lOMoAR cPSD| 32635183
lOMoAR cPSD| 32635183
2024-2025 ANP NOTES ON AUTONOMIC
SYSTEM
Lecture 9- Homeostasis: Introduction to the Autonomic System
Homeostasis: A Defining Feature of Physiology
● Cells and components of cells work best when specific conditions are maintained
(optimal temperature, pH, O2, etc.)
● Different organ systems work cooperatively to promote the well being of the entire body
and to maintain stable internal conditions
● Homeostasis: the ability of the body to maintain a relatively constant internal
environment with changing external conditions (Walter Cannon)
○ Unifying concept of physiology.
Homeostasis
● Homeostasis does not imply that a given physiological function or variable is rigidly
constant.
● Variables fluctuate within a predictable and often narrow range. When disturbed up or
down from the normal range, they are restored to normal.
● Thus, homeostasis is a state of dynamic constancy. A variable like blood glucose may
vary in the short term but is fairly constant when averaged over the long term.
Negative Feedback Mechanism
● Stability of an internal environmental variable achieved by balancing inputs and outputs.
● In a negative feedback control system, a change in the variable being regulated brings
about responses that tend to push the variable in the direction opposite to the original
change.
● The setpoint is the numerical value of the variable measured at steady state.
● Negative feedback minimizes changes from the set point of the system, leading to
stability.
● A steady-state is defined as a system in which a particular variable is not changing, but
energy must be added continuously to maintain a constant condition.
● It differs from equilibrium, in which a particular variable is not changing but no input of
energy is required.
Positive Feedback
● Positive feedback, which accelerates a process, is less common because it pushes values
away from the set point.
● Often used when there is a goal to be attained
\Components of Homeostatic Control Systems
, lOMoAR cPSD| 32635183
● Multiple organ systems control a single variable. Homeostasis requires communication
between different systems.
● Signals relayed by the nervous system and endocrine system (hormones).
● Homeostatic control mechanisms are examples of reflexes.
● A reflex is an involuntary (built-in) response to a particular stimulus. Many reflexes
occur without our awareness.
● A pathway describing a reflex known as a reflex arc.
● Components of a reflex arc: receptor, afferent pathway, integrating center, efferent
pathway, and effector.
Reflex Arc for Body Temperature
● Refer to ppt for chart
Homeostatic Imbalance
● Numerous physiological variables must be maintained homeostatically.
● A person may be homeostatic for one variable but not for another. For (e.g. blood Na+
may be normal but CO2 levels may be abnormally high due to lung disease).
● When homeostasis is lost for one variable, it may trigger a series of changes in other
variables. Dramatic changes in just one variable can have life-threatening consequences.
● Certain diseases or illnesses can be characterized as a loss of homeostasis in one or more
systems in the body (homeostatic imbalance).
● Because so many properties of the internal environment are closely interrelated, it is often
possible to keep one property relatively constant only by moving others away from their
usual set point. This is referred to as competing or “clashing demands”.
The Autonomic Nervous System
● The ANS consists of motor neurons that:
○ Innervate smooth muscles, cardiac muscles, and glands
○ Makes adjustments to ensure optimal support for body activities
○ Shunts blood to areas that need it, adjusts heart rate, blood pressure, digestive
processes, etc.
○ Operates via subconscious control
● Also called the involuntary nervous system or general visceral motor system
Overview of Nervous System Organization
● Refer to ppt for flow chart
● Efferent pathways
● Both the somatic nervous system and autonomic nervous system contain motor fibres but
differ in:
○ Effectors
, lOMoAR cPSD| 32635183
○ Efferent pathways and ganglia
○ Target organ responses to neurotransmitters
● There are two divisions of the ANS:
○ Sympathetic
○ Parasympathetic
Somatic Nervous System
● Effectors
○ Skeletal muscles
● Efferent pathways and ganglia
○ Cell body is in CNS, and a single, thick myelinated (group A) axon extends in
spinal or cranial nerves directly to skeletal muscle
● Target organ responses to neurotransmitters
○ All somatic motor neurons release acetylcholine (ACh)
○ The effect is ALWAYS stimulatory
Autonomic Nervous System
● Effectors: cardiac muscle, smooth muscle, and glands
● Efferent pathways and ganglia: Two-neuron chain
○ Preganglionic neuron: cell body in CNS with thin, lightly myelinated (group B)
preganglionic axon extending to ganglion
○ Postganglionic neuron (outside CNS): cell body synapses with preganglionic axon
in autonomic ganglion with unmyelinated (group C) postganglionic axon that
extends to effector organ
● Target organ responses to neurotransmitters
○ Preganglionic fibers release Ach; Postganglionic fibers release norepinephrine or
ACh at effectors; Effect is stimulatory or inhibitory, depending on the type of
receptor
Divisions of the Autonomic Nervous System
● Two branches of ANS:
○ Parasympathetic division: promotes maintenance functions, conserves energy
○ Sympathetic division: mobilizes body during activity
● Dual innervation: all visceral organs are served by both divisions, but these divisions
cause opposite effects
Role of Parasympathetic Division
● Referred to as “rest-and-digest” system
● Keeps body energy use as low as possible, even while carrying out maintenance activities
lOMoAR cPSD| 32635183
2024-2025 ANP NOTES ON AUTONOMIC
SYSTEM
Lecture 9- Homeostasis: Introduction to the Autonomic System
Homeostasis: A Defining Feature of Physiology
● Cells and components of cells work best when specific conditions are maintained
(optimal temperature, pH, O2, etc.)
● Different organ systems work cooperatively to promote the well being of the entire body
and to maintain stable internal conditions
● Homeostasis: the ability of the body to maintain a relatively constant internal
environment with changing external conditions (Walter Cannon)
○ Unifying concept of physiology.
Homeostasis
● Homeostasis does not imply that a given physiological function or variable is rigidly
constant.
● Variables fluctuate within a predictable and often narrow range. When disturbed up or
down from the normal range, they are restored to normal.
● Thus, homeostasis is a state of dynamic constancy. A variable like blood glucose may
vary in the short term but is fairly constant when averaged over the long term.
Negative Feedback Mechanism
● Stability of an internal environmental variable achieved by balancing inputs and outputs.
● In a negative feedback control system, a change in the variable being regulated brings
about responses that tend to push the variable in the direction opposite to the original
change.
● The setpoint is the numerical value of the variable measured at steady state.
● Negative feedback minimizes changes from the set point of the system, leading to
stability.
● A steady-state is defined as a system in which a particular variable is not changing, but
energy must be added continuously to maintain a constant condition.
● It differs from equilibrium, in which a particular variable is not changing but no input of
energy is required.
Positive Feedback
● Positive feedback, which accelerates a process, is less common because it pushes values
away from the set point.
● Often used when there is a goal to be attained
\Components of Homeostatic Control Systems
, lOMoAR cPSD| 32635183
● Multiple organ systems control a single variable. Homeostasis requires communication
between different systems.
● Signals relayed by the nervous system and endocrine system (hormones).
● Homeostatic control mechanisms are examples of reflexes.
● A reflex is an involuntary (built-in) response to a particular stimulus. Many reflexes
occur without our awareness.
● A pathway describing a reflex known as a reflex arc.
● Components of a reflex arc: receptor, afferent pathway, integrating center, efferent
pathway, and effector.
Reflex Arc for Body Temperature
● Refer to ppt for chart
Homeostatic Imbalance
● Numerous physiological variables must be maintained homeostatically.
● A person may be homeostatic for one variable but not for another. For (e.g. blood Na+
may be normal but CO2 levels may be abnormally high due to lung disease).
● When homeostasis is lost for one variable, it may trigger a series of changes in other
variables. Dramatic changes in just one variable can have life-threatening consequences.
● Certain diseases or illnesses can be characterized as a loss of homeostasis in one or more
systems in the body (homeostatic imbalance).
● Because so many properties of the internal environment are closely interrelated, it is often
possible to keep one property relatively constant only by moving others away from their
usual set point. This is referred to as competing or “clashing demands”.
The Autonomic Nervous System
● The ANS consists of motor neurons that:
○ Innervate smooth muscles, cardiac muscles, and glands
○ Makes adjustments to ensure optimal support for body activities
○ Shunts blood to areas that need it, adjusts heart rate, blood pressure, digestive
processes, etc.
○ Operates via subconscious control
● Also called the involuntary nervous system or general visceral motor system
Overview of Nervous System Organization
● Refer to ppt for flow chart
● Efferent pathways
● Both the somatic nervous system and autonomic nervous system contain motor fibres but
differ in:
○ Effectors
, lOMoAR cPSD| 32635183
○ Efferent pathways and ganglia
○ Target organ responses to neurotransmitters
● There are two divisions of the ANS:
○ Sympathetic
○ Parasympathetic
Somatic Nervous System
● Effectors
○ Skeletal muscles
● Efferent pathways and ganglia
○ Cell body is in CNS, and a single, thick myelinated (group A) axon extends in
spinal or cranial nerves directly to skeletal muscle
● Target organ responses to neurotransmitters
○ All somatic motor neurons release acetylcholine (ACh)
○ The effect is ALWAYS stimulatory
Autonomic Nervous System
● Effectors: cardiac muscle, smooth muscle, and glands
● Efferent pathways and ganglia: Two-neuron chain
○ Preganglionic neuron: cell body in CNS with thin, lightly myelinated (group B)
preganglionic axon extending to ganglion
○ Postganglionic neuron (outside CNS): cell body synapses with preganglionic axon
in autonomic ganglion with unmyelinated (group C) postganglionic axon that
extends to effector organ
● Target organ responses to neurotransmitters
○ Preganglionic fibers release Ach; Postganglionic fibers release norepinephrine or
ACh at effectors; Effect is stimulatory or inhibitory, depending on the type of
receptor
Divisions of the Autonomic Nervous System
● Two branches of ANS:
○ Parasympathetic division: promotes maintenance functions, conserves energy
○ Sympathetic division: mobilizes body during activity
● Dual innervation: all visceral organs are served by both divisions, but these divisions
cause opposite effects
Role of Parasympathetic Division
● Referred to as “rest-and-digest” system
● Keeps body energy use as low as possible, even while carrying out maintenance activities
