Lecture 2: CNS Organization Flashcards
1
Q
What are the 3 major subdivisions of the nervous system?
A
- Central Nervous System
- Peripheral Nervous System
- Autonomic Nervous System
2
Q
What are the main components of the CNS?
A
- Brain
- Spinal Cord
3
Q
What are the main components of the PNS?
A
- Cranial Nerves
- Spinal Nerves
4
Q
What are the main components of the ANS?
A
- Sympathetic
- Para-Sympathetic
5
Q
What are the components of a reflex arc?
A
- Afferent (sensory) Pathways
- Efferent (motor) Pathways
- Association Neurons (interneurons)
6
Q
What are the 3 general functional categories of the brain?
A
- sensory
- motor
- cognitive
7
Q
True or False:
The central nervous system consists of structures arising directly from the neural tube.
A
True
8
Q
What are the four cranial nerves that carry parasympathetic fibers?
A
- CN III
- CN VII
- CN IX
- CN X
9
Q
What are the functions of the brian?
A
- Sorts through and properly routes incoming sensory information.
- Initiates, controls, and coordinates most muscular activity except simple reflexes.
- Site of origin of 12 cranial nerve pairs.
10
Q
What muscular activity does the brain not initiate, control, or coordinate?
A
Simple Reflexes
11
Q
True or False:
The spinal cord is the first CNS structure encountered by most incoming sensory information except sensory fibers in cranial nerves.
A
True
12
Q
What is the spinal cord the last relay station for?
A
Most motor information except ANS motor fibers.
13
Q
Fill in the Blank:
The spinal cord is the site of coordination of
most _____ _____.
A
Reflex Arcs
14
Q
What is the definition of the peripheral nervous system?
A
The PNS is made up of transmission pathways carrying information between the CNS and external/internal environments.
* afferent (sensory) = carry information to the CNS
* efferent (motor) = carry information from the CNS
15
Q
How many pairs of cranial nerves and spinal nerves does the PNS include?
A
Cranial Nerves (12 Pairs)
Spinal Nerves (31 Pairs)
16
Q
What makes up the PNS?
A
- cranial nerves
- spinal nerves
- sensory receptors in the skin and wall of the gut tube as well as in tendons and skeletal muscles
- motor end plates between motor neurons and skeletal muscle fibers
17
Q
True or False:
The autonomic nervous system is entirely motor, no sensory.
A
True
18
Q
What does the ANS innervate?
A
- smooth muscle and glands (viscera)
19
Q
What are the subdivisions of the ANS?
A
- sympathetic system
- fight or flight
- thoracolumbar
- parasympathetic system
- feed and breed
- craniosacral
20
Q
What is the definition of nucleus?
A
An aggregation of dendrites and nerve cell bodies in the CNS.
21
Q
What is the definition of a ganglion?
A
An aggregation of dendrites and nerve cell bodies in the PNS.
22
Q
What is the definition of a nerve?
A
A bundle of fibers (axons) in the PNS.
23
Q
What is the definition of a tract?
A
A bundle of fibers (axons) in the CNS.
24
Q
What is the definition of a commissure?
A
A tract in the CNS that crosses from one side to the other.
25
What is the cell body of a neuron?
The cell body is that part of a neuron that encloses the nucleus and other organelles necessary to maintain and repair the neuron.
26
What are dendrites of a neuron?
Dendrites are branches off the cell body that carry information to the cell body.
Characteristics:
* usually several to many dendrites per neuron
* relatively short, expecially compared to the axon
* often branched
* **Have receptors for neurotransmitters**
* **Conduct local potentials**
27
What is the axon of a neuron?
The axon is that part of the neuron that carries information to another neuron or muscle cell.
Characteristics:
* Usually relatively long
* Single (one per neuron)
* **Conducts action potential (nerve impulses)**
* **Releases Neurotransmitters**
* An axon ends in short branched processes called telodendria.
* telodendria give off endings called terminal boutons
* terminal boutons contain synaptic vesicles filled with neurotransmitters
* Axons may have collateral branches
* The cell membrane of an axon is called the axolemma
* The cytoplasm of an axon is called the axoplasm
* The axon contains mitochondria, neurofilaments, and neurotubules
* An axon is coered by a neurolemma which is:
* made up of schwann cells
* often myelinated
* myelin is formed by Schwann cells
NOTE:
* the axon is the only part of neuron that is ever myelinated
* not all axons are myelinated, even though they are covered by Schwann cells
28
What does white matter refer to?
Areas of myelinated axons.
29
What does gray matter refer to?
Areas of unmyelinated axons, cell bodies, and dendrites.
30
What are the two major branches that spinal nerves divide into?
* dorsal primary ramus
* ventral primary ramus
31
Each spinal nerve in the thoracolumbar region, before branching into primary rami gives off two small branches, what are they?
* White ramus communicans:
* carries myelinated preganglionic fibers
* Gray ramus communicans:
* carries unmyelinated postganglionic fibers back to spinal nerve
32
What is a splanchinic nerve?
A nerve that supplies viscera.
33
What is the prevertebral ganglion a site of?
* typically found anterior to abdominal aorta
* site of synapses between preganglionic myelinated sympathetic neurons and postganglionic non-myelinated neurons
34
What is the paravertebral ganglia a site of?
* site of cell bodies of postganglionic sympathetic nerves
* site of synapses between preganglionic myelinated sympathetic neurons and postganglionic non-myelinated sympathetic neurons
* linked together into a long chain on either side of the vertebral column in the thoracolumbar region.
35
What is a reflex arc?
A reflex arc is a pathway that leaves from an returns to the CNS. It consists minimally of a sensory pathway and a motor pathway.
36
What do afferent (sensory) pathways of a reflex arc function to do?
* somatic afferent pathways carry sensation from non-visceral structures such as the skin and skeletal muscle
* visceral (splanchnic) afferent pathways carry sensations from viscera
37
What do efferent (motor) pathways of a reflex arc function to do?
* somatic efferent pathways carry motor signals to skeletal muscles
* visceral (splanchnic) motor pathways carry motor signals to smooth or cardiac muscles
38
What do association neurons (interneurons) do in the reflex arc pathway?
* some reflex arcs consist only of an efferent neuron and an afferent neuron
* most have intervening neurons, called association neurons or interneurons, in the CNS that modulate the interaction between the afferent and efferent neurons
39
What components make up a synapse?
* presynaptic membrane
* synaptic cleft
* postsynaptic membrane
40
What is a monosynaptic pathway?
These are pathways consisting only of afferent neurons and efferent neurons. Each pathway has a single synapse.
41
What is a polysynaptic pathway?
* These are pathways that include interneurons as well as afferent and efferent neurons.
* Each pathway has multiple synapses.
42
What are the three physiological states that a neuron can be found in?
* Resting
* Excited
* Inhibited
43
Which physiological state would a neuron that has chlorine influxing and potassium effluxing be in?
Inhibitory State
* cell body potential is more negativethan at rest
* typically due to influx of chloride ion or efflux of potassium ion
44
What is the somatosensory axis?
The somatosensory axis refers to the sequence of structures involved in the transmission of a sensory signal from the peripheral receptors to highter brain centers.
45
What are the components of the somatosensory axis pathway?
* peripheral receptors
* afferent neurons
* spinal cord or brainstem
* reticular substance
* medulla, pons, mesencephalon
* cerebellum
* thalamus
* somesthetic areas of cerebral cortex
46
True or False:
All sensory information as to go through the thalamus, except for smell.
True
47
In the somatosensory axis, where do primary afferent neurons synapse?
Synapse in the posterior horns of spinal cord or sensory nuclei in the brain.
48
In the somatosensory axis, where do secondary afferent neurons synapse?
Synapse in the thalamus.
49
In the somatosensory axis, where do tertiary afferent neurons synapse?
Synapse in the somesthetic areas of cerebral cortex.
50
What is the skeletal motor nerve axis?
The skeletal motor nerve axis refers to the sequence of structures involved in the transmission of an action potential from the higher brain centers to skeletal muscles.
51
What makes up the skeletal motor nerve axis?
* motor cortex of cerebrum
* efferent pathways made up of:
* upper motor neurons extending from cortical areas to the anterior horns of the spinal cord
* alpha motor neurons (lower motor neurons) extending to the skeletal muscles
* effectors
* skeletal muscle
NOTE: smooth muscles and glands are supplied by the ANS and have somewhat different pattern.
52
Study for the exam figures 46-2 and 46-3.
53
Which structures make up the processing areas of the skeletal motor nerve axis?
* Basal nuclei (ganglia) in the telencephalon
* putamen
* globus pallidus
* subthalamic nuclei
* Thalamus in the diencephalon
* Spinal cord reflexes
54
Where is acetylcholine secreted from and is it excitatory, inhibitory, or both?
* Secreted by:
* pyramidal cells (cerebral cortex)
* some neurons in the basal nuclei
* alpha motor neurons
* preganglionic neurons of ANS
* postganglionic neurons of the parasympathetic system
* some postganglionic neurons of the sympathetic system
* Usually Excitatory
55
Where is norepinephrine secreted from and is it excitatory, inhibitory, or both?
* Secreted by:
* many neurons located in the brain stem and hypothalamus
* some neurons located in the pons (i.e., locus ceruleus)
* most postganglionic neurons of the sympathetic system
* Both - can be either excitatory or inhibitory
56
Where is dopamine secreted from and is it excitatory, inhibitory, or both?
* Secreted by:
* most neurons originating in the substantia nigra
* Usually inhibitory
57
Where is glycine secreted from and is it excitatory, inhibitory, or both?
* Secreted by:
* synapses in the spinal cord
* Always inhibitory
58
Where is GABA secreted from and is it excitatory, inhibitory, or both?
* Secreted by:
* many areas in the spinal cord and cerebral cortex
* Always inhibitory
59
Where is glutamate secreted from and is it excitatory, inhibitory, or both?
* Secreted by:
* many sensory pathways entering the CNS
* many areas of cerebral cortex
* Always excitatory
60
What is electrotonic conduction?
* Direct spread of electrical current by ion conduction in the dendritic fluids without generating an action potential.
61
Stimulation (or inhibition) of the neuron by electrotonic conduction from the dendrite has special characteristics, what are they?
* Greater excitatory (or inhibitory) effect are caused by synapses that are located near the soma.
62
True or False:
Synapses that lie near the soma have far more effect in causing neuron excitation or inhibition thatn do those that lie far away from the soma.
True
63
What is decremental conduction?
* On a dendrite with excitatory effects near the tip ends have a less negative membrane potential, however, a large share of the EPSP is lost before it reaches the soma. The reason a large share is lost is that the dendrites are long, and their membranes are thin and at least partiallly permeable to potassium and chloride ions, making them "leaky" to electric current.
* Therefore, before the excitatory potentials can reach the soma, a large share of the potential is lost by leakage through the membrane.
* **This decrease in membrane potential as it spreads electrotonically along dendrites toward the soma is called decremental conduction.**
64
True or Fasle:
The farther the excitatory synapse is from the soma of the neuron, the greater will be the decrement and the lesser will be excitatory signal reaching the soma.
True
65
What is the "excitatory state" of a neuron?
* "Excitatory State" is the summated degree of excitatory drive to the neuron.
* the excitatory state occurs when there is a higher degree of excitation compared ot inhibition
* the inhibitory state occurs when there is a hgither degree of inhibition compared to excitation
66
What are dendritic characteristics that result in electrotonic conduction?
* few voltage-gated sodium channels in dendritic membranes
* thresholds too high for action potentials to occur
67
Look over figure 46-11!
Know Well for the Exam!
68
What is the firing rate and characteristics of a dendrite?
* as long as the excitatory rate of a neuron remains above the threshold for excitation, the neuron will fire repetitively
* the firing rate depends on the normal excitatory rate and on the changes in the excitatory rate due to superimposition of additonal excitatory or inhibitory signals
69
Define "fatigue of synaptic transmission".
When excitatory synapses are repetitively stimulated at a rapid rate, the number of discharges by the postsynaptic neuron is at first very great, but the firing rate becomes progressively less in succeeding milliseconds or seconds.
\*\*fatigue is probably the most important means by which the excess excitability of the brain during an epileptic seizure is finally subdued so that the seizure ceases
\*\*thus, the development of fatigue is a protective mechanism against excess neuronal activity
70
What is the mechanism in "fatigue or synaptic transmission"?
* The mechanism of fatigue is mainly exhaustion or partial exhaustion of the stores of transmitter substance in the presynapticterminals.
* the excitatory terminals on many neurons can store enough excitatory transmitter to cause only about 10,000 action potentials, and the transmitter can be exhausted in only a few seconds to a few minutes of rapid stimulation
* 2 other contributing factors:
* progressive inactivation of many of the postsynaptic membrane receptors
* slow development of abnormal concentrations of ions inside the postsynaptic neuronal cell
71
What is the effect of hypoxia on synaptic transmission?
* Neuronal excitability is also highly dependent on an adequate supply of oxygen.
* Cessation of oxygen for only a few seonds can cause complete inexcitability of some neurons.
* This effect is observed when the brain's blood flow is temporarily interrupted because within 3-7 seconds, the person becomes unconscious.
72
What effect on synaptic transmission does acidosis have?
* Acidosis greatly depresses neuronal actiity.
* a fall of pH from 7.4 to below 7.0 usually causes a comatose state
* e.g., In very severe diabetic or uremic acidosis, coma almost always develops
73
What effect on synaptic transmission does alkalsosis cause?
* Alkalosis greatly increases neuronal excitability.
* e.g., a rise in arterial blood pH from the 7.4 norm to 7.8 to 8.0 often causes cerebral epileptic seizures because of increased excitability of some or all of the cerebral neurons.
* in a person who is predisposed to epileptic seizures, even a short period of hyperventiliation may precipitate an epileptic attack
74
What are the effects of caffeine, theophyllin, and theobromine on synaptic transmission?
* Caffeine, theophylline, and theobromine, which are found in coffee, tea, and cocoa, respectively, all **increase** neuronal excitability, presumably by reducing the threshold for excitation of neurons.
75
What effect does strychnine have on synaptic transmission?
* Strychnine is one of the best known of all agents that increase excitability of neurons.
* However, it does not do this by reducing the threshold for excitation of the neurons; instead, it **inhibits the action of some normally inhibitory transmitter substances**, expecially the inhibitory effect of glycine in the spinal cord.
* Therefore, the effects of the excitatory transmitters become overwhelming, and the neurons become so excited that they go into rapidly repetitve discharge, resulting in severe tonic muscle spasms.
76
What effect does anesthetics have on synaptic transmission?
* Most anesthetics increase the neuronal membrane threshold for excitation and thereby decrease synaptic transmission at many points in the nervous system.
* because many of the anesthetics are expecially lipid dolube, it has been reasoned that some of them might change the physical characteistics of the neuronal membranes, making them less responsive to excitatory agents
77
What is the definition of "synaptic delay"?
* Refers to thetime it takes to transmit a signal from a presynaptic neuron to a postsynaptic neuron.
78
What does synaptic delay depend on?
* time it takes to release the NT from the presynaptic neuron
* time it takes for the NT to diffuse across the synaptic cleft
* how the NT acts on the postsynaptic membrane
* the time it takes for the receptor to increase membrane permeability
* time it takes for the inward diffusion of sodium ions
79
What is the minimal time for a synaptic delay?
Minimal Time = 0.5 msec
80
True or False:
Dendrites may extend out for a considerable distance.
True
81
Since dendrites generally cannot transmit action potentials, what do they use instead?
They use electrotonic conduction instead.
82
Which ions are dendritic membranes partially permeable to?
* potassium
* chloride
83
What is much of the electric potential that is generated on a dendrite lost?
current leakage
84
What of conduction does the gradual loss of potential as the depolarization spreads from the site of initiation result in?
Decremental Conduction
* the signal becomes weaker the further it is from the site of initiation
* this is in opposition to action potentials which are constantly renewed along the length of the axon and, therefore, do not decrease in strength
85
True or False:
The excitatoy state occurs when ther eis a higher degree of excitation compared to inhibition. Also, the inhibitory state occurs when there is a higher degree of inhibition compared to excitation.
True
86
Name the two sources of blood supply to the brain.
* Vertebral Arteries
* first branches of the subclavian arteries
* ascend through the transverse foramina of cervical vertebra 1-6
* pass through the foramen magnum
* unite at caudal border of pons to form basilar artery:
* the basilar artery gives off cerebellar arteries and then divides into two posterior cerebral arteries
* Internal Carotids
* terminal branches of the common carotids
* enter cranial cavity through carotid canal in temporal bone
87
What are the components of the Circle of Willis?
* posterior cerebral arteries
* terminal branches of the basilar artery
* posterior communicating arteries
* connect the posterior cerebral arteries to the internal carotids
* internal carotids
* give off anterior and middle cerebral arteries
* anterior cerebral arteries
* branches off the internal carotids
* anterior communicating artery (unpaired)
* connects the two anterior cerebral arteries
88
What is the circle of Willis?
* This is 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.
