Human Nervous System and Sensory Organs

Fundamentals of Neurobiology

Biology is the science that studies living beings and vital phenomena. The Human Nervous System acts as a mechanism of control for bodily functions.

• Nerve Impulse: A physical and chemical phenomenon occurring in the neuron that passes from one neuron to another.
• Reflexes: Automatic and involuntary responses produced by a stimulus.
• Synapse: Functional unions between the terminal branches of the axon of one neuron and the dendrites of another.
• Nerves: A group of fibers that carry sensations and impulses between receptor organs and the brain.
• Learning: The process by which organisms modify their behavior as a result of experience.

Sensory Organs and Perception

• The Eye: Light is processed in the retina through the optic nerve, allowing the body to appreciate color and visual stimuli.
• The Ear: Perceives sounds heard in the inner ear through the auditory nerve.
• The Nose: The olfactory organ containing the yellow pituitary membrane and olfactory nerve for detecting substances.
• The Tongue: Contains taste buds that communicate with the brain.
• The Skin: Facilitates the sense of touch through various nerves.

Anatomy of the Human Nervous System

1. The Neuron

The neuron consists of the nucleus (core), cell body, dendrites, and the myelin sheath. Characteristics of the neuron: The body is star-shaped; the entire nervous system contains dendrites and axons. It leads the nerve impulse from the receptor to the brain and then to the effector organ. Its primary functions include:

• Receiving the stimulus.
• Information integration.

2. The Brain

Key components include: White matter, gray matter, midbrain, thalamus, cerebellum, spinal cord, pons (bump), pituitary gland, hypothalamus, and the corpus callosum.

3. The Skin

The skin structure includes: Hair, sebaceous glands, cells, pain receptors, epidermis, dermis, subcutis, arrector pili muscle, sweat glands, arterioles, and venules.

4. The Ear and Sound

The auditory path includes: Ear canal, eardrum, semicircular canals, auditory nerve, cochlea (snail), temporal bone, Eustachian tube, anvil, stirrup, and the outer ear.

The Autonomic Nervous System

Similarities

• Regulates vital functions such as breathing, digestion, circulation, and excretion.
• Operates independently of the will (involuntary).

The Sympathetic System

• Consists of nerve fibers and ganglionic chains.
• Prepares the body for defense or flight and is activated under stress.

The Parasympathetic System

• Supplies all body organs.
• Slows the heartbeat.
• Contracts the bladder and affects the smooth muscle of the hair.

Behavioral Learning and Conditioning

• Classical Conditioning: The body learns to respond to a stimulus that previously produced no response.
• Instrumental Conditioning: A useful response developed through the manipulation of consequences. This can be positive (increasing satisfaction) or negative (harmful to the subject, reducing the chance of response).

Classification of Sensory Receptors

• Skin: Receptor mechanism (mechanoreceptor).
• Eye: Photoreceptor.
• Nose: Chemoreceptor (including the olfactory bulb, sphenoid sinus, pharyngeal tonsil, tongue, teeth, nasal cartilage, frontal bone, and nasal sinus).
• Ear: Phonoreceptor.