Sensory Systems and Nervous Coordination

Receptors

Internal receptors perceive changes inside the body, such as a rise in blood pressure. External receptors perceive stimuli in the external environment.

Types of Receptors

• Mechanoreceptors: Perceive mechanical stimuli (pressure).
• Thermoreceptors: Perceive changes in temperature.
• Chemoreceptors: Detect chemical substances in the air, water, etc.
• Nociceptors: Perceive pain stimuli.
• Photoreceptors: Light sensitive.

Nervous System

The nervous system analyzes internal and external stimuli perceived by receptors, generating responses. It carries out this function through nerve impulses transmitted by cells called neurons. This system coordinates fast, short-lived responses (e.g., muscle contraction).

Endocrine System

The endocrine system is made up of endocrine glands that release hormones (e.g., adrenaline). Hormones coordinate internal organs through chemical reactions. This system coordinates slower but longer-lasting responses.

Smell

Smell receptors, or olfactory cells, are chemoreceptors that detect gaseous substances entering through the nose. The olfactory mucosa perceives these substances and secretes mucus. The olfactory mucosa sends the perceived smell to the olfactory nerve and then to the brain, which interprets the information.

Touch

Touch receptors, including thermoreceptors, mechanoreceptors, and nociceptors, are located in the skin and are not uniformly distributed.

Taste

Gustatory cells are chemoreceptors located inside bulb-shaped structures called taste buds.

Hearing

The ear contains mechanoreceptors called auditory cells and utilizes fluids for sound transmission.

• Outer Ear: Ear canal and auricle.
• Middle Ear: Eardrum and ossicles (bones).
• Inner Ear: Cochlea (contains auditory cells) and semicircular canals.

Layers of the Eye

1. Sclera & Cornea (covered by the conjunctiva).
2. Choroid & Iris/Pupil (contains aqueous humor).
3. Retina (contains photoreceptors).

Nervous Coordination

The transmitting neuron passes nerve impulses through its axon to the synaptic cleft. Receptor neurons in the postsynaptic membrane create a new impulse, which then travels through the neuron to the next synaptic cleft.

Parts of the Neuron

• Dendrites: Receive nerve impulses.
• Cell Nucleus: Processes information.
• Myelin Sheath: Insulates the axon, preventing signal loss.
• Axon: Transmits nerve impulses.