Coordination and Response Notes

Coordination and Response

• Coordination: Working together of body parts through message transmission.
• Stimuli: Surroundings affect organisms.
• Response: Organisms react to stimuli via specialized cells called receptors.
• Effectors: Parts of the body (e.g., muscles, glands) that react to stimuli.
• Effective communication requires a fast system between effectors and receptors.
• Animals have two coordination methods:
  • Electrical system: Nervous system.
  • Chemical system: Endocrine system (hormones).

The Nervous System

• Two parts:
  • Central Nervous System (CNS): Brain and spinal cord; controls the entire nervous system.
  • Peripheral Nervous System (PNS): Nerves and sense organs; coordinates bodily functions.

Neurons

• Specialized cells that transmit electrical messages (impulses).
• Types: Sensory, motor, and relay neurons.
• Basic parts: Nucleus, cytoplasm, cell membrane.
• Structure adapted for fast impulse transmission.
  • Axon: Long, thin fiber of cytoplasm carrying impulses from the cell body.
  • Dendrites: Pick up impulses from nearby neurons.
  • Myelin sheath: Layer of fat and proteins insulating the axon for faster impulse transmission.
  • Nodes of Ranvier: Narrow gaps in the myelin sheath.
• Sensory Neuron: Transports impulses from receptor cells to the CNS.
• Motor Neuron: Transports impulses from the CNS to effector cells (glands and muscles).
• Relay Neuron: Connects sensory and motor neurons or two of the same type of neurons.

Reflex Arc

• Reflex action: Automatic, quick response to protect the body from danger.
• Reflex arc: The path taken by a reflex action.
• How it works:
  • Stimulus affects receptor cells, converting it to an electrical impulse.
  • Sensory neuron carries the impulse to the CNS.
  • Relay neuron in the spinal cord picks up and crosses the impulse to the motor neuron.
  • Motor neuron carries the impulse to effectors, causing a response.

Synapse

• Junction between two nerve cells.
• Synaptic cleft: Narrow gap between neurons.
• Presynaptic neuron: Neuron before the synapse.
• Postsynaptic neuron: Neuron after the synapse.
• Impulse crosses via neurotransmitters.
  • Vesicles in the presynaptic end release neurotransmitters into the synaptic cleft.
  • Neurotransmitter diffuses across the cleft and attaches to receptors on the postsynaptic end.
  • The shape of the neurotransmitter molecules is complementary to the shape of the receptor molecules.
  • Neurotransmitter is destroyed by enzymes or returned to the presynaptic end.
• Synapse action is one-way, ensuring unidirectional impulse movement.

The Eye

• Sense organ responsible for sight.
• Bony socket (orbit): Accommodates the eyeball and protects it from damage.
• Conjunctiva: Transparent membrane covering the front of the eye; protects the eye and keeps it moist.
• Cornea: Curved, transparent structure refracting light into the eye.
• Aqueous humor: Fluid behind the cornea maintaining its curved structure.
• Iris: Pair of muscles (circular and radial) with a colored pigment.
• Pupil: A gap in the iris; its size adjusts based on light intensity.
• Retina: Back of the eye containing receptor cells (rods and cones).
  • Cones: Work in high light intensity, sensitive to color, tightly packed at the fovea/yellow spot.
  • Rods: Work in low light intensity, sensitive to black and white images, packed tightly around the edges of the retina.
• Fovea/Yellow Spot: Area packed with cones for clear, direct vision.
• Blind spot: Where the optic nerve leaves the eye; no receptors are present, so no image is formed if light falls here.

Pupil-Iris Reflex

• Adjustment of the pupil based on light intensity.
• Low light intensity:
  • Radial muscles contract.
  • Circular muscles relax.
  • Pupil dilates.
  • More light enters the eye.
• High light intensity:
  • Radial muscles relax.
  • Circular muscles contract.
  • Pupil constricts.
  • Less light enters the eye.

Accommodation

• Adjustments in the shape of the lens to focus light from different distances on the retina.
• Lens shape is altered by ciliary muscles and suspensory ligaments.
• Nearby objects:
  • Ciliary muscles contract.
  • Suspensory ligaments slacken.
  • Lens becomes short and fat.
  • More refraction of light.
• Distant objects:
  • Ciliary muscles relax.
  • Suspensory ligaments tighten.
  • Lens becomes long and thin.
  • Less refraction of light.

The Endocrine System

• Coordination and response via hormones (chemical messengers).
• Hormones are made in endocrine glands and carried by blood to target organs.
• Endocrine glands are ductless and have a good blood supply.
• Target organs respond to hormones.
• Hormones are destroyed by the liver after use.

Endocrine Glands and Their Functions:

• Pituitary:
  • Antidiuretic hormone: Kidney – brings about the absorption of water.
• Pancreas (islets of Langerhans):
  • Insulin: Liver & muscles – control glucose levels in the blood.
  • Glucagon: Liver & muscles – control glucose levels in the blood.
• Adrenal glands:
  • Adrenaline: Liver, heart, lungs, skin, gut & eyes – supplies the body with more energy for fighting or running away; increases heart rate, breathing rate, and blood supply.
• Testes:
  • Testosterone: Reproductive structures – development of male secondary characteristics.
• Ovary:
  • Oestrogen: Reproductive structures in females – brings about female secondary characteristics.
  • Progesterone: Reproductive structures in females – helps in the control of the menstrual cycle by maintaining the uterine wall each time ovulation takes place.

Comparison of Nervous and Endocrine System

• Nervous system:
  • Made up of neurons.
  • Information is transmitted in the form of electrical impulses.
  • Impulses transmitted along nerve fibres (axons and dendrites).
  • Impulses travel very quickly.
  • The effect of a nerve impulse usually only lasts for a very short time.
• Endocrine system:
  • Made up of secretory cells.
  • Information is transmitted in the form of chemicals called hormones.
  • Chemicals carried, dissolved in blood plasma.
  • Chemicals travel more slowly.
  • The effect of a hormone may last longer.

Plant Responses

• Plants respond to their environment, though slower than animals.
• Responses involve changes in the rate or direction of growth.
• Growth towards a stimulus: Positive response.
• Growth away from a stimulus: Negative response.

Tropism

• Growth response towards or away from a stimulus.
• Important stimuli: Light and gravity.
• Phototropism: Response to light.
• Geotropism/Gravitropism: Response to gravity.
• Shoots: Grow towards light and away from gravity.
• Roots: Grow towards gravity and away from light.

Auxins

• Plant hormones that influence growth.
• Produced in the tips of shoots and roots.
• Diffuse downwards in the shoot and upwards in the root to regions behind the tips.
• Cause cell elongation and growth.

Effects of Auxins on Phototropism

• Even light distribution: Auxins distribute evenly, causing uniform growth.
• Uneven light distribution: Auxins move to the shady side, causing faster growth on that side.

Response of Plant Parts to Gravity

• Horizontal plant in the dark: Shoots bend upwards (negative gravitropism).
• Auxin collects on the lower side of the stem, causing faster growth there.
• In roots, auxin builds up on the lower surface, slowing down growth on the upper side, causing the radicle to bend downwards (positive gravitropism).