Ch 9Control and Co-ordination — Class 12 Biology, concept-first.

A single-celled organism can run its whole life on simple, direct chemistry, but once cells organise into tissues, organs and organ systems, two extra jobs appear: control over each process individual…

Hydra, a cnidarian, has the most primitive form of true nervous system known -- a diffused nervous system.

Planaria, a flatworm of the phylum Platyhelminthes, is the most primitive animal to possess a true central nervous system (CNS), positioned on the ventral side of the body.

The neural tissue that builds the nervous system is made of two main cell categories: neurons (nerve cells), which actually conduct impulses, and neuroglia (glial cells), which support them.

Neuroglial cells : Neuroglial (glial) cells greatly outnumber neurons in the nervous system, and -- despite arising from the same embryonic tissue layer (ectoderm) as neurons -- they do not conduct im…

A synapse is the junction between two nerve cells, separated by a minute gap (the synaptic cleft), across which a neurotransmitter bridges the impulse from one neuron to the next.

2. Types of synapses. a. Electrical synapse : Synapses come in two structurally and functionally distinct types.

Neurons are specially built to be excitable cells, and the nerve impulse itself is a travelling wave of bioelectrical (electrochemical) disturbance moving along a neuron, generated by shifting electri…

Generation of nerve impulse : 1. Depolarization : Generating a nerve impulse begins with depolarisation.

The human nervous system is well developed and complex, and is broadly organised into three interlocking parts: the central nervous system (CNS -- the brain and spinal cord, lying along the mid-dorsal…

1. Central nervous system (CNS) : Both the brain (inside the cranium) and the spinal cord (inside the vertebral canal) are protected by three meninges, layered from outside in.

A. The Human brain : The human brain -- studied as a whole under the name encephalology -- divides into three main parts: forebrain, midbrain and hindbrain.

iii. Diencephalon : The diencephalon is the part of the forebrain lying below the corpus callosum and above the midbrain, made up of the epithalamus, thalamus and hypothalamus, and enclosing a single,…

Hypothalamus : The hypothalamus forms the floor of the diencephalon, richly supplied with blood vessels (including the hypophyseal portal vein, which carries its hormonal signals to the pituitary), an…

b. Mid brain : The midbrain lies between the diencephalon and the pons varolii and contains the cerebral aqueduct (iter), the narrow canal linking the third and fourth ventricles.

c. Hind brain : The hindbrain, the posterior region of the brain, is made of the pons varolii, the cerebellum and the medulla oblongata.

B. Spinal Cord : The spinal cord is the lower continuation of the medulla oblongata, running inside the vertebral column's neural canal and, like the brain, protected by bony covering and the same thr…

2. Peripheral Nervous System (PNS) - Cranial Nerves : Twelve pairs of cranial nerves, numbered I to XII with Roman numerals, arise from or terminate in the brain of every amniote (reptiles, birds and…

The peripheral nervous system connects the CNS to receptors and effectors throughout the body, and its nerves are classically split by connection point into cranial nerves (linked to the brain, covere…

Reflex Action : A reflex action is a sudden, spontaneous, automatic, involuntary response to a stimulus -- involuntary because it happens without any conscious effort by the brain -- and the pathway i…

3. Autonomic Nervous System (ANS) : The autonomic nervous system (ANS) is a special set of peripheral nerves that regulates involuntary organs -- cardiac muscle, smooth muscle, glands and the like --…

The body possesses a whole family of sensory receptors -- specialised structures able to detect a particular type of stimulus from the external or internal environment and turn it into a nerve impulse…

Eye : The paired eyes, the sensory organs of vision, sit in the bony orbit of the skull cushioned by fat, and each spherical eyeball is protected by the bony socket, eyebrows, eyelids, eyelashes and l…

Ear : The human ear -- the stato-acoustic organ -- performs two distinct jobs, hearing and maintaining body equilibrium, and is anatomically divided into external, middle and internal parts.

Psychological disorders : Nervous-system disorders span psychological and specific organic disease. Psychological (mental) disorders are a wide range of conditions affecting mood, thinking or behaviou…

Chemical coordination : Cells and whole organisms communicate chemically in four broadly recognised ways. Autocrine signalling is a cell releasing a secretion that stimulates itself.

Chemical nature of hormones : Hormones fall into six broad chemical classes. Amines are simple amines: the catecholamines epinephrine (adrenaline) and nor-epinephrine (noradrenaline) from the adrenal…

Properties of Hormones : Hormones share several defining properties: they act as chemical messengers effective at very low concentration; they function as regulators that can inhibit, stimulate or mod…

The book's section 9.10 lists the major endocrine glands one by one, A to J: the hypothalamus, the pituitary, the pineal gland, the thyroid, the parathyroids, the thymus, the adrenal glands, the pancr…

A. Hypothalamus : Considered specifically as an endocrine structure, the hypothalamus is ectodermal in origin and located at the floor of the diencephalon; its major endocrine job is controlling the s…

B. Pituitary gland or hypophysis gland : The pituitary gland (hypophysis) is the smallest endocrine gland, a pea-sized, reddish-grey structure that controls almost every other endocrine gland -- earni…

Hormones of the adenohypophysis - 1. Somatotropin / Growth hormone (GH) : The adenohypophysis (anterior pituitary) secretes several distinct hormones.

Neurohypophysis : The neurohypophysis (posterior pituitary) does not make its own hormones; its pars nervosa simply stores and releases two hormones actually made by hypothalamic neurosecretory cells.…

C. Pineal gland : The pineal gland is given off from the roof of the diencephalon and lies between the two cerebral hemispheres.

D. Thyroid gland : The thyroid gland is the largest endocrine gland, weighing about 25 grams, bilobed and richly vascular, sitting in front of the trachea just below the larynx, its two lobes joined b…

Disorders related to thyroid gland - a. Hyperthyroidism : Hyperthyroidism, caused by raised levels of thyroid hormone, drives up overall metabolic rate and body temperature, producing sweating, hot fl…

E. Parathyroid gland : The four parathyroid glands, named superior and inferior on each side, sit on the posterior surface of the thyroid's two lobes, their cells arranged in a compact mass.

F. Thymus gland : The thymus gland is a soft, pinkish, bilobed mass of lymphoid tissue located in the upper thorax, on the dorsal side of the heart.

G. Adrenal gland / Suprarenal gland : The paired adrenal (suprarenal) glands sit on the upper border of each kidney and, being small, conical and yellowish, have a dual embryonic origin (mesoderm and…

Disorders related to Adrenal cortex : Two named disorders arise specifically from the adrenal cortex. Hyposecretion of both mineralocorticoids and glucocorticoids causes Addison's disease, marked by l…

H. Pancreas : The pancreas develops from endoderm and is both an exocrine gland (its digestive-enzyme role is covered under the digestive system) and an endocrine gland, its endocrine tissue organised…

I. Gonads - i. Ovaries : The gonads -- testes and ovaries -- besides producing gametes, also secrete their own hormones.

J. Diffuse endocrine glands - Placenta : Several organs beyond the named glands secrete hormones diffusely, without forming a single compact gland.

Pheromones : Pheromones -- also called social hormones, sex attractants or external hormones -- are volatile chemical substances that one organism produces and releases to trigger a physiological or b…

Q.1 of the textbook exercise (p218): twelve multiple-choice questions.

Q.2 of the textbook exercise (pp218-219): ten very-very-short-answer questions.

Q.3 of the textbook exercise (p219): one matching question.

Q.4 of the textbook exercise (p219): three very-short-answer questions.

Q.5 of the textbook exercise (p219): thirteen short-answer questions.

Q.6 of the textbook exercise (p219): complete the table of neuroglial cells.

Q.7 of the textbook exercise (pp219-220): twelve long-answer questions.

The textbook's end-of-chapter Project (p220). A guided approach is given.

Sample papers and previous-year board questions for this subject.