CNS Flashcards
Organisation of CNS, general & modified
• Fluid filled core -> Gray matter -> White matter
• Organization is modified in cerebellum and cerebrum
o Fluid filled core -> gray matter -> white matter w/ islands of gray matter (nuclei) -> gray matter (cerebral cortex)
Structures of lateral ventricles and what separates them
a. Structures: anterior horn, posterior horn, inferior horn
b. R & L separated by septum pellucidum
Location of third ventricle and what separates it
a. Inferior to lateral ventricles, separated from lateral ventricles by interventricular foramen
Location of fourth ventricle and what separates it
a. Inferior to third ventricle, separated by cerebral aqueduct
Where does CSP drain from the ventricles
- CSF produced in all ventricles drains downward. Once it reaches 4th ventricle it either drains through the central canal down the spinal cord, or through the medial and lateral apertures to surround brain itself.
Convolutions
Hills and valleys of cerebral hemispheres
Gyros
Elevated ridge
Sulcus
Depression/valley
Precentral gyrus
in front of central sulcus
Post central gyrus
behind central sulcus
Central sulcus
separates frontal & parietal lobe
Parietal-occipital sulcus
separates occipital from parietal lobe
Lateral sulcus
separates temporal from parietal & frontal lobe
Fissure
Very deep sulcus
Longitudinal fissure
divides R & L hemispheres
Transverse fissure
divides cerebrum from cerebellum
Layers of cerebrum
a. Cortex: outer, top part of brain. Has the most complex features necessary for abstract thought, intelligence, etc. Made from gray matter.
b. White matter: myelinated fibers
c. Basal nuclei: islands of gray matter in the white matter
How thick is cerebral cortex and how many percent of brain mass
a. Only a few mm thick but makes up 40% of brain mass due to convolutions
Functions of cerebral cortex
sensation, communication, memory, understanding, voluntary movement
Name 12 broadman areas
Primary motor cortex Premotor cortex Frontal eye field Broca’s area Primary somatosensory cortex Somatosensory association cortex Primary visual cortex Visual association area Primary auditory cortex Auditory association area Olfactory cortex Gustatory cortex
Primary motor cortex
- Allows for voluntary movement
- Located in precentral gyrus
- Contains pyramidal cells and tracts that are a special type of neuron traveling to skeletal muscle, also referred to as corticospinal
Premotor cortex
- Located anterior to primary motor cortex
- Borrows neurons from primary motor cortex
- Controls learned or rhythmic repetitive movement, ex. Typing, playing instrument
Frontal eye field
- Located anterior to premotor complex
2. Controls voluntary eye movement
Broca’s area
- Directs speech—not just ability to phonate but also coordinate tongue, jaw, lip movements etc.
- Also activates when thinking about speaking
Primary somatosensory cortex
- Located on postcentral gyrus
- Receives impulses from skin and skeletal muscles
- Plays role in spatial discrimination
vi. Somatosensory association cortex
- Interprets more of the sensory impulses and spatial discrimination than primary SSC can
Primary visual cortex
- Picks up general characteristics of an object that you see, e.g. “green tall thing narrow at the top”
Visual association area
- Matches impulses w prior experiences and interprets the information to figure out what it is, e.g. “it’s a tree”. Or more specific, “it’s a doug fir”
Primary auditory cortex
- Picks up pitch, rhythm, loudness
Auditory association area
- Allows interpretation—“it’s music”, “it’s bruce springsteen”
Olfactory cortex
- Input from olfactory receptors—smell
2. Doesn’t really have an association area, instead has associations w hypothalamus and limbic system
Gustatory cortex
- Taste, does not have association area
Homunculus
i. Distorted image of body representing neurological map, which neurons go to which part of the body
ii. Size of body part indicates the number of nerves going to that body part, and as such the level of specificity in movement or sensation
iii. Body parts that work closely together are next to each other on the homunculus
iv. There is one for motor function in precentral gyrus and one for somatosensory in post central gyrus
Multimodal association area
i. Where all the sensory areas communicate w each other, interpreting impulses from multiple senses at once
Anterior multimodal association area
- Located in frontal lobe, prefrontal cortex
2. Personality, intellect, complex/abstract thought, learning, conscience, judgment
Posterior multimodal association area
- Recognition of patterns and faces
- Wernicke’s area: written & spoken language understanding—opposite of Broca’s area
- Binding different sensory input into an understanding of coherent story & bigger picture
Fiber tracts/white matter in cerebrum: types of fiber
Commisural fibers
Association fibers
Commisural fibers
connect one side of the brain/spinal cord to the other
Projection fibers, corona radiata, internal capsule
- Allow impulses to go from cortex down to spinal cord and vice versa
- Corona radiata “radiating crown”: where projection fibers start branching out to their final destination in the cortex from the thick tract
- Internal capsule: projection fibers when travelling in tract
Association fibers
Connects association areas on same side of brain
Basal nuclei, function and 3 names
Regulation of movement
Caudate
Putamen
Globus pallidus
Corpus striatum
Basal nuclei caudate and putamen sometimes referred to as corpus striatum, they are striped because the projection fibers internal capsule go through them
Substantia Nigeria
- Involved w basal nuclei but not near the other 3
- Located in midbrain, look like eyebrows, manufacture the precursor to dopamine which is involved in movement regulation
- In parkinson’s disease substantia nigra is being destroyed
Diencephalon, location, 3 parts
Core of the forebrain, sits on top of brain stem
Thalamus
Hypothalamus
Epithalamus
Thalamus structure and function
a. Largest part of diencephalon. Encloses third ventricle.
b. Bi-lobal structure w two bags filled w “skittles” next to eachother. Skittles are nuclei
c. Function: Impulses on their way to the cortex move through the thalamus, which sends them to the appropriate structures—like the post office of the brain
d. Low level of interpretation: pleasant/not pleasant
Hypothalamus structure, location, function
a. Located inferioanterior to thalamus. Just inferior and anterior to hypothalamus is the optic chiasma. Hypothalamus is also attached to the pituitary gland inferiorly.
b. Function: Controls ANS, food intake, emotions, body temperature, water balance, sleep-wake cycle, endocrine functions
Mammillary bodies
Part of hypothalamus. Relay for olfactory senses—look like boobs in ventral view
Infundibulum
Part of hypothalamus. between optic chiasma and mammillary bodies, consists of hypothalamic tissue that connects to the pituitary gland
Epithalamus
Located inferioposterior to thalamus
a. Sleep-wake/circadian rhythm
b. Pineal gland is part of epithalamus and produces melatonin
Brain stem functions and 3 parts
- Programmed, automatic behaviors for survival
- Conducts information from cerebrum to spinal cord
Midbrain, pons, medulla oblongata
Location & Important structures of the midbrain
Midbrain forms superior part of brain stem Cerebral peduncle Superior & inferior colliculi Substantia nigra Superior cerebellar peduncles Reticular formation
Crus cerebri of cerebral peduncles
fiber tracts on either side of hypothalamus, seen on ventral view
Superior & inferior colliculi
4 raised structures seen on dorsal view
i. 2 superior colliculi responsible for moving head & neck in relation to what you’re seeing
ii. 2 inferior colliculi coordinate head & neck movement in relation to hearing—“startle reflex”
Pons location and important structures
Looks like bridge with horizontal fibers going across brain stem, dividing midbrain from medulla oblongata. Deeper fibers are going laterally.
Pneumotaxic Center aka pontine respiratory group (PRG)
Reticular formation
Middle cerebellar peduncles
Medulla oblongata location and important structures
Inferior part of brain stem, attaches to spinal cord Pyramids Olives Primary cardiovascular control Center Primary respiratory control Center Inferior cerebellar peduncles Reticular formation
Pyramids & decussation of pyramids
Part of medulla oblongata: two raised areas–fiber tracts running downward
i. Decussation of pyramids: On inferior part of pyramids there are fibers criss-crossing between the two areas. One of the primary places where contralateral impulses switch over between R and L sides
Olives
Part of medulla oblongata: Raised structures seen on lateral view. Relay stations for impulses from skeletal muscles
Cerebellum function
Regulation of movement and balance
Arbor vitae
white matter at center of cerebellum, looks like a white tree
Anatomy of cerebellum
a. Has two hemispheres, R & L
b. Large amount of gray matter relative to white matter
c. Anterior lobe
d. Posterior lobe
e. Flocculonodular lobe (in anterior inferior medial area)
Cerebellar peduncles & their functions
a. Middle cerebellar peduncle: Receives impulses from motor cortex, e.g. “can we do this movement?”
b. Inferior cerebellar peduncle: Receives impulses from skeletal muscle about what they’re doing (constant)
c. Superior cerebellar peduncle: sends impulses to motor cortex, “here’s the process for doing that movement”.
Limbic system function and structure
- Emotional brain
- Has role in sex drive, multimodal association area, recognizing emotions in facial expressions
- Composed of structures from the diencephalon, cerebrum & the communication system/circuitry
Reticular activating system (RAS)
- Made up of reticular formation tissue
- Arousing cerebral cortex—keeps cortex awake even during sleep by continuously sending impulses
- Filters out extraneous info not needed by cortex, such as being constantly aware of wearing a watch. Awareness is not created until the watch is no longer there.
- RAS can be altered by substances such as LSD. Alcohol, sedatives and tranquilizers decrease RAS activity
- Turning off RAS = coma
Meninges: what are they and 3 layers
Surround and protect brain and spinal cord
Dura mater, arachnoid mater, pia mater
Layers of dura mater
i. 2 layers: periosteal & meningeal
ii. Periosteal layer adheres to bone (skull or vertebrae)
Where do periosteal and meningeal layer of dura mater separate from each other?
iii. The layers are almost always stuck together, except in sinuses which are enlarged vascular pools w venous blood(different from sinuses in cranial bones)
iv. Meningeal layer also “tucks” into certain places
3 places where meningeal layer of dura mater tucks into spaces?
- Falx cerebri: Where meningeal layer tucks into the longitudinal fissure, wrapping each cerebral hemisphere
- Falx cerebelli: meningeal layer between R & L cerebellar hemispheres
- Tentorium cerebelli: meningeal layer in transverse fissure between cerebrum and cerebellum
Arachnoid mater location and structure
i. Spider web-looking tissue deep to the dura mater, separated by a thin serous layer called the subdural space
Arachnoid villi
aka arachnoid granulation: structures from the arachnoid mater protruding through meningeal layer of dura mater into sinus
1. This is where CSF gets reabsorbed into the blood
Pia mater
i. Delicate connective tissue that clings to the brain like plastic wrap
ii. Hard to distinguish, deep to arachnoid mater
What moves CSF in the right direction
Ependymal cells w/ cilia
Choroid plexus
Produces csf in each ventricle of the brain
What gives brain buoyancy
CSF distributed into the subarachnoid space
How much CSF is produced every 8 h
150 ml
Lumbar puncture
i. Place needle into vertebral canal through to the subarachnoid space in an area that doesn’t have the spinal cord
Blood brain barrier: function, structure, areas w/o bbb
- Protective measure that helps maintain a stable environment for the brain
- Brain capillaries do not have intercellular clefts like in other cells, where plasma and interstitial fluid can mix
- In brain capillaries there are instead tight junctions, created by astrocytes, which only allow certain molecules to pass through
- Lipid soluble substances can diffuse freely across the plasma membrane (gases and alcohol are examples)
- Some brain areas don’t have a blood brain barrier in order for them to be able to sample the blood to detect toxins, regulate water balance, body temp, etc. Vomiting area and hypothalamus are examples.
Location and dimensions of spinal cord
Foramen magnum to L1
- ~17in long, <1in thick
Meninges of spinal cord: differences from brain
i. Dura
1. No periosteal layer of dura, only meningeal
2. Epidural space above dura contains fat
iii. Pia mater has Denticulate ligaments: extensions of the pia mater prevents spinal cord from moving around
Cervical & lumbar enlargements
a. Lower portion of cervical spine and top portion of lumbar spine are enlarged because these areas innervate the appendages
Conus medullaris
End of spinal cord
Cauda equine
the spinal nerves coming from conus medullaris & exiting the spinal column on their way to their destination look like a horse tail
Filum terminale
attaches spinal cord at the bottom of column to keep it taught and prevent movement
Funiculi
a. “Elevators”-bundles of nerve fibers with afferent (sensory/up) and efferent (motor/down) pathways in the spinal cord located in the back, side & front of cord
3 ascending pathways (funiculi)
Non-specific (spinothalmic)
Specific (dorsal white columns-medial lemniscal)
Spinocerebellar
Non-specific (spinothalmic) pathway: type of stimuli, where crosses over and synapses, what elevators, how many elevators
- Pain, temperature, coarse touch
- Crosses over in the spinal cord
- Synapses in the spinal cord and the thalamus
- Uses anterolateral elevators
- 3 elevators: from skin/body via medullary nucleus and thalamus to cortex
Specific pathway (dorsal white columns-medial lemniscal) type of stimuli, where crosses over and synapses, what elevators, how many elevators
- Discriminative touch (specific pain point)
- Crosses over at medulla
- Synapses in medulla and thalamus
- Use dorsal column elevators
- 3 elevators: from skin/body via medullary nucleus and thalamus to cortex
Spinocerebellar pathway type of stimuli, where crosses over and synapses, what elevators, how many elevators
- Muscle & tendon stretch
- Synapses in spinal cord
- No cross over
- 2 elevators: from skin/body to cerebellum via spinal cord
2 types of descending pathways
Direct, indirect
Upper motor neuron
from cortex all the way to ventral spinal cord
Lower motor neuron
from ventral horn of spinal cord onward
Direct pathways (descending): aka, type of movement, what elevators
- “Pyramidal tract”
- Fine & fast movement
- Descends spinal cord using lateral & ventral corticospinal (pyramidal) tracts
Indirect pathways (descending): aka, type of movement
- “Extrapyramidal”
2. Coarse limb movement, head-neck movement, balance, eye movement
Where do descending pathways cross over?
Decussation of pyramids in medulla
