. the hindbrain

The cerebrum, thalamus and hypothalamus are the three components of the forebrain. The cerebrum is the most significant region of the brain. The left and right cerebral hemispheres divide the cerebrum into two halves. The corpus callosum is a large white central canal commissure that connects these hemispheres. The cerebral cortex is a layer of cells covering both hemispheres of the brain. The thalamus is a forebrain region positioned in the centre. It has an impact on both sensory and motor signals. The hypothalamus is located at the base of the thalamus. The midbrain is situated between the forebrain and the hindbrain. Corpora quadrigemina, or four lobes are present. The pons, cerebellum and medulla oblongata are all components of the hindbrain. The cerebellum is the brain’s second-largest structure. Between the spinal cord below and the pons above lies the medulla oblongata. The medulla is in charge of controlling stomach secretion, breathing and cardiovascular activities.

Reflex Action and Reflex Arc

A reflex action is an unintentional, instinctive reaction to a stereotype. The neural components involved in reflex action compose the reflex arc. The reflex arc or reflex path includes the following elements:

Receiver (sensory cell receiving stimulus)

↓

Sensory or afferent neuron

↓

The spinal cord’s dorsal root

↓

CNS neuron connections

↓

A motor neuron or efferent

↓

The spinal cord’s ventral root

↓

Organ of action

Sensory Perception and Processing

Mechanical, chemical, electrical and temperature information from the environment are converted into nerve impulses that are delivered to the central nervous system through sensory organs.

Human Eye

The human eye is spherical, with the front one-fifth visible and the remaining four-fifths hidden within the eye orbit. It consists of three layers:

 (i) The outermost sclera (dense connective tissue),

 (ii) Middle choroid (supplied with blood vessels),

 (iii) Innermost retina.

The choroid borders the sclera’s posterior portion. The choroid expands anteriorly to generate the ciliary body. The choroid becomes widely separated from the cornea in front of the ciliary body. It creates a visible coloured region of the eye known as the iris. There is a solid, clear, crystalline biconvex lens right below the pupil. It is maintained in place by ligaments linked to the ciliary body. The retina is made up of three layers of neuronal cells.

(i) Photoreceptor cells 

(ii) Ganglion cells 

(iii) Bipolar cells 

Photoreceptor cells are classified into two types: rods and cones. These proteins are sensitive to light. Cones respond better to high-intensity bright light and colour vision, but rods respond better to low light. The protein present in Rods is known as rhodopsin. Cones are sensitive to three hues: red, green and blue. A densely packed macula lutea with just cones exists on the lateral side of the blind area. The aqueous chamber is a fluid-filled area between the lens and the fluid in the cornea known as aqueous humour. As a result, the vitreous chamber is the gap between the lens and the retina, and the fluid that fills it is known as vitreous humour.

Mechanism of Vision

Rods and cones create action potentials when light rays are focused on the retina. So, opsin and retinal pigment are separated from photosensitive pigment. It helps to generate an action potential, which goes from the optic nerve to the brain’s visual cortex. Images are created on the retina as a result.

The Ear

Hearing and balance are the two fundamental functions of the ears. The ear is divided into three sections:

(i) Outer ear, 

(ii) Middle ear, 

(iii) Inner ear. 

Outer ear components include the pinna and external auditory meatus. Pinna assists in sound creation by collecting vibrations from the ear. Pinna and meatus have wax-secreting glands. The three middle ear ossicles are the malleus, incus, and stapes. The middle ear is connected to the throat via a eustachian tube. The inner ear’s bone labyrinth has three semicircular canals. The cochlea is the labyrinth’s coiled part. Endolymph is the fluid that fills the cochlea. The organ of Corti is a structure placed on the basilar membrane. Hair cells serve as auditory receptors in them.

Mechanism of Hearing

The external ear receives sound waves and transmits them to the eardrum. As a result, the eardrum vibrates. Vibrations are conveyed to the ear ossicles. The cochlea receives vibrations as well. It results in a nerve impulse, which is subsequently sent to the brain’s auditory cortex through the auditory nerve.

Human Neural System

The human neural system is composed of the following systems-

• Central Neural System (CNS): The CNS comprises the brain and the spinal cord and is the place of information processing and control.
• Peripheral Neural System (PNS): The PNS includes all the nerves of the body linked with the CNS.

Generation of Nerve Impulse

• Because their membranes are polarised, neurons are excitable cells that are activated.
• The axonemal membrane is more permeable to K+ ions and less permeable to Na+ ions in the resting phase.
• K+ ions are more concentrated inside the axonemal membrane than outside, but Na+ ions are more concentrated outside. The Na+/K+ pump maintains the ionic gradient.
• The neurons get depolarised when the stimulus is applied because Na+ ions travel into the membrane, and the polarity of the membrane is reversed.
• The action potential, also known as a nerve impulse, is the difference in electrical potential across the plasma membrane. This pattern occurs down the axon.
• The stimulus-induced increase in sodium ion permeability is very short-lived. An increase rapidly follows it in potassium ion permeability. Ions travel outside the membrane and restore the membrane’s resting potential.

Transmission of Impulses

A synapse is a neuromuscular junction where nerve impulses are sent from one neuron to the next. It is created by passing information from one neuron to the next. It is made up of the membranes of presynaptic and postsynaptic neurons.

• The space between the presynaptic and postsynaptic neurons is known as the synaptic cleft.
• Chemical and electrical synapses are the two types of synapses.
• Pre and postsynaptic neurons are close together in electrical synapses. It travels straight from one neuron to the next. It moves more quickly than a chemical synapse.
• Synaptic cleft reports chemical synapse.
• When an impulse or action reaches the axon terminal, it causes the synaptic vesicle to migrate closer to the membrane.
• Neurotransmitter synaptic vesicles are found in these synaptic vesicles.
• Releases neurotransmitters in the synaptic cleft after fusing with the plasma membrane, and the neurotransmitters are released to bind to receptors on postsynaptic membranes. It opens the ion channels and allows ions to enter, causing a new impulse to be generated in the postsynaptic neurons.

Central Nervous System

The central nervous system controls various voluntary and involuntary motions. The brain is well-protected by the skull. The brain is protected by three membranes known as cranial meninges. Membranes include:

• Dura mater ( it is the outer layer)
• Arachnoid (it is the middle layer)
• Pia mater ( it is the inner layer)

The following are the three primary components of the brain:

• Forebrain
• Midbrain
• Hindbrain

Forebrain

The Cerebrum, Thalamus, and Hypothalamus make up the forebrain.

1. Cerebrum

• The largest section of the brain is the cerebrum.
• The cerebral hemispheres are separated longitudinally by the corpus callosum, connecting them.
• The cerebral cortex covers the cerebral hemisphere and folds to generate noticeable folds.
• The motor and sensory areas are located in the cerebral cortex, commonly known as grey matter.
• The association region is responsible for many tasks, including creating links between sensory and motor areas. Because they give the layer an opaque white appearance, this is also known as white matter.

2. Thalamus

The cerebrum wraps around the thalamus. It controls sensory and motor communication.

3. Hypothalamus

It can be found at the base of the thalamus. It is the primary control centre for temperature and hunger and thirst. Hypothalamic hormones are also secreted.

Midbrain

Between the thalamus and the hypothalamus is the midbrain.

• The midbrain is where the cerebral aqueduct runs.
• The corpora quadrigemina are four lobes that make up the dorsal part. The brainstem consists of the midbrain and hindbrain.

Hindbrain

The hindbrain consists of the following:

• Pons with fibre tracts makes up the hindbrain.
• The cerebellum has a convoluted surface that allows for more neurons.
• The spinal cord receives impulses from the medulla oblongata. Respiration, cardiovascular space reflexes and gastric secretions are all controlled by it.

The spontaneous response to the peripheral nervous system is referred to as reflex action or reflex arc.

• It is made up of at least one afferent and one efferent neuron.
• Afferent neurons in the reflex arc receive sensory organ impulses and send them to the CNS. Different neurons carry messages from the CNS to the effectors.

Sensory Reception and Processing

• The eye is a crucial and sensitive sense organ. It allows us to see the world.
• Because they include specific light-sensitive receptor cells, the eyes are known as visual receptors.
• The sclera, choroid, and retina are the three specialised structures that make up the eyeball.
• The white component of the eyeball, called the sclera, keeps the form of the eye.
• Behind the sclera is the choroid layer, which absorbs scattered light and guarantees a crisp image of the retina.
• The iris and the ciliary body are two structures formed by the choroid.
• The iris is a black muscular diaphragm whose role is to govern the size of the pupil.
• The pupil’s job is to control the quantity of light that reaches the retina.
• The lens is attached to the ciliary body. Smooth muscles make up the lens, and contraction of these muscles causes the lens to change form.
• The lens is a protein-based transparent and flexible structure. It forms a picture on the retina, a light-sensitive screen. Aqueous humour is a transparent fluid that fills the lens. The vitreous humour fills the rear layer of the lens.
• The cornea is a clear thin membrane that allows light to enter the eye.
• The fragile third and innermost layer of the eye lens is known as the retina. It receives the focused light from the lens and creates an inverted picture of the item.
• Cones and rods are light-sensitive cells in the retina.
• A pigment called visual violet iodopsin is found in cone cells and is responsible for colour vision in daylight.
• In low light or at night, rod cells operate.
• For a short time after entering the darkroom from the lightroom, an individual cannot see properly. The iris controls the quantity of light that enters the eye. The pupil contracts in the presence of light, allowing less light to reach the eye. When a person enters the darkroom, the pupil expands for a short period, allowing more light to enter the eye.
• The point at which the eye can perceive things is the furthest point of the eye, which is infinity.
• A cataract occurs when the lens becomes milky and blurry. It commonly arises in old age and causes partial or complete vision loss.

Defect of Vision

Vision problems include:

• An abnormal curvature of the eyeball causes myopia. The picture of distant things cannot be seen properly in myopia. Nearsightedness is another name for it.
• Hypermetropia is a condition where people can perceive afar objects but not nearer items. Nearsightedness is another name for this condition. Hypermetropia occurs when the focal length of the eyeball increases and the eyeball grows smaller.
• Presbyopia is caused by the progressive weakening of the ciliary muscles and the decrease in the flexibility of the eye lens.
• Hearing and physiological health are two of the most crucial functions of the ear.
• The three areas of the ear are the outer ear, middle ear, and inner ear.
• The outer ear is composed of the following components:
• Pinna
• Canola is classified as an external auditory meatus. They extend to the tympanic membrane, often known as the eardrum.
• Pinna is an instrument that collects sound and vibrations in the air. The pinna contains wax-producing sebaceous glands.

The Middle Ear Consists of Three Ossicles.

• The malleus connects to the tympanic membrane.
• The third bone attached to the cochlea’s oval window is the stapes.
• Incus
• Ossicles improve the control of sound wave propagation to the inner ear.
• The fluid-filled labyrinth in the inner ear contains two parts: bony and membranous.
• Endolymph fills the labyrinth, and the cochlea is the coiled section of the labyrinth.
• The upper-scale vestibule and lower scala tympani make up the bony labyrinth.
• There is a hair cell in the basilar membrane organ of Corti, which works as an auditory receptor.
• Stereocilia is a collection of processes that extend from the apical region of the brain.
• The vestibular apparatus is a sophisticated mechanism in the inner ear. Three semicircular canals and the otolith organ make up this apparatus. Sacculi and utricle make up this organ.
• The enlarged base of the canals is known as the ampulla. Crista ampullaris, a protruding ridge, is present. The macula is the ridge that runs between the saccule and the utricle.
• Sound waves are received by the external ear and sent to the eardrum, which vibrates in reaction. These sound waves go through the ossicles of the ear.

Sense Organs

Touch, vision, hearing, smell, and taste are the five most significant senses in the human body. These sensory receptors can be found in the skin, mucous membranes, connective tissues and muscles, among other places. They send out numerous sensory signals like heat, cold, pain, etc. The sensory organs collaborate to complete some receptive processes.