Lecture 01a: Introduction to the Autonomic Nervous System Flashcards
What are the two main functions of the nervous system?
- receiving and processing information from the environment
- coordinating and executing appropriate actions in response to stimuli
What is the nervous system comprised of?
neurons and neuroglia
What kind of cells are neurons?
excitable nerve cells
What kind of cells are neuroglia?
non-excitable supporting cells
What is the nervous system structurally divided into?
the CNS and PNS
What makes up the CNS?
brain + spinal cord (tracts + nuclei)
What makes up the PNS?
everything outside of the CNS (nerves + ganglia)
What are tracts?
white matter components
What are nuclei?
gray matter components
What is the peripheral nervous system divided into?
motor (efferent) and sensory (afferent) components
What do efferents do?
they carry signals from the CNS to muscles and glands
What do afferents do?
they carry signals from tissues and organs to the CNS
What is the motor component of the PNS divided into?
somatic and autonomic nervous systems
What is the function of the somatic nervous system?
it innervates skeletal muscle
What is the function of the autonomic nervous system?
it innervates smooth/cardiac muscle and most glands
What is the autonomic nervous system divided into?
the sympathetic and parasympathetic nervous systems
What is the sympathetic nervous system?
“fight or flight”
What is the parasympathetic nervous system?
“rest and digest”
What are the components of the enteric nervous system?
digestive organs only
Examples of somatic sensory
temperature, pain, touch, pressure, proprioception
Examples of visceral sensory
heart rate, nausea, hunger
Examples of somatic motor
contraction of skeletal muscle: movement at joints
Examples of visceral motor
glandular secretion, vasodilation/vasoconstriction
Where does sensory stimuli come from in the visceral nervous system?
from the internal environment
What kind of motor responses come from in the visceral nervous system?
motor control of smooth and cardiac muscle
What are visceral structures?
thoracic, abdominal and pelvic organs
Where are the cell bodies found in the somatic nervous system?
the ventral horn
Where do the cell bodies exit in the somatic nervous system?
through the ventral rootlet and roots into the spinal nerve
What neurotransmitter is released at the neuromuscular junction in somatic efferents?
acetylcholine
How does information travel in somatic efferents?
a single axon that goes from the CNS into peripheral tissues to innervate skeletal muscle
Where are cell bodies found in the visceral nervous system?
the lateral horn
Where do cell bodies exit in the visceral nervous system?
through the ventral rootlets and roots into the spinal nerve
Is the preganglionic neuron myelinated or unmyelinated in the visceral nervous system?
myelinated
What is released once the preganglionic neuron reaches the autonomic ganglion?
acetylcholine
What is activated when acetylcholine is released?
the postganglionic neuron
Is the postganglionic neuron myelinated or unmyelinated in the visceral nervous system?
unmyelinated
What do postganglionic neurons release when they reach their target muscle?
either acetylcholine or norepinephrine
What do visceral neurons innervate?
smooth muscle, cardiac muscle and glands
What kind of innervation does the skin and adrenal gland receive?
sympathetic innervation
What is another name for the sympathetic division?
thoracolumbar outflow T1-L2
What are the 3 characteristics of the preganglionic sympathetic neurons?
(where are their cell bodies found, what are their sizes, what do they release)
- cell bodies in the lateral horns of the spinal cord
- short, myelinated axons
- release acetylcholine
What are the 3 characteristics of the postganglionic sympathetic neurons?
(where are their cell bodies found, what are their sizes, what do they release)
- cell bodies in the sympathetic ganglia
- long, unmyelinated axons
- release norepinephrine
What are sympathetic chains (paravertebral ganglia)?
interconnected ganglia lateral to vertebral column
What are the 3 collateral ganglia?
- celiac ganglion
- superior mesenteric ganglion
- inferior mesenteric ganglion
Where are collateral ganglia found?
anterior to the spinal cord
What is the exception in the sympathetic division?
the adrenal medulla
Why is the adrenal medulla the exception of the sympathetic division?
because it receives direct innervation from preganglionic sympathetic neurons
Why does the adrenal medulla receive direct innervation from preganglionic sympathetic neurons?
because it produces norepinephrine itself
What are the divisions of the sympathetic system?
- white ramus communicans
- grey ramus communicans
- sympathetic chain
- splanchnic nerves
What passes through the white ramus communicans?
preganglionic neuron
What passes through the grey ramus communicans?
postganglionic neuron
What kind of axons are found in the sympathetic chain?
ascending/descending axons
Where do splanchnic nerves synapse?
in collateral ganglia
What happens during sympathetic pathways towards cranial, cervical and thoracic viscera?
preganglionic neurons synapse in superior ganglia of sympathetic chain; postganglionic neurons continue as named sympathetic nerves to target organs
What happens during sympathetic pathways towards abdominal and pelvic viscera?
preganglionic neurons pass through sympathetic chain ganglia and create splanchnic nerves; synapse in collateral ganglia then to target organs
What do postganglionic sympathetic fibers contribute to?
large visceral plexus near target organs
What is another name for the parasympathetic division?
craniosacral outflow (brainstem + S2-S4)
What carries the parasympathetic division?
4 cranial nerves + S2-S4
What are the 4 cranial nerves used in the parasympathetic division?
CN III, CN VII, CN IX, CN X (3, 7, 9, 10)
What nerve is CN III?
oculomotor nerve
What nerve is CN VII?
facial nerve
What nerve is CN IX?
glossopharyngeal nerve
What nerve is CN X?
vagus nerve
What are the 3 characteristics of the preganglionic parasympathetic neurons?
(where are their cell bodies found, what are their sizes, what do they release)
- cell bodies found in the lateral horns of the spinal cord
- long, myelinated axons
- release acetylcholine
What are the 3 characteristics of the postganglionic parasympathetic neurons?
(where are their cell bodies found, what are their sizes, what do they release)
- cell bodies found in parasympathetic ganglia
- short, unmyelinated axons
- release acetylcholine
Where are the visceral ganglia found in the parasympathetic system?
near or within the walls of target organs
What are the 5 major functions of the parasympathetic nervous system?
- salivation
- lacrimation
- urination
- digestion
- defacation
What kind of system is responsible for cutaneous structures like blood vessels, sweat glands and hair follicles?
only the sympathetic nervous system
What kind of system is responsible for the dilation of the pupil (increasing the size)?
sympathetic nervous system
What kind of system is responsible for the constriction of the pupil (decreasing the size)?
parasympathetic nervous system
Does the sympathetic nervous system have single or multiple connections between pre- and post-ganglionic neurons?
multiple connections (widespread influence)
Does the parasympathetic nervous system have single or multiple connections between pre- and post-ganglionic neurons?
it has one or two (localized actions)
Are visceral afferents part of the autonomic nervous system?
no
What do visceral afferents carry?
pain and sensation from organs
What is the structure of visceral afferents?
collections of pseudo unipolar neurons with cell bodies in sensory ganglia
What are dermatomes?
an area of skin innervated by sensory fibers in a single spinal nerve
How are dermatomes distributed?
unilaterally
What are the 4 key dermatomes?
C5-T1: upper limbs
T4: nipples
T10: belly button
L2-S2: lower limbs
What is the definition of referred pain?
tissue injury/other painful stimulus in one area is perceived as pain elsewhere
Why does referred pain happen?
because sensory neurons from visceral and somatic tissues from their dermatomes share similar pathways and may synapse on the same interneurons or higher order neurons
Referred pain pattern for the heart
T1-T4
Referred pain pattern for the diaphragm/lung
C3, C4, C5
Referred pain pattern for the kidneys
T11/T12-L3