Class 11 Biology NCERT Notes- Chapter 18: Neural Control and Coordination

Detailed Study Notes – Chapter 18: Neural Control and Coordination (Class 11 Biology, Notes, PDFs, Quizzes, MCQs)

1. The Principle of Coordination

Coordination is the fundamental process by which two or more organs interact and complement each other’s functions to maintain homeostasis, the stable internal environment of the body. The human body relies on two key systems for this integration:

• The Neural System: Provides rapid, point-to-point coordination through an organised network of neurons.
• The Endocrine System: Provides slower, chemical integration through the release of hormones.

A prime example of coordination is during physical exercise. Increased muscular activity demands more energy and oxygen, leading to an increased rate of respiration and heartbeat, and enhanced blood flow. When the exercise stops, the activities of the nerves, lungs, heart, and kidneys gradually return to normal, demonstrating a synchronised and coordinated effort among multiple organ systems.

2. The Human Neural System

The human neural system is the body’s primary control and communication network. It is composed of highly specialised cells called neurons, which can detect, receive, and transmit various stimuli. The system is broadly divided into two main parts.

2.1 Central Neural System (CNS)

The CNS is the core of the nervous system and serves as the primary site for information processing and control.

• Components: The brain and the spinal cord.

2.2 Peripheral Neural System (PNS)

The PNS consists of all the nerves of the body that are associated with the CNS. It acts as the communication relay between the CNS and the rest of the body.

• Nerve Fibres of the PNS:
  • Afferent Fibres: Transmit sensory impulses from tissues and organs to the CNS.
  • Efferent Fibres: Transmit regulatory (motor) impulses from the CNS to peripheral tissues and organs.
• Divisions of the PNS:
  • Somatic Neural System: Relays impulses from the CNS to the body’s voluntary skeletal muscles.
  • Autonomic Neural System: Transmits impulses from the CNS to involuntary organs and smooth muscles. It is further divided into:
    • Sympathetic Neural System
    • Parasympathetic Neural System
• Visceral Nervous System: A component of the PNS, it comprises the complex network of nerves, fibres, ganglia, and plexuses that carry impulses from the CNS to the viscera (internal organs) and back.

3. The Neuron: Structural and Functional Unit

A neuron is a microscopic cell that serves as the fundamental unit of the neural system.

3.1 Structure of a Neuron

A neuron is composed of three main parts:

1. Cell Body (Soma): Contains the cytoplasm, typical cell organelles, and granular bodies known as Nissl’s granules.
2. Dendrites: Short, repeatedly branching fibres that project from the cell body. They also contain Nissl’s granules and are responsible for transmitting impulses towards the cell body.
3. Axon: A single, long fibre that transmits nerve impulses away from the cell body to a synapse or a neuro-muscular junction. The distal end of the axon is branched, with each branch terminating in a bulb-like synaptic knob. These knobs contain synaptic vesicles filled with chemicals called neurotransmitters.

3.2 Types of Neurons

Based on the number of axons and dendrites, neurons are classified into three types:

• Multipolar Neuron: Has one axon and two or more dendrites. Found in the cerebral cortex.
• Bipolar Neuron: Has one axon and one dendrite. Found in the retina of the eye.
• Unipolar Neuron: Has a cell body with only one axon. Typically found in the embryonic stage.

3.3 Types of Axons

• Myelinated Axons: These nerve fibres are enveloped with Schwann cells, which form a fatty myelin sheath around the axon. The gaps between adjacent myelin sheaths are called nodes of Ranvier. Myelinated fibres are found in spinal and cranial nerves.
• Non-myelinated Axons: These nerve fibres are enclosed by a Schwann cell, but it does not form a myelin sheath. They are commonly found in the autonomic and somatic neural systems.

4. Generation and Conduction of a Nerve Impulse

Neurons are “excitable” cells because their membranes exist in a polarised state, allowing them to conduct electrical signals.

4.1 The Resting Potential

When a neuron is not conducting an impulse, it is in a resting state. The axonal membrane is:

• Comparatively more permeable to potassium ions (K⁺).
• Nearly impermeable to sodium ions (Na⁺) and negatively charged proteins within the axoplasm.

This selective permeability creates an ionic gradient:

• Inside the axon (axoplasm): High concentration of K⁺ and negatively charged proteins; low concentration of Na⁺.
• Outside the axon: High concentration of Na⁺; low concentration of K⁺.

This gradient is actively maintained by the sodium-potassium pump, which transports 3 Na⁺ ions outwards for every 2 K⁺ ions it moves into the cell. The result is a positive charge on the outer surface of the membrane and a negative charge on the inner surface. This electrical potential difference across the resting membrane is called the resting potential.

4.2 The Action Potential

When a stimulus is applied to the polarised membrane:

1. Depolarisation: The membrane at the site of the stimulus becomes freely permeable to Na⁺. This causes a rapid influx of Na⁺, which reverses the polarity of the membrane—the outer surface becomes negative, and the inner surface becomes positive. This electrical potential difference is the action potential, also known as a nerve impulse.
2. Conduction: The action potential at one site (A) creates a current that flows to the adjacent site (B), causing it to depolarise. This sequence is repeated along the entire length of the axon, conducting the impulse forward.
3. Repolarisation: The increased permeability to Na⁺ is very brief. It is quickly followed by a rise in permeability to K⁺. K⁺ ions diffuse out of the membrane, restoring the original resting potential and making the neuron ready for further stimulation.

5. Transmission of Impulses at a Synapse

A synapse is the junction through which a nerve impulse is transmitted from a pre-synaptic neuron to a post-synaptic neuron.

• Electrical Synapse: The membranes of the pre- and post-synaptic neurons are in very close proximity. Electrical current flows directly from one neuron to the next. This transmission is faster than at a chemical synapse but is rare in the human system.
• Chemical Synapse: The pre- and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft. Transmission occurs via neurotransmitters.
  1. An action potential arrives at the axon terminal of the pre-synaptic neuron.
  2. It stimulates synaptic vesicles to move towards the membrane, fuse with it, and release neurotransmitters into the synaptic cleft.
  3. The neurotransmitters bind to specific receptors on the post-synaptic membrane.
  4. This binding opens ion channels, allowing ions to enter the post-synaptic neuron and generate a new potential, which can be either excitatory or inhibitory.

6. The Central Neural System: The Brain

The brain is the central information processing organ and the ‘command and control system’ of the body. It is protected by the skull and three cranial meninges: the outer dura mater, the middle arachnoid, and the inner pia mater.

6.1 Forebrain (Prosencephalon)

The forebrain is the largest part of the brain, consisting of the cerebrum, thalamus, and hypothalamus.

• Cerebrum:
  • Forms the major part of the human brain and is divided longitudinally into left and right cerebral hemispheres, connected by a tract of nerve fibres called the corpus callosum.
  • The outer layer is the cerebral cortex (grey matter), which is folded and contains concentrated neuron cell bodies. It houses motor areas, sensory areas, and association areas responsible for complex functions like memory, communication, and intersensory associations.
  • The inner part is the white matter, composed of myelinated axons.
• Thalamus: A major coordinating centre for sensory and motor signalling, wrapped by the cerebrum.
• Hypothalamus: Located at the base of the thalamus, it controls body temperature and the urges for eating and drinking. It also contains neurosecretory cells that secrete hypothalamic hormones.
• Limbic System: A complex structure formed by the inner parts of the cerebral hemispheres and associated structures like the amygdala and hippocampus. Along with the hypothalamus, it regulates sexual behaviour, emotional reactions (e.g., excitement, pleasure, rage, fear), and motivation.

6.2 Midbrain (Mesencephalon)

The midbrain is located between the forebrain’s thalamus/hypothalamus and the hindbrain’s pons.

• A canal called the cerebral aqueduct passes through it.
• The dorsal portion contains four round swellings known as the corpora quadrigemina.
• It receives and integrates visual, tactile, and auditory inputs.

6.3 Hindbrain (Rhombencephalon)

The hindbrain comprises the pons, cerebellum, and medulla.

• Pons: Consists of fibre tracts that interconnect different regions of the brain.
• Cerebellum: Features a very convoluted surface to provide space for more neurons. It integrates information from the auditory system and semicircular canals of the ear.
• Medulla (Oblongata): Connects to the spinal cord and contains centres that control respiration, cardiovascular reflexes, and gastric secretions.

6.4 Brain Stem

The brain stem is formed by three major regions: the midbrain, pons, and medulla oblongata. It forms the crucial connection between the brain and the spinal cord.

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Q&A Section

Short-Answer Quiz (25 Questions)

Instructions: Answer each question in 2-3 sentences.

1. What is the primary definition of coordination in a biological context?
2. Name the two systems responsible for coordination and integration in the human body and describe their basic method of action.
3. What are the two main divisions of the human neural system?
4. Differentiate between afferent and efferent nerve fibres.
5. What is the function of the somatic neural system?
6. List the three major parts of a neuron.
7. What are Nissl’s granules and where are they found?
8. Describe the function and location of synaptic vesicles.
9. What are the three types of neurons based on their structure?
10. Explain the difference between a myelinated and a non-myelinated axon.
11. Why is the membrane of a resting neuron considered polarised?
12. What role does the sodium-potassium pump play in maintaining the resting potential?
13. What ionic event triggers the depolarisation of a neuron’s membrane?
14. What is an action potential?
15. Briefly describe how a nerve impulse is conducted along an axon.
16. What is a synapse?
17. Compare the speed and mechanism of impulse transmission in electrical versus chemical synapses.
18. What are neurotransmitters and how do they function in a chemical synapse?
19. Name the three layers of the cranial meninges that protect the brain, from outermost to innermost.
20. What is the corpus callosum and what is its function?
21. Distinguish between the grey matter and white matter of the cerebral cortex.
22. What are the primary functions of the hypothalamus?
23. What parts of the brain constitute the brain stem?
24. Which part of the hindbrain controls vital functions like respiration and cardiovascular reflexes?
25. What is the limbic system involved in regulating?

Multiple-Choice Quiz (20 Questions)

Instructions: Choose the best answer for each question.

1. Which of the following is an example of coordination? a) The process of digestion alone. b) The increase in heart rate and respiration during exercise. c) The production of hormones by the endocrine system. d) The filtering of blood by the kidneys.
2. The Central Neural System (CNS) is composed of: a) The brain and all associated nerves. b) Cranial nerves and spinal nerves. c) The brain and the spinal cord. d) The somatic and autonomic systems.
3. Nerve fibres that transmit impulses from tissues to the CNS are called: a) Efferent fibres b) Motor fibres c) Afferent fibres d) Autonomic fibres
4. The autonomic neural system transmits impulses to: a) Skeletal muscles b) The brain c) The spinal cord d) Involuntary organs and smooth muscles
5. Which part of the neuron contains Nissl’s granules? a) Axon terminal and myelin sheath b) Cell body and dendrites c) Synaptic knob only d) Nodes of Ranvier
6. Bipolar neurons, with one axon and one dendrite, are found in the: a) Cerebral cortex b) Embryonic stage c) Retina of the eye d) Spinal nerves
7. The gaps between two adjacent myelin sheaths are called: a) Synaptic clefts b) Schwann cells c) Axon terminals d) Nodes of Ranvier
8. During the resting state, the axonal membrane is more permeable to: a) Na⁺ ions b) K⁺ ions c) Negatively charged proteins d) Ca²⁺ ions
9. The reversal of polarity across a neuronal membrane during impulse generation is called: a) Polarisation b) Repolarisation c) Depolarisation d) Homeostasis
10. In a chemical synapse, what separates the pre- and post-synaptic neurons? a) Corpus callosum b) Myelin sheath c) Synaptic cleft d) Cerebral aqueduct
11. Which type of synapse is faster and allows direct flow of electrical current? a) Chemical synapse b) Electrical synapse c) Neuro-muscular junction d) Inhibitory synapse
12. The cerebrum, thalamus, and hypothalamus are parts of the: a) Hindbrain b) Midbrain c) Brain Stem d) Forebrain
13. Complex functions like memory and communication are the responsibility of which regions in the cerebral cortex? a) Motor areas b) Sensory areas c) Association areas d) Corpora quadrigemina
14. Which structure is a major coordinating centre for sensory and motor signalling? a) Hypothalamus b) Thalamus c) Cerebellum d) Pons
15. Regulation of sexual behaviour and expression of emotional reactions are associated with the: a) Cerebral cortex b) Medulla oblongata c) Limbic system d) Cerebellum
16. The four round swellings called corpora quadrigemina are located in the: a) Forebrain b) Midbrain c) Pons d) Medulla
17. The convoluted surface of the cerebellum provides additional space for: a) Blood vessels b) Cerebrospinal fluid c) Many more neurons d) Storing memories
18. Respiration and gastric secretions are controlled by centres in the: a) Cerebrum b) Cerebellum c) Pons d) Medulla
19. The brain stem is composed of the midbrain, pons, and: a) Thalamus b) Medulla oblongata c) Cerebellum d) Hypothalamus
20. The greyish appearance of the cerebral cortex is due to the concentration of: a) Myelinated axons b) Schwann cells c) Neuron cell bodies d) Synaptic vesicles

Essay Questions (10 Questions with Answers)

1. Explain the process of generating an action potential and its conduction along an axon.
   • Answer: The process begins with a neuron in a polarised resting state, where the outside of the axonal membrane is positively charged and the inside is negatively charged. When a stimulus is applied, the membrane at that site becomes freely permeable to sodium ions (Na⁺). This leads to a rapid influx of Na⁺, which reverses the membrane’s polarity—the outer surface becomes negative and the inner surface becomes positive. This reversal is called depolarisation, and the resulting electrical potential difference is the action potential, or nerve impulse. This action potential creates a current that flows to the adjacent segment of the axon, causing it to depolarise as well. This sequence repeats along the length of the axon, conducting the impulse as a wave of depolarisation.
2. Compare and contrast the Central Neural System (CNS) and the Peripheral Neural System (PNS).
   • Answer: The CNS and PNS are the two main divisions of the human neural system. The CNS consists of the brain and the spinal cord and acts as the central site for information processing and control. In contrast, the PNS comprises all the nerves associated with the CNS that extend throughout the body. The primary function of the PNS is to transmit information between the CNS and the rest of the body, using afferent fibres to send signals to the CNS and efferent fibres to carry commands from the CNS to muscles and organs.
3. Describe the structure of a myelinated neuron, highlighting its key components and their functions.
   • Answer: A myelinated neuron consists of three main parts: the cell body, dendrites, and a myelinated axon. The cell body contains the nucleus and Nissl’s granules. The dendrites are short, branching fibres that receive impulses and transmit them towards the cell body. The axon is a long fibre that transmits impulses away from the cell body. In a myelinated neuron, the axon is enveloped by Schwann cells, which form a fatty myelin sheath. This sheath is interrupted by gaps called the nodes of Ranvier. The axon terminates in synaptic knobs, which contain synaptic vesicles filled with neurotransmitters for passing the signal to the next cell.
4. Detail the sequence of events that occur during the transmission of a nerve impulse across a chemical synapse.
   • Answer: When a nerve impulse (action potential) arrives at the axon terminal of a pre-synaptic neuron, it triggers a series of events. First, it stimulates the synaptic vesicles, which are filled with neurotransmitters, to move towards the pre-synaptic membrane. These vesicles fuse with the membrane and release their neurotransmitter contents into the fluid-filled synaptic cleft. The released neurotransmitters then diffuse across the cleft and bind to their specific receptors located on the post-synaptic membrane. This binding opens ion channels, allowing ions to enter the post-synaptic neuron and generate a new potential, which can be either excitatory or inhibitory.
5. Describe the major components of the forebrain and their primary functions.
   • Answer: The forebrain consists of the cerebrum, thalamus, and hypothalamus. The cerebrum is the largest part, divided into two cerebral hemispheres connected by the corpus callosum. Its outer layer, the cerebral cortex, is responsible for processing sensory information, controlling motor functions, and complex processes like memory and communication via its association areas. The thalamus, located within the cerebrum, is a major coordinating centre for sensory and motor signalling. At the base of the thalamus lies the hypothalamus, which controls body temperature, the urge to eat and drink, and secretes hormones.
6. Explain the concept of the resting potential in a neuron, including the ionic gradients and mechanisms that maintain it.
   • Answer: The resting potential is the electrical potential difference across the plasma membrane of a neuron that is not conducting an impulse. This potential is established because the axonal membrane is selectively permeable, being more permeable to potassium ions (K⁺) and nearly impermeable to sodium ions (Na⁺) and negatively charged proteins inside. This results in a high concentration of K⁺ inside the axon and a high concentration of Na⁺ outside. This ionic gradient is actively maintained by the sodium-potassium pump, which transports three Na⁺ ions out for every two K⁺ ions it pumps in. The overall effect is a net positive charge on the outer surface of the membrane and a net negative charge on the inner surface, creating the polarised state.
7. Differentiate between the somatic and autonomic neural systems.
   • Answer: The somatic and autonomic neural systems are two divisions of the peripheral nervous system (PNS). The somatic neural system is responsible for relaying impulses from the CNS to the body’s skeletal muscles, which are under voluntary control. In contrast, the autonomic neural system transmits impulses from the CNS to the involuntary organs and smooth muscles of the body, such as the heart, lungs, and digestive system. The autonomic system is further divided into the sympathetic and parasympathetic systems, which generally have opposing effects.
8. What is the limbic system, and what are its key functions?
   • Answer: The limbic system is a complex structure within the brain formed by the inner parts of the cerebral hemispheres and a group of associated deep structures like the amygdala and hippocampus. It works closely with the hypothalamus and is involved in a range of functions. Its key roles include the regulation of sexual behaviour, the expression of emotional reactions such as excitement, pleasure, rage, and fear, and controlling motivation.
9. Describe the structure and functions of the hindbrain.
   • Answer: The hindbrain is composed of three main parts: the pons, cerebellum, and medulla oblongata. The pons consists of fibre tracts that serve to interconnect different regions of the brain. The cerebellum has a highly convoluted surface to accommodate a large number of neurons and is involved in integrating information from the auditory system and semicircular canals. The medulla oblongata is connected to the spinal cord and contains vital centres that control autonomic functions such as respiration, cardiovascular reflexes, and gastric secretions.
10. What is the brain stem, and why is it considered a critical part of the brain?
    • Answer: The brain stem is composed of three major regions: the midbrain, pons, and medulla oblongata. It is a critical part of the brain because it forms the connection between the rest of the brain and the spinal cord. It acts as a relay station for nerve signals and contains centres that control fundamental, life-sustaining functions, including respiration, cardiovascular reflexes, and gastric secretions, which are managed by the medulla.

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Answer Keys

Short-Answer Quiz Answer Key

1. Coordination is the process where two or more organs interact and complement each other’s functions to maintain the body’s homeostasis.
2. The neural system provides quick, point-to-point coordination via an organised network. The endocrine system provides slower chemical integration through hormones.
3. The two main divisions are the central neural system (CNS), consisting of the brain and spinal cord, and the peripheral neural system (PNS), comprising all other nerves.
4. Afferent nerve fibres transmit impulses from tissues/organs to the CNS. Efferent fibres transmit regulatory impulses from the CNS to peripheral tissues/organs.
5. The somatic neural system relays impulses from the CNS to the skeletal muscles, which are under voluntary control.
6. The three major parts of a neuron are the cell body, dendrites, and the axon.
7. Nissl’s granules are granular bodies found in the cytoplasm of the cell body and also in the dendrites of a neuron.
8. Synaptic vesicles are located in the synaptic knobs at the end of an axon. They contain chemicals called neurotransmitters, which they release to transmit impulses across a synapse.
9. The three types are multipolar (one axon, multiple dendrites), bipolar (one axon, one dendrite), and unipolar (one axon only).
10. A myelinated axon is enveloped by Schwann cells that form a myelin sheath, with gaps called nodes of Ranvier. A non-myelinated axon is enclosed by a Schwann cell but lacks this myelin sheath.
11. The membrane is polarised because there is an electrical potential difference across it. The outer surface possesses a positive charge while the inner surface is negatively charged, due to an uneven distribution of ions.
12. The sodium-potassium pump actively transports 3 sodium ions (Na⁺) outwards for every 2 potassium ions (K⁺) it brings into the cell. This active transport maintains the concentration gradients necessary for the resting potential.
13. The depolarisation of a neuron’s membrane is triggered by a stimulus that makes the membrane freely permeable to sodium ions (Na⁺), leading to their rapid influx into the cell.
14. An action potential is the electrical potential difference across the plasma membrane at a site that has been depolarised by a stimulus. It is also known as a nerve impulse.
15. An action potential at one site on the axon creates a current that flows to the adjacent site, causing it to depolarise. This process is repeated sequentially along the entire length of the axon.
16. A synapse is a junction between two neurons (a pre-synaptic and a post-synaptic neuron) through which a nerve impulse is transmitted.
17. Transmission across an electrical synapse is very fast as current flows directly between neurons in close proximity. Transmission across a chemical synapse is slower because it relies on the release and diffusion of neurotransmitters across a synaptic cleft.
18. Neurotransmitters are chemicals stored in synaptic vesicles. When released into the synaptic cleft, they bind to receptors on the post-synaptic membrane to generate a new potential in the next neuron.
19. The three layers are the dura mater (outer), arachnoid (middle), and pia mater (inner).
20. The corpus callosum is a large tract of nerve fibres that connects the left and right cerebral hemispheres of the brain, allowing them to communicate.
21. Grey matter forms the outer cerebral cortex and appears greyish due to the high concentration of neuron cell bodies. White matter constitutes the inner part and appears white because it is composed of fibres covered with a myelin sheath.
22. The hypothalamus controls body temperature, the urge for eating and drinking, and contains neurosecretory cells that secrete hypothalamic hormones.
23. The brain stem is constituted by the midbrain, pons, and medulla oblongata.
24. The medulla, part of the hindbrain, contains the centres that control vital functions like respiration and cardiovascular reflexes.
25. The limbic system is involved in regulating sexual behaviour, motivation, and the expression of emotional reactions like excitement, pleasure, rage, and fear.

Multiple-Choice Quiz Answer Key

1. b
2. c
3. c
4. d
5. b
6. c
7. d
8. b
9. c
10. c
11. b
12. d
13. c
14. b
15. c
16. b
17. c
18. d
19. b
20. c

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Glossary of Key Terms

Term	Definition
Action Potential	The electrical potential difference across the plasma membrane at the site of excitation, which is termed a nerve impulse.
Afferent Fibres	Nerve fibres of the PNS that transmit impulses from tissues/organs to the CNS.
Autonomic Neural System	The division of the PNS that transmits impulses from the CNS to the involuntary organs and smooth muscles of the body.
Axon	A long fibre that transmits nerve impulses away from the cell body to a synapse or neuro-muscular junction.
Brain Stem	A structure made of the midbrain, pons, and medulla oblongata that forms the connection between the brain and spinal cord.
Central Neural System (CNS)	The part of the neural system that includes the brain and the spinal cord and is the site of information processing and control.
Cerebellum	A part of the hindbrain with a very convoluted surface that integrates information from the auditory system and semicircular canals.
Cerebral Cortex	The layer of cells covering the cerebral hemisphere, referred to as grey matter, containing motor, sensory, and association areas.
Cerebrum	The major part of the human forebrain, divided into two cerebral hemispheres.
Coordination	The process through which two or more organs interact and complement the functions of one another.
Corpus Callosum	A tract of nerve fibres that connects the left and right cerebral hemispheres.
Dendrites	Short, branching fibres projecting from the cell body of a neuron that transmit impulses towards it.
Depolarisation	The reversal of polarity at a site on a neuron’s membrane, where the outer surface becomes negatively charged and the inner side becomes positively charged.
Efferent Fibres	Nerve fibres of the PNS that transmit regulatory impulses from the CNS to peripheral tissues/organs.
Forebrain	A major part of the brain consisting of the cerebrum, thalamus, and hypothalamus.
Hindbrain	A major part of the brain comprising the pons, cerebellum, and medulla.
Homeostasis	The state of coordinated functions of organs/organ systems to maintain a stable internal body environment.
Hypothalamus	A part of the forebrain that controls body temperature, the urge for eating and drinking, and secretes hormones.
Limbic System	A complex structure including inner parts of the cerebral hemispheres (amygdala, hippocampus, etc.) involved in regulating emotions, motivation, and sexual behaviour.
Medulla (oblongata)	A part of the hindbrain connected to the spinal cord that contains centres to control respiration, cardiovascular reflexes, and gastric secretions.
Midbrain	The part of the brain located between the thalamus/hypothalamus of the forebrain and the pons of the hindbrain.
Myelin Sheath	A sheath formed by Schwann cells that envelops the axons of myelinated nerve fibres.
Neuron	Specialised cells that envelop axons. In myelinated fibres, they form the myelin sheath.
Neurotransmitters	Chemicals contained in synaptic vesicles that are involved in the transmission of impulses at chemical synapses.
Nissl’s Granules	Certain granular bodies found in the cytoplasm of the cell body and dendrites of a neuron.
Nodes of Ranvier	The gaps between two adjacent myelin sheaths on a myelinated axon.
Peripheral Neural System (PNS)	The part of the neural system comprising all the nerves of the body associated with the CNS.
Pons	A part of the hindbrain consisting of fibre tracts that interconnect different regions of the brain.
Resting Potential	The electrical potential difference across the resting plasma membrane of a neuron.
Schwann Cells	A part of the forebrain that is a major coordinating centre for sensory and motor signalling.
Somatic Neural System	The division of the PNS that relays impulses from the CNS to skeletal muscles.
Synapse	A junction through which a nerve impulse is transmitted from one neuron to another.
Synaptic Cleft	The fluid-filled space that separates the membranes of the pre- and post-synaptic neurons at a chemical synapse.
Synaptic Vesicles	Structures within the synaptic knob of an axon terminal that contain neurotransmitters.
Thalamus	A part of the forebrain that is a major coordinating centre for sensory and motor signaling.