Human Nervous System: Brain, Senses, and Memory

Posted on Mar 1, 2025 in Biology

The Human Nervous System: Structure and Function

1.1 The Nerve Pathway

The four elements of a simple nerve pathway are:

  1. Receptor: Detects a stimulus.
  2. Sensory Neuron: Transmits the signal to the central nervous system.
  3. Integration Center: (Usually the spinal cord or brain) Processes the signal.
  4. Motor Neuron: Transmits a signal to an effector.
  5. Effector: Carries out response.

1.2 The Spinal Cord

The spinal cord contains different types of neurons. If the spinal cord is severed, the body becomes paralyzed below the injured area because signals from the brain can no longer reach the areas below.

1.3 Brain Structure and Function

  • Medulla Oblongata: An extension of the spinal cord, it controls vital functions like breathing, heart rate, blood pressure, and swallowing.
  • Cerebellum: Coordinates body movements and posture. It receives information from position sensors and is involved in motor learning.
  • Thalamus: Relays sensory information from all parts of the body to the limbic system and cerebral cortex.
  • Limbic System: Includes the hypothalamus, amygdala, and hippocampus. These structures produce emotions and basic behaviors such as fear, anger, hunger, thirst, and sexual responses. Parts are also important in memory formation.

1.4 Cerebral Hemispheres

The corpus callosum connects the two cerebral hemispheres.

  • Left Hemisphere:
    • Controls the right side of the body.
    • Receives information from the right visual field (RVF), right ear, and left nostril.
    • Contains centers for language, speech, reading, mathematics, and logic.
  • Right Hemisphere:
    • Controls the left side of the body.
    • Receives information from the left visual field, left ear, and right nostril.
    • Contains centers for spatial perception, music, creativity, and recognizing faces and emotions.

1.5 Memory: Working vs. Long-Term

Working memory is the capacity to store temporary information for about 20-40 seconds. Long-term memory is the ability to store and retrieve information over a longer period.

1.6 Taste Perception on the Tongue

Different regions of the tongue perceive different flavors:

  1. Bitter
  2. Sour
  3. Salty
  4. Sweet

1.7 The Path of Sound

Sound waves, formed by oscillations of air molecules, are driven through the ear canal to the eardrum. Pressure changes on the eardrum cause it to vibrate. These vibrations are transmitted along the ossicles (malleus, incus, and stapes), which act as a lever system. The stapes vibrates against the oval window, transmitting the vibrations into the fluid of the inner ear. The eardrum and ossicles convert air vibrations into fluid vibrations.

1.8 Rods and Cones

Cones are concentrated in the fovea and are responsible for color vision. Rods are dominant in the peripheral portions of the retina. They are more sensitive than cones and allow for vision in dim light, but they do not perceive color.

1.9 The Path of Light in the Eye

Light enters through the cornea and passes through the pupil to reach the lens. The lens focuses the image onto the fovea of the retina, where photoreceptor cells (rods and cones) are located.

1.10 Taste vs. Smell

Taste involves substances dissolved in water or saliva. Smell involves molecules that float in the air.

1.11 Pain Generation

When a cut or abrasion damages cells and capillaries, their contents spill into the extracellular fluid. This includes potassium ions (K+), which stimulate pain receptors.

1.12 Complex Thoughts

Complex thoughts are generated in the prefrontal cortex, part of cerebral cortex.

1.13 Cerebral Cortex: Lobes and Senses

A simplified schematic of the cerebral cortex would show the four lobes (frontal, parietal, temporal, and occipital) and their associated sensory areas (e.g., visual cortex in the occipital lobe, auditory cortex in the temporal lobe).