Science study notes

definitions of important things to know

what is homeostasis?

The inside environment of your cells must stay the same. Things like temperature, pH, and levels of ions, glucose, water, and carbon dioxide need to stay within a safe range. Keeping this internal environment stable is called homeostasis.

What is the control centre of our body?

The nervous and endocrine systems direct the action and function of the body. The digestive, respiratory, and circulatory systems work together to remove waste from the body while also absorbing necessary nutrients and compounds. Your circulatory system carries vital nutrients to the skeletal and muscular systems.  

Detailed anatomy of sensory receptors:

• Smell: Gaseous molecules are breathed in and dissolved in the mucus of the nasal cavity. This causes the cilia of chemoreceptors to generate nerve impulses that travel along the olfactory nerve to the brain to be interpreted.

• Sight: Light enters the cornea and pupil (the size of which is regulated by the iris). The lens focuses the light onto the retina at the back of the eye. The retina contains photoreceptors called rods (responsible for black and white vision). And cones (responsible for color vision). Never impulses are sent along the optic nerve to the brain for image interpretation. 

• Hearing (Auditory) and Balance: Outer: Includes the auricle and ear canal. Middle ear: Includes the ear drum and the ossicles (hammer/malleus, anvil/incus, and stirrup. Inner ear: Includes the oval window, semicircular canals (for balance), cochlea, and auditory nerve. 

Sound vibrations travel from the outer ear through the ear canal to the eardrum, then through the ossicles and oval window into the cochlea where they are changed into nerve signals that travel along the auditory nerve to the brain, while the Eustachian tube helps equalise pressure in the middle ear.

• Taste: Chemoreceptors on the tongue detect chemicals interpreted as different tastes like sour, bitter, umami, sweet, and salty. 

• Touch: The skin contains various receptors including pain receptors, light - contact receptors, heat receptors, cold receptors, pressure receptors, and movement receptors. These are distributed through the epidermis and dermis layers. 

Feedback Mechanisms and Thermoregulation:

Negative feedback happens when the body responds in the opposite way to a change to bring things back to normal, like lowering high body temperature or blood levels. For example, if body temperature drops, thermoreceptors in the skin and hypothalamus detect it and the hypothalamus acts as the control centre to help warm the body back up.

Positive feedback happens when the response increases the original change. For example, during breastfeeding, the baby suckling causes more milk to be released.

The endocrine system:

The endocrine system consists of glands that secrete chemical substances called hormones directly into the bloodstream to reach target cells.

Important glands:

Important glands (simple version):

• Thyroid – releases thyroxine, which controls metabolism (how fast the body uses energy).

• Adrenal glands – release adrenaline, which increases heart rate and blood pressure during stress.

• Pancreas – releases insulin, which lowers blood glucose levels.

• Pituitary gland – controls other glands and helps regulate growth and the menstrual cycle.

• Thymus – releases thymosin, which helps the immune system produce white blood cells to fight infection.

The Nervous and Neuron Structure:

The nervous system is made up of the CNS (brain and spinal cord) and the PNS (nerves connecting the body to the CNS). Sensory neurons send messages to the CNS, and motor neurons send messages to muscles or glands. A neuron has dendrites that receive signals, an axon that carries them, and a myelin sheath that speeds up transmission. Messages cross a synapse using chemicals called neurotransmitters to reach the next neuron.

Anatomy and functional areas of the brain:

The brain is divided into different areas that have specific jobs. The frontal lobe controls thinking, decision-making, speech, and movement. The occipital lobe is responsible for vision and reading. The cerebellum controls balance and coordination. The brainstem connects the brain to the spinal cord and controls basic life functions like breathing and heart rate.

Why is negative feedback good?

It keeps the body stable by reversing changes and maintaining homeostasis.

Why do you react without thinking to pain?

Because reflexes are controlled by the spinal cord before the brain processes the pain.

What is the link between glucose, glycogen, and glucagon?

• Insulin turns glucose into glycogen for storage, and glucagon turns glycogen back into glucose for energy.

Which hormone causes male sex organs to grow?

Testostreone:

What is the link between hormones and the menstrual cycle?

Hormones like progesterone help control the menstrual cycle and support pregnancy.

Which neurotransmitters act like “brakes” on emotions?

• Inhibitory neurotransmitters like GABA help calm or slow nerve activity.