Unformatted text preview: ANATOMY & PHYSIOLOGY I
BIOL 2401 JARED GILMORE M.S., B.S.
BIOLOGY PROFESSOR
SAN JACINTO COLLEGE BRAIN REGIONS The adult brain is composed of 100 billion neurons and 1000 billion neuroglia. It can be divided
into 4 major parts: BRAIN STEM, DIENCEPHALON,CEREBRUM and the CEREBELLUM
PROTECTION: 1. cranium
2. meninges: 3 membranes that surround the brain and the spinal cord.
a. DURA MATER: tough fibrous membrane
b. ARACHNOID: middle membrane ( web-like)
c. PIA MATER: inner delicate membrane
Between the arachnoid and the pia mater is a space called the SUBARACHNOID SPACE. This
contains CSF, cerebrospinal fluid.
3. cerebrospinal fluid: This clear, colorless fluid is produced in the brain by a set of
specialized capillaries ( microscopic blood vessels) called the CHOROID PLEXES.
It contains substances that include glucose, proteins, some ions, some white blood cells.
The CSFs duties include: a. delivery of nutrients to the brain cells and removes some wastes
b. allows brain to float in cranium
c. shock absorber
The brain is not solid, but has spaces within it called VENTRICLES. It is within these ventricles
that the CSF is produced by the c.p. from BLOOD, circulated through the ventricles within the
brain and through the central canal of the spinal cord, as well as passing outward to the
subarachnoid space and circulating the surrounding area of the CNS. EPENDYMAL CELLS line
portions of the CSF circulatory pathway and help with the movement of this material.
The CSF will gradually be reabsorbed back into the blood at the superior portion of the brain
through the ARACHNOID VILLI, finger-like extensions of the arachnoid that pass the CSF back
into the blood through the SUPERIOR SAGITTAL SINUS.
HYDROCEPHALUS: a condition in which the pathway of the CSF is blocked, usually due to a
tumor or an inflammation. In children, this may result in an expansion of the cranium and brain
damage. In adults, brain damage can occur.
The treatment includes placement of a SHUNT from a ventricle into the abdominal cavities. Flow of Cerebrospinal Fluid MENINGES VENTRICLES BRAIN REGIONS MENINGES BRAIN SUPPLY BLOOD SUPPLY OF THE BRAIN: The brain is well supplied with blood
vessels that bring the needed O2 and nutrients to the active cells and
removes waste. At the base of the brain is a circle of vessels called the
CIRCLE OF WILLIS.
The adult brain accounts for only 2% of the total weight of the body, yet is
20% of O2 available in the body. A brief interruption of blood flow causes
unconsciousness. If cells are deprived for 4 minutes,they may be
permanently injured, due to the rupturing of the lysosomes.
Glucose, O2, CO2, water and most lipid soluble substances like
alcohol, caffeine and heroin pass rapidly from blood into brain cells.
Other substances, like proteins and many antibiotics, will not pass at all.
This is due to an unusual anatomical feature of the brain called the
BLOOD BRAIN BARRIER.
BBB is formed by brain capillaries that are less permeable than
other capillaries in the body. The endothelial cells are very tight, and with
the astrocytes in the area, are thought to selectively pass some
substances and inhibit the passage of others.
There are several areas of the brain that lacks the BBB ( 3rd and 4th
ventricles). It is thought that some substances can breach the BBB here such as the HIV (AIDS virus) = AIDS-related dementia. BRAIN SUPPLY BRAIN STEM 1. Brain Stem ( medulla oblongata, pons, midbrain = cerebral peduncles, corpora quadrigemina, nuclei)
a. medulla oblongata: a continuation of the spinal cord, forming the inferior portion of the brain stem. All
ascending tracts (sensory) and descending tracts (motor) connect the s.c. and the brain.
( tract: bundle of neuron fibers within the CNS). The M.O. is an area where DECUSSATION of tracts occurs
= crossing over from right to left and left to right. This allows for CONTRALATERAL CONTROL of body.
M.O. is involved with many INVOLUNTARY FUNCTIONS. There are clusters
of gray matter within the white matter. These gray area concentrations are called NUCLEI and each are
composed mostly of cell bodies.
Examples: a. Cardiovascular center - regulates rate and force of heartbeat and diameter of vessels.
b. Medullary rhythmicity center - adjusts rhythm of breathing. In 1950s = During the polio
epidemic, before the development of the vaccine, many ended up on respirators because the polio virus
targets the respiratory center of the medulla.
c. vomiting center, coughing center. sneezing center, hiccuping center b. pons: ( bridge) This is an area that connects medulla to other portions of the brain.It is composed of
tracts.
c. midbrain = cerebral peduncles + corpora quadragemina +nuclei
1.cerebral peduncles: fiber tracts that takes information to the brain.
2.corpora quadragemina: 4 bodies on the posterior side of brain. The 2 superior bumps are the
SUPERIOR COLICULI, involved with reflex movements of the eyes, head and neck in response to visual
stimuli. The 2 INFERIOR COLICULI are involved with reflex movement of the head in response to auditory
stimuli.
3. nuclei example: SUBSTANTIA NIGRA – involved with maintaining muscle tone and coordinating
movements. The major pathology of this area is PARKINSON ’S DISEASE. Parkinson’s is characterized by
tremor of extremities and head as well as rigidity of muscles. DOPAMINE is a inhibitory neurotransmitter,
which is produced by the substantia nigra. The level decreases with Parkinson ’s disease because the cells of
the nuclei degenerate. It can be treated by administering a precursor of dopamine – L-dopa. Stem cell
transplantation from fetal and adult brains is also being investigated. Administering dopamine is not helpful
because it cannot cross the blood-brain barrier. The L-Dopa that is administered will be able to cross the
BBB and be converted into dopamine by CNS neurons. BRAIN STEM BRAIN STEM CRANIAL NERVES DIENCEPHALON 2. DIENCEPHALON: areas surrounding the 3rd ventricle.
Includes thalamus and hypothalamus, as well as the pineal
gland.
a. thalamus: principal relay area for sensory input going to the
cerebral cortex for interpretation.
Also important in learning, awareness, strong emotions like fear
and rage. It is composed of many nuclei
b. hypothalamus: located inferior to the thalamus. Has many
nuclei and very important to maintaining homeostasis. There
are centers that deal with rage, aggression, thirst, hunger, body
temperature, pleasure, feeling of fullness after a meal etc. This
area is extremely important in regulation of hormones.
c. pineal gland: gland found inside of the brain, the size of a
pea. Secretes the hormone MELATONIN, and therefore is an
endocrine gland. Seems to be involved with the wake – sleep
cycle and perhaps the onset of puberty. DIENCEPHALON CEREBELLUM 3. CEREBELLUM: Occupies the lower posterior
aspect of the brain. Each cerebellular lobe is
connected by the VERMIS, an area in the center that
resembles a worm. The unusual arrangement of white
and gray matter resemble a tree and is referred to as
the ARBOR VITAE, the tree of life. The main function
of this area is control of the muscles of the body that
are involved with balancing and constantly receives
input from receptors in the muscles, tendons, joints
and eyes. Injury to cerebellum results in clumsy,
disorganized movements. CEREBELLUM CEREBELLUM CEREBRUM CEREBRUM
The cerebrum is supported on the brain stem and composes most of the brain.
It consists of 2 HEMISPHERES, which are connected by fiber tracts. The largest fiber tract is the
CORPUS COLLOSUM.
The surface of the cerebrum is not smooth in higher animals, but has convolution, called gyri (gyrus)
and sulci (sulcus).This increases the surface area of the brain and allows space for more neurons.
In humans, there is a thin layer of gray matter on the surface of the cerebrum. This cerebral cortex
contains billions of unmyelinated neurons that are associated with higher thinking and performance
( reading, speaking, etc.). Under this area, there is white matter which is referred to as the
CEREBRAL MEDULLA (not to be confused with the medulla oblongata). There are nerve tracts that
fall into 3 main catagories:
ASSOCIATION FIBERS – connect areas within the same hemispheres.
COMMISSURAL FIBERS – connects one hemisphere to the other.
PROJECTION FIBERS – tracts between the brain and parts of spinal cord.
Within the medulla are collections of gray matter, mostly NUCLEI ( collections of cell bodies)
The cerebrum can also be anatomically divided into 5 different lobes.
Frontal, parietal, temporal, occipital and insula ( internal).
Within the cerebrum, there will be a group of structures that are collectively referred to as the LIMBIC
SYSTEM. This includes areas like the AMYGDALA and the HIPPOCAMPUS which are involved with
basic responses such as memory, emotions, reproduction, eating – all concerned with survival.
Lesions of this area result in uncontrolled eating, increased sexual activity and loose of fear.
One of the major sources of sensory stimulation into the limbic system is olfaction. The sense of
smell is vital to many organisms. Some animals can smell water as well as detect PHEROMONES,
which are molecules released by one member of a species and causes a reaction in another
member of the same species. An example is the pheromones released by a dog when she is in heat .
This will attract male dogs to her from as far away as 2 miles. Pheromones appear to also occur in
humans and it has been suggested that those released by women during the menstrual cycle will
have an effect on the cycle of other women living near them. CEREBRUM CEREBRUM CRANIAL NERVES CRANIAL NERVES NUMBER
CN I NAME
Olfactory nerve CN II Optic nerve CN III Oculomotor CN IV
CN V Trochlear
Trigeminal fissure EXAMPLE OF FUNCTION
olfaction
vision superior orbital fissure eyeball movement a. Ophthalmic branch superior orbital fissure sensory info. from skin around eye
“ “ CN VII Facial CN VIII
CN IX Vestibulocochlear
Glossopharyngeal hearing and balance
taste CN X
CN XI
CN XII Vagus
Accessory
Hypoglossal controls internal organs
swallowing
tongue movement superior orbital “ upper jaw rotundum
c. mandibular branch
CN VI
Abducens optic foramen eyeball movement b. maxillary branch Foramen/Fissure
cribriform plate of ethmoid f. “
“
“ lower jaw and chewing
f. ovale
eyeball movement
superior orbital fissure
secretion of saliva and tears stylomastoid foramen
internal auditory meatus
Jugular foramen
Jugular foramen
Jugular f. and f. magnum
Hypoglossal canal CRANIAL NERVES BRAIN STRUCTURES OLFACTORY NERVE OPTIC NERVE OCULOMOTOR NERVE TROCHLEAR NERVE TRIGEMINAL NERVE ABDUCENS NERVE FACIAL NERVE VESTIBULOCOCHLEAR GLOSSOPHARYNGEAL VAGUS NERVE SPINAL ACCESORY HYPOGLOSSAL NERVE 12 CRANIAL NERVES ...
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