Autonomic nervous system ( A.N.S) l Physiology MCQs for dental students

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:

1.   cerebral cortex - brain stem "medulla, pons & midbrain" - cerebellum.

• b) Spinal cord:

1.   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:

1.               Meissner's (Submucosal) plexus: controls Secretory activities.
2.              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:

1.           If it gives a postganglionic response → it passes in ganglion without relay.
2.           If it does not give response → it relays at this ganglion.

 

DIVISIONS OF AUTONOMIC N.S.

1. Sympathetic nervous system (thoraco-lumbar): Arising from LHCs of all thoracic segments and upper 2 lumbar segments (LHCs of T1-L2).
2. 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).