Neural Control and Coordination Class 11 Biology Chapter 18 Notes

Neural Control and Coordination Class 11 Biology Chapter 18 Notes

Coordination of Organ Systems in Human Body

1. Importance of Coordination in Organ Systems:
   • Maintenance of homeostasis necessitates coordinated functions of organ systems.
   • Coordination ensures proper response to changes in internal and external environments.
   • Example: Physical exercise increases energy demand, oxygen supply, respiration rate, heart rate, and blood flow.
2. Coordination during Physical Exercise:
   • Increased muscular activity demands more energy and oxygen supply.
   • Organs like the lungs, heart, blood vessels, and kidneys adjust to meet the increased demands.
   • After exercise, the organs gradually return to their normal conditions.
3. Role of Neural and Endocrine Systems in Coordination:
   • Neural system facilitates quick coordination through point-to-point connections.
   • Endocrine system ensures coordination via chemical integration using hormones.
4. Neural System and its Functions:
   • Organized network of point-to-point connections for rapid coordination.
   • Mechanisms include transmission of nerve impulses and impulse conduction across synapses.
5. Integration of Organ Activities:
   • Neural and endocrine systems work together to synchronize organ functions.
   • Ensure harmonious functioning of muscles, lungs, heart, blood vessels, and kidneys during activities like physical exercise.
6. Mechanisms of Neural Coordination:
   • Understanding the transmission of nerve impulses and their conduction across synapses.
   • Neural coordination enables quick responses to various stimuli and situations.
7. Synchronized Functioning of Organs:
   • Muscles, lungs, heart, blood vessels, kidneys, and other vital organs work in tandem during physical activities.
   • Coordination between the neural and endocrine systems ensures seamless regulation and adjustment.

Neural System

1. Neurons – The Building Blocks:
   • The neural system in all animals comprises specialized cells known as neurons.
   • Neurons possess the unique ability to detect, receive, and transmit various types of stimuli.
2. Neural Organization in Lower Invertebrates:
   • In lower invertebrates like Hydra, the neural organization is relatively simple.
   • It consists of a network of neurons that enable basic sensory and motor functions.
3. Neural Organization in Insects:
   • Insects exhibit a more advanced neural system compared to lower invertebrates.
   • Insects have a rudimentary brain along with numerous ganglia and neural tissues.
   • This complexity allows for more intricate sensory and motor responses.
4. The Developed Neural System in Vertebrates:
   • Vertebrates, including humans, possess a highly developed neural system.
   • This system is characterized by its complexity and sophistication.
   • Vertebrates have well-defined brains, spinal cords, and a multitude of nerves and neural structures.
5. Progressive Evolution of Neural Systems:
   • The neural system’s complexity and organization tend to evolve progressively across species.
   • Higher complexity often correlates with an organism’s cognitive and sensory capabilities.
6. The Role of Neurons:
   • Neurons are the functional units of the neural system.
   • They serve as the information processors, transmitting signals and enabling communication within the body.
7. Importance of Neural System:
   • The neural system is essential for coordinating and regulating various bodily functions.
   • It plays a crucial role in perceiving and responding to the environment.
8. Interconnected Nature of the Neural System:
   • Neurons are interconnected in a vast network, allowing for the integration of information and coordinated responses.
   • The brain and spinal cord act as central hubs for processing and controlling neural signals.
9. Human and Vertebrate Complexity:
   • Vertebrates, particularly humans, exhibit a remarkable level of neural complexity.
   • The human brain, with its intricate structure and functions, is a pinnacle of neural evolution.
10. Ongoing Exploration:
    • Research in neuroscience continually unveils the mysteries of the neural system, enhancing our understanding of its operations and its role in maintaining homeostasis and facilitating complex behaviors.

Human Neural System

The human neural system is a complex network of structures responsible for information processing and control. It consists of two primary divisions:

1. Central Neural System (CNS):
   • Includes the brain and the spinal cord.
   • Functions as the core site for information processing, decision-making, and overall control of the body.
   • It integrates and interprets sensory inputs, initiates motor responses, and regulates bodily functions.
2. Peripheral Neural System (PNS):
   • Comprises all the nerves in the body that are associated with the CNS (brain and spinal cord).
   • Serves as a communication network between the CNS and the rest of the body.
   • The PNS includes various types of nerve fibers that play specific roles.

Nerve Fibers in the PNS:

(a) Afferent Fibers:

• Transmit impulses from peripheral tissues and organs to the CNS.
• Responsible for relaying sensory information, allowing the brain to process and interpret external and internal stimuli.

(b) Efferent Fibers:

• Transmit regulatory impulses from the CNS to the relevant peripheral tissues and organs.
• These impulses initiate motor responses and control the body’s various functions.

Division of the PNS:

The PNS is further divided into two major divisions:

1. Somatic Neural System:
   • Relays impulses from the CNS to skeletal muscles.
   • Responsible for voluntary control of body movements and sensory perception related to the external environment.
2. Autonomic Neural System:
   • Transmits impulses from the CNS to involuntary organs and smooth muscles within the body.
   • Regulates automatic or involuntary functions such as heart rate, digestion, and respiratory rate.

Subdivisions of the Autonomic Neural System:

The autonomic neural system is further classified into two subdivisions:

(a) Sympathetic Neural System:

• Responsible for the “fight or flight” response.
• Activates in situations requiring increased energy expenditure and heightened alertness.
• Increases heart rate, dilates airways, and diverts blood flow to muscles.

(b) Parasympathetic Neural System:

• Promotes the “rest and digest” response.
• Activates during periods of relaxation and recovery.
• Slows heart rate, constricts airways, and directs blood flow to digestive organs.

Visceral Nervous System:

• The visceral nervous system is a component of the PNS that encompasses an intricate network of nerves, fibers, ganglia, and plexuses.
• It facilitates the transmission of impulses between the central nervous system and the visceral organs (organs located in the chest, abdomen, and pelvis) and vice versa.
• The visceral nervous system plays a vital role in regulating the functions of internal organs, ensuring homeostasis, and responding to various physiological needs.

Neuron as the Structural and Functional Unit of the Neural System

• A neuron, also known as a nerve cell, is the fundamental structural and functional unit of the neural system. Neurons are highly specialized for transmitting signals and information throughout the body.

Components of a Neuron:

1. Cell Body (Soma):
   • The cell body is the central part of the neuron.
   • It contains cytoplasm with typical cell organelles such as the nucleus and endoplasmic reticulum.
   • It also contains granular bodies known as Nissl’s granules, which are involved in protein synthesis.
2. Dendrites:
   • Dendrites are short, branching fibers that project from the cell body.
   • They contain Nissl’s granules and transmit impulses toward the cell body.
   • Dendrites receive signals and sensory information from other neurons or sensory receptors.
3. Axon:
   • The axon is a long, slender fiber that extends from the cell body.
   • It may branch at its distal end and terminates in bulb-like structures called synaptic knobs.
   • These synaptic knobs contain synaptic vesicles filled with neurotransmitters, which are chemical messengers.
   • Axons transmit nerve impulses away from the cell body, either to synapses (connections with other neurons) or to neuromuscular junctions (muscle fibers).

Types of Neurons Based on Axon and Dendrite Arrangement:

1. Multipolar Neurons:
   • Multipolar neurons have one axon and two or more dendrites.
   • They are commonly found in the cerebral cortex and play a role in complex information processing and decision-making.
2. Bipolar Neurons:
   • Bipolar neurons have one axon and one dendrite.
   • They are typically found in the retina of the eye and are involved in sensory processes, particularly visual perception.
3. Unipolar Neurons:
   • Unipolar neurons have a single axon extending from the cell body.
   • During the embryonic stage, they are more prevalent.

Types of Axons:

1. Myelinated Axons:
   • Myelinated nerve fibers are wrapped in a protective sheath called myelin.
   • Schwann cells form the myelin sheath around the axon.
   • Nodes of Ranvier are gaps between adjacent myelin sheaths.
   • Myelinated axons are typically found in spinal and cranial nerves.
   • Myelin sheaths increase the speed of nerve impulse conduction.
2. Unmyelinated Axons:
   • Unmyelinated nerve fibers lack the myelin sheath and have Schwann cells that do not form a myelin sheath around the axon.
   • They are commonly found in both the autonomic and somatic neural systems.

Function of Neurons:

• Neurons are responsible for transmitting electrical signals, known as nerve impulses, which convey information and coordinate various functions within the body.
• These impulses are crucial for sensory perception, motor control, and complex cognitive processes.

Generation and Conduction of Nerve Impulse

1. Neuronal Membrane Polarization:
   • Neurons are excitable cells with polarized membranes.
   • The polarized state of the neuron’s membrane is maintained by different types of ion channels that are selectively permeable to specific ions.
   • When a neuron is at rest (not conducting an impulse), the axonal membrane is highly permeable to potassium ions (K+) and almost impermeable to sodium ions (Na+). It is also impermeable to negatively charged proteins in the axoplasm.
   • This results in a high concentration of K+ and negatively charged proteins inside the axon and a low concentration of K+ and a high concentration of Na+ outside the axon. This forms an ionic concentration gradient.
2. Sodium-Potassium Pump:
   • The maintenance of these ionic gradients across the resting membrane is achieved through the action of the sodium-potassium pump.
   • The sodium-potassium pump actively transports 3 sodium ions (Na+) out of the cell for every 2 potassium ions (K+) it transports into the cell.
   • As a result, the outer surface of the axonal membrane becomes positively charged, while the inner surface becomes negatively charged, leading to polarization.
   • The electrical potential difference across the resting plasma membrane is known as the resting potential.
3. Generation of Nerve Impulse (Action Potential):
   • To generate a nerve impulse, a stimulus is applied to a specific site on the polarized membrane (e.g., point A).
   • The membrane at the stimulus site (A) becomes temporarily permeable to sodium ions (Na+).
   • This leads to a rapid influx of Na+ into the axon, resulting in the reversal of polarity at that site.
   • The outer surface becomes negatively charged, and the inner surface becomes positively charged, a process known as depolarization.
   • The electrical potential difference across the membrane at this site is now referred to as the action potential, which is, in essence, a nerve impulse.
4. Conduction of Nerve Impulse:
   • Immediately following the generation of an action potential at one site (e.g., A), the adjacent region (e.g., site B) has a positive charge on the outer surface and a negative charge on the inner surface.
   • This creates a flow of current along the inner surface from site A to site B.
   • On the outer surface, current flows from site B to site A, completing the circuit of current flow.
   • This process reverses the polarity at site B, generating another action potential.
   • The sequence repeats along the length of the axon, allowing the impulse to be conducted from one end to the other.
5. Rapid Restoration of Resting Potential:
   • The increased permeability to Na+ caused by the stimulus is short-lived.
   • Shortly after, there is a rise in permeability to potassium ions (K+).
   • K+ diffuses out of the membrane within a fraction of a second, restoring the resting potential of the membrane at the site of excitation.
   • This quick restoration makes the neuron responsive to further stimulation.

Transmission of Impulses at Synapses

Nerve impulses are transmitted from one neuron to another through specialized junctions known as synapses. These synapses play a crucial role in facilitating communication within the nervous system. There are two main types of synapses: electrical synapses and chemical synapses.

1. Electrical Synapses:
   • At electrical synapses, the membranes of both the pre-synaptic neuron (the neuron sending the signal) and the post-synaptic neuron (the neuron receiving the signal) are in very close proximity.
   • In electrical synapses, electrical current can flow directly from one neuron to the other, just like impulse conduction along a single axon.
   • Transmission of impulses across electrical synapses is exceptionally fast, making them rare in the human nervous system.
2. Chemical Synapses:
   • In contrast, chemical synapses are more common in the human nervous system.
   • At chemical synapses, the membranes of the pre-synaptic and post-synaptic neurons are separated by a small fluid-filled gap known as the synaptic cleft.

Transmission of Impulse at Chemical Synapses:

• The transmission of a nerve impulse at a chemical synapse involves a series of steps and the use of neurotransmitters, which are chemicals that act as messengers between neurons.

1. Storage of Neurotransmitters:
   • Within the axon terminals of the pre-synaptic neuron, there are vesicles filled with neurotransmitters.
2. Arrival of Impulse (Action Potential):
   • When an impulse, or action potential, reaches the axon terminal, it triggers a series of events.
3. Release of Neurotransmitters:
   • The arrival of the action potential stimulates the movement of the synaptic vesicles toward the cell membrane of the pre-synaptic neuron.
   • The vesicles fuse with the plasma membrane and release their neurotransmitters into the synaptic cleft.
4. Binding of Neurotransmitters:
   • The neurotransmitters released into the synaptic cleft bind to their specific receptors located on the post-synaptic neuron’s membrane.
5. Opening of Ion Channels:
   • The binding of neurotransmitters to their receptors on the post-synaptic membrane results in the opening of ion channels.
   • These channels allow the entry of specific ions into the post-synaptic neuron.
6. Generation of New Potential:
   • The entry of ions into the post-synaptic neuron can generate a new electrical potential in that neuron.
   • This new potential can either be excitatory, meaning it makes the post-synaptic neuron more likely to generate an action potential, or inhibitory, meaning it makes the neuron less likely to generate an action potential.

Central Neural System (CNS): The Brain

The human brain serves as the central information processing and control center for the entire body. It plays a pivotal role in numerous functions and is often referred to as the “command and control system.” The brain’s functions are diverse and encompass various aspects of human physiology and behavior.

Functions of the Brain:

1. Control of Voluntary Movements:
   • The brain coordinates and controls voluntary movements, allowing us to perform various physical activities and interact with our environment.
2. Balance and Coordination:
   • It maintains balance and coordination within the body, ensuring smooth motor functions.
3. Regulation of Involuntary Organs:
   • The brain regulates vital involuntary organs such as the lungs, heart, kidneys, and more, maintaining essential bodily functions.
4. Thermoregulation:
   • The brain plays a crucial role in maintaining body temperature (thermoregulation) within a narrow range.
5. Hunger and Thirst:
   • It is involved in the regulation of hunger and thirst, controlling our appetites and thirst responses.
6. Circadian Rhythms:
   • The brain influences the circadian (24-hour) rhythms of the body, governing sleep-wake cycles and various physiological processes.
7. Endocrine Glands:
   • The brain controls the activities of several endocrine glands, such as the pituitary gland, which releases hormones that influence various bodily functions.
8. Processing of Sensory Information:
   • It is the site for processing sensory information, including vision, hearing, and speech perception.
9. Memory and Intelligence:
   • The brain is responsible for memory formation, storage, and retrieval, as well as the capacity for intelligence and problem-solving.
10. Emotions and Thoughts:
    • It plays a central role in generating emotions, thoughts, and complex cognitive functions, contributing to our individual personalities and behaviors.

Protective Structures of the Brain:

• The human brain is well protected by the skull, which encases it. Inside the skull, the brain is further safeguarded by the cranial meninges, which consist of three layers:
  • Dura Mater (Outer Layer): The outermost layer.
  • Arachnoid (Middle Layer): A very thin layer.
  • Pia Mater (Inner Layer): In direct contact with the brain tissue.

Major Divisions of the Brain:

The brain can be divided into three major parts:

1. Forebrain: This includes the cerebrum, which is responsible for complex cognitive functions, such as thinking, memory, and emotions, as well as the diencephalon, which includes the thalamus and hypothalamus, responsible for sensory relay and hormone regulation, respectively.
2. Midbrain: This region plays a role in relaying sensory and motor information.
3. Hindbrain: It consists of the pons, medulla oblongata, and cerebellum. The cerebellum is crucial for motor coordination and balance, while the pons and medulla oblongata are involved in regulating vital functions like breathing and heart rate.

Forebrain: Cerebrum, Thalamus, and Hypothalamus

The forebrain is one of the major divisions of the brain and is responsible for a wide range of complex functions. It consists of three primary structures: the cerebrum, thalamus, and hypothalamus.

1. Cerebrum:
   • The cerebrum is the largest and most prominent part of the human brain.
   • It is divided into two hemispheres, the left and right cerebral hemispheres, which are separated by a deep cleft.
   • These hemispheres are connected by a bundle of nerve fibers called the corpus callosum.
   • The outer layer of the cerebrum is known as the cerebral cortex, which is highly folded, forming prominent folds and grooves. The presence of numerous neuron cell bodies gives the cerebral cortex a grayish appearance, earning it the name “gray matter.”
   • The cerebral cortex contains various regions, including motor areas that control voluntary movements, sensory areas for processing sensory information, and large areas known as association areas, responsible for complex functions such as memory, communication, and intersensory associations.
   • Deep within the cerebrum, beneath the cerebral cortex, are myelinated nerve fiber tracts that make up the “white matter.” These fibers give the inner part of the cerebral hemisphere an opaque white appearance.
2. Thalamus:
   • The thalamus is a key coordinating center for sensory and motor signaling.
   • It acts as a relay station for sensory information from different parts of the body to the cerebral cortex.
   • The thalamus plays a pivotal role in processing and routing sensory data to the appropriate areas of the cerebral cortex for further analysis.
3. Hypothalamus:
   • The hypothalamus is situated at the base of the thalamus and is a vital region of the brain.
   • It contains multiple centers that regulate various physiological functions, including:
     • Body Temperature: The hypothalamus controls body temperature, helping to maintain it within a narrow and stable range.
     • Hunger and Thirst: It regulates feelings of hunger and thirst, influencing eating and drinking behaviors.
     • Neurosecretory Cells: The hypothalamus houses neurosecretory cells that release hormones known as hypothalamic hormones, which control the pituitary gland and, in turn, influence various endocrine processes.
   • The hypothalamus is also a key player in regulating sexual behavior, emotional reactions (e.g., excitement, pleasure, rage, fear), and motivation.
4. Limbic System:
   • The inner regions of the cerebral hemispheres, along with associated deep structures such as the amygdala and hippocampus, form a complex structure known as the limbic lobe or limbic system.
   • The limbic system, along with the hypothalamus, is involved in the regulation of sexual behavior, emotional expressions (e.g., joy, pleasure, anger, fear), and motivation.

Midbrain

The midbrain, also known as the mesencephalon, is a region of the brain that serves as a bridge between the forebrain and the hindbrain. It is positioned between the thalamus and hypothalamus of the forebrain and the pons of the hindbrain.

Key features of the midbrain include:

1. Cerebral Aqueduct:
   • Running through the midbrain is a narrow canal known as the cerebral aqueduct. This canal connects the third and fourth ventricles, which are fluid-filled cavities in the brain responsible for cerebrospinal fluid circulation.
2. Corpora Quadrigemina:
   • The dorsal (upper) portion of the midbrain primarily consists of four prominent round swellings or lobes known as the corpora quadrigemina.
   • The corpora quadrigemina are further divided into two pairs of colliculi:
     • Superior Colliculi: These are the upper pair and are primarily involved in processing visual information and controlling eye movements.
     • Inferior Colliculi: These are the lower pair and play a key role in auditory processing, particularly in the integration and relay of auditory information.

The midbrain has various functions related to sensory processing, and it acts as an important pathway for the transmission of sensory information to higher brain regions. It also plays a role in regulating motor functions and reflexes.

Hindbrain: Pons, Cerebellum, and Medulla Oblongata

The hindbrain is one of the three major divisions of the brain and is located in the posterior part of the brain. It includes the pons, cerebellum, and medulla oblongata, each of which serves distinct functions.

1. Pons:
   • The pons is a region of the hindbrain that consists of fiber tracts connecting various areas of the brain. It forms a bridge, linking the two hemispheres of the cerebellum.
   • The pons plays a role in regulating essential functions such as respiration, facial movements, and sensations such as hearing and taste.
2. Cerebellum:
   • The cerebellum is located posterior to the pons and is characterized by its highly convoluted (folded) surface. These folds provide additional space for a large number of neurons.
   • The cerebellum is primarily responsible for coordinating and fine-tuning motor movements, ensuring precision and balance in voluntary muscle control.
   • It also plays a role in motor learning and cognitive functions related to movement and spatial processing.
3. Medulla Oblongata (Medulla):
   • The medulla oblongata, commonly referred to as the medulla, is located at the base of the brainstem and is directly connected to the spinal cord.
   • The medulla contains various vital centers that control essential physiological functions, including:
     • Respiration: It regulates breathing, ensuring the rhythmic and automatic functioning of the respiratory muscles.
     • Cardiovascular Reflexes: The medulla plays a central role in controlling heart rate, blood pressure, and other cardiovascular reflexes.
     • Gastric Secretions: It regulates gastric secretions and various gastrointestinal functions.

Collectively, the midbrain, pons, and medulla oblongata form the brainstem. The brainstem serves as a critical bridge between the brain and the spinal cord, facilitating the transmission of signals to and from the body. It also plays a pivotal role in regulating fundamental bodily functions, making it indispensable for survival.