Neural Control And Coordination | Class 11 Biology Notes For NEET
Introduction With 💖Learn Sufficient Notes💖
To maintain a healthy and balanced internal environment in our body, also known as homeostasis, it is necessary that all organs and organ systems work together in a well-coordinated manner. Coordination means that two or more organs interact and support each other’s functions to meet the body’s demands. For example, when we do physical exercise, our muscles need more energy. To meet this increased demand, the body increases oxygen supply, which means our lungs breathe faster, the heart beats faster, and blood vessels carry more oxygenated blood. Along with this, the rate of respiration increases to produce more energy in the form of ATP. As a result, many organs such as muscles, lungs, heart, blood vessels, kidneys, and nerves work together actively. But when the exercise is stopped, all these organs slowly go back to their normal resting functions. This whole process shows how different organs work in harmony and respond to changing needs of the body. This is made possible by two major systems – the neural system and the endocrine system. These two systems play a very important role in maintaining coordination and communication in the body. The neural system works like a high-speed network that connects different parts of the body using nerve signals. This system allows quick and specific responses through point-to-point electrical communication. On the other hand, the endocrine system uses hormones, which are chemical messengers, to slowly but steadily bring about longer-lasting changes and coordination among different organs. In this chapter, you will learn in detail about the human neural system, how it works, how nerve impulses are transmitted, and how messages pass from one neuron to another through synapses. Understanding these mechanisms is essential for grasping how our body maintains balance and reacts quickly to both internal and external stimuli.
2. Human Neural System – Structure, Function and Coordination for Class 11 & NEET
The neural system is a vital part of all animals, and it is made up of very special cells called neurons. These neurons are responsible for detecting, receiving, and sending signals or stimuli from one part of the body to another. Neurons help the body respond to both internal and external changes by passing messages rapidly. In lower invertebrates like Hydra, the neural system is very basic and simple. It is made up of a loose network of neurons, which are spread throughout the body. These neurons work together to control basic functions like movement and response to touch. However, in more evolved invertebrates such as insects, the neural system becomes more advanced. Insects have a brain, multiple ganglia (which are small clusters of neurons), and well-organised neural tissues that help in better control and coordination of body parts. When we look at vertebrates like fishes, birds, and humans, the neural system is highly developed and complex. Vertebrates have a well-defined central nervous system (CNS), which includes the brain and spinal cord, and a peripheral nervous system (PNS) that connects all parts of the body to the CNS. This advanced system allows vertebrates to think, learn, remember, sense the environment, and respond with great accuracy and speed. So, as we move from lower to higher animals, the structure and function of the neural system become more complex and efficient, allowing better coordination, control, and communication throughout the body.
3. Detailed Explanation of Human Nervous System – Parts, Functions & more.
1. Division of Human Neural System
The human neural system is broadly divided into two main parts – the Central Neural System (CNS) and the Peripheral Neural System (PNS). This division helps the body manage both internal and external communication effectively. The CNS works as the main control center of the body, while the PNS acts as the messenger system, carrying signals between the body and the CNS.
2. Central Neural System (CNS)
The Central Neural System includes the brain and the spinal cord. It is the primary site where all information is processed and decisions are made. The CNS receives incoming signals, processes them, and sends out appropriate responses. Whether it’s thinking, learning, reacting to a touch, or controlling voluntary and involuntary movements, everything is handled here. Basically, the CNS is the command center of the entire body.
3. Peripheral Neural System (PNS)
The Peripheral Neural System (PNS) consists of all the nerves that are connected to the brain and spinal cord. These nerves act like wires that carry information to and from different parts of the body. The PNS extends throughout the body, ensuring that even the most remote organs and tissues can communicate with the CNS. The main role of the PNS is to link the body with the brain and spinal cord, maintaining constant coordination.
4. Afferent and Efferent Fibres of PNS
The nerve fibres in the PNS are of two main types – afferent fibres and efferent fibres. The afferent fibres are responsible for carrying sensory information from various organs and tissues toward the CNS. For example, when you touch something hot, the afferent nerves send this information to the brain. On the other hand, the efferent fibres carry instructions from the CNS to different organs and muscles to perform a particular action, like moving your hand away from the hot object. This two-way communication system keeps our body responsive and well-coordinated.
5. Somatic Neural System
The Somatic Neural System is a division of the PNS that helps in voluntary control of body movements. It sends motor impulses from the CNS to the skeletal muscles, which are under conscious control. This system allows us to walk, talk, write, lift objects, and perform all kinds of voluntary actions. It acts quickly and is involved in immediate physical responses.
6. Autonomic Neural System
The Autonomic Neural System is also a part of the PNS, but it controls involuntary functions like heartbeat, digestion, and breathing. It sends impulses from the CNS to smooth muscles, glands, and internal organs. Unlike the somatic system, we do not have direct control over these functions. The autonomic system works automatically and ensures that the body’s internal environment stays balanced without any conscious effort.
7. Sympathetic and Parasympathetic Divisions
The Autonomic Neural System is further divided into two parts – the Sympathetic Neural System and the Parasympathetic Neural System. The sympathetic system prepares the body for emergency or stressful situations – also called the “fight or flight” response. It increases heart rate, dilates pupils, and redirects blood to muscles. On the other hand, the parasympathetic system helps the body to relax and return to a normal state after stress – often called the “rest and digest” response. It slows down the heartbeat, promotes digestion, and conserves energy.
8. Visceral Nervous System
The Visceral Nervous System is another component of the peripheral nervous system. It includes all the nerves, fibres, ganglia (nerve cell clusters), and plexuses (nerve networks) that carry signals from the internal organs (viscera) to the CNS and vice versa. It plays a key role in monitoring and regulating the function of vital organs like the heart, lungs, stomach, and intestines. This system ensures that the internal organs function smoothly and remain in coordination with the rest of the body.
4. Neuron – Structure, Types and Function as the Basic Unit of Nervous System
1. Structure of a Neuron
A neuron is the basic structural and functional unit of the human neural system. It is a tiny microscopic cell that plays a major role in transmitting nerve impulses throughout the body. A neuron has three main parts: the cell body, dendrites, and the axon. The cell body, also known as the cyton, contains cytoplasm, normal cell organelles, and unique granules called Nissl’s granules which help in protein synthesis. This is the main metabolic center of the neuron where the cell’s activities are controlled and nutrients are processed.
2. Dendrites – Receiving Ends of a Neuron
Coming out from the cell body are small, tree-like branches known as dendrites. These are short fibres that branch repeatedly and also contain Nissl’s granules. The main function of dendrites is to receive signals or impulses from other neurons or sensory organs and carry them towards the cell body. They act like antennae, picking up incoming messages and helping in the relay of information within the nervous system.
3. Axon – The Signal Sender
The axon is a long, single fibre that extends out from the cell body. At its end, it branches out and each branch ends in a bulb-like structure called the synaptic knob. These knobs contain synaptic vesicles, which hold special chemicals called neurotransmitters. The function of the axon is to transmit nerve impulses away from the cell body either to another neuron across a synapse or to a muscle (neuromuscular junction). This is how signals travel from one cell to another or from the brain to body parts.
4. Types of Neurons Based on Structure
Neurons are classified into three types depending on the number of axons and dendrites they have:
- Multipolar neurons have one axon and two or more dendrites. These are commonly found in the cerebral cortex of the brain and are involved in higher processing functions like thinking and learning.
- Bipolar neurons have one axon and one dendrite. These are found in the retina of the eye and are involved in vision-related activities.
- Unipolar neurons have only a single axon coming from the cell body. These are usually present during the embryonic stages of development.
5. Myelinated and Non-Myelinated Axons
Neurons can also be divided based on the type of axon covering they have. Some axons are myelinated, which means they are covered by Schwann cells that form a myelin sheath around the axon. This sheath helps in speeding up the transmission of nerve impulses. Between the sections of the sheath are small gaps called Nodes of Ranvier, which allow the signal to jump rapidly from node to node. Myelinated fibres are mainly found in the spinal nerves and cranial nerves.
6. Non-Myelinated Axons
In non-myelinated fibres, the Schwann cells are present but they do not form a myelin sheath around the axon. These types of nerve fibres conduct impulses more slowly compared to myelinated ones. Non-myelinated fibres are commonly found in the autonomic nervous system (which controls involuntary activities) and the somatic nervous system (which controls voluntary movements). Both types of fibres are important for different functions in the body.
5. Nerve Impulse – Generation, Conduction & Mechanism
1. Neurons and Their Polarised Membrane
Neurons are special because they are excitable cells, meaning they can generate and conduct electrical signals. At rest (when no signal is being sent), the membrane of a neuron is said to be in a polarised state. This means that the inner side of the neuron’s membrane is negatively charged, and the outer side is positively charged. This polarity happens due to the presence of different types of ion channels in the neuron’s membrane, which are selectively permeable—allowing certain ions to pass more easily than others. At rest, the membrane is more permeable to potassium ions (K⁺) but almost impermeable to sodium ions (Na⁺). Also, negatively charged proteins inside the neuron cannot cross the membrane. As a result, the inside of the neuron (axoplasm) has a high amount of K⁺ and negative proteins, while the fluid outside contains more Na⁺ and less K⁺, creating a concentration gradient.
2. Role of Sodium-Potassium Pump in Resting Potential
To maintain this ionic difference, a special protein called the sodium-potassium pump actively works across the membrane. This pump moves 3 Na⁺ ions out of the cell and brings 2 K⁺ ions into the cell, using energy from ATP. Because of this exchange, the outside becomes more positively charged than the inside. This difference in electrical charge across the membrane is known as the resting potential, which prepares the neuron to respond quickly when a stimulus arrives.
3. What Happens When a Stimulus Arrives – Depolarisation
When a stimulus (like touch or pain) hits a particular point on the neuron membrane (e.g., point A), that area becomes highly permeable to Na⁺ ions. As a result, Na⁺ ions quickly rush into the neuron. This sudden inflow reverses the polarity at point A – the inner surface becomes positively charged, and the outer surface becomes negatively charged. This state is called depolarisation, and the voltage difference across this point is known as the action potential, which is the actual nerve impulse.
4. How the Impulse Travels – Current Flow and Conduction
Just ahead of point A (say point B), the membrane is still at rest – it has positive charge outside and negative inside. So, an electric current flows inside the axon from point A to B, and outside from B to A, completing the circuit of current flow. This movement of current causes the membrane at point B to also depolarise, and a new action potential is generated there. This chain reaction continues along the length of the axon, making the impulse travel forward step-by-step.
5. Repolarisation – Restoring the Resting State
After the action potential is generated at a site, the membrane does not stay depolarised for long. Very soon after the Na⁺ channels close, the membrane becomes more permeable to K⁺ ions, and K⁺ starts moving out of the neuron. This outflow of K⁺ ions restores the original polarity – the inside becomes negative again and the outside becomes positive. This process is known as repolarisation, and the neuron is now ready for another stimulus. The entire process of depolarisation and repolarisation happens in just a fraction of a second.
6. Transmission of Nerve Impulses – Synapses, Neurotransmitters & Signal Flow
In the human nervous system, the transmission of a nerve impulse from one neuron to another happens through a special connection called a synapse. A synapse is a point where the end of one neuron (called the pre-synaptic neuron) connects with another neuron (called the post-synaptic neuron). Between these two neurons, there might be a small fluid-filled gap called the synaptic cleft, but in some cases, the two membranes are extremely close. Synapses are the key structures that allow messages to travel through the nervous system and are essential for neural coordination. There are mainly two types of synapses in the human body – electrical synapses and chemical synapses.
Electrical Synapses – Direct Current Flow Between Neurons
Electrical synapses are the type of synapses where the membranes of the pre-synaptic and post-synaptic neurons are so close that they allow direct flow of electric current from one neuron to another. These types of synapses work in a way that is very similar to how an impulse moves along a single neuron. Since there’s no gap or delay, the impulse transmission in electrical synapses is extremely fast. However, electrical synapses are very rare in the human nervous system. Their main function is to allow quick communication between neurons when speed is crucial, such as in certain reflexes or early development stages.
Chemical Synapses – Neurotransmitter-Based Communication
On the other hand, chemical synapses are the most common type of synapses in the human body. In this type, the membranes of the two neurons are separated by a gap called the synaptic cleft, which is filled with fluid. Since there is a gap, the electric signal cannot directly jump across. Instead, the signal is passed in the form of chemicals called neurotransmitters. These neurotransmitters help bridge the gap between neurons and carry the message across.
How Neurotransmitters Work at Chemical Synapses
When a nerve impulse (also called an action potential) reaches the end of the axon in the pre-synaptic neuron, it stimulates vesicles (tiny bubble-like structures) in the axon terminals. These vesicles are filled with neurotransmitter molecules. As the impulse arrives, the vesicles move toward the membrane of the axon terminal and fuse with it, releasing the neurotransmitters into the synaptic cleft. These neurotransmitters then bind to specific receptors on the post-synaptic neuron’s membrane.
Effect of Neurotransmitter Binding on the Next Neuron
Once neurotransmitters attach to the receptors on the post-synaptic membrane, they cause ion channels to open. This allows certain ions to flow into the post-synaptic neuron. The flow of these ions generates a new electrical potential, which may result in a new nerve impulse in the post-synaptic neuron. This new signal can be either excitatory (which continues the nerve signal) or inhibitory (which blocks the signal). This whole process ensures that communication between neurons happens accurately and efficiently.
7. Brain and Spinal Cord Structure & Functions | Central Nervous System (CNS)
The brain is the most important organ in our nervous system. It works as the main control center of the body, processing all kinds of information. It plays a major role in voluntary actions like moving hands and legs, and also in involuntary functions like heartbeat, breathing, kidney function, and digestion. Apart from this, the brain is responsible for maintaining body balance, controlling body temperature (thermoregulation), managing hunger and thirst, and maintaining the 24-hour internal clock (circadian rhythm). It also helps control the working of endocrine glands (hormone-secreting glands), and influences various aspects of human behaviour, like mood and personality. Most importantly, it is the main center for processing senses like vision and hearing, and also handles speech, memory, emotions, thoughts, intelligence, and learning.
Protection of the Brain – Skull and Cranial Meninges
Since the brain is so delicate and important, it is well-protected by the skull, a bony structure that forms the head. But protection doesn’t stop there. Inside the skull, the brain is wrapped in three special protective coverings known as the cranial meninges. These meninges are made of three layers:
- Dura mater – The outermost layer, which is thick and tough.
- Arachnoid – The middle layer, which is very thin and web-like.
- Pia mater – The innermost layer that is soft and delicate, and stays in direct contact with the brain tissue.
These layers provide cushioning, support, and protection to the brain from injury, infection, and pressure changes.
Major Parts of the Brain – Forebrain, Midbrain, and Hindbrain
The human brain is functionally and structurally divided into three major parts:
- Forebrain – This is the largest part and is involved in thinking, reasoning, memory, and controlling voluntary movements.
- Midbrain – This part acts like a bridge connecting different parts of the brain. It helps in the coordination of sensory information, especially related to vision and hearing.
- Hindbrain – This part controls automatic functions like heartbeat, breathing, and body balance.
Each of these parts has its own role, but they all work together to keep the body functioning smoothly.
8. Forebrain – Structure, Functions of Cerebrum, Thalamus & Hypothalamus
The forebrain is the largest and most developed part of the human brain. It consists of three main parts: the cerebrum, thalamus, and hypothalamus. Among these, the cerebrum forms the biggest portion and plays a key role in thinking, decision-making, memory, emotions, and voluntary actions. A deep groove runs through the center of the cerebrum, dividing it into two hemispheres – the left cerebral hemisphere and the right cerebral hemisphere. These two halves are connected by a bundle of nerve fibers called the corpus callosum, which allows communication between both sides of the brain.
Cerebral Cortex and Its Role in Higher Brain Functions
The outermost layer of the cerebrum is known as the cerebral cortex. This layer is made up of tightly packed neuron cell bodies, which give it a greyish color, and that’s why it is commonly called the “grey matter“. The surface of the cerebral cortex has many folds, which help to increase its surface area for more neuron connections. The cortex includes motor areas (that control muscle movement), sensory areas (that receive signals from the sense organs), and association areas. These association areas are not directly linked to sensing or movement, but they handle complex processes like memory, communication, logical thinking, and integration of different sensory inputs.
White Matter – Inner Layer of the Cerebrum
Beneath the grey matter lies the white matter, which is made of nerve fibers covered with myelin sheath. These myelinated fibers transmit messages quickly between different brain areas. Because of the presence of myelin (which has a whitish appearance), this region looks white and shiny. The white matter acts like a communication highway, ensuring that all parts of the brain work in coordination.
Thalamus – Relay Centre for Sensory and Motor Signals
The thalamus lies just below the cerebrum and acts as a central hub for sensory and motor information. It helps relay signals from the sense organs to the correct parts of the cerebral cortex. It also plays a part in filtering and focusing the sensory input, ensuring that only the important signals are processed. Thus, it is a major coordinating center that helps the brain handle incoming and outgoing signals efficiently.
Hypothalamus – Master Regulator of Body Functions
Just beneath the thalamus is the hypothalamus, a small but extremely important part of the brain. It controls many automatic and vital body functions. It has centers for regulating body temperature, hunger, thirst, and even sleep-wake cycles. The hypothalamus also contains neurosecretory cells, which secrete special hormones known as hypothalamic hormones. These hormones influence the functioning of the pituitary gland, making the hypothalamus a key link between the nervous system and the endocrine system.
Limbic System – The Emotional and Motivational Brain
The inner parts of the cerebral hemispheres, along with some deeply embedded structures like the amygdala and hippocampus, form the limbic system (also known as the limbic lobe). This system, together with the hypothalamus, plays an essential role in controlling emotions, sexual behavior, and motivation. It is responsible for how we feel and react emotionally, including responses like pleasure, fear, anger, and excitement. The limbic system also contributes to long-term memory formation and learning processes, especially related to emotional experiences.
9. Midbrain – Structure, Corpora Quadrigemina & Role in Neural Coordination
The midbrain is a small but important part of the brain that lies between the forebrain and hindbrain. Specifically, it is located below the thalamus and hypothalamus of the forebrain and just above the pons of the hindbrain. This central position allows the midbrain to act as a connecting bridge between different parts of the brain. It plays a major role in relaying information, especially related to visual and auditory responses, motor control, and alertness.
Running through the center of the midbrain is a narrow canal called the cerebral aqueduct. This canal connects two cavities in the brain — the third ventricle (in the forebrain) and the fourth ventricle (in the hindbrain). It allows the flow of cerebrospinal fluid (CSF) between these parts, which helps in protecting the brain and maintaining pressure balance.
The dorsal part (upper side) of the midbrain has four small round swellings called the corpora quadrigemina. These swellings are divided into two pairs — the superior colliculi and the inferior colliculi. The superior colliculi help in processing visual information and coordinating eye movements, while the inferior colliculi deal with auditory signals (sound) and reflexes related to hearing. Together, these structures help the body respond quickly to visual and sound stimuli — like turning your head when you hear a loud noise or when something flashes in front of your eyes.
10. Hindbrain – Structure and Functions of Pons, Cerebellum & Medulla Oblongata
The hindbrain is the lower back portion of the brain that connects directly to the spinal cord. It is made up of three main parts – the pons, the cerebellum, and the medulla oblongata (also called simply the medulla). Each of these parts plays a special role in managing the body’s automatic and coordination-related functions.
The pons is a part of the hindbrain that contains nerve fibers (called fibre tracts). These fibers help connect different areas of the brain to one another. Basically, the pons acts as a bridge, carrying messages between the cerebrum, cerebellum, and medulla. It also plays a role in controlling breathing and helps regulate the rhythm of respiration.
The cerebellum is located just behind the pons and looks like a smaller brain under the main brain. Its surface is highly folded (convoluted), which increases its surface area and allows more neurons to be packed in. This structure makes the cerebellum extremely efficient in handling tasks related to body balance, posture, muscle coordination, and fine motor skills. It ensures that all body movements are smooth and well-coordinated. For example, when you walk, run, or even write, the cerebellum helps you stay in control of your movements.
The medulla oblongata, or simply medulla, is the lowest part of the brain, located right where the brain connects with the spinal cord. It plays a critical role in controlling many vital involuntary functions that we don’t consciously think about. These include breathing (respiration), heart rate and blood pressure (cardiovascular reflexes), and even digestion (like gastric secretions). Because of this, the medulla is considered one of the most important survival centers in the brain.
Together, the midbrain, pons, and medulla oblongata form what is known as the brain stem. The brain stem acts like a communication link between the brain and spinal cord, carrying messages back and forth. It also controls many basic life-sustaining functions, which makes it essential for survival.
11. Neural System – Chapter Summary with Key Concepts & Highlights
The neural system in our body is responsible for coordinating and integrating all the body’s activities. It ensures that all the organs work together properly, maintaining both metabolic processes and homeostasis (internal balance). The working unit of the neural system is the neuron, which is a type of cell that can generate and conduct electrical impulses. This ability comes from the difference in ion concentrations on both sides of the neuron’s membrane. When a neuron is at rest, this difference creates a charge known as the resting potential.
When the neuron is activated, an electrical signal known as a nerve impulse travels along its length (axon). This signal moves in the form of a wave, passing through depolarization (where the inside becomes positively charged) and then repolarization (returning to the resting state). The message from one neuron to another is passed through a synapse, which is the point of contact between the pre-synaptic neuron (sending end) and the post-synaptic neuron (receiving end). Some synapses have a small space called a synaptic cleft between the two neurons. At chemical synapses, special chemicals called neurotransmitters help in passing the message across this gap.
The human neural system is made up of two major parts:
- Central Neural System (CNS)
- Peripheral Neural System (PNS)
The CNS includes the brain and the spinal cord. The brain itself is divided into three main regions:
- The Forebrain,
- The Midbrain,
- The Hindbrain.
The forebrain includes the cerebrum, thalamus, and hypothalamus. The cerebrum is the largest part and is split into left and right halves, which are joined together by a structure called the corpus callosum. A key part of the forebrain is the hypothalamus, which controls body temperature, hunger, and thirst. Inside the cerebral hemispheres, there are deep structures that, along with the hypothalamus, form the limbic system. This system is involved in sense of smell (olfaction), automatic body responses, sexual behavior, emotions like fear or pleasure, and motivation.
The midbrain helps to process and combine sensory information from the eyes (visual), skin (touch), and ears (sound). It acts as a center for integrating visual, tactile, and auditory signals.
The hindbrain includes the pons, cerebellum, and medulla oblongata. The cerebellum plays a key role in maintaining body balance and coordination. It receives information from the semicircular canals of the ears and also from the auditory system to manage body posture. The medulla contains centers that regulate vital processes like breathing, heart rate, and digestive secretions. The pons contains nerve fibers that connect different parts of the brain, helping them to work together smoothly.
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