pns Flashcards
(4 cards)
pns
The autonomic nervous system (ANS) is a part of the peripheral nervous system (PNS). Like the rest of the PNS, it receives sensory input from the body—especially from internal organs (viscera).
But here’s what’s special:
The ANS mainly sends motor (output) signals to the visceral organs—like the heart, stomach, lungs, and eyes—to help maintain homeostasis (internal balance). These responses happen automatically, without us being aware of them, which is why the ANS controls involuntary movements.
Examples of Involuntary ANS Actions:
Pupil constriction in bright light – a parasympathetic response.
Pupil dilation when you’re scared or attracted to someone – a sympathetic response.
Increased heart rate when you’re stressed or exercising – sympathetic.
Slower heart rate and increased digestion when you’re resting – parasympathetic.
automatic vs somatic
🔹 Somatic Nervous System (SNS):
The motor neuron’s cell body is in the CNS.
The axon goes all the way from the CNS to the skeletal muscle.
It uses the neurotransmitter acetylcholine (ACh).
Usually voluntary (like moving your arm), but some actions can be involuntary, like reflexes.
🔹 Autonomic Nervous System (ANS):
Uses two neurons in a chain:
Preganglionic neuron:
Cell body is in the CNS.
Axon leaves the CNS and goes to a ganglion.
Releases neurotransmitter into a synaptic cleft (space between neurons).
Postganglionic neuron:
Cell body is outside the CNS, in the ganglion.
Axon goes to the target muscle or gland (like heart, stomach, etc.).
The signal crosses the synaptic cleft, and sometimes one signal can activate many postganglionic neurons, allowing for a stronger, widespread reaction.
🔹 Neurotransmitters Used:
Parasympathetic division (rest and digest): uses acetylcholine (ACh)
Sympathetic division (fight or flight): mostly uses norepinephrine (NE)
parasympathetic vs sympathetic overview
he Two Arms of the Autonomic Nervous System (ANS):
🔹 1. Sympathetic Division (“Fight or Flight”)
Function: Prepares the body for stressful or emergency situations.
When active: During exercise, fear, anger, excitement, or threat.
Effects on the body:
Increases heart rate
Dilates pupils
Expands airways
Slows digestion
Releases glucose (for energy)
🔹 2. Parasympathetic Division (“Rest and Digest”)
Function: Helps the body relax, recover, and conserve energy.
When active: During calm, restful times (like after eating or while sleeping).
Effects on the body:
Slows heart rate
Constricts pupils
Stimulates digestion
Promotes gland activity
