Coordination and Control

Coordination and Control

14.1 Mammalian Nervous System

1. Role of the Nervous System

   • Function: Coordinates and regulates body functions by transmitting electrical impulses throughout the body.

   • Components: Includes the brain, spinal cord, and nerves.

2. Overview of the Nervous System

   • Central Nervous System (CNS):

     • Components: Brain and spinal cord.

     • Function:

       • Brain processes sensory information, coordinates voluntary and involuntary responses, and handles cognitive functions such as thinking and memory.

       • Spinal cord transmits signals between the brain and the rest of the body and coordinates reflexes.

   • Peripheral Nervous System (PNS):

     • Components: All nerves outside the brain and spinal cord.

     • Function:

       • Sensory Nerves: Carry information from sensory receptors to the CNS.

       • Motor Nerves: Transmit commands from the CNS to muscles and glands.

3. Types of Neurones

   • Sensory Neurones:

     • Function: Transmit impulses from sensory receptors (e.g., skin, eyes) to the CNS.

     • Structure: Long dendrites and short axons.

   • Relay Neurones:

     • Function: Interconnect sensory neurones with motor neurones within the CNS.

     • Structure: Short axons and dendrites.

   • Motor Neurones:

     • Function: Transmit impulses from the CNS to effectors (muscles or glands).

     • Structure: Long axons and short dendrites.

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4. Electrical Impulses

   • Nature of Impulses: Also known as action potentials, travel along neurones to transmit information.

   • Mechanism: Generated by changes in electrical potential across the neuron's membrane, propagating along the axon.

5. Simple Reflex Arcs

   • Components of Reflex Arc:

     • Receptor: Detects the stimulus (e.g., pain receptors in the skin).

     • Sensory Neurone: Carries the impulse from the receptor to the CNS.

     • Relay Neurone: Processes the impulse in the CNS and connects to the motor neurone.

     • Motor Neurone: Carries the impulse from the CNS to the effector.

     • Effector: Executes the response (e.g., muscles contracting).

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6. Reflex Action

   • Definition: A rapid, automatic response to a stimulus that does not require conscious thought, designed to protect the body from harm.

7. Synapse

   • Definition: A junction between two neurones.

   • Function: Allows the transfer of electrical impulses from one neurone to another, facilitating communication within the nervous system.

8. Structure of a Synapse

   • Components:

     • Synaptic Knob: Contains vesicles filled with neurotransmitter molecules.

     • Synaptic Gap (Cleft): The small space between the pre-synaptic neurone and the post-synaptic neurone.

     • Receptor Proteins: Located on the membrane of the post-synaptic neurone; bind with neurotransmitters to propagate the impulse.

9. Events at a Synapse

   • (a) Release of Neurotransmitters: An electrical impulse arriving at the synaptic knob stimulates the release of neurotransmitter molecules from vesicles into the synaptic gap.

   • (b) Diffusion and Binding: Neurotransmitter molecules diffuse across the synaptic gap and bind with receptor proteins on the post-synaptic neurone.

   • (c) Stimulation of Next Neurone: Binding generates a new electrical impulse in the post-synaptic neurone, continuing signal transmission.

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10. Direction of Impulse Travel

• Unidirectional Flow: Synapses ensure that electrical impulses travel in one direction only, preventing backflow of impulses.

14.2 Mammalian Sense Organs

1. Sense Organs

   • Definition: Specialized structures containing receptor cells, responding to specific stimuli (eyes, ears, skin, tongue, nose).

   • Types of Stimuli and Receptors:

     • Light: Detected by photoreceptors in the eyes.

     • Sound: Detected by mechanoreceptors in the ears.

     • Touch: Detected by mechanoreceptors in the skin.

     • Temperature: Detected by thermoreceptors in the skin.

     • Chemicals: Detected by chemoreceptors in the nose (olfaction) and tongue (taste).

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2. Structures of the Eye

   • Cornea: Transparent front part that refracts light.

   • Iris: Colored part that regulates pupil size.

   • Pupil: Opening that allows light entry.

   • Lens: Focuses light onto the retina; flexible for focusing.

   • Ciliary Muscles: Adjust lens shape.

   • Suspensory Ligaments: Connect ciliary muscles to the lens.

   • Retina: Contains photoreceptors (rods and cones).

   • Fovea: Area for sharp vision with high cone concentration.

   • Optic Nerve: Transmits visual information to the brain.

   • Blind Spot: Area where optic nerve exits the eye, lacking photoreceptors.

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3. Functions of Each Part of the Eye

   • (a) Cornea: Refracts light rays to help focus on the retina.

   • (b) Iris: Regulates amount of light entering by adjusting pupil size (circular and radial muscle action).

   • (c) Lens: Focuses light by changing shape.

   • (d) Ciliary Muscles and Suspensory Ligaments: Adjust lens shape to focus on objects at different distances.

   • (e) Retina: Converts light into electrical impulses using rods (low light sensitivity) and cones (color vision).

   • (f) Fovea: Provides sharp vision, vital for detail-oriented tasks.

   • (g) Optic Nerve: Transmits information from retina to brain for image processing.

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4. Pupil Reflex

   • Definition: Automatic response of pupil to light intensity changes.

   • Mechanism:

     • Bright light causes pupil constriction; dim light causes dilation.

     • Circular and radial muscle coordination.

5. Accommodation

   • Definition: Eye's ability to focus on objects at different distances.

   • Mechanism:

     • Distant: Ciliary muscles relax, lens becomes thinner.

     • Near: Ciliary muscles contract, lens thickens, allowing for more light bending.

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Mammalian Hormones

1. Definition of a Hormone

   • Hormones are chemical substances produced by endocrine glands, released into the bloodstream to affect target organs.

   • They regulate functions such as growth, metabolism, and reproduction.

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2. Endocrine Glands and the Hormones They Produce

   • Adrenal Glands: Adrenaline (fight or flight response).

   • Pancreas:

     • Insulin: Lowers blood glucose by promoting uptake.

     • Glucagon: Increases blood glucose by converting glycogen into glucose.

   • Pituitary Gland:

     • FSH: Stimulates egg/sperm development.

     • LH: Triggers ovulation and testosterone production.

   • Testes (males): Testosterone (male characteristics, sperm production).

   • Ovaries (females):

     • Oestrogen: Female characteristics, menstrual cycle regulation.

     • Progesterone: Prepares and maintains uterus for pregnancy.

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3. The Role of Adrenaline

   • Released in response to stress/excitement. Increases heart rate and blood glucose levels for physical actions.

   • Situations triggering release: Stressful events, emergencies, physical exertion.

4. Comparison Between Nervous and Hormonal Control

   • Nervous Control: Fast, electrical impulses, specific target neurons, short-lived effects.

   • Hormonal Control: Slower, chemical signals via blood, can target multiple organs, longer-lasting effects.

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Homeostasis

1. Definition of Homeostasis

   • Process of maintaining a constant internal environment (e.g., temperature, pH, glucose levels), crucial for optimal cell function.

   • Key Internal Conditions: Body temperature (37°C), blood glucose (90 mg/dL), water balance, pH levels (7.4).

2. Negative Feedback and the Concept of Control

   • Negative Feedback Mechanism: Responds to deviation from a set point, counteracting changes to stabilize conditions.

   • Set Point Examples: Temperature (37°C), blood glucose (90 mg/dL).

   • How Negative Feedback Works:

     1. Deviation detected by receptors.

     2. Corrective action is triggered.

     3. Condition returns to set point, stopping corrective action.

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Examples of Negative Feedback

1. Body Temperature Regulation

   • Increase in temperature:

     • Receptors detect change, activating sweat glands for cooling.

   • Decrease in temperature:

     • Receptors activate shivering to generate heat.

2. Blood Glucose Regulation

   • Increase after eating:

     • Pancreas releases insulin to lower glucose levels.

   • Decrease:

     • Pancreas releases glucagon to raise glucose levels.

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Temperature Control

1. Structure of the Skin

   • Key structures include hair, sweat glands, receptors, sensory neurones, blood vessels, and fatty tissue.

   • Functions:

     • Hairs provide insulation.

     • Blood vessels constrict/dilate to regulate heat.

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2. Role of Insulation in Temperature Control

   • Insulation maintains internal temperature by reducing heat loss, aided by fatty tissue and hair.

3. Role of the Hypothalamus and Skin Receptors

   • The hypothalamus monitors temperature and triggers responses based on receptor signals regarding the body's environment.

4. Processes Maintaining Constant Internal Temperature

   • Sweating: Cool body as sweat evaporates.

   • Shivering: Generates heat through rapid muscle contractions.

   • Hair Erector Muscles: Adjust warmth retained.

   • Vasodilation/Vasoconstriction: Control heat loss via blood flow adjustments.

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O Level Biology 5090 – Blood Glucose Control

1. The Need to Control Blood Glucose Concentration

   • Maintaining blood glucose is vital for respiration and preventing damage to cells/tissues.

2. Control of Blood Glucose Concentration by Liver and Pancreas

   • Insulin and Glucagon: Work together for glucose regulation by promoting uptake/storage (insulin) or release (glucagon).

3. Signs of Type 1 Diabetes and Its Treatment

   • Signs: Increased blood glucose, glucose presence in urine.

   • Treatment: Insulin administration to regulate blood glucose levels.