Nervous System Part 3 PDF

Organization of The Nervous System (Function) Part 3 Mohamad Razif bin Othman PRH1016 1  Structural Classification of Neurons Neuroglia Astrocytes Ependymal cells Microglial cells Ol...

Organization of The Nervous System (Function) Part 3 Mohamad Razif bin Othman PRH1016 1  Structural Classification of Neurons Neuroglia Astrocytes Ependymal cells Microglial cells Oligodendrocytes Schwann cells PREVIOUSLY IN PART 2 The brain Protective coverings Cerebrum Cerebellum Brainstem Diencephalon 2 SPINAL CORD Elongated cylinder extending from the brainstem through the foramen magnum of the skull. Gray matter interior surrounded by white matter 31 pairs of spinal nerves attached by dorsal and ventral nerve roots. 3  SPINAL CORD Lies within the spinal cavity and extends from the foramen magnum to the lower border of the first lumbar vertebra. Oval-shaped cylinder that tapers slightly from above downward Two bulges, one in the cervical region and one in the lumbar region Anterior median fissure and posterior median sulcus are two deep grooves; anterior fissure is deeper and wider 4 SPINAL CORD Nerve roots: Fibers of dorsal nerve root Carry sensory information into the spinal canal Dorsal root ganglion- cell bodies of unipolar, sensory neurons make up a small region of gray matter in the dorsal nerve root. Fibers of ventral nerve root Carry motor information out of spinal cord Cell bodies of multipolar, motor neurons are in the gray matter of the spinal cord 5 SPINAL CORD Interneurons are located in the spinal cord’s gray matter core Spinal nerve: a single mixed nerve on each side of the spinal cord where the dorsal and ventral nerve roots join together. Cauda equina - bundle of nerve roots extending (along with the filum terminale) from the conus medullaris (inferior end of spinal cord) 6  CAUDA EQUINA A collection of spinal nerves that descends from the lower part (distal end) of the spinal column, beyond the conus medullaris, and occupies the lower third of the spinal canal (the central space within the spine). The way the nerves splay out resembles a horse's tail, hence the (Latin) name. 7  GREY MATTER The gray matter of the spinal cord consists of nerve cell bodies, dendrites and axon terminals (unmyelinated) and neuroglia. It is pinkish-gray colour because of a rich network of blood vessels. The gray matter forms an H shape and is composed of three columns of neurons- posterior, anterior and lateral horns. The projections of gray matter toward the outer surface of spinal cord are called horns. 8  GREY MATTER The two that run dorsally-posterior horns which function in afferent input. The two that run ventrally-anterior horns which function in efferent somatic output. The two that extend laterally- lateral horns. Function: Integration of spinal reflexes and filtering of information going to higher centres. The nerve fibers that form the cross of the H are known as gray commissure -functions in cross reflexes. 9  WHITE MATTER The white matter gets its name because it is mainly composed of myelinated nerve fibers, and myelin has a whitish colour. The white matter is divided into three pairs of columns or funiculi of myelinated fibers: anterior, posterior, lateral and a commissure area. The bundles of fibers within each funiculus are divided into tracts called fasciculi. Ascending tracts : sensory fibers carry impulse up the spinal cord to the brain. Descending tracts : motor neurons transmit impulse from the brain down the spinal cord 10  LEARNING OUTCOME 4 Describe the structure & function of spinal nerve Define dermatome & myotome. Compare the somatic motor and autonomic structure & function. Compare the sympathetic and parasympathetic structure and function. Compare the difference effect of autonomic nervous system Describe the membrane potentials and impulse transmission process 11 SPINAL NERVE The term spinal nerve generally refer to a mixed spinal nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. Humans have 31 left-right pairs of spinal nerves, each roughly corresponding to a segment of the vertebral column: 8 cervical spinal nerve pairs (C1-C8) 12 thoracic pairs (T1-T12) 5 lumbar pairs (L1-L5) 5 sacral pairs (S1-S5) 1 coccygeal pair. The spinal nerves are part of the peripheral nervous system (PNS). 12 TYPES OF SPINAL NERVES 13 DERMATOMES Region of skin surface area supplied by afferent (sensory) fibres of a given spinal nerve. 16  MYOTOME Skeletal muscle or muscle supplied by efferent (motor) fibers of a given spinal nerve 18 CRANIAL NERVES The brain receives sensory information from and controls the activities of, peripheral structures – head and neck Afferent and efferent nerve fibres run in 12 pairs of cranial nerves, which are identified by individual names and Roman numerals I-XII Within the brain stem lie a number of cell groupings, called the cranial nerve nuclei - the sites of termination of sensory fibres and the origin of the motor fibres that run in cranial nerves 19 12 CRANIAL NERVES 1. Olfactory nerve (I) 2. Optic nerve (II) 3. Oculomotor nerve (III) 4. Trochlear nerve (IV) 5. Trigeminal nerve (V) 6. Abducens nerve (VI) 7. Facial (Intermediate) nerve (VII) 8. Vestibulocochlear nerve (VIII) 9. Glossopharyngeal nerve (IX) 10. Vagus (X) 11. Accessory nerve (XI) 12. Hypoglossal nerve (XII) 20 The 12 CRANIAL NERVES 21 SOMATIC VS AUTONOMIC 23 COMPARISON BETWEEN THE STRUCTURE OF SOMATIC & AUTONOMIC NERVOUS SYSTEMS 24  AUTONOMIC: SYMPATHETIC VS PARASYMPATHETIC It is easy to forget that much of the human nervous system is concerned with routine, involuntary jobs, such as homeostasis, digestion, posture, breathing, etc. This is the job of the autonomic nervous system Its motor functions are split into two divisions, with anatomically distinct neurons. Most body organs are innervated by two separate sets of motor neurons; one from the sympathetic system and one from the parasympathetic system. These neurons have opposite (or antagonistic) effects. In general the sympathetic system stimulates the "fight or flight" responses to threatening situations, while the parasympathetic system relaxes the body. 25 COMPARISON BETWEEN THE STRUCTURE OF SYMPATHETIC & PARASYMPATHETIC NERVOUS SYSTEMS 26 COMPARISON BETWEEN THE STRUCTURE OF SYMPATHETIC & PARASYMPATHETIC NERVOUS SYSTEMS 27 Sympathetic Transmitter Position Origin Lengthofofneurones ofsubstance ganglion fibres Parasympathetic Type of Receptors for neurotransmitters Dominant during danger and stressful activities; Dominant during rest; control controls reaction to routine body activities stress Preganglionic: Nicotinic Preganglionic: Nicotinic Post ganglionic: α 1, α 2, β1, β2. Postganglionic: Muscarinic Noradrenaline/epinephrine Short released at Acetylcholine released at effector Emergepreganglionic effector from thoracic andfibres Long pregangionic Emerge from fibres cranial(lower Brain) and Long Close LumbarPostganglionic toRegions spinaloffibres cord CNS sacral regions Short postganglionic Close of CNS to effector fibres DIFFERENCE EFFECT OF AUTONOMIC 29 LEARNING OUTCOME 5 Describe the concept of membrane potentials. Explain the formation of resting and action potential Describe the mechanism of transmission and spreading of impulse along the axon 30 Action potential: The concept of membrane potentials Resting potential is the negative charge registered when the nerve is at rest and not conducting a nerve impulse. Depolarisation is a change from the negative resting potential to the positive action potential. Re-polarisation is the change in the electrical potential from the positive action potential back to the negative resting potential. ACTION POTENTIALS 32 How the nerve impulse travels along the axon: Refractory potential Action Potential Resting potential The meansNathat +willgates The voltage diffuse diffusion tobeen have this position. backwards opened of Naand If there + from the thevoltage is a high action reaches isthreshold concentration potential to(TH) of Na not able + in then the the channel axon. depolarise This willtoopen the diffuses membrane the next will Na+set channels. offlood This in and voltage means a depolarising gates new action the impulse potential travelsfrom restingsite in one will be established. potential direction (1D)  Transmission of impulse along axon Once an action potential has started it is moved (propagated) along an axon automatically. The local reversal of the membrane potential is detected by the surrounding voltage- gated ion channels, which open when the potential Refractory potential: The axon is in a refractory (ReP) period which means that diffusion backwards of Na+ from the action potential is not able to depolarise the membrane channels. This means the impulse travels in one direction Action Potential: The voltage gates have been opened and there is a high concentration of Na+ in the axon. This diffuses to the next set of voltage gates depolarising from resting potential. Resting potential: The Na+will diffuse to this position. If the voltage reaches threshold (TH) then the 34 channel will open Na+will flood in and a new action potential site will be established.  Transmission of impulse along axon Threshold (TH): The ion channels are either open or closed; there is no half-way position. This means that the action potential always reaches +40mV as it moves along an axon, and it is never attenuated (reduced) by long axons. In other word the action potential is all-or-nothing. Refractory Period (ReP): After an ion channel has opened, it needs a “rest period” before it can open again. This is called the refractory period, and lasts about 2 ms. This means that, although the action potential affects all other ion channels nearby, the upstream ion channels cannot open again since they are in their refractory period, so only the downstream channels open, causing the action potential to move one-way along the axon. The delay caused by refractory period also prevents the summation of Action potentials (one impulse cannot catch up another impulse) 35 END OF PART 3 37