The somatic nervous system controls voluntary muscle movements such as walking and running by sending signals from the brain to skeletal muscles.

The central nervous system (CNS) consists of the brain and spinal cord. Spinal nerves are part of the peripheral nervous system (PNS).

The cerebellum coordinates voluntary movements, such as balance and muscle coordination, by integrating sensory input.

Sycon and Euplectella are sponges (Porifera) that lack a nervous system entirely, while jellyfish have a simple nerve net.

The brachial plexus is a network of nerves that supplies the upper limbs, including the shoulders, arms, and hands.

The sympathetic nervous system prepares the body for 'fight or flight' by increasing heart rate and energy availability.

The parasympathetic system promotes 'rest and digest' functions, including digestion by stimulating digestive enzymes.

The parasympathetic nervous system constricts pupils to protect the eyes from bright light and enhance near vision.

The autonomic nervous system regulates involuntary bodily functions, such as heart rate and digestion, to maintain homeostasis.

GABA is the main inhibitory neurotransmitter in the CNS, reducing neuron excitability to maintain neural balance.

Acetylcholine is the primary neurotransmitter for synapses in the peripheral nervous system, including neuromuscular junctions.

Antidiuretic hormone (ADH) is a peptide hormone, an amino acid derivative, produced by the hypothalamus and stored in the pituitary gland.

Lack of vasopressin (ADH) causes diabetes insipidus, leading to excessive urination and thirst due to improper water reabsorption.

Cortisol promotes gluconeogenesis, converting proteins into glucose, working alongside glucagon to raise blood glucose levels.

Excess secretion of Melanocyte-Stimulating Hormone (MSH) is linked to Addison's disease, causing hyperpigmentation due to adrenal insufficiency.

STH (Somatotropic Hormone or Growth Hormone) is considered a primary hormone as it regulates overall growth and development.

Estrogen is a sex hormone produced by the ovaries, not a gonadotropin. LH and FSH are gonadotropic hormones that stimulate gonadal activity.

In females, testosterone is produced in small amounts by the adrenal cortex and ovaries.

Estrogen promotes the growth of the endometrial lining and induces vascularization to prepare for potential pregnancy.

Insulin facilitates the uptake of glucose from the blood into liver cells, where it is stored as glycogen.