The Sympathetic NS Flashcards
What is the somatic system responsible for?
voluntary movement e.g. writing, running, walking and talking
What is the autonomic system responsible for?
controlling organs in the body (involuntary)
What is the autonomic NS divided into?
sympathetic and parasympathetic nervous systems
Give examples of systems under autonomic control
visceral reactions e.g. food digestion and eye dilation
Where is the hypothalamus located?
at the bottom of the diencephalon
What does the hypothalamus do?
- secrete hormones from the pituitary gland that act on the endocrine glands of the body
- send projections down the spinal cord to control the sympathetic and (in part) parasympathetic nervous systems
What is the hypothalamus sensitive to?
the blood flowing through it
What 3 tissue types does the ANS stimulate?
- cardiac muscle
- smooth muscle
- glands
How is the balance between the parasympathetic and sympathetic nervous systems maintained?
by increasing the amount of stimulation in one part of the system or decreasing the amount of discharge in the other
When does the sympathetic NS dominate?
when a person is in a stressful situation; the body reacts by preparing for ‘fight or flight’
What happens to the body under stress due to the sympathetic NS?
- muscles work harder and need more oxygen and energy
- one breathes faster and the bronchi and bronchioles open up for greater and quicker passage of air
- the heart beats stronger and faster
- the arteries to the heart and voluntary muscle dilate to increase blood flow
- the arteries to the skin and other peripheral areas constrict
- the liver secretes glycogen for quick supply of energy and the GI tract slows down
- pupils dilate
- one sweats to reduce elevated body temperature
What is cardiac output?
the amount of blood pumped by the heart per minute
What is the outflow of the sympathetic NS based on?
a two-neuron motor pathway consisting of preganglionic and postganglionic neurons
Where are the preganglionic neuron cell bodies located?
in the intermediolateral horn of T1 to L2 spinal segments; the thoracolumbar outflow
How do the preganglionic axons leave the spinal cord?
via the ventral roots into the sympathetic (chain) trunk
What is the sympathetic trunk?
a series of ganglia and axon fibres on each side of the vertebral column
What is the chemical transmitter between the postganglionic sympathetic axons and the structures they innervate?
mostly noradrenaline and, in some cases, adrenaline
What is adrenaline and noradrenaline used in hospitals for?
- falling blood pressure and cardiac arrest
- to counteract anaphylactic shock
- to dilate the bronchioles in acute asthma
Where are cell bodies of the sympathetic nerves that supply the heart?
in the intermediolateral horn of T1-T5 spinal segments
What do postsynaptic sympathetic fibres that innervate the heart arise from?
the cervical and superior thoracic ganglia of the sympathetic trunks
Where do the postsynaptic sympathetic fibres that innervate the heart go?
across cardiopulmonary splanchnic nerves and the cardiac plexus to end in the SA and AV nodes
What does stimulation of the SA node and conducting tissue do?
increase the rate of depolarisation of the pacemaker cells while increasing atrioventricular conduction
What does direct adrenergic stimulation from sympathetic nerve fibres to the heart do?
increase atrial and ventricular contractility
What do chromaffin cells do?
secrete more adrenaline into the blood via the CNS to increase heart rate
What are most adrenergic receptors on coronary blood vessels and what do they do?
β2-receptors, which, when activated, causes relaxation of vascular smooth muscles, and therefore, dilation of the arteries
What do sympathetic nerves that supply the lungs arise from?
cell bodies that are located on the T1-T5 paravertebral sympathetic ganglia of the sympathetic trunks
What do the sympathetic nerves travel through?
the pulmonary plexuses which are located posterior to the roots of the lungs
What are the effects of the sympathetic supply to the lungs?
- dilation of bronchial muscle (bronchodilator) which increases oxygen intake
- inhibition to the glands of the bronchial tree which decreases secretion from the glands
- vasoconstriction to bronchial vessels (not pulmonary vessels)
What happens when the glands of the bronchial tree are activated?
they secrete mucus and other enzymes and hormones to essentially lubricate the bronchial tree but under stress, these processes must be cut off to conserve energy
Where are the sympathetic nerves that supply the abdominal viscera found?
in the lateral horn of the thoracic segments T5-T12
Where are the sympathetic nerves that supply the pelvic organs found?
L1-2
Where do the preganglionic axons from T5 to L1/2 synapse?
onto postganglionic neurons outside of the trunk in the pre-aortic ganglia located in front of the abdominal aorta
What do the postganglionic axons do?
“hitch a ride” on the arteries until they reach the glands or smooth muscle to innervate them
What do some postganglionic axons do at the adrenal gland?
synapse on the cells in the adrenal medulla and release adrenaline intro the bloodstream via chromaffin cells to amplify the sympathetic response
What does sympathetic supply of the male internal genital organs do?
cause contraction and initiate ejaculation
What does sympathetic supply of the female internal genital organs do?
cause uterine contraction only in non-pregnant females; in pregnant females, the adrenergic receptors in the uterus switch from beta to alpha to prevent these contractions
What does the sympathetic NS in the neck supply?
- the muscle of the upper eyelid (levator palpebrae superioris)
- dilator pupillae of the eye
- the skin of the face and neck
What can damage to the sympathetic NS result in?
Horner’s syndrome
What is Horner’s syndrome characterised by?
deeply sunken eyes, droopy eyelids and lack of focus as well as flushing of the skin and absence of sweating on the affected side of the face and neck
