Biology: Coordination and Response

Coordination and Response

• Organisms detect changes in their environment and respond, this is called sensitivity. The change that stimulates the response is called a stimulus.
• Stimuli are categorized as external (light, sound, smell, taste, touch, pressure) or internal (blood osmotic pressure, body temperature, blood sugar level).
• Mammals sense stimuli using sensory receptors.
• Receptors convert a stimulus to a nerve impulse.
• Nerve impulses travel to the brain, the integration center.
• The brain interprets the impulses and coordinates an appropriate response.
• The part of the body that responds to the stimulus is called the effector (muscles or glands).
• Receptors and effectors work together to produce suitable responses to changes in the environment.
• Coordination ensures that all parts of an organism function together. This is controlled by the nervous system and endocrine system.

Types of Receptors

• Sensory receptors detect information from the internal and external environment.
• Receptors are sensitive to specific stimuli.
• Examples of sensory receptors:
  • Photoreceptor: Light
  • Thermoreceptor: Temperature change
  • Chemoreceptor: Chemical substances
  • Baroreceptor: Pressure change
  • Mechanoreceptor: Touch, Pressure
  • Nociceptor: Pain

Nervous System

• The nervous system is a network of nerve cells (neurons).
• It is divided into two main systems: the central nervous system (CNS) and the peripheral nervous system (PNS).
• The CNS includes the brain and spinal cord.
• The PNS includes 12 pairs of cranial nerves and 31 pairs of spinal nerves.

Brain

• The brain is the control center for humans.
• It is composed of the cerebrum, hypothalamus, cerebellum, medulla oblongata, and pituitary gland.
• Cerebrum: Controls emotions, senses, personality, and actions.
  • Analyzes, integrates, and correlates stimuli.
  • Responsible for higher mental abilities like learning, and memory.
• Hypothalamus: Regulates homeostasis (body temperature, water balance, blood pressure, hunger, thirst).
• Cerebellum: Maintains balance and coordinates muscle movement.
• Medulla oblongata: Controls involuntary actions (heartbeat, breathing, digestion).
• Pituitary gland: Controls the secretion of hormones by other endocrine glands.

Spinal Cord

• The spinal cord is located within the vertebral column.
• It is surrounded by cerebrospinal fluid, which protects it and provides nutrients.
• Contains white matter (axons) and gray matter (cell bodies).
• Plays a role in processing sensory information, sending responses, controlling reflex actions, and connecting the brain to the peripheral nervous system.

Neurones and Synapses

• Neurons are nerve cells that transmit impulses.
• A neuron consists of a cell body, dendrites, an axon, myelin sheath, nodes of Ranvier, and a synaptic knob.
• Sensory neurons carry impulses from sensory receptors to the CNS.
• Relay neurons connect sensory and motor neurons.
• Motor neurons carry impulses from the CNS to effectors.
• Synapses are junctions between neurons. Signals are transmitted chemically via neurotransmitters (acetylcholine, noradrenaline etc).

Voluntary and Involuntary Actions

• Voluntary actions are conscious and under our control.
• Involuntary actions happen automatically without our conscious awareness.
• Voluntary actions involve stimulation, impulse, neuron, and effector. These actions are controlled by the cerebral cortex and involve skeletal muscles.
• Involuntary actions involve stimulation, impulse, neuron, effector. These actions happen automatically. The medulla oblongata and hypothalamus control involuntary actions; these actions involve smooth muscle and glands.
• Reflex actions are a specific type of involuntary action that occur quickly to protect the body.

Two-Neurone Reflex Arc

• A simple reflex arc involves a sensory neuron and motor neuron.
• Reflexes are fast responses and do not involve the brain at first.
• This is a fast automatic response that doesn't require conscious thought.

Endocrine System

• The endocrine system works with the nervous system in maintaining homeostasis and responding to changes in the environment via hormones.
• Hormones are chemical messengers secreted by glands.
• They are carried in the bloodstream and affect target cells.
• Endocrine glands include the hypothalamus, pituitary gland, thyroid gland, adrenal gland, pancreas, ovaries, and testes.
• These glands secrete hormones that regulate various bodily functions.

Hormone Functions (selected)

• Pituitary gland: secretes hormones that regulate other endocrine glands.
• Thyroid gland: releases thyroxine to control metabolism and growth.
• Adrenal glands: secrete adrenaline/noradrenaline in response to stress, increasing heart rate and blood pressure.
• Pancreas: regulates blood glucose levels.
• Ovaries: secrete estrogen and progesterone regulating sexual characteristics and reproduction.
• Testes: secretes testosterone, regulating sexual characteristics and reproduction.

Health Issues

• Various diseases can affect the nervous and endocrine systems. Examples include epilepsy, Alzheimer's, multiple sclerosis, Parkinson's, Lou Gehrig's disease, ADHD, Autism, Diabetes Mellitus, Diabetes Insipidus, Hypothyroidism, Hyperthyroidism, Dwarfism, and Gigantism.
• Drug abuse/alcohol effects these coordinated systems.

Drugs and Alcohol

• Drugs and alcohol affect human coordination and response.
• Some drugs stimulate the nervous system, while others slow it down.
• Abuse of these substances can have serious health consequences.