PNS Flashcards
1
Q
what’s a nerve?
A
- bundle of many axons in the PNS
- coming down from neurons (cell bodies) in the CNS
- grouped together and coated in myelin
- innervate muscles by conducting messages from the CNS to muscle fibers (efferent)
- conveys sensroy input from muscles back to brain (afferent)
2
Q
spinal nerves
A
- convey motor input to body
- convey sensory input from body
- emerge from SC
3
Q
cranial nerves
A
- convey motor input to head, mouth, articulators, and some internal organs
- emerge from brainstem
4
Q
ganglia
A
- collection of neurons (nerve cell bodies) outside the CNS
- found in the PNS
- perform a certain function, outside the CNS
5
Q
functions of spinal, cranial nerves and ganglia
A
- serve as a connecting system between CNS and body
- engage/provide voluntary and involuntary control over body
6
Q
motor (efferent) neurons
A
sending info from the CNS to the body
7
Q
sensory (afferent) neurons
A
sending info to the CNS from the body
8
Q
somatic nervous system
A
voluntary control of skeletal muscle
-innervation to/from all skeletal muscles
9
Q
outgoing somatic NS
A
- dependent upon tracts leaving the cortex, traveling down the spinal column, and synapsing with new motor neurons before exiting the CNS
- efferent nerves leaving the CNS, now traveling as part of the PNS and synapsing directly with muscle causing muscle movement
10
Q
incoming somatic NS
A
- afferent nerves entering the CNS, coming directly from skin or muscle
- synapsing with other sensory neurons along the way, now traveling as part of the CNS
- provides sensory info from the PNS
11
Q
reflex arcs
A
- provides conscious, voluntary control
- directly mapped sensory-motor systems, in the PNS
- located at the level of the spinals nerves involved in the PNS
- bypasses the CNS all together
- provides immediate responses to external stimuli
- act in a protective manner
12
Q
upper motor neurons location
A
- ALL located in the CNS
- axons do not leave the CNS
- they remain within the brain, the brainstem, and/or the spinal cord
- orginate in the pre-motor cortex of the frontal lobe
13
Q
UMN form the..
A
- corticospinal tracts
- corticoblbar tracts
14
Q
corticospinal tracts
A
projection fibers traveling vertically
-sending axons to synapse with lower motor neurons in the SC
15
Q
cortiobulbar tracts
A
- projection fibers traveling vertically
- sending axons to synapse with cranial nerve nuclei in the brainstem
16
Q
UMNs provide…
A
- DIRECT activation system from the CNS to the PNS
- referred to as the direct pathway, pyramidal tract
17
Q
Lower motor neurons
A
-those neurons which convey the neuron impulse to its final destination
18
Q
location of the LMN
A
- cell body is in the CNS
- axon extends OUT of the SC or brainstem, and INTO the periphery
19
Q
function of the LMNs
A
-receive incoming UMN message from the motor cortex
-transmit the incoming motor impulse to the muscle itself
-cause the muscle to fire/move/contract
entire system= final common pathway
20
Q
other names for LMNs
A
-2nd order neurons, cranial nerve neurons, anterior horn cells, alpha motor neurons
21
Q
motor homunculus
A
- anatomical representation of the degree of innervation
- primary motor cortex via outgoing, efferent tracts
22
Q
sensory homunculus
A
anatomical representation of the degree of sensory input
-provided in the primary sensory strip
via afferent, or incoming tracts
23
Q
corticospinal tract - direct pathway
A
- from the pre-central gyrus (primary motor cortex)
- through the corona radiati (subcortical white matter in the cerebrum)
- converges together at the internal capsule (CNS)
- to the cerebral peduncle in the midbrain of the brainstem
- to the medulla, the lowest part of the brainstem- where the fibers cross midline to the other side=PYRAMIDAL DECUSSATION
- to the level of the SC where the desired muscle is
- to the anterior horn neuron in the SC
- to the dorsal and ventral motor roots which form the spinal nerve
24
Q
where do paired spinal nerves end up?
A
- they occur at each vertebral interval
- emerging from the SC, one on each side of the body
25
31 pairs of spinal nerves
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
26
STUDY SPINAL NERVES
-axons extending from LMNs SLIDE 30
27
where do the motor fibers or spinal nerves originate?
- in the grey matter or the H-shape
- at a group of cells called the anterior (ventral) horn cells
- which occur at the point of connection (synapse) between the incoming motor fibers from the CNS and the new alpha motor neuron in the SC, sending a new motor fiber out to the PNS, where it is then a nerve
28
extrapyramidal tracts (indirect pathways) function
- coordinate and adjust posture, balance
- coordinates and regulates rate, force, timing of movements
- inhibit/control muscle tone, amount of movements
- regulate and inhibit reflexive movements
29
methods of indirect pathways
- relies upon and works best with BG and cerebellum
- works with pyramidal pathways
- modifies messages generated by primary motor cortex
- it is a more complicated round-about
- POLYsynapatic
- does not provide direct input to the LMNs (just edits and fixes)
- has functions outside the system of tracts moving through the pyramidal structure of the brainstem
30
extrapyramidal tract structures
- BG (globus pallidus, caudate nucleus, putamen)
- substantia nigra and subthalamic nucleus
- midbrain (of the brainstem) --> red nucleus and reticular formation
- cerebellum
31
reticular formation
- collection of cells scattered amongst some cranial nerve nuclei and some fiber tracts within the brainstem
- long extension of these cells, throughout midbrain, pons and medulla
- mediates basic level of consciousness
- major player in mediating messages sent to the LMNs
32
red nucleus
- cluster of cells on the midbrain
- receives input from motor cortex and BG and feedback from the cerebellum
- further modifies motor messages on their way down
33
BG structures involved in indirect motor pathways
-substantia nigra and subthalamic nuclei
34
substantia nigra
- techincally located within the brainstem (midbrain) but functionally considered part of the BG
- information to and from the BG
- critical producer of dopamine
35
subthalamic nucleus
- technically part of the thalamic nuclei but functionally considered part of the BG
- receives input from globes pallidus, motor cortex
- head right back into the globes pallidus
36
indirect motor pathway concepts
- some decussate
- some remain ipsilateral
- some do both
- ALL provide indirect influence upon LMNs
- ALL engage in multi-synaptic circultry
- final synapse with inter-neurons to indirectly influence the movement executed by the LMNs
37
interneuron
is a neighboring neuron that is in the gray matter of the SC
- it is sitting there and its main job is to receive input from the indirect system (all the fixed info)
- they send the edited info directly to the LMNs
38
various extrapyramidal tracts
- corticorubral
- corticoreticular
- vestibulospinal
39
corticorubral tract
- INDIRECT
- ipsilateral - then proceeds
- from motor, premotor and sensory strip --> brain stem red nucleus
- rubrospinal (contralateral) --> from the cerebellum and BG to red nucleus - inhibitory control (not too much movement)
40
corticoreticular
- ipsilateral- then proceeds
- from motor, premotor, and sensory strip --> reticular formation in the BS (pons and medulla) --> cerebellum
- supports posture and walking
- reticulospinal (ipsilateral and contralateral) - from reticular formation to LMNs --> maintains tone from trunk and posture
41
vestibulospinal
ipsilateral and contralateral
- from vestibular nuclei, below 4th ventricle, within pons and medulla --> cerebellum and SC
- incorporate info about balance, position, movement of head
42
corticobulbar tracts
-direct motor innervation from CNS to cranial nerves within the brainstem, for control of face, neck, and head
43
corticobulbar tract pathway
- pre-central gyrus
- corona radiati
- internal capsule
- cerebral peduncle in the midbrain (to cerebellum to the brainstem)
- where the cranial nerves exit at various places within the brainstem, to innervate face, head, neck
44
12 cranial nerves
NOT the same spinal nerves
- attached to brain stem, uppermost spinal cord
- exit the brainstem through the foramina of the skull
- serve muscles/organs of head and neck
- not all are LMN (only the ones with motor capacity)
45
reflex arcs- another function of spinal nerves
- automatic, "stimulus response" mechanism
- survival mechanism
- subconcious muscle control
- without having to send sensory info through afferent tract all the way up to the CNS to secure some kind of response
46
what happens in a reflex arc
- sensory receptor
- sensory neuron, in the dorsal root ganglion
- to the sensory/dorsal root of the SN
- enters the dorsal aspect of the SC to posterior horn
- synapses with an interneuron
- interneuron synapses with the LMN
- immediately sends impulse straight back out and right back to the muscle telling it to move
