Anatomy and Histology

1. Level of odor-producing chemicals reaches threshold

2. Receptor potential followed bay action potential are formed

3. Information passed to olfactory nerves, in olfactory bulb

4. Goes into the thalamic and olfactory centers of the brain

5. Received information is interpreted, integrated and memorized for future reference

6. Formation of olfactory memories are also processed by components of limbic system : gyrus and hippocampus 

• Taste buds: sense organs that respond to gustatory stimuli

• Open at the surface to the taste pore

• The majority are locate on the tong projections papillae

• Some in the lining of the mouth and throat (mainly in children)

• Chemoreceptors

• Ca 10000 taste buds in adults

• 3 types of cells:

  • Gustatory cells

  • Supporting cells

  • Basal cell

• Regional differences in their distribution

• Fungiform papillae: ca. 5 taste buds

• Circumvallate papillae: ca 100 taste buds

• Filiform papillae: no taste buds 

Chemoreception

• 10-12 day life span.

• 3 types of cells:

  • Gustatory cells: long microvilli extending into the pore. Taste receptors

  • Supporting cells: long microvilli extending into the pore

  • Slender microvilli, taste hairs extend into surrounding fluids via the taste pore

  • Connected to nerve fibbers

  • Basal cell: precursor of the other cell types 

Unencapsulated: 

1. 1)  Free nerve endings

2. 2)  Merkel cells/tactile discs

3. 3)  Root hair plexi

Papillary layer of the dermis Light touch, pressure, movement Tonic, small receptive field 

Unencapsulated: 

1. 1)  Free nerve endings 

2. 2)  Merkel cells/tactile discs 

3. 3)  Root hair plexi 

Papillary layer of the dermis Light touch, pressure, movement Tonic, small receptive field 

Unencapsulated: 

1. 1)  Free nerve endings 

2. 2)  Merkel cells/tactile discs 

3. 3)  Root hair plexi 

Papillary layer of the dermis Light touch, pressure, movement Tonic, small receptive field 

Encapsulated:

1) Meissner’s/tactile corpuscle

Eyelids, fingertips, lips, nipples, genitalia Coiled, interwoven dendrites covered by Schwann cells in a fibrous capsule (ø 40-60μm) Light touch, movement, vibration

Fast adaptation

2) Ruffini corpuscle

Dermis
Dendrites interwoven with collagenous fibres extending into the dermis
Pressure and distortion of the skin
Slow adaptation
3) Pacini/lamellated corpuscle
Dermis, fingers, breasts, genitalia, viscera Dendrites shielded in concentric cell layers Large, ca. 1mm long
Deep pressure, vibration and pulsing
Fast adaptation 

Encapsulated: 

2) Ruffini corpuscle 

Dermis
Dendrites interwoven with collagenous fibres extending into the dermis
Pressure and distortion of the skin
Slow adaptation

Encapsulated:

Pacini/lamellated corpuscle
Dermis, fingers, breasts, genitalia, viscera Dendrites shielded in concentric cell layers Large, ca. 1mm long
Deep pressure, vibration and pulsing
Fast adaptation 

• Monitor the position of joints, tendons, ligaments, muscles

• Integrated with vestibular system information

• Muscle spindles: muscle length

• Golgi organs: tendon tension

• Free nerve endings: joint tension,

• Pressure, movement, stretching 

• Stretch receptors in organ walls

• Free nerve endings branching within an elastic wall of a hollow organ

• Stretching distorts dendritic branches

• Alteration of action-potential generation 

Fungiform papillae: ca. 5 taste buds 

Circumvallate papillae: ca 100 taste buds 

Filiform papillae: no taste buds 

Types of Receptors

Classification by location

• Exteroceptors: located on or near body surface. Respond to stimuli that arise external to the body. Detect pressure, touch, pain and temperature

• Internoceptors or Visceroceptors: located internally. Receive stimuli from the internal body environment. Activated by pressure, stretching and chemical changes. Also mediate hunger and thirst.

• Proprioceptors: specialized type of visceroceptors. Located in skeletal muscle, joint capsules and tendons. Information of body movement, spatial orientation and muscle stretch 

1. Classification by structure

   • Free nerve endings

     • Simplest, most common

     • Terminates in dendritic knobs

   • Encapsulated nerve endings

     • Connective tissue capsule surrounding their terminal or dendritic end

     • Primarily mechanoreceptors 

Classification by stimulus detected

• Nociceptors: Pain

  • Location: skin, joints and bone periostea, blood vessels, some viscera

  • Free nerve endings, large receptive field (making localizing the source difficult)

  • Thermo, mechano and chemoreceptors

  • Fast pain: “stabing” pain perceived in primary sensory cortex, triggers somatic reflexes

  • Slow pain: “aching” pain activates the thalamus and reticular formation

• Thermoreceptors: Temperature

  • Location: skin dermis, skeletal muscle, liver, hypothalamus

  • Cold and warm receptors, phasic, i.e. adaptation

  • Same pathways as nociception to the primary sensory cortex, thalamus and reticular formation

• Chemoreceptors: Chemical compounds

  • Location: respiratory centres (pH and Pco2), carotid bodies (pH, Pco2, Po2),

    aortic bodies (pH, Pco2, Po2)

  • Water and lipid soluble compounds

• Mechanoreceptors: Touch

• Photoreceptors: Light - 

  • Only in the eye 

Hornhaut (Augen)

• Two components: sclera and cornea

• Provides: structure, protection, points of attachment

• Tough fibro-elastic capsule

• Sclera = opaque, dense

  fibrous connective tissue,

  the “whites” of the eye

• Provides attachment for 6

  extra-ocular muscles

• Nerves and vessels

  penetrate the anterior surface (i.e. blood-shot eyes)

• Corneal limbus: separates sclera and cornea 

Three components: choroid, ciliary body, iris 

Cuboidal epithelium

1. Pigmented epithelial cells –single layer

2. Photoreceptor layer - rod and cone processes

3. Outer limiting membrane - thin eosinophilic structure. Separates photoreceptor layer from outer nuclear layer. Line of intercellular junctions between Muller cells and photoreceptor cells

4. Outer nuclear layer - contains the cell bodies of the rod and cone photoreceptors.

5. Outer plexiform layer - contains synaptic connections between the short axons of the photoreceptor cells and integrating neurones

6. Inner nuclear layer - contains the cell bodies of the integrating neurons

7. Inner plexiform layer - synaptic connections of integrating neurons with

   dendrites of neurones whose axons form the optic tract.

8. Ganglion cell layer – contains the cells bodies of the optic tract neurons.

9. Optic nerve fibers layer - layer of afferent fibres passing towards the optic disc to form the optic nerve.

10. Inner limiting membrane - demarcates the innermost aspect of the retina from the vitreous body VB. Basement membrane of Muller cells. 

• Ca. 100 Million in humans

• Monochrome

• More sensitive to light

• Allow night vision

• Accumulate rhodopsin (purple)

• Absent from fovea and macula

• Increased density toward the

  periphery of the retina 

• Ca. 6 Million in humans

• Color

• Less sensitive to light

• Need more light for stimulation

• Accumulate other opsins: red (60%), green (30%), blue (10%)

• Most densely concentrated in the fovea 

Tympanic membrane: separates the external auditory canal from the middle ear.

• Connective tissue membrane (fibrous layer) lined with skin (cuticular layer) on the outside and mucous membrane (mucous layer) on the inside

• Fibrous layer is mostly type II and III collagen

• Attached to the temporal bone via a

  fibrocartilagenous ring

• Inner surface attached to the handle of the malleus

• Ruptures can heal 

• Smallest bones of the body

• Malleus: handle (connected to tympanic membrane), neck, anterior process (attached to wall), head (articulates with incus)

• Incus: head (articulates with malleus), short limb (attached to wall), long limb (articulates with stapes)

• Stapes: head (articulates with incus), base (fits into oval window) 

Inside vestibule: Utricle and saccule

Inside of the cochlea-earing: Cochlear duct

By the canal-balance: Membranous semicircular canals