2-Motor Examination reflexes practical.pptx

2-Motor Examination reflexes practical.pptx

1. Nerve physiology By Dr. Yasser M. Ashour Professor of Medical Physiology

2. The nervous system is organized to: Receive, Store & Transmit information. Function of nervous system

3. Neurons It is the building unit of nervous system. Specialized conducting cell of the neurologic system which receives, conducts and transmits small electrical signals .

4. Interneurons are a third type of Neurons that form interconnections between other Neurons

5. Multiple Neurons are grouped into pathways Nerves Tract, fasciculus, lemniscus and peduncle

6. N erve fiber A nerve fiber, 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 A neuron typically has one nerve fiber emerging from its cell body that transmits impulses to other neurons, muscles or glands Dys -functioning of the nerve fibre can cause major acquired and inherited neurological disorders that affect both the central nervous system and the peripheral nervous system .

7. Important medical terms Synapse Connections between Neurons in which they communicate via chemical signals ( Neurotransmitter s) Neurologic Pathway : Chain of communicating Neurons Neuraxis Tract (or fasciculus, peduncle or lemniscus ) Bundle of axons in a pathway within the  Central Nervous System  (CNS) Nerve Bundle of axons in a pathway within the  Peripheral Nervous System

8. Neural Nucleus Group of Neuron cell bodies (soma ) with attached group of axons (nerve tracts) Includes brain nuclei,  Cranial Nerve  nuclei, cerebellar nuclei and spinal cord nuclei Ganglia are the  Peripheral Nerve  versions of the CNS neural neuclei

9. Supporting cells Gliocytes The cells which support neurons in the central nervous system. Schwann cells The cells which support peripheral nerves

10. Neuron is consisting of (1) Cell body (soma) (2) Cell Processes (axon and dendrites ).

11. (1) Cell body It contains cytoplasm, nucleus and cell organelles. It contains large number of Nissl granules these granules are the granular endoplasmic reticulum of the neuron. Their functions are the synthesizing of proteins and export it to the cell processes. There is no centrosome in the nerve cell . The cell bodies are present mainly inside the CNS. But some cell bodies are also found in the autonomic and dorsal ganglia.

12. There are processes that emerge from the cell body: - (1) Dendrites (2) Axon (nerve fibres) it arises from a conical part of the cell called axon hillock.  The axon ends up in several terminal branches. Each terminal ends in a disc-like expansion called synaptic knob Axon hillock Cell processes are the nerve fibres which makes the peripheral nerves outside the CNS the nerves tract inside the CNS . (2) Cell processes

13. Axon Dendrites Transmit impulses away from the cell body. Transmit impulses from around of the cell to the cell body. Increase the surface area of the cell. A neuron has only one axon A neuron could have one or more dendrites

14. Axon : The nerve fibres are covered by a cell membrane called axolemma . It is a three layered bilipid membrane that specifies what transported in and out of the nerve cells. The cytoplasm of the nerve fibres is known as axoplasm , it has a high concentration of microtubules, microfilaments and mitochondria.

15. Synaptic knobs are the end branches of a nerve fibre, has swollen ends called axon terminals that join one neuron to another forming a synaptic junction. A single nerve fibre with its multiple branches innervates multiple parts of the brain and generates multiple synaptic terminals

16. The nerve fibres can be as small as a few millimetres or can extend up to one-meter long. The longest nerve fibre of the human body is the sciatic nerve that extends from the  spinal cord   to the big toes of both feet . The diameter of the nerve fibre is also variable ranging from about one micrometre to up to 20 µm.

17. The nerve fibres are covered by a layer of insulating fatty substance called myelin that is composed of Schwann cells and oligodendrocytes . Some of the nerve fibres are unmyelinated as well . Nodes of Ranvier are short unmyelinated segments interspersed in the nerve fibre that serve as the site of action potential generation.

18. The area from where the nerve fibres extend from the body of the nerve cells is called axon hillock . The axon initial segment (AIS) is a separate functional area of the nerve fibres that separates nerve fibres from the rest of the neuron and also helps in initiating action potentials.

19. What are the main functions of the nerves ? Controls the voluntary and involuntary movement of the body. Maintains the balance of the body. Maintains the homeostasis of the body by doing functions such as thermal regulation, etc. Responsible for sensing the stimuli, processing them, and sending the appropriate response. Release chemical regulators

20. Types of nerve fibres according to the presence or absence of myelin sheath Myelinated nerve fiber: Covered by myelin sheath which is interrupted with gaps called nodes of Ranvier Non-Myelinated nerve fiber Not covered by myelin sheath

21. Myelinated nerve fibers Myelinated nerve fibers Axon diameter Large small Myelin sheath Covered by many layers of Schwann cells Surrounded by the cytoplasm of Schwann cells Conduction Salutatory conduction Sweeping conduction Channel Has a large number of voltage gated Na channel Has a less number of voltage gated Na channel Energy consumption less great Colour White in colour Gray in color Sites Including those in the brain and spinal cord In the peripheral nervous system

22. Types of the nerves according to the diameter and velocity of conduction Group Functions Diameter (u) Velocity Meter/sec Spike duration Sensitive to A- Alpha ( a )   Somatic motor, proprioception & annulospiral ending 2-20   10-120   0.5m.sec pressure A-Beta ( b ) Fine touch, proprioception 10-20 60-120 A-Gamma ( g ) Motor to muscle spindle 5-10 30-60 A-Delta ( d ) Temperature (cold), crude touch and pricking 3-5 15-30 B Myelinated autonomic preganglionic fibres . 1-2 5-10 1 O 2 lack C Unmyelinated fibres Less than1 0.5-2 2 Local anesthetic

23. Excitability The nerve fibres are highly excitable structures that respond to several stimuli and can also generate electrical impulses. Stimulus : it is the changes which occur in the environment around the living organism. Types of the stimulus : Electrical stimulus : by using galvanic current and it is preferred Chemical stimulus : O2, Co2, H+, acids and alkali Mechanical stimulus : pain and movements. Physical stimulus : cold and hot. Electromagnetic stimulus : sun rays and light Characters of nerve fibres:

24. Electrical stimulus is preferred because We can control its onset We can control its intensity We can control its duration It resembles the natural stimulus. It leaves the stimulated tissue without damage.

25. Conductivity The electrical impulses generated in the nerve fibers are propagated along its entire length and to different neurons, muscles and glands by synaptic connections. Refractory Period : The nerve fibers can conduct one action potential at once, i.e., the excitability of the fibres is less during conduction and hence a new electrical impulse cannot be generated .

26. Not fatigued The nerve fibers don’t fatigue when they are stimulated continuously . Explain why . the fatigue occur due to 1- exhaustion of neurotransmitter, which is present in the synapse not in the nerve. 2- accumulation of waste production due to metabolism which happens in muscle not in the nerve ) All or None Response : A nerve fiber translates either all of the impulse or none at all. If a stimulus is applied up to a threshold level, an action potential will be generated but increasing the strength of the stimulus will not affect the action potential.

27. It is the ability of the nerve to adapt itself quickly to the continuous stimulating agent. It is of three types : Slowly adapting : pain sensation Moderately adapting : hot and cold sensation Rapid adapting : touch sensation. Adaptation Summation:  If a sub-threshold stimulus is applied, it cannot generate an action potential. However, when multiple sub-threshold stimuli are applied in rapid succession, an action potential is generated