IC1- CNS Flashcards
What are the 3 parts the brain is divided into?
Forebrain, Midbrain and Hindbrain
The forebrain includes? (2)
- Cerebrum
- Diencephalon
The hindbrain includes? (3)
- Medulla oblongata
- Pons
- Cerebellum
The brainstem includes? (3)
- Midbrain
- Pons
- Medulla oblongata
How many pairs of cranial nerves and spinal nerves are there?
- Cranial nerves: 12 pairs
- Spinal nerves: 31 pairs
The cerebrum consists of 2 cerebral hemispheres. What are they separated by?
Longitudinal fissure
What are the 4 lobes of the brain?
- Frontal
- Parietal
- Temporal
- Occipital
The midbrain contains what cranial nerves (2)?
III and IV
What cranial nerves are the nuclei associated within the midbrain? (3)
What else are the nuclei associated with within the midbrain?
III, IV, V
Also associated with visual and auditory pathways
What are the cranial nerves of the hindbrain? (4)
V, VI, VII, VIII
The hindbrain contains which cranial nerves? (4)
V, VI, VII and VIII
What cranial nerves are the nuclei associated within the hindbrain? (4)
V, VI, VII and VIII
What are the 2 types of cells in the brain? Elaborate.
Neurons and non-neuronal cells (glial cells)
Neurons:
- Structural and functional
- Generate/ conduct impulses, are excitable
Non-neuronal cells:
- Non-conducting
- Support and protect neurons
- 10x no. of neurons
Does the cell body of neurons contain a nucleus, golgi complex and mitochondria?
Yes
Does the axonal cytoplasm contain ribosomes, RER and Golgi apparatus?
No
Describe the function of the fast component (50 - 400mm/day) and slow (1 - 4mm/day) component of the axon
Fast component (50 - 400mm/day):
- Transports cytoplasmic proteins and macromolecules required for metabolic and synaptic activity
Slow component (1 - 4mm/day):
- Transports cytoskeleton components down axon
What is the difference between anterograde and retrograde transport?
Anterograde transport:
- From cell body to axon
Retrograde transport:
- Waste materials from axon to cell body for removal
Dendrites conduct impulses ___ (toward/away) the cell body?
Toward
Compare dendrites to axons in terms of physical features and cellular components
Dendrites are relatively short and highly branched. Majority of cytoplasmic components present in dendrites except for Golgi apparatus.
What is the role of dendritic spines?
To increase surface area -> increase ability of dendrites to receive more information
The presynaptic membrane contains voltage-gated Ca2+ channels. Describe how an action potential triggers exocytosis of neurotransmitter into synaptic cleft
- Arrival of an action potential at an axon terminal ->
opening of Ca2+ channels -> influx of Ca2+ ions ->
rise in the cytosolic Ca2+ level - Triggers exocytosis of the neurotransmitter into
the synaptic cleft
Explain what happens upon binding of neurotransmitter to receptors on excitatory synapse
Binding of neurotransmitter
to its receptors -> opening of Na+ channels in the postsynaptic membrane -> depolarization* of the membrane -> action potential in the postsynaptic cell
Explain what happens upon binding of neurotransmitter to receptors on inhibitory synapse
Neurotransmitter binding ->
opening of K+ or Cl- channels in the postsynaptic membrane -> hyperpolarization* of the membrane ->
no action potential in the postsynaptic neuron
What receptors are typically found on inhibitory synapses?
GABA receptors
What are the 3 types of glial cells in the CNS?
- Astrocytes (25%)
- Oligodendrocytes (60-80%)
- Microglia (5-10%)
Function of oligodendrocytes? (1)
Myelin sheath formation
Function of astrocytes? (8)
- Blood-brain barrier (regulate composition of intercellular envt and entry of substances into it)
- Structural support to neurons and ESPECIALLY synapses
- Scar formation
- Secretion of nerve growth factors
- Metabolize neurotransmitters (eg glutamate glutamine shuttle)
- Tripartite synapse
- Water transport
- Excess transport (cerebral edema)
What are the 2 types of astrocytes?
Fibrous astrocytes and protoplasmic astrocytes
Difference between fibrous astrocytes and protoplasmic astrocytes?
Fibrous astrocytes:
- Primarily in white matter
- Long
- Spindly processes with few branches
Protoplasmic astrocytes:
- Gray matter
- Thick
- Lightly branched processes
- Close to neuron cell bodies
What are the difference in functions of oligodendrocytes in white matter vs gray matter?
White matter:
- They are the predominant neuroglial cell
- Product myelin sheath around myelinated fibers in white matter
Gray matter:
- Closely associated with neuron cell bodies, function as satellite cells
What is a cell marker of oligodendrocytes?
CNPase
What is the difference between oligodendrocytes in CNS and in PNS?
In the CNS, individual
oligodendrocytes myelinate portions of several axons
In the PNS, oligodendrocytes are known as Schwann cells. Individual Schwann cells myelinate
portions of only a single axon
What is Nogo-A produced by oligodendrocytes and its function?
Nogo-A is a myelin associated neurite-outgrowth inhibitor.
It inhibits axonal regeneration following injury and ischemia in the CNS.
Describe microglia
Small phagocytic cells that enlarge and
become mobile after injury to the CNS
What are the functions of microglia? (5)
- Brain macrophages
- Immunocompetent
- Phagocytosis
- Involved in neuroinflammation: secretes proinflammatory mediators TNF-α, IL-1β
- Antigen-presentation (MHCII antigen)
In what diseases are microglia implicated in?
Alzheimer’s disease, Parkinson disease, cerebral ischemia (stroke)
What is the marker for microglia?
Lectin, OX42 (complement type 3 receptor)
What are the 3 connective tissue elements in the peripheral nerve structure?
- Epineurium
- Perineurium
- Endoneurium
Describe the epineurium
Connective tissue surrounding the entire nerve
Describe the perineurium
A layer of dense connective tissue around each fascicle of nerve fibres
Describe the endoneurium
A thin, reticular layer that surrounds each individual nerve fibre and contains Schwann cells
What do ganglia (located outside CNS) contain?
They contain satellite cells and connective tissue elements along with neurons
What are satellite cells (amphicytes)?
Satellite cells (amphicytes) form a capsule of cells around neuron cell bodies located in peripheral ganglia
What are the 2 pairs of arteries that supply blood to the brain?
- Left and right internal carotid arteries
- Left and right vertebral arteries
Where does the vertebral artery originate? How does it enter the skull?
Subclavian artery in the neck.
It enters the skull through the foramen magnum
The vertebral artery supplies which 3 parts of the nervous system through which 3 arteries?
Vertebral artery supplies blood to spinal cord, medulla oblongata and cerebellum.
Via the anterior spinal artery, posterior spinal artery and posterior inferior cerebellar artery.
The 2 vertebral arteries join to form a single artery in the midline called?
The basilar artery
The basilar artery gives off branches to supply which 3 parts? Through which 4 arteries?
Basilar artery supplies blood to the pons, cerebellum, and inner ear.
Via the anterior inferior cerebella artery, pontine branches, labyrinthine artery and superior cerebellar artery.
The basilar artery ends by dividing into?
The 2 posterior cerebral arteries
Where does the posterior cerebral artery supply blood to? (4)
- Midbrain
- Medial aspect of occipital lobe
- Base of temporal and occipital lobe
Where does the internal carotid artery originate from?
How does it enter the skull and where is it situated?
The common carotid artery in the neck
It enters the skull through the carotid canals and is situated within cavernous sinus
The internal carotid ends by dividing into?
The anterior cerebral artery and middle cerebral artery
Describe the anterior cerebral artery. (Where and function)
- Passes forward into the medial
longitudinal fissure and then sweeps back to the parieto-occipital sulcus - Supplies most of the medial surface of the hemisphere (except medial aspect of occipital lobe)
Describe the middle cerebral artery. (Where and function)
- Pass laterally between temporal and frontal lobes
- Emerges at lateral fissure, fans out to supply most of the lateral surface of the hemisphere (frontal, parietal, temporal and occipital lobes)
What is the Circle of Willis?
An anastomosis (connection) between the left and right arteries supplying the brain
Benefits of the Circle of Willis?
Limitation of this benefit?
Helps to supply blood to the opposite side if there is SLOW occlusion of artery on one side -> allows time for communicating arteries to enlarge and accomodate increased blood flow
Limitation: only works for SLOW occlusion, NOT fast occlusion
What does the anterior communicating artery help to connect?
Connects the anterior cerebral artery of both sides
What does the posterior communicating artery help to connect?
Connects the middle cerebral artery with the posterior cerebral artery
What medical condition can typically occur at the circle of Willis?
Aneurysms (abnormal out-pocketing of wall of a blood vessel) -> which can lead to stroke if it ruptures
Where does blood from the superficial part of the superior aspect of the brain drain into?
Into the superior sagittal sinus
Where does blood from the inferior part of the brain drain into?
Into the transverse sinus and superficial middle cerebral vein
Where does the superficial middle cerebral vein drains into?
The cavernous sinus
What is the cavernous sinus closely related to? (hint: includes cranial nerves)
Cranial nerves III, IV, V, and VI
and
A part of the internal carotid artery
Where does blood from the centre of the brain drain into?
The deep cerebral veins which drain into the venous sinus
Where does blood at the superior sagittal and straight sinuses flow into?
The transverse sinus -> sigmoid sinus -> internal jugular vein of neck
How does a subdural hemorrhage occur?
When cerebral vein ruptures at the superior cerebral vein as it drains into superior sagittal sinus
What is the SSx of subdural hemorrhage? How long does it take to occur and why?
SSx: dizziness,
headaches, apathy, falling,
confusion, and drowsiness
Takes weeks to occur as the venous pressure is low hence seepage is low
How does the brain capillaries form the BBB?
Function of BBB?
Brain capillaries have tight junctions between endothelial cells which form the BBB
BBB prevents the random entry of water soluble substances into the brain parenchyma
How are metabolites removed from the brain?
By the CSF
What produces CSF?
A delicate, lacelike structure called the choroid plexus in cerebral ventricles
How does CSF travel from the choroid plexus to bathe the brain and spinal cord?
- It flows from the lateral ventricle -> 3rd ventricle, via the cerebral aqueduct -> the 4th ventricle
- It then flows out of the 4th ventricle to bathe the whole brain and spinal cord
How is the CSF absorbed into the superior sagittal sinus?
By arachnoid granulations
What is the most inferior portion of the brain?
Medulla oblongata
What are the cranial nerves of the medulla oblongata? (4)
IX, X, XI, XII
What cranial nerves are the nuclei associated within the medulla oblongata? (5)
What else is the nuclei also associated with in the medulla oblongata?
V, IX, X, XI, XII
Also associated with cardiovascular and respiratory function
What does the cerebellum consist of?
What is it connected to?
A midline portion (vermis) and 2 hemispheres
Connected to the brainstem
Where does the spinal cord taper off into?
The conus medullaris
