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
cerebral crus
- bundle of nerve fibers that connect the cerebrum to the pons
- carries corticospinal tracts
reticular formation
loosely organized web of gray matter that runs vertically through all levels of the brainstem
•clusters of gray matter scattered throughout pons, midbrain and medulla
•occupies space between white fiber tracts and brainstem nuclei
•has connections with many areas of cerebrum
Functions of Reticular Formation Networks
somatic motor control cardiovascular control pain modulation***************** sleep and consciousness habituation
gaze center
allow eyes to track and fixate on objects
Cerebellum
the largest part of the hindbrain and the second largest part of the brain as a whole
•consists of right and left cerebellar hemispheres connected by vermis
•contains more than half of all brain neurons, about 100 billion
cerebellar peduncles
three pairs of stalks that connect the cerebellum to the brainstem
Cerebellar Functions
- monitors muscle contractions and aids in motor coordination
- evaluation of sensory input
- timekeeping center
- hearing
- planning and scheduling tasks
forebrain consists of
–the diencephalon
–the telencephalon
Diencephalon: Thalamus
the “gateway to the cerebral cortex” –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 relaying signals from cerebellum to cerebrum and providing feedback loops between the cerebral cortex and the basal nuclei
–involved in the memory and emotional functions of the limbic system
hypothalamus
major control center of autonomic nervous system and endocrine system
–plays essential roll in homeostatic regulation of all body systems
functions of hypothalamic nuclei
–hormone secretion –autonomic effects –thermoregulation –food and water intake –produce sensations of hunger and satiety –rhythm of sleep and waking –memory –emotional behavior
epithalamus
very small mass of tissue composed of:
–pineal gland –endocrine gland
–habenula–relay from the limbic system to the midbrain
Telencephalon
Cerebrum
cerebrum
largest and most conspicuous part of the human brain
–seat of sensory perception, memory, thought, judgment, and voluntary motor actions
frontal lobe
–voluntary motor functions
–motivation, foresight, planning, memory, mood, emotion, social judgment, and aggression
parietal lobe
–receives and integrates general sensory information, taste and some visual processing
occipital lobe
–primary visual center of brain
temporal lobe
–areas for hearing, smell, learning, memory, and some aspects of vision and emotion
insula
–understanding spoken language, taste and sensory information from visceral receptors
Cerebral White Matter
most of the volume of cerebrum is white matter
–glia and myelinated nerve fibers transmitting signals from one region of the cerebrum to another and between cerebrum and lower brain centers
three types of tracts
projection tracts, commissural tracts, association tracts
long association fibers
connect different lobes of a hemisphere to each other
short association fibers
connect different gyri within a single lobe
Cerebral Cortex
layer covering the surface of the hemispheres
–only 2 –3 mm thick
–cortex constitutes about 40% of the mass of the brain
–contains 14 –16 billion neurons
cerebral gray matter found in three places
–cerebral cortex
–basal nuclei
–limbic system
neural integration
is carried out in the gray matter of the cerebrum
Cerebral Cortex contains two principal types of neurons
stellate cells
pyramidal cells. -only neurons that leave the cortex and connect with other parts of the CNS
basal nuclei
Involved in motor control
limbic system
Creates emotions
cingulate gyrus –
– hippocampus
– amygdala
higher brain functions
sleep, memory, cognition, emotion, sensation, motor control, and language
electroencephalogram
(EEG) –monitors surface electrical activity of the brain waves
brain waves
rhythmic voltage changes resulting from synchronized postsynaptic potentials at the superficial layer of the cerebral cortex
alpha waves 8 –13 Hz
awake and resting with eyes closed and mind wandering
–suppressed when eyes open or performing a mental task
beta waves 14 –30 Hz
–eyes open and performing mental tasks
–accentuated during mental activity and sensory stimulation
theta waves 4 –7 Hz
–drowsy or sleeping adults
–if awake and under emotional stress
delta waves high amplitude, less than 3.5 Hz
–deep sleep in adults
sleep occurs in cycles called
circadian rhythms
–events that reoccur at intervals of about 24 hours
sleep
temporary state of unconsciousness from which one can awaken when stimulated
sleep paralysis
inhibition of muscular activity
coma or hibernation
states of prolonged unconsciousness where individuals cannot be aroused from those states by sensory stimulation
sleep spindles
high spikes resulting from interactions between neurons
of the thalamus and cerebral cortex
slow-wave-sleep(SWS)
EEG dominated by low-frequency, high amplitude delta waves
rhythm of sleep
controlled by a complex interaction between the cerebral cortex, thalamus, hypothalamus, and reticular formation
HYPOTHALAMUS
suprachiasmatic nucleus (SCN)
In hypothalamus
another important control center for sleep
Stage 1
feel drowsy, close our eyes, begin to relax
Stage 2
pass into light sleep
Stage 3
moderate to deep sleep
Stage 4
called slow-wave-sleep(SWS) –EEG dominated by low-frequency, high amplitude delta waves
cognition
the range of mental processes by which we acquire and use knowledge
association areas of cerebral cortex
constitutes about 75% of all brain tissue
parietal lobe association area
perceiving stimuli
temporal lobe association area
identifying stimuli
frontal lobe association area
planning our responses and personality
learning
acquiring new information
memory
information storage and retrieval
forgetting
eliminating trivial information; as important as remembering
amnesia
defects in declarative memory –inability to describe past events
– anterograde amnesia
unable to store new information
– retrograde amnesia
– cannot recall things they knew before the injury
procedural memory
ability to tie your shoes
hippocampus
important memory-forming center
Does not store memories
amygdala
emotional memory
prefrontal cortex
seat of judgment, intent, and control over expression of emotions
primary sensory cortex
sites where sensory input is first received and one becomes conscious of the stimulus
special senses
limited to the head and employ relatively complex sense organs
special senses
5
vision •hearing •equilibrium •taste smell
The General Senses
general (somesthetic, somatosensory, or somatic) senses –distributed over the entire body and employ relatively simple receptors
sensory homunculus
diagram of the primary somesthetic cortex which resembles an upside-down sensory map of the contralateral side of the body
•shows receptors in the lower limbs projecting to the superior and medial parts of the gyrus
somatotopy
the point-to-point correspondence between an area of the body and an area of the CNS
Motor Control
the intention to contract a muscle begins in motor association (premotor) area of frontal lobes
upper motor neurons
pyramidal cells of the precentral gyrus are called upper motor neurons
lower motor neurons
in the brainstem or spinal cord, the fibers from upper motor neurons synapse with lower motor neurons whose axons innervate the skeletal muscles
Highly Important in motor control
basal nuclei
cerebellum
Language
language include several abilities: reading, writing, speaking, and understanding words assigned to different regions of the cerebral cortex
Wernicke area
Understanding and planning
Plan sent to Broca for execution
permits recognition of spoken and written language and creates plan of speech
Broca area
Plan for the muscles movement
generates motor program for the muscles of the larynx, tongue, cheeks and lips
aphasia
any language deficit from lesions in same hemisphere (usually left) containing the Wernicke and Broca areas
anomic aphasia
can speak normally and understand speech, but cannot identify written words or pictures
cerebral lateralization
the difference in the structure and function of the cerebral hemispheres
left hemisphere
categorical hemisphere
–specialized for spoken and written language
–sequential and analytical reasoning (math and science)
–breaks information into fragments and analyzes it in a linear way
right hemisphere
representational hemisphere
–perceives information in a more integrated holistic way
–seat of imagination and insight
–musical and artistic skill
–perception of patterns and spatial relationships
–comparison of sights, sounds, smells, and taste
Cranial Nerves
–most of the input and output travels by way of the spinal cord
–12 pairs of cranial nerves arise from the base of the brain
–exit the cranium through foramina
–lead to muscles and sense organs located mainly in the head and neck
Cranial Nerve Pathways
most cranial nerves carry fibers between brainstem and ipsilateral receptors and effectors
most motor fibers of the cranial nerves begin
in nuclei of brainstem and lead to glands and muscles
sensory fibers begin in receptors located mainly in
head and neck and lead mainly to the brainstem
Cranial Nerve Classification
some cranial nerves are classified as motor, some sensory, others mixed
sensory
(I, II, and VIII)
motor
(III, IV, VI, XI, and XII)
•stimulate muscle but also contain fibers of proprioception
mixed
(V, VII, IX, X)
•sensory functions may be quite unrelated to their motor function
–facial nerve (VII) has sensory role in taste and motor role in facial expression
I
Olfactory Nerve sense of smell Sensory Cribiform foramina Olfactory mucosa to olfactory bulbs to inferior medial of temporal lobe Ipsilateral
II
Optic Nerve provides vision Sensory Optic foramen Retina to thalamus and occipital lobe Hemidesicates
III
Oculomotor Nerve Motor Eye movements Midbrain to eye muscles and to the levator palpebrae superious (only one not innervated by facial nerve ) Superior orbital fissure Ipsilateral
IV
Trochlear Nerve eye movement (superior oblique muscle) Motor Midbrain to superior oblique muscle of the eye Superior orbital fissure CONTRALATERAL
V
Trigeminal Nerve - mixed •largest of the cranial nerves •most important sensory nerve of the face •forks into three divisions: –ophthalmic division (V1) –sensory –maxillary division (V2) –sensory –mandibular division (V3) -mixed
VI
Abducens Nerve Motor Pons to lateral rectus muscle Superior orbital fissure provides eye movement (lateral rectus m.) Ipsilateral
VII
Facial Nerve Mixed Pons to facial muscles Style mastoid foramen Ipsilateral Main nerve for facial expression Carrying taste from anterior 2/3 of tongue
VIII
Vestibulocochlear Nerve Sensory Ipsilateral Inner ear to pons Internal acoustic meatus hearing and equilibrium
IX
Glossopharyngeal Nerve
Mixed
Medula to
Jugular foramen
swallowing, salivation, gagging, control of BP and respiration
•sensations from posterior 1/3 of tongue
X
Vagus Nerve
Mixed
Attaches to medula down to large intestine
Jugular foramen
Most important parasympathetic
•most extensive distribution of any cranial nerve
Carries taste from cheeks,
•major role in the control of cardiac, pulmonary, digestive, and urinary function
•swallowing, speech, regulation of viscera
XI
Accessory Nerve Motor Medula to trapezius, SCM and paletioglossis Jugular foramen Ipsilateral
swallowing, head, neck and shoulder movement
XII
Hypoglossal Nerve
Motor
Medula to extrinsic muscles of the tongue
Hypoglossal canal
tongue movements for speech, food manipulation and swallowing
Trigeminal neuralgia
(tic douloureux)
–recurring episodes of intense stabbing pain in trigeminal nerve area (near mouth or nose)
–pain triggered by touch, drinking, washing face
Bell’s palsy
degenerative disorder of facial nerve causes paralysis of facial muscles on one side
functional magnetic resonance imaging (fMRI)
looks at increase in blood flow to an area (additional glucose is needed in active area)
positron emission tomography (PET) and MRIvisualize
increases in blood flow when brain areas are active
–injection of radioactively labeled glucose
•busy areas of brain “light up”
Cranial nerves
Acromions
Names and functions
Oh once one takes the anatomy final very good vacations are heavenly - names
Some say marry money but my brother says bad business marry money - functions
nonfluent (Broca) aphasia
nonfluent (Broca) aphasia
– lesion in Broca area
– slow speech, difficulty in choosing words, using words that only approximate the correct word
• fluent (Wernicke) aphasia
– lesion in Wernicke area
– speech normal and excessive, but uses jargon that makes little sense
– cannot comprehend written and spoken words
• anomic aphasia
– can speak normally and understand speech, but cannot identify written words or pictures
Cranial V1
.
Cranial V2
.
Cranial V3
.
