B10 Coordination and Response - Comprehensive Notes

B10 Coordination and Response

The Nervous System

• Coordination and Response: Living organisms respond to environmental changes to find food, avoid danger, and find mates.
  • A stimulus is any change in the environment.
  • Responding to stimuli is crucial to survival.
• Humans:
  • Respond to both external and internal environmental changes.
  • Maintaining a constant internal environment is known as homeostasis (auto-regulation to maintain equilibrium), which ensures optimal conditions for metabolic reactions and enzyme function.
• Coordination:
  • Receptor cells detect stimuli.
  • Effector cells (usually muscle cells or glands) bring about the required response.
  • The nervous system and the endocrine system coordinate by connecting receptors to effectors.
• Nervous System:
  • The nervous and endocrine systems have different effects; the organism selects the appropriate system based on the stimulus, or it may use both.
  • Central Nervous System (CNS): brain and spinal cord (made of nerves).
  • Peripheral Nervous System: nerves that carry information from sense organs (receptors) to the CNS and from the CNS to effectors (muscles or glands).
• Neurones:
  • The nervous system is made of cells called neurones.
  • Neurones: specialized cells for conducting electrical impulses rapidly (10-100 m/s).
  • Organized in bundles called nerves.
  • Neurone Structure:
    • Cell body and axon.
    • Axon: longest and thin fibre of cytoplasm extending from the cell body.
    • Dendrites: shorter fibres of cytoplasm.
    • Contains nucleus, cytoplasm, mitochondria, ribosomes, and cell membrane.
• Types of Neurones:
  • Sensory: long with a cell body branching off the middle of the axon; contains myelin sheath.
  • Relay: short with a small cell body at one end and many dendrites branching off it; no myelin sheath.
  • Motor: long with a large cell body at one end with long dendrites branching off it; contains myelin sheath.
• Reflex Arcs
  • Sensory neurones: take the impulse from the receptors to the CNS.
  • Relay neurones: link to other neurones within the CNS.
  • Motor neurones: take an impulse to the effectors to cause a response.

Reflex Arcs

• Responses are coordinated by the brain, but some bypass the conscious part of the brain and happen automatically (involuntary) - reflexes.

• Reflexes are:

  • Automatic
  • Fast
  • Protective

• Reflexes prevent injury and keep you alive!

• Reflex Arc: pathway taken by the information in a reflex.

  • Sensory neurone → Relay neurone → Motor neurone
  • The signal is processed in the spinal cord via a relay neurone, bypassing the brain.

• Reflex components:

  • Stimulus → Receptor → Coordinator → Effector → Response

• Reflex Action Example: Moving hand away from a hot candle.

  • Stimulus: Heat from the candle.
  • Receptor: Temperature receptor in finger.
  • Coordinator: Relay neurone in spinal cord.
  • Effector: Muscle in arm.
  • Response: Arm moves away from candle.

• Sense Organs: parts of the body that detect stimuli; receptors are usually part of a sense organ.

Sense Organs and Their Sensitivities

• Skin: sensitive to pressure, heat, cold (temperature), and pain (touch and temperature).
• Tongue: sensitive to chemicals in food and drink (taste).
• Nose: sensitive to chemicals in the air (smell).
• Ear: sensitive to sound and movement (hearing and balance).
• Eye: sensitive to light (sight).

Endocrine System & Hormones

• Hormone: chemical substance produced by a gland and carried by the blood
  • Hormones alter the activity of one or more specific target organs
  • Chemicals that transmit information from one part to another and cause a change.
• Endocrine system: collective of glands that produce hormones.
• Glands have a good blood supply to quickly release hormones into the bloodstream to reach target organs.
• Hormones are complementary to target receptors (found on cell membrane, or inside cells).
  • If not complementary, there is no effect.
• The liver regulates hormone levels in the blood by transforming or breaking down excess hormones.
• Endocrine glands secrete hormones directly into the blood (capillaries).
• Hormones travel in the blood plasma around the body.
• Hormones only act on cells or organs with the correct receptors (target cells and target organs).

Key Hormones and Their Roles:

• Adrenaline
  • Source: Adrenal gland
  • Role: Readies the body for a "fight or flight" response
  • Effect: Increases heart and breathing rate, dilates pupils
• Insulin
  • Source: Pancreas
  • Role: Lowers blood glucose levels
  • Effect: Causes excess glucose in the blood to be taken up by the muscles and liver and converted into glycogen for storage
• Testosterone
  • Source: Testes
  • Role: Main sex hormone in males
  • Effect: Development of secondary sexual characteristics in males
• Oestrogen
  • Source: Ovaries
  • Role: Main sex hormone in females
  • Effect: Development of secondary sexual characteristics in females and controls menstrual cycle
• Adrenaline:
  • Produced in adrenal glands.
  • Released during stress, excitement, or threat.
  • Prepares the body for extreme physical action (fight or flight response).

Comparison of Nervous and Endocrine Systems

Homeostasis

• Homeostasis: maintenance and regulation of the internal environment within the body within a narrow range of conditions.
• Maintained factors: water, pH, temperature, salts, glucose, carbon dioxide.
• Negative Feedback and Set Points:
  • If a level rises, control systems reduce it.
  • If a level falls, control systems raise it.
  • Continuous cycle to maintain levels within a narrow, normal range.

Homeostasis - Glucose in Blood

• Blood glucose levels are controlled by a negative feedback mechanism involving insulin and glucagon.
• Both hormones are made in the pancreas (islets of Langerhans).
• Insulin: produced when blood glucose rises; stimulates liver and muscle cells to convert excess glucose into glycogen for storage.
• Glucagon: produced when blood glucose falls; stimulates liver and muscle cells to convert stored glycogen into glucose to be released into the blood.
• Process
  • When blood glucose level rises (e.g., after a meal):
    • The pancreas releases insulin.
    • Insulin stimulates liver and muscle cells to take up excess glucose from the blood.
    • Soluble glucose is converted into insoluble glycogen.
    • Blood glucose level decreases back to normal.
  • When blood glucose level falls:
    • The pancreas releases glucagon.
    • Glucagon stimulates liver cells to breakdown glycogen into glucose and release it into the bloodstream.
    • Blood glucose level increases back to normal.
  • Adrenaline also speeds up the conversion of glycogen to glucose (for 'fight or flight').

Homeostasis - Controlling Body Temperature

• Homeostasis: maintaining a constant internal environment.
• Temperature regulation is a homeostatic mechanism.
• The human body needs to keep its core temperature as close to $37^\circ C$ as possible to ensure enzymes work optimally.
• Effects of Temperature Imbalance
  • Hypothermia: If body temperature drops below 35^\\circ C for a significant period, enzyme activity slows down, and metabolic reactions can't occur.
  • Heatstroke: If body temperature rises above 40^\\circ C for a significant period, enzymes denature, and metabolic reactions can't occur.
• Temperature is monitored by special receptors in the brain and skin.
• The CNS coordinates the response by activating effectors to either increase or decrease temperature.
• The hypothalamus coordinates activities related to body temperature regulation and contains thermoreceptors.
• The body uses sweat glands, hair follicles, and blood vessels to regulate heat.

Homeostatic Mechanisms for Temperature Control

• When We Are Hot:
  • Sweat is secreted by sweat glands, cooling the skin by evaporation (heat energy is lost as liquid water becomes water vapour).
  • Hairs lie flat against the skin, allowing air to circulate and increasing heat transfer to the environment by radiation.
  • Vasodilation: blood vessels (arterioles) near the skin surface open up, allowing more blood to flow near the skin's surface, radiating heat to the environment.
• When We Are Cold:
  • Skeletal muscles contract rapidly (shivering), generating heat from respiration.
  • Erect hairs trap a layer of air around the skin, acting as an insulator and preventing heat loss by radiation or convection.
  • Vasoconstriction: blood vessels near the skin surface close up, reducing blood flow near the skin and preventing heat loss.

Summary of Temperature Regulation Processes

• Increase in Body Temperature:
  • Thermoreceptors in the hypothalamus and skin detect the change.
  • Increased sweating.
  • Vasodilation.
  • Hairs lie flat against the skin.
• Decrease in Body Temperature:
  • Thermoreceptors in the hypothalamus and skin detect the change.
  • Vasoconstriction.
  • Shivering.
  • Skin hairs erect.