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Chapter No 12
Coordination & Control
12.1 Coordination
Coordination is the process by which different parts of an organism work together in a smooth and efficient manner to respond to internal and external stimuli.
12.1.1 Types of Coordination
Organisms use coordination to regulate their body functions and respond to stimuli. There are two main types of coordination:
i. Nervous Coordination
This type of coordination is brought about by the nervous system. It involves the brain, spinal cord, and nerves.
Messages are transmitted through electrical impulses.
It allows for quick and immediate responses.
Found only in animals.
ii. Chemical Coordination
This type of coordination is carried out by the endocrine system. It involves hormones secreted by endocrine glands.
Hormones are transported through the bloodstream.
It results in slower but long-lasting responses.
Found in both animals and plants.
12.1.2 Coordination Action
i. Stimuli
Any change in environment (external and internal), which can provoke a response in organism is called Stimuli. Example: heat, cold, pressure, sound waves, presence of chemicals, microbial infections etc.
ii. Receptors:
The organs, tissues or cells that are specifically built to detect particular type of stimuli are called receptors. Example: Ears detect sound waves, eyes detect light, chemicals in air detected by nose
iii. Coordinators:
Coordinators are the organs that receive information from receptors and send messages to effectors (muscles or glands) to produce a suitable response.
- Nervous Coordination In nervous coordination, the brain and spinal cord act as coordinators. They receive information from receptors and send messages through neurons. These messages travel as nerve impulses to the target organs for quick response.
- Chemical Coordination In chemical coordination, various endocrine glands serve as coordinators. They receive information in the form of chemical signals from the body. In response, they secrete specific hormones into the bloodstream. These hormones travel to target organs and control various functions.
iv. Effecters
Effectors are the parts of the body that receive messages from coordinators and produce specific responses to maintain body functions.
- Effectors in Nervous Coordination In this type, neurons carry messages from coordinators (brain and spinal cord) to:
o Muscles – for movement
o Glands – for secretion
These muscles and glands act as effectors.
- Effectors in Chemical Coordination In chemical coordination, hormones carry messages from endocrine glands (coordinators) to target organs or tissues. These target organs or tissues act as effectors. Nephrons in kidneys act as effectors for certain hormones (e.g., ADH). Bones and liver act as effectors for hormones like growth hormone and insulin.
v. Response:
On receiving the message from coordinators, the effector performs action. This action is called response. Example: pulling our hand away from something very hot and the movement of the flower of sunflower towards light are responses.
12.2 Human Nervous System
The nervous system in humans and other higher animals is made up of two major parts:
1. Central Nervous System (CNS) It includes the brain and spinal cord. These are the coordinators that receive information, process it, and send out responses.
- Peripheral Nervous System (PNS) It consists of nerves that arise from the CNS. These nerves spread throughout the body to connect the CNS with sense organs, muscles, and glands.
12.2.1 Neuron or Nerve Cell
The neuron is the basic structural and functional unit of the nervous system.
General Features
The human nervous system is made up of billions of neurons and supporting cells called neuroglial cells. Neurons are specialized to carry nerve impulses:
o From receptors to coordinators (brain/spinal cord)
o From coordinators to effectors (muscles/glands)
Neurons communicate with each other and with other body cells to control body functions.
Structure of Neuron
Part Function Cell Body (Soma): Contains nucleus and most of the cytoplasm Dendrites: Receive impulses and carry them toward the cell body Axon: Carries impulses away from the cell body Schwann Cells: Special neuroglial cells found along axons Myelin Sheath: Fatty layer secreted by Schwann cells; acts as an insulator Nodes of Ranvier: Gaps between myelin-covered areas; allow saltatory conduction
Saltatory Impulse
In myelinated neurons, nerve impulses jump from one node of Ranvier to the next. This jumping is called a saltatory impulse. It makes the impulse faster than in non-myelinated neurons.
Type of Neuron
1. Sensory neurons Sensory neurons conduct sensory information (nerve impulse) from receptors towards the CNS. Sensory neurons have one dendrite and one axon.
o Acts as a relay center between spinal cord and different brain regions
o Receives and modifies sensory impulses (except smell) before they reach the cerebrum
o Plays a role in pain perception, sleep, and consciousness
(ii) Hypothalamus
Lies below the thalamus and above the midbrain Roughly the size of an almond
Functions:
o Connects the nervous system with the endocrine system
o Controls the pituitary gland
o Regulates emotions like pain, pleasure, anger, sorrow
o Controls body temperature, hunger, thirst, and sleep-wake cycle
(iii) Cerebrum
Largest part of the forebrain and the entire brain Controls:
o Voluntary movements (skeletal muscles)
o Intelligence, thinking, emotions, learning
Divided into two cerebral hemispheres Additional Features : Olfactory bulbs : Located at the anterior side; receive signals from olfactory nerves (sense of smell) Cerebral Cortex :
o Upper layer of cerebrum made of grey matter (cell bodies and non-myelinated axons)
o Lower layer Located beneath grey matter made of white matter (myelinated axons)
The surface is folded to increase surface area
The cerebral cortex is divided into four lobes (to be discussed in further detail if needed) Lobe Location Main Function(s) Frontal Front part of the cerebrum^ Controls motor functions, allows conscious control of skeletal muscles, and coordinates movements involved in speech
Parietal Top middle region Contains sensory areas that receive impulses from the skin (touch, pain, temperature)
Occipital Back of the cerebrum Receives and analyzes visual information (sight)
Temporal Side region (near ears) Concerned with hearing and smell
2. Midbrain The midbrain is located between the forebrain and hindbrain. It acts as a bridge connecting the two regions.
Functions:
Receives sensory information and sends it to the appropriate part of the forebrain Controls some auditory reflexes (e.g., turning head toward a sound)
Helps in maintaining posture and balance
3. Hindbrain The hindbrain is the lower back portion of the brain and consists of three main parts:
(i) Medulla Oblongata
It located on top of the spinal cord It acts as a pathway for information between the spinal cord and the brain Functions : Controls involuntary actions such as: Breathing, Heart rate, Blood pressure Also controls reflexes like: Vomiting, Coughing, Sneezing (ii) Cerebellum
Located behind the medulla
Responsible for coordinating muscle movements Functions : Maintains balance and posture Ensures smooth and precise voluntary movements
(iii) Pons
Located on top of the medulla Acts as a bridge between different parts of the brain Functions : Assists the medulla in controlling breathing Connects cerebellum with the spinal cord B. Spinal Cord The spinal cord is a long, tubular bundle of nerves that extends from the brainstem to the lower back. It is a vital part of the central nervous system (CNS).
Protection and Covering
The spinal cord is surrounded and protected by the vertebral column (backbone). Like the brain, it is covered by three protective layers called meninges.
Internal Structure
The outer region is made up of white matter, which contains myelinated axons (nerve fibers). The central (inner) region is butterfly-shaped and consists of grey matter, which contains neuron cell bodies. A small central canal runs through the grey matter and contains cerebrospinal fluid (CSF).
Spinal Nerves
31 pairs of spinal nerves arise along the length of the spinal cord. Each spinal nerve is a mixed nerve (contains both sensory and motor axons). A spinal nerve arises from two roots: Root Contains Function Dorsal Root Sensory axons and a bodies) ganglion^ (cluster of cell Carries sensory impulses into spinal cord
Ventral Root Axons of motor neurons Carries glands^ motor impulses^ out to muscles or These two roots join together to form one mixed spinal nerve.
Functions of the Spinal Cord
- Communication Pathway o Transmits nerve impulses between the brain and body parts (both directions).
- Reflex Center o Coordinates simple reflexes (e.g., knee-jerk, withdrawal from pain) without involving the brain.
Peripheral Nervous System (PNS) The Peripheral Nervous System consists of nerves and ganglia that connect the Central Nervous System (CNS) to the rest of the body.
Reflex Action
A reflex action is a quick, automatic, and involuntary response to a stimulus, without involving the higher brain centers. Example: Withdrawing your hand after touching a hot object
Reflex Arc – The Pathway of Reflex Action
The reflex arc is the path followed by nerve impulses during a reflex action: Step Component Function 1 ⃣ Stimulus Heat from hot object stimulates pain and temperature receptors 2 ⃣ Sensory Neuron Carries impulse from receptors → spinal cord 3 ⃣ Interneuron Present in spinal cord; connects sensory to motor neurons 4️ ⃣ Motor Neuron Carries impulse from spinal cord → muscles 5️ ⃣ Effector (muscles) Muscles contract and withdraw the hand ➡️ Spinal cord acts as the coordinator in this reflex.
Awareness of Pain
While the reflex action is taking place, other interneurons also send impulses to the brain. This makes the person aware of what happened, but after the reflex response is completed.
12.3 Receptors in Human
12.3.1 Eye
1. Location and Protection
Our eyes are located in small portions of the skull known as the orbits or eye sockets.
Eyelids wipe the eyes and prevent dehydration by spreading tears over their surface.
Tears contain substances that help fight bacterial infections.
Eyelashes prevent fine particles from entering the eye.
2. Structure of the Eye
Outer Layer
Sclera The sclera gives the eye most of its white colour and is made of dense connective tissue. It protects the inner components of the eye and maintains its shape. Cornea The cornea is the transparent front part of the sclera. It admits light into the interior of the eye and bends light rays so that they can be focused.
Middle Layer (Choroid)
Choroid The choroid contains blood vessels and gives the inner eye a dark colour. The dark colour prevents disruptive reflections within the eye. Iris and Pupil Behind the cornea, the choroid bends to form a muscular ring called the iris. The iris has a round hole in its centre called the pupil. Light passes through the pupil after striking the cornea. The size of the pupil is adjusted by the muscles of the iris: o In bright light, circular muscles contract, causing the pupil to constrict. o In dim light, radial muscles contract, causing the pupil to dilate. Lens and Ciliary Muscles Behind the iris is a convex lens that focuses light on the retina. The lens is attached to the ciliary muscles via a ring of suspensory ligaments. To see a faraway object clearly, the ciliary muscles relax and the lens becomes less convex. To see a nearby object clearly, the ciliary muscles contract and the lens becomes more convex and round.
Inner Layer (Retina)
Retina The retina is the sensory layer of the eye. It contains photosensitive cells called rods and cones, along with associated neurons. Rods are sensitive to dim light. Cones are sensitive to bright light and detect different colours. Fovea and Optic Disc The fovea is a depression in the retina directly opposite the lens, densely packed with cone cells, and is responsible for colour vision and sharpness. The optic disc is where the optic nerve enters the retina, containing no rods or cones, and is also called the blind spot.
Eye Chambers and Fluids
Anterior Chamber Located between the cornea and the iris. Contains a clear fluid called aqueous humour. Posterior Chamber Located between the iris and the retina. Contains a jelly-like fluid called vitreous humour, which helps maintain the shape of the eye and suspends the delicate lens.
Path of Light and Vision
Light enters the eye and is refracted as it passes through the cornea, aqueous humour, lens, and vitreous humour. The lens focuses light onto the retina, forming an image. Rods and cones generate nerve impulses that travel through the optic nerve to the brain. The brain processes these impulses to create the sensation of vision.
3. Role of Rhodopsin and iodopsin
Rhodopsin Rod cells contain a pigment called rhodopsin. When light falls on rhodopsin, it breaks down to generate a nerve impulse. In the absence of light, breakdown products are converted back into rhodopsin. Night Blindness Rhodopsin is synthesised from vitamin A. A deficiency of vitamin A results in poor night vision, a condition known as night blindness. Iodopsin Cones also contain a pigment known as iodopsin. There are three main types of cones, each containing a specific iodopsin. Each type of cone is sensitive to one of the three primary colours: blue, green, or red. Colour Blindness If any type of cone is not functioning properly, it becomes difficult to recognize that specific colour. A person with this condition is also unable to distinguish between certain colours. This problem is called colour blindness and it is a genetic disorder.
4️. Disorders of the Eye
Myopia (Short Sight) Myopia occurs when the eyeball elongates.
A person with myopia cannot see distant objects clearly.
The image of a distant object is formed in front of the retina.
This problem can be corrected by using a concave lens. Hypermetropia (Long Sight) Hypermetropia occurs when the eyeball shortens.
A person with hypermetropia cannot see near objects clearly.
The Process of Hearing
- Pinna directs sound waves into the auditory canal.
- Sound waves strike the ear drum, producing vibrations.
- Vibrations pass through malleus → incus → stapes. 4️. Stapes sends vibrations to the oval window. 5️. Vibrations move the fluid in the middle duct of the cochlea.
- Receptor cells in the cochlea are stimulated and generate nerve impulses.
- Impulses travel to the brain, which interprets them as sound.
Ears Maintain the Balance of the Body
Semicircular Canals: Detect movement of the head. Vestibule: Detects changes in body posture. Nerve signals from these structures travel via the auditory nerve to the cerebellum, which controls balance.
12.4 Endocrine vs. Exocrine Glands
Endocrine glands:
o Ductless
o Secrete hormones directly into blood
o Example: Pituitary gland, thyroid gland
Exocrine glands:
o Have ducts for releasing secretions
o Examples: Digestive glands, skin glands
Hormones Specific messenger molecules synthesized and secreted by endocrine glands.
12.4.1 Important Endocrine Glands
Pituitary Gland
A pea-shaped gland attached to the hypothalamus of the brain. Produces trophic hormones that influence secretions of other endocrine glands. Some hormones act directly on body tissues. Has two lobes: Anterior lobe and Posterior lobe.
1. Anterior Lobe
Produces several hormones, including:
a. Somatotrophin (Growth Hormone)
Promotes growth of the body. Dwarfism : If the production of somatotrophin hormone is diminished during growing age, the rate of growth decreases. This condition is called dwarfism.. Gigantism : If this hormone is excessively produced during growing age, it leads to gigantism (very tall and overweight). Acromegaly: If somatotrophin is excessively produced after growing age, internal organs and body extremities alone grow large. This condition is known as acromegaly. Persons will have large hands, feet and jawbones
b. Thyroid-Stimulating Hormone (TSH)
Stimulates the thyroid gland to secrete its hormones.
c. Other Anterior Lobe Hormones
Influence reproductive organs. Control adrenal gland activity.
2. Posterior Lobe
Stores and secretes two hormones produced by the hypothalamus:
a. Vasopressin (Antidiuretic Hormone: ADH)
Increases reabsorption of water from nephrons into the blood. When body fluids have low water: o More vasopressin is secreted → more water reabsorbed → less urine produced. When body fluids have excess water: o Less vasopressin is secreted → less water reabsorbed → more urine produced. Diabetes insipidus : If pituitary gland does not secrete this hormone in the required amount, less water is reabsorbed from nephrons and there is excessive loss of water through urine. This condition is known as diabetes insipidus.
b. Oxytocin
Stimulates uterus contractions during childbirth. Necessary for milk ejection from breasts after birth. Thyroid Gland Largest endocrine gland in the human body. Located in the neck region, just below the larynx. Produces hormones that regulate metabolism, growth, and calcium balance.
1. Thyroxin
Requires iodine for production. Function: o Increases breakdown of food (oxidation) to release energy. o Supports body growth. a. Iodine Deficiency Without enough iodine, thyroxin cannot be produced. Causes thyroid gland enlargement → Goitre. b. Hypothyroidism Under-production of thyroxin Low energy production in body. Slowed heart-beat. c. Hyperthyroidism Over-production of thyroxin Increased energy production. Increased heart-beat. Frequent sweating. Shivering of hands.
2. Calcitonin
Reduces calcium ion level in blood. Promotes calcium absorption from blood into bones. Parathyroid Glands Number: Four small glands. Location: On the posterior side of the thyroid gland. Hormone Produced: Parathormone.
1. Function of Parathormone
Increases calcium ion level in blood by promoting release of calcium salts from bones into the blood.
2. Disorders
a. Hyperparathyroidism
Over-production of parathormone Excess calcium salts absorbed from bones into blood. Bones become brittle and weak.
b. Hypoparathyroidism
Under-production of parathormone Low calcium level in blood. Leads to tetany → abnormal muscle contractions affecting muscle function.
Female Gonads – Ovaries
Produce estrogen and progesterone. Functions of these hormones: o Development of female secondary sex characters: Growth and development of breasts.
Feedback Mechanisms
Definition
Endocrine glands do not secrete hormones at a constant rate. Secretion varies according to the needs of the body. Feedback mechanism = Regulation of a process by the output of the same process. Types:
- Negative Feedback
- Positive Feedback
1. Negative Feedback
Definition: Output of a process decreases or inhibits the process. Purpose: Brings a condition back to its normal value. Example – Blood Glucose Regulation: o High Blood Glucose: Pancreas secretes insulin → lowers blood glucose. When glucose returns to normal, insulin secretion stops. o Low Blood Glucose: Pancreas secretes glucagon → raises blood glucose. When glucose returns to normal, glucagon secretion stops.
Key Point: Output (blood glucose level) controls hormone secretion.
2. Positive Feedback
Definition: Output of a process increases the rate of the process. Example – Milk Production: o Suckling by an infant → stimulates hormone production in mother. o Hormone increases milk production. o More suckling → more hormone → more milk.
12.5 Disorders of Nervous System
Categories
- Vascular Disorders – Caused by disturbance in blood supply to the nervous system. o Example: Paralysis.
- Functional Disorders – Caused by disturbance in nerve impulse generation and transmission. o Example: Epilepsy.
12.5.1 Paralysis
Definition: Complete loss of function in one or more muscle groups. Causes: o Damage to the central nervous system (brain or spinal cord). o Stroke (rupture of a blood vessel in the brain or spinal cord). o Blood clot in brain or spinal cord vessels. o Poison from polio viruses. Types: o Weak paralysis throughout the body. o Paralysis on one side of the body. o Paralysis in lower extremities (legs). o Paralysis in all four limbs.
12.5.2 Epilepsy
Definition: Nervous disorder caused by abnormal and excessive discharge of nerve impulses in the brain. Effect: Causes unprovoked seizures (temporary abnormal brain activity with convulsions). Causes:
o In younger people: Genetic or developmental causes. o In people over 4️ 0 years: Brain tumors. o At any age: Head trauma or central nervous system infections. Treatment: o No permanent cure. o Seizures can controlled with antiepileptic (anticonvulsant) drugs. o Medicines must be taken daily for both treatment and prevention of seizures.
