Central Nervous System PDF

Central Nervous System Ahmed H. Arisha DVM. M.SC. Ph.D. [email protected] Tel:01007857984  NEURONS: The structural components of the nervous system…  Types of neurons in the nervous system ◼ Sensory...

Central Nervous System Ahmed H. Arisha DVM. M.SC. Ph.D. [email protected] Tel:01007857984  NEURONS: The structural components of the nervous system…  Types of neurons in the nervous system ◼ Sensory ◼ Motor ◼ interneurons Neural Organization  Organization of the CNS Gray Matter: Contains neuron cell bodies White Matter: Contains cell extensions organized into tracts  To carry out its normal role, the nervous system has three over lapping functions: 1) It uses sensory receptors to monitor changes occurring both inside and outside the body. These changes are called stimuli, and the gathered information is called sensory input. 2) It processes and interprets the sensory input and makes decisions about what should be done at each moment – a process called integration. 3) It then effects a response by activating muscles or glands (effectors) via motor output.  Nerve fibers vs tract fibers In the CNS, collections of axons are called tracts. In the PNS, collections of axons are called nerves Brain: Structure Embryonic Development Embryonic Development Forebrain  Cerebrum 1- cerebral cortex Higher mental processes; Consciousness, memory, judgment, thinking, intelligence, speech and conditioned reflexes. Function of the cerebral cortex Cerebral Cortex  Cerebral cortex--Motor planning, control, and execution of voluntary movements. area of the frontal lobe. Removal of the motor area from one cerebral hemisphere causes paralysis of voluntary muscles of the opposite side  Cerebral cortex--Motor Primary motor cortex (frontal lobe) Coordinates & controls conscious movement Premotor cortex Plans movement Preparation for movement Sensory and spatial guidance of movement Direct control of movements as proximal and Trunk muscles  Cerebral cortex—Motor areas Broca’s area (premotor cortex in one hemisphere) Motor Speech Frontal eye field (premotor cortex ) Voluntary eye movement Primary somatosensory (area 3a ---- motor)  Motor function Cerebral cortex Cerebellum Basal ganglia Red nucleus of the mid brain  Cerebral Cortex—Sensory areas the parietal lobe. the primary cortical regions of the five sensory systems in the brain (taste, olfaction, touch, hearing and vision). sensory information from thalamic nerve projections except for the olfactory system  Cerebral Cortex—Sensory areas Primary somatosensory (area 3b) Interprets sensation from body Somesthetic sensory cortex Integrate sensory input from thalamus Process information of (surface)touch and (deeper tissues) position sense  Cerebral Cortex—Sensory areas Primary Visual (occipital, retinas) Primary Auditory(temporal, Cochlear receptors of the inner ear) Primary Olfactory (uncus, not routed in thalamus) Primary Gustatory (insular lobe) Cerebral Cortex: Motor and Sensory Areas Association areas (sensory and interpretive) visual association areas: It is involved in recognition of nature of seen objects. Lesions in the primary visual area ---- blindness Lesion in visual association area - -- defective visual learning, inability to understand the measuring of written words(word blindness) Association areas (sensory and interpretive) Lesions of primary auditory areas cause deafness. Auditory association area is involved in interpreting the significance of sounds e.g. the meaning of spoken words. Lesions cause auditory aphasia (impossible to interpret the meaning).  Thalamus Coordinate almost all inputs into brain (relay station) All sensory information (except olfaction) is relayed to the cortex via the thalamus Filters all signals Regulate states of sleep and wakefulness Arousal, awareness and Motor activities Damage ==== permanent coma  Hypothalamus Link between nervous and Endocrine system  Hypothalamus: Inputs and Outputs Neural Output Hormonal Output Neural Input Controls the Controls release of autonomic nervous oxytocin for milk system (e.g. lactation emotion) Hormonal Input Used for drives Controls release of and motivated vasopressin for behavior fluid regulation  Hypothalamus Hypothalamic releasing hormones------- anterior pituitary  Hypothalamus Neuro hormones stored in posterior pituitary Oxytocin----uterine contraction, milk letdown Vasopressin— affects renal reabsorption of water Figure 7-12: Synthesis, storage, and release of posterior pituitary hormones  Hypothalamus Autonomic control center Anterior hypothalamus ---- parasympathetic---- bradycardia Posterior hypothalamus ---- sympathetic---- tachycardia  Hypothalamus Body temperature Heat loss center---- Anterior hypothalamus --- parasympathetic Heat gain center ----- Posterior hypothalamus ---- sympathetic  Hypothalamus Food intake Satiety center----- VMH----suppress the desire of food Feeding center-----LHA----- sensation of hunger  Hypothalamus Water balance & thirst Thirst center ---- symptoms of thirst, sensation of thirst (via thalamus to cortex) Osmoreceptors---- supraoptic nuclei------ vasopressin----water reabsorption- --- ↑ TBW Sleep-wake cycle and hormonal circadian cycles (circadian rhythm) Emotions  II- Basal Ganglia - Striatum (caudate nucleus and putamen) - Globus pallidus substantial nigra - Substantial nigra  II- Basal Ganglia Help in selecting the appropriate movement pattern (cortical info about substantial nigra movement plan and situation)  Dopamine containing neurons of the substantial nigra to striatum help in regulating this function In human, diseases of the basal ganglia are characterized by either hyperkinetic like chorea, athetosis hypokinetic as Parkinson’s disease.  Diseases like Parkinson's does not occur naturally in domestic animals Some toxins can destroy dopaminergic neurons such as yellow star thistle ingestion in horses resulting in abnormal lips and tongue movement In birds the cerebral cortex is poorly developed, but the basal ganglia are highly developed so that it can perform nearly all the motor functions including voluntary movements In cat and dog Excision of the cerebral cortex stops some fine motor functions but not all The basal ganglia preserves the ability to walk, eat, fight and sexual activity The limbic system Responsible for smell Amygdala the hippocampus the septal nuclei.  Functions of the limbic system In domestic animals Emotions of importance to survival Self preservation: escape, defense, feeding Species preservation: territorial defense, courtship, mating Damage of the amygdala disrupts emotional reactions of a monkey  Midbrain Relay station for some sensory information and sends them to the forebrain Control of visual reflexes such as pupil response to light intensity in reptiles, birds and mammals (forebrain process visual information) Auditory reflexes and help control posture Major control of the body in fish, amphibians ---- Visual reflexes Hindbrain  Pons Relay signals from forebrain to cerebellum Has nuclei that deals with: sleep, respiration swallowing bladder control hearing Equilibrium taste eye movement posture facial expressions and sensations  Pons Pneumotaxic center---- regulate the change from inspiration to expiration Nuclei for 4 cranial nerves (V-VIII) Trigeminal Abducent Facial vestibulocochlear  Medulla oblongata Deals with autonomic functions as it contain cardiac, respiratory and vasomotor center (breathing, heart rate and blood pressure) Reflex center for vomiting, coughing, sneezing and swallowing Part of the reticular formation Contains nuclei for 4 cranial nerves (IX-XII) Glossopharyngeal vagus Accessory hypoglossal Cerebellum (little brain)  Functions of the cerebellum Historically----- Motor structure cerebellar damage----- impairment in motor control and posture Most of Cerebellar output are part of the motor system The cerebellum is concerned, primarily, with the coordination, adjustment, and smoothing out of movement.  Functions of the cerebellum To achieve this, it receives -------varied sensory information from proprioceptive, tactile, vestibular, auditory and visual receptors. It also receives afferent information from the cerebral cortex and integrates all the afferent information for adjustment of muscular contractions involved in regulation of equilibrium and posture and voluntary movements.  Functions of the cerebellum Motor commands are not initiated in the cerebellum but it modifies signals of the descending pathways to make the movement more adaptive and accurate Cerebellum is important in birds as flight requires considerable coordination  Cerebellum The cerebellum is concerned, primarily, with the coordination, adjustment, and smoothing out of movement Anterior lobe (paleocerebellum) Control antigravity muscles of the body- --- posture Receive proprioceptive input from the spinal cord and vestibular receptor of the inner ear Posterior lobe (neocerebellum) Coordination of the muscle movement Inhibition of involuntary movement (GABA) Fine motor coordination  Flocculonodular lobe Maintenance of equilibrium  Reticular formation Network of nerve pathways and sets of interconnected nuclei located in the brain stem Composed of Ascending reticular formation (RAS)— Sleep wake cycle  Reticular formation Descending reticular formation Posture and equilibrium (motor) Autonomic nervous system activity Coughing, chewing, swallowing and vomiting  Spinal cord Cable of nervous tissue that passes down a channel in the vertebrae from the hindbrain to the end of the tail It consists of spinal cord segments that give rise to spinal nerves Cervical, thoracic, lumbar, sacral, caudal  Cauda equina (horse tail) Caudally streaming spinal roots running to intervertebral foramina in the sacrum and tail Damage -------affects pelvic viscera and the tail  Function of the spinal cord Conduct the sensory information from the PNS to the brain Conduct the motor information from the brain to the effector organs in the PNS Serves as a center for coordination for certain reflexes Reflex movement  Types of neurons in the nervous system ◼ Sensory ◼ Motor ◼ interneurons  Motor neurons ◼ According to their target ⚫ Somatic: CNS------ skeletal muscle ⚫ Visceral: ◼Special (branchial):CNS-----branchial muscles(gills, face and neck) ◼General (autonomic): indirectly innervates cardiac and smooth muscles of the viscera (synapse in the autonomic ganglia)  Motor neurons ◼ General visceral motor neuron ◼ Somatic motor neurons  General visceral (disynaptic) (Monosynaptic)  Motor neurons ◼ According to location ◼ Upper motor neurons: Cerebral cortex---- motor nuclei of the brain stem and the anterior horn of the spinal cord (tracts) ◼ Lower motor neurons: brain stem and spinal cord------- muscles ⚫ Alpha motor neurons: extrafusal muscle fibers-----contraction ⚫ Gamma motor neurons: intrafusal------ muscle spindle----- proprioception Upper Vs lower MNs Motor neurons and Ms contraction  Nerve fibers vs tract fibers In the CNS, collections of axons are called tracts. In the PNS, collections of axons are called nerves Nervous tracts  Nervous tracts A nerve tract, is a bundle of nerve fibers (axons) connecting nuclei of the central nervous system  Nervous tracts Naming Origin------termination Cortico-----spinal tract spinothalamic tract Begins in the cortex Ends in the spinal cord Naming of the nervous tracts  Types of the Tracts 1. Ascending tracts (Sensory tracts) 1. First-order neuron − Delivers sensations to the CNS. The cell body is in the dorsal root ganglion (DRG) 2. Second-order neuron − An interneuron with the cell body in the spinal cord or brain 3. Third-order neuron − Transmits information from the thalamus to the cerebral cortex  Types of the Tracts 2. Descending tracts (Motor tracts)  Types of the Tracts 2. Descending tracts (Motor tracts) 1. Conscious body control [ Pyramidal tracts ]: corticospinal tracts 2. Subconscious control [Extrapyramidal tracts ]: regulation of balance, muscle tone, eye, hand, and upper limb position.  Pyramidal tracts Extrapyramidal tracts Pass through the pyramids Don’t pass of the medulla Directly innervate motor Indirectly control neurons of the anterior horn cells of the spinal cord Fine, isolated, precise and Gross, synergic movements specific movements that require the activity of large groups of muscles Peripheral nervous system (PNS)  Peripheral nervous system No protection (CNS has bone and barrier protection) Nerves and ganglia outside the CNS Spinal------ Mixed Cranial----- all mixed except olfactory and optic nerves (sensory) and the oculomotor (motor)  Peripheral nervous system Function: Transmit signals between the body and CNS Sensory---- state of external and internal environment Motor signals  Sensory axons ----DRG ---- spinal cord Motor axons---- ventral roots---- unit with sensory axon-----mixed nerve  Sensory system A part of the nervous system responsible for processing sensory information Sensory receptors + neural pathway + sensory centers in the brain Animal can sense a wide range of sensations including touch, pressure, pain, temperature, chemicals, light and position  Senses General senses Somatic sensation:- from body wall Touch, pressure, vibration, thermal, pain, proprioception Visceral sensation From internal organs Special senses Smell, taste, vision, hearing, balance  Type of sensation Site of sensation Intensity of sensation Stimuli  Sensory receptors Cells or ends of neurons that detect specific changes in the environment----- chemical gradient, pressure, temperature, sound waves, photons Stimulus= energy Each stimulus has a specific form of energy --- modality Each receptor is designed to respond to a specific model of stimulus---- adequate stimulus  Coding of sensory information It is the ability of the CNS to discriminate (recognize) or identify the; 1.Type of stimulus (modality discrimination) 2.Site of stimulus (locality discrimination) 3.Strength of stimulus (intensity discrimination) Although, all stimuli reach the brain in the same manner i.e. action potential  Sensory receptors Classified according to Receptor morphology Receptor location Rate of receptor adaptation Adequate stimuli  Receptor morphology Free nerve ending----- dendrites with no physical specialization Encapsulate nerve endings----- dendrites enclosed in CT capsule Sense organs----specialized receptor for special senses  Receptor location Exteroceptors--- skin surface---- sensitive to stimuli occurring outside the body--- tactile sensation (touch, pain, temp), vision, hearing, taste Interceptors (visceroceptors)------ visceral organs and BVs---- associated with ANS Proprioceptors-----sk.Ms, tendons, ligaments and joints------ info about body position and location  Rate of receptor adaptation Decrease in the size of receptor potential with a constant stimulus Prolonged exposure to a certain stimulus decreases the rate of receptor response and conscious awareness  Rate of receptor adaptation Slow adapting (tonic) receptor---- action potential over the stimulus duration Pain receptors, joint capsule, muscle spindle  Rate of receptor adaptation Rapidly adapting (phasic) receptor----does not correspond to the duration of stimulus (thermoreceptors and mechanoreceptors)  Tonic Receptors Phasic Receptors slow fast Slow or no adaptation Rapid adaptation Continuous signal Cease firing if strength of transmission for duration a continuous stimulus of stimulus remains constant Monitoring of parameters Allow body to ignore that must be continually constant unimportant evaluated, e.g.: pain information, e.g.: Smell receptors , baroreceptors  Adequate stimulus Each receptor has its own adequate stimulus------ initiation of sensory transduction Baroreceptors ---- pressure in blood Vs Chemoreceptors----- chemical stimuli Hydroreceptors------ changes in humidity Mechanoreceptors----mechanical stress  Nociceptors------ body tissues damage---pain perception Osmoreceptors-----body fluid osmolarity (hypothalamus) Photoreceptors-----light Proprioceptors-----sense of position Thermoreceptors-----changes in temperature Electromagnetic receptors-----electromagnetic waves  Sensory transduction Conversion of one form of energy into another Adequate stimulus energy -------receptor graded potential------ threshold----- action potential---- propagation into the axon-----CNS--- sensation  Sensory pathways Specific pathways transmit info about stimulus terminates in a brain center responsible for this type of sensation Each sensory pathway starts with a sensory unite  Sensory pathways Sensory unite A single afferent neuron and all receptors associated with it Receptive field: All the receptors of afferent neuron that can respond to an adequate stimuli  Sensory pathway First order neuron Second order neuron Third order neuron  General senses 1. Nociceptors (pain receptors)---- Nociception sensation 2. Thermoreceptors (temperature sensors)-----Thermoception sensation 3. Mechanoreceptors A. Tactile Receptors------ Touch sensation B. Proprioceptors-----Proprioception sensation Touch sensation (Tactile receptors) Provide sensations of touch, pressure, and vibrations--- debate specificity Either Encapsulated or Unencapsulated tactile receptors Touch sensation (Tactile receptors) Tactile receptors in the skin are Meissner corpuscles, hair root plexuses, Merkel discs, Ruffini corpuscles, pacinian corpuscles, and free nerve endings  Forms of touch Fine or discriminative touch = sense and localize touch Crude or non-discriminative touch = sense touch without the ability to localize where the stimulus was applied Forms of touch Forms of touch  Touch physiology Physical and psychological well being Regular massage in premature babies improves weight gain and mental development----- stimulate growth hormones production Separation of baby rats for 45 min----- reduction in growth hormones  Proprioception sensation (position movement sensation) Sense of the relative position of neighboring body parts and the strength of effort employed in movement Receptors located in muscles, tendons, ligaments, joints Monitor the position of joints, tension in the tendons and ligaments, and the length of muscle fibers upon contraction Exteroception sensation---- sense from outside Interoception sensation----- sense from inside  Proprioceptors Sensory neurons in the inner ear---- motion and orientation Stretch receptors in the muscle and ligaments Proprioreceptors----- adequate stimuli receptors  Thermoception sensation Thermoreceptors -- free nerve endings --- changes in temperature --- - heat and cold Found in the dermis, skeletal muscles, liver, and hypothalamus  Types of Thermoreceptors Warm receptors: unmyelinated C-fibers---- temp 30-45 c Cold receptors: C-fibers and myelinated fibers---- 35-20c Cold receptors are more numerous than hot receptors These are phasic receptors  Nociception sensation Neural process of encoding and processing noxious stimuli----response and protection Nociceptors(pain)-----mechanical, thermal, chemical stimuli ---- threshold intensity --- signal to spinal CNS Free nerve endings and large receptor fields --- all tissues Hyperalgesia---continuous pain stimulus increase in the excitation of pain fibers  Nociceptive pain Visceral pain-----stretch, ischemia, inflammation but relatively insensitive to burning and cutting Diffused or referred pain, nausea vomition Sickening, deep, squeezing, dull Deep somatic pain---- ligaments , tendons, bones, Bl.Vs--- sprains and broken bone dull aching poorly localized Superficial somatic pain----skin ---- sharp, well defined, clearly located---- minor wounds and burns  Special senses Chemoreception sensation------- receptors sensitive to chemical molecules in the food and air Olfaction Gustation Visual sensation Auditory and vestibular sensation  Olfaction (the sense of smell ) Olfactory receptors – chemical receptors (free nerve cells)---in the upper part of the nasal cavity.  Olfaction Uses: Locate food Mark territory Identify offspring Presence of a mate  Olfaction Airborne stimuli-- chemicals dissolved in the watery mucus -- -Olfactory receptors nasal cavity--- fire an impulse ---- olfactory nerve----brain------ interpreted as odor  Olfaction Olfactory receptors are easily fatigued – many odors are not noticeable after a time-------- rapid adaptation---- arabji cant feel smell of horse stable  Olfaction Olfactory system Main olfactory system-----volatile and airborne substances Accessory olfactory system----- fluid phase stimuli----pheromones  Pheromones Chemicals messages secreted by an animal and sniffed by another animal to modify their behavior Boundary making Food area guiding Alarming Sexual attraction  Olfaction animal vs human Carnivorous has more advanced sense of smell Highly developed sensitivity to scents Larger olfactory region They can detect odor at concentration of 1:10000 of human  Olfaction--- deodorant Only one odor can be perceived at any time----- higher concentration masks that lower ones  Gustation--- sense of taste Taste buds – chemical receptors on the oral cavity that generate nervous impulses resulting in the sense of taste.  Gustation--- sense of taste Human can distinguish four different tastes (sweet, sour, bitter and salt)  sensation of taste Tasted substance----- dissolved-- - solution---taste buds----- impulse-------cranial nerve facial (VII) and glossopharyngeal (IX) nerves----- brain centers--- taste  Gustation--- sense of taste What you think is taste ------- is the sense of smell------ food is tasteless when the nose is blocked------ cats refuse eating Flavors results from a combination of taste bud stimulations and olfactory receptor stimulation.  Gustation--- sense of taste The sense of taste is limited in animals------ only for discrimination between healthful / harmful Preference test ------ such as in dogs------ individual variation When animals has to choose between different food ------pleasant, indifferent or unpleasant  Temperature vs taste Water temperature affects its acceptability in domestic fowls The higher the temperature the less acceptable Fowls reject water placed in sunlight ---- become warmer----thirst (41) Fowls can drink water around freezing point Visual sensation  The Eye Cranial Nerves Optic – vision Oculomotor, abducens and trochlear – eye movement The eye contains 3 layers Sclera Choroid retina  Nictitating membrane Transparent membrane that moves sideway across the eye from the inner corner Function: Cleansing and moistening the cornea without shutting the light Present in birds, crocs, frogs, fish and kangaroo Also in cat and dog  The Eye Sclera – tough fibrous tissue protecting the eye. Front surface is the “white” of our eyes and the cornea. The cornea is transparent, receives no blood supply and is nourished by the aqueous humor. The cornea focus the light entering the eye  The Eye Choroid contains blood vessels ----- supply o2 and nutrients Iris----- involuntary muscles ------colored part--- control the amount of light entering the eye pupil Eye pupil ----- circular or slit (nocturnal animals and cats----protect light sensing tissue from bright light)  The Eye Retina –light sensing receptor cells called rods and cones. Rods – sensitive to dim light---- cant detect color----- pigment from vit A----- deficiency ---- night blindness Cones – color vision----see in details Fovea – area with dense cone cells----- sharp vision  The Eye Lens – composed of transparent, elastic protein; no blood supply nourished by the aqueous humor. Accommodation: the ability to change the focus of the lens between near and distant objects Cloudy lens cause blurred vision (eye cataract)  The Eye fluids of the eyeball – 2 types: Aqueous humor – watery fluid in front of the lens (anterior cavity) nourishes the lens and cornea. Vitreous humor – jelly-like fluid behind the lens (posterior cavity). Literally holds the retina in place and gives structure to the eyeball. Mechanism of vision  Mechanism of vision Light rays from an object----- focused by the cornea, lens, fluids--- - (refraction--- bending of light)----- retina----- activation of cons and rods----- nerve impulse-----optic nerve--- brain----- vision  Color vision In humans and higher primate---- cons and rods are present-- -- rods in dim light (no color) while cons in bright light (color) Other mammals have few cons -------believed to see no or limited range of colors Deer, rat, rabbits and nocturnal animals (cats)----- color blind Birds and fish------ better color vision----- vivid picture------ help in better recognition------ protection and courtship  Visual field binocular vs monocular  Depends on the eye site in the head Binocular----- by both eyes at slightly different angles-- -- enables the animal to estimate the distance to the prey Monocular----- by one eye------give a panoramic view-- ---plant eating animals (rabbit and deer) and horses---- ---help in seeing predators approaching  Blind spot In binocular-----behind ears In monocular----- behind ears and right in front of them (as in horses cant spot whatever between their eyes---- binocular vision------so they look down during walking)  Eyeshine The visible effect of light reflecting surface called tapetum lucidum found behind the retina during dark periods---- as it reflects unabsorbed light--- allowing the retina to absorb extra light---- night vision Types White----fish Blue----horse Green---cats and dogs Red-----rodents and birds Auditory and vestibular sensation hearing and equilibrium  Inner Ear Cochlea – snail shell; contains the Organ of Corti which holds the receptors for hearing. Semicircular (vestibular) portion– contains mechanoreceptors that result in sensing position and equilibrium. give rise to vestibulocochlear nerve VIII  Sound pathway External ear----ear drum----- vibrations------ middle ear----inner ear---cochlea-----spiral organ of corti----- receptors for hearing------ impulses----- vestibulocochlear nerve -----brain center----- hearing Vestibular system and equilibrium  position and equilibrium sensing Sacculus and utriculus have patches of hair cells attached to otoliths----- pulled downward with gravity Change in head position changes the direction of these otoliths----- action potential------ brain center  position and equilibrium sensing Motion---- lagging of the fluid ----- hair cells at the end of the semicircular canals-----impulse---- brain center  position and equilibrium sensing If the signal received from the hair cells doesn't meet what the eye is seeing and felt by the body------ motion sickness (planes and boats)  Thanks Any questions