Neurons, Nervous System, and Sensory Organs: Biology
Neurons: Structure and Function
Neurons are composed of three main parts:
- Cell Body: The thickest part of the neuron, containing the nucleus and most organelles.
- Axon: A large prolongation extending from the cell body, branching out at its end.
- Dendrites: Small, branching prolongations of the cell body.
Neurons connect through dendrites and axons. The small gap separating the dendrites and the branched ends of the axon is called the synapse. They transmit information via electrical signals at speeds up to 100 m/s.
Types of Neurons
- Sensory Neurons: Carry information from receptors to the central nervous system.
- Interneurons: Located within the central nervous system, they connect sensory and motor neurons.
- Motor Neurons: Transmit information from the central nervous system to effectors (muscles and glands).
The Nervous System
Central Nervous System (CNS)
The CNS consists of the brain and the spinal cord.
Peripheral Nervous System (PNS)
The PNS comprises nerves made up of neurons and axons, classified as cranial and spinal nerves.
Brain Components and Functions
- Spinal Bulb: Controls heartbeat, breathing, deglutition, blood vessel constriction and dilation, and reflexes.
- Cerebellum: Regulates muscle control, balance, and posture.
- Hypothalamus: Regulates body temperature and blood pressure.
- Thalamus: Filters information from receptors, allowing only important data to pass through.
- Limbic System: Controls instinctive behaviors related to feeding, aggression, and sexuality.
- Brain: Analyzes information from receptors and initiates voluntary responses.
- Corpus Callosum: Connects the two hemispheres of the brain.
Reflex and Voluntary Actions
A reflex action involves a sensory nerve capturing information, the spinal cord, and a motor nerve connected to an effector, forming a reflex arc. In a voluntary action, the spinal cord acts as a communication channel between the body and the brain, forming a voluntary arc, where we are conscious of the response.
Sensory Organs
Sensory organs, such as the eyes, ears, nostrils, and tongue, are adapted to capture specific stimuli. They contain a high concentration of specialized receptors:
- Eyes: Photoreceptors in the retina.
- Tongue and Olfactory Mucosa: Chemoreceptors.
- Ears: Mechanoreceptors.
The Endocrine System and Hormones
The endocrine system regulates gradual changes in the body. Hormones are chemical messengers that transmit signals throughout the body. Endocrine glands release hormones into the bloodstream, where they travel to target organs. This is not a slow process.
Receptor Types
- Mechanoreceptors: Detect mechanical energy, such as pressure and sound.
- Thermoreceptors: Detect thermal energy, informing about heat and cold.
- Photoreceptors: Detect light energy.
- Nociceptors: Detect various types of potentially harmful energy, responsible for pain.
Important Hormones
- Adrenaline: Produced by the adrenal glands, prepares the body for physical exertion during intense muscular activity.
- Insulin: Produced by the pancreas, decreases blood glucose levels by facilitating its entry into cells.
- Estrogens: Produced by the ovaries, responsible for female sexual characteristics and controlling ovulation cycles.
- Testosterone: Produced by the testicles, responsible for male sexual characteristics and activating bone growth.
Endocrine glands secrete hormones in response to various stimuli, including emotional and chemical signals. In some cases, the nervous system directly stimulates hormone secretion.