Coordination and Response

1.1 Mammalian Nervous System

  • The mammalian nervous system consists of two main parts:

    • Central Nervous System (CNS):

    • Comprises the brain and spinal cord, serving as the area of coordination within the body.

    • Peripheral Nervous System (PNS):

    • Made up of nerves and neurones that coordinate and regulate various body functions.

  • Electrical impulses travel through the neurones, facilitating the coordination and regulation of body functions.

1.2 Types of Neurones

  • Nerve Impulse:

    • An electrical signal that passes along the nerve cells known as neurones.

  • Axons:

    • Ensure minimal delay in impulse transfer between neurones.

  • Dendrites:

    • Extensions forming a network, thus allowing easy communication among neurones.

  • Sensory Neurone:

    • Carries impulses from sensory organs (sensory receptors) to the CNS.

  • Relay Neurone (Interneurone):

    • Acts as the intermediary within the CNS, connecting sensory to motor neurones.

  • Motor Neurone:

    • Transmits impulses from the CNS to effectors (muscles or glands).

1.3 Simple Reflex Arc

  • Reflex Action:

    • An automatic and rapid response that integrates and coordinates stimuli with the responses of effectors (muscles and glands).

    • Example: Quickly removing your hand from a hot metal surface.

  • Involves three types of neurones:

    • A sensory neurone, a relay neurone, and a motor neurone.

  • The gap between neurones is called a synapse.

1.4 How the Simple Reflex Arc Works

  1. A stimulus affects a receptor (a cell or organ that converts a stimulus into an electrical impulse).

  2. A sensory neurone carries impulses from the receptor to the CNS (specifically the spinal cord).

  3. A connector/relay neurone transmits the impulse slowly (due to the absence of myelin sheath) across the spinal cord.

  4. The motor neurone carries impulses from the CNS to the effector.

  5. The effector (muscle or gland) executes the response.

Flowchart of the Reflex Arc

  • Stimulus → Receptor (e.g., in skin) → Sensory Neuron → Relay Neuron (in spinal cord) → Motor Neuron → Effector (e.g., Muscle) → Response (e.g., Pulling hand away)

1.5 Synapse

  • Synapse:

    • A junction between two neurones featuring a gap across which impulses transmit via the diffusion of a neurotransmitter.

    • Synapses ensure that impulses travel in one direction only.

  • Synaptic Cleft:

    • The small gap present between each pair of neurones.

  • Within the neurone's axon, hundreds of tiny vacuoles (vesicles containing a chemical known as neurotransmitter) exist.

  • Upon the arrival of an impulse, the vesicles move to the cell membrane, releasing their contents into the synaptic cleft.

  • The neurotransmitter rapidly diffuses across the gap and binds to receptor molecules on the relay neurone's cell membrane.

    • This occurs due to the complementary shapes of neurotransmitter molecules and the receptors.

1.7 Sense Organs

  • Sense Organ:

    • Composed of groups of receptor cells responding to specific stimuli: light, sound, touch, temperature, and chemicals.

  • Key Components:

    • Cornea: Refracts light.

    • Iris: Regulates light entry through the pupil.

    • Lens: Focuses light onto the retina.

    • Retina: Contains light receptors sensitive to various colors (rods and cones).

    • Optic nerves: Transmit impulses to the brain.

    • Pupil: An aperture allowing light to penetrate.

1.8 Pupil Reflex

  • Adjusts for high and low light intensity.

  • Involuntary Response:

    • Adjusts to light conditions automatically without conscious thought.

1.9 Accommodation

  • Accommodation:

    • The process of adjusting vision for near and distant objects.

    • The lens is elastic, changing shape when attached suspensory ligaments become tight or loose.

    • The contraction or relaxation of ciliary muscles facilitates these changes.

1.10 Rods and Cones

  • Rods:

    • Provide low detail, black & white images suitable for low-intensity lighting (e.g., nighttime).

    • Packed more densely at the retina's outer edge for peripheral vision.

  • Cones:

    • Deliver detailed, colored images, effective in high-light conditions.

    • Concentrated at the fovea, facilitating sharp central vision.

    • Distribution Notes:

    • More rod cells compared to cone cells.

    • No rod cells exist at the fovea's center (location of sharpest vision).

    • The blind spot lacks both rod and cone cells due to the presence of the optic nerve.

1.11 Hormones

  • Hormones:

    • Chemical substances secreted by glands, transported via blood, that modify the activity of specific target organs.

  • Key Endocrine Glands and Their Hormones:

    • Adrenal gland: Produces Adrenaline, which prepares the body for vigorous action.

    • Testes: Secrete Testosterone, promoting male sexual characteristics.

    • Pancreas: Releases Glucagon (increases blood glucose concentration) and Insulin (decreases blood glucose concentration).

    • Ovary: Produces Oestrogen, fostering female sexual characteristics.

  • Adrenaline:

    • Hormone from the adrenal gland that elevates pulse rate, heart rate, and pupil diameter while increasing blood glucose concentration.

    • Secreted during adrenaline-inducing activities, such as bungee jumping or rollercoaster rides.

1.12 Homeostasis

  • Homeostasis:

    • The process of maintaining a consistent internal environment within the body.

    • Insulin's Role:

    • Reduces blood glucose concentration, highlighting its significance in glucose metabolism.

1.13 Comparison of Nervous and Endocrine Systems

Comparison Aspect

Nervous System

Endocrine System

Speed of Action

Very rapid

Can be slow

Duration of Response

Usually within seconds

May last years (e.g., puberty)

Example of Process Controlled

Reflex actions (e.g., blinking)

Development of the reproductive system

Nature of Message

Electrical impulses via nerves

Chemical messengers (hormones) in bloodstream

Area of Response

Localized response (one area usually)

Widespread response (multiple organs)

1.14 Homeostasis: Blood Glucose Control

  • Blood glucose levels are regulated and monitored by the pancreas.

  • Depending on blood glucose levels, the pancreas secretes different hormones:

    • Insulin: Released when blood glucose levels rise; causes the liver to convert excess glucose into glycogen.

    • Glucagon: Released when blood glucose levels fall; prompts the liver to convert stored glycogen back into glucose and release it into the bloodstream.

  • Diabetes:

    • A condition resulting when blood glucose control fails:

    • Type 1 Diabetes:

    • Caused by the destruction of insulin-secreting cells.

    • Symptoms include hyperglycemia (unwell feeling, dry mouth, blurred vision, excessive thirst) and hypoglycemia (exhaustion, confusion, irrational behavior).

    • Treatment involves frequent small meals (avoiding large carbohydrate intake) and insulin injections to manage blood glucose levels.

1.15 Homeostasis: Temperature Regulation

  • Body temperature control is a vital homeostatic mechanism.

  • The optimal temperature for enzyme activity is around 37°C.

  • If body temperature exceeds this threshold, enzymes may denature, reducing catalytic efficiency, which can severely disrupt biological processes such as respiration.

  • Skin Structure:

  • Temperature Regulation Mechanism:

    • The brain, containing thermoreceptors (sensitive to blood temperature), regulates temperature.

    • Skin thermoreceptors send sensory impulses to the brain.

    • The brain responds by sending impulses through motor neurones to skin effectors, maintaining temperature within a narrow range (around 37°C).

    • Fatty tissue beneath the dermis serves as insulative protection against excessive heat loss.

1.16 Vasoconstriction and Vasodilation

  • Vasoconstriction:

    • Blood flow in capillaries decreases due to narrowing of the arterioles leading to skin capillaries when cold, reducing heat loss via radiation since less blood circulates near the skin surface.

  • Vasodilation:

    • Increased blood flow in capillaries results from widening blood vessels to skin capillaries during warmth, facilitating cooling as heat-carrying blood flows quicker through the skin, leading to enhanced heat loss.

1.17 Tropic Responses

  • Auxin:

    • Plant hormones or growth substances that regulate tropisms.

    • Synthesized by cells located at the tips of plant roots and shoots.

  • Gravitropism:

    • A plant's growth response towards (positive) or away (negative) from gravity due to auxins.

    • Auxins facilitate cell elongation based on their response to light and gravity distribution.

  • Phototropism:

    • A plant's growth towards (positive) or away (negative) from light using auxins.

    • If sunlight penetrates from one side, auxins accumulate on the shaded opposite side, causing quicker growth on that side and resulting in the plant bending toward the light source.