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The Nervous System Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Functions of the Nervous System 1. Sensory input – gathering information To monitor changes occurring inside and outside the body (changes = stimuli) 2. Integration – to process and interpret sensory input and decide if action is needed. 3. Motor output A response to integrated stimuli The response activates muscles or glands Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.1a Structural Classification of the Nervous System Central nervous system (CNS) Brain and spinal cord Develops from the embryonic neural tube Peripheral nervous system (PNS) Nerve and ganglia outside the brain and spinal cord Nerves are neuron fibers bundled together by connective tissue Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.2 Functional Classification of the Peripheral Nervous System Sensory (afferent) division Nerve fibers that carry information to the central nervous system Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary Slide 7.3a Nervous Tissue: Support Cells (Neuroglia or Glia) Astrocytes Abundant, star-shaped cells Brace neurons Form barrier between capillaries and neurons Control the chemical environment of the brain (CNS) Microglia (CNS) Spider-like phagocytes Dispose of debris Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.5 Nervous Tissue: Support Cells Ependymal cells (CNS) Line cavities of the brain and spinal cord Circulate cerebrospinal fluid Oligodendrocytes(CNS) Produce myelin sheath around nerve fibers in the central nervous system Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.6 Support Cells of the PNS Satellite cells Protect neuron cell bodies Schwann cells Form myelin sheath in the peripheral nervous system Figure 7.3e Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.7b Nervous Tissue: Neurons Neurons = nerve cells Cells specialized to transmit messages Major regions of neurons Cell body – nucleus and metabolic center of the cell Processes – fibers that extend from the cell body (dendrites and axons) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.8 Neuron Anatomy Cell body Nucleus Large nucleolus Extensions outside the cell body Dendrites – conduct impulses toward the cell body Axon – conduct impulses away from the cell body (only 1!) Figure 7.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.10 Axons and Nerve Impulses Axons end in axonal terminals Axonal terminals contain vesicles with neurotransmitters Axonal terminals are separated from the next neuron by a gap Synaptic cleft – gap between adjacent neurons Synapse – junction between nerves Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.11 Functional Classification of Neurons Sensory (afferent) neurons Carry impulses from the sensory receptors Cutaneous sense organs Proprioceptors – detect stretch or tension Motor (efferent) neurons Carry impulses from the central nervous system Interneurons (association neurons) Found in neural pathways in the central nervous system Connect sensory and motor neurons Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Neuron Classification Figure 7.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.15 Structural Classification of Neurons Multipolar neurons – many extensions from the cell body Bipolar neurons – one axon and one dendrite Unipolar neurons – have a short single process leaving the cell body How Neurons Function (Physiology) Irritability – ability to respond to stimuli Conductivity – ability to transmit an impulse The plasma membrane at rest is polarized Fewer positive ions are inside the cell than outside the cell Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.17 Starting a Nerve Impulse Depolarization – a stimulus depolarizes the neuron’s membrane A deploarized membrane allows sodium (Na+) to flow inside the membrane The exchange of ions initiates an action potential in the neuron Figure 7.9a–c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.18 The Action Potential If the action potential (nerve impulse) starts, it is propagated over the entire axon Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane The sodium-potassium pump restores the original configuration This action requires ATP Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.19 Nerve Impulse Propagation The impulse continues to move toward the cell body Impulses travel faster when fibers have a myelin sheath Figure 7.9c–e Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.20 Continuation of the Nerve Impulse between Neurons Impulses are able to cross the synapse to another nerve Neurotransmitter is released from a nerve’s axon terminal The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter An action potential is started in the dendrite Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.21 How Neurons Communicate at Synapses Figure 7.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.22 Regions of the Brain Cerebral hemispheres Diencephalon Sits on top of the brain stem and is enclosed by the cerebral heispheres Made of three parts: thalamus, hypothalamus, epithalamus Brain stem Attaches to the spinal cord Includes the midbrain, pons, and medulla oblongata Cerebellum Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.12 Slide 7.27 Structure of the Cerebrum Fissures (deep grooves) divide the cerebrum into lobes Surface lobes of the cerebrum include: frontal lobe, parietal lobe, occipital lobe, and temporal lobe Paired (left and right) superior parts of the brain Include more than half of the brain mass The surface is made of ridges (gyri) and grooves (sulci) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Specialized Areas of the Cerebrum Somatic sensory area – receives impulses from the body’s sensory receptors Primary motor area – sends impulses to skeletal muscles Broca’s area – involved in our ability to speak Cerebral areas involved in special senses include: gustatory area (taste), visual area, auditory area, and olfactory area Interpretation areas of the cerebrum Speech/language region General interpretation area Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.30 Specialized Area of the Cerebrum Figure 7.13c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Sensory and Motor Areas of the Cerebral Cortex Figure 7.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.31 Layers of the Cerebrum Gray matter Outer layer that is composed mostly of neuron cell bodies White matter Fiber tracts (bundles of nerve fibers) that carry impulses to and from the cortex inside the gray matter Example: corpus callosum connects hemispheres Basal nuclei – internal islands of gray matter Regulates voluntary motor activities by modifying info sent to the motor cortex Thalamus Surrounds the third ventricle The relay station for sensory impulses Transfers impulses to the correct part of the cortex for localization and interpretation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.35 Hypothalamus Under the thalamus Important autonomic nervous system center Helps regulate body temperature Controls water balance Regulates metabolism An important part of the limbic system (emotions) The pituitary gland is attached to the hypothalamus Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Cerebellum Two hemispheres with convoluted surfaces Provides involuntary coordination of body movements Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Medulla Oblongata The lowest part of the brain stem Merges into the spinal cord Includes important fiber tracts Contains important control centers Heart rate control Blood pressure regulation Breathing Swallowing Vomiting Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.41 Pons The bulging center part of the brain stem Mostly composed of fiber tracts Includes nuclei involved in the control of breathing Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.40 Meninges Three connective tissue layers that cover and protect the brain and spinal cord. Dura mater Double-layered external covering Periosteum – attached to surface of the skull Meningeal layer – outer covering of the brain Folds inward in several areas to connect brain to cranial cavity. Arachnoid layer Middle layer that is web-like Pia mater Internal layer that clings to the surface of the brain and spinal cord Slide Spinal Cord Extends from the medulla oblongata to the region of T12 Provides conduction pathway to (ascending) and from (descending) the brain and is a major reflex center. Figure 7.18 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.52 Spinal Cord Exterior white mater – conduction tracts Internal gray matter - mostly cell bodies Dorsal (posterior) horns contain cell bodies of sensory neurons Anterior (ventral) horns contain cell bodies of motor neurons Central canal filled with cerebrospinal fluid Meninges cover the spinal cord for cushion and protection Nerves leave at the level of each vertebrae Structure of a Nerve Endoneurium surrounds each fiber Groups of fibers are bound into fascicles by perineurium Fascicles are bound together by epineurium Mixed nerves – both sensory and motor fibers Afferent (sensory) nerves – carry impulses toward the CNS Efferent (motor) nerves – carry impulses away from the CNS 12 pairs of cranial nerves serve the head and neck with only one (the vagus nerve) extending to the thoracic and abdominal cavity. There 31 pairs of spinal nerves that exit at the junctions between vertebrae. Autonomic Nervous System The involuntary branch of the nervous system that consists of only motor nerves. Divided into two sections: sympathetic and parasympathetic. Autonomic Functioning Sympathetic – “fight-orflight” Response to unusual stimulus Takes over to increase activities Remember as the “E” division = exercise, excitement, emergency, and embarrassment Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Autonomic Functioning Parasympathetic – housekeeping activites Conserves energy Maintains daily necessary body functions Remember as the “D” division digestion, defecation, and diuresis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide The Reflex Arc Reflex – rapid, predictable, and involuntary responses to stimuli Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector Figure 7.11a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.23 Types of Reflexes and Regulation Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation Somatic reflexes Activation of skeletal muscles Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.25 The Senses General senses of touch (tactile) Temperature- thermoreceptors (heat) Pressure- mechanoreceptors (movement) Pain- mechanoreceptors Special senses Smell- chemoreceptors (chemicals) Taste- chemoreceptors Sight- photoreceptors (light) Hearing- mechanoreceptors Equilibrium- (balance) mechanoreceptors The Eye and Vision 70 percent of all sensory receptors are in the eyes Each eye has over a million nerve fibers Protection for the eye Most of the eye is enclosed in a bony orbit made up of the lacrimal (medial), ethmoid (posterior), sphenoid (lateral), frontal (superior), and zygomatic and maxilla (inferior) A cushion of fat surrounds most of the eye Accessory Structures of the Eye Eyelids- brush particles out of eye or cover eye Eyelashes- trap particles and keep them out of the eye Ciliary glands – modified sweat glands between the eyelashes- secrete acidic sweat to kill bacteria, lubricate eyelashes Accessory Structures of the Eye Conjunctiva Membrane that lines the eyelids Connects to the surface of the eye- forms a seal Secretes mucus to lubricate the eye http://neuromedia.neurobio.ucla.edu/campbell/eyeandear/wp_images/175_conjunctiva.gif Accessory Structures of the Eye Lacrimal apparatus Lacrimal gland – produces lacrimal fluid Lacrimal canals – drains lacrimal fluid from eyes Lacrimal sac – provides passage of lacrimal fluid towards nasal cavity Nasolacrimal duct – empties lacrimal fluid into the nasal cavity Lacrimal fluid contains anibodies and lysozyme to protect, moisten, and lubricate the eye Extrinsic Eye Muscles Muscles attach to the outer surface of the eye that produce eye movements Superior oblique- eyes look out and down Superior rectus- eyes looks up Lateral rectus- eyes look outward Medial rectus- eyes look inward Inferior rectus- eyes looks down Inferior oblique- eyes look in and up Structure of the Eye The wall is composed of three tunics Fibrous tunic – outside layer Choroid – middle layer Sensory tunic – inside layer The Fibrous Tunic Sclera White connective tissue layer Seen anteriorly as the “white of the eye” Semi-transparent The Fibrous Tunic Cornea Transparent, central anterior portion Allows for light to pass through (refracts, or bends, light slightly) Repairs itself easily The only human tissue that can be transplanted without fear of rejection Choroid Layer Blood-rich nutritive tunic Pigment prevents light from scattering (opaque- blocks light from getting in, has melanin) Modified interiorly into two structures Cilliary body – smooth muscle (contracts to adjust the shape of the lens) Iris- pigmented layer that gives eye color (contracts to adjust the size of the pupil- regulates entry of light into the eye) Pupil – rounded opening in the iris Sensory Tunic (Retina) Contains receptor cells (photoreceptors) Rods Cones Signals leave the retina toward the brain through the optic nerve Neurons of the Retina and Vision Rods Most are found towards the edges of the retina Allow dim light vision and peripheral vision (more sensitive to light, do not respond in bright light) Perception is all in gray tones Cones Allow for detailed color vision Densest in the center of the retina Fovea centralis – area of the retina with only cones Respond best in bright light No photoreceptor cells are at the optic disk, or blind spot Cone Sensitivity There are three types of cones Different cones are sensitive to different wavelengths Red-long Green-medium Blue-short Color blindness is the result of lack of one or more cone type How do we see colors? • To see any color, the brain must compare the input from different kinds of cone cells—and then make many other comparisons as well. • The lightning-fast work of judging a color begins in the retina, which has three layers of cells. Signals from the red and green cones in the first layer are compared by specialized red-green "opponent" cells in the second layer. These opponent cells compute the balance between red and green light coming from a particular part of the visual field. Other opponent cells then compare signals from blue cones with the combined signals from red and green cones. COLORBLINDNESS - An inherited trait that is transferred on the sex chromosomes (23rd pair)sex-linked trait - Occurs more often in males - Can not be cured or corrected •Comes from a lack of one or more types of color receptors. •Most are green or red or both and that is due to a lack of red receptors. •Another possibility is to have the color receptors missing entirely, which would result in black and white vision. COLORBLINDNESS TEST PLATES http://www.geocities.com/Heartland/8833/coloreye.html Lens Biconvex crystallike structure Held in place by a suspensory ligament attached to the ciliary body Refracts light greatly Internal Eye Chamber Fluids Aqueous humor Watery fluid found in chamber between the lens and cornea Similar to blood plasma Helps maintain intraocular pressure Provides nutrients for the lens and cornea Reabsorbed into venous blood through the canal of Schlemm Refracts light slightly Internal Eye Chamber Fluids Vitreous humor Gel-like substance behind the lens Keeps the eye from collapsing Lasts a lifetime and is not replaced Refracts light slightly Holds lens and retina in place http://faculty.washington.edu/kepeter/119/images/eye3.jpg Lens Accommodation Light must be focused to a point on the retina for optimal vision The eye is set for distance vision (over 20 ft away) 20/20 vision- at 20 feet, you see what a normal eye would see at 20 feet (20/100- at 20, normal person would see at 100) The lens must change shape to focus for closer objects If the image is focused at the spot where the optic disk is located, nothing will be seen. This is known as the blind spot. There are no photoreceptors there, as nerves and blood vessels pass through this point. Visual Pathway Photoreceptors of the retina Optic nerve Optic nerve crosses at the optic chiasma Optic tracts Thalamus (axons form optic radiation) Visual cortex of the occipital lobe MYOPIA Nearsightedness, or myopia is the difficulty of seeing objects at a distance. Myopia occurs when the eyeball is slightly longer than usual from front to back. This causes light rays to focus at a point in front of the retina, rather than directly on its surface. Concave lenses are used to correct the problem. HYPEROPIA Hyperopia, or farsightedness, is when light entering the eye focuses behind the retina. Hyperoptic eyes are shorter than normal. Hyperopia is treated using a convex lens. http://web.mountain.net/~topeye/images/hyperopia.jpg Eye Reflexes Internal muscles are controlled by the autonomic nervous system Bright light causes pupils to constrict through action of radial (iris) and ciliary muscles Viewing close objects causes accommodation External muscles control eye movement to follow objectsvoluntary, controlled at the frontal eye field Viewing close objects causes convergence (eyes moving medially) The Ear Houses two senses Hearing (interpreted in the auditory cortex of the temporal lobe) Equilibrium (balance) (interpreted in the cerebellum) Receptors are mechanoreceptors Different organs house receptors for each sense Anatomy of the Ear The ear is divided into three areas Outer (external) ear Middle ear Inner ear The External Ear Involved in hearing only Pinna (auricle)- collects sound External auditory canalchannels sound inward Narrow chamber in the temporal bonethrough the external auditory meatus Lined with skin Ceruminous (wax) glands are present Ends at the tympanic membrane (eardrum) The Middle Ear or Tympanic Cavity Air-filled cavity within the temporal bone Only involved in the sense of hearing Two tubes are associated with the inner ear The opening from the auditory canal is covered by the tympanic membrane (eardrum) The auditory tube connecting the middle ear with the throat (also know as the eustacian tube) Allows for equalizing pressure during yawning or swallowing This tube is otherwise collapsed Bones of the Tympanic Cavity Three bones span the cavity Malleus (hammer) Incus (anvil) Stapes (stirrip) Vibrations from eardrum move the malleus These bones transfer sound to the inner ear Inner Ear or Bony Labyrinth Also known as osseous labyrinth- twisted bony tubes A maze of bony chambers within the temporal bone Cochlea Upper chamber is the scala vestibuli Lower chamber is the scala tympani Vestibule Semicircular canals Includes sense organs for hearing and balance Filled with perilymph Vibrations of the stapes push and pull on the membranous oval window, moving the perilymph through the cochlea. The round window is a membrane at the opposite end to relieve pressure. Organ of Corti Located within the cochlea Receptors = hair cells on the basilar membrane Gel-like tectorial membrane is capable of bending hair cells (endolymph in the membranous labyrinth of the cochlear duct flows over it and pushes on the membrane Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe Scala tympani Mechanisms of Hearing Vibrations from sound waves move tectorial membrane (pass through the endolymph fluid filling the membranous labyrinth in the cochlear duct) Hair cells are bent by the membrane An action potential starts in the cochlear nerve The signal is transmitted to the midbrain (for auditory reflexes and then directed to the auditory cortex of the temporal lobe) Continued stimulation can lead to adaptation (over stimulation to the brain makes it stop interpreting the sounds) Organs of Equilibrium Receptor cells are in two structures Vestibule Semicircular canals Equilibrium has two functional parts Static equilibrium- in the vestibule Dynamic equilibrium- in the semicircular canals Static Equilibrium Maculae – receptors in the vestibule Report on the position of the head Send information via the vestibular nerve Anatomy of the maculae Hair cells are embedded in the otolithic membrane Otoliths (tiny stones) float in a gel around the hair cells Movements cause otoliths to bend the hair cells (gravity moves the “rocks” over and pulls the hairs) Dynamic Equilibrium Whole structure is the ampulla Crista ampullaris – receptors in the semicircular canals Tuft of hair cells Cupula (gelatinous cap) covers the hair cells Action of angular head movements The cupula stimulates the hair cells Movement of endolymph pushes the cupula over and pulls the hairs An impulse is sent via the vestibular nerve to the cerebellum Chemical Senses – Taste and Smell Both senses use chemoreceptors Stimulated by chemicals in solution Taste has four types of receptors Smell can differentiate a large range of chemicals Both senses complement each other and respond to many of the same stimuli Olfaction – The Sense of Smell Olfactory receptors are in the roof of the nasal cavity Neurons with long cilia Chemicals must be dissolved in mucus for detection Olfaction – The Sense of Smell Impulses are transmitted via the olfactory nerve Interpretation of smells is made in the cortex (olfactory area of temporal lobe) The Sense of Taste Taste buds house the receptor organs Location of taste buds Most are on the tongue Soft palate Cheeks The Tongue and Taste The tongue is covered with projections called papillae Filiform papillae – sharp with no taste buds Fungifiorm papillae – rounded with taste buds Circumvallate papillae – large papillae with taste buds Taste buds are found on the sides of papillae http://neuromedia.neurobio.ucla.edu/campbell/oral_cavity/wp_images/96_fungiform.gif Structure of Taste Buds Gustatory cells are the receptors Have gustatory hairs (long microvilli) Hairs are stimulated by chemicals dissolved in saliva Structure of Taste Buds Impulses are carried to the gustatory complex (pareital lobe) by several cranial nerves because taste buds are found in different areas Facial nerve Glossopharyngeal nerve Vagus nerve Taste Sensations Sweet receptors Sugars Saccharine Some amino acids Sour receptors Acids Bitter receptors Alkaloids Salty receptors Metal ions Umami Glutamate, aspartate, MSG, meats) http://instruct1.cit.cornell.edu/courses/psych431/student2000/mle6/tonguebig.gif