Neuroscience: Parietal and Occipital Lobes

Parietal Lobe

• The postcentral gyrus is the primary somatosensory cortex, receiving sensory impulses from the body and interpreting them as sensations.
• It maps the body spatially, with areas containing more receptors having a larger representation.
• It determines the location, type, and intensity of a sensation.
• The somatosensory association area, located behind the primary somatosensory area, interprets sensory data, enabling us to identify objects by touch.
• The primary gustatory cortex, located at the base of the insula, receives taste impulses from the tongue.
• The angular gyrus connects Wernicke's area with the primary visual cortex and translates visual information into auditory patterns and vice versa.

Occipital Lobe

• The primary visual cortex receives impulses from the retina, creating a visual image. Damage to this area can cause blindness.
• The visual association areas interpret visual stimuli, processing movement, color, shape, and texture, and storing visual memories.

Association Areas

• Surround the primary sensory cortices, integrating and interpreting sensory data.
• The posterior association area, also called the gnostic area, receives input from all sensory association areas, coordinates sensory data, and generates a single "thought."
• It sends the "thought" to the prefrontal area where decisions are made.
• The posterior association area is also crucial for body awareness.

Medulla of the Cerebral Hemispheres

• Composed primarily of white matter containing axons classified as:
  • Commissural fibers: Link both hemispheres, enabling information sharing, including the corpus callosum.
  • Association fibers: Connect areas within the same hemisphere.
  • Projection fibers: Convey sensory and motor signals between the cortex and lower brain centers.
• The basal nuclei, embedded in the medulla, are divided into the caudate nucleus, putamen, and globus pallidus.
• The basal nuclei are involved in:
  • Receiving sensory input from the cortex.
  • Influencing skeletal muscle movement by sending impulses to the premotor cortex.
    • They help initiate and stop voluntary movements.
    • They prevent spontaneous muscle contractions.
    • They control movement intensity for smooth and orderly movement.
  • Contributing to behavior and cognition.
• The substantia nigra in the midbrain and the subthalamic nucleus in the diencephalon are functionally linked to the basal nuclei.
  • The substantia nigra releases dopamine, primarily an excitatory neurotransmitter with an inhibitory effect on the basal ganglia, to control movement.
  • The death of neurons in the substantia nigra leads to Parkinson's disease.

Parkinson's Disease

• A progressive paralytic disorder characterized by rhythmic movements, slowed voluntary movements, shaking, shuffling gait, swallowing and speech difficulties, rigidity of limbs, and loss of facial expression.
• Results from the loss of dopamine-producing cells in the substantia nigra, causing excessive cortical stimulation via the thalamus.
• This loss of dopamine creates an imbalance between dopamine and acetylcholine.
• Suspected causes include encephalitis, environmental metallic poisons, synthetic heroin use, and head trauma.

Hypothalamus

• A major regulator of homeostasis, containing receptors that monitor blood solutes, sugar levels, temperature, and hormone levels.
• Integrates involuntary motor activities of the autonomic nervous system.
• Directly or indirectly controls the release of many hormones.
• Regulates body temperature.
• Controls food intake through the feeding and satiety centers.
• Contains a thirst center.
• Associated with feelings of rage, aggression, and sexual responses.
• The pacemaker driving biological clock rhythms, containing receptors for melatonin.
• Contains a sleep center.

Pituitary Gland

• The master endocrine gland attached to the hypothalamus by the infundibulum.
• The anterior pituitary produces and stores six hormones, receiving releasing factors from the hypothalamus through a vascular connection.
• The posterior pituitary receives two hormones synthesized in the hypothalamus, transported via neurosecretory cells. When needed, nerve impulses from the hypothalamus release these hormones from the posterior pituitary into the blood.

Midbrain (Mesencephalon)

• Located around the cerebral aqueduct between the third and fourth ventricles.
• Contains nuclei for cranial nerve emergence.
• Houses the cerebral peduncles, which are the main motor and sensory connection between the forebrain and the hindbrain.
• On the dorsal surface, the corpora quadrigemina contain the superior colliculi, visual reflex centers, and the inferior colliculi, which:
  • Relay auditory impulses to the primary auditory cortex.
  • Control reflexes that direct the head for clear hearing.

Hindbrain (Rhombencephalon)

• The pons (bridge) forms part of the anterior wall of the fourth ventricle, allowing the passage of sensory, motor, and cerebellar pathways.
• Links the cerebellum to the midbrain and medulla oblongata, contains nuclei for cranial nerve emergence, and houses the Pontine Respiratory Center involved in respiration.
• The cerebellum, located on the dorsal surface of the brainstem, coordinates skeletal muscle contractions. It receives information from the motor cortex, vestibular apparatus, proprioceptors, and eyes, assessing sensory and motor data to initiate impulses to the motor cortex or spinal cord to regulate muscle contractions.
• The cerebellum contributes to:
  • Coordinating muscle contraction force, direction, and strength for posture and smooth movements.
  • Matching intended movements with actual movements.
  • Storing learned movement patterns for programmed commands.
• Dysfunctions of the cerebellum can lead to:
  • Dysmetria (ataxia): Difficulty controlling muscle contraction and joint movement, resulting in abnormal movement strength, rate, direction, or range.
  • Intention tremor: Shaking that worsens as the individual approaches a goal due to overcorrection for poor directional control.

Primitive Emotional Brain

• Associated with strong emotions (rage, pleasure, fear, sex drives, and sorrow).
• Manages emotional behaviors vital to survival instincts (food and water seeking, reproduction).
• Interacts with higher brain centers, allowing emotions to override logic and vice versa.

Memory

• The process of retaining and retrieving knowledge.
• The hippocampus contributes to short-term and very short-term memory, sending reinforced information to the cortex for long-term storage and consolidation.
• Long-term memory is not localized, it is stored wherever processing occurs.
• The hippocampus potentially determines if information is stored or discarded.
• The hippocampus produces norepinephrine and serotonin, essential for memory formation, and insufficient levels can lead to impaired learning and depression.
• Hippocampal damage can result in anterograde amnesia, interfering with the formation of some new memories.
• Shock immediately after an event prevents long-term memory formation, delayed shock impairs it, and shock after 24 hours does not affect memory.
• The hippocampus is also involved in recalling facts and events (working memory).

Amygdala

• Located at the tip of the caudate nucleus.
• Facilitates long-term memory by attaching strong emotions to sensory input, making those memories more easily stored and recalled.
• Plays a significant role in emotional responses, particularly fear, helping to recognize and express fearful stimuli/situations.

Nucleus Basalis

• Found in the forebrain, connected to the hippocampus and cortex.
• Monitors sensory data and increases activity when the sensation is pleasurable, relevant, useful, vivid, etc.

Test your knowledge on the functions and structures of the parietal and occipital lobes in the brain. This quiz covers topics such as the primary somatosensory cortex, the visual cortex, and their associated functions. Explore how these brain regions contribute to sensory perception and interpretation.