Midterm 2- Autonomic Pathways

Question 1

what neurons does the efferent division of the peripheral nervous system consist of, and what do the neurons control

Answer 1

consists of somatic motor neurons (which control skeletal muscles) and autonomic neurons (which control smooth muscle, cardiac muscle, and glands)

Question 2

differentiate between somatic and autonomic pathways (ie; neurotransmitter release + location of efferent neurons + target tissue)

Answer 2

somatic
- posture and movement
- voluntary
- direct excitatory control
- precise neurotransmitters release at synapses
- efferent neurons located in ventral horn
- target tissue: skeletal muscles
- only one neuron (originates in CNS and terminates on skeletal muscle)

autonomic
- mostly involuntary
- diffuse neurotransmitters release on target
-efferent neurons located in lateral horn
-sympathetic branch (fight or flight; axons from T1-L2)
-parasympathetic branch (rest and digest; axons from cranial nerves and S2-S4)
- two neurons (preganglion neuron from CNS that synapses w/ a postganglionic neuron in an autonomic ganglion; the autonomic post ganglionic neuron synapses onto target tissue @ neuroeffector junction)

Question 3

when is the sympathetic branch dominant? `

Answer 3

• sympathetic response is enhanced
• parasympathetic response is inhibited

Question 4

when is the parasympathetic branch dominant?

Answer 4

• parasympathetic response is enhanced
• sympathetic response is inhibited

Question 5

explain the neurotransmitters for somatic, sympathetic, and parasympathetic

Answer 5

Somatic
- nicotinic ACH receipting at NMJ

both parasympathetic and sympathetic preganglionic neurons release ACH onto nicotinic (ionotropic) receptors on post ganglion cell

most Postganglion parasympathetic neurons secrete norepinephrine (NE) onto adrenergic (metabotropic) receptors on target cell

most post ganglion sympathetic neurons secrete ACH onto muscarinic (metabotropic) receptors on target cell

Question 6

explain dual antagonistic control

Answer 6

• target tissue innervated and modulated by BOTH sympathetic and parasympathetic ganglia, which act in opposite

Question 7

what is an example of antagonistic control?

Answer 7

Neurotransmitters from a sympathetic heart neuron increase heart rate, while neurotransmitters from a parasympathetic neuron decrease it

or

the iris sphincter in the pupil (parasympathetic) and the iris dilator (sympathetic)

Question 8

explain tonic control

Answer 8

target tissue innervated and modulated by EITHER sympathetic or parasympathetic ganglia

Question 9

what is an example of tonic control?

Answer 9

the diameter of a blood vessel is set by the activity of the sympathetic nervous system. a moderate rate of signaling (basal state) from the nerve results in a blood vessel of intermediate diameter. An increase in rate of signaling by the nerve results in constriction of vessel; a decrease in signaling leads to dilation

Question 10

explain what happens at the neuroeffector junction in autonomic pathways

Answer 10

1. action potential arrives at varicosity (which contain neurotransmitters)
2. depolarization opens voltage-gated Ca 2+ channels
3. Ca entry triggers exocytosis of synaptic vesicles
4. NE binds to adrenergic receptor on target
5. receptor activation ceases when NE diffuses away from synapse

neurotransmitters released over surface of target cells
no defined synaptic cleft (slow acting and long effect duration)

Question 11

when does neurotransmitter activation of its receptor terminate?

Answer 11

it terminates when the neurotransmitter
- diffuses away
- is metabolized by enzymes in the ECF
- is actively transported into cells around the synapse
–NE can go back into synaptic vesicles for re release
– NE can be metabolized by monoamine oxidase (MAO)

Question 12

what are some indirect agonists of the neuroeffector junction?

Answer 12

indirect agonists affect the concentration of neurotransmitter (does not affect receptors)
cocaine
- blocks reuptake of NE
- maintains high concentration of NE around target tissue for longer time

SSRIs
- inhibits reuptake of serotonin
- maintains high concentration of serotonin around target tissue for longer time

MAOIs (monoamine oxidase inhibitor)
- prevents degradation of NTs

Question 13

explain the sympathetic branch of pupil

Answer 13

pupillary dilation
iris dilator
via superior cervical ganglion
NT: norepinephrine
Receptor: adrenergic (metabotropic)
the sympathetic system constricts the circular muscles to constrict the pupil

Question 14

explain the parasympathetic branch of the pupil

Answer 14

constriction
iris sphincter
via ciliary ganglion
NT: acetylcholine
Receptor: muscarinic
the parasympathetic system constricts the circular muscles to constrict the pupil

Question 15

where is NE made and primarily released?

Answer 15

NE made and released primarily by sympathetic post-ganglionic neurons

comes from variscosities on post ganglionic sympathetic neurons, which contain tyrosine and NE

NE’s effect is limited to the neuroeffector junction (it is NOT systemic, it is LOCAL)

Question 16

where is EPI released from?

Answer 16

EPI is released from the adrenal glands’ medulla

EPI’s effect is systemic

Hypothalamus (CNS) sends a signal via preganglionic neuron to chromaffin cells in adrenal medulla; more specifically, it synapses ACH onto chromaffin cells , which release EPI into blood stream via calcium mediated exocytosis

85% EPI released
15% NE released, just non functional

Question 17

explain relationship between smooth muscle cells and endothelial cells

Answer 17

endothelial cells connect two blood vessels; they’re in contact w lumen of a blood vessel

smooth muscle cells are oriented perpendicular to axis of blood flow; wrapped around endothelial cells so that way when they contract we get constriction and it narrows the opening of the blood vessel; when they relax, dilation

Question 18

what are the two ways smooth muscle communication is organized?

Answer 18

single unit and multi unit

Question 19

explain the properties of a single unit smooth muscle

Answer 19

• autonomic neuron varicosity is not innervated between smooth muscle cells
• smooth muscle cells connected via gap junctions, relies on receptors located on the smooth muscle cells located closest to autonomic neurons and then use gap junctions to spread communication

Question 20

explain the properties of multi-unit smooth muscles

Answer 20

-smooth muscle cells are independent, no gap junctions
- autonomic neuron innervated between the smooth muscle cells
- allows for finer control

Question 21

where can you find single and multi unit smooth muscles in the body?

Answer 21

single unit: small intestine
multi unit: in the eye

Question 22

explain smooth muscle contraction and how it differs from skeletal muscle contaction

Answer 22

• smooth muscle contraction is longer in time compared to skeletal and cardiac muscle
• smooth muscle likes to maintain a force for a longer period of time due to its given functions (like helping digest food)
• ATP is not abundant in smooth muscle, so they use less energy, but they like to slow down their myosin ATPase in order to maintain force
• contractions can happen with a subthreshold graded potential, after an AP, or even with little to no change in membrane potential

Question 23

actin and myosin in smooth muscle

Answer 23

• there is a lot of actin in smooth muscle (about 10-15 actin per myosin)
• lesser myosin ratio seen in smooth muscle compared to skeletal muscle
• myosin is longer in length in smooth muscle compared to skeletal muscle
  – myosin heads seen to cover entire surface surface of myosin molecules
  – allows smooth muscles to stretch more but still maintain tension

Question 24

what is vascular contraction/relaxation dependent on?

Answer 24

vascular contraction/relaxation depends on variable receptors