AUTONOMIC NERVOUS SYSTEM
Peripheral Nervous System: has afferent division (sensory) and efferent division. Efferent
division is divided into
somatic motor neurons (voluntary
), which control movement of
skeletal muscles, and
autonomic neurons (involuntary)
, which control smooth muscle
(think about layer of arteries and veins, gastrointestinal tract, respiratory tract, etc),
cardiac muscle (heart), glands, and adipose tissues.
A. TWO BRANCHES OF AUTONOMIC NERVOUS SYSTEM (ANS):
Parasympathetic system: known for “rest and digest” controls
Sympathetic system: known for “fight or flight” controls. However, must keep in mind
that in daily mundane activities, sympathetic system also has an important contribution,
for example: its regulation of blood flow to tissues.
Most of the time, para- and sympa alternate to control and fine-tune body functions( for
homeostasis). Only on occasions, such as see a snake, then the control of one system, in
this case sympa-, dominates.
B. ANS AND HOMEOSTASIS:
-After receiving sensory inputs from the somatosensory and visceral receptors, many
brain structures including limbic system, hypothalamus, pons, medulla, and cerebral
cortex send signals to autonomic system, endocrine system, and behavioral state system
to regulate body homeostasis.
Example: Hypothalamus regulates body temperature, water balance, eating behavior,etc.
Medulla for respiration, heart rate, etc
Cerebral cortex and/or limbic system: emotion, etc.
-however, some autonomic reflexes can take place without signal from the brain, yet
these processes can still be influenced by the CNS. These are called spinal reflexes,
including urination, defecation, and penile erection.
2. Types of control
One character of autonomic division is its
mostly for internal
organs. If para- signal is excitatory, then sympa- is inhibitory, and vice versa.
Example: heart rate: since sympa- is fight-or flight response, so of-course it increases the
heart rate, while para- decreases it.
to this antagonistic control is the sweet glands and the smooth muscle in blood
vessels. Only sympathetic branch controls these tissues by adjusting its level (tonic
Another type of control is co-operations of the two branches. Each will work on a
different tissue to aim for a common goal.
Example: para-: controls blood flow for erection, while sympa-controls muscle
contraction for ejaculation
Para- or sympa- both rely of neurotransmitters to affect the target tissues. Sometimes the
types of neurotransmitters receptors on the target determine the control.
Example: sympa- release catecholamines to bind to the adrenergic receptors on the