BIO10004 WK6

• Olfaction (sense of smell)


  Reaches the olfactory epithelium, carries odorant molecules, highly modified neurons, cilia extend to the mucus lining the epithelial surface, interact with odorant-binding receptor proteins

  
• Olfactory organs


  • Located in the nasal cavity, contain olfactory hairs and olfactory receptors, can distinguish 2000-4000 different odours

  
• Olfactory pathways


  Olfactory nerve (cranial nerve NI) - bundle of olfactory receptor axons penetrate the cribriform plate, enter the cranium, synapse in the olfactory bulb of the cerebrum, axons leave the olfactory bulb and travel along the olfactory tract to the olfactory cortex

  
• Sense of taste


  Provides information about food and liquid consumed, five primary taste sensations: saltiness, sourness, bitterness, sweetness, savouriness (umami)
• Sensory organs of taste

  • Papillae contain taste buds, taste receptor cells
• Vision


  Humans rely on vision more than any other special sense, enables the immediate observation of distant objects, visible light is electromagnetic radiation with a wavelength of approximately 400–700 nm
• Iris

  Thin, annular structure responsible for controlling the diameter and size of the pupil, eye colour is defined by the iris
• Retina


  • Thin layer of tissue that lines the back of the eye on the inside, located near the optic nerve, receives light that the lens has focused, converts the light into neural signals, sends these signals on to the brain for visual recognition
• View of retina


  • Optic nerve, major blood vessels of the retina, fovea

  
• Photoreceptors


  • Rods and cones
• Auditory system (sense of hearing)


  Our sense of hearing enables us to detect and interpret sound waves, sound waves enter our body via the ears, the inner ear is shared between two sensory modalities: hearing and equilibrium, both are based on mechanoreceptors (hair cells), cranial nerve VIII (vestibulocochlear nerve) serves both hearing and equilibrium
• Sound waves


  • Hearing 20 Hz -20 kHz, best around 1 kHz
• External ear


  • Auricle (pinna), external acoustic meatus (ear canal), tympanic membrane (eardrum), earwax (cerumen) has lubricating and antibacterial properties
• Middle ear


  • Tympanic cavity contains auditory ossicles (ear bones): malleus (hammer), incus (anvil), stapes (stirrup)
• Inner ear


  • Serves both hearing and equilibrium, cochlea contains the cochlear duct, oval window connected to the base of stapes, round window separates the perilymph of cochlear chambers from air-filled middle ear, semicircular ducts convey information about the rotational movements of the head
• Endocrine system


  Distinctions between nature of cellular communications compared to nervous system
• Classes of hormones


  • Amino acid
  • Protein
  • Lipid derivatives
• Lipid derivative hormones


  • Eicosanoids (derived from arachidonic acid)
  • Steroid hormones (derived from cholesterol)
• Eicosanoids


  Important paracrines that coordinate cellular activities and affect enzymatic processes
• Steroid hormones


  Released by reproductive organs, adrenal glands, and kidneys; remain in circulation longer than secreted peptide hormones
• Hormone transport and inactivation

  • Rapidly released into capillary beds, diffuse throughout body via circulation
  • Inactivated by binding to receptors, absorption/breakdown by cells/liver/kidneys, enzymatic breakdown

  
• Hormone receptors and action

  Hormones can cross cell membrane (direct activation) or rely on second messenger (G-protein)

  
• Pituitary gland


  • Anterior portion releases hormones controlled by hypothalamus
  • Posterior portion releases hypothalamic hormones

  
• Thyroid gland


  • Ductless gland inferior to larynx, two lobes
  • Releases T3 and T4 hormones that bind to receptors in cytoplasm, mitochondria, and nucleus to increase ATP production

  
• Adrenal glands


  • Small, triangular-shaped glands on top of kidneys
  • Produce hormones that regulate metabolism, immune system, blood pressure, stress response, and other essential functions

  
• Pancreas


  • Endocrine gland and exocrine organ
  • Endocrine portion has islet cells that produce hormones (insulin, glucagon, growth hormone inhibiting hormone, pancreatic polypeptide)

  
• Control of blood glucose

  1. Critical function for cells

  2. Needs to be tightly controlled

  3. Circulating energy in body

  4. Complex balance between storing and releasing

  5. Pancreas manages with separate hormones
• Diabetes Mellitus is a disruption of glucostasis
• Olfactory cells


  • Olfactory receptor cells (sense odor and contain cilia)
  • Supporting cells
  • Basal (stem) cells (replacing old and damaged olfactory receptor cells)
• Olfactory nerve


  CN I formed out of a collection of olfactory receptor cell axons, which pass through the cribriform plate and into the roof of the nasal cavity
• Olfactory bulb


  It is the relay station of the olfactory pathway and contains olfactory glomeruli
• Olfactory tract


  It is made up of the axons of mitral relay neurons
• Olfactory cortex


  • Piriform cortex
  • Amygdala
  • Entorhinal cortex
• Olfactory reception


  1. Binding of an odorant to a G protein–coupled receptor in the plasma membrane of an olfactory dendrite

  2. Creation of a depolarization called a generator potential

  3. Generation of action potentials

  4. Carrying of action potentials to the CNS by sensory afferent fibers
• Olfactory pathways


  1. Afferent fibers leave olfactory epithelium and collect into 20 or more bundles

  2. Bundles penetrate the cribriform plate of ethmoid bone to olfactory bulbs of cerebrum where synapse occurs

  3. Axons leaving the olfactory bulb travel along olfactory tract to olfactory cortex of cerebral hemisphere
• Olfactory stimulation is the only type of sensory information that reaches the cerebral cortex directly
• Sensory pathway of taste

  1. Sensory information travels along the facial, glossopharyngeal and vagus cranial nerves, synapsing with neurons of the solitary nucleus in the brain stem

  2. Axons from the solitary nucleus project to the ventral posterior nucleus of the thalamus

  3. Axons from the ventral posterior nucleus project to the gustatory cortex of the cerebral cortex, where taste is processed and consciously perceived
• Sensory pathway of eye sight

  1. Light enters the eye and projects onto the retina, which contains photoreceptors (cones and rods)

  2. Signals from the retinal photoreceptors go to bipolar cells, then to the ganglion cells

  3. Axons of the ganglion cells converge, forming the optic nerve (CN II)

  4. Optic nerve to the optic tract, with hemi decussation of optic nerve fibers at the optic chiasm

  5. From the optic tract, most fibers synapse in the lateral geniculate nucleus (LGN) of the thalamus, with some going to the superior colliculus

  6. From each LGN, neurons travel in the optic radiations (geniculocalcarine fibers) to the primary visual cortex (striate or calcarine cortex, or V1 or area 17)
• Auditory pathway


  1. Sound waves are funneled by the external ear/pinna into the auditory canal, causing the tympanic membrane to vibrate

  2. The vibrations are transmitted through the ossicles (malleus, incus, stapes) to the oval window

  3. The oval window vibrations move the perilymph in the scala vestibuli and scala tympani, causing the basilar membrane to vibrate

  4. The vibrations of the basilar membrane bend the stereocilia on the hair cells of the organ of Corti, generating action potentials in the cochlear nerve

  5. The cochlear nerve sends the signal to the cochlear nuclei in the brainstem, which then send the information to the superior olivary complex, inferior colliculus, and ultimately the auditory cortex
• Endocrine system


  Uses hormones as endocrine communication chemical messengers