Midterm 2 Flashcards
Development of the CNS
- 3rd week – human brain is a hollow tube present in the ball of cells
a. Rises from ectoderm – outer layer of cells
b. Neuralation - 4th week – specializes in the anterior end
a. 4 main divisions
i. Forebrain
ii. Midbrain
iii. Hindbrain
iv. Spinal cord - 4-6 weeks – large increase in cells organized into new structures
a. Forebrain
i. Cerebrum
ii. Diencephalon
b. Midbrain
c. Hindbrain
i. Pons & cerebellum
ii. Medulla oblongata - 11 weeks – tube has enlarged and bent
a. Cerebrum – large increase in cells; wraps around to diencephalon
b. Hindbrain
i. Pons – ventral
ii. Cerebellum – dorsal
- Looks like mini brain
iii. Medulla – transition into spinal cord
- Nucleus of the solidary tract
Derivatives of each section
Forebrain
i. Cerebrum
- Cerebral hemispheres
- lateral ventricles
- Basal ganglia
ii. Diencephalon
- Thalamus
- Hypothalamus
- 3rd ventricle
Midbrain
i. Superior and inferior colliculus
ii. Substantia nigra
Hindbrain
i. Pons
ii. Cerebellum
iii. Medulla
Ventricles
- specialized for what
- remnants of
- location
- structure
Fluid filled cavities within the brain, remnants of the “hollow tube” from which the brain developed
4 ventricles
a. Cerebrum
- third – will be around the hypothalamus
- lateral
b. Hindbrain
- fourth – very small
Structure
a. Filled with CSF – part of the protection of brain
b. Continuous with the central canal – hollow tube in the spinal cord
c. Lined by ependymal cells – glial cells; contribute to BBB (water tight barrier)
- Specialized for transport – allow the movement of certain solutes across
White matter vs grey matter
- where are they present in the brain
Grey matter: Unmyelinated cell bodies, axon terminals, dendrites, and synapses
a. Clusters of neuronal cell bodies are most often found clustered together in nuclei, or on the outer surface of the brain as the cerebral cortex.
i. Nuclei – clusters of cell bodies
- Groups of neurons that do similar things are grouped together – nucleus
ii. Ganglia – “knot” of cells; collection of cell bodies in PNS
- Some groups within CNS are also called a ganglia
b. Outermost layer of cerebrum
c. Thalamus (2)
d. Hypothalamus (3)
White matter: Myelinated axons
a. Make up much of the cerebral cortex
- Large amount of information transfer – signal conduction & information processing
Protection of CNS
- what is a cat scan
CNS is fragile – protective components
a. Bony skull and vertebral column
b. Meninges – three protective and nourishing membranes
- CAT scan – x ray that takes sequential pictures (computerized tomography); gives 3D structure of brain
c. Cerebrospinal fluid (CSF)
d. Blood-Brain barrier
Meninges
- layers
- menginitis
- head injuries
Layers
1. Dura mater – outermost layer; tough leathery layer; tough mother
a. Functions
• Immediately within skull – helps hold in place
• Protective – if skull is cracked, it will protect brain
b. Forms reservoir within – important in circulation
i. Dural sinus – cavity; part of the circulatory system
o Continuous with veins – blood is being collected when draining from brain
o Emissary veins – drains blood from Dural sinus
ii. Any cuts in skull
o Place for bacteria to enter and access venous system and cause infection – can be life threatening
2. Arachnoid membrane – middle; connected to pia mater via fibrous structures
a. Arachnoid trabeculae – webs; hold arachnoid to pia mater
• Arachnoid – spider webs
b. Arachnoid villi – project into Dural sinus; play role in movement of CSF
3. Pia mater – directly on surface of brain; soft and delicate
Meningitis – contagious bacteria, viral, or fungal infection
o Causes swelling of meninges – puts pressure on CNS
o More common in large groups of people
Head injuries – can cause bleeding between layers; really bad really fast
a. epidural bleeding – between the skull and dura
- epi – above dura
- ski accident of actress – killed her after hitting her head on a bunny hill
b. subdural bleeding – between the dura and arachnoid
- sub – beneath dura
c. subarachnoid bleeding – between the arachnoid membrane and the pia mater)
- sub – beneath arachnoid
Cerebrospinal fluid
- circulation
- importance
Circulation
- Produced by choroid plexus – specialized cells within ventricles
- Exits the 4th ventricle through pores – foramen of Magendie (median) and foramen of Luschka (lateral)
- Inters into subarachnoid space - Some circulates around the spinal cord, some circulates into subarachnoid space
- Enters arachnoid villi from subarachnoid space – enters into dural sinus
- Arachnoid villi – granulations; extensions from subarachnoid space into subdural space and dural sinus
- Dural sinus – collects into venous blood; allows movement of waste from brain into circulatory system
Importance
a. Help maintain proper solute concentrations in the ISF surrounding neurons
- Ex. if there is high [K+] – some will move into CFS to keep within set point
b. Waste removal
c. Cushion from brain – prevent physical damage; brain won’t hit the skull
Blood brain barrier
- structure
- neuronal vs non-neuronal blood vessels
- examples of substances that can move through
- function
Barrier between the interstitial fluid of the brain and the plasma of circulatory system
Structure
a. Endothelial cells – have tight junctions (proteins); prevent movement between cells
b. Astrocyte cells – surround the endothelial cells
- End feet – projections that surround all vessels; prevent movement of solutes
c. Non-neural blood vessels
- Not connected via tight junctions
- Fenestrations – pores connecting luminal and extraluminal side
Function
a. Keeps unwanted materials out, keeps wanted materials in.
- Prevents leakage of materials from circulation into brain
- Keeps neurotrophic factors from leaving neural tissue into circulatory
b. Permeability
i. Hydrophobic substances – can diffuse across and directly contact neurons
- Ex. ethanol, steroids, nicotine, Benadryl
- Benadryl – allergy medicine; can come into contact with neurons and inhibit activity by affecting histamine receptors (antagonist)
- This is why is causes drowsiness
ii. Hydrophilic substances – must be transported across cellular layers to make it into neurons
- Ex. glucose or peptide based hormone, insulin, Na+
Spinal cord
- 4 levels
- internal circulatory - what types of movement
- meningeal layers
Major pathway between the CNS & PNS; brain and skin, muscle, joints, and organs.
Four levels o Cervical – neck o Thor – chest o Lumbar – lower back o Sacral/coccygeal – tail bone
Has its own internal circuitry
a. Mediates simple reflexes
b. Generates complicated control programs – rhythmic patterns
i. Ex. used for walking
• Input is initially needed from brain – rhythmic movements are from spinal cord
ii. Ex. patellar reflex – stimulates its own contraction; only travels to spinal cord & does not require brain
Same meningeal layers as brain
o Pia mater – directly on spinal cord
o Arachnoid membrane
o Dura mater
Segments of spinal cord
- autonomic ganglia
Each segment has bilateral sets of roots
- Dorsal – sensory into CNS
a. Differentiated by ganglia – bulge
b. Neurons
o Dendrites – in the PNS
o Cell bodies – in the ganglia
o Axons – will collect and form spinal nerves
c. Autonomic ganglia – contain neurons that regulate ANS - Ventral – control/motor away from CNS
31 pairs of spinal nerves – axons from ventral and dorsal root pairs converge and form
a. After L1-L2, the spinal cord consists of cauda equina – thick elongated nerve endings
• Most nerves have diverged somewhere else – what is left
• “horsetail”
Grey & white matter in spinal cord
White – outside (reverse of brain); myelinated axons
a. Ascending tracts – dorsal surface and outer lateral
- Sensory info
b. Descending tracts – ventral and interior lateral positions
- Somatic & autonomic
Grey – inside (butterfly); neuronal cell bodies, dendrites, unmyelinated synapses a. Sensory nuclei – dorsal horn i. Somatic – first cluster • Cell body of second order sensory neurons – receive info from synaptic terminal of first order sensory neurons (within CNS) ii. Visceral – second cluster • Info from organs and viscera b. Motor nuclei – ventral horn i. Autonomic – more lateral in horn • Control of organs and homeostasis ii. Somatic – more medial in horn • Controls skeletal muscle
Brainstem
- phylogenetically
- consists of
- cranial nerves (what do they control)
- reticular formation
Phylogenetically – oldest region of the brain – primate ancestors still have
o Transition of brain to spinal cord
Consists of
1. Midbrain – critical relay for visual and auditory info
a. Neurons that control movement of eyes & constriction/dilation of pupils
b. Gives rise to groups of diffuse modulatory neurons
2. Pons – acts as a relay station for cerebellum and cerebrum (neither are part of brainstem)
a. Plays role in regulating muscle reflexes involved in equilibrium and posture
b. Proximity to cerebellum – critical in posture, balance, and equilibrium
• Integrating area from cortex
• Allows maintenance of equilibrium with posture
• NOT part of brainstem! – hindbrain only; developmentally in the same area
3. Medulla – contains nuclei that control heart and blood vessel function, respiration, and many digestive functions
a. Vital and nonvital functions
Most of cranial nerves (10/12 pairs) arise from brainstem
a. Cranial nerves – pairs of nerves emerging from CNS
- Sensory, motor, or both
- Controls mouth, tongue, movement of eyes, balance, functioning of organs
Reticular formation – diffused; no real structure/not a tight collection of cell bodies
a. Receives and integrates incoming sensory input – plays critical role in arousal
- Arousal – wakefulness; whether you can focus on certain kinds of info
b. Gives rise to groups of diffuse modulatory neurons
Diffuse modulatory neurons
Neurotransmitters – can have neuromodulatory functions
o Long, slow regulation of neurons – usually through the actions of GPCR
o Ex. no ligand gated ion channels for norepinephrine
Spread axons throughout brain – do not just project to a single location
Nt: histamine, serotonin, norepinephrine, acetylcholine, dopamine
Cerebellum
- processes sensory info from where
Integrating center; “mini brain”
Processes sensory info from muscles, joints, vestibular system, eyes – integrates position and movement of body with intent to move body
1. Important in maintaining balance and controls eye movements
a. Eye movements are important for sense of balance
• Standing on one foot and closes eyes – balance in inhibited
2. Enhances muscle tone and coordinates skilled – voluntary movements
a. Coordinated movement of hands, arms, fingers when picking up a pencil
3. Plays role in planning and initiating voluntary activity by providing input to cortical motor areas
4. Stores procedural memories
a. Motor learning – learning how to do something (ex. a perfect pitch)
Also has recently discovered function in cognition & emotional processing
Diencephalon
- structures
- their functions
Thalamus – main relay center for most types of information
- Receives information from almost every area of the CNS, and sends information to these same areas.
a. Sensory info – often makes first synaptic relay in thalamus & sent to cortex - Sensory, emotional, motor, arousal
a. The whole point of more synaptic connections – have more information processing and integrating info
- Helps contextualize information because it’s combining
Hypothalamus – homeostasis
Functions
1. Controls body temperature
2. Controls thirst and urine output
3. Controls food intake
4. Controls anterior pituitary hormone secretion
5. Produces vasopressin & oxytocin (neuroendocrines)
6. Controls uterine contractions and milk ejection
7. Serves as a major ANS coordinating center
8. Plays role in emotional and behavioral patterns, including reproduction, sexual orientation?
Hypothalamus and sexuality
1991 – Simon LeVay published a paper indicating a morphological difference in a nucleus of the hypothalamus between gay and straight men (INAH3)
o The area in gay men was anatomically more similar to females.
Suggested “sexual orientation has a biological substrate”
Often misinterpreted
1. Religious right – said being gay is a form of brain damage
2. Pro gay people – there is a “genetic cause”
• Also not what he said – only found correlation and biological substrate
Very controversial findings
a. Accused him of having an agenda – he was gay
• LeVay accused of being biased
b. In early 90s and 80s – terrible time to be gay
• AIDS epidemic – no effective treatment
• Fear and anger against gay people
His study was statistically well done – credited for being the pioneer of these kinds of study
Cerebrum
- evolutionarily
- how large
- surface area
- components
Evolutionarily, the newest
o Largest and most distinct part of human brain (makes up about 80% of total brain weight)
Intelligence comes from large surface area compared to other animals
o Gyri and sulci – folds; these are used as landmarks; increases surface area
a. Gyri – ridges
b. Sulci – valleys
Components
- Cortex
- Lateralization
- Wernicke’s and Broca’s area - White matter
- Basal ganglia
- Limbic system
Localization of function in the cerebral cortex
- outdated ideology
Lateralization – side do not have mirror functions; halves are not identical
o Ex. Left-handed persons brain is not a mirror image of right-handed person’s
Many functions are localized to one side – not always the case
1. Left side – for most people; language processing, math processing
a. Very little language processing on right side for most people
• 95% right handed people left dominant for language
• But only 80% left handed people left dominant for language
- many lefties process language on both sides (i.e. it’s complicated_
b. Speech – often
c. General interpretive center – language and math
2. Right side – for most people; spatial recognition, face recognition, aspects of emotion processing and artistic functions
a. Generalizations – not all people process on right side
Lateralization does not refer to right brain person (creative, artistic) vs left brain (logical and analytical) – this idea from 1960’s is considered scientifically unsound
o Stems from phrenology – brain functions were correlated with lumps on skull and brain
Some functions are not localized
o Auditory and visual cortex – both sides
Broca’s and Wernicke’s area
Connected via reciprocal connections (axons go both ways and communicate with each other)
Input for language processing – come from audio or visual information.
a. Listening or reading language
b. Sensory input goes from audio or visual cortex -> Wernicke’s -> Broca’s.
- Integration occurs between these two areas (back and forth)
- Information from Broca’s is then sent to motor cortex to initiate spoken or written action
Damage to either area can be devastating to communication – aphasia
a. Aphasia – inability to comprehend or formulate language
b. Many kinds – not always straight forward & one kind
• Lots of subtle variations – very complex
• Older textbooks may give very defined signs and symptoms
Damage to Wernicke’s area – generalized
a. Receptive aphasia – difficulty understanding spoken or visual language
- Sensory info goes here first
- Can be both spoken and visual language or just one or the other
b. Speech may be nonsensical because of trouble connecting words with meaning (word salad, Jargon aphasia)
- Wernickes = words strung together illogically (real words but don’t make sense structurally)
Damage to Broca’s area
a. Expressive aphasia – difficulty expressing ideas; “can’t get a sentence out”
- They know what they want to say
- May not be able to speak or write or both
b. Often can interpret simple words or sentences – may have trouble with more complicated ones with several elements.
- Having numerous elements in a single sentence
c. Words “distorted” – gibberish; mangle the sounds of the words
- No damage in motor areas (still functioning) – there is a disconnect in how they form proper words
Basal ganglia
- components & functions
- loss resulting in damage
Ganglia – collections of cell bodies (= nuclei).
o The neurons within basal ganglia communicate with each other, and with other brain areas
Several components – form a complex circuit between the motor cortex, premotor cortex, cerebellum, thalamus, and other areas.
a. Through communication with each other and other areas
b. Largely involved in movement
- Pre and motor cortex & cerebellum areas – specifically involved in movement
- Thalamus – relay center between sensory and motor
Loss of any parts of the basal ganglia is devastating – often result in disorders of movement
1. Parkinson’s disease – loss of dopaminergic neurons in BG; causes tremors, loss of ability to move, cognitive deficits.
a. Loss of ability to initiate movement
• Ex. have difficulty getting up from a chair
b. Too much medication – overstimulates neurons; can cause Huntington’s like symptoms
• Ex. Michael J Fox
2. Huntington’s disease – loss of cholinergic neurons in BG
a. Activates the neurons that are lost in Parkinson’s – dopamine movement
b. Causes uncontrollable movements (chorea), loss of coordination, dementia
• Chorea – to dance
Limbic system
- phrenologically
- components & what do components do
- functions
Phrenologically – oldest part of the cerebrum
o Connected with many homeostatic control centers
o Very deep within brain
Components
a. Includes – amygdala, hippocampus, cingulate gyrus
- Hippocampus – learning and memory
- Amygdala and cing gyrus – emotional processing
b. Strongly connected with other areas – thalamus, hypothalamus, parts of the midbrain & parts of brainstem
Function – links higher processing with primitive emotions such as fear, aggression, reward, social and sexual behaviour.
a. “animal brain” – basic animal instinct emotions
b. Regulating basic emotional responses
i. Sensory stimulus – will be arousing stimuli of primitive emotions
• Ex. seeing a bear
ii. Cerebral cortex passes to limbic – processes and sends back to cortex
• Evokes emotion of fear – feedback processing
iii. Hypothalamus and brainstem
• Homeostatic response: Autonomic response – fight or flight activation pathway
• Long term stresses – can alter immune responses
• Somatic motor responses – will feel need to run from bear immediately
Damage to frontal lobe
A lot of what we know about the brain – came from bad situations
a. Ancient Greeks/romans/Persians – doctors and medics in battle
b. Damage to brain and how it affected their behaviour
- Many early scientists thought heart was the “brain”
Phineas gage
a. His job was to put dynamite into drilled holes – tamping down dynamite charge; caused rod to be driven through his brain
b. He survived
- Abolished a large portion of frontal cortex
- He got an infection – he made the recovery
c. Before accident – he was a very smart and nice person
i. After recovery – his personality was very different
• He became argumentative and difficult – swearing
• He changed jobs numerous times – couldn’t do a single thing a long time
d. Historically important cases – stimulated an entire area of research
- Another example – HM in the hippocampus
