Control and Coordination Notes

Multicellular organisms, like most plants and animals, are made up of many cells that need to communicate with each other.
Body systems work together, supplying what is needed.
- Skeletal System
- Respiratory System
- Muscular System
- Circulatory System
- Digestive System
- Nervous System
The nervous and endocrine systems control bodily actions and functions. The digestive, respiratory, and circulatory systems collaborate to eliminate waste while absorbing essential nutrients. The circulatory system delivers nutrients to the skeletal and muscular systems.

Homeostasis is the maintenance of a constant internal environment.
The internal environment needs to be kept constant for cells to survive, including factors like temperature, pH, and concentrations of ions, glucose, water, and carbon dioxide.

Receptors identify changes inside and outside the body.
Receptors are nerve cells located in sense organs such as eyes, ears, nose, tongue, and skin.
Different receptors respond to particular stimuli.

Eye: Photoreceptors in the retina detect light and send nerve impulses along the optic nerve to the brain.
Nose: Gas molecules dissolve in mucus, causing cilia of chemoreceptors to generate nerve impulses along the olfactory nerve to the brain.
Ear: Mechanoreceptors in the cochlea detect vibrations and send impulses along the auditory nerve to the brain.
Tongue: Chemoreceptors detect chemicals, interpreting them as different tastes.
Skin: Thermoreceptors detect heat, and mechanoreceptors detect vibration, pressure, touch, and pain.

Gaseous molecules are breathed in and dissolve in mucus in the nasal cavity.
Chemoreceptors with cilia detect these molecules and generate nerve signals.
These signals are transmitted via the olfactory nerve to the brain for interpretation of smell.

Light enters through the pupil, which is regulated by the iris.
The cornea and lens focus the light onto the retina, where an image is formed.
Photoreceptors (rods for black and white vision, cones for color vision) in the retina convert light into nerve impulses.
These impulses are sent to the brain via the optic nerve, where the image is interpreted.

Sound waves are detected by the outer ear (auricle) and travel through the ear canal to the eardrum, causing it to vibrate.
These vibrations are amplified by the ossicles (hammer, anvil, stirrup) in the middle ear and transmitted to the oval window of the inner ear.
The cochlea in the inner ear contains mechanoreceptors that detect these vibrations and send impulses along the auditory nerve to the brain.
The semicircular canals also contribute to balance.

Taste receptors (papillae) on the tongue detect different tastes: sour, bitter, umami, sweet, and salty.

Once a stimulus is detected by a receptor, a nerve impulse travels to the central nervous system (brain and spinal cord).
The message is processed to determine an appropriate response.
A message is then sent to the appropriate effector.

Effectors (muscles or glands) receive messages from the central nervous system and respond accordingly.
The response depends on the original stimulus.

Stimulus: Change in blood temperature
Receptor: Thermoreceptors in the hypothalamus (brain) and skin
Control Center: Hypothalamus
Effectors:
- Skin (arterioles, sweat glands)
- Muscles (skeletal muscles for shivering, erector-pilli muscles of hairs)
- Endocrine glands (thyroid gland, adrenal medulla)
Responses:
- Dilation or constriction of blood vessels in the skin
- Sweat production
- Shivering
- Raising of hairs for insulation
- Release of thyroxine (increased cell metabolism)
- Release of adrenaline (increased blood supply to muscles)

Negative feedback: The response is in the opposite direction to the stimulus. For example, if chemical levels in the blood are too high, the response is to lower them.
Positive feedback: The response goes in the same direction. An example is breastfeeding, where the baby's suckling stimulates more milk production.

Nervous system: Messages are sent as electrical and then chemical impulses through nerves and nerve centers. It comprises the central nervous system and the peripheral nervous system.
Endocrine system: Glands secrete hormones into the bloodstream to regulate processes in various organs.

Feature	Endocrine System	Nervous System
Speed of message	Slow	Fast
Speed of response	Usually slow	Immediate
Duration of response	Long lasting	Short
Spread of response	Usually slow	Very localised
Message travel	In circulatory system	In nervous system - along nerves and across synapses
Message type	Hormones (chemicals)	Electrical impulse and neurotransmitters (chemicals)

Endocrine glands secrete hormones into the bloodstream.
Hormones are transported throughout the circulatory system to specific target cells to bring about a response.

Endocrine gland	Hormone	Response
Thyroid	Thyroxine	Raises basal metabolic rate
Adrenal	Adrenaline	Increases heart rate and blood pressure during stress
Pancreas	Insulin	Lowers blood glucose levels
Pituitary	Anti-diuretic hormone (ADH)	Reabsorption of water in kidneys
Ovaries	Progesterone	Controls menstrual cycle and pregnancy
Thymus	Thymosin	Stimulates the production of white blood cells to fight infection

Stimulus: Decrease in body temperature
Receptor: Thermoreceptors in the hypothalamus
Control center: Hypothalamus
Effector: Thyroid gland
Response: Thyroxine released, increasing cells' metabolic rate, leading to an increase in body temperature

Sensory neurons carry messages to the central nervous system, and motor neurons carry messages away.
Messages are sent as electrical impulses along neurons and as chemical messages (neurotransmitters) across synapses.

The nervous system includes the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves connecting the central nervous system to the rest of the body).
These systems are made of nerve cells called neurons.
Axons of neurons are grouped to form nerves.

Sensory neurons: Detect changes in the environment and send messages to the central nervous system.
Interneurons: Carry nervous impulses through the central nervous system, linking sensory and motor neurons.
Motor neurons: Cause an organ (muscle or gland) to respond to a stimulus.

The gap between neurons is called a synapse.
Nerve impulses cannot jump across the synapse.
When the nerve impulse reaches the axon terminal, vesicles containing neurotransmitters are transported to the cell membrane of the neuron.
Neurotransmitters are released into the synapse.