A & P Flashcards
How many pairs of spinal nerves are there?
31 pairs. 8 Cx, 12 Tx, 5 Lx, 5 sacral and 1 coccygeal
How many plexus are there?
4
Cx(C1-C4), Brachial (C5-T1), Lx(L1-L4) and Sacral(S1-S4)
Describe the divisions of the lumbosacral plexus.
Ant division- 1. Obturator, 2. Tibial
Post division- 1. Femoral, 2. Superior Glut, 3. Inferior Glut, 4. Peroneal
What is the largest nerve branch coming off femoral nerve?
Saphenous
Describe the microstructure of a peripheral nerve.
Paraneurium- outside of nerve
Epineurium- packing in box
Perineurium- surrounds fascicles (contain axon, myelin and vessels)
Endoneurium-surrounds axon
Describe the different sizes of nerves.
Large fiber- myelinated- proprio, touch, vibration
Small fiber- pain and temperature
Describe the two classifications of neurons.
Gasser: A- alpha motor, B-autonomic and C-small pain fibers
Lloyd: I-1a afferent ‘mm spindle’, II- somatosensory, III-, IV- pain and slow
What are two types of second order motor neurons in PNS?
Type I-normally recruited 1st, small, less myelin, slow, fatigue resistant-oxidative
Type II- normally recruited 2nd, large, more myelin, fast, fatigue fast-glycolic
The spinal cord ends at what level?
L1-L2
A disc bulge at L4-L5 will affect what nerve root?
L5 nerve root, could also affect S1 but most likely L5
Describe a neuron
Has a – charge inside and + charge outside secondary to presence of large – charged proteins inside it.
Cation- K+ and Na+, Anions- CL-, more K+ inside and CL- and Na outside
What is the resting membrane voltage of a neuron?
-70mV- -90mV
How does the Na-K pump help to regulate this?
Actively pumps 3 Na out and 2 K into the cell against the concentration gradient.
What cells produce myelin in CNS?
Oligodendrocytes
What cells produce myelin in PNS?
Schwann cells
What is the primary function of myelin?
increase CV, speed and insulate
How does myelin increase speed?
Salatory conduction along Nodes of Ranvier
How does demyelination decrease speed?
Invagination blocks the voltage gated channels at the node which causes conduction block. Normally have 1mm space in between each Node, with invagination increase the space to 2-3mm decreasing salatory conduction, conduction now occurs through Eddy currents ‘slow conduction process’
What causes an action potential?
The cell is depolarized to -65 - -75mV Na,+K influx. All or none- signal propagates in both directions along cell membrane.
Describe the leading trailing dipole model? This is what happens at cellular level when cell depolarizes.
If depolarization occurs directly under the electrode then will get an initial negative deflection, if it occurs before the electrode moving towards the electrode, then will get an initial positive deflection, then a negative deflection as the single passes under the electrode.
What do isopotential lines represent?
potential/voltage magnitude
What is the current sink?
site where ions are caught (Na) b/w 2 dipoles (site of ion release)
What is a cation?
group of ions having a +charge and moving toward the – electrode. ie NA
What is dipole and quadrapole?
Tripole (+-+), Quadrapole (+–+) (–)-current sink is negative part
What is a motor unit?
1 alpha motor neuron, it’s axon and all the mm fibers it innervates
What is a T-tubule?
Network of tubules filled with extracellular fluid that travels thru mm fiber and is an extension of the sarcolemma.
What is sarcoplasmic reticulum?
Tubules filled with Ca wraps around mm fiber; no connection to sarcolemma or extracellular fluid.
What ion enters the motor terminal branch & stimulates synaptic vesicles to fuse with membrane and release ACH?
Ca
Describe the Henneman Size Principle?
mm recruitment; Type I small fibers recruited 1st, as more force needed, type I fire faster, then Type II large come in
Trace sensory pathway from distal limb to cerebrum
Finger receptor-PN-Plexus-ant. Ramus-spinal nerve-dorsal root-DRG-dorsal root-dorsal horn (post column)- fasiculus gracilis LE and fasiculus cuneuate UE- ascends up to medulla synapse on 2nd order-x over medial lemiscus-ascends thru internal capsule to thamalus- synapse on 3rd order ascends to parietal lobe/postcentral gyrus
Trace motor pathway from cerebrum to muscle.
Frontal lobe/Area 4/precentral gyrus-internal capsule-brainstem to medulla-lateral and anterior cotricospinal tracts. 80-90% x over and descend down lateral column (limbs); 10-20% don’t cross over and descend down anterior column (trunk)- ventral horn and synapse on 2nd order- ventral horn-spinal nerve-ant ramus-plexus-peripheral nerve-muscle
Normal mm fibers of a single motor unit usually are…
all the same fiber type
1st order axons involved in somatosensory system are located in which column of the spinal cord?
Dorsal column
How many sensory neurons are involved in the pathway from receptor in skin of finger to the somatosensory cortex?
3
What do motor studies test?
2nd order motor neuron from ant horn distally
What do sensory studies test?
Peripheral axon of 1st order neurons (II) in the PNS; do not test the central axons of 1st order neuron, 2nd or 3rd order neuron in CNS
Describe how salatory conduction between Nodes of Ranvier increased conduction velocity.
Immature myelin has an internode distance similar to infant at aprox 300 micrometers and as it matures the internode distance increases to 1mm. This results in increased CV as more distance is covered with each ‘jump’.
