CNS Organization (Lec 1B) Flashcards
True or False?
The brain initiates, controls, and coordinates most muscular activity except simple reflexes
True
True or False?
The spinal cord is the last CNS structure encountered by most incoming sensory information and first relay station for most motor information.
False. The spinal cord is the first CNS structure encountered by most incoming sensory information and the last relay station for most motor information
What is the site of coordination of most reflex arcs?
spinal cord
Define the PNS
made up of transmission pathways carrying information between the CNS and external/internal environments
Which direction do afferent (sensory) pathways carry information?
to the CNS
Which direction do (efferent) motor pathways carry information?
away from CNS
What does the PNS include?
cranial nerves (12 pairs), spinal nerves (31 pairs), sensory receptors in the ksin and wall of the gut tube as well as in tendons and skeletal muscles, motor end plates between motor neurons and skeletal muscle fibers
True or False?
The ANS is entirely motor
true
What are short branched process on an axon called?
telodendria
note: telodendria endings are called terminal boutons and contain synaptic vesicles filled with neurtransmitters
True or false?
The axon is the only part of neuron that is ever myelinated
true
note: not all axons are myelinated, even though they are covered by Schwan cells
What is a nucleus?
aggregation of dendrites and nerve cell bodies in the CNS
What is a ganglion?
aggregation of dendrites and nerve cell bodies in the PNS
What is a nerve?
bundle of fibers (axons) in the PNS
What is a tract?
a bundle of fibers (axons) in the CNS
What is a commissure?
tract in the CNS that crosses from one side to the other
True or false?
The CNS consists of structures arising directly from the neural tube
true
What is white matter?
areas of myelinated axons
What is gray matter?
areas of unmyelinated axons, cell bodies, and dendrites
What do white ramus communicans do?
carry myelinated pre ganglion fibers
What do gray ramus communicans do ?
carry unmyelinated postganglionic fibers back to spinal nerve
Describe paravertebral ganglia
linked together into a long chain on either side of the vertebral column, site of cell bodies of postganglionic sympathetic nerves, site of synapses between preganglionic myelinated sympathetic neurons and postganglionic non-myelinated sympathetic neurons
Describe prevertebral ganglion
typically found anterior to abdominal aorta, site of synapses between preganglionic myelinated sympathetic neurons and postganlgionic non-myelinated neurons
What is a reflex arc?
a pathway that leaves from and returns to the CNS. It consists minimally of a sensory and motor pathway
What are the three physiological states of a neuron?
resting: -65mv
excited: -45mv
inhibited: -70mv
True or false?
Simultaneous firing of only a few synapses can summate to produce an action potential on a postsynaptic neuron
False, need simultaneous firing of many synapses on the postsynaptic neuron
Where do primary, secondary, and tertiary afferent neurons synapse?
primary: posterior horns of spinal cord or sensory nuclei in brain
secondary: thalamus
tertiary: somesthetic areas of cerebral cortex
What does the skeletal motor nerve axis refer to?
the sequence of structures involved in the transmission of an action potential from the higher brain centers to skeletal muscles, includes: motor cortex of cerebrum, efferent pathways, and skeletal muscles
What are the three processing areas of the skeletal motor nerve axis?
basal ganglia in the telencephalon, thalamus in the diencephalon, and spinal cord reflexes
What type of NT is acetycholine and what secretes it?
Excitatory NT. Secreted by pyramidal cells, neurons in basal nuclei, alpha motor neurons, preganglionic neurons of ANS, postganglionic neurons of the parasympathetic nervous system, and some postganglionic neurons of the sympathetic nervous system
What type of NT is Norepinepherine and what secretes it?
Can either be excitatory or inhibitory NT. Secreted by neurons located in the brain stem and hypothalamus, some neurons located in the pons, and most postganglionic neurons of the sympathetic system
What type of NT is Dopamine and what secretes it?
Usually an inhibitory NT. Secreted by most neurons originating in the substantial nigra
What type of NT is Glycine and what secretes it?
Always an inhibitory NT. Secreted by synapses in spinal cord
What type of NT is GABA and what secretes it?
Always an inhibitory NT. Secreted by many areas in the spinal cord and cerebral cortex
What type of NT is Glutamate and what secretes it?
Always an excitatory NT. Secreted by many sensory pathways entering the CNS and many areas of cerebral cortex
Can dendrites transmit an action potential?
No, they use electronic conduction instead
What ions is the dendretic membrane partially permeable to?
K+ and Cl-
True or false?
Dendrites are long and membranes are thin
true
What causes much of the potential to be lost in dendrites?
leakage
Describe the difference in signal strength between dendrites and an action potential down an axon
Dendrites: signal becomes weaker the further it is from the site of initiation
AP in axon: constantly renewed along the length of the axon and therefore, doesn’t decrease in strength
Define electronic conduction.
direct spread of electrical current by ion conduction in the dendritic fluids without generating an AP
What are two characteristics of a dendrite that result in electronic conduction?
few voltage-gated Na+ channels in dendritic membrane and thresholds too high for APs to occur
What is the excitatory state of a dendrite?
the summated degree of excitatory drive to the neuron
Explain the firing rate of a dendrite.
As long as the excitatory rate of a neuron remains above threshold for excitation, the neuron will fire repetitively
What is synaptic delay?
the time it takes to transmit a signal from a presynaptic neuron to a postsynaptic neuron
What are the two sources of blood to the brain?
Vertebral arteries and internal carotids
What is the circle of willis?
a pentagonal-shpaed circle of arteries on the ventral surface of the brain that unites the two vertebral and the two internal carotid arteries
What are the components of the circle of willis?
posterior cerebral arteries, posterior communicating arteries, internal carotids, anterior cerebral arteries, anterior communicating artery
What three things do axons contain?
Mitochondria, neurofilaments, and neurotubules
