Lecture# 7 Organization of NS.pptx for physical therapy

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1. NERVOUS SYSTEM Organization of nervous system

2. PHYSIOLOGY LECTURE # 7 THE NERVOUS SYSTEM

3. NERVOUS SYSTEM General organization of Nervous system It is that system of body which receives information from inside and outside the body, processes received information and transmits impulses to control different bodily functions and to maintain a constant internal environment despite extreme changes in external environment.

4. CLASSIFICATION OF NERVOUS SYSTEM CENTRAL NS: BRAIN SPINAL CORD PERIPHERAL NS CRANIO-SPINAL NERVES: cranial nerves(12 pairs) Spinal nerves (31 pairs) AUTONOMIC NS: Sympathetic NS Parasympathetic NS

5. Central Nervous System (CNS) Contains the nerves of the brain and spinal cord It is formed by neurons and supporting cells called neuroglia . Function = coordinating center of incoming/outgoing information

6. Structures of brain and spinal cord are arranged in two layers, namely gray matter and white matter. Gray matter is formed by nerve cell bodies and the proximal parts of nerve fibers, arising from nerve cell body. White matter is formed by remaining parts of nerve fibers. In brain, white matter is placed in the inner part and gray matter is placed in the outer part. In spinal cord it is vice versa.

7. Brain is found in the skull & serves as overall control center for the nervous system Spinal Cord is surrounded by vertebrae and extends down the back of the neck, thorax and abdomen Center of many reflex actions Provides a link between sensory and motor nerves Both are enclosed in 3 protective membranes called the meninges ( piamater , arachnoid mater & dura mater ) Space between meninges contains cerebrospinal fluid which protects and cushions the CNS

8. Peripheral Nervous System (PNS) All parts of the nervous system lying outside the brain and spinal cord. The sensory and motor neurons that connect to the CNS Function = to carry info between organs of the body and the CNS Humans have 12 pairs of cranial nerves (sensory/motor/mixed) which control the head, face, neck, shoulders Except VAGUS nerve – controls internal organs 31 pairs of spinal nerves (mixed) which take impulses to and from the spinal cord

9. PERIPHERAL NERVOUS SYSTEM It is again divided into two subdivisions: 1 . Somatic nervous system 2 . Autonomic nervous system

10. Somatic Nervous System Somatic nervous system is concerned with somatic functions . It includes the nerves supplying the skeletal muscles . Somatic nervous system is responsible for muscular activities and movements of the body Autonomic Nervous System Autonomic nervous system is concerned with regulation of visceral functions. So, it is otherwise called involuntary nervous system. Autonomic nervous system consists of two divisions, Sympathetic division parasympathetic division

11. NEURON Structural and functional unit of nervous system is called neuron. A nerve fibre , also called an axon, is a long and slender projection of nerve cells (or neurons) that carry electrical impulses away from the nerve cell body

12. Parts Cell body Nucleus Nissl bodies Neurofibrils Mitochondria Golgi appratus Processes or neurites Axon : carry impulses away from cell body Dendrites : carry impulses towards the cell body

13. DEPENDING UPON STRUCTURE Based on structure, nerve fibers are classified into two types: i . Myelinated Nerve Fibers Myelinated nerve fibers are the nerve fibers that are covered by myelin sheath. ii. Non-myelinated Nerve Fibers Non-myelinated nerve fibers are the nerve fibers which are not covered by myelin sheath

14. Erlanger and Gasser Classification (Based on Diameter and Conduction Velocity ): Group A Fibers: Myelinated: Heavily myelinated, leading to fast conduction velocity. Subtypes: A α ( Ia ): Largest diameter, fastest conduction, responsible for proprioception (muscle spindle afferents) and motor neurons. A β ( Ib ): Medium diameter, fast conduction, involved in touch, pressure, and proprioception (Golgi tendon organ afferents). A γ:  Medium diameter, fast conduction, involved in motor neurons controlling muscle spindles. A δ:  Small diameter, moderate conduction, responsible for pain, temperature, and touch.

15. Group B Fibers: Myelinated: Moderately myelinated with smaller diameter than A fibers, leading to slower conduction than A fibers. Function: Primarily involved in autonomic functions, such as visceral sensation and motor control. Group C Fibers: Unmyelinated: Smallest diameter, unmyelinated, resulting in slowest conduction velocity. Function: Involved in pain, temperature, and autonomic functions

16. Type Diameter ( µm) Velocity of conduction (m/s) A α 12 - 24 70 – 120 A β 6 - 12 30 – 70 A γ 5 - 6 15 – 30 A δ 2 – 5 12 – 15 B 1 – 2 3 – 10 C < 1.5 0.5 - 2

17. Classification according to no. of processes : Unipolar Bipolar multipolar

18. Classification according to function: 1. Sensory neurons Carry nerve impulses from a receptor to the CNS. Have long dendrites and short axons These nerves transmit sensory information from receptors in the body (like touch, pain, temperature, etc.) to the central nervous system (brain and spinal cord).Example: Nerves that carry the sensation of a hot stove to the brain .

19. 2. Motor neurons Carry nerve impulses from the CNS to an effector ( ex. muscle or gland). Have short dendrites and long axons These nerves carry signals from the central nervous system to muscles and glands, enabling movement and bodily functions . Example : Nerves that allow you to move your arm or control your heart rate.

20. 3. Interneurons Found completely within the CNS. Provide a link within the CNS between sensory neurons and motor neurons. Have short dendrites and long or short axons. These nerves contain both sensory and motor fibers, allowing them to transmit both sensory information and motor commands in the same nerve bundle . Example : Spinal nerves, which carry both sensory information from the body and motor commands to the muscles.

21. DEPENDING UPON SECRETION OF NEUROTRANSMITTER Depending upon the neurotransmitter substance secreted, nerve fibers are divided into two types: i . Adrenergic Nerve Fibers Adrenergic nerve fibers secrete noradrenaline. ii. Cholinergic Nerve Fibers Cholinergic nerve fibers secrete acetylcholine

22. Classification according to length of axon: 1. Golgi Type I Neurons Golgi type I neurons have long axons. Cell body of these neurons is in different parts of central nervous system and their axons reach the remote peripheral organs. 2. Golgi Type II Neurons Neurons of this type have short axons. These neurons are present in cerebral cortex and spinal cord.

23. Classification according to distribution: Nerve fibers can be classified by distribution as somatic (innervating skeletal muscles and skin) or Visceral (innervating internal organs)   Somatic :  These innervate skeletal muscles and the skin, controlling voluntary movements and providing sensory input from the body surface. .   Visceral:   These innervate internal organs, smooth muscles, and glands, regulating involuntary functions like heart rate, digestion, and breathing. 

24. Classification Depending on origin: Nerve fibers can be classified by location into cranial and spinal nerves, with cranial nerves originating from the brain and spinal nerves from the spinal. Cranial Nerves: These nerves originate from the brain and innervate the head, face, and neck . Spinal Nerves: These nerves originate from the spinal cord and innervate the rest of the body.

25. Ganglia Groups of neuron cell bodies that lie within the PNS Not included with nerves since nerves only contain axons and dendrites

26. Sensory part of nervous system Most activities of the nervous system are initiated by sensory experience exciting sensory receptors, whether visual receptors in the eyes, auditory receptors in the ears, tactile receptors on the surface of the body, or other kinds of receptors. This sensory experience can either cause immediate reaction from the brain, or memory of the experience can be stored in the brain for minutes, weeks, or years and determine bodily reactions at some future date.

27. Motor Part of the Nervous System—Effectors The most important eventual role of the nervous system is to control the various bodily activities. This is achieved by controlling 1. Contraction of appropriate skeletal muscles throughout the body (2) Contraction of smooth muscle in the internal organs, and (3) secretion of active chemical substances by both exocrine and endocrine glands in many parts of the body. These activities are collectively called motor functions of the nervous system, and the muscles and glands are called effectors because they are the actual anatomical structures that perform the functions dictated by the nerve signals.

28. Processing of Information “Integrative” Function of the Nervous System When important sensory information excites the mind, it is immediately channeled into proper integrative and motor regions of the brain to cause desired responses. This channeling and processing of information is called the integrative function of the nervous system.

29. Storage of Information—Memory The storage of information is the process we call memory, and this, is a function of the synapses. Most storage occurs in the cerebral cortex, but even the basal regions of the brain and the spinal cord can store small amounts of information Information stored as memory can become part of the processing mechanism used to manage subsequently sensory input. the brain compares new sensory experiences with those stored in memory and in this way develops successful strategies to form a motor output.