cross from one cerebral hemisphere to the other through bridges
For the rat brain: toward the nose For the human brain: toward the forehead in the spinal cord and brainstem: higher
For the rat brain: toward the tail For the human brain: toward the spinal cord. in the spinal cord and brainstem: lower
We conceptually divide the brain into three portions...
1. Cerebrum 2. Cerebellum 3. Brainstem
This structure is 83% of the brain's volume and consists of a pair of half globes called cerebral hemispheres.
Thick folds that separate the hemispheres.
A very deep median groove that separates the right and left hemispheres from each other.
The hemispheres are connected by a thick bundle of nerve fibers.
-Occupies the posterior cranial fossa inferior to the cerebrum. -separated from it by the transverse cerebral fissure. - second largest region of the brain (10% of brains volume, but 50 % of its neurons).
-Its major components, from rostral to caudal, are the diencephalon, midbrain, pons, and medulla oblongata -Caudally, it ends at the foramen magnum of the skull, and the CNS continues below this as the spinal cord.
The brain, like the spinal cord, is composed of...
Gray and white matter
the seat of the neurosomas, dendrites, and synapses—forms a surface layer called the cortex over the cerebrum and cerebellum, and deeper masses called nuclei surrounded by white matter.
The outer layer of some organs such as the adrenal gland, cerebrum and others. it usually covers of encloses tissue called the medulla.
-deep to the cortical gray matter in most of the brain. -is composed of tracts, or bundles of axons, which here connect one part of the brain to another and to the spinal cord.
bundles of axons
The nervous system develops from...
the outermost tissue layer of an embryo
Within the first 3 weeks...
1.a neural plate forms along the dorsal midline of the embryo and sinks into the tissues to form a neural groove, with a raised neural fold along each side. 2.The neural folds roll toward each other and fuse, somewhat like a closing zipper, beginning in the cervical region and progressing both caudally and rostrally 3. by day 26 this creates the hollow neural tube.
A dorsal hollow tube in the embryo that develops into the central nervous system
lumen of the neural tube becomes a fluid-filled space that later constitutes...
1. the central canal of the spinal cord 2. the ventricles of the brain.
As the neural tube develops, some ectodermal cells that originally lay along the margin of the groove separate from the rest and form a longitudinal column on each side.
Neural crest cells give rise to the two inner meninges...
1. arachnoid mater 2. Pia mater
By the fourth week, the neural tube exhibits three anterior dilations
1. Forebrain 2. hindbrain 3. midbrain
By the fifth week, it subdivides into five secondary vesicles, the forebrain divides into two of them...
1. the telecephalon 2. the diencephalon
By the fifth week that three structures are?
1. The telencephalon 2. the Diencephalon 3. The mesencephalon (the midbrain) 4. The metencephalon (the hindbrain) 5. the myelencephalon ( the hindbrain)
The brain is enveloped in three connective tissue membranes, the meninges
1. dura mater 2. arachnoid mater 3. pia mater
The main function of the meninges?
They protect the brain and provide a structural framework for its arteries and veins.
In the cranial cavity, the dura mater consists of two layers—
an outer periosteal layer equivalent to the periosteum of the cranial bones, and an inner meningeal layer
- pressed closely to the cranial bone, but is not attached to the bone (except at limited spaces). - no intervening epidural space
spaces that collect blood that has circulated through the brain
Two major, superficial Dural sinuses...
1. Superior sagittal sinus 2. the transverse sinus
Superior sagittal sinus
found just under the cranium along the median line,
the transverse sinus
which runs horizontally from the rear of the head toward each ear.
a transparent membrane over the brain surface, visible in the caudal half of the cerebrum.
The subarachnoid space
Separates the arachnoid space from the pia mater below it.
Thin, delicate membrane that closely follows all the contours of the brain.
A fluid filled chamber of the brain or heart.
How many ventricles does the brain have?
They are the largest and most rostral ventricles of the brain. there are 2 and they form an arc in each cerebral hemisphere.
Through a tiny pore called the interventricular foramen, each lateral ventricle is connected to the...
a narrow median space inferior to the corpus callosum.
a canal called the ___________ ______________ passes down the core of the midbrain and leads to the fourth ventricle.
The cerebral aqueduct
a small triangular chamber between the pons and cerebellum.
On the floor or wall of each ventricle is a spongy mass of blood capillaries
Cerebrospinal fluid (CSF)
a clear, colorless liquid that fills the ventricles and canals of the CNS and bathes its external surface.
Cerebrospinal fluid serves three purposes:
1. Buoyancy 2. Protection 3. Chemical stability
Because the brain and CSF are similar in density, the brain neither sinks nor floats in the CSF. It hangs from delicate specialized fibroblasts of the arachnoid meninx.
CSF also protects the brain from striking the cranium when the head is jolted.
CSF rinses metabolic wastes from the nervous tissue and regulates its chemical environment.
brain barrier system
strictly regulates what can get from the bloodstream into the tissue fluid of the brain
There are two potential points of entry that must be guarded:
1. the blood capillaries 2. capillaries throughout the choroid plexus
blood-brain barrier (BBB)
-A barrier between the bloodstream and nervous tissue of the brain that is impermeable to many blood solutes and thus prevents them from affecting the brain tissue; formed by the tight junctions between capillary endothelial cells, the basement membrane of the endothelium, and the perivascular feet of astrocytes. -which consists of tight junctions between the endothelial cells that form the capillary walls.
The brain barrier system (BBS) is highly permeable to:
water, glucose, and lipid-soluble substances such as oxygen, carbon dioxide, alcohol, caffeine, nicotine, and anesthetics.
It is slightly permeable to:
It is slightly permeable to sodium, potassium, chloride, and the waste products urea and creatinine
The medulla oblongata
The most caudal part of the brainstem, immediately superior to the foramen magnum of the skull, connecting the spinal cord to the rest of the brain.
The myelencephalon becomes just one adult structure:
The medulla oblongata
The medulla begins...
at the foramen magnum of the skull and extends for about 3 cm rostrally, ending at a groove between the medulla and pons.
A nucleus in the medulla oblongata that transmits efferent signals to the blood vessels and regulates vessel diameter.
The metencephalon develops into two structures:
1. the pons 2. the cerebellum
The mesencephalon becomes just one mature brain structure:
Each peduncle has three main components:
tegmentum, substantia nigra, and cerebral crus
The reticular formation
a loose web of gray matter that runs vertically through all levels of the brainstem, appearing at all three levels.
The functions of these 100 small neural networks that are a part of the reticular formation include the following:
1. Somatic motor control 2. cardiovascular control 3. pain modulation 4. sleep and consciousness 5. habituation
the largest part of the hindbrain and second largest part of the brain as a whole.
Three structures arise from the embryonic diencephalon:
the thalamus, hypothalamus, and epithalamus.
The largest part of the diencephalon, located immediately inferior to the corpus callosum and bulging into each lateral ventricle; a point of synaptic relay of nearly all signals passing from lower levels of the CNS to the cerebrum.
forms the floor and part of the walls of the third ventricle. It extends anteriorly to the optic chiasm (ky-AZ-um), where the optic nerves meet, and posteriorly to a pair of humps called the mammillary31 bodies. major control center of the endocrine and autonomic nervous systems.
functions of the hypothalamus
1. hormone secretion 2. Autonomic effects 3. thermoregulation 4. food and water intake 5. sleep and circadian rhythms 6. memory 7. emotional behavior and sexual response
a very small mass of tissue composed mainly of the pineal gland the habenula32 (a relay from the limbic system to the midbrain), and a thin roof over the third ventricle.
The embryonic telencephalon becomes the...
The frontal lobe
It is chiefly concerned with voluntary motor functions, motivation, foresight, planning, memory, mood, emotion, social judgment, and aggression.
The parietal lobe
primary site for receiving and interpreting signals of the general senses described later; for taste (one of the special senses); and for some visual processing.
The occipital lobe
It is the principal visual center of the brain.
The temporal lobe
It is concerned with hearing, smell, learning, memory, and some aspects of vision and emotion.
it apparently plays roles in understanding spoken language, in taste, and in integrating information from visceral receptors.
extend vertically between higher and lower brain and spinal cord centers, and carry information between the cerebrum and the rest of the body.
enable the two sides of the cerebrum to communicate with each other.
cross from one cerebral hemisphere to the other through bridges
connect different regions within the same cerebral hemisphere
Neural integration is carried out in the gray matter of the cerebrum, which is found in three places:
the cerebral cortex, basal nuclei, and limbic system
the cerebral cortex possesses two principal types of neurons:
stellate cells and pyramidal cells.
About 90% of the human cerebral cortex is a six-layered tissue:
The Limbic System
The basal nuclei
masses of cerebral gray matter buried deep in the white matter, lateral to the thalamus
Neuroanatomists disagree on how many brain centers to classify as basal nuclei, but agree on at least three:
the caudate41 nucleus, putamen42 (pyu-TAY-men), and globus pallidus.
the caudate41 nucleus, putamen42 (pyu-TAY-men), and globus pallidus are collectively called the: