control n coordination

• Neurones play an important role in coordinating communication within the nervous system
• Stimuli is first detected by sensory receptor cells and then transmitted to the sensory neurone
• Neurones have a cell body composed of the nucleus and organelles like mitochondria in the cytoplasm, with extensions called dendrites conducting impulses towards the cell body and axons conducting them away from the cell body
• There are three types of neurones: sensory, motor, and relay, each with different functions based on the position of the cell body within the neurone
• Motor neurones transmit electrical signals from the central nervous system to muscles and glands, sensory neurones transmit impulses from receptors to the central nervous system, and relay neurones transmit electrical impulses from sensory neurones to motor neurones
• The polarised nature of the neurone membrane in the resting state enables neurones to carry electrical impulses called action potentials
• The speed of electrical potential conduction can be increased with the help of myelin sheath, which serves as an insulator of axons and dendrons produced by Schwann cells
• The mechanism by which the speed is increased is known as saltatory conduction, where the action potential jumps between gaps in the myelin sheath called nodes of Ranvier
• Nerve cells are polarised in their resting state due to an imbalance between sodium and potassium ions, resulting in a resting potential of -70mV
• The resting potential is generated and maintained with the help of a sodium-potassium pump, which moves sodium ions out of the neurone, creating an electrochemical gradient
• Upon stimulation, the neurone cell membrane becomes depolarised, leading to the opening of sodium ion channels and the diffusion of sodium ions into the neurone, eventually reaching a potential difference of +30mV
• The action potential travels along the neurone as a wave of depolarisation, triggering another action potential in adjacent regions
• The refractory period follows the action potential, during which the neurone membrane cannot be excited, ensuring action potentials pass in one direction as discrete signals and limiting the number of impulses that can be sent
• Synapses are junctions between two neurones where neurotransmitters are released into the synaptic cleft, binding to receptors on the postsynaptic membrane and triggering the opening of cation channels
• The presence of receptors on the postsynaptic side ensures that the action potential can only travel in one direction
• Muscles:

  • Tendons: non-elastic tissue connecting muscles to bones
  • Ligaments: elastic tissue joining bones together and determining movement at a joint
  • Joints: where two bones are attached for movement, made of fibrous connective tissue and cartilage
  • Skeletal muscles: attached to bones, arranged in antagonistic pairs
  • Antagonistic muscle pairs: muscles that pull in opposite directions, e.g., flexors and extensors like triceps and biceps
• Striated muscle, also known as skeletal muscle, makes up most of the body's muscles and is used for voluntary movement
• Myofibril contraction process:

  1. Impulse at neuromuscular junction releases Ca2+ from sarcoplasmic reticulum

  2. Ca2+ binds to troponin, causing a shape change and tropomyosin moves away from actin

  3. Myosin binds to actin, forming an actomyosin cross bridge

  4. ADP and phosphate ions released cause the power stroke

  5. ATP binds, myosin unbinds from actin

  6. ATP breaks down to ADP and phosphate to return myosin to original position

  7. Ca2+ ions reabsorbed, troponin moves back, and tropomyosin re-covers binding sites
• Role of ATP in myofibril contraction:

  • Allows actomyosin cross bridge to detach and is hydrolyzed for myosin to return to original position (muscle relaxation)
  • Allows reabsorption of Calcium ions via active transport
• Hormones and human menstrual cycle:

  • Four main hormones involved: progesterone, oestrogen, follicle stimulating hormone, and luteinising hormone
  • Roles of hormones include stimulation of egg development, release, and production of other hormones
• Endocrine system:

  • Consists of endocrine glands releasing hormones into the bloodstream
  • Hormones like ADH, glucagon, and insulin play roles in osmoregulation and blood glucose concentration control
• Control and coordination in plants:

  • Plant growth regulators like auxins, gibberellins, abscisic acid, and ethane trigger plant growth responses
  • Auxins promote cell elongation through transport of hydrogen ions into cell walls, enabling cell expansion and growth