Chapter 15: Autonomic Nervous System Flashcards
Somatic nervous system (SNS)
consciously perceived or controlled processes
Autonomic nervous system (ANS)
processes regulated below the conscious level; functions to maintain homeostasis
2 portions of the SNS
1- somatic sensory
2- somatic motor
Somatic sensory
detects stimuli from special sensory organs, skin, and proprioceptors; sends this info to the CNS
Somatic motor
directs voluntary control of skeletal muscles; transmits info from the CNS to skeletal muscles
Voluntary movements involve the
cerebrum
Reflexive movements involve the
brainstem and spinal cord
2 portions of the ANS
1- visceral sensory
2- autonomic motor
Visceral sensory
detects stimuli from internal organs and blood vessels; sends info to CNS
Autonomic motor
directs involuntary control of heart, smooth muscles, and glands and divided into PNS and SNS
SNS motor neurons
- has a single lower motor neuron extending from the CNS
- it has large, myelinated axons
- always releases ACh
ANS motor neurons
- have a chain of two lower motor neurons extending from the CNS
- the preganglionic neuron synapses in a ganglion and always releases Ach
- the postganglionic neuron releases Ach or NE
Preganglionic neuron
releases Ach from synaptic knob to excite the second motor neuron
Postganglionic neuron
releases Ach or norepinephrine from the synaptic knob to either excite or inhibit the effector
Parasympathetic nervous system
- “rest and digest”
- maintains homeostasis at rest
- conserves energy
- replenishes nutrient stores
Sympathetic nervous system
- “fight or flight”
- controls body during times of stress/crisis
PNS neurons
- craniosacral division
- preganglionic neurons in the brainstem or S2-S4 spinal cord
- preganglionic axons are long, and postganglionic axons are short
- ganglia are close to or within the effector organ
- preganglionic axons have few branches
SNS neurons
- thoracolumbar division
- preganglionic neuron in lateral horns of T1-L2
- preganglionic axons are short, and postganglionic axons are long
- ganglia are close to the spinal cord
- preganglionic axons have many branches
What is autonomic tone?
both divisions innervate the same part of the body
Dual innervation
when an organ receives input from both the sympathetic and parasympathetic nervous system
Cooperative effects
when both the PNS and SNS produce a single result
An example of cooperative effects
the body preparing before and after sex (orgasm)
The antagonistic effects between the PNS and the SNS in:
Control of heart rate
Control of muscular activity of the GI tract
Pupil size
- control of heart rate:
PNS decreases heart rate
SNS increases heart rate - control of muscular activity of the GI tract
PNS increases motility
SNS decreases motility - pupil size
PNS constricts pupil
SNS dilates pupil
What body structures are innervated by the SNS only?
- adrenal medulla
- blood vessels supplying skeletal muscles
- sweat glands in the trunk
- arrector pili muscles in the skin
Autonomic reflexes (visceral reflexes)
pre-programmed response to a stimulus generated by a reflex arc
ANS effectors are
- cardiac muscle
- smooth muscle
- glands
How does autonomic reflexes maintain homeostasis?
it enables the ANS to control visceral function
Cardiovascular reflex
decreases blood pressure by detecting stretch receptors in vessel walls which respond to pressure elevation; slow heart rate
Gastrointestinal reflex
- stimulates the secretion of gastric glands by parasympathetic stimulation
- controls the rectum through the parasympathetic reflexes causing contraction to aid the elimination
Micturition reflex
mechanism leading to bladder emptying
How does the cardiovascular reflex affect blood pressure?
decreases blood pressure
What CNS structure is the integration and command center for autonomic function?
the hypothalamus
How is the autonomic system regulated?
ANS is a regulated CNS, not an independent, and is influenced by 4 CNS regions:
1-cerebrum
2-hypothalamus
3-brainstem
4-spinal cord
Mass activation
prepares the body for intense physical activity in emergencies and stress by simultaneously influencing several effectors
