Neuroscience/Objectives/Lecture 25
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Introduction to the forebrain
These are developmental, not functional or anatomical classifications.
List the major subdivisions of the diencephalon.
The diencephalon is medial, subcortical, and sits beneath the fornix and corpus callosum. It consists of four structures:
- Thalamus (dorsal thalamus)
- Hypothalamus
- Subthalamus (ventral thalamus)
- Epithalamus (primarily the pineal gland)
List the major subcomponents of the telencephalon.
- Cerebral cortex
- Basal ganglia
- Hippocampus
- Amygdala
Describe the locations of the lobes of the brain with respect to the horns of the lateral ventricles.
- Anterior horn: frontal lobe
- Posterior horn: occipital lobe
- Inferior horn: temporal lobe
Draw a diagram representing a midsagittal view of the diencephalon and the telencephalon and label the major subdivisions and associated anatomical landmarks.
(H:2-29, 2-30)
Compare the functions of the thalamus and hypothalamus.
The thalamus is a functional gateway to the cortex. For example, sensory afferents from the retina first synapse in the lateral geniculate nucleus of the thalamus and then onward to the primary visual cortex (V1). Thalamic functions resemble the functions in associated cortical areas.
By contrast, the hypothalamus has autonomic functions, has receptors for temperature, regulates the anterior pituitary gland, and synthesizes the hormones oxytocin and vasopressin. Thus the hypothalamus subserves chiefly homeostatic functions whereas the thalamus is primarily a sensory relay.
Describe the general functions of the diencephalon and telencephalon.
Diencephalon:
- Cognition
- Autonomic function
- Endocrine function
- Circadian rhythyms
Telencephalon:
- Perception
- Motor function
- Cognition
- Emotion
Describe the functional difference between "primary" and "association" cortical regions. Locate the primary regions for vision, somatosensation, motor function, audition, and olfaction.
Primary cortex is the initial region of cortex that subserves a particular function. For example, primary visual cortex is the first cortical area to begin processing sensory information from the retina.
Association cortex is an integrative center in the cortex where multiple sensory and motor modalities coalesce.
| Cortex | Brodmann area | Location |
|---|---|---|
| Primary visual | BA 17 | Posterior occipital lobe |
| Somatosensory | BA 3,1,2 | Postcentral gyrus |
| Primary motor | BA 4 | Precentral gyrus |
| Primary auditory | BA 41 | Medial temporal lobe |
| Primary olfactory | BA 34 | Medal temporal lobe |
Define the following terms.
- Brodmann's area
- A contiguous group of neurons that share similar cytoarchitectonics.
- Corpus callosum
- Carries most fibers between homologous contralateral cortical areas. Divided into rostrum, genu, body, and splenium.
- Internal capsule
- Major pathway of fibers to and from cerebral cortex and thalamus, basal ganglia, brainstem, and spinal cord. It passes through the neostriatum, separating it into caudate and putamen. Has three parts: the anterior limb (separates caudate and putamen), genu (near anterior thalamic nucleus), and posterior limb (separates the lentiform nuclei—the putamen and globus pallidus—from the thalamus).
- Anterior commissure
- Carries fibers between the two amygdalae and homologous regions of the contralateral temporal cortex.
- Septum pellucidum
- Thin membrane of gray and white matter separating the lateral ventricles. Rostrally near anterior commissure, it thickens and houses the septal nuclei, which receive afferents from hippocampus and hypothalamus.
- Fornix
- C-shaped bundle of axons that carries information from the hippocampus to the mamillary body, septal nuclei, and nucleus accumbens.
