MT 8 - Nervous system and sensory organs

Question 1

98. Membrane potential

Answer 1

• The potential diff. across a living cell membrane.
• Basis of maintaining it: ion gradient formed bw. the two sides, and by Na+/K+ ATPase pumps.
• Equilibrium pot. drives K+ out of cell and Na+ from EC into cell.
• In plasma membr.; more K+ channels open in resting state, than leak Na+ channels. Therefore, RMP is result of slow outflow of K+.
• Electrogenic pump: If more positive ions are pumped out than in. Task of pump; maintaining conc. difference.
• Presence of all ions together determined final value of membr.pot. Can be calculated using Goldman-Hodkin-Katz equation

Question 2

98. Local response and action potential

Answer 2

• Membr. pot. may be changed artificially in two directions:
• Depolarization: giving pos. charge to IC space to reduce membr.pot.
• Hyperpolarization: giving neg. pot. to IC space to incr. polarization.
• Local response: If depolarization does not reach threshold pot., the pot. change will only be conducted a few mm with decr. intensity. Its propagation depends on physical processes.
• Action potential: If depolarization does reach threshold pot., it evokes an „all-or-none” response with strictly amplitude.
• Hyperpolarization never evokes an AP
• Adaption: In a membrane gradually depolarized by slowly incr. pot., opening of Na+ channels is followed by inactivation, and thus the Na+ influx is inhibited even at higher pot.

Question 3

98. Propagation of action potential

Answer 3

-Generation of AP depends on voltage-dependent ion channels. These channels may be blocked by:
•TTX (tetrodotoxin): From marine fish venom. Specifically blocks voltage-dependent Na+ channels.
•TEA (tetraethylammonium): Specifically blocks voltage-dependent K+ channels.
-In myelinated fibers: AP develops in nodes of Ranvier. In this case AP is propagated by leaping from one node to another. This is called salutatory conduction (fast)
-In non-myelinated fibers: AP propagates step by step (slow)

Question 4

99. Axonal transport and synaptic transmission

Answer 4

• Synaptic transmission (neurotransmission): the process where neurotransmitters are released by a neuron (the presynaptic neuron), and bind to and activate the receptors of another neuron (the postsynaptic neuron)
• Neurotransmitters: signaling molecules. Either small molecular weight substances or larger peptides.
  1. AP conducted through axon in the synaptic nerve ending, prod release of neurotransmitters stored in vesicles.
  2. The neurotransmitters can bind to their specific receptors on the postsynaptic membr.
  3. Result: Hyperpolarization: RMP incr/Depolarization: RMP decr
• Synthesis of peptides and vesicles are only possible in neural soma. Therefore the produced neuropeptides and vesicles must be transp. to presynaptic nerve ending. This process is called axonal transport.
• From soma to nerve ending: Anterograde transport by kinesin
• From nerve ending to soma: Retrograde transport by dynein
• GAP junction: A special synapse, which allows free diffusion of charges between cells.

Question 5

99. Sensors

Answer 5

• The function of the nervous system is based on sensing stimuli from the outer or inner environment. This is accomplished by active participation of membranes of afferent nerve endings.
• The specific stimulus evokes a cation influx, generating a receptor potential. The amplitude of this potential is proportional to the extent of the stimulus, and this extent is coded by first the amplitude, then by the frequency.

Question 6

99. Ion channels

Answer 6

-Ion channels: incr./decr. flow of cations or anions by incr./red. the ion permeability.
Classification:
- Na+, K+, Cl- channels:
o Leak: maintain membr. pot.
o Voltage-dependent: generate AP (Na+, K+)
o Ligand-dependent: Multiple tasks. E.g. n-ACh, glutamate, anion, G-protein mediated
o Mechanoceptive: uptake of tactile and other mechanical stimuli
o Energy sensor: K+ channel sensitive to ATP causes depolariz. according to ATP conc. of the cell.
-Ca2+ channels
o Ryanodine and DHP: blocked by DPH. Mechanically activates the channels. In SR.
o IP3-receptor: Mobilizes Ca from IC Ca stores
o Voltage-dependent: P-, T- and N-types

Question 7

101. The reflexes

Answer 7

•A reflex action/reflex: an involuntary and nearly instantaneous movement in response to a stimulus.
•Types of reflexes:
o Cranial nerve reflexes
o Primitive reflexes
o Other reflexes: e.g. Bainbridge reflex, diving reflex, etc.
o Spinal cord reflexes
•Its 5 main components:
1.receptor cell (tissue, organ)
2.the afferent fiber; afferent neuron and its axon
3.central processing unit
4.the efferent fiber; efferent neuron and its axon
5.effector cell (tissue, organ)
•Two types of reflexes related to effector organ: proprioceptive and exteroceptive
•Common features of proprioceptive and exteroceptive reflexes:
o Response has local character
o Intensity of response is proportional to intensity of stimulus
o Reciprocal innervation is typical
o Higher brain levels modulate the reflex significantly

Question 8

101. The reflexes: Proprioceptive reflexes

Answer 8

• The proproceptive reflexes: spinal reflexes where receptors are in same organ as the effector response.
• Differ from exteroceptive reflex in:
• Adequate stim. is muscle stretching
• Rec. is in muscle spindle, afferent nerve is fast Ia fiber.
• Reflex arch is monosynaptic.
• Almost no latency.
• Response carried out immediately, lasting no longer than stim.
• Reflex does not fatigue.
• Types:
  1. Myotatic reflex (stretch reflex)
  2. Inverse myotatic reflex
  3. Flexor stretch reflex and extensor thrust

Question 9

101. The reflexes: Exteroceptive reflexes

Answer 9

• Spinal reflexes where receptor is outside the effector organ
• Forms the basis of preventing, nociceptive and pain-avoiding behavior
• Acts mainly through activation of flexors and contralateral extensors.
• Usually, receptor is located in skin, and effector in muscle
• Differ from proprioceptive reflexes in..:
• Receptor is tactile
• Extensive polysynaptic network of reflex arch
• Very long latency
• Response is slow and lasts longer than stimulus.
• Muscle easily fatigues.
• A significant contralateral response is evoked
• Afferent activation relaxes ipsilateral extensor muscles through inhibitory interneurons, and significantly activates ipsilateral flexor muscles through excitatory interneurons. ->Limb is moved away from stimulus.

Question 10

101. Movement patterns

Answer 10

•Require an organization more complicated than simple reflexes but are carried out similarly by the control of spinal cord, independently from upper cerebral functions.
•Walking and scratch reflexes are best known
•Their characteristics:
o are stereotype (always identically running)
o extend to more segments
o are rhythmically repeated, with a rhythm independent from the rhythm of the evoking stimulus
o last much longer than the stimulus.
•In the creation of the rhythm, two characteristics of neurons play important roles:
1. adaptation to excitatory effects
2. spontaneous release from inhibitory effects
•Stimulus arriving from sensory ganglion passes through excitatory interneurons when running towards the extensor and the flexor motorneuron.
•Excitatory interneurons send collaterals to inhibitory interneurons that inhibit the oppositely functioning excitatory interneurons. The continuous stim causes adaptation, and from the continuous inhib, neurons are released after a while

Question 11

102. Autonomic nervous system

Answer 11

-Responsible for the automated control of metabolic processes and connection between the organism and the external environment.
-Part of peripheral NS
-Divided into sympathetic and parasympathetic
-Controls the inside of body; viscera and gut
-Thoracolumbar segments of spinal cord
-One axon innervates several cells
-Has mainly effector function.
-Elements in the CNS:
•supraspinal regions have a crucial role in the maintenance of homeostasis
•functions: perception of the actual state (afferentation), processing, and two types of efferentation:
1.Unconscious by activating sympathetic, parasympathetic and endocrine systems.
2.Assembling the appropriate, conscious somatic and motor responses of the behavior.
•Components of the supraspinal system are the frontal and associative cortex, hypothalamus, limbic system, brain stem and the medulla. Also the group of nuclei of cranial nerves responsible for visceral (parasympathetic) functions (cranial nerves III, VII, IX and X).
•III. N.oculomotorius ,VII. N. facialis, IX. N.glossopharyngeus and X. N. vagus

Question 12

105. The physiology of sleeping; the reticular formation

Answer 12

-Reticular formation: an oval area of the brain stem, composed of small neurons forming neural networks.
•Afferents:
1. Info. from viscerosomatic sensory system and from afferent cranial nerves from the head.
2. A particular group of afferents from the sensory and motor cortex, the thalamus and the hypothalamus.
•Efferents:
1.Desc. retic. form. - efferentation to spinal chord
2.Efferents to upper brain areas - non-specific nuclei of the thalamus, cortex, limbic system, cerebellum and hypothalamus.
Functions:
1. Regulation of sleep-wake cycle
2. Conducting sensory info. to the limbic system, altering emotions
3. Coordination of visceral function like circulation, ventilation, swallowing, coughing, and sneezing,
4. Coordination of posture mainly by controlling axial (trunk) muscles.
•Desc. reticular system:
1. Inhibitory (medial) part: activation inhibits the myotatic and other subcortically organized reflexes
2. Facilitating (lateral) part: activation incr. intensity of all motor processes.
•Asc. reticular activating system (ARAS): arouses activity of all upper centers.

Question 13

106. The physiology of sleeping; the limbic system

Answer 13

-A set of brain structures located on both sides of the thalamus, immediately beneath the cerebrum
-Limbic System = Prosencephalon
•Role in primitive cortical mechanisms
o Integrates most primitive cortical mechanisms (emotional, sexual & visceral function)
1. Medial limbic ring
a. Hippocampus, dentate gyrus, area piriformis, cortex near amygdala
2. Basolateral limbic ring/amygdala
a. Cingulated gyrus, amygdala, septum pellucidum, rostral & dorsomedial nucleus of thalamus
-Afferents: Spinothalamic tracts, olfactory tracts.
-Efferents: Papez circuit -> connects parts together & to the cortex

Question 14

106. The physiology of sleeping; behaviour

Answer 14

•Emotional, sexual, visceral, sleep-wake cycle, emotional learning.
•Function:
o Amygdala: rage, attack, sexual mechanisms
o Septal nuclei: fear, defense
o Archipallium: learning
o Limbic system: closely associated with hypothalamus and endocrine function
o Ventromedial nuclei of hypothalamus: emotional centre (controlled by higher brain structures)
•Behaviour and Locomotor activity: Behaviour learnt on basis of inherited motion pattern
o Ordinary behavior pattern: Metabolism, reproduction
o Signaling behaviour pattern: Distance keeping/contact seeking
o Exploratory behaviour pattern

Question 15

103. Sensory mechanism in the central nervous system

Answer 15

-Types of sensory area:
1. Primary sensory area -> Postcentral gyrus
*Mechanical sensations, deviations & proportions
2. Secondary sensory area -> Sylvian fissure
*Pain sensation does not change much throughout life
*Cortical areas relay back on afferent activity of thalamus and spinal cord to adjust sensitivity threshold.
-Types of sensation:
•Mechanical sensation
o Sense of vibration (Pacinian corpuscles)
o Encoding of pressure (Ruffini corpuscles)
o Touch location (Meissner’s corpuscles)
o Hair follicle sensation (hair follicle receptors)
•Other
o Thermal sensation (warm and cold receptors)
o Pain sensation
o Sensation of magnetic field

Question 16

104. Posture control in the central nervous system

Answer 16

-The way CNS regulates sensory info. from other systems to prod. an adequate motor output or muscle activity
-Main sensory systems involved: visual, vestibular and somatosensory
-Vestibular apparatus is most important afferentation of posture
-Efferents determine tone of axial muscles, supporting body against gravitational and ensuring balance and localization of the body
-2 levels:
1. UMS (Upper Motor Systems) -> Supraspinal level
o Determines normal posture and complex voluntary movements
o Cerebellar and basal ganglion system plans and adjusts muscle tone
*Movement initiation, -planning, -plan reconsideration and -execution
2. LMS (Lower Motor Systems) -> Spinal level
o Coordination of movements at spinal level
o Organized on basis of spinal organization
-Types of Postural Reflex:
•Tonic reflex: supports body against gravitation
•Supporting reflex: E.g. cat upside down and dropped, lands on feet
•Statokinetic reflex: positional reflex evoked by movement and position of body during movement
•Planking-Hopping reflex

Question 17

105. Intentional movements

Answer 17

-Motor cortex: small stimulus evokes movement on contralateral side.
•Brodman 4, Primary motor cortex: Precentral gyrus. Responsible for final execution of movements. Also origin of pyramidal tracts.
•Brodman 6 area (premotor cortex): Investigates, determines and sequences movement. Shows somatotopy.
•Brodman 6 area (supplementary area): Centre of intention of complex movement.
-Motor Pathways:
•Pyramidal
o Fibers leave as corticospinal and bulbospinal tracts, giving many collaterals to brain stem, cerebellum and basal ganglia
o Large part of fibers cross over in the pyramid. Most of the uncrossed fibers cross to opposite side in the spinal cord. A very small % remains uncrossed.
o Fibers end on large (alpha) and small (gamma) motor neurons. A small part terminates on interneurons that create indirect connection with alpha and gamma neurons
• Extrapyramidal: 1. rubrospinal tract, 2. vestibulospinal tract, 3. tectospinal tract, 4. reticulospinal tract.
-Stages:
1. Intension to move (limbic)
2. Movement planning (Brodman 6 area)
3. Coordination of movement (cerebellum and basal ggl)
4. Execution of movement (Brodman area->precentral gyrus)
5. Movement (spinal cord -> muscle)
6. Proprioceptions (efferentation)
7. Other afferentation (visual/hearing)
8. Thalamic mediation

Question 18

105. The cerebellum

Answer 18

-“Little brain”, major feature of hindbrain
-Origin of movement, coordination & movement learning
-Main functions:
o Connection and refinement of movement plan
o Learning and storage of complex movement plans
-Vestibulocerebellum (Nucleus Fastigii)
•Archicerebellum
•Flocculonodular lobe: Processes information
•Controls eye movement and balance
•Removal leads to ataxic movement
-Spinocerebellum (Nucleus Interpasti)
•Paleocerebellum
•Finely adjusts muscle tension according to status
•Removal: no fine movements possible
-Cerebrocerebellum (nucleus dieter)
•Neocerebellum
•Roles in movement & learning-related movement
•Roles in timing of movement
•Removal: unable to initiate movements at proper time. Rapid, alternating movement is impossible
-Functional units:
1. Mossy fibers
2. Purkinje fibers
3. Deep nucleus

Question 19

107. Memory and learning

Answer 19

Memory:
• Short-term: Frontal lobe, alpha-2-adrenergic receptor
• Middle term: Medial temporal lobe (hours-days)
• Long term: Repeated stimuli, generates biochem. & morphological changes. Alters many synaptic connections
-Types of simple learning:
1. Habituation: form of learning where an organism decreases or ceases its responses to a stimulus after repeated presentations
o E.g. repeated AP transmission along post-synaptic membrane of sensory neuron causes the opening of a specialized inhibitory K+ channel, decr. the effect of AP freq.
2. Sensitization: non-associative learning process, where repeated stimulus results in the progressive amplification of a response
o Repetition of stim. results in even a small stimulus eliciting a large effect.
-Associative learning: Complex learning in which distinct events in time and space are connected.

Question 20

107. Unconditioned and conditioned reflexes

Answer 20

• Unconditional: Food in dog’s mouth->salivation.
o Congenital motor/secretory response to external stimulus
•Conditioned: Neutral/unconditioned stimuli
o Neutral stimulus becomes connected to unconditioned stimulus and begins to evoke same effect
• Operant reflex: Pleasant/unpleasant stimuli
o Operant conditioning: Link bw. one action and it’s effect (e.g. bell rings, dog expects food, dog salivates in anticipation)
o Pos. and neg. reinforcement
o Building up of a conditioned reflex

Question 21

109. Vision

Answer 21

Morphological basis of vision:
-Retina
o Contains light sensory epithelium and neurons
o Cones = Colour; Rods = light intensity
-Fovea = site of sharp vision. Contains green and red cones only.
-Macula = blue, green and red cones
-Optic Disc: exit of optic nerve. No light-sensitive elements
-Elements of Eye
o Air -> Cornea
o Cornea -> Aqueous humour
o Aqueous humour -> anterior surface of lens
o Posterior surface of lens -> Vitreous humour

Question 22

109. Cellular mechanism of light perception

Answer 22

1. Light sensation is triggered by rods and cones
2. Light abs. by 11-cis-retinal bound to transmembrane protein, opsin.
3. Light transforms this to all-trans-retinal and then to metaretinal
4. Change in protein structure activates G-protein
5. Cation channels open, light hyperpolarizes cell
   - In dark: cations channels are always open (depolarization) to maintain a dark current.

Question 23

109. Colour vision

Answer 23

• Reacts to changes in light intensity independently from wavelength
• At least 2 cones and subsequent central processing are required for the recognition of a colour
• Colour vision incr. visual acuity (ability to distinguish btw objects)

Question 24

111. Inner ear; vestibular apparatus

Answer 24

-Cochlea: a duct forming a spiral turns around a bone column, the modiolus.
*Divided in 3 scala by the basilar membrane, lamina spiralis ossea and vestibular membrane
•scala vestibuli (perilymph)
•scala tympani (perilymph)
•scala media (endolymph)
o The organ of Corti- transducts mechanic vibration to neural signals.
-Organ of Corti
•The hearing organ
•Consists of receptor cells resting on basilar membrane and reaching into the space of cochlear duct (hair cells)
•During displacement of the basilar membrane, the hair cells touch the gelatinous tectorial membrane above them, which leads to their excitation.
•Receptor cells have no axons, their neural impulse is conducted by the bipolar neurons of the spiral ganglion.
oTheir axons towards the CNS form the acoustic nerve

Question 25

111. Inner ear; Hearing

Answer 25

-Auditory perception; ability to perceive sound by detecting vibrations and changes in pressure of the surrounding medium through time.
•Motion of basilar and tectorial membrane, results in back-and-forth deflection of the stereocilia. This process is bi-directional.
•Mechanic stimulation of outer hair cells of the same cell row, specialised to a single frequency, results in the secondary contraction of their stereocilia
•As a result, cell row pulls the tectorial membrane even closer: a frequency-specific amplification occurs. The back-and-forth deflection of the stereocilia results in an alternation of depolarization and hyperpolarization.

Question 26

108. Taste

Answer 26

-Gustation=taste: chemical receptors
-Smell receives gaseous chemical signals
-Taste receives those of liquid phase.
-Receptors = gustatory papillae.
• Filiform - mechanoreceptors
• Fungiform – quickly respond to stimuli
• Circumvallate
• Foliate
- Serous glands of Ebner: ‘wash’ tastebuds
-Tastes: Sweet, sour, bitter, salty, omami
-Taste Pathway:
•Anterior 2/3 tongue = Facial Nerve
• Posterior 1/3 tongue = Glossopharyngeal Nerve
• Radix, epiglottis = Vagus
• Tactic/temp. receptors of oral cavity = Trigeminal nerve

Question 27

108. Olfaction

Answer 27

• Highly sensitive
• Adapts quickly to stimuli
• Has a differential threshold
• Location of source of stimulus is difficult due to diffusion
• Receptors:
*in caudodorsal part of nasal cavity
*in vomeronasal organ
*Receptor cells: bipolar neurons with microvilli, unmyelinated axons terminate on olfactory bulb.
*Supporting cells: microvilli projecting into secretion covering the mucosa.

Question 28

108. Receptors

Answer 28

Classification:
-According to receptor:
o Primary: Stimulus has effect on cation channel of a sensory neuron directly. E.g. olfaction.
o Seconary: Stimulus is sensed by second cell of sensation. E.g. sound reception.
o Tertiary: Afferent nerve fibers belongs only to the third cell involved in transduction of stimulus. E.g. the eye.
-Location of stimulus:
o Exteroceptors: Sensing stimuli from the external environment. E.g. light, sound etc.
o Interoceptors: Sensing stimuli from internal environment. E.g. heat, pressure, partial pressure of gases, tendon receptor, muscle spindles, etc.
- Form of energy of stimulus: Mechanical, thermal, photo or chemical energy
- Type of perception:
o E.g. touch, light, warm, cold, sound, taste, pain, smell.
- Ability to adapt:
o Fast: dynamic, phasic
o Slow: tonic, static
-Types of receptors:
*Free nerve ending: Sense pain and temp.
*Panician corpuscles: sensitive to touch.
*Golgi tendon organ: located at muscle-tendon border. Sense stim. from the internal environment.
-Function: specific stimulus is conducted through the structures, modulating its parameters, and finally reaching the free surface of the fiber.
*On the receptor membrane a pot. charge is generated.
*The mechanical stimulus evokes electronic response of the neuron->sensory transduction takes place.

Question 29

100. General characteristic of the spinal chord

Answer 29

• Spinal cord: collection of nerve cells (grey matter) and nerve fibers (white matters) embedded in the vertebral canal
• Together with the brain, it is a part of the CNS.
• Fibers leave through dorsal and ventral roots that are united before stepping out from the vertebral canal and form spinal nerves of both sides.
• Dorsal root: afferent, spinal sensory ganglion
• Ventral root: efferent, motor fibers
• Spinal cord regions: cervical, thoracic, lumbar and sacral
• The thickest parts are cervical intumescentia; moving FL, and lumbal intumescentia; moving HL
• At cervical and thoracal regions: nerves leave the vertebral canal perpendicularly to the bulbar origin.
• Fibers leaving at lumbal and sacral regions are collected when running down in the vertebral canal (filum terminale or cauda equina), then they leave the vertebral canal through the intervertebral holes.
• On the cross-section nerve cells and fibers are arranged into functional groups.
• Axons of the radicular neurons (root cells) leave the spinal cord while that of the inner cells do not.

Question 30

100. Neural networks

Answer 30

• Neural networks: units based on simple neural connections and organized for complex tasks.
• Convergence: The function of one neuron may be influenced by the function of more, on this neuron synapsing neurons run together.
• Divergence: The axon of one neuron may run to many other neurons through branches of the axon
• Monosynaptic pathway: one synapsis is responsible for the essential functions (e.g. stretch reflexes).
• Polysynaptic pathway: If more than two neurons participate in the reflex
• Function through two main effects:
  1. EPSP, excitatory postsynaptic potential, depolarization
  2. IPSP, inhibitory postsynaptic potential, hyperpolarization
• Disinhibition: inhibition of inhibitory type neuron
• Disfacilitation: inhibition of excitatory neuron
• Interneurons may inhibit or excite.
• Collaterals between parallel neural pathways may generate returning signals (reverberation)

Question 31

100. Rexed zones

Answer 31

-In the grey matter
-With the exception of the lateral horn the grey matter can be divided into Rexed’s fields.
-Laminas I-VI belong to the upper, laminas VII-IX to lower horn.
-In laminas II-III mostly interneurons are found
-Lamina IX is the area of large and smaller motor neurons, and of Renshaw cells responsible for recurrent inhibition.
-Motor cells show a somatotopic arrangement similarly to cerebral motor areas:
o Medially: motoneurons of trunc, ribs and postural muscles
o Laterally: more distant muscles of the limbs
-Radicular cells: cells that leave the vertebral canal.
These include:
1. Somatosensory cells: pseudounipolar cells located in the spinal ganglion
2. Somatomotor cells: found in the ventral horn
3. Sympathetic cells: of the intermediolateral nuclei of the lateral horn (thoracolumbal region)
4. Parasympathetic cells: of the intermediomedial nuclei of the lateral horn (cervicosacral region).
-The cells inside the grey matter are:
o Excitatory and inhibitory interneurons
o Renshaw cells and associational neurons that establish connection between the given segments
*They do not leave the spinal cord

Question 32

100. Dermatomes

Answer 32

• An area of skin mainly supplied by a single spinal nerve
• These skin areas form clearly demarcated stripes in humans and irregular but well distinguishable patterns in animals.
• Important in determination of the origin of skin sensitivity disturbances and in surgical anesthesia
• Vegetative fibers belonging to the same segment are found in the same place in spinal ganglia as the somatosensory, pseudounipolar cells. Central fibers of these run together towards the substantia gelatinosa Roladi, where they synapse to interneurons. After this, sensory and vegetative tracts are separated.
• Painful stimuli of the skin influence visceral function and conversely: diseases of visceral organs may cause hypersensitivity and soreness of the skin.
• Skin zones belonging to a visceral organ are called Head-zones. Knowledge of them has clinical diagnostic significance. The phenomenon is also called referred pain.
• For these reasons certain areas of the skin may have increased sensitivity (hyperesthesia), decreased sensitivity (hypoesthesia) or no sensitivity at all (anesthesia).

Question 33

106. The physiology of sleeping

Answer 33

•During sleep: basal metabolic rate and body temp. are decr., parasymp. dominance can be found.
•Timing and deepness of sleeping varies from sp. to sp.
•Two main phases:
1. SWS (slow wave sleep): Synchronized, low-frequency waves, with relatively high voltage.
2. Paradoxical sleep/REM (rapid eye movements) phase: EEG becomes suddenly synchronized, beta-like rhythm is generated. Eye moves in disorganized manner. In spite of movements, animal can be awoke very hardly.
•Retic. form. is an important active but not sole cause of arousal.
•Nucleus suprachiasmaticus is also necessary in settling normal sleep-wake cycle.
-Phases of sleep:
1. entering sleep
2. superficial sleep
3. deep sleep
4. more deep sleep

Question 34

110. Object viewing, Visual acuity, Visual pathway

Answer 34

-Object viewing:
*Tracking an Object:
•Short distances = movement of eyes only
•Long distances = movment of head
*Pupil Reflex: Myosis = constriction, mydriasis = dilation
- Visual acuity:
*Sharpness of vision.
*The smallest angle under which 2 neighbouring object points can still be distinguished from one another.
- Visual pathway:
•Decussation in optic chiasm
•Axons of retinal ganglion cells project to lateral geniculate body. Fibers reach primary visual cortex.
•Cortical integrating systems
•Primary visual area projects to further brain regions

Question 35

110. Visual field

Answer 35

• Monocular/Binocular.
• Spatial Vision
  1. Binocular vision: points located beyond a certain fixation point are disapparat points. Small distortion happens. Sensed by central neurons at distance.
  2. Monocular vision: almost perfect spatial vision is assured by light intensity, colour, black and white contrasts, head movements and movement of objects relative to one another.

Question 36

103. Physiology of pain

Answer 36

•Pain sensation is based on the receptor function of nociceptive free nerve endings.
•Transmit AP to the center in two phases.
*Receptors: nociceptive free nerve endings
•A delta fibers: fast-conducted, well localizable pain
•C (unmyelinated) fibers: slowly initiated, long lasting and hardly localizable pain
•Rapid pain elicits mainly flexor reflex and immediate defence, the synaptic co- activation is common.
•Slow pain (similarly to visceral pain) causes drop of BP, sweating and nausea.
•Because of significant collaterals and segmental connections of the visceral reception the important phenomenon of referred pain may occur.
•Tactile stimulation around a painful wound decr pain.