Ch 14 The Brain & Cranial Nerves Flashcards
Where do the major parts of the adult brain are directly derived from?
The embyonic brain vesicles
The 5 seconfary brain vesicles:
(from superior to inferior)
1. telecephalon»_space; cerebrum
2. diencephalon»_space; Thylamus/ hypothalamus/ epithalamus
3. mesencephalon»_space; midbrain
4. metenscephalon»_space; pons & cerebellum
5. myelencephalon»_space; medulla oblongata
the ** spinal cord** is located below the myelencephalon
What are the parts of the brain that is already existed at birth?
1) cerebral hemisphere
2) diencephalon
3) cerebellum
4) brain stem:
- midbrain
- pons
- medulla
- oblongata
- spinal cord
At birth, the neonatal brain looks very much like that of an adult and almost all the neurons the brain will ever have are already present
we have:
100 billion neurons
100 trillion connections
supported by 10 trillion neuroglia cells
what are the 4 general structures of an adult brain?
1) cerebrum
- responsible for higher functions; contains a convoluated surface called the Cortex , is divided into left & right **hemispheres **
2) diencephalon
- consists of the thalamus, hypothalamus, limbic system and pituitary gland
3) cerebellum
- coordinate body movement & helps maintain balance and postural control
- involved in planning and coordinating movement on the fly
- also divided into hemispheres (10% brain volme but 50% of brains’ neurons)
4) brain stem
- consists of the midbrain, the pons, and the medulla oblongata, which are involved in autonomic functions
What is the cerebrum?
- convoluted urface f the cerebrum conssists of gyri and sulci (deeper sulci called fissures)
= incerase the area of the brain and form anatomical landmarks - is divided into lobes, which are named according to the bone which protects them
» has layers - the outer = gray matter (nerual cell bodies)
- the inner = white matter (myelinated axons)
(nuclei are clusters of gray matter that lie in deeper regions of the brain)
Where is the longitudinal fissure located?
Between frontal lobes (left & right hemispheres)
- precentral gyrus (primary motor cortex) is loctaed before the central sulcus, in left hemisphere
Where is the central sulcus?
Between the fronal lobes and parietal lobes
- postcentral gyrus (somatosensory cortex) is located in left hemisphere after cetnral sulcus
What are the ventricles of the brain?
During empryonic development, large hollow chambers are foremd int he cerebrum. These cavities are called the Lateral ventricles (one in each hemisphere)
- Lateral ventricles are connected via the interventricular foramen to the third ventricle in the diencephalon
the ventricles are filled w/ CSF and are lined w/ ependymal cells that circulates & absorb CSF via Cilia & microvilli
Explain the location of the third & fourth ventricles
- Lateral ventricles are connected via the interventricular foramen to the third ventricle in the diencephalon
-
Fourth ventricle is located posterior to the brainstem and is connected to the third ventricle by the cerebral aqueduct
(the fourth ventricle is contrinuous w/ the central canal of the spinal cord & contains Apertures that connect w/ the subarachnoid space) 12p
What are the ventricles lined with?
Ependymal cells filled with cerebrospinal fluid (CSF)
- ependymal cells: produces, circulates & absorve CSF via cilia & microvili
The three ways protecting the brain
1) the bony cranium
2) the meninges (= dense irregular CT)
3) cerebral spinal fuid (CSF)
What are the menings?
: the connective tissue converings of the brain & spinal cord = **the menings **
consists 3 layers
1) the dura mater(very thick - right below the skull bones)
- periosteal
- meningeal
2) the arachnoid mater
3) pia mater
2 types of protections & support of the brain
- physical/ mechanical protection:
a) cranium bones
b) cranial meninges
- the cranial dura mater
» an eternal periosteal layer
» an internal meningeal layer
(the spinal dura mater has only one)
- arachnoid mater
- the pia mater
c) CSF
= all continous with those of spinal cord
- biochemical protection:
a) blood brain barrier
= several mechanisms that isolate CNS from general circulation
(e.g. astrocytes)
b) cerebrospinal fluid (CSF)
What is dura-mater?
two layers (both fibrous)
1. outer: fused to periosteum
2. inner: meningeal layer
= between layers: tissue fluids & blood vessels including several large venous sinueses called dural sinuses
- veins of the brain open into these sinuses, which deliver venous blood to** internal jugular veins **of the neck
3 layers of the branial meninges:
**the dura mater/ arachnoid mater/ Pia mater **
**the dura mater: **
- dura mater (endosteal layer)
- dural sinus (collects blood)
- dura mater (meningeal layer)
arachnoid mater:
- arachnoid membrane
- subarachnoid space
- arachnoid trabeculae
pia mater
- is bound to surface of brain by astrocytes
what are those between inner & outer dura mater layers?
tissue fluids & blood vessels including several large venous sinuses
- the veins of the brain open into these sinuses, which deliver venous blood to internal jugular veins of the neck = all connected to your cardiovascular circuit
What is arachnoid mater?
: layer of epithelium w/ web like extensions to pia mater
- subarachnoid space = filled w/ CSF
- pia mater: covers entire surface following folds
anchored by:
- processes (branches) from astroctyes
What are the dural folds?
= sheets of dura mater that dip into deep folds of brain and return to surface
* located within dural folds: dural sinuses (collecting veins - lined with endothelial cells)
Three major dural folds:
1) falx cerebri: in the longitudinal fissure betwen two hemispheres of cererbums
2) tentorium cerebelli: between cerebrum and cerebellum
3) falx cerebelli: between two hemispheres of cerebellum
= seat belt - holds the brain in position
What does the dural sinuses contain?
- venous blood (deoxygenated blood)
- old CSF
What are the protective function of meninges?
1) dural folds: “seat belt” - hold the brain in position
2) cerebrospinal fluid: cushions, supports (floats the brain)
What are the locations and funtions of cerebrospinal fluid?
location:
- 4 ventricles
- subarchnoid space of cranium & spinal cord
- central canal of the spinal cord
functions:
- cushioning
- supporting (floating brain weighs only 50 g when supported by CSF)
- transporting nutrients, chemical messengers & waste
What is the cerebrospinal fluid produced by?
produced by choroid plexuses
= capillaries surrounded by specialized ependymall cells
located “in each of the ventricles”
So what is CSF?
- formed from blood plasma, giving it is a similar composition (sugar, oxygen and nutrients)
- is produced in the choroid plexuses in the ventricles
= capillary fluid is allowe dto filter out of the blood stream, but only certain molecules are permitte past the ependymal cells - contains gluces, O2, CO2, vitatmins, and other ions
(but low K+ cz of its size) - it reenters the blood steram through the arachnoid villi
what is the blood-brain barrier?
- the capillaries supplying the brain are very selective in what they allow to eneter the brain and CSF
- proteins, amino acids, waste products, most drugs and K+ are not permitted access
- the barrier is ineffective against fast-soluble molecules (i.e. alcohol, nicotine, anesthetics)
How does the CSF circulate?
The total volume of CSF at any time = 150mL
the total volume produced/ day = 500 mL
pressure remains constant, because the rate of fluid reabsorption equals the rate of fluid production = 20 mL/hr
- enters subarachnoid space through 2 lateral apertures and a median aperture = flows around brain, spinal cord, and cauda equina and into central canla and ventricles
What is menigitis?
inflammation of the meninges = a serious life threatening conditions
- bacterial/ viral menigitis can spread to the brain or spinal cord
( if the brain become inflamed = encephalitis)
- can be diagnosed by examining a sample of cerebral spinal fluid taken from the subarachnoid space in the spinal column
[drainage of CSF through archnoid granulations]
How does the drainage of CSF happening through arachnoid granulation?
1) extension of arachnoid mater
- project into the superior sagittal sinus (a dural sinus)
2) CSF moves into the superior sagittal sinus, that colelcts CSF and returns it to the jugular veins for frainage to the heart
What is hydrocephalus?
= a condition where CSF accumulates
- in adult, this leads to an increase in intracranial pressure & compression of the brain
- can occur as a result of congenital abnormalities, head injury and meningitis
- in neonates (infants), the bones of the skull have not yet fused as immovable sutures and spaecs bewteen bone still exist. (these space = fontanelles)
- hydrocephalus in the neonates is a serious condition if left untreated; however, the skull can expand to compensate forthe additional volume and temporarily prevent a rise in ICP
(ealry signs invlude bulging at the fontanels- recording head size in the neonate is common practice)
1) internal hydrocephalus: blockage within ventricles
2) external hydrocephalus: blockage at subarachnoid granualtions
explain the unusal architecture of the vasular endothelium aournd brain capillaries.
The vascular endothelium around brain capillaries differs from most other organs of the body in that it forms tight junctions with the end-feet of neraby astrocytes
As a result of this unusal architecture, a blood brain barrier (BBB) is formed:
- astrocytes
- pericytes (contractille)
- tight junctions (between endothelial cells)
What is the funtion of blood brain barrier
funtions: to isolate tissue of CNS from general circulation = tight control over CSF
( basically CSF is filltered blood plasma)
Capillaries in CNS is interlocked by tight junctions
The movement of substances between brain capillaries and interstitial fluid:
- lipid soluble substances: O2, Co2 can diffuse across membrane
-
water, alcohol and ions: Ca++, Na+, K+, Mg++, Cl-, H+
: move through protein channles (most drugs are water soluble & can’t cross BBB) -
larger substacnes: glucose moved by protein channels
= 2,3 both reguire channles & somtimes ATP (slower rate of transport
-
covering surface of capillaries in CNS: astrocytes that control permeability of the endothelium
(compared to blood, CSF is 7.33 has low protein, few WBCs no RBCs & different ion concentrations (through the same overall osmolarity)
The names of the lobes in cerebrum
the lobes of the cerebrum correspond to theboens of the braincase whicih bear the same names
1) frontal lobe
2) parietal lobes
3) temporal lobes
4) occipital lobe
What are the lists of cortex
neurons of common function are localized together in areas of the cortex
1) primary motor cortex (in precentral gyrus)
2) primary somatosensory cortex (in postcentral cortex)
- sensory; behind the central sulcus
3) custatory cortex
4) pretrontal cortex (conscious intellect)
5) guastatory cortex = taste
What is cortex
cortex: gray matter; folds are unique to you
= cell bodies, dendrites axon terminals
generates conscious experience
- sensory sensations are perceptions
- thinking, problems solving, judgement, logic
- forms intentions
- emtions
two hemispheres separated by longitudinals fissure
consists of:
1) thin outer layer of gray metter = cerebral cortex
2) deeper white matter = deep to the neural cortex
3) located deep in white matter = basal nuclei
* nuclei: clusters of neuron cell bodies
What is basal nuclei
basal nuclei = lentiform nucleus (putamen & globus pallidus)
: the basal nuclei are clusters of gray matter that lie deep within the white matter
- they consist of the caudate nucleus, the putamen and the globus pallidus
What is the function of the basal nuclei
plays a role in…
- planning voluntary movement
- sending their signals to the primary motor cortex via the Thalamus
- inhibiting unnecessary movement and antagonist muscles
- destruction of the substantia nigra which controls the basal nuclei occurs in the neurological disease (Parkinson’s disease) and result in the inability to initate voluntary movementsand tremors
functions:
- subconscious control of skeletal muscle tone (not too rigid, not too flaccid)
- coordination of learned movement patterns, generates rhythms (e.g. walking) & body positioning
- linked to speed & accuracy of voluntary movements
Tremors
Rigidity
Posture of body
Accuracy
2 specific functioning areas in the cortex
1) sensory areas: receive sensory information; generate sensation
- somatosensory cortex (postcentral gyrus; sensorying info)
- auditory cortex (sounds)
- gustatory cortex (taste)
- olfactory cortex (smells) : processing the chemicals from smells
2) motor areas : initiate and direct voluntary movements by acting on brainstem and spinal cord
- primary motor cortex (precentral gyrus): muscle contraction where basal nuclei talks to
Sensory & motor cortex representation = cortical homunculus
What are the sensory areas?
1) primary sensory (somatosensory) cortex
- located posterior to the central sulcus in the parietal lobe;
- receives input from sensory receptors in the skin (pressuer, pain, and temperature) and proprioceptors (muscle spindle fibers/ golgi tendon organs/ joint capsule receptors) in the muscles
2) somatosensory (assocation) area
- located posterior to the Primary Sensory cortex
- aids in the interpreation of touch, pain, & temperature
3) primary auditory cortex
- located in the superior portion of the temporal lobe
- receives info from cochlear receptors in the inner ear that allow us to hear
4) olfactory area
- on the medial/ anterior portions of the temporal lobes, the orbitofrontal cortex and part of the limbic system
- receive info from smell receptors in the nasal cavities
5) primary visual area
- located on the posterior tip of the occipital lobe
(the largest of the cortical sensory areas)
- receives info from the retinas of the eyes (left half of the visual cortex = info from the left half of each retina vice versa with the right)
6) visual association area
- surrounds the primary visual cortex; forms many connections with it
- stores info that allows us to recognize visual info
Sensory cortex (somatic sensory crotex; postcentral gyrus) = parietal lobe
What is primary sensory (somatosensory) cortex?
1) primary sensory (somatosensory) cortex
- located posterior to the central sulcus in the parietal lobe;
- receives input from sensory receptors in the skin (pressuer, pain, and temperature) and proprioceptors (muscle spindle fibers/ golgi tendon organs/ joint capsule receptors) in the muscles
What is somatosensory (assocation) area?
2) somatosensory (assocation) area
- located posterior to the Primary Sensory cortex
- aids in the interpreation of touch, pain, & temperature
What is primary auditory cortex?
3) primary auditory cortex
- located in the superior portion of the temporal lobe
= receives information from cochelera receptors in the inner ear that allow us to hear
- Both left & right hemispheres receive info from both ear
What is olfactory area?
4) olfactory area
- located on the medial/ anterior portions of the temporal lobes, the orbitofrontal cortex, and part of the limbic system
= receives info from smell receptors in the nasal cavitites
- info is sent through the olfactory bulb to these cortical areas
what is visual area?
5) visual areas
- located on the posterior tip of the occipital lobe = the largest of the cortical sensory areas
= receives info from the retinas of the eyes, where the left half of the visual cortex represents info from left half each retina, and the right half of the visual cortex represents info from the right half of each retina
What is viusal association area
6) visual association area:
- surrounds the primary visual cortex and forms many conneections with it
- this area stores information that allows us to recognize the visual info (i.g. faces and objects = just aany hepful info in life)
What are the motor areas?
1) primary motor cortex
- located anterior to the central sulcus on the frontal lobe (in the precentral gyrus)
- initiates voluntary movements from triangular shaped neurons (pyramids) - largest cell in CNS (UMNs), synapses w/ anterior horn of spinal cord (LMNs)
- contains pyramial (Betz) cells
2) premotor cortex
- located anterior to the primary motor cortex
- stores info regarding learned motor skills (i.e. plyaing a musical instrument or typing) linked to working memory areas (help to plan & guide movement) = planning centre for which neurons gonna be used
- sends this info to the primary motor cortex
Motor cortex (precentral gyrus) = frontal lobe
What are the association areas?
= interpret incoming sensory info
- somatic motor association area (prepotor cortex) = coordinate the matter (planning)
- somatic sensory association area
- visual association areaa (vision)
- auditory association area
4 integrative areas
= recieve input from many association areas
a) prefrontal cortex - both hemispheres
b) general interpretive area - typically left hemisphere only
c) speech center (Broca’s Area) - typically left hemisphere only
d) Frontal Eye Field - both hemispheres
What is prefrontal cortex?
“both” hemispheres
- receives info from associations areas
- analyzes and interprets info
- registers abstract intellect as well as feelings in response
What is general interpretive area (wernicke area)
typically “LH” only
- provides ability to interpret what is seen & heard
- coordinates visuals & auditory association
- access to memories
(hearing and understanding dialogues)
WHat is speech center (Broca’s Area)
typically in LH only
- regulates breathing & vocalization muscles required to generate speech
What is frontal eye field
both hemispheres
- controls learned “eye” movements as following line of text when you read
List the different function of each hemisphere
Lateralization of the cortex
= parts of each hemisphere is responsible for different functions
left hemisphere
- general interpretive ceter
- speech center
- writing
- analytical tasks
(L = language, logic and writing)
right hemisphere
- analysis by touch
- spatial visualization
- recognizing faces
- analyzing emotional
- content of conversations
- tone
What is neural tract
The cerebral white matter provides communciation between cortical areas and lower structures.
- white matter of cerebrum = tracts (bundles of axons)
- Bundles of axons within the CNS = tracts (are equivalent to nerves in the PNS
3 types of tracts:
1) association fibers: tracts that transfer signals within a hemisphere
2) commissures: tracts that transfer signals between hemispheres
3) projections fibers: tracts that sen signals to the spinal cord
What are the 3 types of nerual tracts
1) association fibers: connect different areas of cortex within single hemisphere
- arcuate fibers: short, connect one gyrus to another
- longitudinal fasciculi: connect frontal lobes to others
2) commisural fibers: connet hemispheres
- corpus callosum
- anterior commissure
(e.g. corpus callosom)
3) projection fibers: connect cortex to cerebelllum, diencephalon, brainstem, and spinal cord
What is the prefrontal cortex
= occupies the anterior portion of the frontal lobe
- very complex area; is involved in determining intellect, personality, complex learning abilities (calle cognition) and memory
- is necessary for our ability to form abstract ideas, show judgement, reasoning, concerning for others and persistence
- these attributes tend to develop over time and are largely dependent upon experience
- also linked with the emotional and learning system of our brain called limbic system
(babies can’t control their emoitons compared to the adults)
3 parts of diencephalon
1) epithalamus
2) thalamus
3) hypothalamus
what is epithelamus
contains: pineal gland
- secretes melatonin (hormone)
- regulate day-night cycle
- reproductive function
What is thalamus
= a cluster of nuclei that sends and receives info to and from the cortex
- to receive sensory info from the special senses and from the regions of the body (touch, pain, proprioception & temperature)
- to relay this info to the appropriate area in the cortex
- recieves info from the Basal Nuclei and relays it to the Primary Motor cortex
(known as the gateway to the cortex)***
What is hypothalamus
= the control center
- lacks a blood brain barrier => responds to changes in blood compositions; influenced by the crebrum, brainstem, spinal cord & CSF
1) coordinate voluntary & autonomic functions
- voluntary: subconscious control of skeletal muscles contractions associated with strong emotions (e.g. stress = fight or flight)
- autonomic function (sympathetic + parasympathetic nervous system): regulate the cardiovascular & vasomotor centers of the medulla oblongata to regulate heart rate, blood pressure and respiration
2) coordination of nervous system & endocrine (hormone) system
: controls the pituitary gland & the regulatory hormone = releases 2 hormones
- ocytocin = nesting hormone experienced by pregnat women stimultates contractions in uterus & mammary glands
- antiduretic hormone (ADH) = regulates salt/ water balance of body
3) produce Emotions & behavioural drives
: contatins feeding center, thirst center
4) Regulation of body temp (preoptic area)
5) adjust RAS activity (heightened alertness or lethargy)
6) control of circadian rhythems = daily rhythms of body function (together w/ epithalamus)
What does brain stem consist of
1) midbrain
2) pons
3) medulla oblongata
The inferior part of the brainstem joins with the spinal cord
What is the general functions of brainstem nuclei
1) site of processing of cranial nerve reflexes
2) a relay center for sensory information going to higher centers
3) uses sensory info to help regulate motor output
examples of reflexes coordinated by the Medulla oblongata:
- cardiovascular cetners: adjust heart rate strength of cardiac contractions & blood flow
- respiratory rhythmicity centers: adjust pace of respiration by controlling diaphragm & intercostal muscles
- reflex center: controls vomittin, hiccupping, swallowing, coughing & sneezing
The 3 parts of midbrain
3 parts of midbrain:
(white matter)
1) cerebral preduncle: connect primary motor cortex with motor neurons in brain and spinal cord; carry ascending sensory info to thalamus
(gray matter)
2) superior colliculus: integrate visual info with ohter sensory inputs; initiate reflex responses to visual stimuli
3) inferior colliculus: relay auditory info to medial geniculate nuceli; intiate reflex responses to auditory stimuli
3 components of pons
(gray matter)
- respiratory centers
1) pneumotaxic center
2) apneustic center
: adjust activities of the respiratory rhythmicity centers in the medulla oblongata
(white matter)
- tracts
3) ascending tracts: carry sensory info from the nucleus cuneatus & nucleus gracilis to the thalamus
4) descending tracts: carry motor copands from higest centers to motor nuclei of cranial or spinal nerves
Structure of the medulla oblongata
Gray matters
(autonomic center)
- reticular fomation
- cardiovascular centers
- respiratory rhythmicity center
- solitary nucleus
(relay stations)
- olivary nucleus
- nucelus cunetus
- nuclus gracilis
What is the reticular activating (RAC)? (e..g structures, functions)
: is formed from nuclei within the midbrain,pons, medulla oblongata
- has tracts that stimulate the cortex, hypothalamus,a nd thalamus = receives stimuli fromt eh sens
- is responsible for the brain’s overall state of arousal and filters out insignificant stimuli
- cardiovascular and respiratory centres = can regulate cardiac and respiratory function
While we are awake, the system functions to stimulate the cortex; however, when we are asleep, it is inhibited by sleep centres in the hypthalamus
= damage to the RAC (reticular activating system) can lead to COMA
The process of falling asleep
- neurons from the eye signal the suprachiasmaotic nucleus (SCN) that the light level is decreasing
- the SCN stimulates the ventrolateral preoptic nucleus
- the ventrolateral preoptic nucleus decreases the activity of the reticular formation
- the decreased activity of the reticular formation “disconnects” the thalamus from the cerebral cortex, in turn decreasing the level of consciousness
WHat is limbic system
Limbic system = a duntional system (not a specific anatomical structure)
includes:
- nuclei in diff parts of brain & tracts that connect them
- hippocampus/ parahippocampal gyrus/ mammillary body/ amygdala/ fornix/ septal nuceli/ hypothalamus/ olfactory bulbs
functions
1) establishes emotional states
2) linkes conscious intellectual functions of cerebral cortex w/ autonomic functions
3) cerates emotional drives (e.g. motivateion, reward, fear)
4) facilitates memory storage and retrieval (required for learning)
12 pairs of cranial nerves
12 pairs of cranial nerves are produced by the brain, 2 of these arise from the cerebrum, the remainder from the brainstem
cranial nerves can service both the somatic and autonomic nervous system
I olfactory
II optic
IIIoculomotr
IV trochelar
V trigeminal
VI abducens
VII facial
VIII vestibulocochlear
IX Glossopharyngeal vagus
X vagus
XI accessory
XII Hypoglossal
olfactory (I) nerve fibers
sends sensory info from nasal cavity to olfactory bulbs of cerebrum (smell)
old
optic (II) nerve
sends visual info to the optic chiasma in cerebrum (vision)
opie
Oculomotor (III) nerve
innervatess 4 of the 6 eyes muscles; controls pupil constriction and muscles of the lens for the PSNS
occasionally
Trochlear (IV) nerve
innervates 1 of the eye muscles (superior oblique)
tries
Trigeminal (V) nerve
supplies sensory fibers to the face and mouth; innervates the muscles of mastication
trigonometry
Abducens (VI) nerve
innervates 1 of the muscles of the eye (lateral rectus)
and
Facial (VII) nerve
- innervates the muscles of the face involved in facial expression
- controls lacrimal and salivary galnds for PSNS
- conveys sensory impulses from tast buds
feels
Vastibulocochelar (VIII) nerve
cochlear branch supplies sensory fibers for sound; vestibular branch transmits impulses regarding balance and equilitbrium
very
Glossopharyngeal (IX) nerve
(glosso = tongue)
(pharyngeal = pharynxs)
innervates the tongue and muscels of the pharynx involved in the swallow and gag reflex
- some sensory fibers of taste sensory fibers from carotid chemoreceptors and baroreceptors
gloomy
Vagus (X) nerve
PSNS fibers supplying the heart, lungs, and gut
- sensory fibers from aortic chemoreceptors and baroreceptors; muscle of the larynx (voice box)
vague
Accessroy (XI) nerve
muscles of the larynx and pharynx
- muscles of the head and neck via the cerviacal plexus (trapezius & sternocleidomastoid)
and
hypoglossal (XII) nerve
innervates the tongue for swallowing & speech via the cervial plexus
hypo (below) + glossal (tongue) = below tongue: speech muscles under the tongue
hyppoactive
Functions of cranial nerves
1) carry sensory info for special senses to CNS (sight, smell, taste, hearing, balance)
2) control muscles of eyes, face, tongue and neck & thorax
3) control superficial muscles of neck, back and upper chest
4) provide parasympathetic inervation to organs of thoracic and abdominopelvic catvities (Vavus = NX)
