Control and Coordination in Plants and Animals

Neurology is the branch of medicine specializing in the diagnosis and treatment of nervous system disorders. Neurologists study the brain, spinal cord, peripheral nerves, and muscles. Urology deals with urinary system, haematology with blood, and herpentology is not a standard medical term (likely misspelling of herpetology, the study of reptiles).

Chordates are defined by five fundamental characteristics: notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail, and endostyle/thyroid gland. The presence of a nervous system (specifically the dorsal hollow nerve cord) is one of these defining features. Limbs, heart, and haemoglobin are not unique to chordates.

Neurons are the longest cells in the human body, with axons extending from the spinal cord to the toes (up to 1 meter). Lymphocytes, osteocytes (bone cells), and leucocytes (white blood cells) are microscopic cells without such elongated processes. The neuron's length enables rapid signal transmission across distances.

The occipital lobe, located at the back of the brain, contains the primary visual cortex and processes visual information. While the optic nerves transmit visual signals, the conscious perception of sight occurs in the occipital lobe. Frontal lobes handle executive functions, parietal lobes process sensory and spatial information, and optic lobes are found in non-mammalian vertebrates.

The vagus nerve (CN X) controls the larynx and is essential for speech and sound production. It innervates the vocal cords via the recurrent laryngeal nerve. The facial nerve (CN VII) controls facial expression, trochlear (CN IV) controls superior oblique eye muscle, and hypoglossal (CN XII) controls tongue movement.

The trigeminal nerve (CN V) is the largest cranial nerve by diameter and root size. It has three major divisions: ophthalmic, maxillary, and mandibular, supplying sensation to most of the face and motor function to muscles of mastication. Optic (CN II) is actually the largest by NUMBER of axons (over 1 million), but trigeminal is largest by physical size.

Reflex actions are automatic, involuntary responses mediated by the spinal cord or brainstem without conscious thought. Sneezing, crying (tear secretion), and yawning are reflexes. Chewing is a voluntary action requiring conscious control and coordination, though it has reflex components.

Cytokinins are plant hormones that delay senescence (aging) by promoting cell division, protein synthesis, and nutrient mobilization. They keep leaves green and slow aging. Abscisic acid promotes senescence and dormancy, gibberellic acid promotes stem elongation, and indole butyric acid (IBA) is an auxin involved in rooting.

During depolarization, voltage-gated sodium (Na+) channels open, allowing Na+ ions to rush INTO the neuron down their concentration gradient. This rapid influx of positive charge makes the membrane potential less negative (more positive), creating the rising phase of the action potential. Potassium (K+) efflux causes repolarization, not depolarization.

Gibberellic acid (GA) promotes internodal elongation in plants, making stems longer between nodes. This is especially important in dwarf varieties and during bolting. Auxins promote cell elongation but are more associated with apical dominance and phototropism. Cytokinins promote cell division, and abscisic acid inhibits growth.

Endocrine glands are ductless glands that secrete hormones directly into the bloodstream through extracellular fluid (ECF). This contrasts with exocrine glands, which secrete into ducts (e.g., sweat glands, salivary glands). The key distinction is that endocrine secretions enter blood circulation, not ducts.

2,4-D (2,4-dichlorophenoxyacetic acid) is a synthetic auxin widely used as a herbicide and plant growth regulator. IAA is natural auxin, GA represents gibberellins, and Zeatin is a natural cytokinin produced in plants.

Prohormones are inactive precursor molecules that must be converted to active hormones through enzymatic processing. This conversion allows the body to regulate hormone levels and control when and where active hormones become available.

  Neurilemma, Axon and Dendrites are part of neuron.

The swallowing center is located in the medulla oblongata of the brainstem. This region contains central pattern generators that coordinate the complex sequence of muscle movements required for safe swallowing, protecting the airway.

The thyroid gland is the largest endocrine gland in the human body, weighing approximately 20-25 grams in adults. The pituitary is smaller (pea-sized), adrenal glands are also smaller, and the pineal gland is tiny compared to the thyroid.

The brain stem consists of three parts: midbrain, pons, and medulla oblongata. The cerebellum is located at the back of the brain but is NOT part of the brain stem - it's a separate structure involved in coordination and balance.