Week I - Nervous System Basics
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- Is the autonomic nervous system considered to be a part of the CNS or PNS?
- PNS
- Explain the location of spinal nerves in relation to their corresponding vertebral levels in the upper and lower spinal cord.
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Upper spinal cord - levels correspond closely to vertebral levels
Lower spinal cord - levels are higher than vertebral levels - What neuronal contents are found in gray matter?
- neuronal somata, dendrites, axonal processes, glial cells
- What neuronal contents are found in white matter?
- pathways (tracts, fasciculi) containing myelinated axons and glial cells
- In the brain where is gray matter located in respects to white matter?
- gray matter is located outside (white matter is found deep to gray matter)
- In the spinal cord where is gray matter found compared to white matter?
- Gray matter is located centrally - gray matter is found deep to white matter
- define and give an example of a multipolar neuron
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(one axon, multiple dendrites)
interneurons - define and give an example of a bipolar neuron
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(one axon, one dendrite)
retinal ganglion cells, olfactory neurons - define and give an example of a pseudounipolar neuron
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(one axon)
Dorsal root ganglion - What is the RER of neurons called? More specifically, where is this RER found?
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Nissl substance
found in dendrites and NEVER in axons - free ribosomes are very characteristic of neurons. How are they arranged in the neuron?
- arranged in polyribosomal rosettes of 5-6 ribosomes forming a central core.
- This is a prominent organelle in many types of neurons. It is found in the cell body, dendrites, and within the axons.
- SER - occupies the space between the RER
- This organelle has Nissl bodies clustered on either side of it. It functions in protein glycosylation / modification
- Golgi apparatus
- This neuron "part" contains acid phosphatases and is involved with degradation of either internal or phagocytosed materials.
- lysosomes. (note: peroxisomes are not very numerous in neurons)
- What are lipofuscin granules?
- the "wear and tear" pigment: tend to accumulate in the neuronal cytoplasm with age.
- Where are mitochondria found in the neuron?
- found in all parts of the neuron
- neuronal mitochondria are in constant motion: they travel between stacks of ER in "roads" called __________.
- plasmastrassen
- Cilia - where found in neurons, function?
- cilia are sometimes found in neurons. Function ill-defined. (may be vestigal)
- Which one (axons or dendrites) appear to taper from the cell body outwards?
- dendrites taper (axons stay the same)
- Where in the dendrite are most synapses found?
- on dendritic spines
- dendritic spines are dynamic and can change shape in response to chronic stimulation. Why would they want to do this?
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1. To increase surface area for synaptic contact
2. To alter the physioelectrical properties of the dendritic surface. - Dendrites can alter their size and shape in response to chronic stimulation. How do they do this?
- By filopodeous outgrowth (dendritic branch will extend)
- There are two kinds of axons (classified on how far they project). What are they called, what is the difference and which are myelinated?
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1. local circuit neurons - project locally, unmyelinated
2. projection neurons - project across long distances, myelinated - What is the function of the axon hillock?
- Site of integration (summation) of all the incoming stimuli to the neuron. This is where the neuron "decides" wether to fire an AP or not.
- Which part of the axon does not contain RER or a Golgi apparatus?
- The axon cylinder
- Define axoplasmic flow - elaborate on the directions of flow.
- flow/transport of molecules throughout the axon. Flow can be anterograde (forward/away from cell body) or retrograde (backward/towards cell body)
- Fast axonal transport relies on microtubules and their associated motor proteins called ___________.
- Kinesins
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What would stimulate structural change in an axon?
How is this mediated? (which cell part) -
chronic stimulation, learning and memory, response to some forms of injury
mediated via axonal growth cones - Two molecular signals that the filopodia of growth cones look for are?
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N-CAM (cell adhesion molecule) &
NGF (neurotrophic agent - neuronal growth factor) - What are the three types of synapses?
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1. chemical
2. electrical
3. neuromuscular - chemical synapses release ______, _________ or _______ into the synaptic cleft.
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chemical signals
neurotransmitters
neuromodulators - A chemical synapse that releases a neuromodulator acts via which mechanism?
- second messenger system response
- What exactly is an electrical synapse?
- A gap junction that allows direct communication between adjacent cells. (Uses ions, Na+, K+, Ca++)
- Of chemical and electrical synapses: which one is unidirectional? Which one is bidirectional?
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unidirectional - chemical
bidirectional - electronic - in the neuromuscular junction the neurotransmitter is always _______ and it is always ________ (+) or (-).
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acetylcholine
excitatory (+) - neurotransmitter receptors embedded in the postsynaptic membrane are usually what type of receptor/channel?
- usually chemically - gated ion channels
- Which is more abundant in the CNS - neurons or glial cells?
- glial cells (~10 times more)
- Are astrocytes and oligodendrocytes classified as microglia or macroglia?
- macroglia
- Where are protoplasmic astrocytes located?
- In the gray matter of the CNS
- Where are fibrous astrocytes located?
- In the white matter
- The functions of astrocytes are many. If summarized, what would you say they are?
- Support cells for the neurons
- What is the glia limitans and what makes it up?
- glia limitans - shields CNS from overlying pia mater and CSF; made from the cell bodies or end feet of astrocytes
- How do astrocytes contribute to the Blood-Brain-Barrier?
- by forming a wall of end feet that surrounds the parenchymal side of capillary endothelium
- Which one (oligodendrocytes or Schwann cells) can individually provide myelin for many different axons?
- Oligodendrocytes (Schwann cells can only provide myelin for one axon)
- Where are interfascicular oligodendrocytes found?
- inbetween nerve fibers in the white matter
- Are oligodendrocytes found in gray matter? If so, where are they found?
- Yes. They are found associating with nerve fibers or forming satellite cells that associate with the neuronal perikaryon
- Oligodendrocytes are found in the ____; Schwann cells are found in the _____.
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O's -> CNS
S -> PNS - What is the scoop on microglia?
- microglia are normally quiescent, but on occasion they can mediate neuro-immune interactions by becoming phagocytically active and demonstrating antigen presentation.
- What will activate microglia?
- cerebral trauma, ischemia, seizure activity, infection
- Where are ependymal cells found and what is their function?
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line the ventricles and central canal of spinal cord.
function - cilia produce current for directional flow of CSF. - What makes up the dura mater?
- a heavy connective tissue sheet covered by a thin layer of sinple squamous epithelium.
- What is the name of the space between the dura and the arachnoid?
- The subdural space
- How many choroid plexi do we have and where are they?
- Four. One in the medial wall of each lateral ventricle; one in the third and one in the fourth ventricles.
- Function of choroid plexus?
- make CSF from plasma
- Total volume of CSF made in the average human per day?
- ~400 mL
- What are the ventricles embryologically derived from?
- the lumen of the neural tube
- What structure connects the lateral ventricles with the third ventricle?
- THe foramen of Monro (interventricular foramen)
- What structure connects the IIIrd ventricle with the IVth?
- The cerebral aqueduct (of Sylvius)
- How does the CSF exit into the subarachnoid space?
- via the IVth ventricle foramina: lateral (2) - Foramen of Luschka and medial - Foramen of Magendie
- Where is the vasculature that supplies the dura found?
- in the subarachnoid space
- What is the name of the structures that anchor the arachnoid menix to the pia mater?
- arachnoid trabeculae
- Which CSF cistern is used clinically to tap for CSF and at what part of the body is it at?
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The Lumbar Cistern
Vertebral levels L4-5
(the spinal cord ends at L1-2) - The choroid plexus secretes about 80% of CSF. Where does the other 20% come from?
- metabolic water (12%) and secretions by the ependyma of ventricles (8%)
- What types of molecules are transported through the blood brain barrier?
- ions and proteins
- How much CSF (on average) is found in the CNS?
- 140 mL
- What is the relationship of glucose in the CSF vs. the plasma?
- CSF glucose is ~66% of plasma glucose
- Is there a Na+/K+/ATPase that maintains CSF concentrations?
- Yes - this pump is essential for maintaining ion concentrations in the CSF
- Compare protein levels in the CSF vs. the plasma. What are the contents of CSF protein?
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CSF protein is LOW compared to plasma protein.
CSF protein is mainly albumin (80%) with some gamma globulins (5-10%) - Are there red or white blood cells found in CSF?
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should be no RBCs
A few WBCs are normal (0-5/mL) -
High RBC levels in the CSF could indicate __________?
High WBC levels in the CSF could indicate _________? -
RBCs-subarachnoid hemorrhage
WBCs-infection - Describe the circulation of CSF
- from ventricles (out the 3 foramina of the IVth ventricle) into the subarachnoid space - To superior sagittal sinus and it's lacunae - enters venous circulation
- What causes a movement of CSF throughout the CNS?
- Pressure differences cause CSF mvmnt. (venous circulation has low pressure, SAS has higher pressure, choroid plexus has an even higher pressure)
- Which type of hydrocephalus leads to increased intracranial pressure? What, in general, causes it?
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communicating hydrocephalus. Caused by
increased CSF production and normal reabsorption OR normal CSF production and decreased reabsorption - Noncommunicating hydrocephalus results from blocked CSF flow. what structures could be blocked to produce this?
- foramen of Monro, Luschka, cerebral aqueduct or decreased reabsorption across the arachnoid villi.
- Do axons of somatic motor neurons contain synapses in the PNS?
- NO. somatic motor neurons synapse in the ventral horn.
- Do axons of visceral motor neurons contain synapses in the PNS?
- YES. visceral motor neurons synapse, often in the sympathetic ganglion
- Preganglionic sympathetics arise from what spinal cord levels?
- T1-L2
- Preganglionic parasympathetics arise from what spinal cord levels?
- S2-4
- Where do dorsal and ventral roots join to form spinal nerves?
- at the intervertebral foramen
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How many vertebrae?
How many pairs of spinal nerves? -
33 vertebrae
31 pairs of spinal nerves - Where does C1 spinal nerve exit? What about C8?
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C1 exits ABOVE the C1 vertebra pedicle
C8 exits BELOW the C7 vertebra pedicle - What is different about the C1 spinal nerve compared to the other spinal nerves?
- C1 is somatic motor only. There is no DRG or dorsal root.
- Where do spinal cord levels exit after C7?
- Starting with spinal nerve C8, the nerves (and all spinal nerves below C8) exit below the corresponding vertebral pedicle.
- What do dorsal rami innervate?
- dorsal rami innervate the deep back muscles and the skin of the back of the head.
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Ventral rami may have up to 3 branches:
1. Gray communicating ramus ________.
2. White communicating ramus ______.
3. Ventral ramus ________. -
1. Grey communicating ramus is found in all spinal nerves
2. White comm. ramus is found from T1-L2 only.
3. Ventral ramus is a continuation to the periphery - Peripheral nerves are referred to as motor, sensory or mixed. However, what do ALL peripheral nerves have?
- ALL peripheral nerves carry visceral (sympathetic) efferents and afferents.
- What are the 4 cranial nerves that have autonomic components? (parasympathetic preganglionic)
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CN III oculomotor
CN VII facial
CN IX glossopharyngeal
CN X vagus - Cranial nerves that are SVE provide motor innervation to which muscles?
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SVE - special VISCERAL effer.
to skeletal muscles of pharyngeal arch derivation (larynx, pharynx, face, mastication) - Which CNs are SSA?
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CN II - sight
CN VIII -hearing, equilibrium - Which CNs are SVA?
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CN IX, VII - taste
Cn I - smell -
Important cervical dermatomes:
C2
C6, C7, C8 (respectively) -
C2 - EOP
C6 - thumb, C7 - middle finger, C8 - little finger - What are the six internal bones of the skull?
- ethmoid, inferior nasal concha, palatine, vomer, lacrimal, ossicles
- Which bone makes up a portion of both the cranial vault and the internal bones?
- The ethmoid bone
- When the skull cap, brain and meninges are removed the cranial fossa are exposed. What are the three cranial fossae?
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anterior
middle
posterior - The foramen cecum is found in the _________ cranial fossa. What structure passes through it?
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* anterior cranial fossa
* The emissary vein passes through it - Through which foramina do the posterior and anterior ethmoidal nerves and vessels pass?
- anterior and posterior ethmoidal foramina
- Through which foramen do the olfactory nerves (CN I) pass through?
- The cribiform plate
- The optic canal has what structures pass through it?
-
optic nerve (CN II)
Opthalminc artery - Which structures pass through the superior orbital fissure?
- CNs III (oculomotor), IV (trochlear), VI (abducens), branches of V1 (opthalmic of trigeminal - frontal, nasociliary, lacrimal), superior opthalmic vein
- V2, the maxillary division of the trigeminal nv. passes through which foramen?
- foramen rotundum
- The foramen ovale has what structures pass through it?
- V3 (mandibular division of trigeminal)
- What passes through the foramen spinosum?
- middle meningeal artery
- which foramen do the internal carotid artery and carotid nerve plexus pass through?
- the carotid canal
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The lesser petrosal nerve is a branch of __________.
The greater petrosal nerve is a branch of _________. -
lesser petrosal -> branch of CN IX (glossopharyngeal)
greater petrosal -> branch of CN VII (facial) - what structures pass through the internal acoustic meatus?
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CN VII (facial)
CN VIII (vestibulocochlear)
labrynthine artery - what structures pass through the jugular foramem?
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CN IX (glossopharyngeal)
CN X (vagus)
CN XI (spinal accessory)
inferior petrosal sinus
sigmoid sinus
posterior meningeal artery - What are the two layers of the dura mater?
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1. endosteal layer (bound by Sharpey's fibers to cranium)
2. menigeal layer - From what does the dura mater recieve its sensory innervation?
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mainly V1, V2, V3
also CNs X and XI - what is the name of the major blood vessel that supplies the dura mater?
- middle meningeal vessels
- A rupture in the middle meningeal vessels will result in a ___________ hematoma.
- extradural hematoma
- where is the falx cerebri found?
- the falx cerebri is found inbetween the cerebral hemispheres.
- a rupture in the superior cervical vein would cause what type of hemorrhage?
- subdural hemorrhage
- a cerebral aneurism would cause what type of hemorrhage?
- subarachnoid hemorrhage
- the common carotid artery is a branch of the _________ artery.
- brachiocephalic
- Which carotid has no branches in the neck?
- the internal carotid
- the vertebral arteries are branches off of the ____________ artery?
- subclavian
- which artery of the head and neck has lots of "bends" and therefore is susceptible to emboli lodging in these bends?
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the internal carotid
(bends appear as it passes through the cavernous sinus) - name the 6 arteries that contribute to the cerebral arterior circle
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1. internal carotid
2. PCA 3. MCA 4. ACA
5. Ant. comm. artery
6. Post. comm. artery - the opthalmic artery is a branch of which artery?
- the internal carotid
- T/F: the retina has arteries.
- FALSE: the retina is avascular
- there are anastomotic connections between the internal and external carotids. Describe 3 of them.
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1. dorsal nasal (from IC to opthalmic) and angular (from EC to facial)
2. dorsal nasal to infraorbital (EC to maxillary)
3. supraorbital (IC) and frontal (EC) - What is the common drainage point for the following veins: supraorbital, supratrochlear, dorsal nasal, pterygoid plexus, emissary, opthalmic. Clinical significance?
- The canvernous sinus is the common drainage point. Bacteria that enter the cavernous sinus have easy access to the CSF -> result is meningitis