Final Flashcards
1
Q
Where is Cardiac Muscle found and is it Voluntary or Involuntary
A
Found only in the heart; Involuntary because it contracts automatically
2
Q
Where is Skeletal Muscle found and is it Voluntary or Involuntary
A
Attached to bone; Voluntary as it can be contracted at will
3
Q
Where is Smooth Muscle found and is it Voluntary or Involuntary
A
Found in digestive tract, blood vessels, bladder, airways, and uterus; Involuntary because it contracts automatically such as when the digestive tract processes food.
4
Q
Define Muscle Tone
A
The continuous state of partial contraction in which muscles are at their optimal resting length
5
Q
What is the length-tension relationship?
A
The strength of a contraction depends upon the length of the fibers before the contraction beings.
6
Q
What nerve must a skeletal muscle be stimulated by in order to contract?
A
Motor Neuron
7
Q
What is the connection between a motor neuron and a muscle fiber?
A
Neuromuscular junction
8
Q
What are the 4 steps of muscle fiber contraction?
A
1) When an impulse reaches the end of a motor neuron it causes small vesicles to fuse with the cell membrane and release acetylcholine (ACh) into the synaptic cleft. 2) The ACh quickly diffuses across the synaptic cleft where it stimulates receptors in the sarcolemma 3)This sends an electrical impulse over the sarcolemma and inward along the T tubules. The impulse in the T tubules causes the sacs in the sarcoplasmic reticulum to release calcium. 4) The calcium binds with the troponin on the actin filament to expose attachment points. In response, the myosin heads of the tick filaments grab onto the thin filaments, and muscle contraction occurs.
9
Q
When do muscles use glucose?
A
If the supply of creatine phosphate is exhausted before the supply of oxygen has reached an acceptable level. Muscles receive much of their glucose from the bloodstream however some is stored within muscle in the form of glycogen. This is called Anaerobic respiration (without oxygen)
10
Q
What is lactic acid?
A
A byproduct of anaerobic respiration which leads to muscle fatigue.
11
Q
What is the role of a muscle?
A
To move a body part
12
Q
Define Prime Mover (in regards to muscle)
A
The main muscle triggering the movement
13
Q
Define Synergists (in regards to muscle)
A
The muscles that assist the prime mover
14
Q
Define hypertrophy and atrophy
A
Muscle enlargement and shrinkage of muscle
15
Q
At rest, muscles obtain most of their energy by metabolizing what?
A
Fatty Acids
16
Q
What is the origin of the muscle?
A
Refers to the end of the muscle that attaches to the more stationary bone
17
Q
What is the belly of the muscle
A
The thick midsection
18
Q
What is the insertion of the muscle
A
The end of the muscle that attaches to the move move-able bones.
19
Q
What 3 muscles are involved in breathing?
A
External Intercostals (elevate ribs), Internal Intercostals (depress ribs), and Diaphragm (enlarges thorax to trigger inspiration
20
Q
What comprises a motor unit? (in regards to muscle)
A
The neuron and all the fibers it stimulates
21
Q
What is muscle Threshold?
A
The minimum voltage needed to cause a muscle fiber to contract
22
Q
What is a Twitch?
A
A single, brief contraction. Occurs when a fiber receives a stimulus at or above threshold.
23
Q
How many bones are found in the adult body?
A
206
24
Q
What does the Axial Skeleton consist of?
A
Skull, rib cage, and vertebral column
25
What does the Appendicular Skeleton consist of?
Limbs, pelvic area, and shoulder area.
26
Where is spongy bone found?
In the ends of long bones and in the middle of most other bones
27
What are Osteoblasts?
Bone forming cells
28
What are Osteocytes
Mature Osteoblasts
29
What are Osteoclasts?
Cells that dissolve unwanted, old or unhealthy bone
30
What is the Diaphysis?
The central shaft-like portion of a long bone.
31
What is the Medullary Cavity?
The central hollow portion of a long bone that contains bone marrow
32
What 4 factors affect bone growth and maintenance?
Heredity (genetics), Nutrition(malnutrition), Hormones(growth hormone, thyroxine, insulin), and Exercise (weight-bearing exercises prevent bone destruction)
33
Where do the Parietal Bones join together?
Top of the head to form the top and sides of the cranial cavity
34
What does the Occipital bone form?
The rear of the skull
35
What does the Frontal Bone Form?
The forehead, and roof of the eye sockets.
36
What does the Ethmoid bone form?
The walls of the eye sockets, the roof and walls of the nasal cavity, and the nasal septum.
37
What does the Sphenoid bone form?
Part of the cranial floor as well as the floor and side walls of the eye sockets. Looks like a giant moth; lies slightly behind the nose and throat; on top of the sphenoid bone is an indented area called the sella turcica which houses the pituitary gland.
38
What do the Temporal Bones form?
The sides of the cranium and part of the cranial floor; also contains the structures of the inner and middle ear.
39
What does the Maxillae form?
Two bones that form the upper jaw
40
What are the Lacrimal Bones?
Paper-thin bones form part of the side wall of the eye socket
41
What do the Zygomatic Bones form?
Shape the cheeks and outer edges of the eye socket
42
What is the Mandible bone?
Largest and strongest bone in face; only facial bone that can move; articulates with the temporal bone at the TMJ; basically its the lower jaw
43
What is the Vomer bone?
Forms inferior half of the nasal septum.
44
What is a Suture Line?
Immovable joints where the bones of the skull join together
45
What is the Hyoid Bone?
A U-shaped bone that sits between the chin and the larynx.
46
What are the 3 regions of the sternum?
Manubrium (broadest portion), Body (largest portion), and Xiphoid Process (important landmark for CPR)
47
How many pairs of ribs do we have?
Twelve
48
Which ribs are the floating ribs?
11 and 12
49
Which ribs are the false ribs?
8-12
50
Which ribs are the true ribs?
1-7
51
What does the Pectoral Girdle consist of?
The clavicle and the scapula
52
What is the Humerus?
Long bone of the upper arm
53
What is the Radius?
One of the two bones of the lower arm; located on the thumb side
54
What is the Ulna?
One of the two bones of the lower arm; located on the pinky side
55
How many metacarpal bones do we have and what do they form?
5; palm of hand
56
How many carpal bones do we have and what do they form?
8; wrist
57
What is the Patella?
Kneecap
58
What does the Fibula stabilize?
The ankle
59
What does the Tibia do?
Bears weight; commonly called the shin bone.
60
What do the tarsal bones comprise?
Ankle
61
What is the Calcaneus bone?
Largest tarsal bone; forms the heel; bears much of the body's weight
62
Describe Chemical Digestion
Digestive enzymes break down food particles into nutrients
63
Describe Mechanical Digestion
Physically breaking down food into smaller pieces beginning with chewing food and continuing with contractions and churning in the stomach.
64
What are the 2 digestive enzymes found in saliva and what do they do?
Amylase (breaks down starch) & Lipase (begins the digestion of fat)
65
What do Goblet cells produce?
Mucous
66
What is mucous?
An enzyme that kills bacteria
67
What connects the pharynx to the stomach?
Esophagus
68
What do mucous cells in the stomach do?
Secrete mucous which protects the stomach lining and keeps the stomach from digesting itself
69
What do Parietal cells in the stomach do?
Secrete hydrochloric acid which kills microbes in swallowed food
70
What do Chiefs cells in the stomach do?
Secrete digestive enzymes such as pepsinogen
71
What is the primary function of the stomach?
Food storage
72
What helps to prevent backflow into the esophagus?
Lower Esophageal Sphincter
73
What is Rugae and what happens to the rugae of the stomach when we eat?
Rugae is the mucosa and submucosa wrinkled into little folds when the stomach is empty. When the stomach is full the rugae flatten and the stomach expands.
74
What is Chyme?
Mixture of food particles and digestive juices
75
What are the primary functions of the liver?
Store and release glucose, process vitamins and minerals, filter toxins, recycle old blood cells.
76
What is the body's largest gland?
The liver
77
Where does the Portal Vein carry nutrient rich blood to the liver from?
Stomach
78
What does the Central Vein do for the liver?
Carries the processed blood out of the liver
79
What is the main purpose of the Gall Bladder?
Store and concentrate bile
80
What is the function of the small intestine?
Nutrient absorption
81
What are the 3 divisions of the small intestine in order?
Duodenum, Jejunum, and Ileum
82
What is Segmentation in the small intestine?
Involves ring-like constrictions that occur at intervals along the small intestine. When the first contracted areas relax, new contractions occur in other locations. This movement breaks up food particles and kneads the contents of the intestines mixing it with digestive juices.
83
Where does the large intestine begin?
Cecum
84
What is the main function of the Large Intestine?
absorb water from the remaining indigestible food matter and transmit the useless waste material from the body.
85
Which vitamins are fat soluble?
A D E K
86
What is the role of intestinal flora in digestion and maintenance of health?
Produce vitamin K & B; Digest materials that have no digestive enzymes
87
What do Alpha cells secrete?
Glucagon
88
What do Beta cells secrete?
Insulin
89
What does glucagon do?
Stimulates the liver to convert glycogen into glucose; this happens between meals when blood glucose levels fall.
90
What does Insulin do?
After eating, when blood glucose levels are higher, insulin stimulates cells to absorb insulin, causing glucose levels to fall.
91
Which vitamins are water-soluble, where are they absorbed & where are they excreted?
C & B; Absorbed by the small intestine; excreted by kidneys
92
What are the 5 most abundant minerals in the body?
Calcium, Magnesium, Phosphorus, Sodium, Potassium
93
What is the main electrolyte in extracellular fluid?
Sodium
94
What is the main electrolyte of intracellular fluid?
Potassium
95
What functions does Calcium play a key role in?
Muscle contractions, nerve transmission, and blood clotting.
96
What does Sodium play a key role in?
How water is distributed throughout the body and the volume of total body water.
97
What does Potassium play a key role in?
Nerve and muscle function
98
What is Acidosis?
A decrease in the pH of the blood due to an accumulation of acids; may result from respiratory or metabolic disturbances
99
What is Alkalosis?
An increase in the pH of the blood due to a loss of acid; may result from respiratory or metabolic disturbances.
100
Define Isotonic
Concentration of solutes is the same as it is in the cell
101
Define Hypertonic
Solution contains a higher concentration of solutes compared to the fluid within the cell
102
Define Hypotonic
Solution contains a lower concentration of solutes compared to the fluid within the cell.
103
What is the normal pH range of blood?
7.35-7.45
104
What is the primary sex organ (gonads) of males?
Testes
105
What is the primary sex organ (gonads) of females?
Ovaries
106
What do the testes do?
Generate sperm and secrete testosterone
107
What is the Vas Deferens?
A tube that carries sperm out of the epididymis to the ejaculatory duct
108
What do gonads produce?
Sperm and eggs
109
What is spermatogonia?
The early stage of sperm
110
By what process to spermatogonia divide?
Mitosis - divide into two daughter cells each with 46 chromosomes
111
What is Spermatogenesis?
The formation of sperm
112
What is included in the female reproductive accessory organs?
Fallopian tubes, uterus and vagina.
113
Where are changes taking place during the Ovarian cycle and Which hormones control the Ovarian cycle?
Ovaries - FHS and LH
114
Where are changes taking place during the Menstrual cycle and Which hormones control the Menstrual cycle?
Uterus - Estrogen and Progesterone
115
How long is the average reproductive cycle?
28 Days
116
What is the first hormone secreted at the onset of puberty?
Gonadotropin-releasing hormone
117
What are gametes?
sex cells
118
Where is sperm stored before ejaculation?
Epididymis
119
Where is testosterone produced?
Interstitial cells of the testes
120
The surge in which hormone causes ovulation?
LH
121
Falling levels of which two hormones trigger menstruation?
Estrogen and progesterone
122
What process are Gametes form through?
Meiosis- During meiosis, the DNA is only replicated or copied one time. However, the cells are divided into four separate cells
123
How does a sensation occur?
Begins when a receptor detects a stimulus, if the stimulus is strong enough, the receptor causes a sensory neuron to send an impulse to the brain and spinal cord, when the impulse arrives at the brain, we may experience a sensation, such as sight or sound.
124
What are Chemoreceptors?
React to various chemicals including odor and taste
125
What are Mechanoreceptors?
Respond to factors- such as pressure, stretch, or vibration
126
What are Thermoreceptors?
Activated by a change in temperature
127
What are Nociceptors?
Pain receptors that respond to tissue damage from trauma as well as from heat, chemicals, pressure, or lack of oxygen
128
What are Photoreceptors
Found only in eyes they respond to light
129
What is referred pain?
Pain originating in a deep organ may be sensed as if its originating from the body's surface- sometimes in a completely different part of the body.
130
What are the main components of the Urinary System?
Kidneys, Ureters, Urinary Bladder, and Urethra
131
What structures are in place to protect the kidneys?
The ribs and a heavy cushion of fat encasing each kidney.
132
Where do structures such as blood vessels, ureters, and nerves enter and leave the kidney?
A slit called the hilum located in a concave notch.
133
What are the functions of the kidney?
A WET BED: Acid Base Balance Water Removal Erythropoiesis (process of making RBC's) Toxin Removal Blood Pressure Control Electrolyte Balance Vitamin D Activation
134
Define Renal Cortex
Outer region of kidney
135
Define Renal Medulla
Inner Region of kidney
136
Define Renal Columns
Extensions from the renal cortex that divide the interior region into cone-shaped sections
137
Define Renal Pyramids
Cone-shaped sections consisting of tubules for transporting urine away from the cortex.
138
Define Minor Calyx
The renal papilla (point of pyramid) extends into a cup that collects urine
139
Define Renal Palilla
The point of the renal pyramids
140
Define Major Calyix
Two or Three minor calyxes join together to form a major calyx
141
Define Renal Pelvis
Receives urine from the major calyxes and continues as the ureter which channels urine to the urinary bladder.
142
Define Renal Artery
Brings blood to the kidney- branches off the abdominal aorta
143
Define Renal Vein
Blood leaves the kidney from here and empties into the inferior vena cava
144
Define Nephron and what is consists of
Microscopic functional units of the kidney. They consist of 2 main components: 1)Renal Corpuscle which filters blood plasma 2)Renal Tubule where urine is formed.
145
Briefly describe Renal Circulation of Blood
The renal artery brings blood to the kidney. As it enters the kidney, the renal artery divides, branching into smaller arteries. The arteries pass through the renal columns and extend into the renal cortex. Blood leaves the kidneys through the renal vein which empties into the inferior vena cava.
146
What is Aldosterone and what are its effects on Blood Volume and Blood Pressure?
Hormone that causes the distal convoluted tubule to retain sodium which leads to retention of water. BP & BV go UP
147
What is Anti-diuretic Hormone and what are its effects on Blood Volume and Blood Pressure?
Hormone that inhibits diuresis (increased production of urine) by stimulating the kidneys to conserve water. BV and BP go UP
148
What is Atrial Natriuetic Peptide hormone and what are its effects on Blood Volume and Blood Pressure?
Secreted by the posterior pituitary gland. Causes the cells of the collecting duct to become more permeable to water. Causes BV and BP to go DOWN.
149
What is Parathyroid Hormone and what are its effects on Blood Volume and Blood Pressure?
Secreted in response to low blood calcium levels. Prompts the renal tubules to reabsorb more calcium and excrete phosphate. No effect on BV or BP
150
What are the Ureters?
Muscular tubes connecting the kidney to the bladder. Approx 25cm or 9.8 inches in length. Peristalic waves help propel urine from the renal pelvis toward the bladder.
151
What is the Urinary Bladder?
A collapsible muscular sac that stores urinecapacity.
152
What is the capacity of the urinary bladder?
500ml is moderately full and 800ml is maximum capacity.
153
Where do infections commonly attack in the bladder?
Trigone
154
What is the Urethra?
Small tube that conveys urine away from the bladder and out of the body. 3cm in females and 20 cm in males. Females are more prone to UTI's because bacteria can easily migrate up the short urethra. The opening of the urethra is called the external urinary meatus.
155
What does the External Urethral Sphincter consist of and is it voluntary or involuntary
Consists of skeletal muscles and is therefore under voluntary control
156
What does the Internal Urethral Sphincter consist of and is it voluntary or involuntary
A ring of smooth muscle that contracts involuntarily to retain urine in the bladder
157
What is Renin?
An enzyme released by the kidneys in response to a drop in blood pressure that causes the conversion of angiotensinogen into angiotensin 1.
158
Define Bowman's Capsule
2 layers of epithelial cells that envelop of glomerulus in an open-ended covering; also called a glomerular capsule.
159
What is not normally found in Urine and can indicate disease process?
Glucose, blood, free hemoglobin, albumin, ketones and bile pigmentation.
160
What might darker or cloudy urine indicate?
Dark urine usually results from poor hydration; Cloudy urine may result from bacteria indicating an infection
161
What might different urine odors indicate?
A pungent smell results when urine is allowed to stand; bacteria multiplies and converts urea into ammonia. A sweet, fruit smell often occurs in diabetics. A rotten odor may indicate a UTI
162
What might a high specific gravity indicate in urine?
Dehydration
163
What is the average pH level of urine?
6.0; higher reflects alkalosis and lower indicates acidosis
164
What does the Lymphatic System consist of?
Lymphatic vessels, lymph, lymphatic tissue, and lymphatic organs.
165
What is Lymph?
A clear, colorless fluid that fills lymphatic capillaries. Lymph moves away from the tissues and toward the heart.
166
What are lymphatic vessels and how do they compare to blood vessels?
Similar to veins, lympthatic vessels also have thin walls and valves to prevent backflow. The walls are formed by a thin layer of epithelial cells, however, unlike veins which cells are tightly joined, the cells overlap loosely allowing gaps to exist between the cells.
167
What are the 3 functions of the Lymphatic system?
Maintenance of Fluid Balance, Absorption of Fats, & Immunity
168
What is flow through the lymphatic vessels aided?
Primarily by the rythmic contractions of the lymphatic vessels as the valves prevent backflow. Flow is aided further by the contraction of skeletal muscles, which squeeze the lymphatic vessels. Respiration causes pressure changes that help propel lymph from the abdominal to the thoracic cavity.
169
Describe the two collecting ducts of the lymphatic system
Right Lymphatic Duct: Drains lymph for the upper right quadrant of the body into the right subclavian wein.
Thoracic Duct: Drains lymph from the rest of the body into the left subclavian vein
170
What are Lymph Nodes and what do they do?
Kidney-shaped masses of lymphatic tissue that lie along the lymphatic vessels; As lymph flows along the fluid trickles into the lymph nodes as the node removes pathogens and other foreign materials.
171
What organs are considered Lymphatic Organs?
Red bone marrow, thymus, lymph nodes, tonsils, and the spleen.
172
What are the primary lymphatic organs and what is their purpose?
Red bone marrow and Thymus; provide a location for B & T lymphcytes to mature.
173
What are secondary lympathic organs and what are their purpose?
Lymph nodes, tonsils, & spleen. Contain lymphocytes that have matured in either the red bone marrow or thymus.
174
What are the tonsils?
Masses of lymphoid tissue; they form a protective circle at the back of the throat and gaurd against pathogens entering the body through the nose or throat. The palatine tonsils are most suseptible to infection of the 3 sets of tonsils.
175
What is the spleen, where does it reside, and what does it do?
Largest lymphatic organ, resides in upper left quadrant. The functions of the spleen include Immunity, Destruction of old red blood cells, blood storage (stores 20-30% of blody's platelets and can rapidly add blood back into circulation), and hematopoiesis. A person can live without a spleen but may be more vulnerable to infection.
176
Describe Non-Specific Immunity
First & Second lines of defense; immune response aimed at a broad range of pathogens. Includes external barriers, phagocytosis, antimicrobial proteins, natural killer cells, inflammation and fever.
177
Describe Specific Immunity
Third line of defense; Occurs when the body retains a memory of a pthogen after defeating it.
178
Differentiate between T & B cells
T Cells also called T lymphocytes develop from stem cells in red bone marrow and travel to the Thymus where they remain until fully functional, after this they travel to lymphatic organs throughout the body.
B Cells also called B lymphocytes also develop in stem cells in red bone marrow, however, they remain there until fully mature. After maturation they leave the bone marrow for lympthatic organs and tissues.
\*\***T** cells mature in the **T**hymus
**B** cells mature in **B**one Marrow\*\*
179
What is an Antigen?
Any molecule that triggers an immune response.
180
What is Cellular Immunity?
Destroys pathogens that exist within a cell. It uses 3 classes of T cells.
**Cytotoxic T Cells** **AKA Killer T Cells:** carry out attack
**Helper T Cells**: Supportive Role
**Memory T Cells**: Remember the pathogen in case of future invasion
181
Fast Fact
Because the cellular immune system is programmed to attack any cell not identified with the "self" it also attacks and tries to destroy transplanted organs and tissues
182
What is Humoral Immunity?
Immune response that uses antibodies to target pathogens outside the host cells. Instead of destroying the antigen directly, it uses antibodies to mark them for later destruction.
183
What is Active Immunity?
When the body makes its own antibodies or T cells against a pathogen. There are 2 types of active Immunity:
**Natural Active Immunity**: When body produces antibodies or T cells after being exposed to a particular antigen.
**Artifical Active Immunity**: When the body makes T cells and antibodies against a disease as a result of a vaccination.
184
What is Passive Immunity?
Results when someone receives antibodies from another person or animal.
Two types of Passive Immunity:
**Natural Passive Immunity**: Results when a fetus acquires antibodies from the mother through the placenta or breastfeeding.
**Artifical Passive Immunity**: Involves obtaining serum from a person or animal that has produces antibodies against a certain pathogen and then injecting it into someone else. Typcially done in emergency cases such as rabies or botulism.
185
What is hypersensitivity?
Involves and inappropriate or excessive response of the immune system. Most common type is an allergy.
186
What is Anaphylaxis?
A severe, immediate reaction that affects the whole body.
Anaphylaxis shock occurs when symptoms worsen to the point that circulatory shock and sudden death may occur.
187
What is an Autoimmune Disease?
The body produces antibodies to attack its own tissues.
188
What are the structures of the Outer Ear?
**Pinna**: Visible part of ear; funnels sound into the auditory canal.
**Auditory Canal**: leads through the temporal bone to the eardrum. Glands lining the canal product secretions that mix with dead skin cells to form cerumen (ear wax), which waterproofs the canal and traps dirty & bacteria.
189
What are the structures of the Middle Ear
**Auditory Ossicles**: 3 smallest bones in the body connect the eardrum to the inner ear and they are named for their shape. They include Malleus, Incus and Stapes.
**Tympanic Membrane**: AKA Eardrum. Separates the outer eat from the middle ear; vibrates freely in response to sound waves.
**Auditory**/**Eustachian** **Tube**: Passageway from the middle eat to the nasopharynx. Purpose is to equalize pressure on both sides of the tympanic membrane. Can also allow infection to spread from throat to middle ear.
190
What are the structures of the inner ear?
**Semicircuar Canals**: Crucial for maintenace of equilibrium and balane
**Vestibule**: This structure contans the organs necessary for sense of balance
**Cochlea**: This snail-like structure contans the stuctures for hearing.
191
Which 2 parts of the inner ear play a key role in balane?
Vestibule and Semicircular canals.
192
What are the strutures of the outer layer of the eye?
**Sclera**: Outermost layer formed by dense connective tissue. It forms the white of the eye.
**Cornea**: Transarent extension of te sclera. Sits over the iris (colored portion) and admits light into the eye.
193
What are the stuctures of the middle layer of the eye?
**Iris**: A ring of colored muscle. Works to adjust the diameter of the pupil and control the amount of light entering the eye.
**Choroid**: highly vascular layer of tissue that supplies oxygen and nutrients to the retina and sclera.
**Ciliary Body**: Thickened extension of the choroid that forms a collar around the lens. Secretes a fluid called aqueous humor.
194
What are the structures of the layer of the inner eye?
**Retina**: Thin layer of light-senstive cells. Inside the retina are rods and cones that are stimulated by light rays to produce an electrical or chemical signal.
**Optic Nerve**: Transmits signals to the brain
195
Define Refraction (in regards to vision)
Bending of light rays so they focus on the retina.
196
Define Convergence in regards to vision and what happens when the eyes fail to converge?
Proper vsion requires the light rays from an object to fall on the same area of each retina. Convergence lines up the visual axis of each eye toward the object so that the light rays fall on the corresponding spots on each retina. If eyes fail to converge, light rays from the objet will fall on different arts of eaach retina resulting in double visio.
197
Define accomodation in regards to the eyes
When the curvature of the lens changes to allow the eye to focus on a near object.
198
What are cataracts?
Clouding of the lens making vision cloudy or blurry. Occur as a part of aging, diabetes, smoking, and prolonged exposure to sunlight.
199
Explain cones and rods
Rods: located at the periphery of the retina, are active in dim light, are responsible for night vision, cannot distinguish colors
Cones: Located at centre of eye with some scattered throughout eye, active in bright light, responsible for sharp vision, responsible for color vision.
