The tissues and organs in the bodies of multicellular organisms do not work independently of each other. They work together performing their many tasks as the needs of the whole body. This means that these activities are coordinated. Coordination also enables the organism to respond to happenings in the world around it.
Life activities are controlled and coordinated i.e., body works as one unit, in which its different organs and systems cooperate and work in harmony with each other.
When a boy runs to catch a ball, he uses hundreds of muscles to move his arms, legs and back. His nervous system uses information from his sense organs and coordinates these muscles. Due to this coordination, the muscles contract in the correct sequence, power and length of time. But that is not all. Such activities involve many other kinds of coordination For example; breathing and heartbeat rates are increased, blood pressure is adjusted, and extra heat is removed at a faster rate from the body.
Types of coordination:
There are two types of coordination systems in organisms which are related to each other.
- Nervous coordination brought about by nervous system and
- Chemical coordination brought about by endocrine system.
Components of coordination
A coordination action has five components;
Stimulus à Receptors àCoordinator àEffecter à Response
We can define a stimulus as any change in environment (external and internal), which can provoke a response in organism.
Touch, light etc. are factors that can bring about certain responses in living organisms. These factors are called stimuli.
More examples of stimuli are heat, cold, pressure, sound waves, presence of chemicals, microbial infections etc.
Stimuli are detected by special organs, tissues or cells of body. The organs, tissue or cells which are specifically built to detect particular type of stimuli are called receptors.
For example sound waves are detected by ears, light is detected by eyes, and chemicals in air are detected by nose and so on.
These are the organs that receive information from receptors and send messages to particular organs for proper action.
In nervous coordination, brain and spinal cord are coordinators. They receive information and send messages through neurons in the form of nerve impulses.
In chemical coordination, various endocrine glands play the role of coordinators. They receive information in the form of various chemicals and send messages by secreting particular hormones blood.
These are the parts of body which receive messages from coordinators and produce particular responses.
In nervous coordination, neurons carry messages from coordinators (brain and spinal card) to muscles and glands, which act as effectors.
In chemical coordination, particular hormones carry messages from coordinators (endocrine glands) to particular target tissues, which act as effectors. For some hormones, nephrons act as effectors. Similarly, bones liver act as effectors for many hormones.
On receiving the message from coordinators, the effectors perform action. This action is called response. Usually, nervous coordination produces immediate but short-living responses while chemical coordination produces slowly but long- living responses.
Pulling our hand away from something very hot .
Structure of Neuron
Neuron consists of following major components:
Cell body, dendrites, axons, Schwann cells, myelin sheath, and nodes of Ranvier
The nucleus and most of the cytoplasm of a neuron is located in its cell body. Different processes extend out from the cell body. These are called dendrites and axons. Dendrites conduct impulses toward cell body and axons conduct impulses away from cell body.
Schwann cells are special neuralgia cells located at regular intervals along axons. In some neurons, Schwann cells secrete a fatty layer called myelin sheath, over axons. Between the areas of myelin on an axon, there are nonmylinated points, called the nodes of Ranvier.
Myelin sheath is an insulator so the membrane coated with the sheath does not conduct nerve impulse. In such a neuron, impulses ‘jump’ over the areas of myelin going from node to node. Such impulses are called saltatory (‘jumping’) impulses This increases the speed of nerve impulse.
Nerve Growth Factor
Unlike ordinary cells, mature neurons never divide. But a protein called nerve-growth- factor promotes the regeneration of broken nerve cells. The degenerating brain cells could be repaired, by using embryonic stem cells.
A nerve impulse is a wave of electrochemical changes that travels along the length of neurons.
Enlist different types of neurons and give their functions briefly.
On the basis of their functions, neurons are classified into three types:
- Sensory neurons conduct sensory information (nerve impulse) from receptors towards the CNS. Sensory neurons have one dendrite and one-axon.
- Interneurons form brain and spinal card. They receive information, interpret them and stimulate motor neurons. They have many dendrites and axons.
- Motor neurons carry information from interneuron’s to muscle or glands (effectors). They have many dendrites but only one axon.
A nerve means the union of several axons that are enveloped by a covering made of lipid. Based on the property of axons, the nerves are classified into three types.
- Sensory nerves contain the axon of sensory neurons only
- Motor nerves contain the axons of motor neurons only.
- Mixed nerves contain the axons of both i.e. sensory and motor neurons.
In certain parts of body, the cell bodies of many neurons form a group enveloped by a membrane. This is called ganglion.
In animals, all life activities are under the control of brain. The structure of brain is suitable to perform these functions.
Brain is situated inside a bony cranium i.e., brain box, (part of skull).
Inside cranium, brain is covered by three layers called meninges. Meninges protect brain and also provide nutrients and oxygen to brain tissue through their capillaries.
The brain contains fluid-filled ventricles that are continuous with the central canal of spinal cord.
- Cerebrospinal fluid
Fluid within ventricles and central canal is called cerebrospinal fluid (CSF)
The Divisions of Brain
There are three major regions in the brain of human and other vertebrates. These are forebrain, midbrain and hindbrain. Important parts of each of these regions are described below.
Forebrain is the largest area of brain. It is most highly developed in humans.
Parts of Forebrain
Following are the important parts of forebrain.
It lies just below the cerebrum.
It serves as a relay centre between various parts of brain and spinal cord. It also receives and modifies sensory impulses (except from nose) before they travel to cerebrum. Thalamus is also involved in pain perception and consciousness (sleep and awakening)
It lies above midbrain and just below thalamus. In humans, it is roughly the size of an almond.
One of the most important functions of hypothalamus is to link nervous syste~ and endocrine system. It controls the secretions of pituitary gland. It also contro s feelings such as rage, pain, pleasure and sorrow.
It is the largest part of forebrain.
It controls skeletal muscles, thinking, intelligence and emotions.
It is divided into two cerebral hemispheres.
The anterior parts of cerebral hemispheres are called olfactory bulbs which receive impulses from olfactory nerves and create the sensation of smell.
The upper layer of cerebral hemispheres i.e. cerebral cortex consists of grey matter. The grey matter of nervous system consists of cell bodies and nonmyelinated axons. Beneath this layer is present the white matter. The white matter of nervous system consists of myelinated axons. Cerebral cortex has a large surface area and is folded in order to fit in skull. It is divided into four lobes.
|Frontal||Controls motor functions, permits conscious control of skeletal muscles and Coordinates movements involved in speech|
|Parietal||Contains sensory areas that receive impulses from skin.|
|Occipital||Receives and analyzes visual information|
|Temporal||Concerned with hearing and smell.|
- Midbrain Location
Midbrain is the part between hindbrain and forebrain and connects the two. Functions
It receives sensory information and sends it to the appropriate part of forebrain. Midbrain also controls some auditory reflexes and posture.
Hindbrain consists of three major pats:
- Medulla Oblongata
It lies on the top of spinal cord.
It controls breathing, heart rate and bold pressure. It also controls many reflexes such as vomiting, coughing, sneezing etc. Information that passes between spinal cord and the rest of brain pass through medulla.
It lies is behind medulla.
It coordinates muscle movements.
It is present on top of medulla.
It assists medulla in controlling breathing. It also serves as a connection between cerebellum and spinal cord.
It is a structure that is deep in the cerebrum. It functions for the formation of new memories. People with a damaged hippocampus cannot remember things that occurred after the damage but can remember things that occurred before damage.
Spinal cord is the continuation of medulla oblongata. It is in fact a tubular bundle of nerves. It starts from brain stem and extend to lower back. Like brain, spinal cord is also covered by meninges. The vertebral column surrounds and protects spinal cord.
White matter Grey matter Sensory neuron
Spinal cord is roughly 40cm long and about as wide as your thumb for most of its length.
The outer region of spinal cord is made of white matter (containing myelinated axons). The central region is butterfly shaped that surrounds the central canal. It is made of grey matter (containing neuron cell bodies).
31 pairs of spinal nerves arise along spinal cord. These are “mixed” nerves because each contains axons of both sensory and motor neurons. At the point where a spinal nerve arises from spinal cord, there are two roots of spinal nerve. Both roots unite and form one mixed spinal nerve.
The dorsal root contains sensory axons and a ganglion where cell bodies are located. The ventral root contains axons of motor neurons.
Spinal cord performs two main functions:
It serves as a link between body parts and brain. Spinal cord transmits nerve impulses from body parts to brain and from brain to body parts. Spinal cord also acts as a coordinator, responsible for some simple reflexes.
PERIPHERAL NERVOUS SYSTEM (PNS)
The peripheral nervous system (PNS) is composed of nerves and ganglia Ganglia are the clusters of neuron cell bodies outside CNS. On the other hand, central nervous system consists of brain and spinal cord.
Cranial and Spinal nerves.
Nerves that arise or lead to brain are called cranial nerves, and the nerves that arise or lead to spinal cord are named as spinal nerves. Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves. Some cranial nerves are sensory, some are motor and some are mixed. On the other hand, all spinal nerves are mixed nerves.
SENSORY PATHWAY AND MOTOR PATHWAY.
The cranial and spinal nerves make two pathways i.e. sensory pathway conducting impulses from receptors to CNS) and motor pathway (conducting impulses from CNS to effectors).
- Motor pathway makes two systems; somatic nervous system and autonomic nervous system
- Somatic Nervous System
It is responsible for the conscious and voluntary actions. It includes all of the motor neurons that conduct impulses from CNS to skeletal muscles.
- Autonomic Nervous System
It is responsible for the activities, which are not under conscious control. It consists of motor neurons that send impulses to cardiac muscles, smooth muscle and glands. Autonomic nervous system comprises of sympathetic system and parasympathetic system.
How sympathetic nervous system helps prepare for “fight or flight “response?
Sympathetic nervous system prepares body to deal with emergency situations. This is often called the “fight or flight” response. During an emergency situation, this system takes necessary actions. For example; it dilates pupils, accelerates heartbeat, increases breathing rate and inhibits digestion. When stress ends, the parasympathetic nervous system takes action and normalizes all the functions. It causes pupils to contract, promotes digestion, and slows the rate of heartbeat and breathing rate.
When central nervous system sends impulses to muscles and glands, two types of actions (responses) result.
- The higher centres of brain control the conscious action or voluntary actions.
When impulses are not passed to the higher centres of brain, it results in responses which are not under conscious control. Such responses are called involuntary actions. Sometimes, the involuntary response produced by the CNS is very quick. Such a response is called reflex action. The pathway followed by the nerve impulses for producing a reflex action, is called reflex arc.
Example The most common example of reflex action is the withdrawal of hand after touching a hot object. In this reflex action, spinal cord acts as coordinator. Heat stimulates temperature and pain receptors in skin. A nerve impulse is generated which is carried by sensory neurons to the interneurons of spinal cord. From interneurons, the impulse is passed to motor neurons, which carry it to the muscles of arm. As a result, the muscles contract to withdraw hand. During it, other interneurons transmit nerve impulses up to brain so that the person becomes aware of pain and what happened.
RECEPTORS FOUND IN HUMAN
The organs or parts which are specifically built to detect particular type of stimuli are called sense organs or receptors. Main receptors in man are eyes, ears, nose, taste, receptors of touch, heat and cold etc
STRUCTURE OF EYE
Our eyes are located in small portions of skull known as the orbits or eye sockets
Eyelids wipe eyes and prevent dehydration. They spread tears on eyes, which contains substances for fighting bacterial infections.
Eyelashes prevent fine particles from entering eye.
The structure of eye can be divided into three main layers.
The outer layer of eyeball consists of sclera and cornea.
- Sclera gives eye most of its white colour. It consists of dense connective tissue and protects the inner components of eye and maintains its shape.
- In the front, sclera forms the transparent Cornea admits light to the interior of eye and bends light rays so that they can be brought to a focus.
The middle layer is called choroid. It contains blood vessels and gives the inner eye a dark colour. The dark colour prevents disruptive reflections within eye.
Iris and Pupil
Behind cornea, choroid bends to form a muscular ring, called iris. There is round hole, called pupil, in the centre of iris. After striking the cornea, light passes through’ the pupil. The size of pupil is adjusted by the muscles of iris Pupil constricts in bright light when the circular muscles of iris contract. Similarly, pupil dilates in dim light when the radial muscles of iris contract.
Lens behind iris, there is a convex lens, which focuses light on retina.
Ciliary muscles and suspensory ligament
Lens is attached to ciliary muscles of eye via a ring of suspensory ligaments. To clearly see an object far away, ciliary muscles are relaxed and lens becomes less convex. When ciliary muscles contract, lens becomes more convex and round.
The inner layer is sensory and is called retina.
Rods and Cones
Retina contains the photosensitive cells called rods and cones and associated neurons.
Rods are sensitive to dim light while cones are sensitive to bright light and so distinguish different colours.
Fovea and Optic disc
Retina has two points i.e. fovea and optic disc.
- Fovea is a dip in retina, directly opposite to lens and is densely packed with cone cells. It is largely responsible for colour vision and sharpness.
- Optic disc is a point on retina where the optic nerve enters retina. There are no rods and cones at this point, that is why it is also referred to as the blind spot.
Aqueous humour and Vitreous humour
The iris divides the cavity of eye into two chambers. The anterior chamber is in front of iris i.e. between cornea and iris; whereas the posterior chamber is between iris and retina.
- The anterior chamber contains a clear fluid known as aqueous humour
- The posterior chamber contains a jelly-like fluid known as vitreous humour. It helps maintain the shape of eye and suspends the delicate lens.
In human eye about 125 lac rods and 7 lac cones are present.
The eyes of cats and dogs shine in the night. The reason for this is the presence of tapetum behind the eye which is a layer capable of reflecting light.
Light from objects enters eye and is refracted when it passes through cornea, aqueous humour, lens and vitreous humour. Lens also focuses light on retina. As a result, the image fails on retina. Rods and cones generate nerve impulses in the optic nerve. These impulses are carried to the brain which makes the sensation of vision.
ROLE OF VITAMIN A WITH THE VISION AND EFFECTS OF ITS DEFICIENCY ON RETINA
Rods contain a pigment called rhodopsin. When light falls on rhodopsin, it breaks for generating a nerve impulse. In the absence of light, the breakdown products are again converted into rhodopsin. Body synthesizes rhodopsin from vitamin A and that is why the deficiency of vitamin A causes poor night vision. This problem is called night blindness.
Disorders of the Eye
The working of eye is affected by the changes in the shape of eyeball.
- Myopia (Short sight)
The elongation of eyeball results in myopia. Such persons are not able to see distant objects clearly. The image of a distant object is formed in front of retina. This problem can be rectified by using concave lens.
- Hypermetropia (Long sight)
It happens when eyeball shortens. Such persons are not able to see near objects clearly. The image is formed behind retina . Convex lens is used to rectify this problem. Figure 12.9
Ali ibn Isa (950-1012) was a famous Arab scientist. He wrote three books on ophthalmology (study of the diseases and surgery of eyes). He described 130 eye diseases and prescribed 143 drugs to, treat these diseases.
Ibn al-Haytham (965-1039), an Arab scientist made significant contributions to the principles of eye and vision. He is regarded as the father of optics (study of the behavior of light). His “Book of Optics” correctly explained and proved the modern theory of vision. He discussed the topics of medicine and dye surgery in his book. He made several improvements to eye surgery and accurately described the process of sight, the structure of eye, image formation in eye and visual system. Ibn al-Haytham also described the principles of pinhole camera. Ibn al-Haytham’s “Book of Optics” has been ranked alongside a book of Isaac Newton. It is one of the most influential books ever written in the history of physics.
Cones also contain a pigment, known as iodopsin. There are three main types of cones and each type has a specific iodopsin. Each type of cone recognizes one of the three primary colours i.e. blue, green and red. If any type of cones is not working well, it becomes difficult to recognize that colour. Such person is also not able to distinguish different colours. This disease is called colour blindness and it is a genetic problem.
How an owl is able to see in dark?
Ans. Owl is not able to see during day time. The reason for this is the deficiency of cones which receive and sense the bright light. But the presence of more rods gives it greater power of vision during night. All animals that search for prey during night have this characteristic.
Hearing is as important as is vision.
Role of Ear
Our ear helps us in hearing and also to maintain the balance or equilibrium of our body.
Parts of Ear
Ear has three main parts i.e. external ear, middle ear, and internal ear.
- External Ear
External ear consists of pinna, auditory canal and ear drum (tympanum).
Pinna is the broad external part, made of cartilage and covered with skin. It helps to direct sound waves into auditory canal. There are special glands in the walls of auditory canal, which produce wax. The wax and the hairs in auditory canal protect ear from small insects, germs and dust. In additions to this, is helps to maintain the temperature and dampness of auditory canal. Auditory canal ends in ear drum. This thin membrane separates external ear from middle ear.
- Middle Ear
Middle ear is a chamber after external ear. Three small bones, called middle ear ossicles, are present in a chain in middle ear.
These movable bones include malleus, incus and stapes. Malleus is attached with ear drum, and then comes incus and finally stapes that is connected with a membrane called oval window. Oval window separates middle ear from inner ear. Middle ear also communicates with the nasal cavity through Eustachian tube. This tube regulates the air pressure on both sides of ear drum
- Inner Ear
Inner ear consists of three parts i.e. vestibule, semicircular canals and cochlea
- Vestibule is present in the centre of inner ear.
- Three canals called semicircular canals are posterior to the vestibule.
- The cochlea is made of three ducts and wraps itself into a coiled tube. Sound receptor cells are present within the middle duct of cochlea.
Stapes is the smallest bone of the human body.
The Process of Hearing
The pinna of the external ear focuses and directs sound waves into auditory canal. The sound waves strike ear drum and produce vibrations in it. From ear drum, the vibrations strike middle ear and produce further vibrations in malleus, incus and then stapes. From stapes, the vibrations strike the oval window and then reach the fluid-filled middle duct of cochlea. The fluid of cochlea is moved and receptor cells are stimulated. The receptor cells generate a nerve impulse, which travels to brain and is interpreted as sound
Deafness is a state in which hearing is not possible. The defect of ear drum, cochlea, middle ear ossicles, or auditory nerve may cause deafness. Infection in eustachian tube may spread to middle ear too. Ear drum may be damaged by an infection in auditory canal. Excessive noise, strong blows on cheek, pointed objects entering auditory canal and attack from insects may also affect hearing.
Ears & the Balance of Body
Semicircular canals and vestibule help to maintain the balance of body. Semicircular canals contain sensory nerves which can detect any movement of head. Vestibule can detect any changes in the posture of body. The neurons coming from these two receptors reach cerebellum through the auditory nerve.