Nervous System Function, Neuron Structure & Sense Organs

Impulse Transmission in the Nervous System

Impulse / nervous system: The stimulus is received and a depolarization takes place in the neuron membrane. The impulse travels along the axon; many axons are insulated by a substance called myelin. When the impulse arrives at the end of the axon it has to cross a gap called the synaptic cleft. Synaptic vesicles fuse with the membrane and release neurotransmitters, which pass to the dendrite of the next neuron. The message then goes to the nervous system and finally to the effectors.

Protection of the Central Nervous System

Protection of the CNS: The brain and the spinal cord are surrounded by three membranes called the meninges and by a liquid called the cerebrospinal fluid (líquido encefalorraquídeo). This fluid cushions (amortigua) and reduces the impact on the CNS.

Neuron: Structure and Types

Neuron: the unit of the nervous system. It has two main parts:

• Cuerpo celular o soma: contiene el núcleo y la mayor parte del citoplasma.
• Prolongaciones: dos tipos:

• Dendritas: cortas y muy ramificadas; interconectan neuronas.
• Axón: prolongación larga y, normalmente, sin ramificar excepto al final; protegido por mielina.

Axón y vaina - fibras nerviosas - fascículos - nervios.

Tipos de neuronas / Types of neurons

• Sensorial / Sensory: transmit electrical signals from receptors to the CNS.
• Motora / Motor: transmit electrical signals from the CNS to effectors.
• Relevo / Relay (interneurons): connect sensory neurons with motor neurons; act as a bridge.

Sense Organs: Smell, Touch, Taste, Hearing, Sight

Organ of Smell

Organ of smell: the olfactory epithelium (not the pituitary gland) senses substances that enter the nose. When receptors are stimulated, they send a nerve impulse to the brain through the olfactory nerve. (Original text mentioned pituitary gland, which is not responsible for smell.)

Organ of Touch

Organ of touch: in the skin there are many receptor cells that send impulses to the nervous system.

Organ of Taste

Organ of taste: taste buds on the tongue sense substances that enter the mouth. They generate nerve impulses that travel to the brain through the taste nerve (cranial nerves involved in taste).

Organ of Hearing and Balance

Organ of hearing and balance: the ear senses sound vibrations that enter through the auditory canal. Those vibrations are transmitted across the eardrum and the middle ear structures to the cochlea, where receptor cells send nerve impulses to the brain through the auditory nerve.

Organ of Sight

Organ of sight: the eyes sense light that enters through the pupil. The lens focuses the light on the retina where an image is formed. This stimulates receptor cells in the retina, which produce nerve impulses that are sent to the brain through the optic nerve.