chapter 16 - brain and cranial nerves Flashcards
1
Q
• brain consists of
A
the brainstem (medulla oblongata, pons, mesencephalon), cerebellum, diencephalon (epithalamus, thalamus, hypothalamus), and cerebrum
2
Q
• cortex
A
= grey matter located on the surface of the cerebrum and cerebellum
3
Q
• nuclei
A
deep clusters of grey matter surrounded by white matter
4
Q
• extremely delicate – requires protection provided by:
A
o bony skull
o cranial meninges
o cerebrospinal fluid
o blood-brain barrier
5
Q
Ventricles
A
• cavities and tubes lined with ependymal cells and filled with cerebrospinal fluid
6
Q
• lateral ventricles
A
relatively large cavities – one within each hemisphere of cerebrum
o connected to third ventricle by interventricular foramen
7
Q
• third ventricle
A
small cavity in center of diencephalon between two halves of thalamus
o cerebral aqueduct – slender canal that passes through mesencephalon and connects third ventricle to fourth ventricle
8
Q
• fourth ventricle
A
= begins between pons and cerebellum to superior portion of medulla oblongata
o continuous with subarachnoid space
o inferior part of medulla oblongata narrows and continues into spinal cord as central canal
9
Q
• hydrocephalus
A
blockage of cerebral aqueduct or fourth ventricle
o blocked at time of birth or due to encephalitis (brain infection), meningitis (infection of meninges covering brain), trauma, and tumors affecting brainstem
o production of CSF continues but blocked exits cause increased intracranial pressure
if skull bones not completely ossified – pressure may severely enlarge the head
compresses blood vessels, dilates ventricles and compresses of nervous tissue resulting in irreversible brain damage
o treated successfully by placing shunt (drainage tube) between ventricles and abdominal cavity
10
Q
Cranial Meninges
A
surround brain and continuous with spinal meninges
• epithelial and connective tissue membranes that protect brain – acting as shock absorbers and preventing contact with skull bones
11
Q
• dura mater
A
dense irregular fibrous connective tissue
o thickest and most superficial
o two layers - adhere tightly to cranial bones
periosteal cranial dura = outermost layer – fused to periosteum of cranial bones
meningeal cranial dura = inner layer that is continuous with dura mater of spinal cord
12
Q
o dural sinuses
A
= spaces formed where two layers of dura mater are separated from each other
lined with endothelium and transport venous blood and cerebrospinal fluid
all veins draining blood from brain empty in dural sinuses that then drain into internal jugular veins
13
Q
o meningeal cranial dural folds
A
partitions that extend into major brain fissures
falx cerebri (Fig 16.3, 16.5) = lies within longitudinal fissure and anchors anteriorly to crista galla of ethmoid bone
14
Q
o subdural space
A
between opposing epithelial of dura and arachnoid mater and contains small amount of serous fluid
15
Q
• arachnoid mater
A
middle thin and wispy layer
o subarachnoid space (Fig 16.5) = network of collagen and elastin fibers between arachnoid and pia maters
contains blood vessels and cerebrospinal fluid
16
Q
• pia mater
A
deepest layer tightly bound to surface of brain
o anchored to surface of brain by processes of astrocytes
17
Q
Cerebral Spinal Fluid (CSF
A
- clear fluid similar to blood serum with most of proteins removed
- provides protective cushion around CNS and allows brain to float within cranial cavity
- provides some nutrients to CNS tissues
18
Q
cerebral spinal fluid produce by ?
A
choroid plexus : specialized ependymal cells, support tissue and capillaries
o formed by invaginations of pia mater into roof of ventricles and covered by ependymal (special epithelial) cells
o ependymal cells secrete Na+ into ventricles and water follows by osmosis
o tight junctions between cells forming barrier
substances do not pass between cells but must be transported across cells
19
Q
cerebral spinal fluid fills…
A
• fills ventricles, subarachnoid space and central canal of spinal cord (Fig 16.7)
o some drains into dura sinuses to be removed by venous circulation
20
Q
blood supply to brain
A
- brain has high metabolic rate and brain neurons not capable of storing high-energy molecules (glycogen)
- requires large, constant blood flow for oxygen and glucose delivery
- receives 15-20% of blood pumped by heart
- interruption of blood flow for seconds can cause unconsciousness – for minutes = irreversible brain damage
21
Q
blood supply to brain via :
A
o internal carotid arteries (Fig 22.12) – enter via carotid canals (temporal bones)
o vertebral arteries – enter via foramen magnum
join to form basilar artery
o cerebral arterial circle (Circle of Willis) (Fig 22.13) = contributions from basilar artery and internal carotid arteries
anterior, middle and posterior cerebral arteries = branches that supply cortex
22
Q
what is a brainstem ?
A
• connects the spinal cord to the brain
• contains three anatomical subdivisions (inferior to superior):
o medulla oblongata, pons, and mesencephalon (midbrain)
• and one functional unit – the reticular formation that spans all three anatomical divisions
• contains many reflex centers essential for survival
23
Q
medulla oblongata
A
most inferior (caudal) portion of brain
o contains sensory and motor tracts
pyramids – prominent enlargements on anterior surface
• contain large descending motor tracts controlling skeletal muscle
24
Q
cranial nerve nuclei
A
= clusters of grey matter composed mostly of neuron cell bodies
25
olivary nuclei
– protrude from anterior surface lateral and superior to pyramids
• nuclei involved in balance, coordination, and modulation of sound from inner ear
• relays information to the cerebellar cortex
part of cranial nerve nuclei
26
brainstem stem serve as
serve as centers for vital reflexes
• cardiovascular centers – regulating heart rate and blood vessel diameter
• respiratory centers – rate and depth of breathing, coughing, sneezing
27
nuclei for cranial nerves
VIIl, IX, X, XI, and XII
28
• pons
– connects brainstem to the cerebellum by cerebellar peduncles
o nuclei for cranial nerves V, VI, VII and VIII
o sleep center that initiates REM (rapid eye movement) sleep
29
• mesencephalon
contains nuclei for cranial nerves III, and IV
| o four sensory nuclei form mounds on dorsal surface = corpora quadrigemina
30
superior colliculi
– receive sensory input from visual, auditory and tactile sensory systems
• involved in reflex movements of head, eyes and body toward stimulus
o “startle reflex”, loud noise, bright light, acute pain
part of mesencephalon
31
inferior colliculi
– involved in hearing
part of mesencephalon
32
o red nucleus
(appears pink due to blood flow) aids in unconscious regulation and coordination of motor activities
part of mesencephalon
33
o substantia nigra
appears dark due to melanin granules) part of the basal nuclei system
involved in maintaining muscle tone and coordinating movement
34
• reticular formation
diffuse system of nuclei scattered throughout length of brainstem
o receives axons from large number of sources
o modulates and controls many functions of the brainstem
o controls state of alertness and consciousness – including sleep-wake cycle
35
Cerebellum
• three parts:
o cerebellar hemispheres (2) – participates with cerebral cortex to plan, practice, smooth and coordinate limb and trunk movements
divided by primary fissure into anterior and posterior lobes
o vermis = narrow central portion
together with medial portion of hemispheres control posture, and allow smooth flowing movements
o flocculonodular lobe = small lobe – lies inferior and anterior to hemispheres – helps control balance and eye movements
36
• grey matter- cerebellum
o on cortex (surface) – has ridges called folia
contains several cell types (neurons): stellate, basket, granule, Golgi, and Purkinje
• Purkinje cells – largest, inhibitory and only cortical neurons that send axons to the cerebellar nuclei
mossy fibers = afferent axons that branch extensively within cerebellum
o and in deep cerebellar nuclei surrounded by white matter
37
• white matter
| location
in medulla – resembles branching tree = arbor vitae
38
• cerebellar peduncles
) link the cerebellum to the posterior portion of the brainstem
39
• ataxia
= loss of muscle coordination in the arms or legs due to cerebellar dysfunction
40
Diencephalon
* between brainstem and cerebrum
| * contains: epithalamus, thalamus, and hypothalamus
41
• epithalamus
roof of third ventricle and is superior and posterior to thalamus
o contains: pineal gland – secretes melatonin
action not completely understood – modulation of biorhythms and sleep-wake cycle
42
• thalamus
largest part with two lateral portions connected in center
| o surrounds third ventricle of brain
43
o receives all sensory input
synapse in thalamus then relayed to appropriate areas of cerebral cortex (Table 16.5)
anterior nuclei – part of limbic system – role in emotions, memory and learning
medial nuclei – provide conscious awareness of emotional states
ventral nuclei
• ventral lateral and ventral anterior relay information to and from basal nuclei, cerebellum and cerebral cortex that allow formation and fine tuning of movement plans
44
• ventral posterior
relays touch, pain, temperature and proprioceptive information to the primary somatosensory cortex of the parietal lobe
45
posterior nuclei
– contains two sets of nuclei: pulvinar and geniculate nuclei
• pulvinar nuclei – project sensory input to association areas of the cerebral cortex
• medial geniculate nucleus – receives auditory information
• lateral geniculate nucleus – receives visual information
46
lateral nuclei
feedback loop relay stations with impact on emotional states and integration of sensory information
47
• hypothalamus
most inferior portion (Fig 16.12, Table 16.6)
| o floor of 3rd ventricle – area superior to optic chiasm to posterior margin of mammillary bodies
48
mammillary bodies
= bulges on ventral surface – part of limbic system and recollective memory
• involved in olfactory and feeding reflexes and emotional responses to odors
49
o infundibulum
stalk containing blood vessels and axons and connects to pituitary gland
o contains several nuclei and tracts
receives sensory input from cerebrum, brain stem and spinal cord
o responds to humoral stimuli – changes in:
CSF and interstitial fluid composition
circulating blood due to high permeability of capillaries in this region
50
infundibulum
| o responds to humoral stimuli – changes in:
CSF and interstitial fluid composition
| circulating blood due to high permeability of capillaries in this region
51
o major functions associated with nuclei
| infundibulum
central controller of endocrine system
• supra-optic and paraventricular nuclei release hormones that have direct effects on tissues
• tuberal nuclei release hormones that control release of hormones from the pituitary gland
major coordinator of autonomic nervous system
temperature regulation and shivering reflex
food and water intake – hunger, thirst and satiety centers, swallowing reflex
emotions – center of limbic system – directly involved in stress-related and psychosomatic illnesses and in feelings of fear and rage
sleep-wake cycle
sexual development and behaviour
52
Cerebrum
* largest portion of the brain and size related to body size
* provides conscious thought, awareness of sensory information and all intellectual functions
* control conscious (voluntary) motor output
53
Cerebrum
| • longitudinal fissure
separates cerebrum into right and left hemispheres
54
• gyri =
folds (ridges) on cerebral cortex – increases surface area
55
• sulci
= grooves between gyri
56
• each hemisphere divided into lobes named for overlying skull bones
Cerebrum
o frontal lobe – voluntary motor function, motivation, aggression, sensation of smell, mood, personality and decision making
central sulcus – extends laterally across cerebrum separating frontal from parietal lobes
• precentral gyrus = ridge anterior to central sulcus – contains primary motor cortex (Fig 16.17)
• postcentral gyrus = ridge posterior to central sulcus – contains primary somatosensory cortex
o receives somatic sensory information – touch, pressure, pain, taste and temperature from dorsal column and spinothalamic tracts
57
o parietal lobe
Cerebrum
sensory information
| parieto-occipital sulcus – separates parietal lobe from occipital lobe
58
o occipital lobe
Cerebrum
visual information
59
o temporal lobe
Cerebrum
– smell and hearing and important role in memory
lateral sulcus – separates temporal lobe from rest of cerebrum
insula – island deep within lateral sulcus – taste information
60
• grey matter
| Cerebrum
o cerebral cortex – ranges from 2 to 6 layers thick
fusiform cells, stellate cells and pyramidal cells
• pyramidal cells = neurons associated with motor cortex and relay voluntary movement information to somatic motor neurons in brain stem and spinal cord
61
o integrative regions
| grey matter on cerebrum
– integrate complex sensory stimuli and motor responses
prefrontal cortex – very complex - extensive connections with other areas of the cortex
• complicated learning and reasoning functions
• emotional context and motivation
• predicts future consequences of actions - associated with feeling of frustration, tension and anxiety
62
o prefrontal lobotomy
until mid-twentieth century = removal of area to treat mental illnesses especially those associated with violent or antisocial behaviour
damage results in difficulty estimating temporal relationship between events (“How long ago did this happen?”, “What happened first?”)
63
hemispheric lateralization
= certain integrative regions present in only one hemisphere
64
• categorical or dominant hemisphere
usually left hemisphere containing speech center and language interpretation center
o usually determines handedness – right-handed actions directed from left hemisphere of brain
o important in performing analytical skills – math and logic
65
• aphasia
condition arising from damage to area associated with language
o affects ability to interpret what is read or heard even though individual words or entities are understood – e.g. “sit” and “here” but not “sit here”
o extreme aphasia – unable to speak or read or understand or interpret speech of others
o recovery possible when condition results from edema or hemorrhage – take months to years
66
Wernicke’s area
near the auditory cortex
| • associated with language comprehension and aids in coordinating access to visual and auditory memories
67
speech center (Broca’s area
along edge of pre-motor cortex on same side as general interpretive center
• associated with speech production
• regulates patterns of breathing and vocalization needed for speech
• coordinates muscles of tongue, cheeks, lips and jaws
• damage to area – person can make sounds but not words
68
dyslexia
disorder affecting comprehension of written words
* developmental dyslexia affects up to 15% of US children – difficulty reading and writing but other intellectual functions normal or above normal
* some forms result from problems processing and sorting visual information
69
representational or non-dominant hemisphere
right hemisphere – allows spatial perception, recognition of faces, emotional context of language, appreciation of art and music
• interpretive centers permit identification of familiar objects by touch, smell, taste or feel
• only 9% of human population is left-handed actions – controlled by right primary motor cortex but still have language centers on left side of brain
o high percentage of musicians and artists are left-handed
70
nuclei
– deep within the medulla (middle of the cerebrum)
71
Alzheimer’s Disease
chronic progressive illness characterized by memory loss and impairment of higher-order cerebral functions – abstract thinking, judgement and personality
• associated with senile dementia – with 50% over age 85 having some form of the condition
• neurofibrillary tangles and plaques in regions associated with memory processing
o nucleus basalis, hippocampus, parahippocampal gyrus
• loss of memory affects both intellectual and motor abilities – develop pronounced decrease in number of cortical neurons in frontal and temporal lobes
• no cure but progression can be slowed by:
o medications and supplements (antioxidants, B vitamins), and mental and physical activity
72
• white matter
in cerebral medulla and contains tracts that connect areas of the cerebral cortex
o association fibers – connect areas of cerebral cortex within same hemisphere
o commissural fibers – connect one cerebral hemisphere to the other
corpus callosum = largest bundle
o projection fibers – connects cerebrum to other parts of brain and spinal cord – form internal capsule
73
Basal Nuclei
• group of functionally related nuclei located bilaterally in inferior cerebrum that interact with nuclei in the diencephalon, and mesencephalon
• involved in planning of movement and pattern generation:
o subconscious control and integration of skeletal muscle tone
o coordination of learned movement patterns
74
• caudate nucleus
large head and thinner tails - follows curve of lateral ventricle
75
• lentiform nucleus
– medially located between insula and lateral wall of diencephalon subdivided into:
o putamen – laterally located
together with caudate nucleus – control cycle of arm and leg movements between the initiation and end of a walking movement pattern
76
o globus pallidus
medially located – controls and adjusts muscle tone to set body position in preparation for a voluntary movement
77
• subthalamic nucleus
– in diencephalon
78
• substantia nigra
in mesencephalon releases dopamine – acts on basal nuclei to suppress excitatory motor output
79
o Parkinson’s Disease
= motor symptoms resulting from a lack of dopamine release from substantia nigra
increased muscle tone, difficulty initiating movement, spasticity - hesitant and jerky voluntary movement, continual resting tremor, automatic positioning and preparatory adjustments no longer occur – resulting in balance problems
treatment with L-Dopa (crosses blood-brain barrier and can be converted to dopamine, surgery, transplantation of fetal brain cells
80
Limbic System
* central role in basic survival functions and behavioural drives, and interpreting sensory input and emotions, facilitating memory storage and retrieval
* deep portions of the cerebrum that form a ring around the diencephalon
* parts of cerebrum, diencephalon and mesencephalon
81
limbic role
= cerebral cortical areas and deep nuclei
o cingulate gyrus (inner surface of longitudinal fissure – superior to corpus callosum)
o parahippocampal gyrus (medial side of temporal lobe)
o dentate gyrus
o hippocampus – nucleus deep within temporal lobe
o amygdala (part of basal nuclei)
82
• fornix
= tract of white matter – connects the hippocampus to thalamus and mammillary bodies of hypothalamus
83
• open head injuries
= cranial contents exposed to outside (brain, blood and/or CSF)
o injuries involving scalp lacerations or damage to the eye, ear or nose should be carefully evaluated for possibility of open head injury
o in skull fractures in which meninges torn – CSF may leak from nose if fracture in frontal area, or the ear if fracture is in the temporal area
84
• closed head injuries
cranial cavity remains intact
o more common resulting from head striking hard surface or object striking head resulting in brain trauma
coup = brain injury at site of impact
contrecoup = brain injury occurring on opposite side of brain from the impact as a result of the brain moving within the skull
85
o concussion
mild TBI usually accompanied by a period of unconsciousness
minor = immediate but transient impairment of neural function – loss of consciousness, blurred vision, some degree of amnesia
severe = extended periods of unconsciousness and abnormal neurological function – vomiting, convulsions or seizures, slurred speech, weakness, numbness in arms and legs, dilated pupils
• associated with contusions (bruises), hemorrhages, or lacerations (tears) of the brain tissue
treatment – rest and avoid further trauma
86
• diffuse brain injury
– results from shaking (“shaken baby syndrome”) or car accidents (“whip-lash”)
o damage to many small blood vessels and nerves especially around brainstem
87
• chronic traumatic encephalopathy (CTE)
results from repeated sports-related head trauma
o boxers, football, soccer
o prevalence unknown and no cure
88
• hemorrhagic brain injury
involves hemorrhage (bleeding) and accumulation of blood – hematoma
89
o epidural hemorrhage
(hematoma) = outside the dura (~1% major head injuries)
tear of middle meningeal artery, vein, or dural sinus in middle portion of cranial cavity
pressure of blood distorts underlying soft tissues of brain
individual losses consciousness from minutes to hours after injury and death follows if untreated
treatment = drilling hole in skull allowing blood to drain
90
o subdural hemorrhage
– more common (up to 10% of major head injuries)
tears in cortical veins or dural venous sinuses in superior portion of cranial cavity
appear within hours of head injury
chronic subdural hematomas – slow bleeding over extended period (weeks to months)
• common in elderly and in people who abuse alcohol
91
Cranial Nerves
• 12 pairs of cranial nerves on ventrolateral surface of brain (Fig 16.22)
• may be: sensory, special sensory, somatic motor, and/or parasympathetic motor, or mixed (sensory and motor) in function (Table 16.12)
o sensory = special senses (vision, smell, hearing, taste, equilibrium) and general senses (touch, proprioception, temperature, pain, pressure)
o somatic motor = control of skeletal muscles
o parasympathetic = regulation of glands and cardiac and smooth muscles
92
cranial nerves are indicated by
• indicated by Roman numerals from anterior (rostral) to posterior (caudal)
93
• Olfactory nerve (I) (
special sensory for smell – from olfactory epithelium through cribriform plate of ethmoid bone to olfactory bulbs and olfactory tracts
o only cranial nerve directly attached to cerebrum
94
remaining cranial nerve originate or terminate where ?
• remaining cranial nerves originate or terminate within nuclei of diencephalon or brain stem
95
• Optic nerve (II)
special sensory for vision - attaches directly to diencephalon
o passes through optic canal of sphenoid bone
o optic chiasm – medial (nasal) fibers from each optic nerve cross over to opposite side
o optic tracts = medial (nasal) fibers from contralateral side and lateral (temporal) fibers from ipsilateral side
o lateral geniculate of thalamus – then optic radiations to occipital cortex
• cranial nerves III-X, and XII – connect to brainstem
o N III, N IV, ophthalmic branch of N V, and N VI pass through superior orbital fissure of sphenoid (Fig 16.26)
96
• Oculomotor nerve (III) (Fig 16.25)
somatic motor and parasympathetic
o supplies 4 of the muscles that move the eye: superior, inferior, and medial rectus muscles and inferior oblique muscles
o levator palpebrae superioris – raises upper eyelid
o smooth muscle that regulates the size of the pupil and shape of the lens of the eye
97
• Trochlear nerve (IV)
somatic motor – controls movement of superior oblique muscle only
98
• Trigeminal nerve (V)
mixed nerve - sensory and somatic motor
o only cranial nerve involved in sensory cutaneous innervation of head
three sensory divisions: ophthalmic, maxillary, and mandibular
99
• ophthalmic branch
= sensory – innervates orbital structures, the nasal cavity and sinuses and the skin of the forehead, eyebrows, eyelids and nose
100
• maxillary branch
= sensory - passes through foramen rotundum of sphenoid bone
| o sensory innervation of maxillary teeth, palate and gingiva, and skin of lower eyelid, upper lip, cheek and nose
101
• mandibular branch
motor and sensory - passes through foramen ovale of sphenoid bone
o sensory innervation of mandibular teeth, tongue and gingiva
102
sensory innervation of blood vessels
responsible for pain of headache
103
o motor to muscles of mastication
one middle ear muscle, one palatine muscle and two throat muscles
o proprioceptive information from same muscles plus temporomandibular joint, tongue, cheek
damage may impede chewing
104
o tic douloureux (trigeminal neuralgia)
sudden onset severe pain on one side face triggered by contact with lip, tongue or gums
adults over 40 – cause unknown
temporarily controlled by drug therapy but surgical therapy (rhizotomy) but cutting or cauterizing (burning) sensory nerve trunks carrying pain sensations
105
• Abducens nerve (VI)
somatic motor – only to lateral rectus muscle of eye
106
• Facial nerve (VII)
mixed nerve - somatic motor, sensory, parasympathetic
o passes through internal acoustic meatus of temporal bone
o somatic motor control all muscles of facial expression, small muscle in middle ear, and two hyoid muscles
o sensory for taste – anterior 2/3 of tongue
o parasympathetic: lacrimal glands, submandibular and sublingual salivary glands
o Bell’s Palsy = viral infection resulting in inflammation of facial nerve resulting in paralysis of facial muscles on affected side and loss of taste sensation (Clinical case, p.281)
condition usually painless and resolves after few weeks or months
• recovery can be accelerated by corticosteroids and antiviral drugs
107
• medulla oblongata
contains sensory and motor nuclei for N VIII (vestibular nerve), N IX, N X, N XI, N Xll
nerves IX, X, and XI - pass through jugular foramen (between occipital and temporal bones)
108
• Vestibulocochlear Nerve (VIII)
= special sensory for hearing, balance and equilibrium
o passes through internal acoustic meatus of temporal bone
o vestibular nerve – receptors in vestibule and semicircular canals – involved in balance and equilibrium
o cochlear nerve – receptors in cochlea – involved in hearing
109
• Glossopharyngeal Nerve (IX)
mixed nerve - somatic motor, sensory, parasympathetic
o somatic motor: one muscle of pharynx – involved in swallowing
o parasympathetic: parotid salivary glands
o sensory for: taste – posterior 1/3 of tongue, tactile sensation from posterior tongue, middle ear and pharynx, carotid arteries (blood pressure, carbon dioxide, oxygen and pH levels of blood)
110
• Vagus nerve (X)
mixed nerve - somatic motor, sensory, parasympathetic
o branches radiate extensively
o somatic motor: muscles of soft palate, pharynx, and larynx
damage to laryngeal branch can interfere with normal speech
o sensory: taste at root of tongue, inferior pharynx and larynx, aortic arch (blood pressure, carbon dioxide, oxygen and pH levels of blood), thoracic and abdominal organs
o parasympathetic* = main output for regulating viscera - smooth muscle function of thoracic (lungs) and abdominal organs (digestive organs and kidneys), and cardiac muscle
111
• Accessory nerve (XI)
somatic motor - cranial root (connects to vagus) and spinal roots
o sternocleidomastoid and trapezius muscles
112
• Hypoglossal nerve (XII)
somatic motor
o passes through hypoglossal canal of occipital bone
o supplies intrinsic muscles of tongue, thyrohyoid and geniohyoid muscles
113
• cranial reflexes
arcs involving sensory and motor fibers of cranial nerves (Table 16.13)
o clinically important – means of assessing cranial nerve, specific nuclei and tracts in the brain
