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CENTRAL NERVOUS SYSTEM (CNS)

Physiology I. CENTRAL NERVOUS SYSTEM (CNS). Dr Than Kyaw 4 December 2011. Lecture-outline. Gross anatomy of the brain General functions limbic system Motor system, UMN and LMN Spinal reflex Vestibular apparatus and postural control. Parts of the Brain. Cortex (gray) Medulla (white)

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CENTRAL NERVOUS SYSTEM (CNS)

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  1. Physiology I CENTRAL NERVOUS SYSTEM (CNS) Dr Than Kyaw 4 December 2011

  2. Lecture-outline • Gross anatomy of the brain • General functions • limbic system • Motor system, UMN and LMN • Spinal reflex • Vestibular apparatus and postural control

  3. Parts of the Brain Cortex (gray) Medulla (white) Basal nuclei 1. Cerebrum - 2 pairs (cerebral hemisphere) 2. Cerebellum (unpaired) 3. Brain stem (a) Interbrain Pituitary gland Hypothalmus Subthalmus Thalmus epithalmus (b) Midbrain (c) Pons (d) Medulla oblongata

  4. Sheep brain Gyrus/ridge Fissure/sulcus

  5. Sheep brain : sagittal section

  6. Sheep brain : Ventral view

  7. Peripheral Nervous system Cranial nerves 12 – pairs 11 pairs – in head 1 pair – in head and stretches up to visceral organs (Vagus nerve) Spinal nerves - in pairs - numbers vary with species

  8. Cranial nerves I Olfactory (smell) II Optic (Retina; Vision) III Oculomotor (Most ms of eye) IV Trochlear (eye: dorobl ms) V Trigeminal (eye, face, ms of mastication) VI Abducens (retractor, lateral eye ms) VII Facial (ear, taste, salivary glands, facial ms) VIII Vestibulocochlear (hearing, equilibrium) IX Glossopharyngeal (pharynx, tongue) X Vagus (Pharynx, larynx, visceral structures in the thorax and abdomen) XI Accessory (MS of shoulder and neck) XII Hypoglossal (Tongue ms)

  9. Functions of the brain cerebral cortex • Gray matter – most of neuronal cell bodies • - unlike spinal cord – it lies on the exterior • Voluntary movement (initiation) • - impulses from the areas in one hemisphere cause movement of • muscle on the opposite side of the body • Sensations brought into conscious • Higher functions – educational, reasoning, planning • Specific sensory areas (centers) • - body sense areas – receives impulses from the skin • (touch, warmth, cold, pain localization) • - receives impulses from muscle, tendon, joints- impulses from eye (sight), ear (hearing), nose (smell), tongue (taste),

  10. Dog Brain – Cross-section of Cerebral Hemispheres Grey matter white matter Corpus callosum Lateral ventricles Basal nuclei

  11. Cerebral cortex and its functions White matter – beneath gray matter - contain myelinated nerve fibers connecting different parts of the cortex, 2 hemis-spheres, other parts of the brain and spinal cord Basal neuclei– lie deep within cerebral hemispheres (Basal ganglia) - composed large pool of neurones - control complex semi-voluntary movements - e.g. walking, running, vomitting

  12. Cerebellum • Not concerned with sensation and consciousness • Concerned with automatic adjustment to prevent distortion of inertia and momentum (balance and posture) Interbrain • Hypothalmus – consists of pituitary gland (endocrine gld) • - Complex sensing and neurosecretory functions • - Centers for thermoregulation, hunger, thirst, sleeppatterns, sexdrive • Thalmus– relaycenter: impulses from all areas of the body are transmitted to thalmus for transfer to the cerebral cortex • Epithalmus – olfactory correlation center • - pineal gland: gonadal hormone

  13. Mid brain • Auditory reflex centers • Visualreflex centers • Several descending tracts Pons - Main function - relay centerfor many signals to and from the cerebrum, cerebellum and spinal cord

  14. Medula oblongata • - Many ascending and descending pathways • Sensory and motor nuclei for ten cranial nerves originated • A large part of central mechanism of postural reflexes (hopping, righting, placing) • Vital regulatory centers • - heart rate, vasomotortone (bld v/s muscles) Blood pressure, respiration, • - Contain reflexes • - motor swallowing, coughing, vomitting, sneezing and secretory activities of the digestive tract

  15. Limbic System • Components of limbic system • the cortex, • Cingulategyrus • Hippocampus • hypothalamus, thalamus, • Amygdalaand • basal nuclei (several areas deep within the cerebrum)

  16. Functions of limbic system Behavior and control of our behavior Emotions - nature of the sensations, pleasant or unpleasant • - rage, fear, anger, pain, pleasure, sorrow • - This helps guide the individual into appropriate behavior that • is more likely to be beneficial (survival). • - Learning and memory All these functions are controlled through the Reward and punishment function of the limbic system. Reward (satisfaction) e.gsatisfiction after eating, drinking, success…etc Punishment (displeasure, fear, terror, pain..etc)

  17. Memory • Limbic system - involved in memory formation • Hippocampus, structure deep in the cerebrum and a part of limbic system - necessary to form new memories • Damage of hippocampus - cannot remember things since the time the damage occurred butcan remember from before that time. • Short-term memory - probably stored as electrical differences because they can be removed by the application of an electrical shock. - Long-term memory - probably stored as new or different synapses. Research shows that learning is associated with an increased number of synapses. Forgetting is associated with a decreased number.

  18. Motor neurons Two types:1. Upper motor neurons (UMNs) 2. Lower motor neurons (LMNs) Upper and Lower Motor Neurons Somatic motor neurons (include both UMN &LMN) - Cell bodies within CNS - Their axons extend from CNS to contact skeletal. - carry motor information down to the final common pathway (any motor neurons that connects to a muscle)

  19. Lower Motor Neurone (red line)

  20. Upper motor neurons (UMNs) • Motor neurons within CNS • Regulate the activity of a LMN • Initiate voluntary movement • maintain relatively stable body posture and balance Upper motor neuron lesions • Reflexes and voluntary activity possible but abnormal • Decreased control of active movement, particularly slowness • Babinski sign (human): big toe is raised (extended) rather than curled downwards (flexed) upon appropriate stimulation of the sole of the foot.

  21. Lower motor neurons (LMNs) • The nerves connecting the spinal cord to the muscles • Relay the movement instructions provided by the UMN, • to the muscles A lower motor neuron lesion Symptoms - Muscle paresis/paralysis, hypotonia/atonia, hyporeflexia/areflexia - The extensor Babinski reflex is usually absent. - End-stage muscle denervation: Muscle wasting, fasciculations Causes - Common causes: injuries by trauma to peripheral nerves

  22. Spinal Cord • - Run inside the vertebral column • Paired spinal nerves from the vertebrae • receive sensory afferent fibers (dorsal root) • gives off motor efferent fibers (ventral root)

  23. Number of vertebrae Spinal nerves = Number of vertebrae x 2

  24. Spinal Cord • - Gray matter – nerve cell bodies and processes • White matter – bundles of nerve fibers having common origin, termination and function; these bundles connect brain stem and higher centers with spinal nerves

  25. (Afferent, sensory) (Efferent, motor)

  26. Grey matter Dorsal funiculus White matter Dorsal horn lateral funiculus ventral funiculus ventral median fissure Cross section of spinal cord : dog; C2 region

  27. Dendrites ("tree branches") receive info from other neurons • The axon conducts the impulse to other neurons via axon terminals • Types of specialized neurons • - afferent (sensory) neurons • - interneurons (only connecting to other neurons) • - motor neurons.

  28. Reflex and Reflex arc - A reflex is a rapid automatic response to a stimulus • - An accidental touch to a hot object automatic jerk of hand away • Automatic blinking when an object approaches the eye • Cats twist their bodies in the air when falling so they land on their paws • sneezing • the constriction of the pupil of the eye in bright light A reflex arc: the path taken by the nerve impulses in a reflex

  29. Components of a reflex arc • A receptor • An afferent limb • central connection • An efferent limb • An effector organ

  30. Spinal reflex • e.g. The knee jerk reflex • - A stretch receptor in the extensor muscle (patellar ligament) reports the hammer tap to the vertebral column by neurons. • Those connect to motor neurons that return to the muscle and make it flex. • A spinal interneuron also receives the nerve impulse and connects to another set of motor neurons that inhibit the antagonistic muscle.

  31. Reflex centers • Located throughout the CNS • Simplest reflex – associated with the spinal cord • Complex reflex – carried out through reflex center in the brain - medulla oblongata and pons (e.g. swallowing, H/R) - cerebellum – centers associated with locomotion and postures - hypothalmus – regulatory centers; e.g temperature - midbrain – visual and auditory reflexes

  32. Cerebrospinal fluid - produced by the choroid plexus tissue located within the brain • flows through a series of cavities (ventricles) out of the brain and • down along the spinal cord • CSF is kept separate from the blood supply by the blood-brain • barrier.

  33. Lateral ventricle

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