Sensory%20Receptors

1
(No Transcript)
2
(No Transcript)
3
(No Transcript)
4
Sensory Receptors

• topography of sensation peripheral sensitivity
  a area of synaptic endings in CNS
• Mechanoreceptors
• detect tactile sensation (touch, pressure,
  vibration)
• skin tactile sensation (Meissners corpuscles,
  free nerve endings)
• deep tissue sensation (Pacinian corpuscles,
  muscle endings)
• Thermoreceptors
• detect changes in temperatures (cold and warmth)

5
Sensory Receptors

• Photoreceptors
• detect light (rods and cones)
• Chemoreceptors
• detect chemical molecules
• taste (taste buds), smell (olfactory
  epithelium), pH, osmolarity, pO2, pCO2, Na
• Nociceptors
• detect pain sensation (free nerve endings)

6
Sensory System

• somatic sensory area I and sensory association
  areas
• contralateral represenation
• network of neurons between thalamus, visual
  cortex, auditory cortex, and motor cortex
• adaptation of sensory receptors
  (desensitization)
• convergence vs. divergence of neurons
• Wernickes area for language comprehension
  (auditory receptive, visual, and Wernickes
  aphasia)

7
Motor System

• dominant hemisphere
• contralateral system
• Primary motor cortex
• control of voluntary movements
• topographic organization
• Premotor area
• pattern of movement involving group of muscles
• Supplementary motor area
• bilateral movements
• positional and fixation movements

8
Motor System

• Brocas area and speech
• receives inputs from Wernickes area
• speech response and articulation (motor aphasia)
• Voluntary eye movement field
• eye and eyelid movements (blinking)
• Head rotation area
• directional movement
• associated with eye movement field
• Hand skills area
• coordinate movements of hands

9
(No Transcript)
10
(No Transcript)
11
Motor Cortex

• primary and secondary motor areas
• glutamate (excitatory) and GABA (inhibitory)
• thalamocortical system
• inputs from primary and secondary sensory areas
• parieto-occipitotemporal association area
  (spatial coordination, language comprehension,
  naming of objects)
• prefrontal association area (complex pattern and
  sequences of motor activities, working memory)

12
(No Transcript)
13
Basal Ganglia

• caudate nucleus, putamen, globus pallidus,
  substantia nigra, subthalamic nucleus
• complex patterns of motor activity
• putamen circuit (patterns of motor activity)
• caudate circuit (sequences of motor activity)
• dopamine, GABA, NE, serotonin, glutamate
• Parkinsons disease and Huntingtons Chorea

14
Brain Stem

• midbrain, pons, and medulla
• controls respiration, cardiovascular system, GI
  function, equilibrium, eye movement
• reticular and vestibular nuclei (positional and
  antigravity muscles)

15
(No Transcript)
16
Cerebellum

• control of rapid muscular activities
• lesion causes loss of coordination of motor
  activities
• Functions
• sequences motor activities
• corrective adjustments
• program of muscle contraction (motor cortex)
• positional changes of body (sensory cortex)
• peripheral sensory feedback (expected vs. actual)

17
Intelligent Functions

• Limbic association areas
• behavior, emotions, motivation
• Thought
• cerebral cortex, thalamus, limbic system,
  reticular formation
• Memory
• hippocampus
• positive vs. negative memory
• generation of synaptic transmission (memory
  trace)
• short-, intermediate-, and long-term memory
• consolidation of memory

18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
Neuron

• Dendrite
• receptive area for transmission of impulse
• Cell body (soma)
• integration center (gray matter)
• nuclei (CNS), ganglia (PNS)
• Axon
• conducts signals away from neuron (white matter)
• axon collaterals

26
Membrane Potential

• Resting membrane potential
• ECF Na142 mM, K4 mM
• ICF Na14 mM, K140 mM
• concentration gradient
• ion channels
• -60-90 mV
• maintained by Na-K-ATPase pump

27
(No Transcript)
28
Action Potential

• Depolarization phase
• opening and closing of Na channels
• Repolarization phase
• opening and closing of K channels
• Hyperpolarization phase
• leakage K channels
• Threshold potential
• -65-45 mV
• all-or-none principle
• Refractory period

29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
Myelination

• myelin sheath consists of sphingomyelin
• synthesized by oligodendroglia (CNS) Schwann
  cells (PNS)
• node of Ranvier (saltatory conduction)
• pain neurons (nociception)

35
(No Transcript)
36
Synapse

• presynaptic vs. postsynaptic neuron
• chemical synapse (neurotransmitters)
• excitatory (EPSP) vs. inhibitory (IPSP) synapse
• axo-dendritic, axo-somatic, and axo-axonic
  synapse

37
Events of Synapse

• Action potential arrives at presynaptic terminal
• Opening of Ca2-channels and influx of Ca2
• Aligning of synaptic vesicles and fusion with
  presynaptic membrane
• Release of neurotransmitters into synaptic cleft
  via exocytosis
• Neurotransmitters bind to postsynaptic membrane
  receptors
• Activation of ion channels, second messenger
  system

38
(No Transcript)
39
Removal of Signals

• diffusion of neurotransmitters into interstitium
• enzymatic degradation of neurotransmitters
  (acetylcholinesterase, monoamine oxidase,
  catechol-O-methyltransferase)
• re-uptake of neurotransmitters into presynaptic
  terminal

40
(No Transcript)
41
Accommodation

• refractive power of lens (changes from 20-34
  diopters due to change in lens shape)
• 70 zonular fibers attached radially to lens and
  ciliary body
• ciliary muscle (meridional and circular fibers)
  is controlled by parasympathetic CN III
• contraction of ciliary muscle ? relaxes zonular
  fibers ? spherical lens (highest diopter) ? near
  vision
• relaxation of ciliary muscle ? tension on
  zonular fibers ? flattened lens (lowest diopter)
  ? far vision

42
Vision

• Emmetropia
• normal eye
• Presbyopia
• loss of accommodation (14 diopters ? 0 diopter)
• Hyperopia
• short eyeball or weak accommodation
• light is focus behind the retina for near vision
• corrected by convex lens

43
(No Transcript)
44
(No Transcript)
45
Vision

• Myopia
• lengthy eyeball or excessive accommodation
• light is focused in front of retina for far
  vision
• corrected by concave lens
• Astigmatism
• refractive error due to uneven curvature of lens
• Cataracts
• cloudy or opaque lens due to denaturation and
  coagulation of lens proteins
• Glaucoma
• increased intraocular pressure (2030 mmHg)

46
(No Transcript)
47
Pupil

• iris alters pupillary diameter (pupillary
  aperture)
• low pupillary aperture ? greater depth of focus

48
Intraocular Fluid

• Aqueous humor
• synthesized by ciliary processes (23 ml/min)
• freely flowing fluid consisting of Na, Cl-,
  HCO3-, glucose, AA, H2O
• secreted into posterior chamber ? anterior
  chamber ? meshwork of trabeculae ? canal of
  Schlemn ? extraocular veins
• Vitreous humor
• gelatinous mass consisting of proteoglycans
• in vitreous body

49
Intraocular Pressure

• 1220 mmHg
• regulated by resistance to outflow of aqueous
  humor
• 2.5 ml/min via canal of Schlemn
• phagocytes at trabecular meshwork destroys
  debris
• Glaucoma
• compression of optic nerve due to increased IOP
• acute accumulation of WBC or debris with injury
• chronic fibrous occlusion of trabeculae

50
(No Transcript)
51
Retina

• Layers of retina
• pigment layer ? photoreceptor layer ? nuclear
  layer ? ganglionic layer ? optic nerve fibers
• Photoreceptors
• 100 million rods (light) and 3 million cones
  (color)
• fovea center of retina consisting mostly of
  cones
• rhodopsin (rods) vs. color pigments (cones)
• melanin within pigment layer prevents light
  reflection
• Blood supply
• central retinal artery and choroid vessels

52
(No Transcript)
53
Conduction of Sound

• pitch of sound 2020,000 Hz (frequency)
• loudness of sound db (intensity)
• tympanic membrane ? malleus ? incus ? stapes ?
  oval window ? cochlea

54
Cochlea

• scala vestibuli, scala media, scala tympani
• vestibular membrane, basilar membrane, tectorial
  membrane
• perilymph fills SV ST, CSF (high Na and low
  K)
• endolymph fills SM, secreted by stria
  vascularis (low Na and high K)
• Basilar membrane
• 20,00030,000 elastic basilar fibers fixed at
  modiolus
• length of fibers increase but diameter decreases
  from base to helicotrema
• rigidity decreases from base to apex
• high frequency (base) vs. low frequency (apex)

55
(No Transcript)
56
Organ of Corti

• inner (90 stimuli to auditory nerves) and
  outer hair cells
• Hair cells
• stereocilia from hair cells are embedded in
  tectorial membrane
• bending of stereocilia toward scala vestibuli
  stimulates
• Intensity of sound
• altered amplitude of vibration of hair cells ?
  altered excitation rate of nerve endings

57
Deafness

• Nerve deafness
• impairment of cochlea or auditory nerve
• degeneration of cochlea (aging)
• Conduction deafness
• impaired transmission of sound
• fibrosis of ossicles, infection (osteosclerosis)

58
Vestibular System

• vestibular apparatus detects equilibrium
• Linear acceleration
• utricle (horizontal) and saccule (vertical)
• macula as sensory organ contains hair cells
  embedded in otolithic membrane
• bases of hair cells synapse to form vestibular
  nerve
• Angular acceleration
• 3 semicircular canals filled with endolymph
• ampulla as sensory organ contains hair cells

59
Taste

• 3,000 10,000 taste buds
• sour, salty, sweet, and bitter (highest
  sensitivity)
• sweet and salty taste buds (tip of tongue)
• sour taste (lateral sides of tongue)
• bitter taste (posterior tongue and soft palate)
• taste preference

60
Smell

• 100 million olfactory cells
• olfactory receptors line olfactory membranes
• floral, musky, camphoraceous, pepperminity,
  ethereal, pungent, putrid
• associated with emotion