Surface Anatomy of Forebrain - The Parietal Lobe

Name the 3 major areas of the lateral surface of the parietal lobe.

1. Postcentral gyrus

2. Superior parietal lobule

3. Inferior parietal lobule

Describe the anatomical position of the postcentral gyrus in relation to adjacent structures.

• The postcentral gyrus sits just behind the central sulcus

• It is separated from the precentral gyrus (motor cortex) by the central sulcus

• It is the most anterior part of the parietal lobe on the lateral surface

Which functional area is housed within the postcentral gyrus?

• Primary somatosensory cortex

• This cortex processes touch, proprioception, pain and temperature from the contralateral body

Describe the anatomical position of the superior parietal lobule.

• The superior parietal lobule sits behind the postcentral gyrus

• It lies above the inferior parietal lobule

• The two parietal lobules are separated by the intraparietal sulcus

Name the two gyri into which the inferior parietal lobule is divided.

The inferior parietal lobule is divided into:

• Supramarginal gyrus — anterior

• Angular gyrus — posterior

Describe the language-related function of the inferior parietal lobule and which hemisphere is predominantly responsible.

• The inferior parietal lobule (plus nearby temporal regions) in the dominant left hemisphere — is crucial for language comprehension

• This region contains Wernicke’s area

• Damage here causes Wernicke’s aphasia → fluent but meaningless speech with poor comprehension

What is Wernicke's area, where is it located, and what is the clinical consequence of its damage?

• Wernicke’s area is the brain’s language comprehension centre

• It sits in the dominant (usually left) hemisphere, mainly in the inferior parietal lobule and extending into the superior temporal gyrus

• Damage causes Wernicke’s aphasia → fluent but meaningless speech with severely impaired comprehension

What structures are found on the medial surface of the parietal lobe?

The medial surface of the parietal lobe contains two key structures:

1. Posterior paracentral lobule

   • Medial extension of the postcentral gyrus (sensory leg/foot area)

2. Precuneus

   • Large medial parietal region behind the paracentral lobule

List the three main general functions of the parietal lobe.

The parietal lobe has three major functions:

1. Somatosensory processing & localisation

   • Primary somatosensory cortex in the postcentral gyrus

2. Language comprehension

   • Inferior parietal lobule in the dominant (usually left) hemisphere

3. Spatial orientation & attention

   • Superior parietal regions handling where things are and where to direct attention

Which parietal region is responsible for processing and localising somatosensory information, and how is it organised?

• Region: Primary somatosensory cortex in the postcentral gyrus

• Role: Processes and localises touch, pain, temperature, and proprioception

• Organisation: Arranged as a sensory homunculus, mapping the contralateral body with precise spatial detail

Correlate each of the three general parietal functions to its specific anatomical location within the lobe.

1. Somatosensory processing
   → Postcentral gyrus (primary somatosensory cortex)

2. Language comprehension
   → Inferior parietal lobule (Wernicke’s area, dominant/left hemisphere)

3. Spatial orientation & attention
   → Superior parietal lobule and intraparietal sulcus

What deficits might you expect from a large left parietal lobe lesion and why?

A big left parietal lesion can cause:

1. Contralateral sensory loss
   → Damage to the postcentral gyrus (primary somatosensory cortex)

2. Wernicke’s (receptive) aphasia
   → Damage to the inferior parietal lobule / Wernicke’s area in the dominant (left) hemisphere

3. Possible spatial/attentional problems
   → Parietal regions also support attention and spatial processing

A patient suffers a stroke affecting the postcentral gyrus. Which function is most directly impaired?

• Somatosensory processing

• The postcentral gyrus houses the primary somatosensory cortex; damage causes contralateral hemisensory loss