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Sensory System. Transmits sensory information collected by receptors to the CNS. Outline. 1- General principles of sensory physiology 2- The somatosensory System 3- Olfaction 4- Taste 5- Hearing and Equilibrium 6- Vision. Outline. 1- General principles of sensory physiology

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sensory system
Sensory System
  • Transmits sensory information collected by receptors to the CNS
outline
Outline

1- General principles of sensory physiology

2- The somatosensory System

3- Olfaction

4- Taste

5- Hearing and Equilibrium

6- Vision

outline3
Outline

1- General principles of sensory physiology

2- The somatosensory System

3- Olfaction

4- Taste

5- Hearing and Equilibrium

6- Vision

1 general principles of sensory physiology
1- General Principles of Sensory Physiology
  • Receptor physiology
  • Sensory pathways
  • Sensory coding
sensory receptors
Somatic

-- Chemoreceptors (taste, smell, smell)

-- Thermoreceptors (temperature)

-- Photoreceptors (vision)

-- Baroreceptors (sound, balance)

-- Proprioreceptors (muscle stretch)

Visceral

-- Chemoreceptors (chemicals in blood, osmoreceptors)

-- Baroreceptors (blood pressure)

Sensory receptors
sensory transduction
Receptors transform an external signal into a membrane potential

Two types of receptor cells:

- a nerve cell

- a specialized epithelial cell

Sensory transduction
receptor adaptation
Tonic receptors

-- slow acting, -- no adaptation: continue to for impulses as long as the stimulus is there

(ex: proprioreceptors)

Phasic receptors

-- quick acting, adapt: stop firing when stimuli are constant (ex: smell)

Receptor adaptation
sensory coding
A receptor must convey the type of information it is sending  the kind of receptor activated determined the signal recognition by the brain

It must convey the intensity of the stimulus the stronger the signals, the more frequent will be the APs

It must send information about the location and receptive field, characteristic of the receptor

Sensory coding
sensory pathways
The sensory pathways convey the type and location of the sensory stimulus

The type: because of the type of receptor activated

The location: because the brain has a map of the location of each receptor

Sensory pathways
outline11
Outline

1- General principles of sensory physiology

2- The somatosensory System

3- Olfaction

4- Taste

5- Hearing and Equilibrium

6- Vision

the somatosensory system
The Somatosensory System
  • Types of receptors

- Mechanoreceptors:

-- Proprioreceptors in tendons, ligaments

and muscles  body position

-- Touch receptors in the skin: free nerve endings, Merkel’s disks and Meissner’s corpuscles (superficial touch), hair follicles, Pacinian corpuscles and Ruffini’s ending

- Thermoreceptors: Warm receptors (30-45oC) and cold receptors (20-35oC)

- Nociceptors: respond to noxious stimuli

Figure 10.6

pain perception
Pain perception
  • Fast pain: sharp and well localized, transmitted by myelinated axons
  • Slow pain: dull aching sensation, not well localized, transmitted by unmyelinated axons
  • Visceral pain: not as well localized as pain originating from the skin  pain impulses travel on secondary axons dedicated to the somatic afferents  referred pain
referred pain
Referred pain

Figure 10.16a

outline19
Outline

1- General principles of sensory physiology

2- The somatosensory System

3- Olfaction

4- Taste

5- Hearing and Equilibrium

6- Vision

olfaction
Specialized neurons present in the olfactory epithelium in the nose.

They project cilia into a mucus layer. The cilia are able to bind to odorant molecules  the binding triggers an AP which is transmitted to the olfactory area of the olfactory bulb  olfactory cortex (lower frontal area and limbic system of the brain

Each olfactory receptor is specialized for 1 odorant molecule

Olfaction
outline21
Outline

1- General principles of sensory physiology

2- The somatosensory System

3- Olfaction

4- Taste

5- Hearing and Equilibrium

6- Vision

taste
Receptors for taste are modified epithelial cell present in taste buds located on the tongue, roof of the mouth and pharynxTaste
slide23
Four primary types of taste receptors : sour, salt, sweet and bitter (and a new one: umami)
  • The binding of the receptor to a taste molecule triggers the entry of calcium in the cell  release of neurotransmitter in a synapse with a neuron
neural pathway
Neural pathway
  • Taste impulses travel through nerves VII, IX and X to a gustatory nucleus in the medulla oblongata (cross over)  thalamus  gustatory cortex located in the parietal lobe in the mouth area.
outline27
Outline

1- General principles of sensory physiology

2- The somatosensory System

3- Olfaction

4- Taste

5- Hearing and Equilibrium

6- Vision

hearing
Hearing
  • Sounds are waves of compressed air traveling through space

- sound intensity wave height

- pitch  wave frequency

hearing31
1- The sound waves enter the external auditory canal and trigger vibrations of the tympanic membrane

2- The tympanic membrane induces a vibration of the ossicles

3- the last ossicle, the stapes, transmits amplified vibrations to the oval window

4- The vibrations induce waves in the perilymph of the various inner ear chambers

5- the round window absorbs excess energy and prevent wave reverberation

6- the fluid wave is transduced into an electrical signal by the auditory receptors, the organs of Corti located on the basilar membrane

Hearing
receptors for sound the organ of corti
The hair cells of the organ of Corti transduce fluid wave into an electrical signal

The energy of the wave causes the basilar and vestibular membrane to move, thus displacing the cilia from the organ of Corti

Receptors for sound: the organ of Corti
signal transduction
Movements of the cilia open or close potassium channels  changes in the state of polarization of the hair cell

Changes in potassium leakage due to cilia bending trigger changes in neurotransmitters exocytosis

The neurotransmitters send an electrical signal to an afferent neuron of the cochlear nerve

The louder the sound, the more the cilia bend, the more numerous are the APs produced

Signal transduction
coding for pitch
The location of the organs of Corti on the basilar membrane codes for pitch

- Organs of Corti located near the oval window are more sensitive to high pitch sounds while the ones located toward the tip of the cochlea respond more readily to low pitch sound

Coding for pitch
neural pathway for sounds
Neural pathway for sounds
  • Cochlear nerve  nucleus in medulla oblongata  thalamus  auditory cortex in the temporal lobe
  • So, how do we perceive the direction from which a sound is coming from?
equilibrium
Ability to detect head position and movement (or acceleration)

Change of speed = linear acceleration (utricle and saccule)

Turning = rotational acceleration (semi-circular canals)

Equilibrium
utricle and saccule
Sensory cells have cilia extending into a gelatinous material topped by otoliths

Saccule detects backward-frontward movement

Utricle detects changes relative to gravity

Utricle and saccule
semi circular canals
The receptors in the ampulla are hair cells with cilia extruding into a gelatinous mass (cupula)

When the head rotates, the cupula moves  cilia pulled APs (vestibular nerve  cerebellum …)

Semi-circular canals
outline44
Outline

1- General principles of sensory physiology

2- The somatosensory System

3- Olfaction

4- Taste

5- Hearing and Equilibrium

6- Vision

vision47
Vision
  • In order to see an object:

- 1- the pattern of the object must fall on the vision receptors (rods and cones in the retina)  accommodation

- 2- the amount of light entering the eye must be regulated (too much light will “bleach out” the signals)

- 3- the energy from the waves of photons must be transduced into electrical signals

- 4- The brain must receive and interpret the signals

accommodation
Accommodation
  • It is the process of adjusting the shape of the lens so that the external image fall exactly on the retina
accommodation49
Accommodation
  • Object is far  the lens flattens
  • Object is near  the lens rounds

Figure 10.25

accommodation abnormalities
Accommodation abnormalities
  • Myopia
  • Hyperopia
  • Astigmatism: the cornea is irregular  irregular pattern of vision
  • Presbyopia: stiffening of the lens occurring with aging  increased difficulty with near vision
regulation of the amount of light entering the eye
The iris controls the amount of light entering the eye cavities

The contraction of radial or circular smooth muscles located within the iris permit changes in the pupil diameter

Regulation of the amount of light entering the eye
eye abnormalities
Glaucoma

Cataract

Eye abnormalities

Figure 10.27b

retinal structure
Three cell layers:

-- outer layer: photoreceptors- rods and cones

-- middle layer: bipolar neurons

-- inner layer: ganglion cells

Retinal structure
phototransduction
Photons hit the pigment of a photoreceptor    enzymes are activated in the cell which modify its state of polarization  the signals are sent to visual area of the occipital lobe of the brain through the optic nervePhototransduction
neural processing
Neural processing
  • The bipolar neurons and ganglion cells process the signal
  • In the fovea where the acuity is the highest: 1 cone  1 bipolar cell  1 ganglion cell
  • At the periphery: many rods  1 bipolar cell … acuity is much decreased
  • Other cells in the retina participate in signal processing
neural pathway62
What will happen if the left optic nerve is severed?

What will happen if a person has a tumor in the pituitary gland (just below the optic chiasmata) and the inner fibers are destroyed?

What will happen if a person suffers a brain tumor on the right side of the brain around the lateral geniculate body?

Neural pathway
readings
Readings:
  • Chp. 10, p. 253-301
  • Not expected:
  • Pain gate-control theory, p. 268.
  • Phototransduction, p. 277-280