Human Senses and Nervous System Functions

The Tongue and the Sense of Taste

33. The Tongue and Taste.
The tongue contains taste cells that are sensitive to various chemicals. These cells allow us to distinguish between different flavors.

• Flavors: Salty, sweet, sour, bitter, and umami (savory).
• Taste buds: These are the specific locations where taste cells are situated.

The Ear: Hearing and Balance

34. The Ear.
The ear performs two primary biological functions:

Hearing Mechanism

Hearing results from the pinna capturing external vibrations. These vibrations travel through the ear canal and cause the eardrum to vibrate. The vibrations then reach the ossicular chain and enter the cochlea (snail shell), where auditory cells send nerve impulses to the brain to interpret sounds.

Balance and Motion

Balance allows us to notice changes in the motion of the body. The cochlea contains fluid-filled ducts and specialized cells dedicated to maintaining balance.

Vision and the Visual Process

35. Vision.
Vision allows us to perceive information from the environment, including light, color, and images.

The Process of Sight

1. The eye perceives light and focuses it on the retina. The cornea, the outer lens, directs light to the pupil. The iris regulates light by opening or closing. The lens, an internal lens, focuses light into the eye to form a sharp, inverted image.
2. The retina converts light stimuli into impulses. Photoreceptor cells in the retina are excited by light and send nerve impulses to the brain via the optic nerve, which interprets the information as visual light.

The Human Nervous System

36. Nervous System.
The nervous system receives information from receptors and sends corresponding answers to the effectors.

Central Nervous System (CNS)

The CNS is responsible for processing and coordinating information:

• Brain: The brain interprets information, controls voluntary movements, and manages advanced cognitive features.
• Brain stem: This connects the brain to the spinal cord and controls involuntary movements.

Peripheral Nervous System (PNS)

The PNS consists of ganglia and nerves that connect the Central Nervous System with the rest of the body:

• Somatic Nervous System: This transmits nerve impulses for voluntary movements.
• Autonomic Nervous System: This includes the sympathetic and parasympathetic systems, which function to control involuntary movements and internal regulations.

Neurons, Nerve Impulses, and Synapses

37. Neurons.
Neurons are the fundamental units of the nervous system. Their primary parts include:

• Cell body: The core of the neuron.
• Dendrites: Branching structures extending from the cell body.
• Axon: A long extension from the cell body.
• Nerve fiber: Formed by axons; a nerve is an assembly of these fibers.

Nerve Impulses and Synapses

Nerve impulses travel from the neuron cell body to the end of the axon. When the impulse reaches the end of the axon, it releases neurotransmitters that carry the nerve impulse across the synapse to another neuron.