Autonomic Nervous System Flashcards
Autonomic NS
Involuntary branch of the nervous system
- cardiac muscle
- smooth muscle
- most exocrine glands
- some endocrine glands
- adipose tissue
Sympathetic
-thoracic and lumbar origin
Parasympathetic
-cranial and sacral origin
Parasympathetic vs Sympathetic
Parasympathetic
- relaxation
- food processing
- energy absorption
Sympathetic
- uses energy
- increases metabolism
Autonomic Nerve Pathway
CNS - preganglionic fiber to autonomic ganglion to postganglionic fiber to effector organ
Neurotransmitter release at pre and post ganglionic fibers
Preganglionic fibers
-both divisions release ACh
Postganglionic fibers
-parasympathetic: ACh - cholinergic fibers
-sympathetic (majority): norepinephrine - adrenergic fibers
-end in numerous swellings - variscosities
Sympathetic Activation **
Preganglionic neurons release ACh
- cholinergic fibers
- onto nicotinic receptors
Postganglionic neurons release
NE
-adrenergic fibers
-onto adrenergic receptors
ACh
- sweat glands
- blood vessels of skeletal muscles
Adrenal medulla
- modified sympathetic ganglion
- release of hormones into the circulatory system (NE and E)
Parasympathetic Activation **
Preganglionic and postganglionic neurons release ACh - cholinergic fibers
Receptors:
- nicotinic
- muscarinic
Dual Innervation/Antagonistic Control
Precise Control
- instructions from both divisions
- opposing effects
Heart:
S: increased rate and force of contraction
PS: decreased rate and force of contraction
Digestive tract:
S: decreased motility
PS: increased motility
Bladder:
S: relaxation
PS: contraction
Eye:
S: dilation of pupil
PS: constriction of pupil
Brain activity:
S: increased alertness
PS: none
Tonic Control
- one signal is always present
- decreasing or increasing signal controls activity e.g.. blood vessel diameter
- smooth muscle in most blood vessels under sympathetic control
- decreased signal dilates vessel
- increased signal constricts
- intermediate signal always present
Autonomic Tone
-resting level of spontaneous activity
-exists for both antagonistic and tonic control mechanisms
eg. antagonistic control: heart rate
tonic control: blood vessel diameter
Hypothalamus
Links ANS and Endocrine systems
- anterior pituitary hormone secretion
- produces pituitary hormones
- thirst and urine output
- food intake
- uterine contractions and milk excretion
- participates in the sleep-wake cycle
Clinical Note: Memory
- short term memory
- long term memory
- memory consolidation is the conversion of short-term to long-term
- at the cellular level, memory consolidation involves changes in neurons and synapses
- increased neurotransmitter release
- facilitation at synapses
- formation of additional synaptic connections
Clinical note: Ageing
- reduction in brain size
- reduction in the number of neurons
- decrease in blood flow
- changes in synaptic organisation
- intracellular and extracellular changes in neurons
Clinical Note: Alzheimer’s Disease
- impaired short term memory followed by long term loss
- confusion, disorientation, personality changes
- death generally 4-12 years post diagnosis
- characteristic brain lesions, extracellular changes, neurofibrillary tangles
- neuronal cell death and loss of synaptic communication result in dementia
Two classes of drugs
- increase levels of ACh
- interferes with NMDA receptors (bind glutamate)
