Unit IX (46-49) - The Nervous System - General Principles Flashcards
What are the two major types of synapses?
Chemical
Electrical
Guyton Ch. 46
What are the two components of postsynaptic receptor proteins
Binding component Ionophore component (ion channel and second messenger activator)
Guyton Ch. 46
What is the initial step for excitation of the postsynaptic membrane?
Opening of Na channels
What event inhibits the postsynaptic membrane?
Opening of Cl channels
Where and how is acetylcholine synthesized?
in presynaptic terminal
- acetyl coenzyme A + choline (mediated by choline acetyltransferase)
- stored in vesicles
- released in the synaptic cleft
- quickly split by cholinesterase
- choline is transported back into the terminal to make more acetylcholine
Which of the following electrolytes is lowest extracellularly?
A. Cl
B. Na
C. K
C.
What is the difference between Type A and Type C nerve fibers?
Type A - large/medium sized myelinated fibers
Type C - small unmyelinated fibers (all postganglionic autonomic fibers) - conducts impulse at low velocities
What are two mechanisms to prevent nervous tissue overactivity?
inhibitory circuits - (like a negative feedback loop)
synaptic fatigue - synaptic transmission becomes weaker after prolonged and intense excitation
What type of fibers are associated with fast pain?
Adelta fibers
What type of fibers are associated with slow pain?
C fibers
Which of the following neurotransmitters is usually associated with fast pain in the neospinothalamic tract? A. Glutamate B. Substance P C. Acetylcholine D. GABA
A. glutamate - fast pain (Ad fibers)
Substance P is likely associated with slow pain in the paleospinothalamic tract
Which of the following neurotransmitters is usually associated with slow pain in the paleospinothalamic tract? A. Glutamate B. Substance P C. Acetylcholine D. GABA
B. substance P - slow pain (C fibers)
What are the different types of neurons involved in function of the spinal cord?
interneurons (in gray matter)
anterior motor neurons
- alpha (innervate large skeletal muscle fibers)
- gamma (innervate small special skeletal m. fibers)
What are the two types of muscle spindle intrafusal fibers?
- nuclear bag muscle fibers
- nuclear chain fibers
Primary sensory nerve ending is excited by both but secondary nerve endings are only excited by nuclear chain fibers.
What is a mass reflex?
massive discharge in large portions of the spinal cord
can be stimulated by: strong pain stimulus to skin or excessive filling of the gut or bladder
what is spinal shock?
when the spinal cord is suddenly transected essentially all for function (including cord reflexes) immediately become depressed.
should return to normal ~a couple to 24 hrs
arterial BP falls due to decreased sympathetic stimulation
stretch reflexes - first to return followed by flexor reflexes and postural antigravity reflexes
Explain the pyramidal (corticospinal) tract and its function
leave the cortex
through the brainstem - forming the pyramids of the medulla
majority of fibers cross to the opposite side
descend into lateral corticospinal tracts
terminate on interneurons in intermediate regions of gray matter.
Very few fibers do not cross to the opposite side
ipsilaterally in ventral corticospinal tracts
Explain the extrapyramidal (rubrispinal) tract and its function
receives many direct fibers from primary motor cortex through corticorubral tract and branching fibers from the corticospinal tract
crosses to the opposite side of the lower brainstem
What does the brain stem control?
respiration cardiovascular system partial control of GI function equilibrium eye movement
What are the parts of the vestibular apparatus?
bony labyrinth
membranous labyrinth
functional part of the vestibular apparatus
3 semicircular canals
utricle
sacculeWhat do the utricle and the saccule detect and how?
utricle - horizontal plane
determining orientation of the head when the head is upright
saccule - vertical plane
determines the location of the head when lying down
What do the semicircular ducts detect and how?
anterior, posteroir and lateral (horizontal) semicircular ducts
arranged at right angles to one another
in ducts and ampulla - endolymph
flow of endolymph - excites the ampulla
How does the vestibular system stabilize the eyes?
each time the head is suddenly rotated: signals from semicircular ducts can cause the eyes to move
transmitted through the vestibular nuclei and the medial longitudinal fasciculus
initially eye movement opposite to rotation (slow phase) then ocular muscles stretched too much –> fast movement to relax ocular muscles with direction of rotation (fast phase) = physiologic nystagmus
A lesion to the flocculonodular lobe or caudal cerebellar peduncles results in what syndrome?
paradoxical vestibular
loss of inhibitory influence on vestibular nuclei
- overexcitation on side of lesion
- vestibular signs away from the lesion
head tilt to the opposite side
fast phase of nystagmus towards the lesion
-often CP deficits on the side of the lesion
What are the tasks of the cerebellum?
helps sequence motor activities
monitors motor activities
helps plan the next movement
What are the functions of the purkinje cells?
inhibit deep nuclear cells
when rapid movement occurs - signal from cerebral motor cortex or brainstem increases deep nuclear cell excitation then inhibitory signals from purkinje cells.
What is the putamen circuit?
pathway for executing learned movement patterns
begin in premotor and supplementary area of motor cortex
lesion - parkinson disease, akinesia
What is the caudate circuit?
cognitive control of motor function - using a sensory input and info already in memory.
What neurotransmitters are important in the basal ganglia?
dopamine (mostly inhibitory)
GABA (always inhibitory)
ACh
norepi, serotonin
What are the parts of the basal ganglia?
caudate nucleus putamen globus pallidus substantia nigra subthalamic nucleus
Where do autonomic preganglionic neurons originate?
intermediolateral horn of cord
Where do autonomic postganglionic neurons originate?
sympathetic chain ganglion or peripheral sympathetic ganglion
What cranial nerves carry parasympathetic fibers from the CNS?
III - pupillary sphincter, cilliary muscle of eye
VII - lacrimal, nasal and submandibular glands
IX - parotid gland
X (75% of fibers)
lowermost part of spinal cord - descending colon, rectum, bladder
What are the two types of acetylcholine receptors?
muscarinic
nicotinic
Which of the following can decrease neuronal excitability? A. Caffeine B. Theophylline C. Theobromine D. Serotonin
D. Serotonin
Resting membrane potential of a spinal motor neuron? A. -45 mV B. -65mV C. -70 mV D. -90 mV
B. -65mV
- 45mV - excited neuron
- 70mV - inhibited neuron
- 90mV - RMP of skeletal muscles and peripheral nerves
Which system transmits somatosensory information with the highest degree of temporal and spatial fidelity? A. Anterolateral system B. Dorsal column-medial lemniscal system C. Corticospinal system D. Spinocerebellar system
B. Dorsal column-medial lemniscal system
Temporal and spacial fidelity is enhced in the dorsal column-medial lemniscal system compared with the anterolateral system.
Guyton 13th ed. p 610
Slow pain is also referred to as burning, aching, or throbbing pain and can be associated with which of the following?
A. Tissue damage or destruction
B. inactivation of warmth receptors
C. Type Ad sensory fibers
D. Certain encapsulated receptors such as pacinian corpuscles
A. tissue damage
The release of neurotransmitter at a chemical synapse in the central nervous system is dependent upon which of the following?
A. Synthesis of acetylcholinesterase
B. Hyperpolerization of the synaptic terminal
C. Opening of ligand-gated ion calcium channels
D. Influx of calcium into the pre-synaptic terminal
D. Influx of calcium into the pre-synaptic terminal
When this influx occurs, synaptic vesicles fuse with the pre-synaptic membrane and release the transmitter agent into the synaptic cleft.
Guyton 13th ed. p 582
- When treating critically ill patients with intravenous fluids, which two ions are most important to the neuronal membrane potential?
a. Na+ and Cl–
b. K+ and Cl–
c. Ca2+ and Cl–
d. K+ and Ca2+
e. Na+ and K+
E. Na+ and K+
Cunningham Ch. 4 - The neuron
- During an excitatory postsynaptic potential in a neural membrane, which of the following is the most important ion flow?
a. Sodium ions diffuse out of the cell.
b. Sodium ions diffuse into the cell.
c. Potassium ions diffuse out of the cell.
d. Potassium ions pumped in by the Na+, K+ pump
B. Sodium ions diffuse into the cell.
Cunningham Ch. 4 - The neuron
- At the neuromuscular junction, Ca2+ ions are necessary for:
a. Binding the transmitter with the postsynaptic receptor.
b. Facilitating diffusion of the transmitter to the postsynaptic membrane.
c. Splitting the transmitter in the cleft, thus deactivating the transmitter.
d. Fusing the presynaptic vesicle with the presynaptic membrane, thus releasing the transmitter.
e. Metabolizing the transmitter within the presynaptic vesicle.
B. Facilitating diffusion of the transmitter to the postsynaptic membrane.
Which one of the following is true with regard to the termination of synaptic action at the neuromuscular junction?
a. The reuptake of intact acetylcholine molecules into the motor neuron terminal is responsible.
b. Diffusion of acetylcholine away from the synapse is solely responsible.
c. Acetylcholinesterase rapidly breaks down acetylcholine into choline and acetate.
d. Dissociation of acetylcholine from the muscarinic receptor, after binding for several seconds, is solely responsible.
C. Acetylcholinesterase rapidly breaks down acetylcholine
into choline and acetate.
- Several antagonist drugs compete with acetylcholine for the postsynaptic receptor at the neuromuscular junction. If you overdosed your patient with one of these competitive drugs, what would the antidote need to do at the synapse?
a. Decrease the release of acetylcholine.
b. Decrease the effectiveness of acetylcholinesterase.
c. Decrease the influx of Ca2+ into the motor neuron
terminal.
d. Decrease the action potential frequency on the motor neuron.
e. None of the above.
B. Decrease the effectiveness of acetylcholinesterase.
