Autonomic innervation in the cardiovascular system Flashcards
State 6 actions of the sympathetic nervous system
Raises HR
Increases force of contraction
Constricts most blood vessels
Slows GI transit
Constricts sphincters
Bronchodilates
Increase sweating
Dilates pupil (mydriasis)
State 6 actions of the parasympathetic nervous system
Slows HR (no effect on force)
Relaxes blood vessels
Speeds up GI transit
Relaxes sphincters
Increases salivation
Bronchoconstricts
Constricts pupil (miosis)
Describe the sympathetic supply to the head
Preganglionic fibres originate in hypothalamus
They descend to T1 & synapse with preganglionic neurons in the lateral horn and exit the spinal cord with T1 spinal nerve
Travel to sympathetic chain
Run up chain to cervical ganglia & synapse with postganglionic fibres
Enter head as plexus around internal carotid artery
Supply face via external carotid artery
Name the three sympathetic ganglia in the neck
Superior cervical: near the base of the skill (C1-C4)
Middle cervical (C5-C6)
Stellate: near apex of the lung (C7-T1)
Describe the structural organisation of the sympathetic nervous system
The cell bodies of sympathetic nerves lie in the lateral grey horn of the spinal cord from T1-L2.
Pre-ganglionic neurons have axons that travel through the ventral root (motor efferent) of their segmental spinal nerve and enter the sympathetic chain.
One chain is located on each side of the vertebral column (paravertebral) are are positioned in front of the ventral rami. The sympathetic chain extends from the base of the skull to coccyx where the two chains converge.
The sympathetic chain is made up of ganglia which is where preganglionic neurones synapse with postganglionic neurones.
Postganglionic fibres then leave the ganglia and are redistributed along the rami of spinal nerves via grey rami communicantes
How would the sympathetic nervous system be affected by damage to the spinal cord at T1?
What would the effect be?
T1 is the first branch of sympathetic neurons to enter the chain fron the spinal cord.
Fibres from T1-T4 enter the sympathetic chain and extend into the head and neck with
Damage to the spinal cord at T1 could remove or reduce sympathetic supply to the head and neck.
Could result in Horner’s syndrome
How would injury at L1 vertebrae affect the autonomic nervous system?
The L1 vertebral level contains the roots of the sacral spinal nerves S1-S5. (L1-L5 spinal cord levels are at T11-T12).
Therefore damage to the L1 vertebrae will mainly affect the parasympathetic nervous system which has outflow from S2-S4. The sympathetic nervous system will not be affected as much or at all because outflow terminates at L1.
Describe the features of Horners syndrome
Loss of sympathetic supply to the head and neck
Pupil constriction (miosis)
Vasodilation
Ptosis (drooping eyelids)
Lack of sweating (anhydrosis)
Name 3 common causes of Horner’s syndrome
Pancoast tumour (apex of the lung)
Tumour at the base of the skull
Lyphadenopathy
Iatrogenic (surgery)
Trauma
Describe the structural organisation of the parasympathetic system
There are two clusters of preganglionic neurons at each end of the spinal cord - 4 cranial nerves (CNIII, CNVII, CNIX and CNX) and three spinal nerves (S2-S4).
Parasympathetic nuclei of the cranial nerves sit in the brainstem. Postganglionic fibres from the cranial nerves travel with branches of CN V (trigeminal nerve) except for the vagus nerve.
Sacral parasympathetic outflow comes from preganglionic neurons with cell bodies in S2-S4 of the spinal cord. Axons leave the spinal cord through the ventral root and leave the spinal nerves as separate pelvic nerves.
Name the four parasympathtic outflows from the crainal nerves
CN III - oculomotor nerve
CN VII - facial nerve
CN IX - glossopharyngeal
CN X - vagus nerve
What are the actions of the ANS on the heart?
Alters:
Heart rate (chronotropic)
Force of heart contraction and stroke work (inotropic)
Speed of conduction through the AV node (dromotropic)
What are the actions of the ANS on blood vessels?
Contraction of smooth muscle in vessel wall
Dilation of coronary arteries
Dilation of arterioles – alter peripheral vascular resistance
Describe the autonomic innervation of the heart
Branches from both the parasympathetic and sympathetic systems contribute to the formation of the cardiac plexus.
This lies posterior to the aortic arch, to the bifurcation of the trachea.
Branches of the cardiac plexus affect nodal tissue which control the activity of the heart.
Vagus nerve: SA node and AV node
Sympathetic: SA node, AV node, Ventricular muscle
What is the prinipal transmitter released on the heart in response to sympathetic innervation
Noradrenaline
Sympathetic: Preganglionic - ACh, postganglionic - NA
Describe the parasympathetic outflow of the cranial nerves
CN III: Preganglionic fibre leaves the brainstem and synapses with the ciliary ganglion. Postsynaptic fibres travel with CN V1 (opthalmic division) to the eyes. Brings about pupil constriction and accomodation
CN VII: Preganglionic fibres send branches to the pterygopalatine ganglion and submandibular ganglion. From the pterygopalatine ganglion, branches of CNVII travel with CN V2 to the mucus membranes above the maxilla. From the submandibular gangion, fibres travel with CN V3 to the mucus membranes and glands of the mandible.
CN IX: Preganglionic fibres travel to the otic ganglion via the lesser petrosal nerve. Postganglionic fibres travel to the parotid gland with CN V3
CN X: the vagus nerve leaves the brainstem and travels to specific organs, contributes to thoracic plexuse and prevertebral plexus in the abdomen and pelvis
