CNS Organization Flashcards
What are the main components of the CNS?
Brain
Spinal cord
What are the major components of the PNS?
Cranial nerves
Spinal nerves
What are the major divisions of the ANS?
Sympathetic
Parasympathetic
What are the general functional categories of the brain?
Sensory
Motor
Cognitive
What are the two major pathwys of the peripheral nervous system?
Afferent (sensory)
Efferent (motor)
What are the two major components of the ANS?
Sympathetic
Parasympathetic
What is the term for an aggregation of dendrites and nerve cell bodies in the CNS?
Nucleus
What is the term for an aggregation of dendrites and nerve cell bodies in the PNS?
Ganglion
What is the term for a bundle of fibers in the PNS?
Nerve
What is the term for a bundle of fibers (axons) in the CNS?
Tract
What are the three major subdivisions of the nervous system?
CNS
PNS
ANS
What is a reflex arc?
A pathway that leavs from and returns to the CNS. It consists of a sensory (afferent) and motor (efferent) pathway and also involves interneurons.
What is the term for a tract in the CNS that crosses from one side to another?
Commissure
What does white matter include?
Areas of myelinated axons
What does gray matter include?
Areas of unmyelinated axons, cell bodies and dendrites.
What are the components of a synapse?
Presynaptic membrane (have vesicles of neurotransmitters)
Synaptic cleft
Postsynaptic membrane (have receptors for neurotransmitters).
What are monosynaptic pathways?
Pathways consisting only of afferent neurons and efferent neurons. Each pathway has a single synapse.
What are polysynaptic pathways?
Pathways that include interneurons as well as afferent and efferent neurons. Each pathway has multiple synapses.
What are the three physiological states of a neuron?
Resting
Excited
Inhibited
What is the cell body potential at resting state?
-65 mV.
What is the cell body potential in an excited state?
-45 mV.
This is typically due to influx of sodium ions.
What is the cell body potential at an inhibited state?
-70 mV
It is typically due to influx of chloride ion or efflux of potassium ion.
What is the somatosensory axis?
The sequence of structures involved in the transmission of a sensory signal from the peripheral receptors to higher brain centers.
What are the components of the somatosensory axis?
Peripheral receptors
Afferent neurons
Spinal cord or brainstem
Reticular substance (medulla, pons, mesencephalon)
Cerebellum
Thalamus
Somesthetic areas of cerebral cortex
How are afferent neurons arranged in the somatosensory axis?
Primary afferent (synapse in posterior horns of spinal cord or sensory nuclei)
Secondary afferent neurons
Tertiary afferent neurons
Where do secondary afferent neurons synapse?
In the thalamus
Where do tertiary afferent neurons synapse?
Int he somesthetic areas of cerebral cortex.
What is the skeletal motor nerve axis?
The sequence of structures involved in the transmission of an actional potential from the higher brain centers to skeletal muscls.
What are the components of the skeletal motor nerve axis?
Motor cortex of cerebrum
Efferent pathways (upper motor neurons, alpha motor nuerons)
Effectors (skeletal muscle)
What are the processing areas of the skeletal motor nerve axis?
Basal nuclei (putamen, globus pallidus, subthalamic nuclei)
Thalamus in the diencephalon
Spinal cord reflexes
Where is acetylcholine secreted?
Pyramidal cells (cerebral cortex)
Basal nuclei
Alpha motor neurons
Postganglionic neurons of ANS
Postgangionic neurons of parasympathetic and sympathetic system
Is acetylcholine excitatory, inhibitory, or both?
Excitatory
What is norepinephrine secreted by?
Brain stem
Hypothalamus
Pons
Postganglionic nurons of sympathetic system
Is norepineprhine excitatory, inhibitory or both?
Both
What is dopamine secreted by?
Substantia nigra
Is dopamine excitatory, inhibitory or both?
Inhibitory
What is glycine secreted by?
Synapses in the spinal cord
Is glycine excitatory, inhibitory or both?
Inhibitory
What is GABA secreted by?
The spinal cord and cerebral cortex
Is GABA excitatory, inhibitory or both?
Inhibitory
What is glutamate secreted by?
Sensory pathways entering the CNS
Cerebral cortex
Is glutamate excitatory, inhibitory or both?
Excitatory
What is electronic conduction?
The direct spread of electrical current by an ion conduction in the dendritic fluids without generating an action potential.
What dendritic characteristics result in electronic conduction?
Few voltage gated sodium channels in dendritic membranes.
Thresholds too high for action potentials 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 excitation.
What is decremental conduction?
The decrease in membrane potential as it spreads electronically along dendrites twowards the soma. It occurs because the dendrite membranes are thin and permeable to potassium and chloride ions.
Define the excitatory state of a neuron.
The excitatory state occurs when there is a higher degree of excitation compared to inhibition.
What is “fatigue of synaptic transmission”
When the firing rate of an excitatory synapse becomes progressively less. It causese a decrease in excitability.
What is the mechanism of fatigue?
The exhaustion of stores of neuroteansmitters in the presynaptic terminals.
It also occurs from progessive inactivation of many of the postsynaptic membrane receptors and slow development of abnormal concentrations inside the postsynaptic neuronal cell.
What is the effect of alkalosis on neuronal excitability?
It increasese neuronal excitability.
What is the effect of acidosis on neuronal activity?
Acidosis greatly depresses neuronal activity.
What is the effect of hypoxia on synaptic transmission?
Snaptic transmission is greatly decreased and can cause inexcitability of some neurons.
What is the effect of caffeine, theophyllin and theobromine on synaptic transmission?
They all increase neuronal excitability
What is the effect of strychnine on neuronal excitability?
It increases neuronal excitability.
What is the effect of anesthetics on neuronal excitability?
It decreases synaptic transmission.
What is synaptic delay?
The minimal period of time required for transmitter discharge, diffusion, receptor acivity and inward diffusion of sodium.
What factors affect synaptic delay?
A. Time it takes to release NT from presynaptic neuron
B. Time it takes for NT to diffuse across the cleft.
C. How the NT acts on the postsynaptic membrane
D. Time it takes for eceptor to increase membrane permeability.
E. Time it takes for inward diffusion of sodium ions.
F. All of the above
F. All of the above
What is the minimal time for a synaptic delay?
0.5 msec
Refers to the time it takes to transmit a signal from the presynaptic neuron to a postsynaptic neuron.
What are thewo sources of blood supply to the brain?
Vertebral arteries
Internal carotids
What is the circle of Willis?
A pentagonal-shaped circle of arteries on the ventral surface of the brain that unites the two vertebral and the two internal carotid arteries.
It is an important anastomosis between these two pairs of arteries.
What are the components of the circle of willis?
Posterior cerebral arteries
Posterior communicating arteries (connects posterior cerebral arteries to the internal carotids)
Internal carotids
Anterior cerebral arteries
Anterior communicating artery (connects the two anterior cerebral arteries)
