NEET Important Chapter - Neural Control and Coordination

This article is created to help NEET aspirants prepare in a systematic manner. It will not only boost your preparation level but come in handy during last-minute revision. To ensure this, this article has been made short and crisp. It contains essential notes and important questions related to Neural Control and Coordination. 

It covers all the important concepts such as the nervous system, neurons, brain, etc. so at the end nothing will be left to revise.  Along with this, it contains FAQs regarding the NEET exam. Read ahead to find more information. 

Important Topics of Chemical Coordination and Integration

• Nervous System

• Human Nervous System

• Neuron

• Mechanism of vision

• Hormones and Hormonal Disorders

• Mechanism of hearing

• Conduction of Nerve Impulse

• Diseases of the Nervous System

Important Concepts

Nervous System

The neural system is composed of highly specialised cells called neurons which can detect, receive and transmit different kinds of stimuli.

• The lower invertebrates have a very basic neurological organisation.

• Sponges do not have neurons.

• In hydra, the nervous system is composed of a network of neurons called a nerve net.

• Planaria has two nerve cords that join to form a rudimentary brain.

• The neurological system of the earthworm is more developed, with a well-developed ventral nerve cord, paired segmental ganglia, and segmental nerves.

• In insects, a brain is present along with a number of ganglia and neural tissues. 

• The neural system in vertebrates is more developed.

• The PNS has two types of nerve fibres: Afferent fibres (sensory) and Efferent fibres.

• The afferent nerve fibres transmit impulses from tissues/organs to the CNS and the efferent fibres (motor) transmit regulatory impulses from the CNS to the concerned peripheral tissues/organs.

Neurons

• Neurons are microscopic structures that are structural and functional units of the neural system.

• The structure of a neuron is composed of three major parts, namely, the cell body, dendrites and axon.

• The cell body contains cytoplasm, cell organelles, and Nissl's granules, which are small granular entities.

• Short fibres which branch repeatedly and project out of the cell body also contain Nissl’s granules and are called dendrites. 

• Dendrites transmit impulses toward the cell body.

• The axon is a long branched fibre with a branched distal end.

• Each branch terminates in a bulb-like structure known as a synaptic knob, which contains synaptic vesicles containing neurotransmitter molecules.

Nerve impulses are transmitted from the cell body to a synapse through the axons.

Types of Neurons

Based on the number of axons and dendrites, neurons are divided into three types., i.e., Unipolar, Bipolar, and Multipolar

Nerve Impulse

• Since the membranes of neurons are polarised, they are called excitable cells.

• Membranes are polarised because there are different types of ion channels present on the neural membrane. 

• Different ions selectively pass these ion channels.

• The resting potential is defined as the electrical potential difference across the plasma membrane at rest.

• The resting potential of the membrane is approx -70 mV.

• When a neuron is not transmitting any impulse, it means it is at the resting phase. The membrane of the axon is more permeable to potassium ions (K+) and almost impermeable to sodium ions (Na+) when it is at rest.

• Similarly, negatively charged proteins in the axoplasm are impermeable to the membrane.

• As a result, the axoplasm within the axon has a high concentration of K+ and negatively charged proteins, but a low quantity of Na+.

• The fluid outside the axon, on the other hand, includes a low concentration of K+ and a high concentration of Na+, forming a concentration gradient.

• The active transport of ions by the sodium-potassium pump, which transfers 3 Na+ outside for 2K+ into the cell, maintains these ionic gradients across the resting membrane.

• As a result, the axonal membrane's outer surface has a positive charge, whereas its inner surface has a negative charge and is therefore polarised. 

• The resting potential is defined as the difference in electrical potential across the plasma membrane at rest.

Impulse Generation and Conduction

• The stimulus delivered at point A on the polarised membrane becomes freely permeable to Na+.

• This causes a fast influx of Na+, followed by polarity reversal at that site. (outside negative and inside positive-depolarisation, approx. +30mV)

• At sites immediately ahead, the membrane has a positive charge on the outer surface and a negative charge on its inner surface. 

• Now, the current flows on the inner surface from site A to site B and At site B, the polarity is reversed, and an action potential is formed. As a result, the impulse (action potential) produced at site A reaches Site B.

• The process is repeated along the length of the axon, and the impulse is transmitted as a result.

Transmission of Nerve Impulse

• At the point where a chemical synapse forms, the membranes of the pre-and postsynaptic neurons are separated at the synaptic cleft. 

• Here, neurotransmitters (chemicals) are involved in impulse transmission. 

• The migration of synaptic vesicles towards the membrane is stimulated when an impulse (action potential) arrives at the axon terminal and synaptic vesicles fuse with the plasma membrane releasing neurotransmitters in the synaptic cleft.

• Ca2+ ion influx in the presynaptic cleft helps in the movement of synaptic vesicles.

• The released neurotransmitters from synaptic vesicles bind to their specific receptors, present on the postsynaptic membrane.

• This binding opens ion channels, allowing ions to enter the postsynaptic neuron and generate a new potential.

Human Brain

• The forebrain, midbrain, and hindbrain are the three major parts of the brain. 

• The cerebrum, thalamus, and hypothalamus make up the forebrain. 

• The midbrain is situated between the forebrain's thalamus/hypothalamus and the pons of the hindbrain. 

• The pons, cerebellum, and medulla make up the hindbrain (also called the medulla oblongata).

Reflex Action and Reflex Arc

• Reflex action refers to the complete process of responding to peripheral nervous stimuli that occurs automatically and needs the involvement of a part of the central nervous system (spinal cord).

• The afferent neuron gets a signal from a sensory organ and sends it into the CNS via a dorsal nerve root (at the level of the spinal cord).

• After that, the efferent neuron sends signals from the CNS to the effector.

• As a result, the stimulus and response form a reflex arc. For example;  knee jerk reflex.

(Image will be uploaded soon)

Sense Organs

1. Eye

• The eyeball's wall is made up of three layers.

• The sclera is the outer layer, which is made up of dense connective tissue. The cornea is the anterior part of this layer.

• Choroid is the middle layer.

• The retina is the inner layer, which comprises three layers of neural cells – ganglion cells, bipolar cells, and photoreceptor cells, such as rods and cones – arranged from inside to outside.

• Photopigments are light-sensitive proteins found in rod and cone cells.

• Cones are responsible for daytime (photopic) and colour vision, while rods are responsible for twilight (scotopic) vision.

• A purplish-red protein termed rhodopsin, or visual purple, is found in the rods and contains a vitamin A derivative.

2. Ear

• The ear is divided into three parts anatomically: the outer ear, the middle ear, and the inner ear.

• The pinna and external auditory meatus make up the outer ear (canal). The pinna gathers vibrations in the air which produces sound.

• Malleus, incus, and stapes are three ossicles in the middle ear.

• The pharynx and the middle ear cavity are connected by a Eustachian tube. Its main role is in equalising the pressures on either side of the eardrum.

• The fluid-filled inner ear is called a labyrinth. The cochlea is the coiled section of the labyrinth.

Functions of Different Parts of the Ear

The table in the image below shows the functions performed by the different parts of the ear.

Mechanism of Hearing

• The external ear receives sound waves and transmits them to the eardrum.

• The eardrum vibrates in response to sound waves, and these vibrations are conveyed to the oval window via the ossicles of the ear (malleus, incus, and stapes).

• The vibrations enter through the oval window and then into the cochlea fluid, where they produce waves in the lymphs.

• The waves cause the basilar membrane to ripple, and this causes the hair cells to bend and press against the tectorial membrane.

• In the corresponding afferent neurons, nerve impulses are produced as a result.

• The afferent fibres convey these impulses to the auditory cortex of the brain via auditory nerves, where they are analysed and the sound is recognised.

Diseases of Nervous System

1. Poliomyelitis - Poliomyelitis is an acute viral infection that causes damage to cell bodies of the motor neuron in the anterior horn of the spinal cord.

2. Meningitis - It is  an inflammation of the meninges, and it is caused by an infection by the pathogen.  The meninges can be infected by a variety of bacteria and viruses.

3. Parkinson's Disease - It is caused by the destruction of the neurons of the basal ganglia that produce the neurotransmitter dopamine. Thus dopamine is reduced in the brain. Symptoms: Tremors and shaking in the limbs, slowed voluntary movements, and depression.

4. Wilson's Disease - Along with all symptoms of Parkinson's disease, we can also notice the degeneration of the liver tissues as well in this disease. Copper metabolism is disrupted, resulting in liver and brain damage. Wilson's disease is caused by lenticular nucleus injury which is a part of basal ganglia.

5. Alzheimer's Disease - It is caused due to destruction of vast numbers of neurons in the hippocampus (a part of the brain). There is a loss of neurotransmitter acetylcholine.

6. Schizophrenia - Drugs that increase dopamine activity in the brain tend to intensify schizophrenic symptoms. When the family of the patient criticises them harshly, for example; “you are nothing but trouble", the patients are more likely to relapse. Hallucinations such as seeing objects or hearing voices that aren't really there, delusions like beliefs that aren't based in reality, speech problems, disordered mental processes, and disordered behaviours are all symptoms of this disease.

Solved example from Chapter

1. How might a hit to the back of the neck influence a person's central nervous system?

Ans: It would result in a loss of cognitive ability as well as physical disorders. Furthermore, it has the potential to disrupt emotional or behavioural functioning. Tetraplegia can result from cervical injury.

Key point to remember: Cervical vertebrae allow head motion and support the weight of the head.

2. Distinguish between chemical and electrical transmission.

Ans: 

Key point to remember: 

Chemical transmission - chemical synapse

Electrical synapse - electrical synapse

Solved Problems of Previous Year Questions

1. The resting membrane potential is established primarily due to: 

a. Sodium-potassium pump 

b. Efflux of potassium 

c. Influx of sodium 

d. Influx of chloride 

Ans: b. Efflux of potassium

The potential difference across a neuron's plasma membrane when no stimulation is applied is known as resting membrane potential. The polarised state of the neuron is the name for this phase.

The sodium-potassium pump transports 3Na+ ions out of the cell for every 2K+ ions it moves into the cell during this phase. As a result, sodium ions are more concentrated outside the membrane than inside. The concentration of K+ ions is higher on the interior of the cell than it is on the exterior.

Trick to remember: 

Influx - Transport of ions inside the cell through plasma membrane

Efflux - Transport of ions outside of the cell through plasma membrane

2. A characteristic of the human cornea is: 

a. absence of blood circulation 

b. cause cataract in old age 

c. has lacrimal glands for secreting tears 

d. secreted by conjunctiva and glandular layer 

Ans: a. absence of blood circulation

Cornea is the front part of the sclera, which is the eye's outer layer. It is transparent and the only region of the eye that is not supplied with blood. It takes in oxygen from the atmosphere. As a result, cornea transplants are effective in the majority of instances, and body rejection is quite rare. Keratoplasty is a procedure that involves the transplantation of a cornea.

Trick to remember: Cornea transplantation is effective because of the absence of blood supply.

Practice Questions

1. Which component of the human eye is photosensitive?

Ans: The retina is the light-sensitive layer that lines the interior of the eye and is made up primarily of light-sensitive cells known as rods and cones.

2. What function is the Eustachian tube supposed to play?

Ans: It joins the pharynx and the middle ear cavity, allowing pressures on both sections of the eardrum to equalise it. Towards the pharyngeal mouth of the tube, there is a valve that is normally closed. It opens to balance the air pressure on both portions of the tympanic membrane after swallowing, yawning, or an unexpected shift in altitude as air leaves or enters the tympanic cavity.

Key point to remember: Eustachian tube - Balancing the air pressure

Conclusion

This article is created by keeping in mind the students who are preparing for NEET 2022 or will be preparing for NEET in the future. It covers all of the major concepts of the chapter which makes it ideal for quick and successful preparation as well as revision. It covers key points, and tricks to remember the answers, which makes it ideal for studying the topics and retaining the concepts.