Coordination refers to the way multiple bodies interact with one another and work in harmony. The coordination between the neural and endocrine systems ensures that all activities are coordinated and integrated in a coordinated manner. While the hormonal system allows for chemical integration through hormones, the neural system supplies a structured network of point-to–point connections for swift coordination.
Let us examine in greater detail the process and results of neural coordination.
The Neural System
- It is composed of neurons – extremely specialized cells that are required to transmit and receive various types of signals
- Lower invertebrates, such as Hydra, have a neuron network
- There are many neural tissues and ganglia in the neural system of insects. It is exceedingly developed among vertebrates
Nervous System in Humans
The following sections make up the nervous system of humans:
Autonomic Nervous system
- It consists of nerve fibres, and is responsible for controlling the involuntary activities of the body
- It includes the parasympathetic as well as sympathetic nervous system
Central Nervous System
- The central nervous systems of vertebrates are dorsal, hollow, and non-ganglionated. But, those of the invertebrates are ventral, strong, and contain ganglions
- Further divisions of the central nervous network include the brain and spinal cord
Peripheral Nervous System
- It comprises nerves that connect between the central nervous systems and various body parts
- This includes both the spinal as well as the cranial nerves
- All the voluntary functions of the body are controlled by it
Neurons
- Neurons are formed by three main parts – axon, cell body and dendrites. The cell’s cytoplasm is made up of a few granules known as Nissl’s granules and a few cell organelles
- The dendrites – short fibres that repetitively branch and arise from the cell’s body – send impulses to the cells of the body
- Axons can be described as long fibres that are branched at their distal ends. Each branch terminates in a bulb-like structure called synaptic knot, which is composed of synaptic-vesicles that contain neurotransmitters
- Nerve impulses from the cell body to the synapse are transmitted by Axon. According to the number or dendrites, neurons can be divided into one of three types: multipolar or two or numerous dendrites. The axons may be myelinated or unmyelinated
- Around the axon, the Myelin Sheath is formed by the Schwann cell that is surrounded by the myelinated nerve fibre
- Nodes of ranvier are gaps between myelin sheaths that are adjacent
Nerve Impulse Conduction:
- When neurons are at rest, meaning they don’t conduct any impulses, the axon membrane is more absorbent to ions of potassium. However, it is resistant towards ions of sodium and also the negatively charged proteins found within the axoplasm
- Plasma in the axons is low in sodium ions but high in potassium ions. However, the external liquid of an axon is high in sodium ions but low in potassium ions. Thus, it forms a concentration gradient
- The sodium-potassium pump is responsible for the active transfer of ions across membranes. Three sodium ions are transported outwards while two potassium ions move inside the cell. This transportation of ions causes the external surface of the membrane to be charged positively and the internal surface to be negatively charged thus polarising the cell and further developing a potential of rest
- When stimuli are applied at a site on a membrane that is polarized, it results in the membrane becoming freely absorbent to sodium ions thus causing them to enter the cell. The membrane’s inner side gets charged positively, and its outer side is negatively charged. When this happens, the membrane is in a state of depolarisation
- Action potential refers to the electrical difference created across the membrane of plasma
- This region acts as a stimulus to the nearby membrane thus depolarising it. The movement of the sodium ions located externally, causes the membrane to get depolarised. This is how impulses occur
Nerve Impulse Transmission:
- Synapses are created by membranes of a postsynaptic and presynaptic neuron that allow nerve impulses to be transferred from one neuron in the brain to another
- There are two types of synapses – chemical synapses and electrical synapses
- The movement of synaptic-vesicles to the membrane is triggered the moment an impulse hits the axon terminal. The vesicles fuse with the plasma membrane and neurotransmitters are released into the synaptic cell. These neurotransmitters hold together to form specific receptors on the postsynaptic membrane
Reflex Action & Reflex Arc
- Reflex action is the reaction to a peripheral nerve stimulus involuntarily, which requires a part of the CNS to be involved
- A minimum of one each – efferent and afferent neuron – is required in the reflex pathway
- Signals from the sensory organs are received by the afferent neuron which in turn conveys them to the Central Nervous System (CNS)
- On the other hand, the efferent neuron relays signals from the CNS to the organ or effector
The Human Ear
- The ear serves two functions: it is responsible for hearing and keeping the body balanced. The human ears are divided into the inner ear, middle ear and outer ear
- Pinna and the external auditory meatus form the outer ear. The sound waves collected by the pinna are channelised to the external auditory meatus which are then amplified
- Three ossicles attached to one another – malleus, stapes and incus – together form the middle ear
- Through the eustachian tube, the middle of the ear cavity is connected to the pharynx. It assists in equalisation of pressures on both sides of the eardrum
- The inner ear is called a labyrinth. It is made up of two parts, the bony as well as the membranous labyrinths
The Human Eye
- The eye is the most vital organ within the human body. The eyeball has three layers – the outer layer contains a thick connective tissue known as Sclera, the frontal portion is the cornea, and the middle layer known as choroid comprises numerous blood vessels. The ciliary head further continues ahead and forms an opaque and pigmented structure termed the iris
- The eyeball contains a clear lens that is held in place by the ligaments attached to the ciliary. The pupil is the aperture surrounding the iris. The size of the pupil is controlled by the muscle fibres within the iris