Control and Coordination Exercise Solutions | KalviGavani

A synapse is the tiny gap (20-30 nm) between the axon terminal of one neuron (presynaptic) and the dendrite of the next neuron (postsynaptic). The sequence:

1. An electrical impulse travels down the axon of the presynaptic neuron. 2. At the axon terminal, the impulse triggers synaptic vesicles to release neurotransmitters (chemical messengers like acetylcholine) into the synaptic cleft. 3. The neurotransmitters diffuse across the cleft and bind to specific receptors on the postsynaptic membrane. 4. This binding opens ion channels, generating a new electrical impulse in the postsynaptic neuron. 5. The neurotransmitter is quickly broken down by enzymes (e.g., acetylcholinesterase) to prevent continuous stimulation.

Thus, signal transmission at a synapse involves: electrical signal --> chemical signal --> electrical signal.

The cerebellum, located in the hindbrain, maintains posture, balance, and equilibrium. It receives information from the vestibular apparatus of the inner ear (body position) and proprioceptors in muscles and joints, then fine-tunes motor commands to skeletal muscles. Damage to the cerebellum causes unsteady gait, loss of coordination, and inability to maintain balance.

Chemical coordination in animals is carried out by the endocrine system. Endocrine glands are ductless glands that secrete hormones directly into the bloodstream. Key features:

• Hormones are chemical messengers produced in minute quantities.
• They travel through the blood to reach specific target organs or cells that have matching receptors.
• The response is slower than nerve impulses (seconds to hours) but lasts longer (hours to weeks).
• Hormones regulate growth, metabolism, reproduction, water balance, and responses to stress.
• Example: Adrenaline from the adrenal gland prepares the body for emergency; insulin from the pancreas lowers blood glucose.

Iodine is an essential component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Without adequate iodine:

• The thyroid gland cannot produce enough thyroxine.
• The pituitary responds by secreting more TSH (Thyroid Stimulating Hormone) to stimulate the thyroid.
• The thyroid gland enlarges due to overstimulation -- a condition called goitre (swelling in the neck).
• In children, iodine deficiency causes cretinism (stunted growth and intellectual disability).

Iodised salt contains potassium iodate (KIO3), providing the daily iodine requirement (about 150 micrograms for adults). This is the simplest public health measure to prevent iodine deficiency disorders.

Adrenaline (epinephrine) from the adrenal medulla triggers the "fight or flight" response:

• Heart rate and blood pressure increase -- more blood is pumped to skeletal muscles and the brain.
• Breathing rate increases -- bronchioles dilate, more oxygen reaches the lungs and blood.
• Liver releases glucose into the blood -- glycogen is broken down, providing extra energy.
• Digestive system slows down -- blood is diverted away from the gut to muscles.
• Pupils dilate -- more light enters the eyes for better vision.
• Sweating increases -- to cool the body during heightened activity.
• Skin blood vessels constrict in some areas -- redirecting blood to vital organs and muscles.

These changes collectively prepare the body for rapid, intense action in response to danger or stress.

When a tendril comes in contact with a support (touch stimulus -- thigmotropism):

1. The side of the tendril in contact with the support experiences less growth. 2. Auxin migrates to the opposite (non-contact) side of the tendril. 3. Higher auxin concentration on the non-contact side promotes cell elongation on that side. 4. The non-contact side grows faster and longer than the contact side. 5. This unequal growth causes the tendril to coil around the support.

This is an example of positive thigmotropism -- directional growth in response to touch.

Plants lack a nervous system. Coordination is achieved entirely through phytohormones (plant hormones):

• Plant cells in one region secrete hormones that diffuse or are actively transported to other parts.
• Each hormone has specific effects depending on its concentration and the target tissue.
• Auxin: produced at shoot tips; promotes cell elongation; causes phototropism and geotropism.
• Gibberellin: promotes stem elongation and seed germination.
• Cytokinin: produced in roots; promotes cell division; delays ageing in leaves.
• Ethylene: a gaseous hormone; promotes fruit ripening and leaf fall.
• Abscisic acid (ABA): inhibits growth; closes stomata during water stress; promotes seed dormancy.
• Plant responses are generally slower than animal nervous responses but are effective for growth regulation and adaptation to environmental changes.

Receptors are specialised cells or nerve endings that detect specific stimuli (light, sound, chemicals, temperature, pressure, pain) and convert them into electrical impulses sent to the CNS.

If receptors malfunction:

• Pain receptors damaged: Cannot feel pain -- injuries, burns, and internal damage go unnoticed, leading to severe harm.
• Photoreceptors (rods/cones) damaged: Vision loss or colour blindness.
• Auditory receptors (hair cells in cochlea) damaged: Hearing loss or deafness.
• Olfactory receptors damaged: Loss of smell (anosmia).
• Gustatory receptors damaged: Loss of taste (ageusia).
• Thermoreceptors damaged: Cannot sense heat/cold -- risk of frostbite or burns.

Receptors are essential for the body to perceive the environment and respond appropriately. Without them, the body is disconnected from its surroundings.

A neuron has three main parts:

• Cell body (cyton): Contains the nucleus, Nissl's granules (rough ER), and controls all metabolic activities of the neuron.
• Dendrites: Short, highly branched processes arising from the cell body; they receive impulses from receptors or other neurons and transmit them towards the cell body.
• Axon: A single, long fibre extending from the cell body; it carries impulses away from the cell body. The axon is covered by a myelin sheath (formed by Schwann cells) which insulates it and speeds up transmission. Gaps in the myelin sheath are called Nodes of Ranvier; they allow saltatory (jumping) conduction. The axon ends in swollen axon terminals (boutons) that release neurotransmitters at the synapse.

Function: Neurons are the structural and functional units of the nervous system. They receive stimuli via dendrites, generate and conduct electrical impulses along the axon, and transmit signals to other neurons, muscles, or glands through synapses.

Diagram description: Draw an oval cell body with a nucleus. Show multiple short, branching dendrites on one side. Show a single long axon extending from the other side, with a myelin sheath (segmented covering) and nodes of Ranvier (gaps). At the end of the axon, draw branching axon terminals with small synaptic vesicles.

(a) Insulin (b) Thyroxin (c) Oestrogen (d) Cytokinin

(a) Dendrite (b) Synapse (c) Axon (d) Impulse

(a) Thinking (b) Regulating heartbeat (c) Balancing the body (d) All of the above

Receptors are specialised structures that detect changes (stimuli) in the internal and external environment and convert them into electrical impulses. They are the entry point of the nervous system's information flow.

Types of receptors:

• Photoreceptors (eye): detect light
• Mechanoreceptors (skin, ear): detect pressure, touch, sound
• Chemoreceptors (nose, tongue): detect chemicals (smell, taste)
• Thermoreceptors (skin): detect heat and cold
• Nociceptors (pain receptors): detect tissue damage

Problems if receptors do not work properly:

• Without pain receptors, a person may suffer severe burns, fractures, or internal injuries without realising it -- leading to life-threatening complications.
• Without photoreceptors, a person becomes blind and cannot respond to visual dangers.
• Without thermoreceptors, a person cannot sense heat and may touch boiling objects or not feel frostbite.
• Without chemoreceptors, a person cannot detect spoiled food (smell/taste) and may consume toxic substances.

Structure of a neuron:

1. Cell body (Soma/Cyton): Star-shaped or oval; contains the nucleus and cytoplasm with Nissl's granules (clusters of rough endoplasmic reticulum and ribosomes). It integrates signals received from dendrites. 2. Dendrites: Multiple short, branching extensions from the cell body. They increase the surface area for receiving impulses from other neurons or sensory receptors. They carry impulses towards the cell body. 3. Axon: A single long cylindrical extension (can be up to 1 metre long in some neurons). It carries impulses away from the cell body towards the synapse. 4. Myelin sheath: A white fatty layer around the axon formed by Schwann cells. It acts as insulation and increases the speed of impulse conduction (up to 120 m/s in myelinated neurons vs 2 m/s in unmyelinated ones). 5. Nodes of Ranvier: Regularly spaced gaps in the myelin sheath. Impulses "jump" from node to node (saltatory conduction), making transmission much faster. 6. Axon terminals (Boutons): The branched endings of the axon. They contain synaptic vesicles filled with neurotransmitters. These are released into the synapse to stimulate the next neuron or effector.

Function: The neuron is the fundamental unit of the nervous system. It receives signals through dendrites, processes them in the cell body, conducts the impulse along the axon, and transmits the signal to the next neuron or effector organ via the synapse. This enables rapid communication throughout the body.

Diagram description for the exam: Draw a large oval cell body with a dark circle inside (nucleus). Draw 3-4 short, branching dendrites on the top. Draw one long axon extending from the bottom right, with segmented myelin sheath blocks. Mark 2-3 gaps as "Node of Ranvier." At the end, draw branching axon terminals with small circles (synaptic vesicles). Label all parts clearly.

Phototropism is the directional growth movement of a plant organ in response to light.

Mechanism of positive phototropism in shoots:

1. When a plant shoot is illuminated from one side, the plant hormone auxin (indole-3-acetic acid, IAA) is synthesised at the shoot tip. 2. Auxin diffuses downwards but is redistributed laterally -- it moves from the illuminated side to the shaded side of the shoot. 3. Light causes auxin breakdown or redistribution away from the lit side, so auxin concentration becomes higher on the shaded side. 4. Auxin promotes cell elongation. The cells on the shaded side elongate more than those on the lit side. 5. This unequal growth causes the shoot to bend towards the light source (positive phototropism).

Roots show negative phototropism: In roots, high auxin concentration inhibits cell elongation. When light shines on one side, auxin accumulates on the shaded side and inhibits growth there, causing the root to bend away from light.

This mechanism was demonstrated by Darwin and Went's experiments with oat coleoptiles, which showed that the shoot tip produces a diffusible substance (auxin) responsible for phototropic bending.

The spinal cord is a cylindrical bundle of nerve fibres running inside the vertebral column. It serves three critical functions:

1. Ascending (sensory) tracts: Carry sensory impulses from receptors all over the body (except the head) to the brain. 2. Descending (motor) tracts: Carry motor impulses from the brain to muscles and glands throughout the body. 3. Reflex centre: Coordinates spinal reflexes without involving the brain.

If the spinal cord is injured at a particular level:

• Sensory signals from below the injury site are disrupted: The person loses sensation (touch, pain, temperature, pressure) in body parts below the level of injury. This can lead to injuries going unnoticed.
• Motor signals to muscles below the injury are disrupted: This causes paralysis -- inability to move limbs and body parts below the injury (paraplegia if lower body, quadriplegia if neck level).
• Reflex actions are disrupted: Reflexes controlled by the injured spinal segment cannot function properly.
• Autonomic functions may be affected: Bladder and bowel control, sexual function, and blood pressure regulation can be impaired.
• Spinal shock: Immediately after injury, there may be complete loss of all spinal cord functions below the injury, including all reflexes.

Plants do not have a nervous system or endocrine glands. Instead, chemical coordination is achieved through phytohormones (plant hormones) that are produced by cells in one region and transported to (or diffuse to) other regions where they exert specific effects.

The interaction of these hormones -- often acting antagonistically (e.g., auxin vs cytokinin for apical dominance) -- provides the plant with a sophisticated system to respond to environmental stimuli and regulate growth and development.

A system of control and coordination is essential for survival because:

1. Response to environmental stimuli: Organisms must detect changes in their surroundings (light, temperature, danger, food) and respond quickly and appropriately to survive. 2. Maintaining homeostasis: Internal conditions (body temperature, blood sugar, water balance, pH) must be kept within narrow limits for cells to function properly. 3. Integration of organ systems: Different organs and systems (digestive, circulatory, respiratory, excretory) must work together in a coordinated manner for the organism to function as a whole. 4. Growth and development: Regulated growth (e.g., through growth hormone, thyroxine, auxin) ensures the body develops properly from embryo to adult. 5. Reproduction: Hormonal coordination controls the timing of reproductive processes (puberty, menstrual cycle, pregnancy). 6. Protection from harm: Reflex actions and emergency responses (adrenaline surge) protect the organism from immediate danger. 7. Adaptation and learning: The nervous system enables organisms to learn from experience and adapt behaviour.

Without control and coordination, the body would be a collection of uncoordinated parts unable to respond, adapt, or survive.

Key point: All reflex actions are involuntary, but not all involuntary actions are reflexes. Reflexes are a specific type of involuntary action designed for speed and protection.

Both systems work together: In many situations, the nervous and endocrine systems are linked. For example, the hypothalamus (nervous tissue) controls the pituitary gland (endocrine), which in turn regulates other endocrine glands. Adrenaline release is triggered by nerve signals from the sympathetic nervous system to the adrenal medulla. This neuroendocrine integration ensures the body responds comprehensively to stimuli.