14 The Senses Flashcards
THE SENSES
What is sensation?
The concious perception of stimuli
Sensation does not occur until nerve signals arrive at the cerebral cortex of the brain
THE SENSES
How does sensation occur?
- sensory receptors respond to environmental stimuli
- nerve impulses travel to the cerebral cortex
- sensation!
THE SENSES
What is sensory adaptation?
Sensory adaptation is the decrease in stimulus perception which can occur with repetative stimuli (i.e. odor or vision)
THE SENSES
What are sensory receptors?
Dendrites of neurons specialized to detect certain types of stimuli:
- Exteroceptors: detect stimuli from outside the body (taste, hearing, vision)
- interoceptors: receive stimuli from inside the body (change in blood pressure, pH, osmolarity (salt), gastrointestinal or urinary tract distention)
THE SENSES
Types of sensory receptors
- chemoreceptors: respond to nearby chemicals - taste, smell, pH, etc.
- pain receptors: type of chemoreceptor that responds to chemical released by damaged tissues
- photo receptors: responds to light energy
- mechanoreceptors: responds to forces such as pressure - sound, position, touch
- thermoreceptors: stimulated by temperature change
THE SENSES
The Knee-Jerk Reflex
Proprioceptors called spindle cells inside muscle monitor muscle length to maintain posture.
When suddenly stretched, the spindle cells fire action potentials to spinal cord interneurons, causing them to send action potentials back down motor neurons.
This causes contraction of mucle fibers to decrease muscle length, and return to its original length.
THE SENSES
What mechanoreceptors are involved in reflex actions?
Proprioceptors
They are in skin, muscles, joints, tendons, organs
THE SENSES
Cuteneous Receptors
In the dermis, they make the skin sensitive to touch, pressure, pain and temperature.
THE SENSES
Taste Receptors
Sensitive to sweet, sour, salty and bitter tastes in food
3,000 taste buds, mostly on the tongue
80-90% of what we perceive is taste is actually due to the sense of smell
THE SENSES
Smell Receptors
10-20 million olfactory cells (modified neurons) in the nasal cavity
Olfactory cells are in the roof of nasal cavity. Each has only one of several thousand types of receptor proteins - each smell stimulates certain combinations of receptors.
Direct connection to the Limbic System of the brain, generates emotion and memory.
THE SENSES
Vision: Anatomy of the Eye
What are the 2 compartments of the eye?
- Anterior Chamber: between the cornea and lens filled with a clear fluid called aqueous humor
- Posterior Chamber: most of the eye, behind the lens, contains a clear gelatinous material called vitreous humor.
THE SENSES
The Eye’s 3 layers
- Sclera: outer, mostly white and fibrous except the cornea (clear)
- Choroid: middle, darkly pigmented vascular layer
- Retina: inner layer containing photoreceptors
THE SENSES
Front of the Eye: Cornea
Cornea
Transparent portion of the sclera that (along with the lens) transmits and refracts (bends) light
THE SENSES
Front of the Eye: Iris
Iris
colored portion of the eye, controls how much light enters the eye by opening and closing pupil, the dark hole in the center is the iris
THE SENSES
Front of the Eye: Ciliary Body
Ciliary Body
Muscular structure behind the iris that controls the shape of the lens and iris
THE SENSES
Front of the Eye: Lens
Lens
refracts and focuses light rays on the retina
(you strain more when you look at things close up)
THE SENSES
Retina
Contains photoreceptors called rods and cones
The fovea centralis is a central area of the retina densely packed with cones, where images are focused
Rods and cones synapse with neurons in the retina that form the optic nerve, which takes nerve impuses generated by light striking the retina to the brain
THE SENSES
Rods
Located mostly in the periphery of retina
important for peripheral and night vision - extremely sensitive to low light, but not sensitive to color
THE SENSES
Cones
Located mostly in the fovea centralis (central retina)
Important for detection of central fine detail and color but not sensitive to dim light
THE SENSES
Photoreceptors of the retina
Rods, contain visual pigment Rhodopsin, made of opsin and retinal (made from Vit A)
Cones, also contain Rhodopsin, but 3 different kinds of cones contain red, green and blue pigments, each sensitive to different wavelength (colors) of light
Light energy causes rhodopsin to split into retinal and opsin. This causes a cascade of chemical reactions that eventually result the rod or cone sending neural impulses to the brain.
THE SENSES
Blind Spots
where the optic nerve leaves the eye.
Having no cones and rods, the spot on the retina with no vision.
THE SENSES
How the eyes are connected to the brain?
We have stereo vision since our eye is divided.
Both eyes contain:
right visual cortex
left visual cortex
thalamic nucleus
optic tract
optic charisma
optic nerve
THE SENSES
Abnormalities of the Eye
Color Blindness: genetic disability most common in males in which they usually cannot correctly see shades of red and green.
Cataracts: lens of the eye become cloudy
Glaucoma: fluid pressure builds up in the eye
Astigmatism: the cornea or lens is uneven, leading to a fuzzy image on the retina
Nearsightedness: eyeball is too long making it hard to see far away objects
Farsightedness: eyeball is too short making it hard to see near objects
THE SENSES
Anatomy of the Ear
3 Divisions:
Outer Ear - for hearing, air filled, pinna to ear drum
Middle Ear - for hearing, air filled, ear drum to oval window
Inner Ear - for hearing and balance, cochlea and semicirular canals, filled with fluid (no air)
