Lec 01B- CNS Organization Flashcards
What are the 2 parts of the CNS?
- brain
- spinal cord
What are the 2 parts of the PNS?
- cranial nerves
- spinal nerves
What are the 2 parts of the ANS?
- sympathetic
- parasympathetic
What are the 3 functions of the brain?
- sorts through and properly routes incoming sensory information
- Initiates, controls, and coordinates most muscular activity except simple reflexes
- site of CN
What 4 CN carry parasympathetic fibers?
3, 7, 9, 10
The spinal cord is the 1st CNS structure encountered by most incoming sensory information except _____________
sensory fibers in CN
The spinal cord is the last relay station for most motor information except __________
ANS motor fibers
The spinal cord is the site of coordination of most _________
reflex arcs
Afferent (sensory) pathways carry information _______ the CNS
to
Efferent (motor) pathways carry information ________ the CNS
from
How many spinal nerves are there?
31
The ANS is entirely ________
motor
What does the ANS innervate?
smooth muscle and glands (viscera)
Which ANS subdivision is also called thoracolumbar?
sympathetic
Which ANS subdivision is also called craniosacral?
parasympathetic
What is the cell body?
- trophic unit
- perikaryon
What are the dendrites?
receptive unit
What is the axon?
conductive unit
What part of the neuron encloses the nucleus and other organelles necessary to maintain and repair the neuron?
cell body
What have receptors for nt and conduct local potentials?
dendrites
What conducts AP and releases nt?
axon
What are telodendria?
short branched processes at the end of axons
What do telodendria give off?
terminal boutons
What do terminal boutons contain?
sympathetic vesicles filled with nt
What kind of branches may axons have?
collateral branches
What does the axon contain?
- mitochondria
- neurofilaments
- neurotubules
What covers an axon?
neurolemma
What is the neurolemma made of?
- Schwann cells
- often myelinated
What part of the neuron is myelinated?
axon
**not all axons are myelinated
What is an aggregation of dendrites and nerve cell bodies in the CNS?
nucleus
What is an aggregation of dendrites and nerve cell bodies in the PNS?
ganglion
What is a bundle of fibers/axons in the PNS?
nerve
What is a bundle of fibers/axons in the CNS?
tract
What is the tract n the CNS that crosses from one side to the other?
commissure
What areas are white matter?
myelinated axons
What areas are gray matter?
unmyelinated axons, cell bodies, dendrites
What are the 2 major branches of spinal nerves?
- dorsal primary ramus
- ventral primary ramus
What are the 2 small branches that the thoracolumbar spinal nerves branch into before branching into primary rami?
- white ramus communicans
- gray ramus communicans
What kind of fibers do the white ramus communicans carry?
myelinated prganglionic fibers
What kind of fibers do the gray ramus communicans carry?
unmyelinated postganglionic fibers back to the spinal nerve
What are the 3 spinal nerve ganglia?
- paravertebral ganglia
- splanchnic nerve
- prevertebral ganglion
What is the site of cell bodies of postganglionic sympathetic nerves?
paravertebral ganglia
What is the site of synapses between preganglionic myelinated sympathetic neurons and postganglionic non-myelinated neurons?
prevertebral ganglia
What does the splanchnic nerve supply?
viscera
What ganglia links together into a long chain on either side of the vertebral column in the thoracolumbar region?
paravertebral ganglia
What ganglia are typically found anterior to the abdominal aorta?
prevertebral ganglia
What is the site of synapses between preganglionic myelinated sympathetic neurons and postganglionic non-myelinated sympathetic neurons?
paravertebral ganglia
What is a reflex arc?
- pathway that leaves from and returns to the CNS
- sensory and motor pathway
Where do somatic afferent pathways carry sensations from?
non-visceral structures
skin and skeletal muscle
Where do visceral (splanchnic) afferent pathways carry sensations from?
viscera
Where do somatic efferent pathways carry motor signals to?
skeletal muscles
Where do visceral (splanchnic) motor pathways carry motor signals to?
smooth or cardiac muscles
What are interneurons?
- intervening neurons
- modulate interaction between afferent and efferent neurons
What are the 3 components of a synapse?
- presynaptic membrane
- synaptic cleft
- postsynaptic memrbane
What do monsynaptic pathways consist of?
only afferent and efferent neurons
**single synapse
What do polysynaptic pathways consist of?
- interneurons
- afferent and efferent neurons
**multiple synapses
What is the resting cell body potential?
-65 mV
What is the excited cell body potential?
-45 mV
More (+) due to Na influx
What is the inhibited cell body potential?
-70 mV
More (-) due to Cl- influx or K+ efflux
What causes superimposed AP?
simultaneous firing of many synapses on the postsynaptic neuron
What is the somatosensory axis?
sequence of structures involved in the transmission of a sensory signal from the peripheral receptors to higher brain centers
What are the 7 components of the somatosensory axis?
1- Peripheral receptors 2- Afferent neurons 3- Spinal cord/brainstem 4- Reticular substance (medulla, pons, mesencephalon) 5- Cerebellum 6- Thalamus 7- Somesthetic areas of cerebral cortex
Where do the primary afferent neurons synapse?
posterior horns of the spinal cord or sensory nuclei in the brain
Where do the secondary afferent neurons synapse?
thalamus
Where do the tertiary afferent neurons synapse?
somesthetic areas of cerebral cortex
What is the skeletal motor nerve axis?
sequence of structures involved in the transmission of an AP from higher brain centers to skeletal muscles
What are the 3 components of the skeletal motor nerve axis?
1- Motor cortex of cerebrum
2- Efferent pathways (upper and alpha motor neurons)
3- Effectors (skeletal muscles)
What are the efferent pathways of the skeletal motor nerve axis made up of?
- Upper motor neurons extending from cortical areas to the anterior horns of the spinal cord
- Alpha (lower) motor neurons extending to the skeletal muscles
Why do smooth muscles and glands have a different pattern of AP transmission than skeletal muscles?
they are supplied by the ANS
What 3 structures contain the processing areas of the skeletal motor nerve axis?
1- basal ganglia (nuclei) in the telencephalon
2- thalamus in the diencephalon
3- spinal cord reflexes
What are the 3 basal ganglia in the telencephalon?
- putamen
- globus pallidus
- subthalamic nuclei
What 6 areas secrete Ach?
1- Pyramidal cells (cerebral cortex)
2- Some neurons in basal nuclei
3- Alpha motor neurons
4- Preganglionic neurons of ANS
5- Postganglionic neurons of parasympathetic system
6- Some postganglionic neurons of sympathetic system
Is Ach excitatory or inhibitory?
excitatory
What 3 areas secrete NE?
1- Neurons in brain stem and hypothalamus
2- Neurons located in pons (locus ceruleus)
3- Most postganglionic neurons of sympathetic system
Is NE excitatory or inhibitory?
either excitatory or inhibitory
What secretes dopamine?
most neurons originating in the substantial nigra
Is dopamine excitatory or inhibitory?
inhibitory
What secretes glycine?
synapses in the spinal cord
Is glycine excitatory or inhibitory?
inhibitory
What secretes GABA?
many areas in the spinal cord and cerebral cortex
Is GABA excitatory or inhibitory?
inhibitory
What 2 areas secrete glutamate?
- many sensory pathways entering the CNS
- many areas of cerebral cortex
Is glutamate excitatory or inhibitory?
excitatory
Where can dendrites receive signals from?
a large spatial area around a motor neuron
What do dendrites use instead of transmitting APs?
electronic conduction
What are dendritic membranes partially permeable to?
K+
Cl-
Why is much of the potential lost on dendrites?
because of leakage of ions
What kind of conduction results from the gradual loss of the potential as the depolarization spreads from the site of initiation?
decremental conduction
Do APs decrease in strength?
NO
What is electronic conduction?
Direct spread of electrical current by ion conduction in the dendritic fluids without generating an AP
What are the 2 dendritic characteristics that result in electronic conduction?
- Few VG-Na+ channels in dendritic membranes
- Thresholds = too high for AP to occur
What is the excitatory state?
The summated degree of excitatory drive to the neuron
When does the excitatory state occur?
when there is a higher degree of excitation compared to inhibition
When does the inhibitory state occur?
when there is a higher degree of inhibition compared to the excitation
When will the neuron fire repetitively?
as long as the excitatory rate of a neuron remains above the threshold for excitation
What does the firing rate depend on?
the normal excitatory rate and the changes in that rate due to superimposition of additional excitatory or inhibitory signals
What 5 things does the synaptic delay depend on?
1- Time it takes to release nt from presynaptic neuron
2- Time it takes for nt to diffuse across synaptic cleft
3- How nt acts on the postsynaptic membrane
4- Time it takes for receptor to increase membrane permeability
5- Time it takes for inward diffusion of Na+ ions
What are the 2 sources of blood for the brain?
- vertebral arteries
- internal carotids
What do the vertebral arteries ascend through?
transverse foramina of CV 1-6
What do the vertebral arteries pass through?
foramen magnum
Where do the vertebral arteries unite?
at the caudal border of the pons to form the basilar artery
What does the basilar artery give off?
cerebellar arteries
Then it divides into 2 posterior cerebral arteries
Where are the vertebral arteries located?
1st branches of the subclavian arteries
Where are the internal carotids located?
terminal branches of the common carotids
What do the internal carotids enter through?
enter the cranial cavity through carotid canal in temporal bone
What is the Circle of Willis?
- on ventral surface of brain
- unites the 2 vertebral arteries and the 2 internal carotid arteries
What are the 5 components of the Circle of Willis?
1- Posterior cerebral arteries 2- Posterior communicating arteries 3- Internal carotids 4- Anterior cerebral arteries 5- Anterior communicating artery (unpaired)
What are the posterior cerebral arteries?
terminal branches of the basilar artery
What do the posterior communicating arteries connect?
posterior cerebral arteries to the internal carotids
What does the internal carotids give off?
the anterior and middle cerebral arteries
What do the anterior cerebral arteries branch off from?
the internal carotids
What does the anterior communicating artery connect?
the 2 anterior cerebral arteries
