functional neuroanatomy the visceral nervous system (ans) · 2014-07-22 · 1 functional...
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Functional
neuroanatomy
the visceral
nervous system
(ANS)
27
Chris Thomson
BVSc(Hons), Dip ACVIM (Neurol), Dip ECVN, PhD
VTH, IVABS, Massey University
Palmerston North, New Zealand
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How do you evaluate the ANS in
your neurological examination?
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Visceral Nervous System
– Efferent system, afferents use the
same pathways
– Visceral afferent system
• Receptors
– Pressure, stretch and chemical changes
• Single neuron with peripheral ganglion
• Axons – cranial and spinal nerves
– CNN ganglia – geniculate (VII), petrosal (IX),
distal (X)
– Spinal ganglia
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Visceral afferent system
• Input via cranial nerves– Brainstem – Solitary nucleus (CN VII, IX, X) – GVA, SVA (taste)
» Reflex function via reticular formation e.g. respiratory, CVS
» Conscious perception – solitarothalamic tract
• Input via spinal nerves– Reflexes – sympathetic or parasympathetic
» e.g. tachy- or bradycardia
– Conscious perception to thalamus
Fig 6.7 Thomson and Hahn
Visceral afferent system
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Referred Pain
– Dermatomal distribution of referred pain
• Visceral afferent stimulation
– Stretch, distension, ischaemia
• Confusion with exteroception synapsing on same
dorsal horn
– Low density innervation
– Infrequent stimulation
– Viscerovisceral reflex
• causing cutaneous vasospasm and local
mediators?
– Occurrence in vet med?
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Somatic/exteroception
Cartoon by Gary Larson
Visceral afferent/
interoception
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What is the visceral motor system?
• Autonomic nervous system ANS– Purely efferent system (?)
– Innervates smooth and cardiac muscle and glands
– Two functional components• Differentiated morphologically,
pharmacologically and physiologically
• Parasympathetic NS
– Housekeeping system ‘rest and digest’
• Sympathetic NS
– Prepares the body for flight or to fight
– Dual innervation all body systems
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What is anatomical
arrangement of the VNS?
• Central nervous system (CNS) components
– Brain
• Forebrain (diencephalon) and brainstem
– Spinal cord
• Thoracic, lumbar, sacral
• Peripheral nervous system (PNS)
– Cranial and spinal nerves
– Efferent – two neuron system with peripheral ganglia
– (Afferent – single neuron and peripheral (spinal) ganglia)
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What are the anatomical concepts
of the ANS?• How many neurons?
– One CNS neuron• Brain or spinal cord
– Two neurons in the PNS (p106)• 1st neuron cell body in CNS
• 2nd neuron cell body in ganglion
• May pass through several ganglia without synapsing
– Terminology – pre and post synaptic neurons
• Where do ANS fibres leave CNS?– Parasympathetic NS = craniosacral NS
– Sympathetic NS = thoracolumbar NS
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What are the central controls for VNS?
• Hypothalamus
• Central regulator– Receives input
• From viscera
– Via CN VII, IX and X
» To nucleus solitarius in myelencephalon = principal visceral sensory nucleus
– Via segmental spinal nerves
» To spinal cord
– From telencephalon
» Emotional input
– Output
• Neural via brainstem and spinal cord
• Humoral via hypophysis
Dog brain, median section
H
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Add A23
Where are ANS NCB located?
Fig 1.7 Thomson and Hahn,
functional nuclear columns, spinal
cord and brainstem
From Fig A23, Thomson and Hahn,
Dog, TS myelencephalon
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• Spinal cord grey matter– Dorsal horn
• Sensory/afferent NCB
– Ventral horn • Motor/efferent NCB to striated muscle
– Intermediate horn• Motor/efferent NCB of ANS
• Thoracolumbar and sacral cord only
Fig 4.6 Thomson and Hahn
TS C7 and T8 spinal cords
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Peripheral
components of
the ANS
Fig 12.2 Thomson and Hahn
• 2-neuron + ganglion
• Location of ganglion PS vs Symp
• Neurotransmitter
• Terminology• Pre and post ganglionic???
• Pre and post synaptic
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ANS
Fig 12.1 Thomson and Hahn, ANS
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How do sympathetic fibres innervate all
viscera?
• Thoracolumbar outflow from CNS– C8/T1 to L4/5
– Thoracic cavity • Sympathetic chain of nerves and paravertebral ganglia
– Abdominal and pelvic cavities• Fusion of fibres to form prevertebral ganglia
– e.g. celic, cranial and caudal mesenteric ganglia
– Head• Supplied by spinal nerves from C8-T7
• Via vagosympathetic trunk
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Sympathetic trunk and ganglia
Fig 12.3 Thomson and Hahn
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How do parasympathetic fibres
innervate all viscera?
• Craniosacral outflow from CNS– Cranial nerves from brain
• To head region
– CN III, VII, IX, X
• To cervical, thoracic and abdominal viscera
– CN X via vagosympathetic trunk
– Segmental spinal nerves from sacral spinal cord• S1, S2, S3
• To pelvic viscera
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Vagus N.
Fig 12.4 Thomson and Hahn
Thoracic portion of the vagus nerve
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Figs 10.8 and 9 Thomson and Hahn,
Pupillary light reflex
Pupillary light reflex
• Signs of dysfunction
– Afferent lesion
• Other signs?
– Efferent lesion
• Other signs?
Autonomic
innervation of the
eye
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Fig 12.5 Thomson and Hahn,
Sympathetic innervation of the head
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Pupillary Function in Acute Brain Disease
• Miosis
– Compression of mesencephalon
– Mechanism?• parasympathetic nucleus of CN III
– facilitation or loss of inhibition?
• Loss of sympathetic function?
• Mydriasis
– Loss of parasympathetic nucleus of CN III function
– Unfavourable prognosis
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Innervation of pelvic viscera
Fig 12.7 Thomson and Hahn
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Innervation of the Urinary Bladder
• Micturition
– Primarily reflex function but controlled by
higher areas
• Brainstem centres
– Affect LMN and autonomic outflow
• Cerebrum
– Initiates learned toileting behaviour
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Storage Voiding
Parasympathetic - detrusor relaxation + detrusor
contraction
Sympathetic + b receptors
bladder wall
inhibition of detrusor
+ a bladder neck
sm muscle
contracts
- b receptors in the
bladder wall
- a bladder neck
muscle
Somatic + striated sphincter
contracts
- striated sphincter
relaxes
Urinary Bladder Function
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Lesions affecting urinary bladder
Fig 12.8 Thomson and Hahn
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Defaecation
• Primarily reflex
– Local enteric plexus
– Ascending paths for conscious perception
• which funiculus?– dorsal funiculus
– Sphincters • Striated muscle
• Origin and nerve?– pudendal nerve from S1-S3
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The Neuro Exam
• Aim to assess:
1) Mentation/arousal and
behaviour
2) Posture and gait
Sensory function – proprioception,
tactile
Motor function – gait, spinal reflexes
Coordination
Balance
4) Cranial nerves
5) Visceral function
6) Spinal pain-hyperpathia
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