Temporal Lobe Primary auditory cortex

On its superior and lateral aspect, the temporal lobe contains the primary auditory cortex. Auditory cortex (areas 41 and 42) is located on the two transverse gyri of Heschl, which cross the superior temporal lobe deep within the lateral sulcus. Much of the remaining superior temporal gyrus is occupied by area 22 (auditory association cortex), which receives a considerable projection from both areas 41 and 42 and projects widely to both parietal and occipital cortices.

Patients with unilateral damage to the primary auditory cortex show little loss of auditory sensitivity but have some difficulty in localizing sounds in the contralateral sound field. Area 22 is a component of Wernicke area in the dominant hemisphere, and lesions here produce a Wernicke aphasia.

Internal capsule

Figure IV-10-12. Internal Capsule: Arterial Supply

Table IV-10-1. Internal Capsule: Arterial Supply

Internal Capsule

Arterial Supply

Tracts

Anterior limb

Anterior cerebral artery

Thalamocortical

Genu

Middle cerebral artery

Corticobulbar

Posterior limb

Middle cerebral artery

Corticospinal, all somatosensory thalamocortical projections

Note; The posterior cerebral artery also supplies the optic radiations.

Note; The posterior cerebral artery also supplies the optic radiations.

Corpus callosum

Genu

Cerebral Arteries Supply

Third ventricle

Figure IV-10-12. Internal Capsule: Arterial Supply

Optic radiations

Anterior limb

Genu

Posterior limb

Corpus callosum

Lateral ventricle

Third ventricle

Transcortical Apraxia:

Resulting from occlusion of the anterior cerebral artery

3. Left arm cannot be moved in response to the verbal command

Left motor cortex

Wernicke area and angular gyrus

Wernicke area and angular gyrus

Right motor cortex Corpus callosum

1. Verbal command to move the left arm interpreted

2. Right motor cortex is disconnected from the left cortex by the lesion in the corpus callosum

Alexia without Agraphia

Resulting from occlusion of the left posterior cerebral artery

Language area in communication with the motor cortex (both sides)

Right motor cortex Corpus callosum

Left visual cortex (lesion) -cannot process

Right visual cortex

Anterior cerebral artery Posterior cerebral artery

Right visual cortex

Visual information from right visual cortex blocked by lesion -cannot get to language area

Result: Alexia

Figure IV-10-13. Symptoms Following Occlusion of the Cerebral Arteries

Table IV-10-2. Symptoms Following Occlusion of the Cerebral Arteries

Anterior Cerebral

Middle Cerebral

Posterior Cerebral

Contralateral spastic paralysis and anesthesia of the lower limbs

Contralateral spastic paralysis and anesthesia of the body excluding the lower limbs (mainly arms and face)

Contralateral homonomous hemianopsia (usually with macular sparing)

Urinary incontinence

LEFT SIDE

RIGHT SIDE

LEFT SIDE: Alexia without agraphia (see above)— cannot read, but can write

Transcortical apraxia— cannot move left arm in response to a command

Aphasias*: Broca, Wernicke, global, or conduction

Parietal lobe:

1. Inattention and neglect of the contralateral side ofthe body

2. Spatial perception defects

Gerstmann Syndrome (parietal lobe-angular gyrus):

1. R-L disorientation

2. Finger agnosia

3. Acaicula

4. Agraphia

"Examples of disconnect syndromes

"Examples of disconnect syndromes

Lateral Ventricle Caudate Nucleus Internal Capsule Cerebellum

Figure IV-10-14. Horizontal Section

Chapter Summary

The external layer of the gray matter covering the surface of the cortex is characterized by numerous convolutions called gyri, separated by grooves called sulci. The cortex is divided into the frontal, parietal, occipital, and temporal lobes by several prominent sulci. Different areas of the cortex are concerned with sensory and motor functions. The frontal lobe contains the primary motor and premotor cortex, frontal eye field, and Broca speech area. The primary somatosensory and association cortex is found in the parietal lobe. The temporal lobe contains the primary auditory cortex and Wernicke area. The primary visual cortex is at the posterior pole of the occipital lobe.

The blood supply of the cortex is supplied by branches of the two internal carotid arteries and two vertebral arteries. On the ventral surface of the brain, the anterior cerebral and middle cerebral branches of the internal carotid arteries connect with the posterior cerebral artery, derived from the basilar artery form the circle of Willis. This circle of vessels is completed by the anterior and posterior communicating arteries. The middle carotid artery mainly supplies the lateral surface of the frontal, parietal, and upper asped of the temporal lobe. Deep branches also supply part of the basal ganglia and internal capsule. The anterior cerebral artery supplies the medial aspect of the frontal and parietal lobes. The entire occipital lobe, lower aspect of temporal lobe, and the midbrain are supplied by the posterior cerebral artery.

The homunculus of the motor and sensory cortex indicates that the upper limb and head are demonstrated on the lateral surface of the cortex. The pelvis and the lower limb are represented on the medial surface of the hemispheres. Therefore, the motor and sensory fundions of the lower limb are supplied by the anterior cerebral artery while the motor and sensory functions of the upper limb and head is supplied by the middle cerebral artery.

The primary language centere (Broca and Wernicke areas) are functionally located only in the dominant hemisphere, usually the left hemisphere. Both of these are supplied by the middle cerebral artery. Lesions of the Broca area result in motor or expressive aphasia (intad comprehension). Lesions of the Wernicke area produce receptive aphasia (lack of comprehension), Condudion aphasia results from a lesion of the arcuate fasciculus that connects the Broca and Wernicke areas.

The internal capsule is a large mass of white matter that conducts almost all tracts to and from the cerebral cortex. It is divided into an anterior limb, genu, and posterior limb. The anterior limb is supplied by the anterior cerebral artery, and the genu and posterior limb are supplied by the middle cerebral artery. The primary motor and sensory systems course through the posterior limb and genu.

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