Structure & Function Flashcards
What is the CNS? What is the peripheral nervous system?
What are bundles of neuronal cell bodies called in each? What axons come into/out of each?
1) CNS = brain + spinal cord, communicates via peripheral nervous system
2) peripheral nervous system - everything outside the CNS, convey info b/w peripheral structures and CNS
3) CNS- called nuclei
PNS- called ganglion
4) sensory neurons (afferent) come INTO the CNS and motor axons (efferent) LEAVE the CNS
Somatic/autonomic systems:
functions/signals carried
where are neurons located
1) Somatic- carries signals to/from muscles, tendons, joints, skins; conveys pain, temp, touch, proprioception (self-awareness)
Motor neurons- ventral horn of spinal cord
Sensory neurons- dorsal root (spinal) and cranial nerve ganglia
2) Autonomic- carries signals to/from internal organs; conveys distension
either parasympathetic (dine and recline) or sympathetic (flight or fight)
Motor neurons- preganglionic are in the CNS
postganglionic neurons are in PNS ganglia
What are the classifications for neurons? Classify motor and sensory neurons and where they are located
Multipolar, bipolar, unipolar- number of dendritic processes attached to cell body Motor neuron (efferent)- multipolar, carry info AWAY from CNS; located in ventral horn of spinal cord Sensory neuron (afferent)- unipolar, carry info TO CNS; located in dorsal root ganglia or cranial nerve ganglia
What are the spinal cord segments? How do spinal nerves exit?
1) 31 segments/spinal nerves
From top of spinal cord: cervical (8), thoracic (12), lumbar (5), sacral (5), and coccygeal (1)
2) spinal nerves exit the vertebral canal through the intervertebral foramen
C1-C7 exit ABOVE (E.g. C3 exits between C2 and C3)
C8 and below all exit BELOW (e.g. T5 exits between T5 and T6)
How does the spinal nerve attach to the spinal cord? Describe structure and what it innervates
1) Spinal nerve attached to cord via ventral and dorsal roots
ventral- ONLY motor neurons
dorsal- ONLY sensory neurons
2) Dorsal and ventral roots fuse at spinal nerve, which branches again into dorsal ramus and ventral ramus
3) Dorsal rami innervate:
-skin on back
-true back muscles (e.g. erector spinae)
-zygapophyseal joints (joint bw articular processes of two adjacent vertebral processes- allow for flexion/extension of vertebrae)
Ventral rami innervate:
-everything else
What are dermatomes?
Skin slices that divide up the body- each dermatome is innervated by ventral or dorsal rami
They overlap–> for complete anesthesia you need to knock out segments before and after e.g. for T10 dermatomal segment anesthesia, knock out T9, T10, and T11 ventral rami
Describe the parts of the autonomic nervous system and how nerve fibers are distributed
Autonomic nervous system is part of the peripheral nervous system; is comprised of sympathetic and parasympathetic divisions
Sympathetic- fight or flight, nerve fibers distributed with spinal nerves/blood vessels
Parasympathetic- dine and recline, nerve fibers distributed with cranial nerves and pelvic autonomic nerves
Compare motor neurons of somatic and visceral(autonomic) systems
1) Similarities- both multipolar neurons, carry signals away from CNS
2) Differences-
- structures innervated- voluntary skeletal muscle (somatic), smooth muscle and cardiac muscle and glands (autonomic)
- pathway- 1 motor neuron (somatic), 2 motor neurons with preganglionic in CNS and postganglionic in PNC fibers (autonomic)
Compare motor neurons of the sympathetic and parasympathetic system
1) Similarities: require 2 neuron pathway with 1st in CNS, 2nd in PNS
2) Differences:
-functions- fight or flight (symp), dine and recline (parasymp)
-sympathetic have short preganglionic and long post ganglionic
parasympathetic have long preganglionic and short post ganglionic
-location of preganglionic- sympathetic in lateral horn of T1-L2, parasympathetic in brainstem or sacral spinal cord
-location of postganglionic- sympathetic in paravertebral/prevertebral ganglia, parasympathetic in terminal parasympathetic ganglia
*sympathetic neurons all over the body
Describe schematic pathway of sympathetic motor nerve innervation to the trunk
Trunk innervated by T1-L2 postganglionic sympathetic nerve fibers
1) preganglionic cell body of motor neuron in lateral horn
2) axon exits via ventral root, spinal nerve, ventral ramus
3) enters paravertebral ganglion (sympathetic chain of ganglia next to vertebral column) via white ramus communicans
4) preganglion synapses onto postganglionic cell bodies
5) postganglion axon exits via gray ramus communicans into ventral ramus
6) distributed to its final destination
Describe schematic pathway of sympathetic motor nerve innervation to the upper/lower limbs
Upper/lower limbs do not have preganglionic cell bodies nor white rami communicans (white rami for preganglionic neurons)
1) preganglionic cell body of motor neuron in lateral horn
2) axon exits via ventral root, spinal nerve, ventral ramus
3) enters paravertebral ganglion (sympathetic chain of ganglia next to vertebral column) via white ramus communicans
4) does NOT synapse here, either ascends or descends the paravertebral ganglion chain
5) then it synapses on the postganglionic neuron attached to the target spinal cord segment
6) postganglion axon exits via gray ramus communicans into ventral ramus
7) distributed to final destination
Describe general distribution of parasympathetic motor nerve innervation
- More limited distribution than sympathetic system
- Neurons distributed to visceral structures throughout the head, neck, thorax, abdomen, pelvis, and perinuem
- does not innervate smooth muscle/glands associated with somatic structures –> not in trunk or limbs
- Craniosacral outflow
Compare sensory neurons of somatic and visceral (autonomic) systems
1) Similarities: unipolar neurons with cell bodies in a ganglion
same pathway- one motor neuron from dorsal root to dorsal horn
2) Differences:
-structures innervated- skin muscle + joints (somatic), visceral glands + blood vessels (autonomic)
-sensations- pain, temp, touch, prioprioception (somatic), distension, hunger, nausea (autonomic)
-location of cell bodies- dorsal root ganglia from C2-coccyx (somatic), dorsal root ganglia from T1-L2 (autonomic)
*sensory follows same pathway as motor
Why does referred pain occur? Describe the schematic pathway involved in referred pain from the heart
1) Referred pain occurs because visceral/autonomic afferent/sensory fibers synapse on the same neurons in the dorsal horn of spinal cord segments T1-L2 as do somatic afferent/sensory fibers (follow same pathway back)
so the brain is confused whether the pain is coming from the heart or upper arm because those sensory neurons are in the same place
2) Heart –> visceral nerve –> superior cervical ganglion –> descends chain to paravertebral ganglion –> exits via white ramus communicans –> ventral ramus –> spinal nerve –> dorsal root ganglion –> dorsal horn –> SYNAPSES
Where does the spinal cord end? What segment of the vertebral column is present in this region?
What can be done in that area? What is the landmark in that area?
1) Ends at level of L1/L2, tapers at conus medullaris, nerve roots that continue down from there are called cauda equina
* lower sacral segment*
2) Can insert needle to draw fluid
3) iliac crest which you can palpate, is at L4
What is the intervertebral disk? What is its function? What is it composed of?
Why do we get shorter as we get older?
1) cartilaginous joint between vertebral bodies
2) shock absorber, mobility between vertebrae
3) outer lying anulus fibrosis - made of cartilage and connective tissue
inner nucleus pulposus- few cells, lot of ECM with proteoglycans, water-containing (adult remnant of notochord)
*distributes pressure (water squeezed out- shorter end of day)
4) fewer proteoglycans in the np–> less water bound–> shorter
What is the intervertebral foramen? What is its function? What forms its boundaries?
1) space between two spinal vertebrae
2) passageway of spinal nerves in/out of the vertebral column
3) Anterior: vertebrae above, below + intervertebral disk
posterior: superior/inferior processes + facet joint
How are spinal nerves numbered?
Cervical: C3 nerve passes between vertebrae C2 and C3
Thoracic/lumbar: L1 nerve passes through vertebrae L1 and L2
1) What is the most common direction of a herniated nucleus pulposus? Why?
2) When do hernias become symptomatic? How do we trace the cause?
1) Posterior laterally
posterior is where the anulus fibrosis is weakest
there is a posterior longitudinal ligament so the np will be pushed laterally
2) when the spinal nerves/roots become compressed- can trace back which nerves depending on the affected dermatome/myotome
Dermatome symptoms- tingling (paresthesia), pain, reduced sensation
Myotome symptoms- muscle weakness (paresis), paralysis
What can cause impingement of spinal nerves/roots? What number nerve is affected?
1) -herniated nucleus pulposus (on anterior side)
-osteoarthritis at facet joint (on posterior side) - osteophyte bone spurs encroach on foramen
-stenosis (caused by thickening ligamentum flavum or facet joint)
-spondyolysis/spondyolisthesis
2) number nerve below the intervertebral disk e.g. L5 nerve affected when hernia at IV disk L4/L5
can also affect multiple nerves if the hernia is more medial
What are the types of stenosis?
Central stenosis- entire vertebral canal narrows, can compress nerves/roots, cauda equina, spinal cord
Foraminal stenosis- IV foramen narrows, compresses spinal nerves/roots
What is spondyolysis? What is spondylolisthesis?
Spondyolysis- fracture of the isthmus (neck of the scottie dog)
Spondyolisthesis- breakage of the isthmus
both cause nerve compression
Define electrical conductance, membrane diffusion potential, current , electrogenic, diffusion potential
Membrane potential - voltage difference between inside/outside plasma membrane because of ion concentration gradient
Current- flow of ions
Electrical conductance- ability to conduct current
Electrogenic- ability to create electricity bc of ion gradient–> conduct action potential e.g. pump
Explain distribution of Na+, Cl-, K+ across plasma membrane
Describe action of ATPase and its role
More Na+, Ca2+ outside the cell, more K+ inside the cell
some Na+ will leak inside and K+ outside down their concentration gradient
but ATPase maintains the electrochemical gradient by pumping 3 Na+ out and 2K+ in - so outside of cell is more positive than inside
What is the resting membrane potential (RMP) for a motor neuron? What is it influenced by?
1) -90mV
2) RMP set by K+ concentration gradient; larger the gradient –> more negative the cell
What is the Nernst potential?
Membrane potential at which there is no net flux of a given ion
Describe the phases of an action potential
1) Resting-
2) Depolarization
3) Repolarization
4) Refraction
What happens if you have hyperkalemia?
hyperkalemia- high plasma K+
Acute: depolarizes the cell –> excitability
Chronic: membrane potential clamped –> Na+ voltage gated channels inactive –> impairs excitability–> fewer action potentials –> leads to arrhythmia
Compare and contrast the properties of pacemaker and plateau action potentials
Pacemaker potential (SA node): self-perpetuating without stimulus gradual depolarization initially due to If and Ca2+ in, K out; Ca2+ channel opening causes action potential, repolarization via K+ channels Plateau potential (smooth muscle, cardiomyocyte): rapid Na+ depolarization, inward Ca2+ and outward K+ cause plateau phase, then rapid K+ repolarization
How is the action potential propagated along an axon towards the axon terminal?
action potential excites adjacent portions through Na+ migration – > adjacent membrane depolarization –> Na+ channels opened
What is the impact of motor neurons that are myelinated?
Action potentials move a lot faster because of saltatory conduction as they jump from one unmyelinated part (node of Ranvier) to another
unmyelinated- cable-like, takes longer e.g. pain fiber
Describe the sensation of pain. How do local anesthetics work?
1) Stimulus –> activates nocicepters –> action potential in pain afferents –> Ascend spinal cord –> end in thalamus and relay pain
2) Local anesthetics block the action potential in afferent sensory neurons–> protonated in the cell –> bind to Na+ channels and inactivate –> threshold not reached –> no action potential
Describe differences between electrical and chemical synapses. What are excitatory vs inhibitory neurotransmitters?
Electrical- v rare, in connexons in gap junctions, physical connection
Chemical- use neurotransmitters to relay action potential
e.g. acetylcholine (for neuromuscular)
excitatory- glutamate, aspartate
inhibitory- GABA, glycine
Describe how chemical synapses work. Difference between ionotropic and metabotropic transmission
chemical synapse- where neurons signal to each other or muscle cells (neuromuscular junction)
1) Action potential activates Ca2+ channel in presynaptic membrane
2) Rapid Ca2+ influx
3) Ca2+ dependent signaling cascade
4) synaptic vesicles fuse with presynaptic membrane
5) neurotransmitters released
6) bind with receptor on postsynaptic membrane
7) response
8) transmission terminated when neurotransmitters broken down or taken up again in the presynaptic neuron
Ionotropic- activate ligand -gated ion channels directly - v FAST
metabotropic - includes receptor mediated signaling - much SLOWER
What is synaptic fatigue?
Comes from depletion of neurotransmitters, postsynaptic receptor desensitization, disruption in ion gradient of postsynaptic neuron
Determine effect of each agent on action potential/neurotransmission:
- Nicotine: is not hydrolyzed by cholinesterase.
- alpha toxins: are found in cobra venom and curare; toxins out-compete ACh for binding to the ACh receptor. Although alpha toxins bind the ACh receptor, they do not activate it.
- beta-bungarotoxin: is a member of the family of cholinesterase inhibitors that are common in various arachnid and snake venoms. Bungarotoxins block the activity of cholinesterase.
- Botulinus toxin A, B, and C; tetanus: each block ACh release.
- Tetrodotoxin: is found in several marine species, It blocks voltage-gated Na+ channels in nerves and cardiac muscle.
- Dendrotoxin: derived from the venom of the green mamba snake, it blocks neuronal voltage-gated K+ channels in motor neurons.
- Nicotine: activation of the ACh receptor is more sustained than that induced by ACh.
- alpha toxins: The activation of ligand-gated Na+ channels within the post-junctional membrane is prevented.
- beta-bungarotoxin: promote highly erratic and abnormal muscle contractions that result in muscle spasm.
- Botulinus toxin A, B, and C; tetanus: prevent muscle contraction.
- Tetrodotoxin: depolarization within nerves is prevented; cardiac failure due to impaired cardiomyocyte contractility.
- Dendrotoxin: AP duration is increased, and this results in the enhanced release of ACh within the neuromuscular junction; hyperexcitability, convulsions may result.
How are action potentials initiated?
any event that depolarizes membrane potential e.g. electrical, chemical, mechanical
subthreshold changes due to subthreshold stimuli = graded potential
graded potentials can sum to reach threshold potential
Describe:
1) non-vascular circulation
2) cardiovascular
3) lymph vascular
1) Non-vascular circulation - fluid leaves vascular system, gong into extravascular space, and then reenters e.g. CSF, synovial fluid
2) Cardiovascular- 2 way system (heart –> tissues –> heart), heart acts asa pump that creates pressure gradient, in low pressure there are valves
3) Lymph vascular- 1 way system (tissues –> heart), no pump
T/F: All veins have valves
False. Portal veins do not have valves, neither do veins communicating between veins of face/scalp, nor dural venous sinuses within the skull
Lymph vascular system: What does it do? What are the pathways of drainage? What is the clinical relevance re: cancer? Where are the major lymph node groups?
1) Rid body of waste, toxins; transport lymph, which contains white blood cells
2) LHS of head/neck/thorax, left upper limb, EVERYTHING below diaphragm –> thoracic duct
RHS of head/neck/thorax, right upper limb –> right lymphatic duct
3) Need to know where lymphatic drainage of the breast occurs because cancer spreads through the breast first before metastasizing through the body
4) cervical (neck), axillary (arm), inguinal (groin), popliteal (knee), mastoid (head)
What are the main functions of the cardiovascular system. Describe in particular thermoregulation mechanisms
1) Transportation- O2, Co2, nutrients, waste
2) Communication- hormones
3) Thermoregulation- normally warm blood from artery is brought to cutaneous vasculature (ie skin) and heat is diffused, veins have cooler blood (how body maintains a constant temp)
BUT when its cold, need an A-V shunt; when shunt is open, blood flows from artery to vein without going to skin –> conserve heat, but deprive O2 to the skin –> ischemia –> frostbite
SO you have venae comitantes (paired veins), 2 veins flanking artery which creates thermal gradient –> allows heat to transfer –> conserve heat but dont reduce blood flow to skin e.g. in limbs, chest wall
examples: brachial artery, ulnar artery, radial artery
Describe:
End arteries
Collateral circulation
What is costal notching
1) End arteries - if you have occlusion–> no blood flow–> cell dies
anatomical - full responsibility for providing blood e.g. in retina
functional- shared responsibility, but cell will still die e.g. coronary artery –> myocardial infarction
2) Collateral circulation - anastomosis (connection) of arteries to have multiple pathways of blood flow –> no cell death *can only happen in veins without valves
e.g. in brain, limbs
3) costal notching - when aorta is occluded but internal thoracic arteries are fine –> intercostal arteries used as collateral pathways–> they grow thicker –> bone resorption (bone broken down) along rib, clinical finding for aorta obstruction
Describe the process of neurulation (ectodermal neural plate –> neuroectodermal tube).
What does the neural tube become?
1) begins at level of first 5 somites - post gastrulation and notochord
TF from mesoderm–> increased FGF, decreased BMP4 (wants to form epidermis)
cranial end –> chordin, noggin
caudal end –> FGF, Wnt, retinoic acid
2) Neural plate hinges and forms neural groove and neural folds
3) neural folds fuse in dorsal midline EXCEPT for rostral and caudal neopores –> forms neural tube
4) First rostral neopore closes, then caudal
5) caudal end formed by secondary neurulation of caudal eminence
*neural tube becomes brain and spinal cord (CNS)
Describe development of neural crest cells. What are their derivatives?
1) Neural crest cells detach rostral to caudal during neurulation and migrate
2) melanocytes, sensory ganglia, schwann cells, adrenal medulla, bones/conn tissue of the face, meninges, etc.
Describe the differentiation of somites (somites = segmented paraxial mesoderm).
1) Somites differentiate under influence of shh
low shh –> Dermomyotome (skin + muscle)
high shh –> sclerotome (bone vertebrae and ribs)
2) sclerotome cells migrate and surround notochord to form vertebral bodies and surround neural tube to form vertebral arches (pedicles + laminae)
somites C5-T1 = upper limb bud (C5 - T1 is brachial plexus)
somites L2-S3 = lower limb bud (L2-S3 is lumbosacral plexus)
# somites = # vertebrae, influences # of spinal nerves
3) dermomyotome splits into dermotome and myotome
myotome - muscles (back, limbs)
dermatome- skin
Describe the types of folding during neurulation and their effects (cephalocaudal folding)
lateral folding- creates gut tube, body cavities, brings embryo into the amniotic cavity
cranial folding- how mouth moves to ventral surface, heart moves down to thorax
caudal folding - establishes reproductive, urinary, digestive systems at caudal ends
Describe the changes in the position of the ending of the spinal cord during devlpt
early fetal devlpt- spinal cord is whole length of embryo
later fetal devlpt- differential growth so formation of cauda equina and filum terminale
birth- spinal cord ends at L3/L4
adult- spinal cord ends at L1/L2
Describe the most common neural tube defects
1) rostral neopore closing defects –> anencephaly
2) caudal neopore closing defects –> spina bifida
occulta- lack of fusion of vertebral arches (tamest) - mesoderm cant migrate between neural tube and ectoderm to establish vertebral arch, there is hair on top
meningocele- multiple vertebrae missing, protrusion of meninges but spinal cord normal
meningomyelocele- protrusion of meninges but spinal cord is not normal –> some neuro deficits
rachischisis- neural tube doesnt fuse- exposed neural tube tissue –> lots of neuro tube defects e.g. paralysis from waist down
Where does spinal cord develop from?
Cervical, thoracic, lumbar regions –> neural tube
*why spina bifidas occur in lumbar region
saccral region–> where old primitive streak was (primitive node to cloacal membrane) is –> mesoderm
Describe the process of limb development and rotation
Limbs formed in lateral plate mesoderm (secretes FGF) and induced by adjacent somites
upper limb bud- C5 to T1 somites, lower limb bud- L2 to S3 (devlps 2 days later)
3 axes:
1) proximo-distal- determines order of limb segments –> apical ectodermal ridge (AER) induced by BMP, leads to proliferation of mesenchymal core of limb buds and differentiation
2) rostro-caudal (anterior/posterior)- determines order of digits –> differentiation through zone of polarizing activity (ZPA) at caudal end which releases shh –> regulate hox gene expression
closest to ZPA –> digit #5
3) dorso-ventral axis- in the upper limb dorsal is extensor and ventral is flexor, switched in the lower limb
this is because lower limb rotates 180 degrees
