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Definition
During the first 3 weeks of gestation, the human embryo's neural tube flexes as it grows, forming the three primary brain vesicles colloquially called
the forebrain, midbrain, and
hindbrain. The 1st and 3rd
vesicles further divide forming
5 secondary brain vesicles in a
process called encephalization. |
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Definition
| is the continuation of the spinal cord and consists of the medulla oblongata, pons and midbrain |
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Definition
| is the second largest part of the brain. |
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Definition
| gives rise to the thalamus & hypothalamus. |
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Definition
is the newest (evolutionarily) and largest part of the brain as a whole.
It is in the cerebral cortex that perception, thought, imagination, judgment, and decision making occur. |
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Term
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Definition
The cranial meninges are continuous with the spinal meninges and mirror their structure
and function – they also bear the
same names:
a tough outer dura mater, a spidery arachnoid mater and a thin, delicate pia mater |
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Term
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Definition
has two layers – an external periosteal layer and an internal meningeal layer; the spinal dura mater has only one.
In the brain, extensions of the dura mater form hard, non-compliant membranes that divide the intracranial vault in various ways:.
The 3 important dural extensions are the falx cerebri, the falx cerebelli, and the tentorium cerebelli. |
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Definition
| a strong sickle-shaped fold of dura mater which descends vertically in the longitudinal fissure and separates the two cerebral hemispheres |
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Definition
is a
small triangular
process that separates
the two cerebellar
hemispheres. |
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Definition
Clinically, the tentorium cerebelli is important because brain tumors are often characterized as supratentorial (above the tentorium) and infratentorial (below the tentorium). Most childhood tumors are infratentorial, while most adult tumors are supratentorial.
Since the tentorium is a hard structure, if there is any brain swelling the brain can get partly pushed down and herniate through the tentorium, which becomes a life-threatening event. |
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Term
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Definition
a clear fluid that circulates through the internal cavities in the brain (called brain ventricles) and spinal cord (the central canal) and also flows over and around the brain and cord in the subarachnoid space. In essence, the brain "floats" in it.
CSF absorbs shock and protects the brain and the cord.
It also helps transport nutrients and wastes between blood and nervous tissues. |
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Term
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Definition
| lateral ventricles interventricular foramina third ventricle cerebral aqueduct fourth ventricle median aperture (of Magendie ) and the lateral apertures (of Luschka ) SAS |
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Definition
CSF is gradually reabsorbed back into the blood through the arachnoid villi (finger-like projections that extend into the dural sinuses).
In this graphic, the
arachnoid villi are
seen projecting
into the superior
sagittal sinus. A cluster of
arachnoid villi is called
an arachnoid granulation. |
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Term
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Definition
Failure of CSF to form and drain normally results in a buildup of pressure called hydrocephalus.
Hydrocephalus occurs with congenital abnormalities, head injury, meningitis,
and episodes of bleeding into the brain. |
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Term
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Definition
The brain stem is superior to, but continuous with, the spinal cord. Developmentally, it does not represent a single structure, but rather a group
of anatomical components
considered collectively.
It is made up of
the midbrain, pons, and medulla oblongata. |
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Term
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Definition
The medulla begins below the pons and it contains all the ascending and desending tracts extending between the spinal cord and cerebrum. The medulla contains nuclei which are regulators for various vital body functionshas two external bulges called the pyramids formed by the largest motor tracts in the body.
Axons from the left pyramid cross over to the right and axons on the right cross over to
the left (decussation of
pyramids) – so that the left
hemisphere of the brain
controls the right
side muscles, while the right
hemisphere controls the left side. |
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Term
| Vital functional centers regulated by the medulla: |
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Definition
Vital functional centers regulated by the medulla include:
The cardiovascular center – controls the rate and force of heartbeat, and the diameter of blood vessels
The respiratory rhythmicity center – controls the rate and rhythm of breathing
The vomiting, coughing, and sneezing centers
The nuclei associated with 5 of the 12 cranial nerves originates in the medulla (CN VIII – XII).
A portion of the 4th ventricle extends to the medulla. |
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Definition
The pons lies directly above the medulla and anterior to the cerebellum (2.5 cm). It acts as a bridge connecting the spinal cord with the brain and parts of the brain with
each other. Together with the medulla, areas in the pons help control breathing (inhalation and exhalation).
The pontine respiratory group is normally inactive during quiet breathing. This group of neurons acts like an “off-switch” to terminate medullary inspiratory activity.
Early termination of inspiration leads to an increase in the rate of breathing (which is why this center was formerly know as the “pneumotaxic center” - taxic meaning fast).
The pons contains the nuclei associated with 4 pairs of cranial nerves: V - VIII
Cranial nerve V
emerges directly
from the pons.
VI, VII, and VIII
emerge from the
space between
the pons and
the medulla. |
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Term
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Definition
The cerebral aqueduct passes through the midbrain connecting the 3rd ventricle above with the 4th ventricles below (both locations of CSF formation and circulation.)On the anterior part of the midbrain are found the “little feet” of the cerebral peduncles.
The peduncles contain axons of the corticospinal, corticobulbar, and corticopontine tracts which conduct nerve impulses from motor areas in the cerebral cortex to the spinal
cord, medulla,
and pons,
respectively. |
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Term
| superior and inferior colliculi |
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Definition
On the posterior part of the midbrain are four rounded elevations known as the superior and inferior colliculi which serve as reflex centers for certain visual and auditory reflexes,
and also the
startle reflex.
It is the origin of
cranial nerves III
and IV. |
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Term
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Definition
The midbrain contains several other nuclei, including the darkly pigmented substantia nigra. Neurons that release dopamine, extending from the substantia nigra, help control subconscious muscle activities; loss of these neurons is associated with Parkinson
disease.
The red nucleus
helps control
voluntary movements
of the limbs. |
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Term
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Definition
In addition to the well-defined nuclei already described, much of the brain stem consists of a netlike arrangement of neuronal cell bodies and small bundles of myelinated axons known as the reticular formation.
The ascending portion of this network is called the reticular activating
system (RAS), and
consists of sensory
axons that project to
the cerebral cortex. |
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Term
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Definition
The RAS functions to maintain consciousness, a state of wakefulness in which an individual is fully alert, aware, and oriented. Inactivation of the RAS produces sleep, a state of partial consciousness from which an individual can be aroused.
It also prevents sensory
overload by filtering
out insignificant
information. |
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Term
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Definition
The cerebellum’s central constricted area is the vermis and the lateral “wings” or lobes are the cerebellar hemispheres .
The cerebellum compares intended movements with what is happening with skeletal muscles, and regulates posture, equilibrium, and balance. |
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Definition
The thalamus functions as a relay station for all sensory impulses to the cerebral cortex (except smell, which belong to the hypothalamus). Pain, temp, touch, and pressure are all relayed to the thalamus en route to the higher centers of the cerebral cortex.
While not precisely localized here (that occurs in the cerebral cortex), all of these peripheral sensations are processed in the thalamus in conjunction with their attendant memories and the emotions they evoke. |
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Definition
The epithalamus is superior and posterior to the thalamus.
It consists of the pineal gland (secretes melatonin) and habenular nuclei (emotional responses to odors).
More melatonin is
secreted in darkness
than light, and it is
thought to promote
sleepiness and help
regulate our
biological clocks. |
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Term
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Definition
The hypothalamus controls many homeostatic functions:
It controls the Autonomic Nervous System (ANS).
It coordinates between NS and endocrine systems.
It controls body temperature (measured by blood flowing through it).
It regulates hunger/thirst
and feelings of satiety.
It assists with the internal
circadian clock by
regulating biological activity. |
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Term
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Definition
is the “seat of our intelligence”– it’s because of neurons in the cortex that we are able to read, write, speak, remember, and plan our life.
The cerebrum consists of an outer cerebral cortex, an internal region of cerebral white matter, and gray
matter nuclei deep within
the white matter. |
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