chapter10 Flashcards
ANS
regulates and controls visceral functions, HR, BP, DIGESTION, TEMP, and REPRODUCTIVE FUNCTION.
How is visceral control achieved?
By reflex arcs that consist of visceral afferent neurons that send messages from periphery to CNS that receives this input and VISCERAL MOTOR OUTPUT.
In CNS, aside from the BRAIN and SP, what else are included?
CN II, retina
In CNS, what provides myelin?
Oligodendrocytes
In CNS, can axons regenerate?
NO
What are the components of PNS?
peripheral ganglia & cell bodies, sensory receptors, peripheral portions of SC & CN (except CN II); afferent & efferent
In PNS, what provides myelin?
Schwann cells
In PNS, can axons regenerate?
YES
Human brain contains….
more glial cells then neurons
Corollary
Damage to specific part of brain causes predictable symptoms, enabling physician to establish anatomical location of prob
What fibrillary structures composed the specialized regions of neurons?
- neurofilaments/intermediate filaments
- microtubules
- thin filaments
What do the cytoskeleton enable axons and dendrites to do?
Capacity to change shape
Plasticity believes to play role in synaptic alterations linked with learning and memory
Cell body
Responsible for neuronal housekeeping functions and synthesis, processing of proteins
Dendrites
Receive info
Contains receptors that bind and respond to NTs
Contains mRNA, golgi, ribosomes
Axons
Send info away from cell body
self reliant in energy metabolism, taking up glucose and oxygen to produce ATP
Long and have high density of Na+ channels
Initial segment of axon
spike initiation zone
Untampered, unmyelinated region where AP arises
Non-myelinated axon
AP travels down the axon by CONTINUOUS PROPAGATION
Myelinated axon
AP jumps from one node of Ranvier to another by SALTATORY CONDUCTION.
How are presynaptic terminals designed?
designed for rapid conversion of neuron;’s electrical signal into a chemical signal
What does a synapse comprise of?
Presynaptic terminal, postsynaptic membrane and space b/w 2 synaptic clefts
How can amplification of signals occur?
dendritic spines; infolding of plasma membrane
Why can neurons be thought of as highly specialized endocrine cells?
Neurons Package and store
hormones and hormone - like molecules which the
neurons release rapidly into the extracellular
space by exocytosis in response to external stimuli
What play important roles in dictating vectorial transport of proteins ana organelles?
microtubule-associated proteins, microtubules
What are the 2 major MAPs found in brain?
MAP-2 (High molecular weight protein); MAP-1
Tau proteins (low molecular weight)
MAP-2
abundant in dendrites and assist in dendrite formation
Tau proteins
confined in axons
prevent formation of axon without altering formation of dendrites
What causes hyperphosphorylated tau proteins?
pathological aggregates called NEUROFIBRILLARY TANGLES that are a hallmark in Alzheimer’s.
Where are the plus ends of microtubule of axons pointed to?
Away from cell body, polarizing flow of material into and out of axon.
How are microtubules organized in dendrites?
Do not form consistent orientation
function is similar to soma/cell body
What are principal freight of fast axoplasmic transport?
Membranous organelles including vesicles and mitochondria
where proteins, lipids, polysaccharides are sequestered for a speedy ride
What is a microtubule dependent-motor protein?
KINESIN - fast anterograde transport
What is the function of kinesin?
an ATPase helps microtubule to move organelles and vesicles
What to axons use for fast retrograde transport (movement of materials back toward cell body)?
Brain dynein or MAP-1C
How does MAP-1C move?
also an ATPase that helps microtubules transport materials but direction is going back to cell body.
What is a cortical motor neuron?
Affects different brain areas - dorsal root ganglion
a projection neuron
Cortical inhibitory neuron
an interneuron
Affects only nearly neurons - retinal bipolar cell
What is an example of a pyramid shaped cell?
Hippocampal pyramidal neuron
What is an example of radial-shaped cell?
Cortical stellate cell
Examples of afferent/sensory neurons
- sensory nucleus of CN V (trigeminal)
- dorsal root ganglion cell
examples of efferent/motor neurons
- spinal motor neurons
- motor neurons in ANS
How does information travel in special visceral neurons”
Info travels to or from structures derived from branchial arch region of embryo
Special somatic neurons
Handle only sensory info
Neurons arise from organs of special sense
What germ layer does NS and skin arise from?
Ectoderm
NOTOCHORD
specialized cord of mesodermal cells underling ectoderm
What forms the neural tube and what cells direct process of neurulation?
Neuroectoderm; directed by cells of not-chord
What structures arise from neural tube?
Brain, spinal cord
What arise from lumen of neural tube?
4th ventricle of brain; central canal of SC
What arise from NEURAL CREST?
- majority of PNS
- peripheral cells of ANS
- chromaffin cells of adrenal medulla
- sympathetic ganglia
- unipolar neurons
- satellite cells
- Schwann cells
- pigment cells of skin
- CN V, VII, IX, X
what arise from telencephalon?
Basal ganglia. Cerebral cortex
What arise from diencephalon?
thalamus, hypothalamus, subthalamus, neurohypophysis
What forms from mesencephalon?
midbrain
metencephalon forms…
pons, cerebellum
myelencephalon forms…
medulla
What is the groove formed as neural tube thickens with cell proliferation?
Sulcus limitans
The sulcus limitans divides neural tube into
Basal plate - ventral; develops into ventral horn in SC; efferent neurons
Alar plate - dorsal; afferent neurons; dorsal horn
What are neuroepithelial cells?
Rapidly dividing stem cells that give rise to neurons and glial cells
what does the ventricular zone of neuroepithelial cells produce?
Progenitor cells that produce neurons, oligodendrocytes, astrocytes, ependymal cells
what influences rate of cell division?
Epidermal growth factor, platelet-derived GF, growth hormones
neuronal progenitor cells
appear earliest and produce
nearly the entire complement of adult neurons during
early embryonic life.
What helps neurons migrate to their anatomical positions?
Adhesion molecules
how do radial cells help neurons migrate?
Contacted by migrating neurons and they determine direction of neuronal migration
Cell-cell adhesion molecules
promote selective cellular aggregation
Examples: cadherins - ca2+ dependent
neural cell adhesion molecules (n-cam) - ca2+ independent
Laminin and fibronectin
extracellular matrix molecules/glycoproteins that form cellular roadway where migrating cells can interact
Secreted by astrocytes, neurons
Integrin (cell matrix adhesion molecule)
Bind laminin and fibronectin together making axons move together in fascicles
Expressed at axon surface
What is the ability of a cell to follow chemical signals emitted from target cell? Give example.
Chemotaxis; growth cones/regenerating axons
Netrin
attracts developing axons destined to cross midline
Cephalocele
partial brain herniation through skull defect - cranium bifidum
meningocele
meningeal herniation through skull or spine defect
Spina bifida occulta
vertebral arch defect ONLY
Spina bifida cystica
herniation of dura and arachnoid through vertebral defect
myelomeningocele
herniatIon of SC and meninges through vertebral defect
What are the ONLY NEURONS that can regenerate and divide throughout adult life?
Olfactory bulb neurons
What are the main cells that proliferate at the brain injury site?
Microglial cells
Astrocytic glial scar
- reaction of brain to injuries
- produced by enlargement of astrocytes and increased expression of glial acidic fibrillary protein
Lesion divides the axon in proximal and distal segments
Wallerian degeneration
Distal segment degenerates
Chromatolysis
process were neuron cell bodies swell and undergo characteristic rearrangement of organelles after axonal injury
What is transneuronal or trans-synaptic degeneration of neuron?
degeneration of healthy neurons that are synaptically connected to injured neurons
what is retrograde degeneration?
Healthy neuron degenerates because it synapsed with an injured cell
What is anterograde degeneration?
a neuron that received synaptic contacts from an injured cell
What interconnect the 2 cerebral hemispheres?
Corpus callosum and small white matter tracts
What contains 50% of CNS neuron but only 10% of CNS volume?
CEREBELLUM - little brain
40 afferent: 1 efferent ratio
What kind of info does cerebellum process?
Visual and auditory input
What are the 3 parts of cerebellum?
- vestibulocerebellum
- spinocerebellum
- cerebrocerebellum
vestibulocerebellum FUNCTION
- maintains body balance via vestibular system and inner ear
spinocerebellum FUNCTIOn
- helps regulate muscle tone
- receives strong input from muscle stretch receptors thru connections in brain stem and SC
cerebrocerebellum FUNCTION
- coordinates motor behavior
- receives projections from sensorimotor portions of cerebral cortex
largest part of cerebellum
Cerebrocerebellum
What is the sorting center for sensory input and sends it to cerebral cortex?
thalamus
controls arousal and memory function
thalamus
What disease severely impairs movement but when subthalamus is stimulated it is possible to improve movement?
Parkinson’s disease
What receives projections from basal ganglia that are important motor function?
Subthalamus
what is the master regulator of endocrine and ANS?
HYPOTHALAMUS
What are the important control centers of ANS?
brain stem: midbrain, pons, medulla
What is the reticular formation part of brain stem?
contains loosely interconnected collection of neurons and fiber
midbrain
control eye movement
(CN III, CN IV)
(Occulomotor, trochlear)
Pons
control mastication, eye movements, facial muscles
(CN 5, 6, 7)
- CN 8: hearing and equilibrium
medulla
somatic motor neurons
(CN XI, XII) - spinal accessory, hypoglossal
Together w/ pons: involved respiration, digestion, HR, BP
(CN 9, 10) - glossopharyngeal, vagus)
What is the most important descending tract?
Lateral corticospinal tract
where can we find both ascending and descending tracts?
white portion of SC
white matter?
where can we find 90% of the cell bodies of lateral corticospinal tract?
contralateral cervical cortex
Segmental reflex
sensory fibers enter SC and synapse directly w/ motor neurons in same segment
intersegmental reflex
incoming fibers synapse w/ neurons in other spinal segments
suprasegment reflex
incoming signals travel rostrally to brain stem before they synapse
organized bundle of axons in PNS
peripheral nerves
loose CT that surrounds an individual axon
Endoneurium
CT sheath the covers fascicles
perineurium
matrix of CT that surrounds groups of fascicles
Epineurium
Bundles of axons
fascicles
Fasciculations
small twitches of muscle cells that happen when motor axon is first damaged but has not lost it’s continuity;
can be seen under the skin
fibrillation
muscle fibers twitching spontaneously
diseases that affect the PNS…affect what first?
longest nerves of body (SC to feet)
Then when disease progresses, involvement will move centripetally (leg toward trunk) then goes to portions of legs and arms
Stocking and glove defect
both hands and feet are affected
