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The NERVOUS System. Functions of the Nervous System l Sensory –senses stimuli from both within the body and from the external environment l Integrative.

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Presentation on theme: "The NERVOUS System. Functions of the Nervous System l Sensory –senses stimuli from both within the body and from the external environment l Integrative."— Presentation transcript:

1 The NERVOUS System

2 Functions of the Nervous System l Sensory –senses stimuli from both within the body and from the external environment l Integrative –analyzes, interprets, and stores information about the stimuli it has receives from the sensory portion of the nervous system l Motor –responds to stimuli by some type of action l muscular contraction l glandular secretion

3 Divisions of the Nervous System l Central Nervous System (CNS) l Peripheral Nervous System (PNS) l Somatic Nervous System (SNS) –Voluntary l Autonomic Nervous System (ANS) –Involuntary l Sympathetic Division l Parasympathetic Division

4 The brain and spinal cord are part of which nervous system? A.) parasympathetic nervous system B.) central nervous system C.) peripheral nervous system D.) parasympathetic nervous system

5 Nervous System Schematic

6 The Central Nervous System l Consists of the brain and the spinal cord l Sorts incoming sensory information l Generates thoughts and emotions l Forms and stores memories l Stimulates muscle contractions l Stimulates glandular secretions

7 The Peripheral Nervous System l Connects sensory receptors, muscles, and glands in the peripheral parts of the body to the central nervous system l Consists of cranial and spinal nerves l Afferent Neurons (Sensory) –conduct nerve impulses from sensory receptors toward the CNS l Efferent Neurons (Motor) –conduct nerve impulses from the CNS to muscles and glands

8 The Somatic Nervous System l Made up of sensory neurons that convey information from the cutaneous and special sense receptors in the head, body wall, and extremities to the CNS l Also contains the motor neurons from the CNS that conduct impulses to the skeletal muscles

9 The Autonomic Nervous System l Contains sensory neurons mainly from the viscera that convey information to the CNS l Contains the efferent neurons that conduct impulses to smooth muscle, cardiac muscle, and glands l Unconscious control l Two divisions of the ANS –Sympathetic Division - stimulatory effect –Parasympathetic Division - inhibitory effect

10 The two major divisions of the nervous system are? A.) peripheral and autonomic B.) central and somatic C.) peripheral and central

11 The two division of the autonomic nervous system are? A.) central and peripheral B.) somatic and senory C.) sympathetic and parasympathetic

12 The two major divisions of the peripheral nervous system are? A.) somatic and autonomic B.) sympathetic and parasympathetic C.) central and peripheral

13 Neurons l The nerve cells responsible for the special functions of the nervous system –sensing- remembering- thinking –controlling muscle activity –controlling glandular secretions l Synapse - the functional relay points between two neurons or between a neuron and an effector organ –Neuromuscular Junction –Neuroglandular Junction

14 Parts of A Neuron l Cell Body (Soma or Perikaryon) –nucleus, cytoplasm, organelles of a neuron l Dendrites - tapered, highly branched processes protruding from the cell body –usually very short – AFFERENT FUNCTION l Axons - long, thin, cylindrical process –usually myelinated – EFFERENT FUNCTION

15 Which way is efferent? A.) away B.) towards

16 Neuron

17 Neurons


19 Neuroglia l Nervous system cells that support, nurture and protect the neurons l Types of Neuroglia found in the CNS –Astrocytes –Oligodendrocytes –Microglia –Ependymal Cells l Types of Neuroglia found in the PNS –Neurolemmocytes (Schwann Cells)

20 Astrocytes l Star-shaped cells with many processes l Participate in metabolism of neurotransmitters l Maintain K+ balance for generation of nervous impulses l Participate in brain development l Help form the blood brain barrier l Provide a link between neurons and blood vessels

21 Astrocyte

22 Oligodendrocytes l Small cells with few processes l Form a supporting network around the neurons by twining around neurons and producing a lipid and protein wrapping around the neurons (myelin sheath)

23 Oligodendrocyte

24 Microglia l Small phagocytic cells that protect the central nervous system by engulfing and invading microbes l Clears away debris from dead cells

25 Microglia

26 Ependymal Cells l Neuroglia cells that line the brain ventricles l Line the central canal of the spinal cord l Helps form and circulate cerebral spinal fluid

27 Ependymal Cells

28 Which neuroglia is phagocytic and cleans away debris? A.) astrocytes B.) microglia C.) oligodendrocytes D.) ependymal cells

29 Which neuroglia is responsible for the producing CSF? A.) astrocytes B.) microglia C.) ependymal cells

30 Which neuroglia helps to maintain the blood-brain barrier? A.) astrocytes B.) microglia C.) oligodendrocytes D.) ependymal cells

31 Neuroglia of the PNS l Schwann Cells - Neurolemmocytes –Cells responsible for producing the myelin sheaths around the PNS neurons

32 Schwann Cell Myelination

33 Schwann Cell (Neurolemmocyte)

34 Myelination l The process of developing or producing a Myelin Sheath l Insulates the axon of a neuron l Increases the speed of nerve impulse conduction –CNS - oligodendrocytes –PNS - neurolemmocytes (Schwann Cells) l Diseases such as Tay-Sachs disease and Multiple Sclerosis involve destruction of the myelin sheaths around the nerve

35 Which neuroglia are responsible for the myelin in the peripheral nervous system? A.) oligodendrocytes B.) microglia C.) schawann cells D.) astrocytes

36 Myelination

37 Myelinated Axon

38 Unmyelinated Axon

39 Neurophysiology The transmission of nerve (electrical) impulses from nervous tissue to other nervous tissue, organs, glands, and muscles.

40 Neuron Membrane Potential

41 Neuron Action Potential

42 Transmission of Nerve Impulses l An electrical event due to movement of ions across a membrane l Also called an action potential –Lasts about 1 msec (1/1000 of a second) –Dependent upon diameter of the axon l larger diameter axons msec (1/2500 sec) –2500 impulses per second l smaller diameter axons - 4 msec (1/250 sec) –250 impulses per second

43 All or None Principle l If depolarization reaches a threshold, an action potential (impulse) is conducted l Each action potential (impulse) is conducted at maximum strength unless there are toxic materials within the cell or the membrane has been disrupted

44 Neuron Impulse

45 Action Potential l Resting Neuron- More + outside than inside the cell. (Na+) l Depolarization-stimulation, Na+ rushes in and changes the membrane charge, creating an action potential. l Repolarization-K+ ions diffuse outside cell l Refractory-No impulses can be sent. Na+ and K+ restored.

46 What ion moves into the cell after a stimulus, creating an action potential? A.) K+ B.) Cl- C.) Na+ D.) O2

47 Where will I find most of the K+ ions? A.) outside the cell--intercellular B.) In the heart C.) inside the cell--intracellular

48 What is depolarization? A.) A time when no impulse can be sent B.) When K+ and Na+ are restored to their original position C.) Where Na+ ions rush into the cell creating an action potential

49 Neuron Action Potential

50 Types of Impulse Conduction l Continuous Conduction - step by step depolarization of each sequential, adjacent area of of the nerve cell membrane –typical of unmyelinated nerve fibers –type of action potential in muscle fibers l Saltatory Conduction - the jumping of an action potential across specialized neurofibril nodes along the axon –Nodes of Ranvier

51 Nerve Conduction

52 Gray and White Matter l White Matter - the aggregation of myelinated processes from many neurons –Visible upon freshly dissected brain or spinal tissue –White color is due to myelination l Gray Matter - unmyelinated nerve cell bodies, axons, dendrites, ganglia, and axon terminals –Appears gray because of lack of myelin

53 Which matter is myeliated? A.) white B.) gray

54 Gray and White Matter

55 Protection and Coverings of the Brain l Protected by the cranial bones and the cranial meninges –Dura Mater - outer layer –Arachnoid - middle layer –Pia Mater - inner layer l Also protected by cerebrospinal fluid –fluid that nourishes and protects the brain and spinal cord –continuously circulates through the subarachnoid space around the brain and throughout the cavities within the brain

56 Meninges of the Brain

57 Cerebrospinal Fluid l Mechanical Protection –Serves as a shock absorbing medium –Buoys the brain so it literally floats within the cranial cavity l Chemical Protection –Provides an optimal chemical environment for neural signaling l Circulation –Acts as a medium for exchange of nutrients and waste products between the blood and nervous tissue

58 Transmission of Nerve Impulses at Synapses l Most nervous conduction is from neuron to neuron (interneurons - 90%) l Types of Synapses –Axon to dendrite –Axon to soma –Axon to axon l Two ways to transmit impulses across a synapse –Electrical Synapses –Chemical Synapses

59 Meninges l Connective tissue covering found around the brain and spinal cord l Three layered membrane –Dura Mater - outer most layer l dense irregular connective tissue –Arachnoid - middle layer l spider web arrangement of collagen fibers –Pia Mater - inner most meninges l very delicate layer of thin tissue

60 Which mater is the outside layer, also the "tough mother" A.) arachnoid B.) pia mater C.) dura mater


62 Arachnoid mater

63 Spinal Cord Protective Coverings l Dura Mater l Arachnoid l Pia Mater

64 Reflexes l Fast, predictable, automatic responses to changes in the environment that help maintain homeostasis l Somatic Reflexes - involve skeletal muscles l Visceral (Autonomic) Reflexes - involve responses of smooth muscles, the heart, and glands l Involve the spinal nerves

65 The Reflex Arc l A response by the body involving only the body segment being affected and the spinal cord –Brain does not have to be involved l Receptor - the distal end of a sensory neuron (dendrite) –Responds to a specific stimulus l a change in internal or external environment –Triggers a nerve impulse

66 l Sensory Neuron - the neuron located in the gray matter of the spinal cord –conducts impulses from the receptor to the spinal cord l Integrating Center - a region within the CNS (spinal cord or brain) that interprets the information from the sensory neuron and initiates an appropriate response l Motor Neurons - the neurons arising from the integrating center that relay a nerve impulse to the part of the body that will respond to the stimulus

67 l Effector - the part of the body that responds to the motor nerve impulse (usually a muscle or a gland) –Effector - skeletal muscle - somatic reflex –Effector - cardiac, smooth muscle, or gland -visceral reflex

68 The Reflex Arc

69 Is the sensory neuron afferent or efferent? A.) afferent B.) efferent

70 Reflex Arc Examples l Stretch Reflex - results in the contraction of a muscle if it has been stretched suddenly l Tendon Reflex - results in the contraction of a muscle when a tendon is stretched suddenly l Flexor (Withdrawal) Reflex - sudden contraction and removal of a body segment as a result of a pain stimulus

71 Tendon Reflex

72 Withdrawal Reflex l also called Flexor/Withdrawal Flexor/Withdrawal Reflex Reflex

73 The BRAIN


75 l One of the largest organs in the body l Controls all mental functions l Component of the CNS l Composed of over 100 billion neurons l Comprises 2-3% of body weight l Utilizes over 20% of bodys energy

76 Major Divisions of the BRAIN l CEREBRUM - occupies most of the cranium and is divided into right and left halves called hemispheres l CEREBELLUM - the posterior-inferior portion of the brain l BRAIN STEM - consists of the medulla oblongata, the pons, and the midbrain –it is continuous with the spinal cord l DIENCEPHALON - located above the brainstem, composed primarily of the: –Thalamus- Hypothalamus


78 The Brain

79 Ventricles l Cavities within the brain l Lateral ventricles (2) - located within each hemisphere in the cerebrum l Third ventricle - a vertical slit between the lateral ventricles and inferior to the right and left halves of the thalamus l Fourth ventricle - space between the brainstem and the cerebellum

80 Ventricles of the Brain

81 Choroid Plexus l Network of capillaries in the walls of the ventricles l Covered with ependymal cells that form the cerebrospinal fluid l These ependymal cells are so close together they form the blood-brain barrier. –Selectively permeable barrier –Protects the brain and spinal cord from potentially harmful substances in the blood

82 What kind of cells help to form the blood brain barrier and the CSF? A.) muscle B.) astrocyte C.) ependymal

83 Flow of Cerebro- Spinal Fluid


85 Blood Supply to the Brain l One of the most metabolically active organs in the body l Makes up only 2-3% of body weight but uses about 20% of available O 2 at rest l Well supplied with O 2 and nutrients l Only nutritional source for brain metabolic activity is glucose l Capillaries in the brain are much less leaky than other capillaries in the body and form a blood brain barrier

86 The Brain Stem l The most inferior portion of the brain l Connects the brain to the spinal cord l Composed of Three Areas –The Medulla Oblongata –The Pons –The Midbrain

87 The Medulla Oblongata l Most inferior portion of the brain stem l Connects the brain stem to the spinal cord l Respiratory Center –Adjusts rhythm and depth of breathing l Cardiovascular Center –Regulates heart rate and contraction force –Influences vasoconstriction and vasodilation l Also controls coughing, vomiting, swallowing, and hiccupping

88 The Medulla Oblongata



91 The Pons l Lies superior to the medulla oblongata l Together with the respiratory center in the medulla helps control respiration

92 The Pons


94 The Midbrain l Superior to the pons l Connects the brain stem to the diencephalon

95 The Midbrain

96 Pons and Midbrain

97 The Diencephalon l Area of the brain containing the: –Thalamus –Hypothalamus

98 The Thalamus l Oval structure that makes up 80% of the diencephalon l Comprised of a pair of oval masses (mostly gray matter) l Principle relay station between the various sections of the brain

99 The Thalamus




103 The Hypothalamus l A small portion of the diencephalon located below the thalamus l One of the main regulators of homeostasis in the body l Lacks a blood brain barrier l Partially protected by the sella turcica of the sphenoid bone

104 Functions of the Hypothalamus l coordinates Nervous System and Endocrine System activities to maintain Homeostasis –Thirst, Hunger, Satiety –Sleep Patterns and Waking States –Sex Drive, Maturation, Aggression, and Rage –influences movement of food through the Gastrointestinal Tract –production and secretion of hormones That control other Endocrine Glands

105 The Hypothalamus

106 What is the job of the thalamus? A.) thirst, hunger B.) relay station C.) sleep patterns

107 Hypothalamus


109 The Cerebrum l Largest division of the brain l Occupies most of the cranium l Accounts for 85% of brain mass l Divided into right and left hemispheres –Longitudinal Fissure –Corpus Callosum l Cerebral cortex - the outer surface area of the cerebrum –Composed mainly of gray matter –Contains billions of neurons

110 The Cerebrum


112 l Gyri –Cortical folds l Sulci –Shallow grooves l Fissures –Deep grooves –Longitudina l fissure – separates right and left hemispheres Copyright 2009, John Wiley & Sons, Inc.

113 Lobes of the Cerebrum l Named after the bones that cover them –Frontal Lobe –Parietal Lobe –Temporal Lobe –Occipital Lobe

114 Frontal Lobe l Motor Areas –Controls movement of voluntary skeletal muscles l Association Areas –Carry on high level intellectual processing l Problem Solving - Reasoning - Planning l Concentration - Memory - Behavior l Emotions - Expressions


116 Parietal Lobe l Sensory Areas –Interprets sensations such as: –touch - pressure - pain on the surface of the skin l Association Areas –Understanding of speech –Using words to express thoughts and feelings

117 Temporal Lobe l Sensory Areas –Hearing and balance l Association Areas –Interpret sensory experiences –Memory of visual scenes - music - smells and other complex sensory patterns


119 Occipital Lobe l Sensory Areas –Visual processing and interpretation l Association Areas –Combines visual images with sensory experience


121 Which part of the brain deals with sight? A.) frontal B.) parietal C.) occipital D.) temporal

122 Which part of the brain is responsible for personality and thought processes A.) frontal B.) parietal C.) occipital D.) temporal

123 Which part of the brain is responsible for pain? A.) frontal B.) parietal C.) occipital D.) temporal

124 Which part of the brain is responsible for hearing? A.) frontal B.) parietal C.) occipital D.) temporal

125 The Cerebellum

126 Cerebellum and Brainstem

127 The Cerebellum l Second largest portion of the brain l Occupies the inferior and posterior aspects of the cranial cavity l Processes sensory information –Balance- Coordination –Maintains postural equilibrium



130 Nervous System Disorders and Homeostatic Imbalances

131 Alzheimers Disease (AD) l Disabling neurological disorder that effects about 11% of the population l Fourth leading cause of brain death among the elderly l A chronic, organic, mental disorder, a form of pre-senile dementia due to atrophy of neurons of the frontal and occipital lobes l AD patients usually die from complications due to being bedridden

132 Amyotrophic Lateral Sclerosis (ALS) l Also known as Lou Gehrigs Disease l A relatively rare neurological disorder l A syndrome marked by muscular weakness and atrophy with spasticity and hyperflexion due to degeneration of the motor neurons of the spinal cord, medulla, and cortex l A degenerative disease l No known cure

133 Bacterial Meningitis l Infection of the meninges by the bacterium Haemophilus Influenzae l Usually affects children under age 5 l Symptoms include severe headaches and fever l Can lead to brain damage and even death if not treated

134 Cerebral Palsy (CP) l A group of motor disorders due to loss of muscle control l Caused by damage to the motor areas of the brain during fetal development, birth, or infancy l About 70% of CP individuals are somewhat mentally retarded due to the inability to hear well or speak fluently l Not a progressive disease but the symptoms are irreversible

135 Epilepsy l Short, recurrent, periodic, attacks of motor, sensory, or psychological malfunction l Characterized by seizures which can result in involuntary skeletal muscle contraction, loss of muscle control, inability to sense light, noise, and smell, and loss of consciousness l Most epileptic seizures are idiopathic

136 Multiple Sclerosis (MS) l The progressive destruction of the myelin sheaths of neurons of the CNS l The sheaths deteriorates to scleroses –hardened scars or plaques l short circuits nerve transmission l Cause is unknown –May be a type of an autoimmune disease l No known cure l Progressive loss of function with intermittent periods of remission

137 Parkinsons Disease (PD) l A progressive disorder of the CNS that usually affects individuals over 60 l Cause is unknown but a toxic environmental factor is suspected l Chemical basis of the disease appears to be to little dopamine and too much Ach l Treatment includes increasing levels of dopamine and decreasing Ach –Difficult because dopamine does not cross the blood brain barrier

138 l A chronic nervous disease characterized by a fine, slowly spreading tremor, muscle weakness and rigidity, and a peculiar gait l Other causes may include brain damage at birth, metabolic disturbances, infections, toxins, vascular disturbances, head injuries, and tumors and abscesses of the brain l Usually can be controlled with drug therapy –GABA - gamma aminobutyric acid

139 l Symptoms include muscle tremor, muscle rigidity, bradykinesia, hypokinesia or dyskinesia, speech and walking impairment l Attempting to transplant fetal nervous tissue into the damaged area of the brain of some Parkinsons Disease patients

140 Cerebral Vascular Accident (CVA) - Stroke l The most common brain disorder l Characterized by slurred speech, loss of or blurred vision, dizziness, weakness, paralysis of a limb or hemiplegia, coma, and death l Ischemic CVA - due to lack of blood supply to a particular area of the brain l Hemorrhagic CVA - due to the rupture of a blood vessel in the brain

141 Risk Factors for Stroke l hypertension l heart disease l smoking l diabetes l atherosclerosis l hyperlipidemia l obesity l excessive alcohol intake

142 Brain Tumor

143 Shingles

144 Sensations and Special Senses

145 Senses Specialized structures of the nervous system which provide information about the environment in which we live to help maintain homeostasis nervous system which provide information about the environment in which we live to help maintain homeostasis

146 Functions of Special Senses l Sensory - monitoring the body and the external environment for changing conditions

147 Sensory Pathways l All pathways begin with a receptor and the sensory information is transmitted to the CNS l Always begins with a stimulus –change in the environment

148 The sensory pathway always begins with a ? A.) stimulus B.) effector C.) muscle D.) affector

149 Receptors l Structures which provide feedback about the environment l Are impulse specific –Only respond to one type of stimulus l Many have sensory function adaptations –May end as bare dendrites or be a complex organ

150 Vision l The most complex of the special senses –Over 70% of the sensory receptors in the body are photoreceptors for sight l Visual organs, the eyes are supported by a number of accessory structures and internal organs –Dependent upon photoreceptors in the eyes

151 The Eye

152 Accessory Structures of the Eye l Eyelids - protects the anterior surface –Conjunctiva - the mucous membrane of the eyelid –Helps moisten and lubricate the eyeball l Lacrimal Apparatus - secretes tears –lacrimal gland- lacrimal sac –lacrimal canals- nasolacrimal duct –moistens and lubricates the eyeball –fights against infection (enzymes in tears) l Extrinsic Muscles of the Eyeball (6) –skeletal muscles that move the eyeball

153 Which is not an accessory structure of the eye? A.) eyelid B.) lacrimal apparatus C.) sclera D.) extrinsic muscles


155 Accessory Structures of the Eye

156 Structure of the Eye l The wall consists of three layers of tissue or tunics l Fibrous Tunic - outer layer l Vascular Tunic - middle layer l Nervous Tunic - inner layer

157 Which IS NOT one of the three tunics of the eye? A.) muscular B.) vascular C.) nervous D.) fibrous

158 Fibrous Tunic l Thick, outermost layer of the eyeball l Sclera - the posterior white portion –Forms most of the fibrous tunic –The whites of the eye l Cornea - the anterior transparent portion of the fibrous tunic –Bulges outward slightly

159 Which IS NOT a part of the fibrous tunic? A.) cornea B.) sclera C.) eyelid


161 Fibrous Tunic

162 Vascular Tunic l Extremely vascular l Supplies blood to numerous structures of the eye –Choroid- Ciliary Body –Iris ciliary process (secretes aqueous Lens humor) ciliary muscle ciliary muscle zonular fibers--ligaments zonular fibers--ligaments

163 Vascular Tunic

164 l Choroid - posterior, thin portion of the vascular tunic –A thin, dark brown membrane that lines most of the internal surface of the sclera l Ciliary Body - anterior, thick portion of the vascular tunic –Thickest part of the vascular tunic –Consists of smooth muscle fibers –Attaches to the lens by ligaments –Changes the thickness and shape of the lens.- –Secretes aqueous humor

165 Cavities of the Eyeball Copyright 2009, John Wiley & Sons, Inc.

166 Ciliary Body

167 l Iris - anterior, colored portion of the Vascular Tunic –contraction of its smooth muscle accounts for dilation or constriction of the Pupils (openings to the inner cavities of the eyes) l Lens - special tissue which focuses and directs light entering the eye –suspended by the Ciliary Body –located behind the Iris –alteration of the shape of the lens to accommodate for near or far vision focusing (Accommodation)

168 Which part of the vascular tunic changes the thickness and shape of the lens? A.) cornea B.) extrinsic muscles C.) iris D.) ciliary body

169 The Lens

170 Iris – Pupil Diameter

171 Nervous Tunic l The inner layer of the eye l Retina - a thin fragile layer of neurons that forms the inner lining of the eyeballs posterior wall –Lines the posterior cavity and contains the photoreceptor cells (rods and cones), bipolar neurons, and ganglion cells l Optic Nerve - axons and ganglion cells –Transmits images to the occipital lobe of the brain for interpretation of what we see

172 Which IS NOT part of the nervous tunic? A.) inner layer of the eye B.) the optic nerve C.) the retina D.) choroid

173 Nervous Tunic

174 Rods and Cones l Rods - elongated cylindrical dendrites that are sensitive to varying light conditions –Allows us to see under varying light intensities (night vision) l Cones - dendrites with tapered ends –Color sensitive –Determines the sharpness of vision

175 Which dendrites allow you to see color? A.) rods B.) cones

176 Rods and Cones


178 Other Structures of the Nervous Tunic l Optic Disc - blind spot where the optic nerve exits the retina l Fovea Centralis - an area of the retina containing many cone cells –the area of sharpest vision

179 Color Blindness and Night Blindness l Color blindness- inherited inability to distinguish between certain colors. –Result from the absence of one of the three types of cones. –Most common type: red-green color blindness. l Night blindness or Nyctalopia- vitamin A deficiency. Copyright 2009, John Wiley & Sons, Inc.

180 Select all that are true A.) the sclera is in the nervous tunic B.) optic disc is the blind spot C.) fovea centralis is the point of sharpest vision D.) cones give black and white vision

181 Retina


183 Elements of Vision in the Eye l Vision spectrum of the eye –only detect three colors –Red- Green- Blue l Aspects of vision of the eye –color –motion –form –depth

184 Refraction l the bending of light rays as it travels through the eye l the pathway of light as it travels through the eye l influenced by: –shape of the lens –shape and thickness of the cornea –amount and consistency of the Aqueous and Vitreous Humor

185 Refraction

186 Vision Abnormalities

187 Physiology of Vision l Rods and cones convert light waves into a series of signals that results in the generation of an action potential in the ganglion cells –Both rods and cones contain pigments that decompose when exposed to light –The decomposition of the pigments is what generates the action potential

188 Rods and cones contain which of the following that creates color? A.) vessels B.) pigments C.) hormones

189 Visual Pathways l From the rods and cones, the nervous impulse is passed on to bipolar neurons and then on to ganglion cells l Axons from the ganglion cells extend out of the eye and converge to from the optic nerve l The optic nerves cross behind the eye at an area known as the optic chiasma l The optic nerve terminates at the thalamus

190 l Visual impulses from the thalamus are transmitted by other neurons to the occipital lobe of the cerebral cortex where the impulses are interpreted as the sense of sight.

191 Visual Pathway

192 Hearing l Dependent upon special organs within the ear l The ears are also associated with maintaining equilibrium and balance l Three Regions of the Ears –Outer Ear –Middle Ear –Inner Ear

193 The Ear

194 Outer Ear l Direct sound waves toward the eardrum l Auricle - the outer appendage l Auditory Canal - a tube that extends into the temporal bone

195 The Outer Ear

196 Middle Ear

197 l An air-filled space within the temporal bone l Tympanic Cavity - contains the auditory ossicles –Smallest bones in the body l Malleus (hammer) l Incus (anvil) l Stapes (stirrup)

198 l Auditory (Eustachian) Tube - a tube from the middle ear to the pharynx –Allows for pressure equalization between the middle ear and the atmosphere l Tympanic Membrane (Eardrum) - thin, semitransparent membrane separating the outer and the middle ear –Vibrates in response to sound waves striking it –The vibrations are then transmitted to the auditory ossicles

199 Which structure allows for equalization of pressure within the ear? A.) tympanic membrane B.) eustacian tube C.) ossicles

200 Middle Ear Structures

201 l The tympanic membrane and auditory ossicles convert sound waves into mechanical movement within the middle ear and then transmit that motion to the oval window l The oval window opens into the cochlea of the inner ear l Within the inner ear the vibrations of the stapes causes the fluid within the inner ear to move stimulating the receptors for hearing

202 The Three Regions of the Inner Ear l Formed by the canals of the bony labyrinth and the series of sacs of the membranous labyrinth l Involved in both the sense of hearing and the maintenance of balance and equilibrium l Cochlea l Vestibule l Semicircular Canals

203 Which is not a part of the inner ear? A.) ossicles B.) vestibule C.) cochlea D.) semicircular canal

204 The Inner Ear

205 Inner Ear Structures

206 l The Semicircular Canals - three loops that lie at right angles to each other l The Vestibule - the chamber between the cochlea and the semicircular canals –Both the semicircular canals and the vestibule are involved with maintaining balance or equilibrium l The Cochlea - shape resembles a snail shell –Contains the organs of hearing (Corti) l Receptor cells that move in response to endolymph motion l Releases neurotransmitters that stimulate nerve impulses

207 Chose the two structures involved with balance and equilibrium A.) semicircular canals B.) organ of corti C.) tympanic membrane D.) vestibule

208 The Cochlea

209 Organ of Corti

210 Cross Section of Cochlea

211 Inner Ear (Labyrinth) l Consists of a winding, complicated series of passageways or canals l Bony Labyrinth - a series of canals within the temporal bone –Contains perilymph l Membranous Labyrinth - an internal series of sacs and tubes –Contains endolymph –Conforms to the bony labyrinth shape –Also helps form the shape of the three regions of the inner ear

212 Vestibulocochlear Nerve

213 Nerve Pathways l Sound waves cause the tympanic membrane to vibrate l The vibration of the tympanic membrane causes the stapes to move back and forth l Movement of the stapes back and forth pushes the oval window in and out producing waves in the perilymph of the inner ear

214 l Pressure waves in the perilymph push the vestibular membrane inward increasing the pressure of the endolymph within the cochlear duct l The hair cells in the Organ of Corti convert the motion of the endolymph to the release of neurotransmitters l These neurotransmitters stimulate a nerve impulse in a sensory branch of the Vestibulocochlear Nerve (CN #VIII)

215 l The impulse is then transferred through the midbrain and the thalamus and finally terminates in the temporal lobe of the cerebral cortex where the sound is interpreted

216 What causes the tympanic membrane to vibrate? A.) nerve impulses B.) movement of fluid C.) sound waves D.) muscle movement

217 Physiology of Hearing

218 Clinical Terms Diseases and Disorders

219 Ametropia l Myopia - nearsightedness –Imaged focused in front of the retina l Presbyopia - a defect in vision in advancing age involving loss of accommodation or recession of near point (results in farsightedness) l Hyperopia - farsightedness –Image focused in back of the retina

220 Farsightedness due to old age is? A.) presbyopia B.) myopia C.) hyperopia


222 Cataracts l Abnormal loss of transparency of the lens l Vision becomes blurry or cloudy l Can be removed and have an artificial lens inserted l Most often occurs to individuals over the age of 50. Exposure to sunlight and smoking increases the risk.


224 l Conjunctivitis - inflammation of the conjunctiva, the mucous membrane that lines the eyelid and is reflected to the eyeball. Also known as Pink Eye l Strabismus – cross-eyed



227 Glaucoma l A group of eye diseases characterized by elevated intraocular pressure in the eye resulting in atrophy of the optic nerve which may lead to blindness l Caused by an obstruction of the outflow of the aqueous humor l Minor cases can be treated with eye drops l More severe cases may require a surgical incision into the iris of the eye


229 Macular Degeneration l The destruction or tearing away of the retina from the back of the eye l Commonly occurs in the region of the retina known as the macula lutea l Can be caused by: –Vascular diseases (diabetes) –Chronic increased pressure (glaucoma) –Sudden blow or impact to the head or eye (Detached Retina)

230 Which disorder is characterized by an increase in intraocular pressure? A.) strabismus B.) macular degeneration C.) hordeolum D.) glaucoma


232 Hordeolum

233 Vertigo l A condition of dizziness and spatial disorientation l In some individuals it is due to heights or fear of high places l A spinning sensation that may result in loss of balance and equilibrium

234 Tinnitus l Ringing or tinkling sounds or sensations in the ear

235 Middle Ear Infection l Infection of the tympanic membrane or other structures associated with the middle ear (Otitis Media)

236 Deafness l Loss of the ability to hear l Conductive Deafness: deafness resulting from any condition that prevents sound waves from being transmitted to the auditory receptors l Sensorineural Deafness: deafness due to defective function of the cochlea, organ of Corti, or the auditory nerve


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