Neural Control and Coordination: Nervous System & Neurons

Neural control and coordination refer to the combined processes by which the nervous system regulates and synchronizes the activities of different organs and tissues in a living organism.

• Coordination is the process by which two or more organs interact and complement the functions of each other. 
• Increased muscle activity during exercise increases oxygen supply and energy demand.
• When we stop exercising, our nerves, heart, lungs, and kidneys all return to normal function.
• Thus, all organ functions are properly integrated to provide the appropriate conditions for exercising.
• Similarly, in the human body, the neurological and endocrine systems work together to coordinate all of the organ activities.
• The neurological system is a system of point-to-point communication that allows for quick communication.
• It is also known as the nervous system.
• The endocrine system relies on hormones for chemical production.

Key Terms: Neuron, Human Nervous System, Human Brain, Nerve Impulse, Reflex Arc, Eye, Ear, Sensory Receptors, Neural system, Human eye, Human ear

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Neural System

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The neural system is comprised of highly specialized cells known as neurons, which can receive and transmit different types of signals.

• The neurological system of low-spinal animals like Hydra is incredibly simple, consisting of a network of neurons.
• When the brain of an insect comprises a vast number of ganglia and neural tissues, it is optimally structured.
• Outside the central nervous system, ganglia are a collection of cells.
• Invertebrates, on the other hand, have a more advanced neural system than vertebrates.

Neural Systems

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Human Nervous System

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Central Nervous System, Peripheral Nervous System, and Autonomic Nervous System are the three components of the human nervous system.

• The brain and spinal cord are linked through the central nervous system.
• A place for information processing and control, often known as the CNS.
• The cerebrum, cerebellum, medulla oblongata, midbrain, and brainstem are all parts of the brain.
• The brainstem helps the hypothalamus function by regulating temperature and supporting it in its duties.
• Memory and cerebellar activities are controlled by the cerebrum.
• The autonomic nervous system (involuntary) and the somatic nervous system are both parts of the peripheral nervous system (voluntary).
• It is made up of two types of nerve fibers that are connected to the CNS: afferent fibers and efferent fibers.
• The autonomic neural system (ANS) transmits impulses from the CNS to the involuntary organs and smooth muscles of the body, whereas the somatic neural system (SNS) transmits impulses from the CNS to the skeletal muscles.
• The autonomic nervous system is then separated into two parts: a sympathetic nervous system and a parasympathetic nervous system.
• The first is effective in battle, panic, and fleeing circumstances (3F).
• The latter is effective during periods of relaxation or digestion.

Human Nervous System

Neurons

The structural and functional unit of the nervous system is the neuron. A neuron is a microscopic structure that consists of three major components: the cell body, dendrites, and axon.

• The cytoplasm of a cell body contains conventional cell organelles and Nissl's granules, which are granular bodies.
• Dendrites are small strands that emerge from the cell body and contain Nissl granules.
• Dendrites are responsible for conveying electrical impulses from the cell body to the dendrites.
• Axon is a long fibre with branching at the end.
• Each of these branches is broken down into a synaptic knob, which is a bulb-shaped structure with chemical synaptic vesicles called neurotransmitters that flow in a single direction.
• Myelinated and unmyelinated nerve fibres are the two types of axons; myelinated nerve fibres are wrapped with Schwann cells that form the myelin sheath around the axon and are found in the spinal cord and cranial nerves.
• The intervals between two neighbouring myelin sheets are known as Ranvier Nodes. Non-myelinated nerve fibre contains Schwann cells but does not produce a myelin coating around the axon. It is widespread in the ANS and SNS.

Neuron

Axons are responsible for transporting nerves from the body cell to the synapse or neuromuscular junction.

Neurons are classified into three categories based on the number of axons and dendrites:

• Multipolar Neurons are found in the cerebral cortex and have one axon and two or more dendrites.
• Bipolar Neurons are found in the retina of the eye and have one axon and one dendrite.
• Unipolar Neurons are discovered in the embryonic phase and have only one axon.

Neurons are excited cells that carry electricity, hence their name. Their membrane is polarised, and the axolemma, a neural membrane, contains many types of ion channels. Different ions are easily penetrated by these ions.

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Nerve Impulse Conduction

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The axon membrane is more permeable to potassium ions but impermeable to sodium ions and the negatively charged proteins found in the axoplasm when neurons are in their resting phase (not conducting any impulse).

• Plasma in axons has a low sodium ion concentration and a higher potassium ion and protein concentration.
• The liquid outside the axon, on the other hand, has a high sodium ion concentration and a low potassium ion concentration, resulting in a concentration gradient.
• The sodium-potassium pump actively transports ions across the membrane, with three sodium ions moving outwards and two potassium ions moving into the cell.
• As a result, the outer surface of the membrane becomes positively charged while the inner surface becomes negatively charged, resulting in the cell becoming polarised and developing a resting potential.
• When a stimulus is provided to a polarised membrane at a specific location, the membrane becomes permeable to sodium ions, allowing sodium ions to enter the cell.
• The membrane's outside side becomes negatively charged, while the inner side becomes positively charged.
• The membrane has now become depolarized.
• The action potential is the electrical potential difference created across the plasma membrane at this location.
• This area serves as a trigger for the depolarization of the membrane's neighboring area.
• The migration of sodium ions outside the cell causes the preceding membrane to repolarize.
• This is the way impulses are carried out.

Conduction of Nerve impulses

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Nerve Impulse Transmission

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Synapses, which are produced by the membranes of a presynaptic and postsynaptic neuron, convey nerve impulses from one neuron to another.

• The two types of synapses are electrical and chemical synapses.
• The migration of synaptic vesicles towards the membrane is triggered when an impulse reaches the axon terminal.
• In the synaptic cleft, the plasma membrane and vesicles fuse and release neurotransmitters, which bind to specific receptors on the postsynaptic membranes.

Nerve Impulse Transmission

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Reflex Arc and Reflex Action

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Responding to peripheral nerve stimulation is an involuntary procedure that necessitates the involvement of a component of the CNS known as a reflex action.

• At least one efferent neuron and one afferent neuron make up the reflex pathway.
• The afferent neuron receives and sends signals from sensory organs to the Central Nervous System.
• Signals are sent from the CNS to the effector organ via the efferent neuron.

Reflex Arc and Reflex Action

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Human Brain

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The brain is highly protected by the skull. The brain is protected by three membranes known as cranial meninges.

These membranes are made up of Dura mater ( outer layer), Arachnoid (middle layer), and Piamater ( inner layer).

The three main sections of the brain are as follows:

Forebrain

Cerebrum, Thalamus, and Hypothalamus make up the forebrain. The greatest section of the brain is the cerebrum.

• The cerebral hemispheres are separated longitudinally by the corpus callosum, which connects them.
• The cerebral cortex covers the cerebral hemisphere and folds to generate noticeable folds.
• The motor and sensory areas are located in the cerebral cortex, which is also known as grey matter.
• The Association area is responsible for a variety of tasks, including creating connections between sensory and motor areas.
• Because they give the layer an opaque white appearance, this is also known as white matter.
• The cerebrum wraps around the thalamus. Sensory and motor signaling are both regulated by it.
• At the base of the thalamus is the hypothalamus.
• It is the primary control centre for temperature and hunger and thirst.
• Hypothalamic hormones are also secreted by this gland.

Midbrain

Between the thalamus and the hypothalamus is the midbrain.

• The cerebral aqueduct runs across the middle of the brain.
• The corpora quadrigemina, or four lobes, make up the dorsal part.
• The brainstem is made up of the hindbrain and midbrain.

Hindbrain 

Pons with fibre tracts makes up the hindbrain.

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

Human Brain

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Human Eye

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The human eye is the most vital organ in the body.

• The eyeball's wall is made up of three layers: the sclera, which is a dense connective tissue, the cornea, which is the front portion of the eyeball, and the choroid, which is made up of numerous blood veins.
• The ciliary body continues forward, forming the iris, a pigmented and opaque structure.
• A clear lens is maintained in place by ligaments attached to the ciliary body of the eyeball.
• The pupil is the opening in front of the lens that is encompassed by the iris and whose diameter is controlled by iris muscle fibres.

Human Eye

Also read: Why do we have two eyes?

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Human Ear

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Hearing and regulating body equilibrium are two sensory functions of the ear.

• The outer ear, middle ear, and inner ear are the three parts of the human ear.
• The external auditory meatus and pinna make up the outer ear.
• The external auditory meatus extends to the eardrum, and the pinna gathers vibrations that produce sound.
• The malleus, incus, and stapes are three ossicles that are connected in the middle ear.
• Through the eustachian tube, the middle ear chamber is connected to the pharynx. It aids in the balance of pressures on both sides of the eardrum.
• The bony and membranous labyrinths make up the inner ear, which is known as the labyrinth.

Human Ear

Sense Organs

Touch, vision, hearing, smell, and taste are the five most vital senses in the human body.

• These sensory receptors can be found in the skin, mucous membranes, connective tissues, and muscles, among other places.
• They send out numerous sensory signals such as heat, cold, pain, and so forth.
• The sensory organs collaborate to carry out a certain receptive function.

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Things to Remember

• The nervous system, also known as the neurological system, is a point-to-point communication mechanism that allows for speedy communication, whereas the endocrine system relies on hormones to produce chemicals.
• The human brain, which serves as the processing unit of the human body, is in charge of coordination. The central nervous system and the peripheral nervous system both support it.
• The neuron is the functional and structural unit of the nervous system. The cell body, dendrites, and axon are the three major components of a neuron, which are tiny structures.
• A condition of relaxation in which the neuron does not exert any force is defined as the strength of the resting membrane. Potassium ions (K+) are rapidly absorbed by axonal membranes, but sodium ions (Na+) are almost absent.
• The eyes are referred to as visual receptors because they contain specific light-sensitive receptor cells, whereas the ear is responsible for hearing and bodily maintenance.
• Touch, vision, hearing, smell, and taste are the five most vital senses in the human body. These sensory receptors can be found all over the body.