0-1 Chapter 14 Brain and Cranial Nerves Flashcards
rostral
toward the forehead
caudal
toward the spinal cord
three major portions of the brain
cerebrum, cerebellum, brainstem
cerebrum
cerebrum is 83% of brain volume; cerebral hemispheres, gyri and sulci, longitudinal fissure, corpus callosum
cerebellum
cerebellum contains 50% of the neurons; second largest brain region, located in posterior cranial fossa
brainstem
brainstem the portion of the brain that remains if the cerebrum and cerebellum are removed; diencephalon, midbrain, pons, and medulla oblongata
Cerebrum
longitudinal fissure
deep groove that separates cerebral hemispheres
Cerebrum
gyri
thick folds
Cerebrum
sulci
shallow grooves
Cerebrum
corpus callosum
thick nerve bundle at bottom of longitudinal fissure that connects hemispheres
Cerebellum
about 10% of brain volume
•contains over 50% of brain neurons
•marked by gyri, sulci, and fissures
Cerebellum
occupies
occupies posterior cranial fossa
brainstem
what remains of the brain if the cerebrum and cerebellum are removed
major components
–midbrain
–pons
–medulla oblongata
gray matter
the seat of neuron cell bodies, dendrites, and synapses
–dull white color when fresh, due to little myelin
–forms surface layer, cortex, over cerebrum and cerebellum
–forms nuclei deep within brain
white matter
bundles of axons
–lies deep to cortical gray matter, opposite relationship in the spinal cord
–pearly white color from myelin around nerve fibers
–composed of tracts, bundles of axons, that connect one part of the brain to another, and to the spinal cord
meninges
three connective tissue membranes that envelop the brain
–lies between the nervous tissue and bone
–as in spinal cord, they are the dura mater, arachnoid mater, and the pia mater
–protect the brain and provide structural framework for its arteries and veins
dura mater
in cranial cavity -2 layers
- outer periosteal
* inner meningeal
outer periosteal
equivalent to periosteum of cranial bones
inner meningeal
continues into vertebral canal and forms dural sac around spinal cord
cranial dura mater is pressed closely against
cranial bones
•no epidural space
•not attached to bone except: around foramen magnum, sella turcica, the cristagalli, and sutures of the skull
•layers separated by dural sinuses –collect blood circulating through brain
dura mater
folds inward to extend between parts of the brain
- falx cerebri
- tentorium cerebelli
- falx cerebelli
falx cerebri
separates the two cerebral hemispheres
tentorium cerebelli
separates cerebrum from cerebellum
falx cerebelli
separates the right and left halves of cerebellum
arachnoid mater
–transparent membrane over brain surface
–subarachnoid space separates it from pia mater below
–subdural space separates it from dura mater above in some places
pia mater
–very thin membrane that follows contours of brain, even dipping into sulci
–not usually visible without a microscope
meningitis
inflammation of the meninges
–serious disease of infancy & childhood
–especially between 3 months and 2 years of age
•caused by bacterial and virus invasion of the CNS by way of the nose and throat
•pia mater and arachnoid are most often affected
bacterial meningitis
can cause swelling the brain, enlarging the ventricles, and hemorrhage
ventricles
four internal chambers within the brain
choroid plexus
spongy mass of blood capillaries on the floor of each ventricle
ependyma
neuroglia that lines the ventricles and covers choroid plexus
–produces cerebrospinal fluid
cerebrospinal fluid (CSF)
clear, colorless liquid that fills the ventricles and canals of CNS
–bathes its external surface
CSF continually flows through and around the CNS
–driven by its own pressure, beating of ependymal cilia, and pulsations of the brain produced by each heartbeat
CSF is reabsorbed by
arachnoid villi
arachnoid villi
–cauliflower-shaped extension of the arachnoid meninx
–protrudes through dura mater
–into superior sagittal sinus
–CSF penetrates the walls of the villi and mixes with the blood in the sinus
Functions of CSF
buoyancy
protection
buoyancy
–allows brain to attain considerable size without being impaired by its own weight
–if it rested heavily on floor of cranium, the pressure would kill the nervous tissue
protection
–protects the brain from striking the cranium when the head is jolted
–shaken child syndrome and concussions do occur from severe jolting
chemical stability
–flow of CSF rinses away metabolic wastes from nervous tissue and homeostatically regulates its chemical environment
Blood Supply to the Brain
brain is only 2% of the adult body weight, and receives 15% of the blood
–750 mL/min
brain barrier system
strictly regulates what substances can get from the bloodstream into the tissue fluid of the brain
•two points of entry must be guarded:
–blood capillaries throughout the brain tissue
–capillaries of the choroid plexus
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
endothelial cells can
exclude harmful substances from passing to the brain tissue while allowing necessary ones to pass
blood-CSF barrier
protects the brain at the choroid plexus
–form tight junctions between the ependymal cells
–tight junctions are absent from ependymal cells elsewhere
•important to allow exchange between brain tissue and CSF
blood barrier system is highly permeable to
water, glucose, and lipid-soluble substances such as oxygen, carbon dioxide, alcohol, caffeine, nicotine, and anesthetics
slightly permeable
to sodium, potassium, chloride, and the waste products urea and creatinine
circumventricular organs
(CVOs) –places in the third and fourth ventricles where the barrier is absent
•blood has direct access to the brain
Hindbrain
Medulla Oblongata
Medulla Oblongata
- begins at foramen magnum of the skull
- extends for about 3 cm rostrally and ends at a groove between the medulla and pons
- slightly wider than spinal cord
Medulla Oblongata
nerves & Cranial nerves
- all nerve fibers connecting the brain to the spinal cord pass through the medulla
- four pairs of cranial nerves begin or end in medulla -IX, X, XI, XII
pyramids
pair of external ridges on anterior surface
contain descending fibers called corticospinal tracts
–carry motor signals to skeletal muscles
Medulla Oblongata
centers
- cardiac center
- vasomotor center
- respiratory centers
- reflex centers
cardiac center
–adjusts rate and force of heart
vasomotor center
–adjusts blood vessel diameter
respiratory centers
–control rate and depth of breathing
reflex centers
for coughing, sneezing, gagging, swallowing, vomiting, salivation, sweating, movements of tongue and head
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 & respiratory centers
metencephalon
develops into the pons and cerebellum
pons
anterior bulge in brainstem, rostral to medulla
cerebral peduncles
connect cerebellum to pons and midbrain
Pons
- ascending sensory tracts
- descending motor tracts
- pathways in and out of cerebellum
Pons
cranial nerves
V, VI, VII, and VIII
sensory roles
hearing, equilibrium, taste, facial sensations
motor roles
eye movement, facial expressions, chewing, swallowing, urination, and secretion of saliva and tears
reticular formation
reticular formation in pons contains additional nuclei concerned with:
–sleep, respiration, and posture
midbrain
–short segment of brainstem that connects the hindbrain to the forebrain
–contains cerebral aqueduct
–contains continuations of the medial lemniscus and reticular formation
midbrain
cranial nerves
contains the motor nuclei of two cranial nerves that control eye movements –CN III (oculomotor) and CN IV (trochlear)
tectum
roof-like part of the midbrain posterior to cerebral aqueduct
cerebral peduncles
two stalks that anchor the cerebrum to the brainstem anterior to the cerebral aqueduct
cerebral peduncles
–each consists of three main components
tegmentum, substantia nigra, and cerebral crus
tegmentum
- dominated by the red nucleus
* connections go to and from cerebellum
substantia nigra
- dark gray to black nucleus pigmented with melanin
* motor center that relays inhibitory signals to thalamus & basal nuclei preventing unwanted body movement