Autonomic nervous system ( A.N.S) l Physiology MCQs for dental students
introduction in Autonomic nervous system
All body functions could be regulated by either:
- a) Nervous system (rapid onset, short period).
- b) Chemical regulation as hormones &enzymes (slow, prolonged long lasting).
THE NERVOUS SYSTEM is classified into:
1. Central Nervous System (C.N.S.):
- protected by bone "skull and vertebral column"
- a) Brain:
- cerebral cortex - brain stem "medulla, pons & midbrain" - cerebellum.
- b) Spinal cord:
- formed of 31 segments:
- 8 cervical (C), 12 thoracic (T), 5 lumbar (L), 5 sacral (S) & 1 coccygeal.
2. Peripheral nervous system: not protected by bones
Somatic
nervous system (sensory and motor "voluntary") is
formed of:-
- Cranial nerves (12 pairs) and all Spinal nerves (31 pairs).
Autonomic nervous system (A.N.S.):
- which
controls involuntary activities of heart, exocrine glands
& smooth muscles.
Enteric nervous system:
- A local
system that regulates activities of gastrointestinal tract (GIT).
- Present
in between walls of GIT.
- Consists
of large number of nerve cell&fiber interconnected to form two distinct
plexuses:
- Meissner's (Submucosal)
plexus: controls Secretory activities.
- Auerbach's
(Myenteric) plexus: controls Motor activities
- Both plexuses act under
control of Autonomic N.S which regulate its secretory&motor
activities.
Autonomic N.S. includes 2 types of fibers:
Afferent fibers:
- which carry sensations from viscera to C.N.S.
- This system is widely distributed
Efferent fibers:
- which emerges from C.N.S. to reach visceral organs and smooth muscle
Autonomic
N.S. has 2 Efferent neurons:-
- The A.N.S reaches its target organs via autonomic nerve which is efferent axon of 2 nerve cell.
AUTONOMIC GANGLIA
Definition:
- A Collection of nerve Cells outside C.N.S
surrounded by Connective tissue Capsule.
Contain :
- nerve fibers of pre-ganglionic & cells
of post-ganglionic neurons.
- At which transmission of impulses occurs chemically by Acetyl Choline.
TYPES OF AUTONOMIC GANGLIA:
A-according to site:
- 1-Lateral paravertebral
- 2-Collateral prevertebral
- 3-Terminal peripheral
- 4-Adrenal medulla
B-According to type:
- 1-Sympathetic:
(all lateral+4collateral)
- 2-Parasymathetic:
(all terminal +4 collateral)
- 3-Modified sympathetic ganglion: (suprarenal medulla)
Functions:
- 1. Relay stations for pre-ganglionic fibers.
- 2. Distribution
centers as the ratio of pre to post-ganglionic fibers is (1:8). Pre-ganglionic impulses are distributed into
several post-ganglionic neurons then post-ganglionic
distributed to various organs.
- 3. Site of action of autonomic Drugs.
To determine site of relay in autonomic ganglia (=Nicotine test):
- Nicotine
first stimulates, then inhibits ganglia cells, but has no effect
on nerve fibers.
- Ganglia are painted with nicotine large dose, and then a pre-ganglionic fiber is electrically stimulated:
- If it gives a postganglionic response → it passes in ganglion without relay.
- If it does not give response → it relays at this ganglion.
DIVISIONS OF AUTONOMIC N.S.
- Sympathetic nervous system (thoraco-lumbar): Arising from LHCs of all thoracic segments and upper 2 lumbar segments (LHCs of T1-L2).
- Parasympathetic nervous system (Cranio-sacral): Arising
from
- a) Cranial
nerves i.e. III, VII, IX & X.
- b) LHCs of 2nd, 3rd and 4th sacral segments of spinal cord (LHCs of S2,3,4).
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