The Brain II: Structures
Each hemisphere of the cerebrum is distinct and has four major components: the cerebral cortex (cortical processing), the hippocampal formation (memory), amygdala (emotions) and basal ganglia (motor control processing, behavior, emotions). These structures function in combination to mediate human behavior through their complex neural connections.
Structures located rostral to the tentorium are supratentorial. The major supratentorial structures are the cerebral hemispheres, basal ganglia, thalamus, hypothalamus, and cranial nerves I (olfactory) and II (optic). Cranial nerves I and II arise from the cerebral hemispheres. Cranial nerve I, the bilateral olfactory bulbs and nerves are located at the base of each frontal lobe. Cranial nerve II, the optic pathway, connects the eyes to their respective optic nerves to the optic chiasm and optic tracts.
The diencephalon (subpart) represents a zone of transition between the cerebral hemisphere at the supratentorial (upper) level and the structures in the posterior fossa. The diencephalon consists of the third ventricle and those structures related to it, including the thalamus, hypothalamus, optic pathways and pineal body. At the base of the hypothalamus is an important neuroendocrine structure, the pituitary gland. It is centrally located in the skull nestled in the bony sella turcica (turkish saddle). The corpus callosum on the medial surface of the hemispheres is a prominent fiber tract transferring information from one hemisphere to another. The remaining prominent structures on the medial surface process memory and emotion are part of the limbic lobe.
Structures located within the skull and caudal to the tentorium but above the foramen magnum are in the posterior fossa. The major structures in the posterior fossa are brainstem, pons, cerebellum and medulla. The cerebellum is positioned dorsal to the fourth ventricle, pons and medulla and consists of two hemispheres and a midline vermis (worm).
A rigid membrane arising from the skull and a fold in the dura mater form the falx cerebri and the tentorium cerebelli, a fold in the dura mater (protective covering) that forms a partition between the cerebrum and cerebellum (little brain), and the foramen magnum, the opening of the skull to the spinal canal in the base of the skull divides the cranial cavity into spaces, supports major components of the brain and defines the major neurologic regions: supratentorial, posterior fossa, spinal, and peripheral. The tentorium lies in a nearly horizontal plane and attaches laterally to the petrous ridges on the inside of the skull and posteriorly to the occipital bone. The cerebral hemispheres in the anterior and middle fossae are above the tentorium and the cerebellum and brainstem in the posterior fossa are below the tentorium cerebelli. Cranial nerves III through XII are located in the posterior fossa.
1. The falx cerebri separates the two cerebral hemispheres
2. the tentorium cerebelli separates the cerebellum from the cerebral hemipheres.
Corpus Callosum
The corpus callosum (callused hand) is a massive bundle of myelinated axons whose cell bodies lie in the cerebral hemispheres (superior to the thalamus) that contains axons that interconnect the otherwise independent halves of cortex on the two sides of the brain (inter-hemispheric). Tracts containing axons that interconnect the two sides of the brain are called commissures, and the corpus callosum is the largest of the brain's commissures. To integrate the functions of the two halves of the cerebral cortex, axons of the corpus callosum course through each of its four principal parts: rostrum, genu, body, and splenium. Information between the occipital lobes travels through the splenium of the corpus callosum, whereas information from the other lobes travels through the rostrum, genu, and body.
Thalamus
Rostral and lateral to the midbrain are two bilaterally symmetrical, egg-shaped masses, the thalamus, which are the highest subcortical centers for hearing, touch, pain and temperature, taste and other sensory inputs. The thalamus projects broadly to enormous territories of cerebral cortex (the thalamocortical connections) and locally to receive corticothalamic connections.
Corona Radiata and the Internal Capsule
There are billions of white matter fibers in the cerebral cortex that carry information to and from the cortex. The radiating masses of subcortical white fibers are called the corona radiata. The corona radiata condenses to form the internal capsule, a V-shaped mass of fibers essentially encapsulates the lenticular nucleus. It traverses caudally between the lenticular nucleus that it encapsulates laterally and the caudate nucleus and thalamus medially, continuing into the midbrain as the crus cerebri. Ascending fibers within the capsule arise primarily from the thalamus; desceding fibers originate from all areas of the cortex.
The internal capsule is divided into five components. The anterior limb, the genu, the posterior limb, the retrolenticular fibers and the sublenticular fibers.
Subcortical Nuclei
More lateral to the thalamus and internal capsule are the three massive subcortical telencephalic nuclei; the caudate nucleus, the putamen and the globus pallidus. These centers are responsible for the involuntary control of stereotyped motor behavior, stepping, and gross postural adjustments. Damage to them or the cerebellum affects the timing and coordination of muscle contractions and relaxation but has little effect on strength, which is largely controlled by the corticospinal tract. Just lateral to these nuclei is a piece of cortex, the insula (island), deep in the white matter; this lobe has an important role in hearing and speech.
Hippocampus
The hippocampus (seahorse) is an excellent example of a structure whose three-dimensional organization can only be appreciated by careful study. A horizontal dissection cuts through part of the dorsal half of the C-Shaped hippocampus. You can see this upper portion in a transverse section which reveals some parts of the hippocampus (alveus, dentate gyrus, fimbria) and demonstrates that the hippocampus is a continuous structure with regional variation. Thus to really see the hippocampus as it is in situ, imagine two C-shaped structures joined at the top (by the hippocampal commissure) then flared out laterally so that the foot of the C protrudes deep into the tip of the temporal lobes. From the top, it might look something like a wishbone whose central part was the commissure and whose distal parts were the tips of each wishbone. The hippocampus is part of the limbic system and it has a vital role in memory and learning, especially in the formation and storage of short-term memory.
Hypothalamus
Rostral and ventral to the thalamus is the hypothalamus, a small but critically important group of nuclei whose neurons regulate water/salt balance, blood pressure and temperature, feeding and satiety, reproduction and other visceral interactions.
Hypothalamus - homeostasis, weight problem, stress, glucocorticoids
cushing syndrome - excessive release of cortisol excessive breakdown of food which causes you to feel more hungry if you over eat get obese
hypothyroidism - low level thyroid hormones - low metabolic rates - all food ends up as fat, obesity depression also associated w/
appetite control & the hypothalamus
homeostasis - leptin - important indicator of fat storage, direct feedback from adipose
Midbrain
Superior to the pons but slightly caudal to it is the midbrain, which is a relay and integrative center for vision and hearing, respectively and contains many discrete nuclei of it's own.
The Pons
Much of the cerebellar outflow moves through the pons (bridge) to reach subcortical (beneath the cortex) centers before proceeding to the motor cortex. In its turn, the cortex can reach the pons via cortico-pontine projections and the cerebellum via cortico-ponto-cerebellar pathways. The pons also has many different nuclear subdivisions, some related to motor behavior for the head others related to cranial sensation. Like the medulla, it contains various ascending and descending fiber tracts.
As a rule throughout the brain, motor functions are commonly localized in ventral structures, while sensory structures are the more dorsal.
Question: What symptoms might you expect from damage to the dorsal medulla?
The Cerebellum
Slightly dorsal and caudal to the medulla is the cerebellum (small brain), which is concerned with the subconscious regulation of muscle stretch during stereotyped motor responses like walking, standing, swimming and in anti-gravitational motor adjustments. Ultimately, the cerebellar outflow reaches the motor cortex where it plays a role in the integration of conscious and subconscious motor programming.
Question: What clinical effects might a lesion of the motor cortex have on the cerebellum, and motor behavior?
A Subconscious regulation of muscle tone, which is among the normal roles of the cerebellum, would be impaired.
The person would be hypotonic, have too little muscle tone.
The Medulla
Just rostral to the spinal cord in the midsagittal plane is a small bulge on it's ventral surface, the medulla which contains many discrete nuclei (collections of cell bodies with particular functions) and the axons of ascending pathways coming from the spinal cord to the brain as well as descending axons of cortical origin. The latter are called collectively corticofugal and those terminating in the medulla would be defined as corticomedullary or since the brain stem has a bulb like shape as corticobulbar. Thus medullary nuclei can be influenced by cortical neurons. Another property that defines the medulla is its glistening white appearance that represents the myelinated sheathes of axons, a fatty capsule of lipid rings that surround the axon and allow it to send neuronal signals across long distance with great speed and faithfulness to the transmission of information.
The cerebrum is continuous with the brain stem which is in turn attached to the spinal cord.
1. The falx cerebri separates the two cerebral hemispheres
2. the tentorium cerebelli separates the cerebellum from the cerebral hemipheres.
Basal Ganglia
The basal ganglia are a complex of subcortical telencephalic nuclei that integrate cerebellar and cortical influences for motor planning and execution. The basal ganglia has both direct and indirect pathways with antagonistic functions on the motor thalamus and cortex.
Neurological signs can be positive or negative, positive signs in neuromuscular disease include tremor, athetosis, chorea, ballism and dystonia; negative signs are paralysis or paresis. Parkinson's disease reveals principles of striatal function since the reduction of disinhibition in the direct striatal pathway allows inhibition to predominate, resulting in poverty of movement, rigidity and mask-like faces. In Huntington's disease leads to dementia, paralysis and death.
Structures located rostral to the tentorium are supratentorial. The major supratentorial structures are the cerebral hemispheres, basal ganglia, thalamus, hypothalamus, and cranial nerves I (olfactory) and II (optic). Cranial nerves I and II arise from the cerebral hemispheres. Cranial nerve I, the bilateral olfactory bulbs and nerves are located at the base of each frontal lobe. Cranial nerve II, the optic pathway, connects the eyes to their respective optic nerves to the optic chiasm and optic tracts.
The diencephalon (subpart) represents a zone of transition between the cerebral hemisphere at the supratentorial (upper) level and the structures in the posterior fossa. The diencephalon consists of the third ventricle and those structures related to it, including the thalamus, hypothalamus, optic pathways and pineal body. At the base of the hypothalamus is an important neuroendocrine structure, the pituitary gland. It is centrally located in the skull nestled in the bony sella turcica (turkish saddle). The corpus callosum on the medial surface of the hemispheres is a prominent fiber tract transferring information from one hemisphere to another. The remaining prominent structures on the medial surface process memory and emotion are part of the limbic lobe.
Structures located within the skull and caudal to the tentorium but above the foramen magnum are in the posterior fossa. The major structures in the posterior fossa are brainstem, pons, cerebellum and medulla. The cerebellum is positioned dorsal to the fourth ventricle, pons and medulla and consists of two hemispheres and a midline vermis (worm).
A rigid membrane arising from the skull and a fold in the dura mater form the falx cerebri and the tentorium cerebelli, a fold in the dura mater (protective covering) that forms a partition between the cerebrum and cerebellum (little brain), and the foramen magnum, the opening of the skull to the spinal canal in the base of the skull divides the cranial cavity into spaces, supports major components of the brain and defines the major neurologic regions: supratentorial, posterior fossa, spinal, and peripheral. The tentorium lies in a nearly horizontal plane and attaches laterally to the petrous ridges on the inside of the skull and posteriorly to the occipital bone. The cerebral hemispheres in the anterior and middle fossae are above the tentorium and the cerebellum and brainstem in the posterior fossa are below the tentorium cerebelli. Cranial nerves III through XII are located in the posterior fossa.
1. The falx cerebri separates the two cerebral hemispheres
2. the tentorium cerebelli separates the cerebellum from the cerebral hemipheres.
Corpus Callosum
The corpus callosum (callused hand) is a massive bundle of myelinated axons whose cell bodies lie in the cerebral hemispheres (superior to the thalamus) that contains axons that interconnect the otherwise independent halves of cortex on the two sides of the brain (inter-hemispheric). Tracts containing axons that interconnect the two sides of the brain are called commissures, and the corpus callosum is the largest of the brain's commissures. To integrate the functions of the two halves of the cerebral cortex, axons of the corpus callosum course through each of its four principal parts: rostrum, genu, body, and splenium. Information between the occipital lobes travels through the splenium of the corpus callosum, whereas information from the other lobes travels through the rostrum, genu, and body.
Thalamus
Rostral and lateral to the midbrain are two bilaterally symmetrical, egg-shaped masses, the thalamus, which are the highest subcortical centers for hearing, touch, pain and temperature, taste and other sensory inputs. The thalamus projects broadly to enormous territories of cerebral cortex (the thalamocortical connections) and locally to receive corticothalamic connections.
Corona Radiata and the Internal Capsule
There are billions of white matter fibers in the cerebral cortex that carry information to and from the cortex. The radiating masses of subcortical white fibers are called the corona radiata. The corona radiata condenses to form the internal capsule, a V-shaped mass of fibers essentially encapsulates the lenticular nucleus. It traverses caudally between the lenticular nucleus that it encapsulates laterally and the caudate nucleus and thalamus medially, continuing into the midbrain as the crus cerebri. Ascending fibers within the capsule arise primarily from the thalamus; desceding fibers originate from all areas of the cortex.
The internal capsule is divided into five components. The anterior limb, the genu, the posterior limb, the retrolenticular fibers and the sublenticular fibers.
Subcortical Nuclei
More lateral to the thalamus and internal capsule are the three massive subcortical telencephalic nuclei; the caudate nucleus, the putamen and the globus pallidus. These centers are responsible for the involuntary control of stereotyped motor behavior, stepping, and gross postural adjustments. Damage to them or the cerebellum affects the timing and coordination of muscle contractions and relaxation but has little effect on strength, which is largely controlled by the corticospinal tract. Just lateral to these nuclei is a piece of cortex, the insula (island), deep in the white matter; this lobe has an important role in hearing and speech.
Hippocampus
The hippocampus (seahorse) is an excellent example of a structure whose three-dimensional organization can only be appreciated by careful study. A horizontal dissection cuts through part of the dorsal half of the C-Shaped hippocampus. You can see this upper portion in a transverse section which reveals some parts of the hippocampus (alveus, dentate gyrus, fimbria) and demonstrates that the hippocampus is a continuous structure with regional variation. Thus to really see the hippocampus as it is in situ, imagine two C-shaped structures joined at the top (by the hippocampal commissure) then flared out laterally so that the foot of the C protrudes deep into the tip of the temporal lobes. From the top, it might look something like a wishbone whose central part was the commissure and whose distal parts were the tips of each wishbone. The hippocampus is part of the limbic system and it has a vital role in memory and learning, especially in the formation and storage of short-term memory.
Hypothalamus
Rostral and ventral to the thalamus is the hypothalamus, a small but critically important group of nuclei whose neurons regulate water/salt balance, blood pressure and temperature, feeding and satiety, reproduction and other visceral interactions.
Hypothalamus - homeostasis, weight problem, stress, glucocorticoids
cushing syndrome - excessive release of cortisol excessive breakdown of food which causes you to feel more hungry if you over eat get obese
hypothyroidism - low level thyroid hormones - low metabolic rates - all food ends up as fat, obesity depression also associated w/
appetite control & the hypothalamus
homeostasis - leptin - important indicator of fat storage, direct feedback from adipose
- activates satiety center which inhibits eating behavior
Midbrain
Superior to the pons but slightly caudal to it is the midbrain, which is a relay and integrative center for vision and hearing, respectively and contains many discrete nuclei of it's own.
The Pons
Much of the cerebellar outflow moves through the pons (bridge) to reach subcortical (beneath the cortex) centers before proceeding to the motor cortex. In its turn, the cortex can reach the pons via cortico-pontine projections and the cerebellum via cortico-ponto-cerebellar pathways. The pons also has many different nuclear subdivisions, some related to motor behavior for the head others related to cranial sensation. Like the medulla, it contains various ascending and descending fiber tracts.
As a rule throughout the brain, motor functions are commonly localized in ventral structures, while sensory structures are the more dorsal.
Question: What symptoms might you expect from damage to the dorsal medulla?
The Cerebellum
Slightly dorsal and caudal to the medulla is the cerebellum (small brain), which is concerned with the subconscious regulation of muscle stretch during stereotyped motor responses like walking, standing, swimming and in anti-gravitational motor adjustments. Ultimately, the cerebellar outflow reaches the motor cortex where it plays a role in the integration of conscious and subconscious motor programming.
Question: What clinical effects might a lesion of the motor cortex have on the cerebellum, and motor behavior?
A Subconscious regulation of muscle tone, which is among the normal roles of the cerebellum, would be impaired.
The person would be hypotonic, have too little muscle tone.
The Medulla
Just rostral to the spinal cord in the midsagittal plane is a small bulge on it's ventral surface, the medulla which contains many discrete nuclei (collections of cell bodies with particular functions) and the axons of ascending pathways coming from the spinal cord to the brain as well as descending axons of cortical origin. The latter are called collectively corticofugal and those terminating in the medulla would be defined as corticomedullary or since the brain stem has a bulb like shape as corticobulbar. Thus medullary nuclei can be influenced by cortical neurons. Another property that defines the medulla is its glistening white appearance that represents the myelinated sheathes of axons, a fatty capsule of lipid rings that surround the axon and allow it to send neuronal signals across long distance with great speed and faithfulness to the transmission of information.
The cerebrum is continuous with the brain stem which is in turn attached to the spinal cord.
1. The falx cerebri separates the two cerebral hemispheres
2. the tentorium cerebelli separates the cerebellum from the cerebral hemipheres.
Basal Ganglia
The basal ganglia are a complex of subcortical telencephalic nuclei that integrate cerebellar and cortical influences for motor planning and execution. The basal ganglia has both direct and indirect pathways with antagonistic functions on the motor thalamus and cortex.
Neurological signs can be positive or negative, positive signs in neuromuscular disease include tremor, athetosis, chorea, ballism and dystonia; negative signs are paralysis or paresis. Parkinson's disease reveals principles of striatal function since the reduction of disinhibition in the direct striatal pathway allows inhibition to predominate, resulting in poverty of movement, rigidity and mask-like faces. In Huntington's disease leads to dementia, paralysis and death.
A rigid membrane arising from the skull and the dura mater form the falx cerebri and tentorium cerebelli which divide the cranial cavity into spaces and supports the major components of the brain.
Just above the hypothalamus lies the thalamus, whose oval outline can be imagined along the midline.
A better view appears in a dorsal dissection, where the caudal free surface of the thalamus actually protrudes somewhat into the midbrain.
The thalamus is an egg-shaped mass whose major axis runs rostro-caudal with the large end posterior.
Which modalities are represented in the thalamus?
Two commissures are readily identified.
The largest, the corpus callosum, lies above the thalamus and extends from the vicinity of the midbrain through the diencephalon and deep into the telencephalon. The axons within it join the dorsal parts of two hemispheres in a kind mirror-like symmetry; where one hemisphere projects, the other does too.
About halfway along its length but beneath it and just ahead of the thalamus is the much smaller group of commissural axons forming the anterior commissure. These axons join the ventral parts of the telencephalon.
Which type of sensory input might be expected to dominate the anterior commissure?
Above the corpus callosum is a long, flattened piece of cerebral cortex, the cingulate gyrus which in the sheep is enormous. Cingulate cortex neurons are part of the limbic system, a group of cortical and subcortical areas concerned with emotion, motivation, feeding, sexuality and autonomic responses. The cingulate cortex has strong inputs to the hypothalamus, (via corticohypothalamic connections) and it, in turn is greatly influenced by the frontal lobes (corticocortical inputs) which are responsible for long-term planning and for evaluating the consequences of sensory and motor actions.
Beneath the corpus callosum and extending onto the ventral surface of the brain is the orbital cortex whose influence is primarily autonomic and limbic.
What diencephalic structure exerts neural control of the pituitary. Which part of the ventricular system is associated with the diencephalon? Just above the pituitary are the optic (II) nerves, whose fusion creates the chiasm.
What is the optic nerve? Where do its axons originate and to where do they project?
What sort of defect would result from cutting one nerve after the chiasm?
Locate the corpus callosum and at its caudal end follow to visual cortex, what is this cavity?
Dark crumbly material on the ventricular floor, identify this substance.
Just above the hypothalamus lies the thalamus, whose oval outline can be imagined along the midline.
A better view appears in a dorsal dissection, where the caudal free surface of the thalamus actually protrudes somewhat into the midbrain.
The thalamus is an egg-shaped mass whose major axis runs rostro-caudal with the large end posterior.
Which modalities are represented in the thalamus?
Two commissures are readily identified.
The largest, the corpus callosum, lies above the thalamus and extends from the vicinity of the midbrain through the diencephalon and deep into the telencephalon. The axons within it join the dorsal parts of two hemispheres in a kind mirror-like symmetry; where one hemisphere projects, the other does too.
About halfway along its length but beneath it and just ahead of the thalamus is the much smaller group of commissural axons forming the anterior commissure. These axons join the ventral parts of the telencephalon.
Which type of sensory input might be expected to dominate the anterior commissure?
Above the corpus callosum is a long, flattened piece of cerebral cortex, the cingulate gyrus which in the sheep is enormous. Cingulate cortex neurons are part of the limbic system, a group of cortical and subcortical areas concerned with emotion, motivation, feeding, sexuality and autonomic responses. The cingulate cortex has strong inputs to the hypothalamus, (via corticohypothalamic connections) and it, in turn is greatly influenced by the frontal lobes (corticocortical inputs) which are responsible for long-term planning and for evaluating the consequences of sensory and motor actions.
Beneath the corpus callosum and extending onto the ventral surface of the brain is the orbital cortex whose influence is primarily autonomic and limbic.
What diencephalic structure exerts neural control of the pituitary. Which part of the ventricular system is associated with the diencephalon? Just above the pituitary are the optic (II) nerves, whose fusion creates the chiasm.
What is the optic nerve? Where do its axons originate and to where do they project?
What sort of defect would result from cutting one nerve after the chiasm?
Locate the corpus callosum and at its caudal end follow to visual cortex, what is this cavity?
Dark crumbly material on the ventricular floor, identify this substance.