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ANATOMY OF THE BRAIN

BIG PICTURE

The brain contains millions of neurons arranged in a vast array of synaptic connections that provide seemingly unfathomable circuitry. Through that circuitry the brain directs movement, processes sensory input, and processes language and communication, learning, and memory.

DIVISIONS OF THE BRAIN

The brain is divided into the cerebrum, diencephalon, brainstem, and cerebellum (Figure 16-1A and B).

Figure 16-1:

A. Lateral view of the brain. B. Medial view of the sagittal section of the brain.

CEREBRUM

The organ of thought, and serves as the control site of the nervous system, enabling us to possess the qualities associated with consciousness such as perception, communication, understanding, and memory. The cerebral hemispheres consist of elevations (gyri) and valleys (sulci), with a longitudinal cerebral fissure separating the two cerebral hemispheres. Each cerebral hemisphere is divided into lobes, which correspond roughly to the overlying bones of the skull.

  • Frontal lobe. Located in the anterior cranial fossa; contains the primary motor cortex, which regulates motor output (voluntary movement). Additional functions include hypothesizing future consequences from current actions, conscience, short-term memory, planning, and motivation.

  • Central sulcus. Separates frontal and parietal lobes in the coronal plane.

  • Parietal lobe. Positioned between the frontal and occipital lobes above the lateral sulcus; contains the primary sensory cortex, which directs the integrating of sensory input. Additionally plays an important role in visuospatial processing.

  • Occipital lobe. Located in the posterior cranial fossa above the tentorium cerebelli; contains the primary visual cortex, which is the visual processing center of the brain.

  • Lateral sulcus. Separates frontal and parietal lobes from the temporal lobe.

  • Temporal lobe. Located in the middle cranial fossa below the lateral sulcus; functions include auditory processing, language recognition, interpretation of visual stimuli, and the formation of new and long-term memories.

DIENCEPHALON

Consists of the thalamus, hypothalamus, epithalamus, and subthalamus, and is situated between the cerebrum and the brainstem.

PITUITARY GLAND

Called the “master gland” because it orchestrates the activities of many other endocrine glands. It is small and bean-shaped.

  • Suspended from the hypothalamus by the infundibulum and housed in the sella turcica (a depression in the sphenoid bone).

BRAINSTEM

Consists of the midbrain, pons, and medulla oblongata.

  • Midbrain (mesencephalon). Contains the nuclei for the oculomotor (CN III) and trochlear (CN IV) nerves. The cerebral aqueduct is a portion of the ventricular system and courses through the center of the midbrain to connect the third and fourth ventricles.

  • Pons. Positioned against the clivus and the dorsum sellae; contains the nuclei for the trigeminal (CN V), abducens (CN VI), facial (CN VII), and vestibulocochlear (CN VIII) nerves.

  • Medulla ...

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