Exam (elaborations)
Exam (elaborations) Medical BioSciences (MBS214) long answers
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- Medical BioSciences (MBS214)
- Institution
- University Of The Western Cape (UWC)
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MBS214 - SUPP 2019SECTION C:
1. a) Referred pain is pain perceived at a location other than the site of the painful stimulus/ origin. It
is the result of a network of interconnecting sensory nerves that supplies many different tissues.
b) Statoconia is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in
the vestibular system of vertebrates.
c) Sensory integration is a term that has been used to describe processes in the brain that allow us
to take information we receive from our 5 senses, organize it and respond appropriately.
d) The fornix is a C-shaped bundle of nerve fibers in the brain that acts as the major output tract of
the hippocampus. The fornix also carries some afferent fibers to the hippocampus from structures
in the diencephalon and forebrain. It is part of the limbic system.
2. a) Parkinson's disease is a progressive neurodegenerative disorder that primarily affects the motor
system. It is characterized by the loss of dopamine-producing cells in a specific region of the brain
called the substantia nigra, resulting in a dopamine deficiency. This dopamine deficiency leads to
motor symptoms such as tremors, rigidity, bradykinesia (slowness of movement), and postural
instability.
The basal ganglia is a group of interconnected structures in the brain that plays a crucial role in
motor control and movement regulation. It consists of several key components, including the
striatum, globus pallidus, substantia nigra, and subthalamic nucleus.
The indirect pathway is one of the major pathways within the basal ganglia circuitry involved in
motor control. It acts as a regulatory pathway that helps modulate and inhibit unwanted
movements. In Parkinson's disease, dysfunction of the indirect pathway contributes to the motor
symptoms observed in affected individuals.
In summary, dysfunction of the indirect pathway, resulting from dopamine deficiency in Parkinson's
disease, contributes to the motor symptoms observed in affected individuals. The hyperactivity of
the indirect pathway leads to excessive inhibition of the GPi/SNr, resulting in decreased thalamic
output and reduced activation of the motor cortex. Understanding the involvement of the basal
ganglia pathways, including the indirect pathway, is crucial for developing effective therapies to
manage Parkinson's disease.
b) The pyramidal tracts, also known as the corticospinal tracts, are major pathways in the central
nervous system that are involved in the voluntary control of movement. These tracts originate in
the cerebral cortex and extend down through the brainstem and spinal cord.
There are two main pyramidal tracts:
1. Lateral corticospinal tract: The majority of fibers from the pyramidal cells in the primary motor
cortex cross over at the level of the medulla, forming the lateral corticospinal tract. These fibers
descend on the opposite side of the body, synapsing with lower motor neurons in the ventral horn
of the spinal cord. The lateral corticospinal tract is responsible for controlling voluntary movements
of the limbs and digits.
2. Anterior corticospinal tract: A smaller portion of fibers from the pyramidal cells do not cross over
at the level of the medulla and instead descend on the same side of the body. These fibers form the
anterior corticospinal tract. They travel down the spinal cord and eventually cross over at lower
levels before synapsing with lower motor neurons. The anterior corticospinal tract is involved in
controlling axial and proximal muscles of the body.
, In summary, the pyramidal tracts, or corticospinal tracts, are essential neural pathways involved in
the voluntary control of movement. They transmit motor signals from the cerebral cortex to the
spinal cord, enabling precise and coordinated muscle contractions.
3. a) The focal distance refers to the distance between the lens and the focal point, where the light
rays converge or diverge. It is influenced by several factors:
1. Lens shape and curvature: The shape and curvature of the lens play a significant role in
determining the focal distance. A convex lens, which is thicker in the middle and thinner at the
edges, converges light rays and has a shorter focal distance. In contrast, a concave lens, which is
thinner in the middle and thicker at the edges, diverges light rays and has a longer focal distance.
2. Refractive index: The refractive index of a material determines how much light is bent or
refracted as it passes through the medium. A higher refractive index causes light to bend more,
resulting in a shorter focal distance. Materials with a lower refractive index have a longer focal
distance.
3. Lens thickness: The thickness of the lens affects the focal distance. Thicker lenses have a shorter
focal distance, while thinner lenses have a longer focal distance.
4. Object distance: The distance between the object being viewed and the lens affects the focal
distance. When the object is closer to the lens, the focal distance is shorter. Conversely, when the
object is farther away, the focal distance is longer.
5. Wavelength of light: The wavelength of light also influences the focal distance. Different
wavelengths of light are refracted to varying degrees by the lens, resulting in variations in the focal
distance. This phenomenon is known as chromatic aberration.
6. Medium between the lens and object: The medium between the lens and object can impact the
focal distance. Light travels at different speeds through different mediums. For example, light travels
more slowly in denser mediums like water or glass compared to air. This change in speed affects the
bending of light and can alter the focal distance.
Understanding the factors that affect the focal distance is crucial in optics and lens design, as it
helps determine the properties and applications of various optical systems, such as cameras,
telescopes, and eyeglasses.
b) With age, damage accumulates: tympanic membrane gets less flexible, articulations between
ossicles stiffen and round window may begin to ossify.
c) Photoreception is the process by which the specialized cells in the retina of the eye, known as
photoreceptor cells, detect and respond to light stimuli. There are two types of photoreceptor cells
in the retina: rods and cones.
1. Rods: Rods are highly sensitive to low levels of light and are responsible for vision in dim lighting
conditions, such as at night. Rods contain a visual pigment called rhodopsin, which consists of a
protein called opsin and a light-sensitive molecule called retinal.
2. Cones: Cones are responsible for color vision and visual acuity. They are concentrated in the
central part of the retina called the macula. Cones contain different types of visual pigments, each
sensitive to different wavelengths of light, allowing for color discrimination.
The process of photoreception begins when light enters the eye and reaches the retina. The
photons of light are absorbed by the visual pigments in the photoreceptor cells, triggering a series
of events that result in the generation of electrical signals. This process can be summarized as
follows:
, 1. Absorption of light: When a photon of light strikes a visual pigment molecule within a
photoreceptor cell, it causes the retinal molecule to change shape. This change in shape activates
the visual pigment, initiating the process of phototransduction.
2. Phototransduction: The activated visual pigment activates a cascade of biochemical reactions
within the photoreceptor cell. These reactions involve the activation of enzymes, the opening and
closing of ion channels, and changes in the electrical potential of the cell membrane. Ultimately,
these processes lead to the generation of an electrical signal.
3. Signal transmission: The electrical signal generated in the photoreceptor cells is then transmitted
to other cells in the retina, such as bipolar cells and ganglion cells, through a series of chemical and
electrical events. The signal is further processed and integrated in the retina before being
transmitted to the visual cortex of the brain via the optic nerve.
Bleaching and Regeneration of Visual Pigments:
After absorbing light, the visual pigments undergo a process called bleaching, where the retinal
molecule changes its conformation and separates from the opsin protein. This bleaching of the
visual pigment makes the photoreceptor temporarily insensitive to light stimuli.
To regain sensitivity to light, the visual pigment must be regenerated. This process involves the
enzymatic conversion of the retinal back to its original form, ready to bind to opsin and form the
visual pigment once again. The regeneration of visual pigments occurs through a series of metabolic
reactions that take place within the photoreceptor cells.
The rate of regeneration varies between rods and cones and can be influenced by factors such as
light exposure and metabolic activity. In bright light conditions, the regeneration process may take
longer, leading to temporary desensitization of the photoreceptors and decreased visual sensitivity.
Overall, the process of photoreception, bleaching, and regeneration of visual pigments is essential
for our ability to perceive and interpret visual stimuli, allowing us to see the world around us.
4.
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