Flashcards in Physiology - Exam 2, Deck #2 - Nervous Deck (208):
What is the Central Nervous System (CNS)?
Brain and Spinal Cord;
What are Nuclei?
Groups of neuron cells bodies within the CNS
What are Tracts?
-Group of nerve fibers (axons) that interconnect regions of the CNS;
-Integrative function of the CNS
What is the Peripheral Nervous System (PNS)?
Nerves, ganglia, and nerves plexuses;
-OUTSIDE the CNS;
-Consists of cranial and spinal nerves and associated ganglia
**Cranial = 12 pair
**Spinal = 31 pair
What is an Association Neuron (interneuron)?
Multipolar neuron located ENTIRELY in the CNS
What is a Sensory Neuron (afferent - in)?
Neuron that transmits impulse from a sensory receptor INTO the CNS
What are Motor Neurons (efferent - out)?
Neuron that transmits impulses from the CNS to an effector organ (ex. muscle)
What is a Nerve?
A collection of axons, or nerve fibers, packaged within the same connective tissue sheath in the PNS
What is a Somatic Motor Nerve?
-Voluntary effector organs;
-Nerve that stimulates the contraction of SKELETAL MUSCLES
What is an Autonomic Motor Nerve?
-Involuntary effector organs;
-Nerve that stimulates contraction (or inhibits) of SMOOTH and CARDIAC MUSCLES and that stimulates glandular secretion;
-Both sympathetic and parasympathetic branches
What are Neuroglia cells?
-Supporting cells of the nervous system;
-Derived from the same embryonic tissue layer as the neurons = the ECTODERM;
-Unlike neurons, neuroglial cells CAN DIVIDE throughout like;
*Brain tumors are glial cells
What are the types of PNS Glial Cells?
1. Schwann cells - Guillain-Barre syndrome
2. Satelite cells = ganglionic gliocytes
What are the types of CNS Glial Cells?
1. Oligodendrocytes - Multiple Sclerosis
What are Schwann Cells?
-Form myelin sheaths around peripheral axons;
-Results in saltatory conduction
What are Satellite Cells?
-Support functions of PNS neurons within sensory and autonomic ganglia;
-Also called ganglion gliocytes
What are Oliogodendrocytes?
-Form myelin sheaths around CNS axons
What are Astrocytes?
-Help regulates the passage of molecules from the blood to the brain, and contribute to the blood-brain barrier
What are Microglia?
-Amoeboid cells within the CNS that are phagocytic
What are Ependyma?
-Form epithelial lining of the brain cavities (ventricles) and the central canal of the spinal cord;
-Cover tufts of capillaries to form the choroid plexus;
-Choroid plexus produces cerebrospinal fluid
What is Multiple Sclerosis (MS)?
-Chronic, degenerativem remitting, and relapsing disease that destroys myelin sheaths of neurons throughout the CNS;
-Initially, lesion form on myelin sheaths and become hardened SCLEROSES;
-Prohibits the normal conduction of impulses, resulting in loss of function
Why is MS commonly misdiagnosed?
-Widespread myelin degeneration leads to a greater variety of symptoms than other neurological disease;
-And common remissions
What is Guillian-Barre Syndrome?
-Autoimmune disease of PNS;
-Functially equivalent to MS of the CNS;
-Can recover over time
What is the Autonomic Nervous System?
-Provides autonomic control of INVOLUNTARY effectors;
-Cardiac muscle, smooth muscle, and glands;
-2 neurons b/w CNS and effector =
1. Impulses from CNS by an axon that synapses with a second autonomic neuron;
2. Second neuron innervates the effector
What is a Preganglionic Neuron?
First neuron between the CNS and effector;
-Axon is found in the gray matter of the brain or spinal cord;
-Synapses with the second in an AUTONOMIC GANGLION;
-Preganglionic neuron → acetylcholine
What is a Postganglionic Neuron?
Second neuron between CNS and effector;
-Axon extends from the autonomic ganglion to the effector organ;
--Sympathetic → norepinephrine , +
--Parasympathetic → acetylcholine
What are the divisions of the Autonomic Nervous System?
1. Sympathetic (Thoracolumbar) Division: T1 → L2;
2. Parasympathetic (craniosacral) Division
3. Adrenergic and cholinergic synaptic transmission
4. Other autonomic neurotransmitters
5. Organs with dual innervation
What is Mass Activation by the Sympathetic Division?
Occurs when almost all postganglionic neurons fire simultaneously due to the DIVERGENCE of preganglionic fibers and CONVERGENCE of post ganglionic nerve fibers
What is the Paravertebral Ganglia?
A double row of sympathetic ganglia where most sympathetic nerve fibers separate from somatic motor fibers and synapse with postganglionic neurons
Where do preganglionic fibers from the upper thoracic level go?
Preganglionic fibers that exit from the upper thoracic level go to the neck, where they innervate smooth muscles and glands of the head and neck
Where do preganglionic fibers from below the diaphragm go>
They pass through the sympathetic chain of the ganglia WITHOUT synapsing;
-Beyond the sympathetic chain they become SPLANCHNIC NERVES
What are the Collateral or Prevertebral Ganglia?
-Preganglionic fibers in the SPLANCHNIC nerves synapse in the collateral ganglia;
-Includes = celiac, superior mesenteric, and inferior mesenteric ganglia;
-Postganglionic fibers then innervated the digestive, urinary, and reproductive systems
What is the Sympathoadrenal System?
-Adrenal medulla is derived from the same embryonic tissue as the postganglionic sympathetic neurons;
-Adrenal medulla secretes Epi and some NE under sympathetic stimulation;
-Because the adrenal medulla is stimulated in part by the mass activation of the sympathetic system the two are group
What is the Parasympathetic (Craniosacral) Division of the Autonomic Nervous System?
Preganglionic fibers come from the brain and the 2-4th sacral levels of the spinal cord;
-Preganglionic synapse in the ganglia next to or actually in the organs innervated — terminal ganglia;
-Innervate the lower LI, rectum, urinary and reproductive systems
What are Terminal Ganglia?
Ganglia of the Parasympathetic division that are next to or actually in the organs innervated;
-Supply the postganglionic fibers that synapse with the effector cells
What is Cholinergic Synaptic Transmission?
-Utilizes ACETYLCHOLINE =
-Ach is the neurotransmitter of the PREganglionic fibers of the symp. and para. division;
-Ach is also the transmitter most released by para. postganglionic fibers at synapses with effects
What is Adregenic Synaptic Transmission?
-Utilizes NOREPINEPHRINE =
- NE is the neurotransmitter released by most postganglionic sympathetic nerve fibers;
-Exceptions = some innervate skeletal muscles and sweat glands and release Ach (cholinergic)
What are the Cathecholamines?
Epinephrine, Norepinephrine, and Dopamine;
-All derived from the amino acids TYROSINE
What is the transformation of Tyrosine to Epinephrine?
1. Tyrosine (AA);
4. Norepinephrine (neurotransmitter/hormone);
5. Epinephrine (major hormone of the adrenal medulla)
What are “synapses en passant"
-Synapses in passing;
-Found in smooth muscles;
-Bulging synapses along the neurons of sympathetic and parasympathetic neurons;
-Can exhibit antagonistic effects on each other
What are some other Autonomic Neurotransmitters?
-Some postganglionic autonomic axons don’t involve norepinephrine or Ach = “Nonadregenic, noncholergenic”
EX: ATP, vasoactive intestinal peptide (VIP), and nitric oxide (NO)
What is Dual Innervation?
Most visceral organs are innervated by sympathetic and parasympathetic fibers;
-Effects may be antagonistic, complementary, or cooperative
What is Action Potential?
Abrupt pulse-like changes in the membrane potential lasting a few ten thousandths to a few thousandths of a second;
-AP moves along the nerve fibers and yields a nerve signal
What can elicit an AP in a nerve fiber?
*Any factor that suddenly increases the permeability to SODIUM IONS;
1. Electrical stimulation;
2. Mechanical compression of the fiber;
3. Application of chemicals to the membrane
What are the Components of an Action Potential?
1. Voltage regulated Na+ gates OPEN — Na+ diffuses INTO the cell;
2. Membrane DEPOLARIZES from −70mV to +30mV;
-3. Voltage regulated K+ gates open — K+ diffuses OUT OF the cell = Less depolarization;
4. Membrane potential depolarizes from +30mV to −70mV
What occurs when the depolarization stimulus hits the cell?
1. Membrane at resting potential of −70mV;
2. Depolarization stimulus acts on the cell — depolarizes to THRESHOLD at ~-50mV;
3. Na+ diffuses IN causing abrupt depolarization to +30mV = ACTION POTENTIAL;
4. Repolarization follows as K+ diffuses OUT of the cell — will depolarizes slightly below resting potential
What is the role of the Na-K Pump Diffusion Potentials in creating APs?
-Na-K pump generates resting membrane potential;
-At the start of the AP, Na+ permeability increases 5000x then returns to 73;
-Followed by an increase in K+ permeability as the inside of the membrane REPOLARIZES;
-Quick membrane change from (-) to (+) and back to (-) on the inside
What is the Plateau of APs?
-Repolarization does not take place right after depolarization;
-Remains on a plateau near the peak of the spike, before depolarization begins;
-Mostly occurs in the HEART, lasting 200-300msec causing contraction for this entire period
How are the Refractory Periods (plateaus) elongated in Cardiac (heart) fibers?
-Heart contracts as syncytium (all together) & thus can sustain force;
-Its AP lasts about 250 msec ;
-Has a REFRACTORY PERIOD almost as long as AP;
-Cannot be stimulated to contract again until has relaxed
What causes the elongated plateau during depolarization-depolarization?
1. Delay in the closure of Na+ channels = longer diffusion IN;
2. Small influx of Ca2+ maintains inside + for longer;
3. Permeability of K+ channels DECREASES 5x at the start of the AP in excitable membranes that have plateaus = DELAYS outflow of K+ and repolarization
What is Saltatory Conduction?
Propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials;
-Made possible by myelinated and unmyelinated fibers
What are the 2 types of nerve fibers in a nerve?
1. Myelinated — rapid conduction velocity;
2. Unmyelinated — slower conduction velocity
What are Myelinated Nerve Fibers?
-Surrounded by an insulator material called MYELIN;
-Myelin greatly increases the velocity of impulse traveling on the fibers;
1. Control rapid body movements by skeletal muscles
2. Transmit sensory signals from receptors to CNS
What are Unmyelinated Nerve Fibers?
-About twice as many small fibers WITHOUT myelin sheaths;
-Conduct APs SLOWLY — no rapid contractions;
1. Control subconscious activities via ANS
What are the subconscious actions controlled by unmyelinated nerves?
1. Excitability of the heart
2. Contaction of blood vessels
3. GI movements
4. Emptying of the urinary bladder
5. Sensory impulses that DON’T require immediate attention (ex: aching type of pain, crude touch or pressure receptors)
What is Myelin?
A LIPID that will not conduct electrical current;
-Acts as an INSULATOR around the fibers;
-About every 1mm along the length of the fibers the myelin is broken by a NODE OF RANVIER
What happens at the Nodes of Ranvier?
At the Node of Ranvier typical membrane depolarization can occur but BENEATH the myelin sheath depolarization DOESN’T take place;
-Nerve impulses are transmitted along the myelinated nerve by SALTATORY CONDUCTION
What is the Mode of Action for Saltatory Conduction?
1. Node of Ranvier becomes depolarized;
2. Electrical current spreads along the outside of the myelin sheath to the next Node and it depolarizes;
3. Process repeats from node to node
What makes Saltatory Conduction so valuable?
-Jumping of impulse from node to node increases velocity of conduction;
-Prevents depolarization of large areas of the nerve fiber and prevents leakage of large amounts of Na+ into the fibers and of K+ out of the fiber;
-Conserves energy that would be required by the Na
What is the All-or-None Law?
Once stimulated a nerve fiber always responds at the same amplitude of response
What is a Refractory Period?
Period of time of axon membrane is producing an action potential it is INCAPABLE of responding to further stimulation;
Absolute + Relative Periods
What are the components of the Total Refractory Period?
1. Absolute Refractory Period — due to inactivated Na+ channels;
2. Relative Refractory Period — due to continued outward diffusion of K+
What is the Absolute Refractory Period?
Elapsed time following a depolarization stimulus when the axon CANNOT be deloparized again regardless of stimulus strength
What is Relative Refractory Period?
Follows the absolute refractory period;
-When only a stronger than normal stimulus will produce a second action potential
What does Summation effect?
1. Neural physiology –the additive effects of graded nerve potentials
2. Muscle physiology – The additive effects of contractions of different muscle fiber motor units
What is Spatial Summation?
If voltage of stimulation is increased from 0 to the maximum voltage there is an increase in the number of nerve fibers stimulated;
-recruitment of variable numbers of nerve fibers in a nerve
What is a Minimal Stimulus or Threshold Stimulus?
The least possible voltage that will cause the nerve to fiber;
-Voltage at which only ONE nerve fiber stimulated to fire
What is a Maximal Stimulus?
The least possible voltage at which ALL nerve fibers in a nerve are stimulated
What is Temporal Summation?
-variation in number of action potentials sent along a nerve fiber per second;
-Frequency is limited by the refractory period of the nerve fiber
What are Gap Junctions?
Adjacent cells that are electrically coupled are held together by GAP JUNCTIONS — electrical synapses;
-Membranes of two cells are separated by only two nanometers;
-Composed of 12 proteins know as CONNEXINS
Where are gap junctions found?
Between electrically coupled cells of CARDIAC and some SMOOTH muscles;
-Allow excitation and rhythmic connotation of larges numbers of muscle cells;
-Seen in some regions of the brain
What are Connexins?
12 proteins that make up gap junctions;
-Form a water-filled pore for molecules pass from one cell to the next
What is a Synapse?
-Juncture between 2 neurons;
-Has the capability of transmitting some signals and refusing others;
**Variable Transmission of Signals = makes synapses the most important determinant of the CNS
What is Excitatory Postsynaptic Potential (EPSP)?
Some presynaptic terminals release EXCITATORY TRANSMITTER SUBSTANCES — acetylcholine;
-Elicits Excitatory Postsynpatic Potential by the opening of Na+ channels;
-Summation of excitatory postsynaptic potential (EPSP) leads to discharge of the EFFERENT neuron
What is Inhibitory Postsynaptic Potential (IPSP)?
-Some presynaptic terminals release INHIBITORY TRANSMITTER SUBSTANCES — GABA, serotonin or glutamine;
-Opens K+ channels
What causes the effect of the per synaptic terminals?
LARGE numbers of presynaptic terminals must fire for the action potential to transmit to the efferent neuron
What initiates a synaptic transmission?
-AP travels don the afferent nerve fiber to synaptic knob;
-AP causes cause Ach to be released from transmitter
What happens when the AP reaches the synaptic knob?
-Ca2+ channels are OPENED — calcium diffused into the know and binds protein SYNAPTOTAGM N;
-Occurs close to where synaptic vesicles are attached to the plasma membrane by SNARE
What is Synaptotagm N?
Protein that serves as a Ca2+ sensor, forming a Ca2+ complex in the cytoplasm of the cell being targeted by the nerve transmission
How many acetylcholine are in each vesicle?
10^4 acetylcholine molecules/vesicle
What is SNARE?
Complex of proteins that bind docked vesicles to the plasma membrane of the muscles cells
What allows the release of acetylcholine (neurotransmitter)?
The complete fusion of the vesicle and plasma membranes;
-A pore is formed that allows Ach release when the Ca2+ synaptotagm n complex displaces part of the SNARE
How quickly is Ach released?
In less than 100 microseconds after increased intracellular Ca2+
Where does the Ach go?
Ach diffuses across the synaptic cleft and attaches to receptor protein molecules on the postsynaptic neuron
How does Ach generate a EPSP?
Ach + receptor molecule alters the permeability of the plasma membrane Na+ channel;
Na+ enters the postsynaptic neuron generating an excitatory postsynaptic potential ;
-Enough Ach attached to receptors = large depolarization and AP goes over entire neuron
What is the mechanism of a Synaptic Transmission?
1. AP reaches axon terminals;
2. Voltage-gated Ca2+ channels open;
3. Ca2+ binds to sensor protein in cytoplasm;
4. Ca2+-protein complex stimulates fusion and exocytosis of neurotransmitter
What is Cholinesterase?
Enzymes that splits Ach into ACETIC ACID and CHOLINE in about 1/500 sec;
-Prevents continued stimulation of the postsynaptic cell unless more Ach is released
What are special characteristics of Synaptic Transmission?
1. One way conduction;
2. Synapse fatigues easily while nerve fibers fatigue hardly at all — Important to stopping a though or movement;
3. Memory function of the synapse
What is Facilitation of synapses?
Need 25 presynaptic terminals to discharge neurotransmitters for an AP, but only 20 terminals to fire;
-Facilitated so that firing of 5 more presynaptic terminals in a short period of time will result in the AP being sent to the efferent neuron
What happens when large numbers of impulses pass through a synapse?
Synapse becomes permanently facilitated so that impulses from the same origin can pass EASIER;
-How MEMORY occurs in CNS
What is Memory?
Storage of info;
-Can be self initiated without sensory input
How do Hypnotics, Anestethetics, and Acidosis affect neuronal circuits?
All DEPRESS transmission of impulses across the synapse
How do Alkalosis and mental stimulants (caffeine, benzedrine, and strychnine) affect neuronal circuits?
All FACILITATE (enhance) synaptic transmission;
-Strychnine causes spontaneous discharge;
-Different neurons have different thresholds
What is a Neuronal Pool?
Accumulations of neurons making up the numerous anatomical regions of the CNS
What is an Area of Stimulation?
sphere of influence upon neurons with which the neuron synapses
What is a Sphere of Influence?
Area of neurons that are acted by each incoming nerve fiber;
-Greater the number of presynaptic terminals that connect with a given efferent neuron, the greater the sphere of influence over it
What is the Discharge Zone?
Presynaptic neuron causes the postsynaptic neuron to fire;
-Efferent neurons that have enough presynaptic terminals ending on them so that they will excite every time an incoming fiber is stimulated
What is the Facilitated Zone?
Presynaptic neuron fires causes the postsynaptic neurons membrane potential to approach but not reach the threshold potential
What are the types of circuits in a neuronal pools?
1. One incoming — one out going neuron;
2. Diverging or amplifying circuit;
3. Converging circuit;
4. Inhibitory circuit
When does one incoming fiber stimulate one outgoing neuron?
NEVER exists in this form;
-Synapse simply acts as a SWITCH in this case
What is a Diverging or Amplifying Circuit?
Single incoming fiber enters the neuronal pool and branching occurs to more and more neurons
Where does an Amplifying Circuit occur?
-CNS control of skeletal muscles;
-50,000 amplification = ONE cell of motor cortex stimulates 50,000 neuromuscular junctions
Where does a DIVERGING Circuit occur?
-Multiple tracts = one source neuron branches to different PARTS of the nervous system
EX: Sensory info from dorsal spine follows 2 paths to the brain = 1. Cerebellum; 2. Thalamus + cerebral cortex
What is a Converging Circuit?
-Simultaneous control of one neuron by two or more input neurons;
-Mostly sensory branch of the nervous system;
1. Single Source
2. Multiple Sources
What is a Single Source Converging Circuit?
An excitatory field comes from more than one neuron in a sensory receptor field to a single neuron synapsing with it
What is a Multi-Source Converging Circuit?
Allows summation of info from several different sources
What is an Inhibitory Circuit?
Shuts off one pathway while opening another;
1. Respiratory center – inspiratory and expiratory oscillation
2. Vasomotor center – Cardiac excitatory and inhibitory oscillations
What is After Discharge of a neuronal pool?
-A signal entering a pool causes a prolonged output discharge, called the AFTER-DISCHARGE, even after the incoming signal is over;
-Usually stops due to fatigue
What is the After Discharge of a Synaptic transmission?
15 mSEC before development of the postsynaptic potential
What is the After Discharge of a REVERBERATING Circuit?
-Basis of innumerable CNS activities;
-One input neuron elicits responses that last seconds, hours, or a lifetime
What are some Reverberating Circuits?
-Life long respiratory rhythm
-Sleep- awake cycle
-Rhythmic- walking movement
What is a Parallel Circuit?
-Repeats a DEFINITE number of times with a lag at each synapse of 0.5 mSEC;
-Differ as to number of neurons in parallel
-Can be combined with a diverging circuit to perform mathematical calculations
What is a Neuromuscular Junction?
Connection between the end of a large myelinated nerve fiber and a skeletal muscle fiber;
-Each skeletal muscle fiber is supplied with at least one junction
What is a Motor Unit?
Combo of nerve fiber + all muscle fibers it innervates
What is different in the the action of Motor Units and muscles?
Motor units exhibit the ALL or NONE phenomenon;
Muscles DO NOT
What events occur at a neuromuscular junction?
Action potential moves done the AFFERENT nerve fiber to the region of the SOLE PLATE and the action potential causes Ach to be released from the transmitter vesicle
What is a Sole Plate?
The large and complex terminal formation by which the axon of a motor neuron establishes synaptic contact with a striated muscle fiber
What is the Effect of Curare (drug) on the neuromuscular junction?
-Blocks transmission of the impulse at the neuromuscular junction by making the muscle membrane RESISTANT to Ach;
-Compete with Ach for the receptor sites on the motor end plate;
= No muscle stimulation
What is the Effect of Neostigmine and Physostigmine like drugs on the neuromuscular junction?
Neostigmine and Physostigmine have the OPPOSITE effect of Curare;
-ENHANCE transmission of the impulse at the junction;
-INHIBIT cholinesterase that would breakdown Ach;
-Leading to a buildup of Ach at the motor end plate
What does the build of Ach at the motor end plate cause?
-Every time the muscle depolarizes it immediately depolarizes;
-Muscle fiber receives a succession of impulses and becomes spastic
What is the Effect of Diisopropulfluorophosphate on the neuromuscular junction?
Nerves gas causes the breakdown of cholinesterase for several weeks;
-NO degradation of Ach
How does Ca2+ effect the neuromuscular junction?
Number of vesicles releasing Ach increases directly with Ca2+ concentration
How does Mg2+ effect the neuromuscular junction?
Number of vesicles releasing Ach decreases as the concentration of Mg2+ increases
What are Sensory Receptors?
-Relay environmental stimuli to the CNS;
-detect intensity gradients of such sensory stimuli as touch, sound, light, smell, taste, cold and warmth
What are Receptor (Generator) Potentials?
-Produced by Sensory Receptors in proportion to the strength of the environmental stimulus and send pulse encoded information to the CNS for processing
What determines the info sent from the sensory receptors to the CNS?
-Pulse encoded information is propagated to the CNS by variation in the FREQUENCY of the action potentials but NOT by variation in their AMPLITUDE
What are Mechanoreceptors?
Detect mechanical deformation of the receptor or adjacent cells;
EX: hearing, equilibrium, and touch receptors
What are Thermoreceptors?
Detect changes in temperature
What are Nociceptors?
Detect PAIN, usually caused by physical damage or chemical damage to the tissue
What are Electromagnetic Receptors?
Detect light on the retina of the eye
what are Chemoreceptors?
Detect taste, smell, PO2, mOsM, PCO2 of body fluids
What are Primary Receptors?
*Free Nerve Endings;
-Taste and pain receptors;
What are Secondary Receptors?
*ALL other human receptors;
-Have specialized EPITHELIAL cells which form synapses with transmitting neurons;
What is Receptor Potential?
Local potential in the neighborhood of nerve endings caused by whatever type of stimulus excites the receptor
What is Local Flow of Current?
Caused by the receptor potential that in turn excites action potentials in the sensory nerve fibers
What are the ways in which receptor potentials can be elicited?
1. Primary or
2. Secondary Receptors
How do Primary Receptors elicit receptor potential?
Mechanically deform or chemically alter the terminal nerve ending ITSELF;
-Causes ions to diffuse through the nerve membrane, thereby setting up the receptor potential
How do Secondary Receptor Cells elicit receptor potential?
Lie adjacent to the nerve ending and synapse with them;
-Sound enters the cochlea of the ear — hair cells (receptor cells) like on the basilar membrane develop receptor potentials;
-These RPs in turn stimulate nerve fibrils intertwining the hair cells
What are the components of the eye that make it like a camera?
1. Lens system
2. Variable aperature system = Iris and pupil
3. Film = retina
4. Photochemistry = Chemicals of rods and cones
What are the 4 surfaces or interfaces of the Lens of the Eye?
1. Air — anterior surface of the cornea;
2. Posterior surface of cornea — aqueous humor;
3. Aqueos humor — anterior suface of lens;
4. Posterior surface of lens — vitreous humor
What is a Reduced Eye?
Schematic representation of the optics of the eye;
-All refractive surfaces of the eye are algebraically summed and considered to be a single lens;
-Useful for simple optical calculations
Where are images focused in the eye?
Images are focused on the RETINA
What is Accommodation of the eye?
Ability of the eye to change the refractive index of the lends and hence the focus of light on the retina
What is the mechanism of Accommodation of the eye?
Altering the refractive power of the crystalline lends of the eye in young children;
-Occurs by contraction of the ciliary muscle against suspensory ligaments
What is Presbyopia?
-With age the lens loses the elastic nature and loses the power of accommodation;
-Eye remains focused permanently at an almost constant distance depending on the the individual characteristics of the persons’ eye;
-age 40-45 = bifocals
What are the Errors of Refraction Lens Correction?
2. Hypermetropia = Hyperopia = farsightedness
3. Myopia = near-sightedness
What is Emmetropia?
-When ciliary muscle is completely relaxed, parallel light rays from distant objects are i sharp focus on the retina
What is Hypermetropia?
= Hyperopia = farsightedness;
-Can’t focus CLOSE UP;
-Eyeball is too short or lens is too weak when ciliary muscle is relaxed;
-CONVEX lens would correct
What is Myopia?
-Can’t focus on DISTANCE;
-When ciliary muscle is relaxed, lens is strong enough that light rays forming from distant objects are focused in front of the retina;
-Eyeball is too long, or too much power in the lens;
-No mechanism which can ever focus distant object sharply;
-CONCAVE would correct
What is Astigmatism?
A refractive error of the lens system of the eye usually due to an oblong cornea or lens
What is Cataracts?
Common lens abnormality in older people;
-Denaturation of the crystalline structure of the lens protein;
-IMPLANTED LENES would correct
What is the Variable Aperture System of the Eye?
-Made of the PUPIL and IRIS;
-Iris controls the amount of light that is allowed to enter the eye = increase in darkness, reduce in brightness
How does the Iris control light entering the eye?
-Changes in the side of the iris changes the size of the pupil;
-Diameter of the pupil - 1.5-8mm;
-Light entering = diameter squared;
-Amount of light can vary 30x
What is the Retina?
“The Film of the eye”;
-Light sensitive portion of the eye, containing the CONES and the RODS;
-Retina is connected to the optic nerve which runs to the cerebral cortex
What the Cones of the retina?
Mainly responsible for COLOR vision
What are the Rods of the retina?
Mainly responsible for vision in the dark;
Where does light enter the retina?
Inner limiting membrane layer
What is the Photochemistry of Vision?
Rods and Cones contains chemicals that breakdown when hit by light;
-Optic nerve is excited and sends the signal from the eye (retina) to the brain (cerebral cortex)
What is the chemical breakdown in the eye?
Rhodopsin — Opsin (protein) + Retinene;
*All cones cell have retinene, but the protein varies
What are the 3 types of cones?
How does Rhodopsin change when exposed to light?
Splits into opsin and 11-cis-retinene;
-Cis-retinene is converted to all-trans-retinene;
-Converted back to cis-retinene and recombines with opsin = Rhodopsin is reformed
What is Color Blindness?
Caused by a congenital lack of one or more types of cones, usually the absence of either red or green cones
What are Dichromats?
People who only have 2 functioning cones within their eye
What is Deuteranopia?
Absence of functioning GREEN cones (M cones);
-Most common form
What is Protanopia?
Absence of functioning RED cones (L cones;
What is Tritanopia?
Absence of functioning BLUE cones (S cones);
When can’t someone distinguish red from green?
Having only one cone in the middle to long wavelength region (red or green cones);
-Red and green pigments (photopsins) are cded on the X chromosome = much more common in MEN;
-Men = 8%, Women = 0.5%
What is Hearing?
A MECHANORECEPTOR Sense;
-The tympanic membrane and the ossicular system transmits sound through the middle ear to the inner ear
What is the Tympanic Membrane?
-Cone shaped with concavity facing downward towards the auditory canal
What makes up the Ossicular System?
3. Stapes → Oval window to the Cochlea
What is the Malleus of the Ear?
Handle is attached to the sneter of the tympanic membrane
What is the Incus of the Ear?
Tightly bound to the other end of the malleus by ligaments so whenever the malleus moves so does the incus;
-Opposite end of the incus in turn articulates with the stamp of the STAPES
What is the Stapes of the Ear?
The faceplate of the stapes lies against the membranous labyrinth in the opening of the OVAL WINDOW into the COCHLEA (inner ear)
What is the Cochlea?
-A system of 3 tubes coiled side-by-side;
-Sound waves are transmitted into the cochlea through the OVAL WINDOW
What are the 3 tubes of the Cochlea?
1. Scala vestibuli
2. Scala media
3. Scala tympani
What is the Vestibular Membrane?
Separates the Scala Vestibuli from the the Scala Media;
-So thin and easily moved that it DOESN’T play a role in sound transmission
What is the Basilar Membrane?
Separates the Scala Media and the Scala Tympani;
-On the surface of the Basilar Membrane lies the SPIRAL ORGAN OF CORTI
What is the Spiral Organ of Corti?
-Receptor organ that generates nerve impulses in response to vibration of the fibers of the Basilar Membrane;
-Contains a serious of mechanically sensitive cells know as HAIR CELLS
What are Hair Cells?
Mechanically sensitive cells;
-Receptive end-organs that generate nerve impulses in response to sound vibrations
How are Hair Cells arranged?
-One inner row the length of the Basilar Membrane;
-Several outer rows in the cochlea =
— 3 rows in the basal turn;
— 4 rows in the middle turn;
— 5 rows in the apical turn
How are sounds waves transmitted through the Cochlea?
1. Sounds waves enter the Scala Vestibuli from the faceplate of the Stapes at the oval window;
2. At the distal cochlea, Scala Vestibuli and Scala Tympani open directly to each other = HELICOTREMA;
What is the Helicotrema?
The opening between the Scala Vestibuli and the Scala Tymapni;
-Where sound waves pass
What determines PITCH?
The speed of the STAPES movement is directly related to the the frequency of the sound
What occurs at a HIGH Frequency of sound?
Fluid moves through the basilar membrane, causing it to bulge back and forth with each sound vibration
What occurs at LOW Frequency of sound?
Most of the fluid moves through the HELICOTREMA
What determines Frequency Coding of Sound Waves?
The variation in fluid movement through the ear due to variation of in the vibration of basilar membrane fibers at high and low frequencies
What is the function of Spiral Organ of Corti?
-Membrane basilar fibers vibrate UPWARD;
-In and out motion of the basilar membrane cause hair cells to go back and forth again the TECTORIAL MEMBRANE;
-Movement of hair cells excites the cochlea nerve fibers upon vibration of the basilar membrane
What determines Loudness?
Determined by the amplitude of variations of the basilar membrane and hair cells
What determine Frequency Variation?
Due to hair cell movement in different places along the basilar membrane
What happens at HIGH PITCH sounds?
Higher-pitched sounds produce a peak displacement close to the base of the basilar membrane
What happens at LOWER-PITCH sounds?
Lower-pitch sounds produce a peak displacement further toward the apex
What provides a neural code of Pitch Discriminaton?
The neurons that originate in hair cells that are where displacement is the greatest, will be stimulated more than those neurons in other regions
What is Equilibrium?
Sense that provides orientation with respect to gravity;
-Due to the Vestibular Apparatus
What are the parts of the Vestibular Apparatus?
1. the Otolith organs
2. Semicircular canals
**Sensory hair cells process the info from these about VELOCITY
What is the function of the Otolith Organs?
-Includes the UTRICLE and SACCULE;
-Provides info about linear acceleration
What is the function of the Semicircular Canals?
Provide info about rotational or angular acceleration
What is the sense of Taste?
Function of TRANSDUCTION of taste buds in the mouth
What are the Primary Sensation of Taste?
1. Sour=Acid – H+ channels
2. Salty – Na+ channels
3. Sweet and umami (savory = meaty flavor) – sugars and glutamate via G-protein coupled receptors
4. Bitter – Quinine via G-protein coupled receptors
How is the Taste Bud arranged?
-On the papillae of the tongue;
-Outer tips of taste cells are arranged around a minute TASTE PORE;
-the tip of each cell, several microvilli a or TASTE HAIRS protrude through the taste pore into the mouth cavity
What are the Microvilli or Taste Hairs?
Provide the receptor surface for taste
How are taste cells of SALTY activated?
Depolarization by Na+ ions
How are taste cells of SOUR activated?
Depolarization by H+;
How are taste cells of SWEET/UMAMI activated?
-Sugars and glutamate via G-protein coupled receptors;
-Followed by second messengers
How are taste cells of BITTER activated?
-Quinine via G-protein coupled receptors;
-Followed by second messengers
Where does the sense of SMELL come from?
OLFACTORY MEMBRANE which is high up in the nasal cavity
What are Olfactory Cells?
Consists of receptor cells which are bipolar nerve cells derived originally from the CNS
How many smell can humans experience?
up to 10,000 different odors
How does the brain handle smells?
Brain integrates signals from several sensory neurons that have different olfactory receptor proteins and then interpret the patter as a “FINGERPRINT” for that odor