Lecture #20

1. Lecture #20 Nervous System

2. Two organ systems coordinate and direct activities of a body • Nervous system • Swift, brief responses to stimuli • Endocrine system • Adjusts metabolic operations • Directs long-term changes

3. Anatomical Classification of the Nervous System • Central Nervous System • Brain and spinal cord • Peripheral Nervous System • All neural tissue outside CNS

4. Cells in Nervous Tissue • Neurons • Neuroglia

5. Neuroglia (Glia) • about half the volume of cells in the CNS • smaller than neurons • 5 to 50 times more numerous • do NOT generate electrical impulses • divide by mitosis • two types in the PNS • Schwann cells • Satellite cells • four types in the CNS • Astrocytes • Oligodendrocytes • Microglia • Ependymal cells

6. Astrocytes • Largest of glial cells • Star shaped with many processes projecting from the cell body • Help form and maintain blood-brain barrier • Provide structural support for neurons • Regulate ion concentrations for generation of nerve impulses/action potentials • Regulate nutrient concentrations for neuron survival • Take up excess neurotransmitters • Repair nervous tissue

7. Oligodendrocytes • Most common glial cell type • fewer processes than astrocytes • round or oval cell body • forms myelin sheath around the axons of neurons in CNS • form a supportive network around CNS neurons • analogous to Schwann cells of PNS

8. Microglia • Small cells found near blood vessels • Phagocytic role - clear away dead cells • protect CNS from disease through phagocytosis of microbes • migrate to areas of injury where they clear away debris of • injured cells - may also kill healthy cells

9. Ependymal Cells CNS PNS Neuron VENTRICLE Astrocyte Cilia Oligodendrocyte • epithelial cells that line the cerebral cavities (ventricles) & central canal • produce & circulate the cerebrospinal fluid (CSF) found in these chambers • form a structure with capillaries called a choroid plexus • CSF = colourless liquid that protects the brain and SC against • chemical & physical injuries, carries oxygen, glucose and other necessary chemicals from the blood to neurons and neuroglia Schwann cell Microglial cell Ependymal cell Capillary

10. PNS: Satellite Cells • Flat cells surrounding PNS axons • Support neurons in the PNS

11. PNS: Schwann Cells Neurilemma • each cell produces part of the myelin sheath surrounding an axon in the PNS • outmost layer of the sheath = neurilemma • contributes to regeneration of PNSaxons • regions of no myelin = Nodes of Ranvier

12. The Neuron • -comprised of: • cell body or soma • dendrites • an axon -neurofilaments – cytoskeleton of the neuron -Nissl bodies – endoplasmic reticulum -perikaryon – region outside of the nucleus

13. Neurons 2. Dendrites (little trees) - the receiving or input portion of the neuron -short, tapering and highly branched -surfaces specialized for contact with other neurons -bind the chemicals of neuronal communication = neurotransmitters -help trigger the nerve impulse in neurons = action potential

15. 3. Axons • long, thin cylindrical process of the neuron • conduct the action potential away from cell body toward another neuron • joins the cell body at a cone-shaped elevation = axon hillock • axon hillock becomes the axon • between the axon hillock and the axon = trigger zone – site where the action potential arises • cytoplasm = axoplasm • plasma membrane = axolemma • axon and collaterals end in fine processes called axon terminals • swollen tips called synaptic end bulbs contain vesicles filled with neurotransmitters • NTs are released when the action potential enters the end bulb

16. Synapses Dendrites Stimulus Axon hillock • synapse points of communication between two neurons • two types • 1. chemical – two neurons separated by a synaptic cleft • requires the release of chemicals called neurotransmitters from the pre-synaptic neuron and the binding of this neurotransmitter by the post-synaptic neuron • majority of chemical synapses formed between end bulb and dendrites • some can form between end bulbs and cell body Nucleus Cellbody Presynapticcell Axon Signaldirection • 2. electrical – direct connection between pre- and post-synaptic neuron • - connected via gap junctions • faster of the two synapses Synapse Synaptic terminals Synapticterminals Postsynaptic cell Neurotransmitter

17. Functional Classification of Neurons Dendrites • Sensory (afferent) neurons - PNS • transport sensory information from skin, muscles, joints, sense organs & viscera to CNS • Motor (efferent) neurons - PNS • send motor nerve impulses to muscles & glands • Interneurons (association) neurons- CNS • connect sensory to motor neurons • 90% of neurons in the body Axon Cellbody Sensory neuron Motor neuron

18. Organization of vertebrate nervous systems • brain provides the processing/integrative functions • the spinal cord conducts information to and from the brain and body • spinal cord and brain develop from the dorsal hollow nerve cord • front end of the nerve cord expands to become the brain • embryologic development of the brain results in the formation of a: • forebrain – gives rise to the cerebrum & the diencephalon • midbrain – gives rise to the midbrain • hindbrain - gives rise to the pons, medulla & cerebellum • the remaining nerve cord becomes the spinal cord

19. Divisions of the nervous system Central NervousSystem(information processing) Peripheral NervousSystem Efferent neurons Afferent neurons Autonomicnervous system Motorsystem Sensoryreceptors Control ofskeletal muscle Sympatheticdivision Parasympatheticdivision Internaland externalstimuli Entericdivision Control of smooth muscles,cardiac muscles, glands

20. The peripheral nervous system • the somatic nervous system controls voluntary motor impulses to skeletal muscle • also receives sensory input from muscles, joints, tendons and skin • the autonomic nervous system has sympathetic, parasympathetic, and enteric divisions • the sympathetic division regulates arousal and the “fight-or-flight” response • the parasympatheticdivision has antagonistic effects on sympathetic target organs and promotes calming and a return to “rest and digest” functions • The enteric division controls activity of the digestive tract, pancreas, and gallbladder

21. The ANS Sympathetic division Parasympathetic division Action on target organs: Action on target organs: Constricts pupilof eye Dilates pupil of eye Inhibits salivarygland secretion Stimulates salivarygland secretion Sympatheticganglia Constrictsbronchi in lungs Relaxes bronchiin lungs Cervical Slows heart Accelerates heart Stimulates activityof stomach andintestines Inhibits activity ofstomach and intestines Thoracic Inhibits activityof pancreas Stimulates activityof pancreas Stimulates glucoserelease from liver;inhibits gallbladder Stimulatesgallbladder Lumbar Stimulatesadrenal medulla Promotes emptyingof bladder Inhibits emptyingof bladder Sacral Promotes erectionof genitalia Promotes ejaculationand vaginal contractions Synapse

22. Functional divisions of the peripheral nervous system • Afferent • Sensory information from receptors into CNS • Efferent • Motor commands from the brain to muscles and glands • Somatic division • Voluntary control over skeletal muscle • Autonomic division • Involuntary regulation of smooth and cardiac muscle, glands

23. fish: • CNS consisting of a brain and spinal cord • sensory receptors widely distributed over the body • touch and temperature • also are specialized receptors for smell, vision, hearing, equilibrium and balance • e.g. external nares – snouts of fishes – lead to olfactory receptors • receptors for equilibrium, balance and hearing are located in the inner ear • lateral-line system – along each side of the fish and branching over the head • responsive to pressure, vibration • how the fish “hears”

24. amphibians: • brain is similar to other vertebrates • brain develops from three embryologic divisions: forebrain (smell, autonomic control centers), midbrain (vision) & hindbrain (heart rate and respiration) • sensory receptors over the skin • bare nerve endings for heat, cold and pain • lateral-line system just like fishes – response to vibrations • chemoreceptors in the nasal epithelium, linings of the mouth and tongue and over the skin • vision becomes an important sense • hunt via sight • number of adaptations have taken place to create the terrestrial eye • eyes become located on the front of the head – not the sides • this provides binocular vision for improved depth perception • lower eyelid called the nictating membrane is moveable and cleans the eye surface • orbital glands to wash and lubricate the eye • lens is large and round – set back from the cornea and is surrounded by a fold of epithelium called the iris • focusing requires refraction of light – provided by the cornea and changing the position of the lens • to focus on close objects – the lens is moved forward • retina contains photoreceptors called rods and cones

25. hearing also becomes well developed in the amphibians • auditory system transmits both vibrations and sound • ears of frogs and toads consists of a tympanic membrane, a middle ear and an inner ear • vocalization • sound production apparatus – larynx and vocal cords • mainly a reproductive function of the male frog • salamanders do not vocalize • advertisement calls to announce territory • breeding calls • female responds with reciprocation calls to indicate receptiveness • distress calls – loud enough to scare the predator

26. reptile: • brain is similar to other vertebrates • increased cerebral size vs. amphibians to accommodate the increased sense of smell • increased cerebellum • hearing mainly for the detection of vibration (can have a lateral line system) • vision is the dominant sense in most reptiles • optic lobe is larger in reptiles vs. amphibians • snakes – focus by moving the lens forward • all other reptiles focus by rounding the lens by the action of ciliarymuscles surrounding the lens • some reptiles possess a median or parietal eye – for distinguishing light and dark • olfactory senses are better developed in reptiles than in amphibians • development of a partial secondary palate to increase the surface area for olfactory epithelium • may also possess blind-ending pouches = Jacobson’s (vomeronasal) organs • snakes – use forked tongues to bring in air particles into the mouth – travel to the Jacobson’s organs for “smelling” • heat sensitive pits in vipers – “sixth sense” • pits located between the eyes and nostrils • minute temp differences are seen as infrared rays • used in prey location

27. Major Regions of the Mammalian Brain

28. Neuronal Organization: CNS • Two kinds of neural tissue found in both brain and spinal cord: • Gray matter = neuroglial cells + unmyelinated axons, and dendrites/cell bodies of neurons • -when it forms the outer layer of the cerebrum = cerebral cortex • Gray matter also found as nuclei deep in the brain = clusters of neuronal cell bodies in the CNS • Collections of nuclei can form a center (higher brain function)

29. Neuronal Organization: CNS • 2. White matter = myelinated axons • Cell bodies found in gray matter • White matter tracts = bundles of axons • For the conduction of nerve impulses • Brain – three types of tracts (commisural, association, projection) • Spinal cord - Two types: sensory and motor tracts (ascending and descending) male vs. female brain: http://www.youtube.com/watch?v=L29KmQxEA3E

30. Cerebrum • Cerebrum= largest portion • -left and right cerebralhemispheres divided by the longitudinal fissure • -connected by an accumulation of white matter - the corpus callosum • -folded into ridges and grooves: grooves = sulci • -sulci divide the cerebrum into lobes • -ridges = gyri(gyrus)

31. The Cerebral Cortex -outermost layer of the cerebrum, contains billions of gray matter neurons – less than 5mm thick!! -white matter tracts extend out and run to other gray matter areas (either another gyrus or a nucleus) -the cortex of each gyri contains neurons for the specific processing of sensation, voluntary movement, speech, all thought processes -gyri can be classified as: primary or association areas -primary areas are for the initial processing of raw sensory information or motor commands - e.g. primary visual, auditory & gustatory areas -also contains gyri that are called association areas for integration and analysis of specific sensory info & help in making of “decisions” e.g. somatosensory, visual, auditory, language and common integrative areas

32. Human brain Cerebrum (includingcerebral cortex) The Cerebral Cortex Thalamus • awareness of surroundings, language, cognition, memory and consciousness • cognition: • job of the neocortex • first 6 layers of the cerebral cortex • the more convoluted the neocortex (i.e more gyri and sulci) – the higher the cognitive function???? • may not be true • birds can be relatively smart • do not have a convoluted neocortex Midbrain Hindbrain Cerebellum Avian brainto scale Cerebrum(including pallium) Avian brain Cerebellum Hindbrain Thalamus Midbrain

33. The Cerebral Cortex • sensory processing: • numerous gyri whose cerebral cortex processes sensory information • parietal lobe – somatosensory areas & gustatory areas • primary somatosensory gyrus– receives sensory information from the skin, muscles and joints • temporal lobe – auditory areas • occipital lobe – visual areas • once sensory information is processed – info gets sent to the frontal lobe where movements are planned • one of the major areas for this – primary motor area in the frontal lobe

34. Frontal lobe Parietal lobe Shoulder Upper arm Trunk Elbow Trunk Head Forearm Knee Neck Leg Hip Hip Wrist Elbow Hand Forearm Fingers Hand Fingers Thumb Thumb Eye Neck Nose Brow Eye Face Genitalia Lips Toes Face Teeth Gums Lips Jaw Jaw Tongue Pharynx Tongue Primarysomatosensorycortex Primarymotor cortex Abdominalorgans

35. The Cerebral Cortex Max • language and speech: • French physician Pierre Broca – involved in mapping cognitive functions to specific areas of the cerebral cortex • became interested in those patients who could understand language but could not speak • identified an area of the left front lobe in the majority of people = Broca’s area • damage to this area results in the inability to speak (aphasia) – but the ability to understand language • responsible for motor commands to the muscles of the face • active when speaking • in the left temporal lobe = Wernicke’s area (Karl Wernicke) • active when hearing language • damage to this area – able to speak BUT unable to understand language Hearingwords Seeingwords Min Speakingwords Generatingwords

36. Lateralization • Broca’s areas and Wernicke’s area are in the left hemisphere in most people • these people are mostly right-handed also • Broca’s area is active in 96% of right-handed people but only 76% of left-handed people • language is principally the job of the left hemisphere • along with math and logical thought • right hemisphere will have other distinct functions • recognition of faces, patterns, spatial relationships and non-verbal thinking • differences in the function of the hemispheres is referred to as lateralization • when the two hemispheres work together – do so through the commissures – corpus callosum, anterior & posterior commissures

37. The Frontal Lobe • motor commands • personality • decision making • damage to the frontal lobe can affect all of these • but intellect and memory are left intact • specific destruction of the frontal lobe to affect personality = lobotomy

38. The basal ganglia: -made up of several gray matter nuclei found deep within the cerebrum 1. receives sensory input from the cerebral cortex & provides output to the motor areas of the cortex 2. integrates motor commands 3. regulates the initiation & termination of muscle movements 4. also functions to anticipate body movements & controls subconscious contraction of skeletal muscle • comprised of the: • 1. striatum • caudate nucleus • putamen • nucleus accumbens • 2. globus pallidus • 3. claustrum • 4. substantia nigra • 5. subthalmic nucleus

39. Diencephalon • Diencephalon • includes the hypothalamus, thalamus, epithalamus and subthalamus • thalamus: 80% of the diencephalon • paired oval shaped lobes of gray matter organized into nuclei, interconnected with white matter tracts • major relay station for most sensory impulses from the SC, brain stem into the cerebrum • relays motor information from the cerebellum to the cerebrum (for coordination) • crude perception of pain, heat and pressure (refined in cerebrum) Diencephalon Thalamus Pineal gland Brainstem Hypothalamus Midbrain Pituitary gland Pons Medullaoblongata Spinal cord

40. hypothalamus • -emotions, autonomic functions, hormone production • -made of numerous nuclei and tracts Diencephalon • 1. control of the ANS – integrates signals from the ANS (regulated smooth and cardiac muscle contraction) • major regulator of visceral activities (heart rate, food movements, contraction of bladder) • 2. produces hormones & connects with pituitary to regulate its activity 3. regulates emotional and behavioral patterns – rage, aggression, pain and pleasure + sexual arousal 4. regulates eating & drinking – hypothalamus contains a thirst center which responds to a rise in osmotic pressure in the ECF (dehydration) 5. controls body temperature – monitors temp of blood flowing through the hypothalamus

41. Diencephalon • epithalamus= pineal gland • – part of the endocrine system • -secretes the hormone melatonin • -increased secretion in dark • -promote sleepiness and helps set the circadian rhythms of the body (awake/sleep period)

42. BRAIN STEM • comprised of three structures: midbrain, pons & medulla

43. BRAIN STEM • Medulla oblongata • continuation of the spinal cord • inferior part of the brain stem • relays sensory information and controls automatic motor functions • white matter connects the white matter of the spinal cord with the rest of the brain • contains several nuclei also - these nuclei regulate autonomic functions - reflex centers for regulating heartbeat and BP (cardiovascular center), respiration (respiratory center), plus vomiting, coughing, sneezing, hiccuping and swallowing

44. BRAIN STEM • Pons = “bridge” • connection point from cerebrum to cerebellum – via white matter tracts • nuclei help control both voluntary & involuntary motor responses • e.g.Pneumotaxic and apneustic nuclei – help regulate breathing with medulla

45. BRAIN STEM • Midbrain (Mesencephalon) • relay station between the cerebrum and the spinal cord and cerebellum • contains white matter tracts that connect the midbrain to the cerebrum = cerebral peduncles • White matter tracts that conduct impulses from the cerebrum to the pons and medulla into the spinal cord • contains white matter tracts that connect the midbrain to the cerebellum = cerebellar peduncles • one nucleus = substantianigra – produces large amounts of dopamine - loss of these neurons = Parkinsons

46. Cerebellum • divided into hemispheres with lobes - like the cerebrum • anterior and posterior lobes • has a superficial layer of gray matter called the cerebellar cortex - like the brain • deep to this gray matter are tracts of white matter (arbor vitae) and gray matter nuclei • controls voluntary and involuntary motor activities • evaluates and coordinates motor activities initiated by the cerebrum and corrects problems by sending info back to the cerebrum • regulate posture & balance

47. Integrative Functions • Arousal and Sleep • Memory and Learning • Emotions • Language and speech

48. Protection: The Cranial Meninges • Cranium is covered with protective membranes = meninges • Cranial meninges are continuous with spinal meninges • 3 layers: • 1. outer, fibrous dura mater – forms sheets (falx) that separate the cerebrum and the cerebellum into the hemispheres and the cerebellum from the cerebrum • in the cranial region - comprised of an outer endosteal layer and an inner meningeal layer • 2. middle arachnoid mater • 3. inner, thin pia mater

49. Cranial Meninges • -there are spaces between these membranes • A. subarachnoid space: between the arachnoid and pia mater • large veins run through the subarachnoid space • connecting membranes joining the pia and arachnoid mater also found here (arachnoid trabeculae) • B. subdural space: between the arachnoid and the dura mater • C. epidural space – between the dura mater and the vertebral canal in the spinal column

50. Protection: CSF • brain contains fluid-filled chambers = Ventricles • 2 lateral ventricles, 1 third ventricle, 1 fourth ventricle • connects to the central canal which runs into the spinal canal • these chambers contain cerebrospinal fluid • made by specialized structures in the ventricles – choroid plexus (contain ependymal cells) • continually circulates - ventricles and central canal to subarachnoid space • all CSF makes its way back to the subarachnoid space