Question Answer
Sensory Systems -are specialized epithelial cells or neurons that transduce environmental signals into
neural signals.
-The enviromental signals that can be detected
include mechanical force, light, sounds, chemicals, and temperature.
Types of sensory transducers Mechanoreceptors





respond to mechanical stimulus
-Pacinian corpuscles
-joint receptors
-Stretch receptors in muscle
-Hair cells in auditory and vestibular systems
-Baroreceptors in carotid sinus
Photoreceptors Rods and cones of the retina
Chemoreceptors -Olfactory receptors
-Taste receptors
-Carotid body O2 receptors
Nociceptors Extremes of temperature and pain
A-alpha FIBER large alpha-motoneurons
Conduction velocity: fastest
A-beta FIBER Touch, pressure
Conduction velocity: Medium
A-gamma FIBER gamma-motoneurons to muscle spindles (intrafusal fibers) Conduction velocity: Medium
A-delta FIBER Touch, pressure, temperature, and pain Conduction velocity: Medium
B FIBER preganglionic autonomic fibers
Conduction velocity: Medium
C FIBER Slow pain, postganglionic autonomic fibers Conduction velocity: Slowest
Receptive field is an area of the body that, when stimulated, changes the firing rate of a sensory neuron
If the firing rate of the sensory neuron is increased, the receptive field is ? excitatory
If the firing rate of the sensory neuron is *decreased, the receptive field is ? inhibitory.
in sensory transduction, after the stimulus arrives the sensory receptor (photon of light on retina, molecule of NaCl on tongue), what happens next? Ion channels are opened in the sensory receptor, allowing current to flow.
Usually the current is INWARD, which is DEPOLARIZATION of the receptor.
in sensory transduction, The change in membrane potential produced by the stimulus is the ? receptor potential, or generator potential
(Muscle spindle, pressure, slow pain)
PHASIC SENSORY RECEPTORS RAPIDLY APAPTING (pacinian corpucle, light touch)
Pain you feel at first, but then…show a decline in action potential frequency with time in response to a constant stimulus
Sensory pathways from the sensory receptor to the cerebral cortex:

Sensory receptors -are activated by ?

environmental stilmuli. -may be specialized epithelial cells (taste receptors, auditory hair cell). -may be primary afferent neurons (olfactory chemoreceptors).
Sensory pathways from the sensory receptor to the cerebral cortex:

Sensory receptors-transduce the stimulus into?

electrical energy ( receptor potential).
Sensory pathways from the sensory receptor to the cerebral cortex:

First-order neurons -are the primary AFFERENT neurons that receive the transduced signal and send the information to the ?


Cell bodies of the primary afferent neurons are in dorsal root or spinal cord ganglia

Sensory pathways from the sensory receptor to the cerebral cortex:

Second-order neurons are located in the ?

spinal cord or brain stem. -receive information from one or more primary AFFERENT neurons in relay nuclei and transmit it to the thalamus
Axons of second-order neurons usually cross the midline in a relay nucleus in the spinal cord before they ascend to the ? thalamus.

Therefore, sensory information originating on one side of the body ascends to the contralateral thalamus

Third-order neurons -are located in the relay nuclei of the? thalamus.

From there, encoded sensory information ascends to the cerebral cortex

Fourth-order neurons -are located in the appropriate sensory area of the ? cerebral cortex.

The information received results in a CONSCIOUS PERECEPTION of the stimulus

Somatosensory system The somatosensory system processes information about touch, pain and temperature
Somatosensory pathways 1. Dorsal column system

2. Anterolateral system

Types of somatosensory receptors 1. Mechanoreceptors (for touch)

2. Thermoreceptors (temperature)

3. nociceptors (pain)

Pathways in the somatosensory system :

Dorsal column system

-processes sensations of fine touch, pressure, two-point discrimination, vibration.
In the dorsal column system, primary afferent neurons have cell bodies in the DORSAL ROOT. Their axons ascend ipsilaterally to the nucleus gracilis and nucleus cutaneus of the medulla.

From the medulla?

second-order neurons cross the midline and ascend to the contralateral thalamus, where they synapse on third-order neurons. Third-order neurons ascend to the somatosensory cortex, where they synapse on fourth-order neurons.
dorsal column system:
primary afferent neurons in dorsal root into-Medulla, second order neurons into contralateral thalamus, and synapse on 3rd order neurons to?
somatosensory cortex, where they synapse on fourth-order neurons
Dorsal column system:

neurons involved?

primary afferent neurons(dorsal root)
axons (nucleus gracilis/nucleus cutaneous of medulla)
second order neurons(contralateral thalamus)
third order neurons (somatosensory cortex)
fourth order neurons
Pathways in the somatosensory system :

Anterolateral system

-processes sensations of temperature, pain, and light touch. -consists primarily of group of fibers, which enter the spinal cord and terminate in the dorsal horn.
Thalamus Information from different parts of the body is arranged somatotopically
Pain is associated with the detection and perception of noxious stimuli (nociception)
The receptors for pain are free nerve endings in the? skin, muscle, and viscera
Neurotransmitters for nociceptors include ? substance P
Inhibition of the release of substance P is the basis of pain relief by ? opioids
Fast pain is carried by ? group A-delta fibers.

It has a rapid onset and offset, and is localized

Slow pain is carried by ? C fibers.

It is characterized as aching, burning, or throbbing that is poorly localized.

Referred pain Pain of visceral origin is referred to sites on the skin and follow the dermatome rule.

These sites are innervated by nerves that arise from the same segment of the spinal cord.

For example: ischemic heart pain is referred to the chest and should

Two-point touch threshold If each point touches the receptive fields of different sensory neurons, two separate points of touch will be felt.

If both caliper points touch the receptive field of one sensory neuron, only one point of touch will be felt.

Taste and Smell The senses of Gustation (taste) and Olfaction (smell) fall under the category of CHEMORECEPTION
Taste and Smell:

Specialized cells act as receptors for certain chemical compounds. Gustation and Olfaction are chemical senses because ?

the receptors they contain are sensitive to the molecules in the food we eat, along with the air Gustatory System
Gustatory System the sensory system for the sense of taste
In humans, the sense of TASTE is transduced by? TASTE BUDS and is conveyed via THREE of the twelve cranial nerves
. Cranial nerve 7, the facial nerve, carries taste sensations from ? the anterior two thirds of the tongue and soft palate
Cranial nerve 9 the glossopharyngeal nerve carries taste sensations from? the posterior one third of the tongue
the vagus nerve carries some taste sensations from ? the back of the oral cavity (i.e. pharynx and epiglottis
Dendritic endings of C7, C9, AND VAGUS nerves are located around the taste buds and relay sensations of touch and temperature. Taste sensations are passed to ? the medulla oblongata, (second order neurons)TO the thalamus, (3rd order neurons)TO postcentral gyrus of cerebral cortex which is devoted to SENSATIONS OF THE TONGUE
Taste sensations are passed to the ? medulla oblongata, where the neurons synapse with second-order neurons that project to the thalamus
In taste, AFTER THE THALAMUS, third-order neurons project to the area of the? postcentral gyrus of the cerebral cortex that is devoted to sensations from the tongue
Types of Taste


the simplest receptor found in the mouth is the salt (NaCl) receptor

how salt is tasted -ion channel in taste cell wall allows Na+ ions to enter cell
-this depolarizes the cell, and opens voltage-regulated Ca2+ gates
-the cell is then flooded with ions and leads to neurotransmitter release
Types of Taste


Sour taste signals the presence of acidic compounds (H+ ions in solution). There are three different receptor proteins at work in sour taste. The first is a simple ion channel which allows hydrogen ions to flow directly into the cell
Types of taste


Bitter compounds act through structures in the taste cell walls called G-protein coupled receptors (GPCR’s).

When the bitter compound activates the GPCR, it in turn releases GUSTDUCIN, the G-protein it was coupled to.

Types of taste


Like bitter tastes, sweet taste transduction involves GPCR’s.
bitter and sweet both involve GPCR's
Olfactory System
Receptor cells
-are located in the olfactory epithelium.

-are true neurons that conduct action potentials into the CNS

Olfactory System A. Receptor cells

CN 1 (Olfactory) carry info from the olfactory receptor cells to the?


-The axons of the olfactory nerves are unmyelinated C fibers and are among the SMALLEST and SLOWEST in the nervous system

Olfactory epithelium is also innervated by CN V (trigeminal), which? detects noxious or painful stimuli, such as ammonia.
ANOSMIA-NO SENSE OF SMELL because…olfactory nerves pass through the CRIBIFORM PLATE on their way to the OLFACTORY BULB
The response to Ammonia will be intact after fracture of the cribiform plate because this response is carried on by? CN 5
Olfactory System:

Mitral cells in the olfactory bulb

-are SECOND-order neurons.

-output of the mitral cells forms the olfactory tract, which projects to the cortex

in transduction in the olfactory receptor neurons, Odorant molecules bind to receptors located on ?
cilia of the olfactory receptor neurons
in transduction in the olfactory receptor neurons , after receptors located on cilia of olfactory receptor neurons are activated, they in activate what?
G proteins (G olf), which in turn activate adenylate cyclase.

in transduction in the olfactory receptor neurons, follwoing ativation of G proteins that activate adenylate cyclase, there is an increase of what?

in intracellular (cAMP) that opens Na+ channels in the olfactory receptor membrane and produces a depolarizing receptor potential
in transduction in the olfactory receptor neurons, follwing an increase in cAMP and opeing of Na+ channels in olfactory receptor membrane and production of depolarizing receptor potentia, the inital segment of the axon to threshold is?


Phantosmia is the phenomenon of smelling odors that aren't really present.
Dysosmia When things smell differently than they should
Anosmia Anosmia is the lack of olfaction, or a loss of the sense of smell
Sclera white part of eyeball, outter layer

maintains, protects and supports the shape of the eye.

retina deepest layer
choroid inbetween sclera(outer), and retina(inner)
Anatomy of the Eye The human eye is a elongated ball about 1-inch (2.5 cm) in diameter and is protected by a bony socket in the skull. The eye has three layers or coats that make up the exterior wall of the eyeball, which are the sclera, choroid, and retina.
The front of the sclera is transparent and is called the? cornea

The cornea refracts light rays and acts like the outer window of the eye.