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rostral
toward the forehead (anterior/superior)
caudal
toward the spinal cord (posterior/inferior)
cerebrum, cerebellum, brainstem
what are the three major portions of the brain?
cerebrum
is 83% of the brain volume; has cerebral hemispheres, gyri and sulci, longitudinal fissure, and corpus callosum; differentiates brain from other organisms because we have abstract thought and language
cerebellum
contains 50% of the neurons in the brain; second largest brain region, located in the posterior cranial fossa; doesn’t have functions that are absolutely necessary usually so you would be able to survive a stroke if it occurred here; almost exclusively gray matter
brainstem
includes the diencephalon, midbrain, pons, and medulla oblongata; has most similarities between organisms because it is involved in regulation of blood pressure, heart rate, thirst, etc
longitudinal fissure
deep groove that separates cerebral hemispheres
gyri
thick folds
sulci
shallow grooves
corpus callosum
thick nerve bundle at the bottom of the longitudinal fissure that connects hemispheres; made exclusively of white matter; females tend to have larger ones
we want wrinkly brains because that indicates a higher performing brain; in fetal alcohol syndrome the cerebrum is much smoother
explain wrinkles in brain
transverse cerebral fissure
separates the cerebellum from the cerebrum
gray matter
seat of neurosomas, dendrites, and synapses
dull color due to little myelin; forms surface layer (cortex) over cerebrum and cerebellum; forms nuclei deep within the brain
characteristics of gray matter in the brain
white matter
bundles of axons
lies deep to cortical gray matter, which is opposite in the spinal cord; pearly white color from myelin around nerve fibers; composed of tracts, or bundles of axons, that connect one part of the brain to another, and to the spinal cord
characteristics of white matter in the brain
meninges
three connective tissue membranes that envelop the brain
lies between the nervous tissue and bone; they are the dura mater, arachnoid mater, pia mater; protect the brain and provide the structural framework for its arteries and veins
characteristics of the meninges in the brain
inflammation of the meninges; serious disease of infancy and childhood (especially between 3 months and 2 years old); caused by a bacterial or viral invasion of the CNS by way of the nose and throat
what is meningitis?
outer periosteal which is equivalent to the periosteum of cranial bones; inner meningeal which continues into the vertebral canal and forms dural sheath around the spinal cord; these layers are separated by dural sinuses which collect blood circulating through the brain
what are the two layers of the cranial dura mater and what are they separated by?
there is no epidural space; it is not directly attached to bone except around foramen magnum, sella turcica, crista galli, and sutures of the skull
dura mater is pressed closely against cranial bones which means what?
dural sinuses
cavity or space in dura mater of brain; filled with blood being sent back to the heart; the arachnoid sticks up into this
transparent membrane over the brain surface; subarachnoid space separates it from the pia mater below; subdural space separates it from the dura mater above in some places; where most of the CSF circulates
characteristics of the arachnoid mater in the brain
very thin membrane that follows contours of the brain, even dipping into sulci; has lots of capillaries
characteristics of the pia mater
ventricles
four internal chambers within the brain
2 with one in each cerebral hemisphere
how many lateral ventricles are there?
interventricular foramen
tiny pore that connects to the third ventricle from the lateral ventricle
third ventricle
narrow medial space beneath the corpus callosum
cerebral aqueduct
what runs through the midbrain and connects the third and fourth ventricle?
fourth ventricle
small triangular chamber between pons and cerebellum; it connects to the central canal that runs through the spinal cord
choroid plexus
spongy mass of blood capillaries on the floor of each ventricle; has has ependymal cells
ependymal
type of neuroglia that lines ventricles and covers the choroid plexus; produces CSF
cerebrospinal fluid
clear, colorless liquid that fills the ventricles and canals of the CNS; bathes the external surface
500 mL/day
brain produces and absorbs how much CSF?
production begins with filtration of blood plasma through capillaries of the brain; ependymal cells modify the filtrate, so CSF has more sodium and chloride than plasma, but less potassium, calcium, glucose, and very little protein
how is CSF produced?
hydration influences the production of CSF (if dehydrate, less is produced); state of mind influences production (sleeping has increased ependymal activity so more CSF production); during sleep, CSF carries away waste and debris
association between hydration and sleeping with CSF?
buoyancy
allows brain to attain considerable size without being impaired by its own weight; if it rested heavily on the floor of the cranium instead of CSF, the pressure would kill the nervous tissue - function of CSF
protection
protects the brain from striking the cranium when the head is jolted; shaken child syndrome and concussions do occur from severe jolting - function of CSF
chemical stability
flow of CSF rinses away metabolic wastes from nervous tissue and homeostatically regulates its chemical environment (astrocytes involved in this)
moves from areas of high to low pressure; CSF is pressurized where there is the highest concentration of ependymal cells which is the choroid plexus; CSF flows from the lateral ventricle, to the third, to the fourth, to either the surface of nervous tissue or the central canal of the spinal cord
how does CSF move?
15% of the blood and the brain is 2% of an adult’s body weight
how much blood does the brain receive and what percentage of adult body weight is the brain?
blood brain barrier
filters the fluid that goes into the meninges; keeps vast majority of the big things out
for ATP and therefore, oxygen and glucose; this means they need a constant supply of blood
what do neurons have a high demand for?
a 10-second interruption may cause loss of consciousness; a 1 to 2 minute interruption can cause significant impairment of neural function; going 4 minutes without blood causes irreversible brain damage
what happens with interruption of blood flow to neurons?
brain barrier system
regulates what substances can get from the bloodstream into tissue fluid of the brain because although blood is crucial, it can also contain harmful agents; this is promoted by astrocytes; capillaries have tight junctions so liquid doesn’t leak and fluid travels through the cytoplasm of the cells to generate CSF
blood brain barrier
protects blood capillaries throughout brain tissue
consists of tight junctions between endothelial cells that form the capillary walls; astrocytes reach out and contact capillaries with their perivascular feet; anything leaving the blood must pass through the cells, not between them; endothelial cells can exclude harmful substances from passing to the brain tissue while allowing necessary ones to pass
characteristics of the blood brain barrier
blood-CSF barrier
protects brain at the choroid plexus
forms tight junctions between the ependymal cells; tight junctions are absent from ependymal cells elsewhere; they are important to allow exchange between brain tissue and CSF
characteristics of the blood-CSF barrier
highly permeable to water, glucose, and lipid-soluble substances such as oxygen, CO2, alcohol, caffeine, nicotine, and anesthetics; slightly permeable to sodium, potassium, chloride, and the waste products urea and creatinine; tiny molecules and amphipathic molecules can get through; this is why drugs need to be polar to dissolve in the bloodstream and nonpolar to get through the barrier
permeability of the blood brain barrier since it does not have perfect regulation
brain barrier system
what can be an obstacle for delivering medications such as antibiotics and cancer drugs
trauma and inflammation
what can damage the brain barrier system and allow pathogens to enter brain tissue?
circumventricular organs
places in the third and fourth ventricles where the barrier is absent; blood has direct access to the brain; enables the brain to monitor and respond to fluctuations in blood glucose, pH, osmolarity, and other variables; these afford a route for invasion by the human immunodeficiency virus (HIV)
through the circumventricular organs
what is the primary method of entrance for pathogens into the CNS?
medulla oblongata
begins at the foramen magnum of the skull; extends about 3 cm rostrally and ends at a groove just below the pons; slightly wider than the spinal cord
pyramids
pair of ridges on anterior surface of the medulla oblongata resembling side-by-side baseball bats; they are separated by the anterior median fissure; carry motor signals to skeletal muscles
4
how many pairs of cranial nerves begin or end in the medulla?
olives
prominent bulges lateral to each pyramid in the medulla oblongata
medulla
all ascending or descending fibers connecting the brain and spinal cord pass through what?
neurosomas of second order sensory neurons
what is something the medulla houses?
inferior olivary nucleus
relay center for signals to cerebellum
reticular formation
loose network of nuclei extending throughout the medulla, pons, and midbrain; contains cardiac, vasomotor, and respiratory centers; helps to integrate the entire brain stem; has basal motor sensors which control contraction/relaxation of blood vessels and are respiratory and heart rate rhythm centers
pons
anterior bulge in brainstem, rostral to medulla
cerebellar peduncles
thick stalks on posterior pons that connect it (and the midbrain) to the cerebellum; has ascending sensory tracts, descending motor tracts, and pathways in and out of the cerebellum
4
how many cranial nerves associated with the pons?
hearing, equilibrium, taste, facial sensations
sensory roles of cranial nerves in the pons
eye movement, facial expressions, chewing, swallowing, urination, and secretion of saliva and tears
motor roles of cranial nerves in the pons
sleep, respiration, posture
reticular formation in the pons contains additional nuclei concerned with what?
short segment of brainstem that connects hindbrain to forebrain; contains the cerebral aqueduct; contains continuations of reticular formation; contains motor nuclei of two cranial nerves that control eye movements (oculomotor, and trochlear)
some characteristics of the midbrain
cerebral aqueduct
surrounded by central gray matter involved in controlling pain
tectum
roof-like part of the midbrain posterior to the cerebral aqueduct
upper pair (superior colliculi) function in visual attention, tracking moving objects, and some reflexes; lower pair (inferior colliculi) receives signals from the inner ear and relays them to the other parts of the brain, especially the thalamus
explain the four bulges (corpora quadrigemina) of the tectum in the midbrain
cerebral peduncles
two anterior midbrain stalks that anchor the cerebrum to the brainstem
tegmentum, substantia nigra, and one other
what are the three parts of the peduncle in the midbrain?
tegmentum
peduncle of the midbrain; dominated by red nucleus; has a pink color due to the high density of blood vessels; connections go to and from cerebellum for motor control
substantia nigra
peduncle of the midbrain; black nucleus pigmented with melanin; motor center that relays inhibitory signals to the thalamus and basal nuclei preventing unwanted body movement; degeneration of neurons leads to tremors of Parkinson’s disease
loose web of gray matter that runs vertically through all levels of the brainstem; occupies space between white fiber tracts and brainstem nuclei; has connections with many areas of cerebrum (more than 100 small neural networks without distinct boundaries); radiates out from the thalamus
characteristics of the reticular formation
adjust muscle tension to maintain tone, balance, and posture especially during body movements; relay signals from eyes and ears to cerebellum, integrates visual, auditory, balance, and motion stimuli into motor coordination; gaze centers; central pattern generators
what does the somatic motor control do? (functions in the reticular formation)
gaze centers
allow eyes to track and fixate on objects
central pattern generators
neural pools that produce rhythmic signals to the muscles of breathing and swallowing
cardiac and vasomotor centers of the medulla oblongata (heart rate and constriction of blood vessels)
cardiovascular control function in the reticular formation
some pain signals ascend through the reticular formation; some descending analgesic pathways begin in the reticular formation and they end in the spinal cord where they black the transmission of pain signals
pain modulation function in the reticular formation
reticular formation plays a central role in consciousness, alertness, and sleep; injury here can result in irreversible coma (pons)
sleep and consciousness function in the reticular formation
reticular activating system modulates activity in cerebral cortex so that it ignores repetitive, inconsequential stimuli
habituation function in reticular formation
cerebellum
largest part of the hindbrain and second largest part of the brain as a whole
consists of right and left cerebellar hemispheres connected by vermis; has superficial cortex of gray matter with folds, branching white matter, and deep nuclei; contains more than half of all brain neurons (small granule cells and large purkinje cells with axons that synapse on deep nuclei)
characteristics of the cerebellum
cerebellar peduncles
three pairs of stalks that connect brainstem and cerebellum (their fibers carry signals to and from the cerebellum)
inferior peduncles
connected to medulla oblongata; most spinal input enters the cerebellum through here
middle peduncles
connected to pons; most input from the rest of the brain enters through middle peduncle
superior peduncles
connected to midbrain; carries cerebellar output
primarily motor coordination and locomotor activity; along with sensory, linguistic, emotional, and other nonmotor functions
functions of cerebellum
diencephalon and telencephalon
two parts of the forebrain
diencephalon
encloses the third ventricle; most rostral part of the brainstem
telencephalon
develops chiefly into the cerebrum
thalamus, hypothalamus, epithalamus
three parts of the diencephalon
thalamus
ovoid mass on each side of the brain perched at the superior end of the brainstem beneath the cerebral hemispheres
thalamus
constitutes about 4/5s of the diencephalon; two thalami are joined medially by a narrow intermediate mass; composed of at least 23 nuclei within five major functional groups
thalamus
what is the “gateway to the cerebral cortex”; nearly all input to the cerebrum passes by way of synapses in the thalamic nuclei, filter information on its way to the cerebral cortex
cerebral cortex
gray matter on the surface of the cerebrum
thalamus
plays key role in motor control by relaying signals from cerebellum to cerebrum and providing feedback loops between the cerebral cortex and the basal nuclei
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