Physiology Lecture 2 PDF

# Physiology | A.N.S - Lecture 2 ## Learning Outcomes: - By the end of the A.N.S lectures, you are expected to: - Describe the functional organization of A.N.S. - Identify the basic characteristics of sympathetic and parasympathetic nervous systems. ## Introduction The functions of the diffe...

# Physiology | A.N.S - Lecture 2 ## Learning Outcomes: - By the end of the A.N.S lectures, you are expected to: - Describe the functional organization of A.N.S. - Identify the basic characteristics of sympathetic and parasympathetic nervous systems. ## Introduction The functions of the different systems in the body are regulated mainly by two systems: - **The nervous system:** - Rapid control system - Regulate functions of the body through nerve impulses that travel along peripheral nerves. - **The endocrine system:** - Slow control system - Regulate functions of the body by secreting hormones that circulate in the blood to reach target organs. The functions of the two systems are complementary. ## Functions of the Nervous System 1. **Sensory Input:** gathering information - To monitor changes occurring inside and outside the body (changes = stimuli) 2. **Integration:** - To process and interpret sensory input and decide if action is needed. 3. **Motor Output:** - A response to integrated stimuli - The response activates muscles or glands ## Organization of the Nervous System 1. **Anatomically** the nervous system is divided into: - **Central nervous system** (brain and spinal cord) - The brain includes the cerebrum, cerebellum, and brain stem (Mid-brain, pons & medulla oblongata). - The spinal cord is formed of 31 segments: 8 cervical segments, 12 Thoracic segments, 5 Lumbar segments, 5 sacral segments, and 1 coccygeal segment. - **Peripheral nervous system** - Consists mainly of the nerves that extend from the brain and spinal cord. 2. **According to site of origin, nerves are classified into:** - **Cranial nerves:** (12 pairs arising from the brain) carry impulses to and from the brain. - **Spinal nerves:** (31 pairs arising from the spinal cord, one pair from each segment) carry impulses to and from the spinal cord. ## Functional Classification of the Peripheral Nervous System (PNS) - **Sensory (afferent) division:** - Nerve fibers that carry information from peripheral (receptors) to the central nervous system - Include visual receptors, auditory receptors, chemoreceptors, and somatosensory or touch receptors. - **Motor (efferent) division:** - Nerve fibers that carry impulses from the central nervous system to the peripheral organs. ## Central Nervous System (CNS) - **Structure:** Brain and spinal cord - **Function:** Integrative and control centers ## Peripheral Nervous System (PNS) - **Structure:** Cranial nerves and spinal nerves - **Function:** Communication lines between the CNS and the rest of the body ### Sensory (afferent) Division - **Structure:** Somatic and visceral sensory nerve fibers - **Function:** Conducts impulses from receptors to the CNS ### Motor (efferent) Division - **Structure:** Motor nerve fibers - **Function:** Conducts impulses from the CNS to effectors (muscles and glands) ## Autonomic Nervous System (ANS) - **Structure:** Visceral motor (involuntary) - **Function:** Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands ### Sympathetic Division - **Function:** Mobilizes body systems during activity ("fight or flight") ### Parasympathetic Division - **Function:** Conserves energy, promotes "housekeeping" functions during rest. ## Somatic Nervous System - **Structure:** Somatic motor (voluntary) - **Function:** Conducts impulses from the CNS to skeletal muscles. ## Physiologically the nervous system is divided into: - **Somatic nervous system:** which controls the voluntary movements of the body by skeletal muscles. - **Autonomic nervous system:** this system regulates the visceral functions of the body. Involuntary control of visceral organs (heart, lung, kidneys, GIT, bladder, sexual organs, glands). The functions of somatic and autonomic nervous systems are interrelated and complementary. ## Structural and Functional Unit of the Nervous System - **Neuron** is the structural unit of the nervous system - **The functional unit of nervous system is the reflex action (arc)**. - **Definition:** The reflex action is an involuntary beneficial inborn response to a stimulus. ## Reflex Arc - **Poly synaptic Reflex** - the reflex involves more than one synapse. ## The reflex action - **Pathway (The reflex arc)** which consists of 5 different components: 1. **A receptor:** A sensitive structure that can be stimulated by slight changes in external or internal environments. 2. **An afferent neuron:** It carries nerve impulse from the different receptors to the central nervous system. 3. **The Centre:** It is present inside the central nervous system (CNS). 4. **An efferent neuron:** It conducts nerve impulses from the CNS to the effector organ. 5. **An effector organ:** It may be a skeletal muscle, smooth muscle, cardiac muscle or gland. ## Somatic Efferent Innervation - The pathway involves a single myelinated nerve fiber that travels from the CNS to the effector organ. - The neurotransmitter release from the motor nerve fiber is acetylcholine (ACh), which binds to receptors on the skeletal muscle and results in muscle contraction. ## Autonomic Efferent Innervation - The pathway involves two neurons: - **Preganglionic neuron:** This neuron originates in the CNS and travels to an autonomic ganglion. - **Postganglionic neuron:** This neuron originates in the autonomic ganglion and travels to the effector organ. - The neurotransmitter released from the preganglionic neuron is always acetylcholine (ACh). - The neurotransmitter released from the postganglionic neuron varies depending on the division of the autonomic nervous system: - **Sympathetic Division:** Norepinephrine (NE). - **Parasympathetic Division:** Acetylcholine (ACh). ## Autonomic Nervous System - Autonomic nervous system is made up of two neurons in series that connect the central nervous system and the effector cells. - The first neuron has its cell body in the central nervous system. The synapse between the two neurons is outside the central nervous system, in a cell cluster called an autonomic ganglion. - The nerve fibers passing between the central nervous system and the ganglia are called preganglionic fibers; those passing between the ganglia and the effector cells are postganglionic fibers. ## The autonomic nervous system (ANS) (involuntary, or visceral nervous system) - **Divisions of autonomic nervous system:** 1. **Sympathetic nervous system (Thoracolumbar outflow):** It arises from all thoracic and upper three lumbar segments of the spinal cord (T1-L2). 2. **Parasympathetic nervous system (Cranio-sacral outflow):** It arises from some cranial nerves (III, VII, IX, and X) and sacral segments (S2, 3, 4) of the spinal cord. ## Autonomic ganglia: - It is a group of cell bodies of neurons outside the CNS. (It is a site of physiological contact between pre and post-ganglionic fibres) ## Types of autonomic ganglia: 1. **Lateral / paravertebral ganglia (sympathetic chain)** - They lie on each side of the vertebral column forming two chains known as sympathetic chains. - They are the sites of relay of sympathetic fibers to head and neck, and thoracic viscera. 2. **Prevertebral / Collateral ganglia** - They lie between the sympathetic chain and the organ of supply. - They are the site of relay of the preganglionic sympathetic fibers that supply the abdomen and pelvis. - Collateral ganglia- the celiac, superior mesenteric, and inferior mesenteric ganglia- are in the abdominal cavity, closer to the innervated organ. 3. **Terminal ganglia (parasympathetic):** - They are present near or even within the innervated organs - They are the sites of relay of all parasympathetic fibers. ## Functions of the autonomic ganglia: 1. **Site of relay:** They are cell stations for relay of preganglionic fibers coming from CNS. 2. **The ganglia act as distributing centres:** Each preganglionic axon diverges to many postganglionic neurons. 3. **The chemical transmitter of autonomic ganglia is acetylcholine (Site of chemical transmission: Ach).** ## Table: Classical comparison of sympathetic and parasympathetic divisions of autonomic nervous system | Feature | Sympathetic Division | Parasympathetic Division | |---|---|---| | Location of preganglionic neuron | Thoracolumbar segments of spinal cord | Nuclei of III, VII, IX and X cranial nerves and sacral (S2 to S4) segments of spinal cord | | Location of postganglionic neuron | Away from target organ | Near or in the target organ | | Length of preganglionic fibers | Relatively short | Relatively long | | Length of postganglionic fibers | Relatively long | Relatively short | | Preganglionic neurotransmitter | Acetylcholine | Acetylcholine | | Postganglionic neurotransmitter | Noradrenaline | Acetylcholine | ## Comparison of Peripheral Organization and Transmitters Released by Somatomotor and Autonomic Nervous Systems: - **Somatomotor Nervous System:** The neuron that leaves the spinal cord projects directly to the effector organ. - **Autonomic Nervous System:** There is a synapse between the neuron that leaves the spinal cord and the effector organ (except for neurons that innervate the adrenal medulla). - **Note that all neurons that leave the central nervous system release acetylcholine (ACh). DA, dopamine; Epi, epinephrine; NE, norepinephrine.** ## Conclusion: This lecture has covered the basic anatomy and physiology of the autonomic nervous system (ANS). The ANS is a complex system that plays a vital role in regulating many important bodily functions. Understanding the ANS is essential for understanding many different physiological processes, including heart rate, blood pressure, digestion, and breathing. The ANS is also involved in many different diseases, including hypertension, diabetes, and Parkinson's disease. ## Any Question? - The image includes a light bulb with a question mark inside. # Thank You