Lecture 4- Somatic and Autonomic Efferents

Question 1

Describe a reflex arc pathways

Answer 1

Somatic from nerve to muscle

Autonomic from sensory receptor to CNS

Question 2

Reflex arch explanation: Somatic pathway

Answer 2

Originates at anterior horn cell of SC
Signal travels down myelinated axon of AHC towards mixed peripheral nerve
Ends at neuromuscular junction at target skeletal muscle

Question 3

Boundary caps

Answer 3

Made by neural crest cells
Separates the point of exit of the motor axons from the ventral neural tube and the entry into the dorsal tube of the spinal axons from the dorsal roots
Acts as a selective filter which allow the passage of outgoing and incoming axons but serve as a barrier to keep cells in the appropriate compartment

Question 4

Absence of boundary caps

Answer 4

Many cell bodies translocate away from the lateral motor column into the space outside the neural tube

Question 5

Neuromuscular junction

Answer 5

Terminal boutons containing ACh
Junctional folds
Striated muscle

Question 6

Autonomic pathways

Answer 6

Consists of a chain of 2 neurons
Preganglonic neuron originating in CNS
Postganglion neuron going to effector organ
Site of synapse at autonomic ganglia
Preganglionic- ACh and nicotinic cholinergic receptor
Postganglionic- NE and adrenergic receptors

Question 7

Sympathetic ganglia

Answer 7

Preganglionic, have dendrites and cell bodies within the lateral grey horn of thoracic and lumbar segments of SC
Mainly multipolar neurons with fine Nissl bodies
Cell bodies encapsulated by satellite cells
Capsule surrounding individual ganglia

Question 8

Parasympathetic ganglia

Answer 8

Preganglionic neurons located in the nuclei of the brainstem and the lateral horn of the sacral SC
Multipolar neurons located within viscera, particularly within walls of digestive tract
No connective tissue surrounding ganglia
Few satellite cells

Question 9

Parasympathetic ganglia histology

Answer 9

Located in the organ that is being innervated
Eccentrically placed nuclei
Satellite cell nuclei
Nerve fibers

Question 10

Sympathetic ganglia histology

Answer 10

Found along sympathetic chain
No well-defined satellite capsules
Eccentrically placed nuclei
Smaller than sensory neurons of spinal ganglia

Question 11

Neuroeffector junction

Answer 11

The synapse between an efferent neuron and the effector organ
Neurotransmitters are released at swellings: vericosities
When action potentials reach the vericosities, they are propagated along by voltage-gated Na and K channels, but in addition also have voltage gated Ca channels

Question 12

Peripheral nerve associated layers

Answer 12

Endoneurium
Perineurium
Epineurium

Question 13

Endoneurium

Answer 13

Includes loose connective tissue surrounding each individual nerve fiber

Question 14

Perineurium

Answer 14

Includes specialized connective tissue surrounding each nerve fascicle

Question 15

Epineurium

Answer 15

Dense irregular connective tissue

Surrounds entire peripheral nerve and fills the space between nerve fascicles

Question 16

Peripheral nerve support cell

Answer 16

Schwann cell

Question 17

Regeneration and repair of a peripheral nerve

Answer 17

Requires classification of injury

A-E

Question 18

PN injury A

Answer 18

Neurapraxia
Transient, non-degenerative lesion
Transient conduction block, eg: carpel tunnel
No Surgery indicated

Question 19

PN injury B

Answer 19

Axonotmesis
Degenerative lesion in continuity
Axonal disruption
No surgery indicated, observe for clinical manifestations

Question 20

PN injury C

Answer 20

Endoneurium disruption
Commonly caused by compression
Delay surgery, observe for 6 months, surgical intervention is function is disrupted

Question 21

PN injury D

Answer 21

Partial section
Endo and perineurium disruption, only epineurium intact
Caused by blunt transection injuries
Delay repair, assess neural deficit, surgical exploration if necessary

Question 22

PN injury E

Answer 22

Neurotomesis
Complete section
Whole nerve transected, lacerating injury
Immediate repair necessary