Final Lab Practical

Unit 13

Identify structures and functions of the brain and describe its gross anatomy

The brain is divided into 4 regions: the cerebral hemispheres (collectively the cerebrum), the diencephalon, the cerebellum, and the brainstem.
The brain contains hollow spaces called ventricles that are filled with cerebrospinal fluid.
- The largest of the ventricles are the lateral ventricles which are located in the right and left cerebral hemispheres.
  - The different regions of each lateral ventricle are named horns: the anterior, posterior, and inferior horns.
    - The anterior horns of the lateral ventricles are connected by a small opening called the interventricular foramen which leads to the smaller third ventricle housed within the diencephalon. The third ventricle is continuous with the fourth ventricle, found in the brainstem via a small canal called the cerebral aqueduct. The fourth ventricle is continuous with the central canal, a hollow passageway that runs down the central spinal cord.
  - Within each of the 4 ventricles there is a collection of blood vessels known as the choroid plexuses. As blood flows through the choroid plexus fluid filters out into the ventricles and at that point it is called CSF. The largest choroid plexuses are within the lateral ventricles.
    - Ventricles are lined by neuroglial cells called ependymal cells whose cilia beat to circulate CSF.
    - One of the main purposes of CSF is to reduce brain weight as the brain is buoyant in the CSF.
The cerebrum is the most superior portion of the brain and is responsible for the brain’s cognitive functions including learning and language, conscious interpretation of sensory information, conscious planning of movement, and personality. The two cerebral hemispheres are separated from one another by a deep groove called the longitudinal fissure and are separated from the cerebellum by the transverse fissure.
The cerebral surface consists of elevated ridges called gyri and shallow grooves called sulci. These are adaptations that increase the brain’s surface area and make it more compact. Also increases the speed at which cerebral neurons communicate.
The cerebrum consists of 5 lobes, the frontal parietal, temporal, occipital, and deep insula lobes.The lateral sulcus separates the frontal and temporal lobes and the central sulcus separates the frontal and parietal lobes.
On either side of the central sulcus are two prominent gyri: the anterior precentral gyrus which houses the primary motor cortex and the posterior postcentral gyrus which houses the primary somatosensory cortex. A less prominent sulcus, the parieto-occipital sulcus separate the parietal and occipital lobes.
The outer 2 mm of the cerebrum is a region known as the cerebral cortex. Here we find unmyelinated parts of the cerebral neurons, including cell bodies, dendrites, and unmyelinated axons. The lack of myelin gives the cerebral cortex a gray color. This is called gray matter. The cell bodies and processes of the cerebral cortex communicate with other parts of the nervous system by bundles of myelinated axons called white matter.
- Gray matter isn’t confined to the cerebral cortex. Clusters of cell bodies called nuclei are found throughout the white matter of the cerebrum. Some nuclei are grouped together into functional systems such as the basal nuclei: the caudate nucleus, putamen, and globus pallidus. These three nuclei are responsible for the smooth onset of voluntary motion.
The largest tract of cerebral white matter is the corpus callosum which connects the right and left cerebral hemispheres.
Another prominent tract of white matter is the fornix.
The limbic system contains some of the most evolutionarily ancient parts of the brain. A key component is the limbic system is the limbic lobe of the cerebrum, a ring of gray matter on the medial side of the cerebral hemisphere.
Embedded in the temporal lobe is a seahorse shaped nucleus called the hippocampus which has a critical role in learning and memory. The hippocampus is connected to the fornix through which its output is delivered to other parts of the brain.
- Hippo have good memory 👍
An almond shaped nucleus called the amygdala plays a role in emotional expression, particularly fear.
The diencephalon is in the central core of the brain and is composed of three main parts:
- Thalamus- Makes up 80% of the diencephalon and is a large, central, egg-shaped mass of gray and white matter. There are two thalmic lobes that are connected by a small band of white matter called the intermediate mass of the thalamus. The thalamus is a major integration center and a major relay center that edits and sorts information going into the cerebrum.
  - Functions as a gateway into the cerebrum!!!
- Hypothalamus- Deceptively small structure that contains the nuclei whose neurons help to regulate the endocrine system, monitor the sleep-wake cycle, control thirst, hunger, and body temperature, and monitor the autonomic nervous system.
  - On the posteroinferior surface of the hypothalamus is a pair of gray matter clusters called mammillary bodies which play a role in learning and memory.
  - An endocrine organ called the pituitary gland is connected to the hypothalamus by a stalk called the infundibulum.
- Epithalamus is the posterior and superior part of the diencephalon and contains an endocrine organ called the pineal gland. This secretes the hormone melatonin which helps regulate the sleep-wake cycle.
The cerebellum consists of two highly convoluted lobes connected by the vermis. The outer portion of the cerebellum is known as the cerebellar cortex which is gray matter while the inner region is white matter. The cerebellar white matter is called the arbor vitae because of its resemblance to the branches of a tree. The cerebellum coordinates and plans ongoing motor activities and is critical in reducing and preventing motor error with movement.
The brainstem induces the automatic functions of the body.
- The most superior portion is the midbrain which has roles in movement, sensation, and certain reflexes
- There are two projections called the superior and inferior colliculi which relay visual and auditory stimuli to the thalamus respectively.
- The pons has nuclei that are involved in controlling the rhythm for breathing and the sleep cycle.
- The last segment of the brainstem, the medulla oblongata, or simply medulla, is continuous inferiorly with the spinal cord. The nuclei in the medulla work with those of the pons to control ventilation and are also involved in regulating heart rate, BP, and certain reflexes such as vomiting.
A set of 3 membranes called meninges surround the brain
- Dura matter- The outermost meninx is the thick, leathery, double-layered dura matter.
  - Has two layers, the superficial periosteal layer which is fused to the skull and the deeper meningeal layer which is continuous with the dura matter of the spinal cord.
  - The two layers of the dura are fused, but there are three regions where the meningeal layer separates from the periosteal layer. This dives into the brain to form three structures. At these locations the two layers of the dura separate forming spaces collectively called the dural sinuses. All deoxygenated blood from the brain drains into the dural sinuses which in turn drains into veins exiting the head and neck.
    - The falx cerebri resides in the longitudinal fissure and forms a partition between the right and left cerebral hemispheres. Its attachment to the crista galli of the ethmoid bone anchors it in place.
    - The falx cerebelli which separates the two cerebellar hemispheres
    - The tentorium cerebelli which resides in the transverse fissure and separates the cerebrum from the cerebellum.
      - A TENT FOR THE CEREBELLUM LOOK AT DIAGRAM
- Arachnoid matter- The middle meninx which is separated from the dura by a potential space called the subdural space. Small bundles of the arachnoid matter called the arachnoid granulations project into the dural sinuses and allow CSF to reenter the blood.
- Pia matter- The thinnest, innermost meninx which clings to the surface of the cerebral hemispheres and follows the contours of the sulci and gyri. Richly supplied with blood vessels. There is a space between the pia matter and the arachnoid matter called the subarachnoid space which is filled with CSF.

Identify structures and functions of the spinal cord and describe its anatomical organization

The medulla oblongata passes through the foramen magnum of the occipital bone and becomes the spinal cord. Along its length are two notable bulges, the cervical and lumbar enlargements. The spinal cord is wider in these areas due to the high number of nerve roots that attach at these locations going to and coming from the upper and lower limbs.
The spinal cord does not extend the entire length of the vertebral column rather, it ends between the first and second lumbar vertebrae. Here it tapers to form the end of the spinal cord called the conus medullaris. Extending from the conus medullaris is a tuft of nerve roots called the cauda equina which fills the remainder of the vertebral column to the sacrum and the nerve roots exit out of the appropriate foramina to become spinal nerves. These nerve roots give off spinal nerves that supply the lower limbs and the pelvis. They are also involved in the voluntary control of urination and defecation.
The spinal cord is protected by a set of spinal meninges which are continuous with the cranial meninges.
- The cranial and spinal meninges are similar in name and structure, the dura matter is the outer meninx, the arachnoid matter is the middle meninx, which is separate from the dura by a thin potential space called the subdural space, and the pia matter is the inner meninx which is separated from the arachnoid matter by the CSF-filled subarachnoid space.
- The difference between the cranial and spinal meninges includes that the spinal dura does matter consists of only one layer rather than two like the cranial dura does. The single dural layer does not attach to the vertebral column, creating a fat filled epidural space between the spinal dura and the interior vertebral foramen. There is no epidural space around the brain because of the periosteal layer of the cranial dura being fused to the skull. Additionally, in the spinal cord there are small extensions of the pia matter called denticulate ligaments which secure the spinal cord to the vertebral column. The pia matter also continues long after the spinal cord ends, forming a long, fibrous extension called the filum terminale. That eventually attaches to the coccyx.
The external surface of the spinal cord has two indentations. Anteriorly is the anterior median fissure and posteriorly is the much narrower posterior median sulcus.
Internally the spinal cord consists of a butterfly shaped core of gray matter that surrounds the CSF-filled central canal. Opposite to the brain, here the gray matter is on the inside and the white matter is on the outside. The gray matter is divided into regions, or horns.
- The anterior horns contain the cell bodies of motor neurons. The axons of the neurons of the anterior horn exit the spinal cord, forming the anterior root, which eventually becomes part of a spinal nerve
- The posterior horns contain the cell bodies of sensory neurons. These cell bodies receive input from the axons of pseudounipolar neurons in the PNS that enter the spinal cord via the posterior root. The cell bodies of these pseudounipolar neurons are located just lateral to the spinal cord in a swollen knob called the posterior root ganglion.
- The lateral horns are found in the thoracic and lumbar regions of the spinal cord. They contain the cell bodies of autonomic neurons from the sympathetic nervous system. This division of the autonomic nervous system maintains the homeostasis of variables such as heart rate and BP during periods of stress.
Surrounding the spinal gray matter is the spinal white matter which is divided into three columns or funiculi. The anterior, posterior, and lateral funiculi. Each funiculus contains myelinated axons grouped into bundles called tracts. Tracts contain axons that have the same beginning and end points and the same general function.
- Ascending tracts carry sensory information from sensory neurons to the brain
- Descending tracts carry motor information from the brain to the motor neurons.

Identify and describe overall structure and functions of the CNS and PNS

Central Nervous System
Structure
- Brain: The brain is the command center of the nervous system and is composed of different regions responsible for various functions such as cognition, sensory processing, motor control, and homeostasis.
- Spinal Cord: The spinal cord is a long, cylindrical bundle of nerve fibers that extends from the base of the brain down the vertebral column. It serves as a pathway for nerve impulses traveling to and from the brain and controls reflex actions.
Functions
- Integration: The CNS integrates sensory information received from the PNS to generate appropriate responses.
- Control: It regulates voluntary and involuntary bodily functions, including movement, sensation, perception, and higher cognitive processes like memory and emotion.
- Homeostasis: The CNS maintains internal balance by regulating physiological processes such as body temperature, blood pressure, and metabolism.
- Learning and Memory: It plays a crucial role in learning and memory formation by processing and storing information received from the environment.
Peripheral Nervous System
Structure
- Nerves: The PNS consists of nerves that extend from the brain and spinal cord to various parts of the body. These nerves transmit sensory information from sensory receptors to the CNS and carry motor commands from the CNS to muscles and glands.
- Ganglia: Ganglia are clusters of nerve cell bodies located outside the CNS. They function as relay stations for integrating and transmitting nerve signals.
Function
- Sensory Input: The PNS gathers sensory information from the external environment and internal body conditions through sensory receptors such as touch receptors, pain receptors, and proprioceptors.
- Motor Output: It transmits motor commands from the CNS to muscles and glands, controlling voluntary movements and involuntary processes like digestion and heart rate.
- Autonomic Functions: The PNS includes the autonomic nervous system (ANS), which regulates involuntary bodily functions such as heart rate, digestion, and respiratory rate.
- Reflex Actions: The PNS coordinates rapid, involuntary responses to stimuli through reflex arcs, which involve sensory neurons, interneurons in the spinal cord, and motor neurons.

Units 12&14

Identify and describe overall structure of the CNS and PNS

The central nervous system consists of the brain and spinal cord
- PLEASE SEE ABOVE UNIT 13
The PNS consists of nerves (cranial and spinal nerves).
- Cranial nerves- Nerves that bring information to and from the brain and brainstem
- Spinal nerves- Nerves that bring information to and from the spinal cord
The PNS can be divided into two divisions based on function:
- The motor/efferent division which innervates muscle cells and glands
- The sensory/afferent division which innervates the skin, joints, special sensory organs, and other sensory receptors.
- These can further be divided based on the structures they serve
  - The somatic sensory and somatic motor divisions which serve skin and skeletal muscles, respectively
  - The visceral sensory and visceral motor divisions which serve smooth muscle, cardiac muscle, and glands.
    - The visceral motor division controls most of our automatic functions such as heart rate, BP, digestion, and urine production and is also KNOWN AS THE ANS!!!

Identify the spinal nerves and plexuses on anatomical models and printed figures

Each of the 31 pairs of spinal nerves forms from the fusion of the anterior and posterior roots of the spinal cord.
- The anterior roots carry motor axons emerging from the spinal cord
- The posterior roots carry sensory axons to the spinal cord
Each spinal nerve carries BOTH motor and sensory axons so all spinal nerves are mixed nerves.
After the anterior and posterior roots fuse to form the spinal nerve it splits into three branches: a posterior ramus, anterior ramus, and a small meningeal branch.
- The posterior rami serves the skin, joints, and musculature of the posterior trunk.
- The meningeal branches reenter the vertebral canal to innervate spinal structures
- The larger anterior rami travel anteriorly to supply the muscles of the upper and lower limbs, the anterior thorax, the abdomen, and part of the back.

Identify Locations and functions of anterior rami of the spinal nerves

^^^
The anterior rami of the thoracic spinal nerves travel between the ribs as 11 separate pairs of intercostal nerves that innervate the intercostal muscles, the abdominal muscles, and the skin of the chest and abdomen
The anterior rami of the cervical, lumbar, and sacral nerves, combine to form four large plexuses or networks of nerves:
Plexuses
- Cervical
  - Consist of the anterior rami of C1-C4 and some of C5.
  - Serves the skin of the head and the neck and certain neck muscles.
  - Major branch is the phrenic nerve which serves the diaphragm triggering inspiration during breathing.
- Brachial
  - Anterior rami of C5-T1.
  - C5-C6 form the superior trunk, C7 forms the middle trunk, and C8 and T1 unite to form the inferior trunk.
  - Each trunk splits into an anterior division and posterior division that becomes the cords of the plexus.
    - The anterior division of the inferior trunk forms the medial cord which descends in the medial arm.
    - The anterior divisions of the superior and middle trunks unite to form the lateral cord, which descends in the lateral arm.
    - The posterior divisions of each trunk unite to form the posterior cord which is located in the posterior arm.
    - Relevant nerves:
      - Axillary- Branch of the posterior cord and serves structures near the axilla including the deltoid, teres minor, and the skin
      - Musculocutaneous- Distal continuation of the lateral cord as a result is located in the lateral arm and provides motor innervation to the muscles that flex the forearm and sensory innervation from the skin of the lateral forearm
      - Radial- Distal continuation of the posterior cord and is located in the posterior upper limb. Serves the muscles that extend the forearm and hand and provides sensory innervation from the skin in the lateral hand
      - Ulnar- Funny bone nerve, distal continuation of the medial cord. Begins posteriorly but curves around the medial epicondyle of the humerus crossing over the anterior side of the forearm. Here the nerve is superficial and what hurts when you hit your funny bone. Provides motor innervation to muscles of the forearm that flexes the hand most of the intrinsic muscles. Provides sensory innervation from the skin over the medial hand.
      - Median= Results from fusion of portions of the medial and lateral cords. Travels down the middle of the arm and forearm. Supplies motor innervation from the skin over the anterior and lateral hand. As it enters the wrist it travels under a band of CT called the flexor retinaculum. CTS baby girlllll
- Lumbar
  - Consists of the anterior rami of L1-L4 with a small contribution of T12.
    - Iliohypogastric and ilioinguinal nerves- Provide motor innervation to the transversus abdominis muscle which compresses abdominal contents and the internal oblique muscles which laterally flexes and rotates the vertebral column. Supply sensory innervation to the skin of the pelvic area.
    - Genitofemoral nerve- Curves around medially to provide motor innervation to the cremaster muscle in males ew. It also provides sensory innervation from the skin around the anteromedial thigh and genitals in all sexes.
    - Femoral nerve- Largest nerve of this plexus and provides motor innervation to most of the anterior thigh muscles that extend the knee and sensory innervation from the skin of the anterior and medial thigh. It gives off a large sensory branch called the saphenous nerve which supplies the knee, medial leg, and foot.
    - Lateral femoral cutaneous nerve- Provides sensory innervation from the skin of the anterolateral thigh
    - Obturator nerve- Located in the medial thigh. Supplies motor innervation to the medial thigh muscles and sensory innervation from the skin of the proximal medial thigh.
- Sacral
  - Forms from the anterior rami of L4-S4
    - Superior gluteal nerve- First branch which supplies motor innervation to the muscles that abduct the thigh, including the gluteus medius, gluteus minimus, and tensor fascia lata muscles.
    - Inferior gluteal nerve- Provides motor innervation to the gluteus maximus muscle
    - Pudendal nerve- Smaller branch which provides motor innervation to the muscles of the pelvic floor and anogenital sphincters. Provides sensory innervation from the genitalia.
    - Posterior femoral cutaneous nerve- Located in the posterior thigh where it provides sensory innervation from the skin
    - Sciatic nerve is the largest nerve of the body. Travels in the posterior thigh where it splits into two branches, the tibial and common fibular nerves.
      - Tibial nerve provides motor innervation to muscles that flex the leg and plantarflex the foot and flex the toes.

Gives off a small superficial sensory branch called the sural nerve which supplies the skin of the posterior leg and foot

- - - - The common fibular nerve divides into superficial and deep branches. The superficial branch provides motor innervation to the lateral leg and the deep branch supplies motor innervation to the anterior muscles of the leg that dorsiflex the foot and the intrinsic muscles of the foot.

Describe a simple spinal reflex arc

Reflex- Involuntary predictable motor response to a stimulus
The pathway through which information travels is called a reflex arc
- Steps of a reflex arc
  - Sensory receptor detects the stimulus
  - Sensory afferent neurons bring the stimulus to the CNS
  - The CNS processes and integrates the information
  - The CNS sends its output via motor efferent neurons to an effector
  - The effector performs the triggered action
    - THIS IS A FEEDBACK LOOP (SEIF) YOU ALREADY KNOW THIS!!!!!

Describe the effects of the two branches of the autonomic nervous system on the body systems

The ANS is the largely involuntary branch of the PNS charged with maintaining homeostasis of several different physiological variables in the face of changing conditions.
The ANS has two branches, the sympathetic nervous system and the parasympathetic nervous system
- The cell bodies of the neurons of the SNS are located in the thoracic and lumbar regions of the spinal cord. This regulates the fight or flight response.
- Executed by any excitement, emotion, exercise, or even standing up
- The axons of the SNS release epinephrine, norepinephrine, and acetylcholine which trigger the following effects
  - Increased rate and force of heart contractions increasing BP
  - Construction of the BVs serving the abdominal viscera and skin which also increases BP
  - Dilation of the bronchioles
  - Decreased secretion from digestive glands
  - Decreased production of urine
  - Increased metabolic rate
  - Increased release of fatty acids and glucose
  - Dilation of the pupils
  - Release of epinephrine from the adrenal medulla
- The cell bodies of the neurons of the PSNS are located in cranial nerve nuclei and in the sacral portion of the spinal cord. Regulates the rest and recovery response. Axons release neurotransmitter acetylcholine which has the following effects:
  - Decreased heart rate, decreasing BP
  - Dilation of the blood vessels serving the skin and abdominal viscera which decreases BP
    - This is an indirect effect resulting from sympathetic nerve inhibition.
  - Mild constriction of the bronchioles
  - Increased activity of the smooth muscle of the digest tract and increased secretion from digestive glands
  - Increased urine production
  - Storage of fats and glucose
  - Constrictions of the pupils
  - Adjustment of the lens for near visitation
- The PSNS is generally subordinate to the SNS however neither branch of the ANS is completely inactive. Both divisions work together.

Unit 15

Describe the functions of the structures of an eye

External
- Lacrimal apparatus- Produces and drains tears. This includes the:
  - Lacrimal gland- Located in the superolateral orbit which produces the aqueous component of tears called lacrimal fluid
  - Lacrimal fluid protects the eye. Its water and solutes keep the eyeball moist for lubrication and to wash away debris. The immune proteins in lacrimal fluid protect the eyeball from bacteria and other pathogens
    - Fun fact: the eyeball is generally immune privileged, meaning it is exempt from the general inflammatory response of the immune system so it’s not really protected in that regard. This ^^ makes me feel a lot better because the eye at least has some immune coverage!
  - Tears drain into lacrimal canals near the medial canthus then drain into the :
  - Lacrimal sac- Found in a depression in the lacrimal bone.
  - From there tears travel through the nasolacrimal duct and finally empty into the nasal cavity just inferior to the nasal concha
  - Anteriorly the eye is covered by eyelids/PALPEBRAE. The palpebrae meet medially and laterally at the medial and lateral canthi
  - The lacrimal caruncle is medial to the canthus and contains sebaceous and sweat glands that lubricate the palpebrae.
    - There are several structures in and around the palpebrae including two muscles that open and close the eye that insert into and around the palpebrae, the levator palpebrae superioris and the orbicularis oculi muscle
    - Each palpebra has a stiff tarsal plate composed of dense CT and is associated with a sebaceous gland known as a tarsal gland. They produce the lipid component of tears which coats the aqueous portion and facilitates drainage into the lacrimal canals.
Internal
- Internal surfaces of the palpebrae are lined with a thin mucous membrane called palpebral conjunctiva. Where this membrane contacts the eyeball, it curls around and becomes the bulbar conjunctiva which lines much of the eyeball’s superficial surface
  - Conjunctivitis??
- Extrinsic eye muscles- Move the eyeball. There are 6
  - Lateral rectus muscle- Moves eye laterally
  - Medial rectus muscle- Moves eye medially
  - Superior rectus muscle- Moves eye superiorly
  - Inferior rectus muscle- Moves eye inferiorly
  - Superior oblique muscles- Moves the eyeball inferior and laterally
  - Inferior oblique muscle- Moves the eye superiorly and laterally
The eyeball is divided into the anterior and posterior cavities. The boundary for the cavities is a crystalline structure known as the lens.
- The lens is one of the structures in the eye that refracts (bends) light coming into the eye to focus it
- The anterior cavity is anterior to the lens and is filled with aqueous humor. Aqueous humor is produced relatively constantly and drained by the scleral venous sinus.
- The posterior cavity is posterior to the lens and contains a thicker fluid called vitreous humor. Unlike aqueous humor, vitreous humor is present at birth and remains relatively unchanged throughout life. Both fluids help to refract light coming into the eye.
The eye has three distinct tissue layers
- Fibrous tunic- The outermost layer which consists mostly of dense irregular CT and is avascular. Has two parts:
  - Sclera- White part of the eye and makes up the posteriorly ⅚ of the fibrous tunic. Which is because of numerous collagen fibers that contribute to its thickness and toughness (similar to how a joint capsule or ligament is white)
  - Cornea- Clear structure that makes up the anterior ⅙ of the fibrous tunic. Fourth refractor medium of the eyeball and accounts for about ⅔ of the eye’s refractive power
- Vascular tunic- AKA uvea, carries most of the blood supply to the tissues of the eye. Has three parts
  - Choroid- Highly vascular and makes up the posterior part of the vascular tunic. Brown in color to prevent light scattering in the eye
  - Ciliary body- Located on the anterior aspect of the vascular tunic. Made chiefly of the ciliary muscle (smooth muscle fibers that control the shape of the lens). Attaches to the lens via small suspensory ligaments. Also produces aqueous humor
  - Iris- Most anterior portion of the vascular tunic. Consists of smooth muscle fibers arranged around an opening called the pupil. As the fibers contract the pupil either constricts or dilates. The iris also divides the anterior cavity in two small divisions
    - Anterior segment- Anterior to the iris
    - Posterior segment- Posterior to the iris.
- Sensory tunic- Consists of the retina and optic nerve.
  - Retina- Thin, delicate structure that contains three layers of neurons
    - Photoreceptors called rods and cones that detect light
      - Rods- Scattered throughout the retina and are responsible for vision in DIM, reduced light and for peripheral vision.

Produce vision in black and white only

- - - - Cones- Concentrated at the posterior portion of the retina. Found in highest numbers in the macula lutea. At the center of the macula lutea is the fovea centralis which contains only cones. Cones are responsible for color and short vision in bright light.
    - Bipolar neurons that receive input from photoreceptors
    - Ganglion cells whose axons converge to form the optic nerve or cranial nerve II.
      - The optic nerves exit from the posterior orbit and partially exchange axons at the X-shaped optic chiasma before diverging into the two optic tracts. The input is eventually delivered to the visual cortex in the occipital lobe of the brain.

Trace the structures through which light passes as it travels from the cornea to the retina

Vision is produced when photos stimulate rods and cones. These rays travel parallel to one another, but when it passes through a translucent medium, it bends or refracts.
Light has to pass through four refractive media before it hits the retina: the cornea, the aqueous humor, the lens, and the vitreous humor.
- Of these, the cornea and the lens have the greatest refractive power because light refracts more when it strikes an object's surface at an angle. If that surface is curved or more angled at the edges, light is refracted unevenly, being more bent at the edges than in the middle.
- Both the cornea and lens have a convex shape. As light hits the edges of the lens, where it’s bent more, they bend inward or converge. When light rays converge on the retina at a point known as the focal point, the light rays are focused. The cornea is convex enough that it accounts for about 2/3s of the eye’s refractive power by itself.
  - The cornea alone provides most of the necessary refraction when viewing distant objects.
- When viewing nearer objects, additional refraction is needed by the lens. This is accomplished with the help of the ciliary muscle which contracts causing the ciliary body to move closer to the lens and removes tension on the supersensory ligaments. This causes the lens to become rounder, an adjustment called accommodation.
  - Accommodation allows the lens to become more convex providing the additional refraction necessary to focus light on the retinal.
  - When the eye switches to a distant object again, the ciliary muscle relaxes which moves the ciliary body farther away from the lens and points tension on the suspensory ligaments. This flattens the lens making it less convex and allows the cornea to again become the primary refractive medium.

Conduct and interpret the tests used to evaluated visual acuity, astigmatism, the ability to accommodate for close vision, and color vision

Visual acuity- Standard eye chart.
- Interpretation- Ex. for 20/40 vision: An individual can only clearly see objects from 20 feet away that someone with healthy vision would be able to see from 40 feet away.
Astigmatism- Chart. If any of the lines appear blurry or gray an astigmatism may be present. All lines should appear equal and black.
Ability to accommodate for close vision- Healthy pupils dilate when you look at something far away and shrink when you look at things that are near. If yours don't adjust at all, your test results will show abnormal reaction to accommodation.
Color vision- Color plate test. This is the most common type of color vision deficiency test. During this test, your eye doctor will ask you to look at a circle made of many different colored dots. Inside the circle is a shape that’s also made of dots — like a number, a letter, or a squiggly line. If the shape blends into the background and you can’t see it, you may have a type of color vision deficiency. Different color plates can check for different types of color vision deficiency.

Describe four conditions that can lead to defective vision

Nearsightedness/myopia- Nearsightedness usually results when the eye is too long or oval-shaped rather than round. It also may result when the curve of the cornea is too steep. With these changes, light rays come to a point in front of the retina and cross. The messages sent from the retina to the brain are perceived as blurry.
Farsightedness/Hyperopia- Farsightedness occurs when your eyeball is shorter than normal or your cornea is curved too little.
Astigmatism- Characterized by irregularities in the surfaces in the cornea and/or the lens. These irregularities cause the vision to become blurred because these structures are unable to focus light precisely on the retina
Presbyopia- A gradual, age-related loss of the eyes' ability to focus actively on nearby objects. As per professor, inability to go between near and far often requires bifocals.

Demonstrate and describe the blind spot, photopupillary reflex, accommodation pupillary reflex, near point of a accommodation, and convergence reflex visual tests

Blind spot- There are no rods or cones at the posterior most aspect of the eye where the optic nerve leaves the eyeball. This is called the optic disc or the blind spot because of its lack of photoreceptors means this region can produce no images.
- + and dot test. Close one eye and align the open eye with +, move closer to the + until the dot is no longer visible, this is your blind spot.
Photopupillary reflex- The pupillary light reflex is an autonomic reflex that constricts the pupil in response to light, thereby adjusting the amount of light that reaches the retina. Pupillary constriction occurs via innervation of the iris sphincter muscle, which is controlled by the parasympathetic system.
- Shining light in pupil. Shine once to make sure pupil constricts, shine again to make sure other pupil constricts. Repeat on the contralateral side.
Accommodation pupillary reflex- A three-part reflex that brings near objects into focus through lens thickening, pupillary constriction, and inward rotation of the eyes—eye convergence.
- Having a patient look at the tip of the doctor's index finger as they move it closer to the patient's nose. The doctor observes if the pupils get smaller as the index finger gets closer.
Near point of accommodation- the closest point at which an object can be placed and still form a focused image on the retina, within the eye's accommodation range.
- Have the patient fixate on a near target and move the test card toward the eye until the print blurs.
Convergence reflex- The accommodation reflex is a reflex action of the eye, in response to focusing on a near object, then looking at a distant object, comprising coordinated changes in vergence, lens shape and pupil size. It is dependent on cranial nerve II, superior centers and cranial nerve III.
- Move pointy object toward face until it blurs or becomes double then pull back. Repeat 2x.