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1. Section 4
Recap
a) What is the function of the basal nuclei?
b) Which brain area processes the sensation of fear?
c) Define long term potentiation.
d) Name the three parts of the cerebellum.
e) Describe the way in which reflexes can be
categorized.

2. Answers
a) (1) inhibit muscle tone, (2) maintain purposeful
motor activity while suppressing useless patterns
of movement, and (3) coordinate slow, sustained
movements related to posture
b) Amygdala
c) With long-term potentiation, in response to
increased use at a given pre-existing synapse,
modifications take place in the postsynaptic
neuron and/or presynaptic neuron that enhance
the future ability of the presynaptic neuron to
excite the postsynaptic neuron.

3. d) Vestibulocerebellum, spinocerebellum,
cerebrocerebellum
e) (1) as spinal or cranial, (2) as innate or
conditioned, (3) as somatic or autonomic, and (4)
as monosynaptic or polysynaptic

4. The Peripheral Nervous
System: Afferent Division

5. The PNS has nerve fibers that carry
information between the CNS and body
regions. It afferent division sends
information about the external and
internal environment to the CNS.
• Visceral afferent pathways convey subconscious
information from the internal viscera.
• Sensory information is conveyed to the level of
conscious awareness. It is sensory afferent.
• Sensory information can be either a somatic sensation
from the skin or proprioception from the muscles,
joints, skin, and inner. This information can also
involve the special senses: vision, hearing, taste, and
smell

6. Perception is the conscious
awareness of the external world.
• It is created by the brain from a pattern of
nerve impulses sent to the brain from sensory
receptors.
• The brain interprets an input. Human
perceptions do not replicate reality.

7. Receptors are structures at the
peripheral endings of afferent
neurons. Receptors detect stimuli.
• Each type of receptor has an adequate stimulus.
Types of receptors are:
• photoreceptor - respond to visible wavelength of light
• mechanoreceptor - sensitive to mechanical energy
• thermoreceptor - sensitive to heat and cold
• osmoreceptor - detect changes in the concentration of
solutes in body fluids
• chemoreceptor - sensitive to specific chemicals such as the
concentration of oxygen in the blood
• nociceptor - a pain receptor that is sensitive to tissue damage

8. A stimulus alters the membrane permeability of the
cells of a receptor. This leads to the production of a
graded receptor potential.
• The receptor can be a specialized ending of an afferent neuron or a cell
closely associated with the peripheral ending of a neuron.
• This change in membrane permeability can lead to the influx of sodium
ions. This produces receptor (generator) potentials.
• The magnitude of the receptor potential represents the intensity of the
stimulus.
• A receptor potential of sufficient magnitude can produce an action
potential. This action potential is propagated along an afferent fiber to
the CNS.

9. By adaptation receptors can adjust to sustained
stimulation. With sustained stimulus length, the
extent of receptor depolarization decreases. This
adaption can be slow or rapid.
• Tonic receptors adapt
slowly or do not adapt.
• Phasic receptors adapt
rapidly.
• The Pacinian corpuscle
detects pressure and
vibrations in the skin. It
adapts rapidly.

10. Tonic receptors
Tonic receptors do not adapt or slow to adapt
Phasic receptors
Phasic receptors are rapidly adapting
Continue to respond to stimulus generate
action potential to relay Information to the CNS.
Constant rate of firing /Keep sending an AP as long as
stimulus is applied.
Eg. of phasic receptor: After time, no longer respond to constant
stimulus. tactile (touch). When you put something on your watch,
you soon become accustomed to it because of these receptors’
rapid adaptation.
There is sustained stimulus
there is a reduced response to the stimulus, but there is still a response.
Despite sustained stimulus =
response decreases/stop
The frequency of action potentials diminishes
or stop if the stimulus is unchanging.

11. Sensory
receptor in
human skin

12. Afferent pathways reaching the spinal
cord can be part of a reflex arc or can be
relayed to the brain by ascending
pathways.
• Somatosensory pathways convey conscious somatic
sensations.
• A receptor detects a stimulus. A specific receptor detects a
specific stimulus for each kind of sense modality.
• A first-order sensory neuron sends a signal from the receptor
to the spinal cord.
• The first-order neuron synapses with a second-order neuron
in the spinal cord or medulla.
• The second-order neuron synapses with a third-order neuron
in the thalamus.
• Each afferent and ascending pathway excites a defined area
of the cerebral cortex.

13. Acuity for a sensation refers to
discriminative ability.
• The smaller the receptive
field for a sense on the skin
surface, the greater the
acuity. The receptive field is
a circumscribed area of the
skin surrounding the point of
stimulation.
• Lateral inhibition also
influences receptor acuity
from the skin. The center of
a stimulus inhibits less
excited areas on the fringe
of the stimulus.

14. Stimulation of nociceptors
produces the perception of pain.
• Motivational and emotional responses also
affect the perception of pain.
• There are three categories of pain receptors.
• mechanical receptors respond to mechanical
damage
• thermal receptors respond to temperature
extremes
• polymodal nociceptors respond to damaging
stimuli

15. There are fast and slow afferent
pain fibers.
• A-delta fibers fire at rates of 30 meters per second.
• C fibers fire at 12 meters per second.
• There is a higher-level processing of pain
input.
• Ascending pathways for pain are in the
somatosensory cortex, thalamus, and reticular
formation. The brain has a built-in analgesic
system.

16. Section 5
The senses

17. The eye is a sensory organ for
vision. It has receptors that
detect light.
• Mechanisms that protect the eye include the
action of the eyelashes, secretion of tears
from the lacrimal glands, and the eyelashes.

18. The eye is a fluid-filled sphere enclosed
by three specialized tissue layers.
• The sclera is a tough outer covering of connective tissue. It surrounds the
cornea anteriorly. Light passing through the eye passes through the cornea
first.
• The middle layer is the choroid with blood vessels. It is specialized
anteriorly into the, ciliary body, suspensory ligaments and iris.
• The retina is the innermost layer. It has cells named rods and cones.
• Inside the eye, the lens separates the aqueous humor (anteriorly, carries
nutrients) and the vitreous body (posteriorly, maintains the eyeball shape).
• The aqueous humor is produced from the ciliary body and drains into the
blood at the edge of the cornea.

19. The iris is circular and pigmented. It is two layers of
smooth muscle that control the amount of light passing
through the pupil and into the eye.
• Its circular muscle constricts the pupil. Its radial muscle dilates
the pupil.
• Structures of the eye refract incoming light, focusing the image
properly on the inside surface of the retina.
• Light rays diverge from every point of a viewed light source.
• Convex structures of the eye produce convergence of these
diverging rays.

20. The cornea and lens are refractive
structures of the eye.
• They offer convex surfaces to focus
diverging light rays. By converging
these light rays, they bring the light rays
to an optimal position on the focal point
of the retina.
• As a viewed object becomes closer, the
convexity of the lens increases.
• As a viewed becomes more distant, the
convexity of the lens decreases.

21. Accommodation is the change of the strength
and shape of the lens. The shape of the lens
changes for focusing on images of varying
distance from the eye.
• The action of the ciliary muscle and suspensory
ligaments change the shape of the lens during
accommodation.
• As the ciliary muscle contracts, the tension on the
suspensory ligaments decreases. The lens assumes
a more spherical shape. This occurs during
accommodation on a closer object being viewed.
• As the muscle relaxes, the tension on the suspensory
ligaments increases. The lens flattens somewhat.
This occurs during accommodation on a more distant
object being viewed.

22. Light passes through several retinal
layers before reaching retinal receptors.
• Photoreceptors transform light into electrical signals for transmission to
the CNS.
• Rods and cones are retinal cells closest to the choroid. Only cones are
found in the fovea of the retina. This is the point of most distinct vision.
The fovea is surrounded by the macula lutea.
• There is a middle layer of bipolar cells in the retina.
• Ganglion cells are on the other side of the middle layer. Their axons join
to form the optic nerve which exits from the eye at the optic disc.

23. Phototransduction is the conversion
of light stimuli into neural signals.
• A photoreceptor consists of three parts:
an outer segment, an inner segment,
and a synaptic terminal.
• Photoreceptors are found in the outer
segment.
• Rhodopsin is the pigment found in rods.
Rods are cells that have chemically-
gated sodium channels that open in the
absence of light. Rods are active,
producing gray vision in the dark.
• The three photopigments in the cones
are: red, green, and blue. They respond
selectively to various wavelengths of
light, making color vision possible. The
cones are active cells, producing sharp
color vision in the presence of light.
• Color vision depends on the ratio of
stimulation of the three types of cones.

24. The sensitivity of the eyes varies
through dark and light adaptation.
• By dark adaptation you can gradually
distinguish objects as you enter a dark area.
It is due to the regeneration of rod
photopigments that had been broken down by
previous light exposure.
• By light adaptation you can gradually
distinguish objects as you enter an area with
more light. It is due to the rapid breakdown of
cone photopigments.

25. Visual information is modified and
separated before reaching the visual
cortex on the occipital lobe.
• The information reaching the visual cortex is
not a replica of the visual field.
• The thalamus and visual cortexes elaborate
the visual message.
• There is a hierarchy of visual processing.
• Visual processing goes to other areas of the
brain not involved in vision perception.

26. The ear consists of the external,
middle, and inner ear.
• The external and middle ear transmit sound waves to the fluid-
filled inner ears.
• In the inner ear the cochlea has receptors that convert sound
waves into nerve impulses.
• The vestibular apparatus of the inner ear is involved with the
sense of equilibrium.
• Each inner ear region has mechanoreceptors.

27. For hearing hair cells in the cochlea are
disturbed by vibrations from airborne
sound waves. Mechanical deformations
of these hair cells produce action
potentials that travel to the brain.
• The external ear plays a role in sound
localization. It consists of the pinna, external
auditory meatus, and tympanum.
• The tympanum vibrates in unison with sound
waves of the external ear.

28. Sound waves consist of
alternating regions of
compression and rarefaction of
air molecules.
• The pitch of sound depends on the frequency
of air waves.
• The loudness of sound depends on the
amplitude of air waves.
• The timbre of sound is determined by
overtones.

29. Middle ear bones conduct a signal
(vibrations) from the tympanic membrane
to the inner ear.
• The inner ear amplifies
tympanic movements and
transmits them to the oval
window.
• The movement of the oval
window produces waves that
travel through the fluid in the
cochlea. The cochlea
contains the organ of Corti,
the sense organ for hearing.

30. Waves in the cochlea fluid move
the basilar membrane in the
cochlea.
• These waves have the same frequency as the
sound waves in the air.
• Different frequencies of waves disturb different
parts of the membrane.
• Hair cells are mounted on the basilar
membrane. They are reflected in relation to
an overhanging tectorial membrane. Different
groups of hair cells move to different
frequencies.

31. Pitch discrimination depends on
the region of the basilar
membrane that vibrates.
• A mechanical change in a group of hair cells is
changed into neural signals.
• They are transmitted to the auditory cortex of
the temporal lobe of the brain.
• The brain interprets this incoming series of
signals for sound perception.

32. The semicircular canals of the vestibular
apparatus detect rotational acceleration or
deceleration changes in the body.
• The utricle and saccule of the vestibular apparatus
detect changes in the rate of linear motion in any
direction.

33. The structures of the vestibular
apparatus have hair cells that are
sensitive to mechanical deformation.
• These cells are sensitive to fluid shifts and the
movement of other structures, such as
otoliths in the saccule and utricle.
• Neural signals are generated by changes in
these hair cells. These cells are transmitted
to the brain for interpretation.

34. Chemoreceptors detect chemical changes
for the senses of taste and smell.
• Taste receptors are located within taste buds in the tongue. Dissolved molecules
bind to receptor sites producing receptor potentials.
• All tastes are varying combinations of the four basic tastes: salt, sweet, sweet,
and bitter. A fifth taste has been recognized.
• Any chemical produces the differential stimulation of the four receptors for taste.
• This generates a pattern of action potentials that travels along afferent pathways
to the brain.
• One pathway passes through the limbic system for emotional and behavioral
processing. Another pathway passes through the thalamus to the cerebral cortex
for conscious processing.

35. Olfactory receptors in the nose are
specialized ending of afferent neurons.
• Different olfactory receptors detect discrete parts of an odor.
• Odor discrimination is coded by patterns of activity in the
olfactory bulb glomeruli. Afferent signals are sorted by scent
component.
• The olfactory system adapts quickly

36. • https://www.youtube.com/watch?v=mFm3yA1nslE
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• https://www.youtube.com/watch?v=Ie2j7GpC4JU&
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• https://www.youtube.com/watch?v=o0DYP-
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• https://www.youtube.com/watch?v=unWnZvXJH2o
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