Special Senses Flashcards
Physiology
Difference between somatic and special senses
Receptors for somatic senses are widely distributed, whereas special senses receptors located in specialised organs in the head
Somatic signals interpreted by parietal lobe, organised according to body areas, whilst
special senses signals interpreted by specialised
areas of the brain
Five basic tastes
Bitter
Sour
Salty
Sweet
Umami
Taste sensation of salty (explain)
The substance responsible for this taste is the salt crystal made of sodium and chloride. Mineral salts such as those containing potassium or magnesium can also cause a salty taste.
Taste sensation of sweet (explain)
Usually due to sugar or derivatives such as fructose or lactose. But other types include some protein building blocks like amino acids, and also alcohols in fruit juices or alcoholic drinks.
Taste sensation of sour (explain)
Most things that taste sour are acidic solutions like lemon juice or organic acids. This “sour”
sensation is caused by hydrogen ions.
Taste sensation of bitter (explain)
Bitter tastes are caused by many different substances. e.g. alkaloids like nicotine & caffeine
There are about 35 different proteins in the sensory cells that respond to bitter substances.
Taste sensation of umami (explain)
The savoury taste, which can be compared to the taste of a meat broth, is usually caused by glutamic acid (ripe tomatoes, meat and cheese) or aspartic acid (legumes, chicken and eggs).
Smell - Pathway to the brain (explain)
40,000,000 olfactory receptor neurons in olfactory bulb
->
olfactory tract
->
olfactory cortex of temporal lobe - conscious sensation of smell
-> amygdala (emotional response) OR hippocampus (memory)
After being exposed to a smell for an extended period, our brain stops registering it—this is called “olfactory adaptation.“
Sense of Smell Peaks in Spring and Summer: Research shows that our sense of smell can be more sensitive in warmer temperatures, likely because heat causes molecules to move faster, making scents more noticeable.
Our bodies release subtle chemical signals (called pheromones) that others can detect, even unconsciously. Studies have shown that people can sometimes pick up on fear or happiness through smell alone. In humans, pheromones are believed to play a subtle but fascinating role in attraction.
3 layers of the eyeball
- Sclera and Cornea - outer layer
- Uvea (vascular) - middle layer
- retina - inner layer
The Lens (explain)
Focuses Light on the Retina - bends incoming light rays to form a clear image on the retina
Accommodation for Distance -
1. For close objects - ciliary muscles contract, suspensory ligaments slacken, allows the lens to become more curved, focuses lights from nearby objects
2. For distant objects - ciliary muscles relax, suspensory ligaments taught, making lens thinner, focuses light from far away objects
Fine-Tuning visual clarity - works with the cornea to adjust focus and provide sharp vision
Vision - The Retina (explain)
Derived from neuroectoderm – an extension of the brain
Comprises 2 layers of nerve cells:
1. Outer retinal pigmented ‘epithelium’
2. Inner sensory retina
The sensory retina is made of 9 layers of different cell types. Contains the rods and cones – specialist photoreceptor neurons
Four cell groups are found here:
*Photoreceptor neurons – rods & cones
*Conducting neurons – bipolar & ganglion cells
*Association neurons –horizontal & amacrine cells
*Neuroglial cells – Müller cells
Vision - Rods and Cones (explain)
To allow us to visualise our surroundings light energy is converted into action potentials so that a signal may be sent to the visual cortex of the occipital lobe.
This is carried out specifically by the photoreceptor cells
Rods - perceive light intensity (pigment rhodopsin)
Cones - perceive colour
Rhodopsin enables vision in dim light conditions by a process called dark adaptation, it greatly increases the sensitivity of the rods to light.
Vision - Optic Nerve (explain)
At the optic disk, axons from the ganglion cells merge to
form the optic nerve.
This is also known as the blind spot, as there are no photoreceptors present here
Hearing - Ossicles (explain)
3 ossicles :
- malleus (hammer)
- incus (anvil)
- stapes (stirrup)
Composed of compact bone and articulated by synovial joints
Work like a lever system increasing the force transmitted – convert sound waves to mechanical (hydraulic) vibrations in
tissues and fluid-filled chambers
Stapedius & tensor tympani are skeletal muscles that dampen
effects of loud noise
Transmit vibrations to the oval window (opening of the bony
labyrinth of inner ear)
Hearing - Cochlea (explain)
Spiral bony canal with central bony axis (modiolus).
Bony spiral = Bony labyrinth.
Modiolus contains the spiral ganglion and cochlear nerve.
Cochlear duct (Scala media) – endolymph-filled part of membranous labyrinth runs up the middle of the bony spiral.
Hearing - Organ of Corti (explain)
- Cochlear duct divides cochlea into 3 parallel chamber
- Above and below the cochlear duct are two perilymph-filled chambers - Scala vestibuli (upper) and Scala tympani (lower) – they communicate with each other at the apex of the cochlea through a small channel
- The 3 contiguous spiral compartments separated by
membranous partitions extend the full length of the cochlea
Mechanism of Hearing (5 steps)
- Sound waves enter ear and cause the tympanic membrane to vibrate
- Tympanic membrane vibration moves auditory ossicles; sound waves are amplified
- The stapes at the oval window generates pressure waves in the perilymph within the scala vestibuli
- Pressure waves cause the vestibular membrane to move, resulting in pressure wave formation in the endolymph within the cochlear duct and displacement of a specific region of the basilar membrane. Hair cells in the organ of Corti are distorted, initiating a nerve signal in the cochlear branch of CN VIII
- Remaining pressure waves are trasnferred to the scala tympani and exit the inner ear via the round window
Mechanism of Hearing - further details
Displacement of stereocilia because of shearing stress
between tectorial membrane and basilar membrane causes hair cells to depolarise sending impulses to auditory cortex via cochlear nerve.
High frequency sounds cause maximal vibration of basilar
membrane at base of cochlea.
Amplitude discrimination (loudness) depends on degree of displacement of basilar membrane.
Hearing loss (3)
- Auditory processing disorder (brain problem)
- Conductive (outer/middle ear problem) - fluid/earwax build-up, perforated eardrum, damaged ossicles
- Sensorineural (cochlea problem) - ototoxic medications, loud noise, age
