Chapter 12 - The Central Nervous System Flashcards
Embryonic Development
During the third week the ectoderm thickens forming what is known as a neural plate (dorsal midline axis of the embryo) this plate invaginate forming a groove that’s flanked with neural folds, as the neural groove deepens the edges fuse to form a neural tube, once it’s formed it detaches and it sinks to a deeper position
Embryonic Development: Neural Tube
- Formed by the 4th week of pregnancy, it differentiates into the CNS, there needs to be folic acid to close the neural tube
Embryonic Development: Primary Brain Vesicles
- Once neural tube forms its anterior end begins to expand forming the brain, the remainder of the neural tube becomes the spinal chord
a. Prosencephalon – aka forebrain → telencephalon and diencephalon
b. Mesencephalon – aka midbrain → mesencephalon
c. Rhombencephalon – aka hindbrain → metencephalon and myelencephalon
Embryonic Development: Secondary Brain Vesicles
- Appear in the 5th week from the PRIMARY BRAIN VESCILES
a. Telencephalon – aka end brain → cerebrum (cerebral hemispheres which are made up of the cortex, white matter and basal nuclei
b. Diencephalon – aka interbrain → thalamus, hypothalamus, epithalamis, and retina
c. Mesencephalon → mid brain of the brain stem
d. Metencephalon → pons
e. Myelencephalon → medulla oblongata
Embryonic Development: Flexures
- Midbrain and cervical – move the forebrain toward the brain stem and they’re formed because the brain grows faster than the skull
Embryonic Development: Adult Brain Structures
a. Cerebrum – two cerebral hemispheres come together
b. Diencephalon – thalamus, hypothalamus, epithalamis and retina
c. Midbrain – forms the brain stem along with other hindbrain structure
d. Pons – mesencephalon which also helps form the brain stem
e. Cerebellum – metenephalon helps form the brain stem
f. Medulla oblongata – myelencephalon and it helps form the brain stem
General Organization: Adult Brain Regions
a. Cerebral hemispheres
b. Diencephalon
c. Brain stem
d. Cerebellum
General Organization: Ventricles
Fluid filled and they’re continues enlargements that are formed by the central cavity of the neural tube, they’re continues with one another and the central canal of the spinal cord. CSF – cerebral spinal fluid and are lined by apendipal cells (neuroliga)
General Organization: Ventricles - Lateral
Paired found in cerebral hemispheres and they’re large C shaped chambers, anteriorly they lie close together and they’re separated by the septum pellucidum
i. Horns – anterior horn posterior horn and inferior horn
ii. Septum pellucidum – divides the lateral ventricles; thin median membrane that’s basically a transparent wall
General Organization: Ventricles - Third
Narrow found in the diencephalon that communicated with the lateral ventricles via interventicular foramen and the 4th ventricles
General Organization: Ventricles - Cerebral Aqueduct
Connects the 3rd and 4th ventricles; it is canal like
General Organization: Ventricles - Fourth Ventricle
Found in the hindbrain dorsal to the pons and superior to the medulla
i. Apertures – they connect the ventricles to subarachnoid space (fluid filled space found surround the brain); 2 types median and lateral
CNS Arrangement
a. Central cavity – hole in the middle
b. Inner gray matter core – area closest to the central cavity (butterfly shaped for spinal cord) mostly neuron cell bodies
c. Outer white matter – mostly mylinated fiber tracks (majority of CNS)
d. Gray matter nuclei – little circles within the outer white matter
e. Cortex of gray matter – only found in cerebellum which is basically the outer layer
Cerebral Hemispheres: Markings
a. Gyri – elevated ridges or tissue that’s found on the surface of the cerebral hemispheres
b. Sulci – shallow grooves
c. Fissures – deeper grooves
i. Longitudinal fissure – midline of the brain that separates the hemispheres
ii. Transverse cerebral fissure – separates the hemispheres from the cerebellum
Cerebral Hemispheres: Lobes
a. Frontal lobe
i. Central sulcus – divides the frontal and parietal lobes
ii. Precentral gyrus – anterior to the central sulcus
b. Parietal lobe
i. Postcentral gyrus – found posterior to the precentral gyrus
ii. Parieto-occipital sulcus – divides the parietal and occipital lobes
c. Occipital lobe – back of head
d. Temporal lobe – side of head
i. Lateral sulcus – divides that temporal and the parietal lobe
e. Insula – buried deep within the lateral sulcus and it forms part of its floor
Cerebral Hemispheres: Cerebral Cortex
Grey matter, neuron cell bodies, dendrites, associated gilia cells, but NO fiber tracks (aware of ourselves, sensations, communicate, remember, understand and innate voluntary movements)
Cerebral Hemispheres: Cerebral Cortex - Motor Areas (voluntary) - Primary Motor Cortex
A. Location – precentral gyrus of each hemisphere in the frontal lobe
B. Function – consciously control precise or skilled voluntary movement of our skeletal muscles
C. Pyramidal cells – large neurons found in the gyri that control movements
D. Somatotropy – mapping of the body in the CNS structures
Cerebral Hemispheres: Cerebral Cortex - Motor Areas (voluntary) - Premotor Cortex
A. Location – found anterior to the precentral gyrus or premotor cortext
B. Function – controls learned motor skills or a repetitious or patterned nature (typing); it coordinated region of several muscle groups
Cerebral Hemispheres: Cerebral Cortex - Motor Areas (voluntary) - Broca’s Area
A. Location – only in the left hemisphere, it’s found anterior to the inferior region of the premotor area
B. Function – directs muscles that are involved in speech production
Cerebral Hemispheres: Cerebral Cortex - Motor Areas (voluntary) - Frontal Eye Field
A. Location – partially in and anterior to the premotor cortext and superior to broca’s area
B. Function – controls voluntary movements
Cerebral Hemispheres: Cerebral Cortex - Sensory Areas - Primary Somatosensory Cortex
A. Location – in the post central gyri of the parietal lobe, posterior to the primary motor cortex
B. Function – receive information from the general sensory receptors in the skin and other receptors in skeletal muscles, joints and tendons
C. Somatotropy
Cerebral Hemispheres: Cerebral Cortex - Sensory Areas - Somatosensory Association Cortex
A. Location – posterior to the primary somatosensory cortex
B. Function – integrate sensory inputs (temperature and pressure) to produces an understanding of an object that is being felt
Cerebral Hemispheres: Cerebral Cortex - Sensory Areas - Primary Visual Cortex
A. Location – extreme posterior tip of the occipital lobe, most of it is buried deep within the sulcus and found in the medial part of the occipital lobe
B. Function – receives visual information that originates from the retina
Cerebral Hemispheres: Cerebral Cortex - Sensory Areas - Visual Association Area
A. Location – surround the PVC and it makes up the majority of the occipital lobe
B. Function – uses past visual experiences to interpret visual stimuli enabling up to recognize what we are seeing
Cerebral Hemispheres: Cerebral Cortex - Sensory Areas - Primary Auditory Cortex
A. Location – at the superior margin of the temporal lobe butting the lateral sulcus
B. Function – interprets sound for pitch loudness and location
Cerebral Hemispheres: Cerebral Cortex - Sensory Areas - Auditory Association Area
A. Location – posterior to the primary auditory cortex
B. Function – permits the perception of sound stimulus as either speech, scream, or music and it stores sound memories here
Cerebral Hemispheres: Cerebral Cortex - Sensory Areas - Primary Olfactory Cortex
A. Location – lies on the medial aspect of temporal lobe, it has a hook like region (uncus) that’s referred to as the piriform lobe
B. Function – responsible for smell and conscious awareness of different odors
Cerebral Hemispheres: Cerebral Cortex - Sensory Areas - Gustatory Cortex
A. Location – found in the insula lobe deep to the temporal lobe
B. Function – responsible for taste and perception of taste stimuli
Cerebral Hemispheres: Cerebral Cortex - Sensory Areas - Visceral Sensory Area
A. Location – in the cortex of the insula posterior to the gustatory cortex
B. Function – perception of visceral sensation (organs) upset stomach or full bladder
Cerebral Hemispheres: Cerebral Cortex - Sensory Areas - Vestibular Cortex
A. Location – exact is unknown but it’s somewhere at the posterior part of the insula adjacent parietal cortex
B. Function – equilibrium
Cerebral Hemispheres: Cerebral Cortex - Multimodal Association Areas - Anterior Association Area (prefrontal cortex)
A. Location – found on the frontal lobe
B. Function – involved with intellect, complex learning abilities, info recall and personality
Cerebral Hemispheres: Cerebral Cortex - Multimodal Association Areas - Posterior Association Area
A. Location – large region encompassing parts of the temporal, parietal and occipital lobes
B. Function – recognizes patterns and faces localizing us with our surroundings
C. Wernicke’s area – involved in understanding written and spoken language
Cerebral Hemispheres: Cerebral Cortex - Multimodal Association Areas - Limbic Association Area
A. Location – includes singulate gyris, parahippocampal gyris and the hippocampus
B. Function – provide the emotional impact that makes a scene important to us
Cerebral Hemispheres: Cerebral White Matter
Mainly mylinated white fibers
a. Function – communication between cerebral areas, cerebral cortex, and the lower CNS
b. Commissures – connect corresponding grey areas of the two hemispheres enabling them to function as a coordinating whole
i. Corpus callosum – largest commissure found superior the lateral ventricles deep in the longitudinal fissue
ii. Anterior and posterior commissures – less predominate
c. Association fibers – connect different parts of the same hemispheres
d. Projection fibers – send sensory information to the cerebral cortex and they take motor output
i. Internal capsule – compact band of projection fibers that are found at the top of the brain stem
ii. Corona radiata – fan like fiber that are found radiating through the cerebral white matter to the cortex
Cerebral Hemispheres: Basal Nuclei
Influences muscle movement and helps regulate attention and cognition. Also regulates intensity of slow or stereotype movements and inhibits antagonistic and unnecessary movements
a. Corpus striatum – made up of the lentiform and caudate nucleus
i. Caudate nucleus
ii. Lentiform nucleus
A. Putamen – outside
B. Globus pallidus – medial
b. Function
Diencephalon
It forms central core of the forebrain and it’s surrounded by the hemispheres; has 3 structures; the grey matter areas enclose the ventricles
Diencephalon: Thalamus
Consists of bilateral egg shape nuclei which form the superior lateral walls of the ventricle, contains a large number of nuclei (the nuclei have functional specialties – projects fibers to and from a specific region of the cerebral cortex)
a. Organization
i. Nuclei – ventricle posterioral lateral nuclei – it receives impulses from the general somatic sensory receptors (touch, pressure and pain)
ii. Interthalamic adhesion – aka intermediate mass and it connects nuclei at the midline
Diencephalon: Thalamus - Functions
b. Functions – relay station for incoming information to the cerebral cortex, its job is to sort sensations, mediates motor actives, mediates cortical arousal, and mediates learning and memory
i. Sensory inputs – afferent impulse reach the thalamus then it recognizes the sensations that it receives then it classifies it and sorts it as pleasant or unpleasant
ii. Other inputs – mostly all other inputs which are a sending to the cerebral cortex which run though there. They participant in regulation of emotion and visceral function from the hypothalamus and impulses that help direct the activity of the motor cortices for the cerebellum and basal nuclei
Diencephalon: Hypothalamus
Named for its position (below the thalamus) – it caps the brain stem and it forms the inferioral lateral walls of the 3rd ventricle, it mergers into the midbrain inferiorly. It extends from the optic chiasma to the posterior image of the mammillary bodies
a. Organization
i. Nuclei – mammillary bodies and various others
ii. Optic chiasma – cross over point of the optic nerves
iii. Infundibulum – found between the optic chiasma and the mammillary bodies, it’s a stalk of hypothalamic tissue that connect the pituitary gland to the base of the hypothalamus
iv. Mammillary bodies – paired pea like nuclei that buldge anteriorly from the hypothalamus; relay stations in the olfactory pathways
Diencephalon: Hypothalamus - Function
main visceral control center of the body and it’s Function - Important to the overall body homeostacious
i. Autonomic nervous system control – peripheral nerves that regulate cardiac and smooth muscles and the secretion of glands
ii. Emotional response – perception of pleasure, fear, rage, rhythms and drives
iii. Body temperature regulation – sweating and shivering (heat generating action)
iv. Regulation of food intake – regulates feelings of hunger and sacity (full feeling)
v. Regulation of water balance and thirst – osmo receptions that excite the nuclei which triggers ADH release via the posterior pituitary (ADH - antidiuretic hormone- causes kidneys to retain water, same conditions stimulate hypothalamic neurons making us feel thirsty)
vi. Regulation of sleep cycles – via supra optic chiasmatic nuclei which sets sleep cycle timing to daylight and darkness
vii. Endocrine system control – releasing and inhibiting hormones; supra optic and paravintriculer nuclei which produce oxytocin
Diencephalon: Epithalamus
Most dorsal portion of the diencephalon and it forms the roof of the 3rd ventricle
a. Pineal gland – aka the body – it extends from its posterior border and its visible externally, secretes a hormone called melatonin (sleep inducing signal and an antioxidant) it helps regulate sleep wake cycle with the hypothalamic nuclei
Brain Stem
Accounts for about 2.5% of the total brain mass – histological it is similar to the spinal cord- deep grey matter surrounded by white matter, the brain stem has nuclei of grey matter which are embedded in the white matter. Brain stem centers produce rigidly programmed automatic behaviors that are necessary for survival. The nuclei of the brain stem is associated with 10 of the 12 pairs of the cranial nerves
Brain Stem: Midbrain
Midbrain – in between the diencephalon and pons
a. Cerebral peduncles – two bulges located on the ventral aspect of the brain stem and they form vertical pillars that help hold up the cerebrum, they contain large cortical spinal that is descending toward the spinal cord
b. Superior cerebellar peduncles – fiber tracts and they connect the midbrain to the cerebellum dorsally
c. Corpora quadrigemina – 4 dome like protrusions found on the dorsal midbrain, they’re nuclei are found scattered in the surrounding in the white matter
i. Superior colliculi – visual reflex centers that coordinate head and eye movements when we visually follow a moving object
ii. Inferior colliculi – auditory relay from your hearing receptors of the ear to the sensory cortex they act in reflexives to sound (in the startle reflex)
d. Periaqueductal gray matter – surrounds the cerebral aqueduct (which runs through the midbrain); it’s involved in pain suppression, defensive behavior, reproductive behavior and in consciousness; contains nuclei of the ocular motor nerve (cranial nerve 3) and nuclei of trochlear nerve (cranial nerve 4)
e. Substantia nigra – pigmented nuclei in each side of the midbrain white matter; located deep to the cerebellar peduncle – it reflex a high content of melanin, it’s a precursor of dopamine (which is released by those neurons) degeneration of dopamine neurons is the cause of Parkinson’s
f. Red nucleus – pigmented nuclei that’s embedded in each of the midbrains white matter it lies deep to the substantia nigra and its reddish color is due to its rich blood supply and iron pigments, it’s a relay nuclei in the descending motor pathways effect limb flections
Brain Stem - Pons
Pons – bulging brain stem region that’s wedged between the midbrain and the medulla oblongata, dorsally it forms the anterior wall of the 4th ventricle, it’s composed of conduction tracts
a. Middle cerebellar peduncles – superficial fibers that are orientated transversely and going dorsally they connect the pons bilaterally with the 2 sides of the cerebellum dorsally. It contains cranial nerve 5 – aka trigeminal nerve, CN VI – abducens nerve, CN VII – facial nerve
Brain Stem - Medulla Oblongata
Most inferior part of the brain stem and it blends into the spinal cord at the foreman magnum , the central canal of the spinal cord continues upward into the medulla where it broadens out to form the cavity of the 4th ventricle
a. Pyramids – two longitudinal ridges that are flanking the midline on the medulla’s ventral aspect, they’re formed by the partial tracts that are descending from the motor cortex
i. Decussation of the pyramids – cross over point where most fibers cross over to the opposite side before continuing into the spinal cord
b. Inferior cerebellar peduncles – fiber tracts that connect the medulla to the cerebellum dorsally
c. Olives and inferior olivary nuclei – structures that are found lateral to the pyramids and their oval swelling that are mainly caused by wavy folds of grey matter. They relay sensory information on the state of stretch of muscles and joints to the cerebellum. CN XII – hypoglossal canal, CN IX – glassopharyngeal, X – vagus nerve are associated with this area
d. Vestibular nuclear complex – mediates response that maintain equilibrium
e. Functions – visceral motor center (changes blood vessel diameter – regulates blood pressure)
i. Cardiovascular center – adjusts the force and rate of heart contractions – heart rate
ii. Respiratory center – rate and depth of breathing
iii. Other visceral centers – vomiting center, hiccupping center, swallowing center, coughing and sneezing center
Cerebellum - Structures
a. Cerebellar hemispheres – apple sized and they’re connected medially by the structure vermis
b. Vermis – worm like and it connects the cerebellar hemispheres
c. Folia – pleat like gyra that are found on the surface of the cerebellum
d. Anterior lobe – top of the cerebellum
i. Primary fissure – middle
e. Posterior lobe – bottom back
i. Horizontal fissure – in between posterior and anterior lobes
f. Flocculonodular lobe – small propeller shaped structure that found deep to the vermis and posterior lobe, it cannot be seen at the surface view. It receives input from the equilibrium apparatus (helps maintain posture for balance)
g. Cortex – thin outer layer of grey matter
i. Purkinje cells – large cells, extensively branched dendrites, only cortical neurons that send axons through the white matter to synapse with the central nuclei of the cerebellum
h. White matter and arbor vitae – distinctive pattern that resembles a branching tree
i. Dentate nuclei – small deeply situated paired masses of grey matter
Cerebellum - Functions
a. Coordination – functions to coordinate the bodies movements, it uses the cerebellar peduncle and the cerebellar processing
b. Cognition – recognizes and predicts sequences of events so it may adjust body movements, some none motor functions (word association and puzzle solving)
Functional Brain Systems - Limbic System
AKA – affective brain – group of structures, its cerebral structures encircle the upper part of the brain stem
a. Function – emotional reactions (feelings)
b. Location – medial aspect of each cerebral hemisphere and the diencephalon
c. Structures
i. Amygdala – almond shaped nucleus that sits on the tail of the caudate nucleus, it recognizes facial expressions and elicits response
ii. Cingulate gyrus – plays a role in expressing emotions through gestures and involved in solving mental conflicts when frustrated
iii. Hippocampus – plays a role in memory
iv. Fornix – links the limbic together along with other fiber tracts
Functional Brain Systems - Reticular Formation
Composed of loosely clustered neurons in white matter
a. Function it has to send a continuous stem of impulses, it filters sensory imputes, and it motor arm
b. Location – extends through the central core of the medulla, pons and midbrain
c. Structures
i. Raphe nuclei, medial group of nuclei, and lateral group of nuclei – neurons that form 3 broad columns along the brain stem.
ii. Raphe nuclei – are found in the midline and they’re a medial group of nuclei and laterally flanked they’ll have lateral nuclei
Brain Protection
- Skull – bone
- Meninges – 3 connective tissue membranes found external to the CNS, they cover and protect the CNS and the blood vessels, they enclose the Venus sinuses, some lasers contain CSF (cerebral spinal fluid) also form partitions
- Cerebrospinal fluid – found in and around the CNS, watery broth
a. Functions – nourish the brain to form liquid cushion which gives buoyancy to the CNS
b. Choroid plexuses – hang from roof of each ventricle and they form CSF, enclosed by pia mater and a layer of amendable cells - Blood-brain barrier – 3rd structure protecting the brain
a. Functions – has protective mechanisms to maintain a stable environment for the brain
b. Components
i. Endothelium – capillary wall
ii. Basal lamina – surrounding the external face of each capillary
iii. Astrocytes
c. Variations - varies where it’s found (3rd-4th is completely absent)
Brain Protection: Meninges - Dura Mater
Leathery, strongest menix, surrounds the brain, 2 layered sheet of fibrous connective tissue
i. Periosteal layer – superficial layer that’s attached to the inner surface of the skull
ii. Meningeal layer – found to be deeper layer and it forms the true external covering of the brain and it continues codially in the vertebral column as the spinal dura mater
iii. Dural sinuses – collect venus blood from the brain and direct the blood to the internal jugular vein
iv. Dural septa – flat partitions that subdivide the cranial cavity and basically inward extentions of meningeal dura mater
A. Falx cerebri – large sickle shaped fold that dips into the longitudinal fissure between the two hemispheres, anteriorly the false cerbri attaches to the crysta gala (looks like a shower cap)
B. Falx cerebelli – in between the cerebellum, posterior continuation of the falx cerebri, cerebella runs along the vermis of the cerebellum
C. Tentorium cerebelli – resembles a tent that’s found over the cerebellum this is a horizontal fold that extends into the transverse fissure
Brain Protection: Meninges - Arachnoid Mater
Middle menix, it’s a loose brain covering and it’s separated from the dura mater
i. Subdural space – narrow serous cavity and it separates the arachnoid mater from the dura mater
ii. Subarachnoid space – wide and found beneath the arachnoid membrane, it’s filled with CSF
iii. Arachnoid villi – knob like projections of the arachnoid mater and it protrudes superiorly through the dura mater and into the superior sagittial sinus
Brain Protection: Meninges - Pia Mater
Delectate connective tissue, it’s richly invested with tiny blood vessels, it clings tightly to the brain
Spinal Cord
¾ thick, 17 inches long
A. Location – enclosed in the vertebral column and it extends from the foreman magnum to the 2-3 lumbar vertebrae, finishes just inferior to the ribs
B. Functions – provides a 2 way conduction pathway to and from the brain
Spinal Cord: Protection
- Vertebral column
- Meninges
a. Spinal dura mater – single layer which is not attached to the boney walls of the vertebral column
i. Epidural space – found between the boney vertebra and the spinal dura mater, filled with a soft padding of fat and a network of veins
b. Arachnoid mater and pia mater - - Cerebrospinal fluid – fills the subarachnoid space between the arachnoid and pia mater
Spinal Cord: Macroscopic Structures
- Denticulate ligaments – saw tooth shelves of pia mater and they secure the spinal cord to the tough dura mater
- Cervical enlargement – about the width of the thumb
- Lumbar enlargement
- Conus medullaris – where the spinal cord ends, inferior tapering cone shaped spinal cord area
- Cauda equina – collection of nerve roots at the inferior end of the vertebral column
- Filum terminale – fibrous extensions of the conus and they’re covered in pia mater, they extend inferiorly from the conus medullaris to the coccyx bone, it anchors the spinal cord in place
Spinal Cord: Microscopic Structures
Anterior median fissure – aka ventral median fissue and posterior median sulcus – they run the length of the cord and divide it in half
Spinal Cord: Microscopic Structures - Gray Matter
Letter H or butterfly
a. Gray commissure – cross bar of gray matter and it encloses the central canal
b. Dorsal horns – dorsal projections of gray matter (where it connections to the spinal cord)
i. Dorsal roots – formed by afferent fibers carrying impulses from peripheral sensory receptors
c. Ventral horns – ventral projections of gray matter (front of the spinal cord)
i. Ventral roots – motor neurons which send out their axons to skeletal muscles via the ventral rootlets
d. Lateral horns – small pair of grey matter present in the thoracic and superior lumbar segments ONLY (it comes out of the sides)
Spinal Cord: Microscopic Structures - White Matter
Mylinated and unmylinated nerve fibers that allow communication between brain and spinal cord
a. Anterior (ventral), lateral, and posterior (dorsal) funiculi – divisions of the white matter on the spinal cord, each contains several different fiber tracts
b. Ascending, descending, and transverse fibers
i. ascending – they conduct sensory fibers upward
ii. descending – delivery efferent impulses from the brain to the spinal cord
iii. transverse – connect the two hemispheres of the brain
