Ch. 14 Anatomy

what is rostal?

toward the forehead (anterior and superior)

what is caudal?

toward the spinal cord (posterior and inferior)

what are the three major portions of the brain?

* cerebrum
* cerebellum
* brainstem

what is the cerebrum?

83% of brain volume; cerebral hemispheres, gyro and sulk, longitudinal fissure, corpus callosum

what is the cerebellum?

contains 50% of the neurons; second largest brain region, located in posterior cranial fossa

what is the brainstem?

the portion of the brain that remains if the cerebrum and cerebellum are removed; diencephalon, midbrains, pons, and medulla oblongata

what is the longitudinal fissure?

deep groove that separates cerebral hemispheres

what are gyri?

thick folds; “mountains”

what are sulci?

shallow grooves; “valleys”

what is the corpus callosum?

thick nerve bundle at bottom of longitudinal fissure that connects hemispheres

what is the cerebellum?

* occupies posterior cranial fossa
* about 10% of brain volume
* contains over 50% of the brain neurons

what is the brainstem?

* what remains of the brain if the cerebrum and cerebellum are removed
* major components
* diencephalon
* midbrain
* pons
* medulla oblongata

what is gray matter?

* the seat of neurosomas, dendrites, and synapses
* dull color due to little myelin\]
* forms surface layer over cerebrum and cerebellum

what is white matter?

* bundles of axons
* lies deep to cortical gray matter
* pearly white color form 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

what are meninges?

* three connective tissue membranes that envelop the brain
* lie between the nervous tissue and bone
* protect the brain and provide structural framework for its arteries and veins

what is meningitis?

* inflammation of the meninges
* serious disease of infancy and childhood
* caused by bacterial or viral invasion of the CNS by way pf the nose and throat

what is the cranial dura mater?

* has two layers
* dura mater is pressed closely against cranial bones
* fold inward to extend between parts of brain
* No epidural space

what are the two layers of the cranial dura mater?

* outer periosteal- equivalent to the periosteum of cranial bones
* inner meningeal- continues into vertebral canal and forms dural sheath around spinal cord

what is the arachnoid space?

* transparent membrane over the brain space surface
* subarachnoid space separates it from Pia mater below
* subdural space separates it from dura mater above in some places

what is the Pia mater?

* very thin membrane that follows contours of brain, even dipping into sulci
* mot usually visible without a microscope

how many ventricles are in the brain?

* two lateral ventricles: on tin each cerebral hemisphere
* third ventricle: narrow medial space beneath corpus callosum
* fourth ventricle: small triangular chamber between pons and cerebellum

what is the choroid plexus?

spongy mass of blood capillaries on the floor of each ventricle

what are ependymal cells?

types of neuroglia that lines ventricles and covers choroid plexus

what is cerebrospinal fluid?

* clear, colorless liquid that fills the ventricles and canals of CNS
* brain produces and absorbs 500 ml/day
* production begins with filtration of blood plasma through capillaries of the brain

what are the functions of CSF?

* buoyancy
* protection
* chemical stability

what is 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

what is protection from CSF?

* protects the brain from striking cranium when the head is jolted
* shaken child syndrome and concussions do occur from severe jolting

what is chemical stability of CSF?

flow of CSF lines away metabolic rates from nervous tissue and homeostatically regulates its chemical environment

what is the brain barrier system?

regulates what substances can get from bloodstream into tissue fluid of the brain

what two points of entry must be guarded?

* blood capillaries throughout the brain tissue
* capillaries of the choroid plexus

what is the blood-brain barrier?

* protects blood capillaries through out brain tissue
* consists of tight junctions between endothelial cells that form the capillary walls
* anything leaving the blood must pass through the cells, and not between them
* endothelial cells can exclude harmful substances from passing to the brain tissue while allowing necessary ones to pass

what is the blood-CSF barrier?

* protects brain at the choroid plexus
* forms tight junction between the ependymal cells
* tight junctions are absent from ependymal cells elsewhere
* brain barrier system is highly permeable to water, glucose, and lipid-soluble substances such as oxygen, CO2, alcohol, caffeine, nicotine, and anesthetics

where is the medulla oblongata located?

* beings at the foramen magnum of the skull
* extends about 3 cm rostrally and ens at a groove below the pons
* slightly wider than the spinal cord
* houses neuromas of second-order sensory neurons

what are the pyramids?

* pair of ridges on the anterior surface resembling side-by-side baseball bats
* four pairs of cranial nerves begin or end in the medulla
* carry motor signals to skeletal muscles

what are olives?

* prominent bulges lateral to each pyramid
* inferior olivary nucleus- relay center for signals to cerebellum

what is the reticular formation?

loose network of nuclei extending throughout the medulla, pons, and midbrain

what are the pons?

* the anterior bulge in the brainstem, rostral to the medulla
* cranial nerve V, VI, VII, and VIII
* reticular formation in pons contains additional nuclei concerned with sleep, respiration, posture

what are the cerebellum peduncles?

thick stalks on posterior pons that connect it (and the midbrain) to the cerebellum

what is the midbrain?

* short segment of brainstem that connects hindbrain to forebrain
* contains cerebral aqueduct
* contains continuous of reticular formation
* contains motor nuclei of two cranial nerves that control eye movements

what is the tectum?

* roof-like part of the midbrain posterior to cerebral aqueduct
* exhibits four bulges, the corpora quadridgemina

what are the four pairs of bulges?

* upper pair, superior colliculi, function in visual attention, tracking moving objects, and some reflexes
* lower pair, the inferior colliculi, receives signals from the inner ear and relays them to other parts of the brain

what is the cerebral peduncles?

* two anterior midbrain stalks that anchor the cerebrum to the brainstem
* each peduncle has three parts
* tegmentum, substantial nigra, and one other

what is the tegmentum?

* dominated by red nucleus
* pink color due to high density of blood vessels
* connections go to and from cerebellum for motor control

what is the substantia nigra?

* black nucleus pigmented with melanin
* motor center that relays inhibitory signals to thalamus and basal nuclei preventing unwanted body movement
* degeneration of neurons leads to tremors or Parkinson disease

what is the reticular formation?

* loose web of gray matter that runs vertically through all levels of brainstem
* occupies space between white fiber tracts and brainstem nuclei
* has connection with many areas of cerebrum

what are the functions of networks?

* somatic motor control
* cardiovascular control
* pain modulation
* sleep and consciousness
* habituation

what is the somatic motor control?

* adjust muscle tension to maintain tone, balance, and posture, especially during body movements
* relay signals from eyes and ears to cerebellum
* integrate visual, auditory, balance and motion stimuli into motor coordination

what are gaze centers?

allow eyes to track and fixate on objects

what are central pattern generators?

neural pools that produce rhythmic signals to the muscle of breathing and swallowing

what is cardiovascular control?

cardiac and vasomotor centers of medulla oblongata

what is pain modulation?

* some pain signals ascend through the reticular formation
* some descending analgesic pathways begin in the reticular formation

what is sleep and consciousness?

* reticular formation plays a central role in consciousness, alertness and sleep
* injury here can result in irreversible coma

what is habituation?

* reticular activation system modulates activity in cerebral cortex so that it ignores repetitive, inconsequential stimuli

what is the cerebellum?

* the largest part of the hindbrain and second largest part as a whole
* consists of right and left cerebellar hemispheres connected by vermis
* contains more than half of all brain neurons- about 100 million
* known to be important for motor coordination and locomotor ability

what is the cerebellar peduncles?

three pairs of stalks that connect brainstem and cerebellum

what are the inferior peduncles?

* connected to medulla oblongata
* most spinal input enters the cerebellum through inferior peduncle

what are the middle peduncles?

* connected to the pons
* most input from rest of the brain enters through middle peduncle

what are the superior peduncles?

* connected to the midbrain
* carries cerebellar output

what are the several sensory, linguistic, emotional, and other nonvoter functions of the cerebellum?

* comparing texture of objects
* perceiving space
* recognizing objects from different views
* keeping judge of elapsed time and maintaining tapping rhythm
* helping direct eye movements that compensate for head movements
* judging the pitch of tomes and distinguishing between similar spoken words
* helping in verbal association tasks
* planning, scheduling, and emotion control

what does the forebrain consist of?

* diencephalon
* telencephalon

what is the diencephalon?

* encloses third ventricle
* most rostral part of the brainstem

what is the telencephalon?

develops chiefly into the cerebrum

what are the three parts of the diencephalon?

* thalamus
* hypothalamus
* epithalamus

what is the thalamus?

* ovoid mass on each side of the brain perched at the superior end of the brainstem beneath the cerebral hemispheres
* constitues about four-fifths of the diencephalon

what does the thalamus do?

* nearly all input to the cerebrum passes by way of synapses in the thalamic nuclei, filters information on its way to cerebral cortex
* plays key role in motor control by relying signals from cerebellum to cerebrum and providing feedback loops between the cerebral cortex and basal nuclei
* involves in the memory and emotional functions of the limbic system

what is the hypothalamus?

* forms part of the walls and floor of the ventricle
* extends anteriorly to optic chasm and posteriorly to mammillary bodies

what are the hypothalamic nuclei?

* hormone secretion
* automatic effects

what does the hormone secretion of the hypothalamus do?

* controls anterior pituitary, thereby regulating growth, metabolism, reproduction, and stress responses
* produces posterior pituitary hormones for labor contractions, lactation, and water conservations

what does the automatic effects of the hypothalamus do?

* major integration center for automatic nervous system
* influences heart rates, blood pressure, gastrointestinal secretions, motility, etc.

what are the functions of the hypothalamus?

* thermoregulation
* food and water intake
* sleep and circadian rhythms
* memory
* emotional behavior and sexual response

what is the epithalamus?

very small mass of tissue composed of the pineal gland, habenula, and thin roof over the third ventricle

what is the pineal gland?

endocrine gland

what is the habenula?

relay from the limbic system to the midbrain

what is the cerebrum?

* largest, most conspicuous part of human brain
* two cerebral hemispheres divided by longitudinal fissure
* seat of sensory perception, memory, thought, judgment, and voluntary motor actions

what is the cerebral white matter?

* most volume of cerebrum is white matter
* tracts are bundles of nerve fibers in the central nervous system

what are the three types of tracts?

* projection tracts
* commissural tracts
* association tracts

what are projection tracts?

extend vertically between higher and lower brain and spinal cord centers

what are association tracts?

* connect different regions within the same cerebral hemisphere
* long fibers connect different lobes; short fibers connect gyro within a lobe

what are commissural tracts?

cross from one cerebral hemisphere to the other allowing communication between two sides of cerebrum

what is carried out in the gray matter of the cerebrum?

neural integration

where are cerebral gray matter found?

* cerebral cortex
* limbic system
* basal nuclei

what is the cerebral cortex?

* covers surface of the hemispheres
* only 2 to 3 mm thick
* constitutes about 40% of brain mass

what are the two types of neurons in the cerebral cortex?

* stellate cells
* pyramida cells

what are stellate cells?

* have spheroid neurosomas with dendrites projecting in all directions
* receive sensory input and process information on a local level

what are pyramida cells?

* tall, and conical, with apex toward the brain surface
* a thick dendrite with many branches
* include the output neurons of the cerebrum
* only neurons that leave the cortex and connect with other parts of the CNS

what is the limbic system?

* important center of emotion and learning
* there is a limbic system in each cerebral hemisphere
* components are connected through a loop of fiber tracts

what are the prominent components of the limbic system?

* cingulate gyrus
* hippocampus
* amygdala

what is the cingulate gyrus?

arches over corpus callosum in frontal and parietal lobes

what is the hippocampus?

in medial temporal lobe (memory functions)

what is the amygdala?

immediately rostral to hippocampus (emotion functions)

what sensations occur in the limbic system?

* gratification
* aversion

what is gratification?

sensations of pleasure or reward

what is aversion?

sensations of fear or sorrow

what is the basal nuclei?

* masses of cerebral gray matter buried deep in the white matter
* receive input from the substania nirga of the midbrain and the motor areas of the cortex
* send signals back to both of these locations
* involved in motor control

what are the three Brian centers that form the basal nuclei?

* caudate nucleus
* putamen
* globus pallidus

what is the lentiform nucleus?

putamen and globus pallidus together

what are the integrative functions of the brain?

* sleep
* memory
* cognition
* emotion
* sensation
* motor control
* language

what interactions occur in the brain?

interaction between cerebral cortex, basal nuclei, brainstem, and cerebellum

what is the primary sensory cortex?

* sites where sensory input is first received and one becomes conscious of the stimulus
* association areas near primary sensory areas process and interpret that sensory information

what is the primary visual cortex?

* bordered by visual association areas
* make cognitive sense of visual stimuli