Download AUTONOMIC NERVOUS SYSTEM

CHAPTER Xb
PDL 101 HUMAN ANATOMY
& PHYSIOLOGY
Ms. K. GOWRI. M.Pharm.,
Lecturer.
AUTONOMIC NERVOUS SYSTEM
The autonomic or involuntary part of the nervous system controls the
functions of the body carried out automatically i.e initiated in the brain
below the level of the cerebrum.
• Effect of autonomic control are rapid and essential for
homeostasis
Effector organs are
• smooth muscle
• cardiac muscle
• glands
Effect of autonomic stimulation include
• changes in rate and force of heartbeat
• stimulation or depression of secretion of glands
• vasoconstriction or vasodilation
• bronchoconstriction or bronchodilation
• changes in size of the pupils of the eyes.
Divisions of ANS
ANS is divided into two divisions
• sympathetic (thoracolumbar outflow)
• parasympathetic (craniosacral outflow)
These two divisions have both structural and functional
differences. Each division has two efferent neurons in its
peripheral pathways between the CNS and effector organs.
These are :
• Preganglionic neurons
• Postganglionic nervous system
SYMPATHETIC NERVOUS SYSTEM:
Neurons convey impulses from their origin in the hypothalamus,
reticular formation and medulla oblongata to effetcor organs
and tissues.
PREGANGLIONIC NEURONS:
Has its cell body in lateral column of gry matter in the spinal
cord between the levels of the 1st thoracic and 2nd or 3rd lumbar
vertebrae.
Acetylcholine is the neurotransmitter.
POSTGANGLIONIC NEURONS:
Has its cell body in a ganglion and terminates in the organ or
tissue supplied.
SYMPATHETIC GANGLIA:
THE LATERAL CHAINS OF SYMPATHETIC GANGLIA:
The lateral chains of ganglia extend from upper cervical level to
the sacrum , one chain lying on each side of the body vertebrae.
• Ganglia are attached to each other by nerve fibres.
• Preganglionic neurons emerge from cord may synapse
with the cell body of postganglionic neuron.
EX: Nerve which dilates the pupil of the eye leaves the cord
at the level of 1st thoracic vertebrae and passes the chain to
the cervical ganglion before it synapses with cell body of post
synaptic neuron
PREVERTEBRAL GANGLION
These are three prevertebral ganglia situated in the abdominal
cavity close to the origin of arteries of the same names
• Coelaic ganglion
• Superior mesenteric ganglion
• Inferior mesenteric ganglion
Ganglia consists of nerve cell bodies rather diffusely
distributed among a network of nerve fibres from plexuses.
PARASYMPATHETIC NERVOUS SYSTEM:
Two neurons ( preganglionic and postganglionic are involved
in the transistion of impulses from their source to the effector
organ.
PEGANGLIONIC NEURON:
This has its cell body either in the brain or in the spinal cord.
Originating in the brain are cranial nerves III,VII,IX and X.
Fibres leaves the cord in sacral segments 2, 3 & 4 and
synapse with postganglionis neurons in the walls of pelvic
organ.
POSTGANGLIONIC NEURON:
This has its cell body either in ganglion or in the wall of the
organ supplied.
MOTOR PATHWAYS:
Neurons which transmit nerve impulses away
from the brain are motor neurons
• Motor stimulation results in contraction of skeletal
muscle and smooth muscle, cardiac muscle and the
secretion by glands controlled by nerves of the ANS
Voluntary muscle movement:
Contraction of the muscle which move the joints is,in the
main under conscious control,whicl means that the stimulus
to contract originates the level of consciousness in the
cerebrum.
• Efferent nerve impulses are transmitted from the brain
to the body via bundles of nerve fibres or tracts in the
spinal cord.
• Motor pathways from the brain to the muscles are made
up of two neurons
• Pyramidal
• Extrapyramidal
• Motor fibres form the pyramidal tracts travel through
the internal capsule and are the main pathway for
impulses to voluntary muscles.
• Motor fibres that do not pass through internal capsule
form the extrapyramidal tracts and have connection
with many parts of the brain including basal nuclei and
thalamus.
UPPER MOTOR NEURON: This has its cell body in the
precentral sulcus area of the cerebrum. In case of spinal
cord, they form lateral corticospinal tracts of white matter
LOWER MOTOR NEURON: Has its cell body in the
anterior horn of grey matter in the spinal cord. Lower
motor neuron described as the final common pathway for
the transmission of nerve impulses to skeletal muscles.
Outcome of these influences is smooth , coordinated
muscle movement, some of which is voluntary and some
are involuntary
INVOLUNTARY MUSCLE MOVEMENT:
Upper motor neurons: These have their cell bodies in the
brain at a level below the cerebrum i.e in the midbrain ,
brain stem, cerebellum or spinal cord.
Influences muscle activity in relation to the maintenance
of posture and balance, the coordination of muscle
movement and the control of muscle tone
SPINAL REFLEXES:
Consists of 3 elements:
• Sensory neurons
• Connector neurons in the spinal cord
• Lower motor neurons
• A reflex action is an immediate motor response to a
sensory stimulus
• These stimulate many connector and lower motor
neurons in the cord which results in the contraction
of many skeletal muscles of the hand, arm and
shoulder. Reflex action takes place very quickly
• EX: if it is a precious plate that is very hot when
lifted every effort will be made to overcome the pain
to prevent dropping it.
STRETCH REFLEXES:
Only two neurons are involved.
Cell body of the lower motor neuron is stimulated by
sensory neuron
EX: knee jerk- This type of reflex can be demonstrated
at any point where a stretched tendon crosses a joint.
Used as a test of the integrity of the reflex arc.
This type of reflex has a protective function – it
prevents excessive joint movement that may damage
tendons, ligaments and muscles.
SENSORY PATHWAYS:
Two main sources of sensation transmitted to brain via
the spinal cord
1. The skin:
Sensory receptors in the skin called cutaneous receptors
are stimulated by pain, heat, cold and touch
Nerve impulses generated are conducted by three
neurons to the sensory area in the opp hemispheres of the
cerebrum where the sensation and its location are perceived
Decussation occurs either at the level of entry into cord or in the
medulla
2. The tendons , muscles and joints: sensory receptors
are nerve endings in these structures called
propriceptors and are stimulated by stretch.
Nerve impulses have two destinations :
(i) by a three- neuron system , the impulses reach the sensoty
area of the opposite hemisphere of the cerebrum.
(ii) by a two- neuron system the nerve impulses rach the
cerebellar hemisphere on the same side.