AUTONOMIC NERVOUS SYSTEM
The
major nerves that leave the brain or spinal cord are the cranial nerves or
spinal nerves respectively
·
CENTRAL NERVOUS SYSTEM
•BRAIN
•SPINAL CORD
·
PERIPHERAL NERVOUS SYSTEM
•SOMATIC AFFERENT
skin, skeletal muscle,
joints —> CNS
•SOMATIC EFFERENT
CNS —> skeletal muscle
•VISCERAL AFFERENT
smooth muscle, glands,
heart—> CNS
•VISCERAL EFFERENT (Autonomic)
CNS —> smooth muscle,
glands, heart
·
CRANIAL NERVES
•identified by roman numeral which refects their relative position anterior to posterior
•unlike spinal nerves, some
contain only sensory nerves, others are mixed
|
1 |
Olfactory |
|
2 |
Optic |
|
3 |
Oculomotor |
|
4 |
Trochlear |
|
5 |
Trigeminal |
|
6 |
Abducent |
|
7 |
Facial |
|
8 |
Vestibulocochlear |
|
9 |
Glossopharangeal |
|
10 |
Vagus |
|
11 |
Accessory |
|
12 |
Hypoglossal |
·
VISCERAL EFFERENT NERVES
•emerge from CNS in select
cranial nerves + ant roots of spinal
nerves
T1—T12, L1—L2, S2—S4
•T1—T12, L1—L2:
thoracolumbar —> make up the sympathetic division of the ANS
•Cranial nerves &
S2—S4: craniosacral —> part of the parasympathetic division of the ANS
•carry impulses from spine
or cranium —> synapse centres [ganglion]
•presynaptic; post synaptic
•parasympathetic ganglia
closer to target organ
•sympathetic ganglia close
to CNS organised in vertical chains lateral to spinal cord (sympathetic trunk)
·
Heart Nervous Supply
The heart is well supplied by both sympathetic &
parasympathetic (vagal) nerves.
The two atria are especially well
supplied with large numbers of sympathetic & parasympathetic nerves; but the ventricles are supplied mainly
by sympathetic nerves & far fewer parasympathetic fibres.
Sympathetic stimulation —> increased
heart rate & contractile strength
Parasympathetic stimulation —>
decreased heart rate & contractile strength (to a lesser degree)
All the Vagal & sympathetic cardiac
nerves converge on the Cardiac plexus; the plexus lies
between the aortic arch and the tracheal bifurcation
·
VAGUS X
|
Type of nerve |
Site of origin |
Site of termination |
Function |
|
Sensory-afferent |
Mucus
membrane lining respiratory & digestive tracts Pharynx,
larynx, trachea, esophagus, heart, abdominal viscera |
Medulla |
Taste
& sensation from larynx, neck, thorax & abdomen |
|
Motor-efferent |
Medulla |
Muscles
of pharynx & larynx Parasym
fibres to abdominal & thoracic viscera [motor
to all smooth muscle; almost all
thoracic & abdominal organs] |
Swallowing,
movement of pharynx & larynx Inhibitory
fibres to heart; secretion of gastric glands & pancreas; vasodilator
fibres to abdominal viscera [secretory to all? glands] |
• The vagus [cranial nerve X] has branches to serve the pharynx,
larynx, and heart, as well as the oesophhagus, stomach and small intestine
• the longest cranial nerves essential for speech, swallowing . .
. . communicates through 13 branches
vasovagal
reflex: stimulation of
the vagus nerve by reflex in which the irritation of the larynx or trachea
results in bradycardia
K. C. Potger
Copyright © 2001