Veterinary Physiology 1 - Nervous System Lecture 4 (PDF)

VETM 1502: VETERINARY PHYSIOLOGY 1 LECTURE: NERVOUS SYSTEM #4 – CNS VS PNS Kavita R. Lall, B.Sc. (Hons.), D.V.M. (Hons.), M.Sc. (Dist.) OUTLINE  Learning objectives  Central nervous system  Peripheral nervous system  Somatic nervous system ...

VETM 1502: VETERINARY PHYSIOLOGY 1 LECTURE: NERVOUS SYSTEM #4 – CNS VS PNS Kavita R. Lall, B.Sc. (Hons.), D.V.M. (Hons.), M.Sc. (Dist.) OUTLINE  Learning objectives  Central nervous system  Peripheral nervous system  Somatic nervous system  Autonomic nervous system LEARNING OBJECTIVES  Understand the importance of the different nervous system divisions and their roles  Explain what constitutes the central and peripheral nervous systems  Discuss the ascending and descending pathways within the central nervous system  Differentiate between the somatic nervous system and autonomic nervous system  Differentiate between the sympathetic and parasympathetic nervous system CENTRAL NERVOUS SYSTEM  Formed by neurons of the brain and spinal cord  Groups of neuronal cell bodies are called nuclei  Groups of axons are arranged into tracts CENTRAL NERVOUS SYSTEM CONT’D  CNS sensory neurons carry information to the cerebellum, brain stem and cerebrum for further interpretation  Uses ascending and descending pathways to communicate with the external environment CENTRAL NERVOUS SYSTEM CONT’D Ascending pathways  Sensory information from the periphery of the animal ascends through the spinal cord and enters the higher levels of the brain (somatosensory cortex or cerebellum)  Carry sensations from pain, thermal, tactile, muscle and joint receptors CENTRAL NERVOUS SYSTEM CONT’D Ascending pathways – cerebral cortex  This sensory information reaches higher levels within the brain and therefore consciousness CENTRAL NERVOUS SYSTEM CONT’D  Dorsal column medial lemniscus system  Fasciculus gracilis  Fasciculus cuneatus  Spinothalamic tracts  Lateral  Anterior  Spinoreticular tract  Spinocervicothalamic tracts  Spinothalamic pathway is the major pain relay system in mammals  Spinocervicothalamic pathway plays an equally important role in pain transmission in dogs and cats; absent in man Pathway/tract Sensations First-order Second-order Third-order Final destination Fasciculus Proprioception Dorsal root Nucleus gracilis gracilis and fine touch, ganglia. Axons of medulla pressure and enter the CNS in oblongata. vibration from dorsal roots and Axons cross over hindlimbs and join fasciculus before existing caudal trunk gracilis medial lemniscus Somatosensory Ventral nuclei of cortex (on thalamus opposite side of Fasciculus Dorsal root stimulus) cuneatus Proprioception ganglia. Axons Nucleus and fine touch, enter CNS in cuneatus of pressure and dorsal roots and medulla vibration from join fasciculus oblongata. forelimbs and cuneatus Axons cross over cranial trunk before existing medial lemniscus Pathway/tract Sensations First-order Second-order Third-order Final destination Lateral Pain and Dorsal root Interneurons in Spinothalamic temperature ganglia. Axons dorsal horn. enter CNS in Axons enter dorsal roots lateral spinothalamic tract on opposite side Somatosensory Ventral nuclei of cortex (on thalamus opposite side of Anterior Crude touch and Dorsal root Interneurons in stimulus) spinothalamic pressure ganglia. Axons dorsal horn. enter CNS in Axons enter dorsal roots anterior spinothalamic tract on opposite side Pathway/tract Sensations First-order Second-order Third- Fourth-order Final order destination Spinoreticular True pain Dorsal root Posterior Reticular Intradmedian Somatosensory sensation, as ganglia. grey column. formation nucleus of cortex, the pain lasts Axons enter Most fibres in the the thalamic thalamus, longer, less CNS in remain medulla intralaminar hypothalamus, localized and dorsal roots uncrossed oblongata, nuclei limbic system more and ascend in pons and persistent; the lateral mid-brain thought to be white column more primitive than the spino- thalamic tract; influences level of consciousness Pathway/tract Sensations First-order Second-order Third-order Fourth- Final order destination Spino- Touch, Dorsal root Marginal Lateral Ventral Somatosensory cervicothalamic temperature ganglia. Nucleus or cervical nuclei of cortex (on and pain Axons Nucleus nucleus. thalamus opposite side of enter CNS Proprius. Cross the stimulus) in dorsal Ascend midline and roots ipsilaterally ascend to the to the upper contralateral cervical thalamus spinal cord CENTRAL NERVOUS SYSTEM CONT’D Ascending pathways – cerebellum  Spinocerebellar tracts transmit information from proprioceptors  Involved in co-ordination  This sensory information does not reach consciousness  Pathway/tract Sensations First-order Second-order Final destination Cuneocerebellar Proprioception from Dorsal root Lateral cuneate nucleus in Cerebellum via forelimbs ganglia. Ascend caudal medulla oblongata. the inferior in the fasciculus These axons from the cerebellar peduncle cuneatus nucleus form the (restiform body) cuneocerebellar tract, which joins the dorsal spinocerebellar tract  Pathway/tract Sensations First-order Second-order Final destination Dorsal Proprioception Nucleus dorsalis; Cerebellum via spinocerebellar from hindlimbs ascends ipsilaterally the inferior cerebellar tract peduncle(restiform Dorsal root ganglia. body) Axons enter CNS in Ventral Same as dorsal dorsal roots Nucleus dorsalis; most spinocerebellar spinocerebellar neurons cross at the Cerebellum via tract but it takes a anterior white the superior cerebellar less direct route to commissure  pons peduncle the cerebellum *ones that crossed make a second cross within the cerebellum, to terminate on the ipsilateral side CENTRAL NERVOUS SYSTEM CONT’D Descending pathways  Motor pathways carrying signals from the brain to skeletal muscle and smooth muscle  Consists of upper and lower motor neurons CENTRAL NERVOUS SYSTEM CONT’D  The connections between the motor cortex in the forebrain and motor neurons within the spinal cord are made up of two tracts  Pyramidal system  Extrapyramidal system CENTRAL NERVOUS SYSTEM CONT’D Pyramidal system (Corticospinal)  Produces fine movements associated with skill and are fundamental in the control and coordination of muscle groups that require concentration and conscious thought to control (most developed in primates; cats - aids in grooming)  In most domestic species these tracts are primarily involved in control of the jaw, lips and aspects of the face  Composed of direct connections with no synapses within the brainstem  Nerve fibres originate in the cerebral cortex and then pass to the thalamus and medulla oblongata  Some fibres cross in the medulla oblongata, while others remain ipsilateral until they leave the spinal cord where they cross the midline of the body CENTRAL NERVOUS SYSTEM CONT’D Extrapyramidal system  Has synapses within the brainstem  Tracts run outside the pyramids of the medulla oblongata  Contains various multisynaptic pathways that relay within several nuclei in the brain  Other parts of the extrapyramidal tract take origin from the tectum and reticular formation and synapses within the brainstem  The cerebellum utilizes this influence to ensure that movements are coordinated CENTRAL NERVOUS SYSTEM CONT’D  Responsible for the control of larger muscles and groups of muscles  Constitutes a major part of the coordination system in which groups of muscles are used to maintain posture and smooth movements during locomotion  These types of movements do not require the same level of conscious input or concentration as those of the pyramidal tract  It is the most important system in domestic species CENTRAL NERVOUS SYSTEM CONT’D  Many neurons, which relay within nuclei, are involved in the extrapyramidal tract  Red nucleus  Substantia nigra  Caudate nucleus  Subthalamic nuclei  Olivary nuclei  Neurons that relay in the red nucleus and reticular formation relay directly onto lower motor neurons whilst others relay to other nuclei CENTRAL NERVOUS SYSTEM CONT’D  Rubrospinal tract  Activates flexor muscles  Fine motor control  Reticulospinal tract  Pontine RST  Activates extensors  Contributes to voluntary movements and increase in muscle tone in response to alerting or activating stimuli  Medullary RST  Inhibits voluntary movements  Inhibits extensors  Reduces muscle tone CENTRAL NERVOUS SYSTEM CONT’D  Vestibulospinal tract  Activates extensors  Postural, balance and tone adjustments  Tectospinal tract  Involved in control of head and neck muscles  Involved in reflex responses to visual and auditory stimuli CENTRAL NERVOUS SYSTEM CONT’D UMN vs LMN  Upper motor neurons  Neurons in the descending tracts  Brain and brainstem to the ventral horn of the spinal cord  Lower motor neurons  Neurons leaving the spinal cord  From the ventral horn of the spinal cord to the peripheral muscles PERIPHERAL NERVOUS SYSTEM  All nervous structures located outside of the brain and spinal cord  Provides communication from the receptors to the CNS (sensory) and from the CNS to the effector organs (motor)  Peripheral nerves are myelinated  Somatic motor nerves – controls skeletal muscles  Autonomic motor nerves – controls cardiac muscle, smooth muscles and glands SOMATIC NERVOUS SYSTEM  Allows an animal to process information about its environment and controls motor movements  Sensory and motor neurons have only one synapse  Made up of the cranial nerves and spinal nerves  ACh is the main neurotransmitter released AUTONOMIC NERVOUS SYSTEM  Supplies efferent information to cardiac muscle, smooth muscle and glands  Nerve fibres are of 2 types 1. Pre-ganglionic nerve fibres  Nerve fibre from CNS to cells of ganglia for synapse  Small  Myelinated  Conduction velocity: 3-15 m/sec, representing class B fibres 2. Post-ganglionic nerve fibres  Nerve fibre from ganglia to effector organ  Small  Non-myelinated  Class C fibres with conduction velocity of 0.7-2.3 m/sec AUTONOMIC NERVOUS SYSTEM CONT’D  Neurotransmitters:  ACh  Produced by pre-ganglionic fibres of both sympathetic and parasympathetic systems  Post-ganglionic fibre of parasympathetic system  Adrenaline/Noradrenaline  Post-ganglionic fibres of sympathetic system AUTONOMIC NERVOUS SYSTEM CONT’D  Sympathetic nervous system  Origin: Thoracolumbar region  Ganglia location: Close to spinal cord  Post-ganglionic fibre length: Long  Post-ganglionic branching: Many; multiple organs can be mobilized at once AUTONOMIC NERVOUS SYSTEM CONT’D  Sympathetic trunk  Composed of chain ganglia (vertebral ganglia)  Paired structure having a ganglion for each thoracic, lumbar, sacral and upper coccygeal nerve  Allows nerve fibres to travel to spinal nerves that are above and below ones from which they originate AUTONOMIC NERVOUS SYSTEM CONT’D  Parasympathetic nervous system  Origin: Craniosacral region  Ganglia location: Close to target organ  Post-ganglionic fibre length: Short  Post-ganglionic branching: Little branching THE END