Overview
This lecture covers the control and coordination systems in humans and plants, focusing on the nervous system, endocrine system, reflex actions, plant movements, and plant hormones.
Human Nervous System
- The nervous system has two main parts: Central Nervous System (CNS) and Peripheral Nervous System (PNS).
- CNS consists of the brain and spinal cord; PNS is made up of nerves connecting the CNS to the body.
- Types of nerves in PNS: spinal nerves (spinal cord), cranial nerves (brain), and visceral nerves (internal organs).
- Key terms: stimulus (change in environment), receptor (detects stimulus), effector (responds), and response (resulting action).
Neuron Structure and Function
- Neuron is the structural/functional unit of the nervous system.
- Main parts: dendrite (receives signals), cell body/soma, axon (transmits impulses), myelin sheath (insulation), nerve endings/synaptic nodes.
- Signal transmission: chemical signal received, converted to electrical, transmitted along axon, reconverted to chemical at synapse.
- Synapse: gap between two neurons where signal transfer occurs.
Nerve Impulse and Neuron Types
- Nerve impulse: wave of electrical/chemical signals in neurons.
- Three neuron types: sensory (from receptor to CNS), motor (from CNS to effector), interneuron/relay neuron (connect sensory and motor).
Brain and Spinal Cord
- Brain is the body's coordinating center, protected by the cranium and three membranes (meninges) with cerebrospinal fluid (CSF).
- Brain parts: forebrain (cerebrum, thalamus, hypothalamus), midbrain (connections), hindbrain (cerebellum for balance, medulla for involuntary actions, pons regulates respiration).
- Spinal cord: cylindrical, encased in vertebral column, 31 pairs of nerves arise.
Reflex Action and Arc
- Reflex action: quick, automatic response to stimulus, mainly via spinal cord.
- Reflex arc: pathway from stimulus to receptor → sensory neuron → spinal cord/interneuron → motor neuron → effector → response.
- Brain stores information from reflex for future learning.
Endocrine System and Hormones
- Glands secrete substances; endocrine glands secrete hormones (no ducts), exocrine glands have ducts.
- Major endocrine glands: hypothalamus (controls pituitary), pituitary (growth hormone), thyroid (thyroxine, metabolism), parathyroid (calcium balance), thymus (immune system), pancreas (insulin & glucagon for blood sugar), adrenal (adrenaline for emergency), testes (testosterone), ovaries (estrogen, progesterone).
- Feedback mechanism regulates hormone levels.
Control and Coordination in Plants
- Plants coordinate via movements and hormones, without a nervous system.
- Movements: tropic (growth-related, directional, eg. roots towards water—hydrotropism, shoots towards light—phototropism), nastics (non-growth, non-directional, eg. touch-me-not closing).
- Differences: tropic—slow, permanent; nasty—fast, reversible.
Plant Hormones
- Key plant hormones: auxin (growth, response to light/gravity), gibberellin (seed germination/shoot growth), cytokinin (cell division, stomata opening), ethylene (fruit ripening), abscisic acid (growth inhibition/seed dormancy).
- Plant hormones regulate germination, growth, flowering, fruiting, growth inhibition, and seed dormancy.
Key Terms & Definitions
- Central Nervous System (CNS) — Brain and spinal cord.
- Peripheral Nervous System (PNS) — Nerves outside CNS.
- Neuron — Basic nerve cell; conducts impulses.
- Synapse — Gap between neurons where signals transfer.
- Hormone — Chemical messenger produced by endocrine glands.
- Reflex Arc — Pathway of a reflex action.
- Tropic Movement — Plant growth movement towards/away from stimulus.
- Nastic Movement — Plant movement not related to direction/growth.
- Auxin — Plant hormone for cell elongation/growth.
- Gibberellin — Hormone for seed germination/shoot elongation.
- Cytokinin — Hormone for cell division/stomata opening.
- Ethylene — Hormone for fruit ripening.
- Abscisic Acid — Hormone inhibiting growth/promoting dormancy.
Action Items / Next Steps
- Practice drawing and labeling neuron and brain diagrams.
- Review and memorize the functions of all major hormones and glands.
- Compare and contrast tropic and nastic movements in plants.
- Complete any assigned textbook readings and practice NCERT questions for this chapter.