Chapter 9 - The Senses Flashcards
Describe the sensory pathway (4 parts)
1) Receptors - detect changes and generate impulses. Usually very specific with respect to the kinds of changes they respond to. (retina detects light rays). Once a stimulus has affected receptors, they all respond in the same way by generating electrical nerve impulses.
2) Sensory Neurons - transmit impulses from receptors to the CNS. Found in both spinal nerves and cranial nerves - each carries impulses from only one type of receptor.
3) sensory tracts - white matter in trhe spinal cord or brain that transmits the impulses to a specific part of the brain
4) Sensory areas- most are in the cerebral cortex. They feel and interpret sensations. Begins in infancy and continues throughout life.
What are the characteristics of sensations? (5 parts)
1) Projection - the sensation seems to come from the area where the receptors were stimulated (touch something, the sensation seems to be in your hand, but is felt by your cerebral cortex). The ability to know the specific area of the body that is receiving the brains projection is called localization.
2) Intensity - some sensations are felt more distinctly and to a greater degree than are others. When more receptors are stimulated, more impulses will arrive in the sensory area of the brain. (dim vs bright light)
3) Contrast - the effect of a previous or simultaneous sensation on a current sensation, may be exaggerated or diminished. (jumping into water on hot day, water may feel very cool at first, and seem colder than it actually is)
4) Adaptation - becoming unaware of a continuing stimulus. (water in pool seemed cold at first but seems to warm up after a few minutes)
5) After-image - the sensation remains in te consciousness even after the stimulus has stopped (very bright light seems to linger, ears are ringing)
What are cutaneous senses?
Skin contains thousands of receptors - dermis of the skin and subcutaneous tissues contain receptors for sensations of touch, pressure, heat,cold, itch, and pain.
-They provide us with information about the external environment and also about the skin itself.
What are encapsulated nerve endings
The receptors for touch and pressure.
What are free nerve endings?
Receptors for heat cold, itch and pain - also respond to any intense stimulus.
What is neuropathy?
Damage to nerves that impairs sensation. Often a development of diabetes.
-i.e. walking on a wood floor is painful.
What part of the brain contains the sensory areas for the skin?
The parietal lobes. Sensitivity is determined by the number of receptors present. The number of receptors corresponds to the size of the sensory area in the cerebral cortex - the greater the number of cutaneous receptors, the greater the number of cortex neurons devoted to receiving and interpreting their impulses.
-Hands an face have the most receptors.
What is referred pain?
Sometime pain that originates in an internal organ may be felt in a cutaneous area.
- i.e. the pain of a MI may be felt in the left arm or shoulder.
- Referred pain is a creation of the brain
- think “brain freeze” when eating something very cold quickly - stimulates blood vessels in the roof of the mouth to constrict and then dilate. It happens so quickly that these impulses are interpreted as pain even though no damage is being done.
What is muscle sense?
Stretch receptors detect stretching of muscles and generate impulses, which enable the brain to create a mental picture to know where the muscles are and how they are positioned.
- Conscious muscles sense is felt and interpreted by the parietal lobes
- unconscious muscle sense is used by the cerebellum to coordinate voluntary movements and is part of what we call muscle memory.
How does the sense of taste work
- Receptors are found in taste buds (most on papillae on tongue). These are chemoreceptors that detect chemicals in solution in the mouth.
- 5 general types of taste receptors (sweet, sour, salty, bitter, savory.)
- Tongue also has receptors for pain which can detect heat of spcicy foods.,
- tongue and oral muscosa contain receptors for touch (texture of foods)
- some taste preference found to be genetic.
- impulses from taste buds transmitted by the facial and glosspharyngelal nerves to the taste areas in the parietal-temporal cortex.
How does the sense of smell work?
Receptor for smell (olfaction) are chemoreceptors that detect vaporized chemicals that have been sniffed into the upper nasal cavities. Similar to taste- there are specific scent receptors
- Olfactory receptors generate impulses carried by the olfactory nerves through the ethmoid bone to the olfactory bulb. Ends in the olfactory areas of the temporal lobes.
- Human smell is very poorly developed compared with other animals (dogs smells 2000x more acute)
How does hunger and thirst work?
They are visceral sensations
- triggered by internal changes
- receptors for both are believed to detect changes in blood nutrient levels (from hormones produced in the stomach and small intestine such as leptin) –> collected by the hypothalamus.
- Hunger is projected to the stomach, which contracts
- Thirst is projected to the mouth and pharynx, and less saliva is produced.
Described the function of eyelids.
- Eyelids contain skeletal muscles that enables them to close and cover the eyeball.
- Eyelashes deflect air currents to slow evaporation from the surface of the eyes and keep dust out.Eyelids lined with thin membrane called conjunctiva - inflammation of this is called conjunctivitis (may be caused by allergies or bacteria - makes eyes red, itchy, water)
What is the lacrimal apparatus?
It is the function of tear development.
- Lacrimal glands (in upper outer corner of the eyeball) produce tears.
- Secretion of tears occurs constantly, but is increased by presense of irritating chemicals.
- small ducts take tears to anterior of the eyeball.
- Tears are mostly water (1% sodium chloride)
- Tears contain lysoyme - which inhibits growth of most bacteria
- Ducts take tears to the lacrimal sac, which leads to the nasolcrimal duct, which empties tears into the nasal cavity (why crying makes the nose run)
What is the orbit (eye)
Most of the eyeball is within and protected by the orbit, formed by the lacrimal, maxilla, zygomatic, frontal, sphenoid and ethmoid bones.
How does the eyeball move?
6 extrinsic muscles of the eye are attached to the orbit.
4 rectus muscles that move the eyeball up/down and side to side.
-3 cranial nerves that innervate these muscles (oculomotor, trochlear, abducens)
-Very rapid and complex cooprdinagttion that we do not have to think about.
-Convergence of both eyes on an object is very important to insure a single image.
Name the layers of the eyeball (3)
1) Outer sclera
2) Middle Choroid layer
3) Inner retina.
Define the outer sclera (eye)
The thickest layer, made of fibrous connective tissue, most anterior portion is the cornea. Sclera is transparent. Cornea has no capillaries, covers the iris and pupil inside the eye, first part of the eye that refracts light rays.
Define the Choroid layer (eye)
Contains blood vessels and dark blue pigment (from melanin), absorbs light within the eyeball and prevents glare.
- Anterior portion modified into ciliary body and iris
- Ciliary body is a smooth muscle that surround edge of the lens and is connected to the lens by suspensory ligaments
- The lens is made of transparent, elastic protein, has no capillaries. Shape is changed by the cicliary muscle.
- -Iris - just in front of the lens (circular) - colored part of the eye (from melaninm color is genetic), 2 sets of smooth muscle fibers in the iris change the diameter of the pupil (central opening). Contraction of the radial fibers dilates the pupil and lets in more light (sympathetic response). Contraction constricts the pupil (parasympathetic response.
