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Flashcards in Module 10: Special Senses Deck (313)
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Determining the Direction of Sound

• superior olivary nucleus divided into lateral and medial nuclei
• LATERAL NUCLEI detects direction by the difference in sound intensities between the 2 ears
• MEDIAL NUCLEI detects direction by the time lag between acoustic signals entering the ears



• nerve deafness - impairment of the cochlea or the auditory nerve
• conduction deafness - impairment of tympanic membrane or ossicles


Functions of the Vestibular System

• Maintains of posture and equilibrium
• Fixation of the visual horizon during rapid head movements


Maintaining Balance

• The vestibular system determines the position and motion of your head in space.


There are two components to monitoring motion:

1. Detecting rotation
- what happens when you shake or nod your head.
- This is called angular acceleration.

2. Detecting motion along a line
- what happens when the elevator drops beneath you or when your body begins to lean to one side
- This is called linear acceleration.


Vestibular System: Function

• Detects angular and linear acceleration
- Important in maintaining balance, posture, and vision
• Connections with brainstem, cerebellum, and somatic sensory cortices to provide info about the motions and position of the head and body


Elements of the Vestibular Labyrinth

• Continuous with the cochlea

• Three semicircular canals - Detect angular acceleration

• Two otolith organs:
- Utricle and saccule
- Detect linear acceleration

• Vestibular nerve fibers
- synapse with hair cells
- have cell bodies in Scarpa's ganglion


Semicircular canals: Structure

• each semicircular canal contains an ampulla
- Contains hair cells embedded in sensory epithelium called crista ampullaris
- Cilia of hair cells project into gelatinous cap called cupula (sensitive to the movement of the fluid)


Semicircular canals: Function

♦ Specialized for responding to rotational acceleration of the head
- Head rotation results in intertial movement of endolymph in opposite direction

♦ Bends cupula which bends hair cells
- Same mechanical/electrical coupling as in auditory hair cells

♦ Excites/suppresses release of NTs from hair cells depending on direction of movement


Semicircular canals: Function 2

♦ Stereocilia maintain directionality on both sides of the head
- Bending towards kinocilium >> opens mechanically gated cation channels >> K+ influx
>> depolarization
- Bending away from kinocilium >> closes channels that are open during resting state >> hyperpolarization

♦ Paired canals work together to signal head movement
- With turning of the head, hair cells on one side of the body send excitatory signals to the brain while hair cells on the opposite side are inhibited


Otolith Organs: Structure

♦ Two otolith organs; utricle and saccule
- Each contains a sensory epithleium called the macula
*Horizontally oriented in utricle
*Vertically oriented in saccule

♦ cilia of hair cells embedded in gelatinous otolithic membrane
- Embedded on surface are calcium carbonate crystals called the otoliths


Otolith Organs: Function

• Specialized to respond to gravity and linear acceleration
- Otoliths have a higher density than endolymph
*Shift when angle of head changes
*Causes otolithic membrane to shift in same direction
*Cilia of certain hair cells deflected (Excites/suppresses release of NTs from hair cells depending on orientation of cilia)


Otolith Organs: Function

• kinocilia of each hair cell are oriented in different directions in relation to striola
- Utricle: towards striola
- Saccule: away from striola

• Same sensory transduction as semicircular canals
- Bending of cilia towards kinocilium depolarizes the hair cell


Vestibular Pathways

• vestibular afferents synapse on vestibular nuclei located in medulla and pons


Vestibular Nuclei integrate information from vestibular, visual, and somatic receptors and send collaterals to

1. Cerebellum - Sends corrective adjustments to motor cortex: maintenance of balance and posture

2. nuclei of cranial nerves - Control coupled movements of the eyes, maintain focus and visual field

3. nuclei of accessory nerves - Control head movement and assist with equilibrium

4. ventral posterior nucleus of thalamus and vestibular area in cerebral cortex (part of primary somatosensory cortex)
- Conscious awareness of the position and movement of head


• Senses falling/tipping (contracts limb muscles for postural support )

Vestibulospinal Reflexes


• acts on the neck musculature to stabilize the head if body moves

Vestibulocollic Reflexes


• stabilizes visual image during head movement (causes eyes to move simultaneously in the opposite direction and in equal magnitude to head movement)

Vestibulo-ocular Reflexes


Vestibulo-Ocular Reflex (VOR)

Example: head movement to the LEFT

1. inertia of endolymph movement to the right in horizontal vestibular canals causes:
a) increased firing of left vestibular afferent
b) decreased firing of right vestibular afferent

2. Excitatory connections with contralateral abducens nuclei (lateral rectus) and inhibitory connections to ispilateral side

3. Excitatory connection to inhibitory interneuron in contralateral vestibular nuclei

4. Movement of the eyes to the right


Core Temperature vs Skin Temperature

• Core temperature
- More constant
- Temperature of internal organs

• Skin temperature
- Affected by temperature of environment
- Surface temperature of the body


What’s in between the core and skin temperature?

• We have insulators present in our body in the form of Fats (subcutaneous tissue)


How does heat transfer occur from the core of the body to the skin?

• Through blood flow


• important way of heat production; kahit na nakaupo ka lang dyan you are still generating heat

Basal Metabolic Rate


Extra metabolism secondary to:

• Muscle activity
• Thyroxine (also GH, Testosterone)
• Sympathetic stimulation of cells
• Increased chemical activity of cell
• Thermogenic effect of food



• Radiation (60%)
• Conduction (objects: 3%; air: 15%)
• Convection - conduction to air; air current should be present
• Evaporation (22%) eg insensible water loss(we cannot control it)


• Stimulation of the ANTERIOR hypothalamus-preoptic area (thermoregulator center) —> activates sympathetic response —> stimulation of sweat glands
• In lower animals, surface is covered with fur and with no sweat glands, they release excess heat through PANTING mechanism
• Neurotransmitter: Acetylcholine



REGULATION OF BODY TEMPERATURE (Peripheral Temperature sensors)

• Skin sensory receptors
- Detects body surface temperature

• Deep body temperature receptors
- Located in the spinal cord, abdominal viscera, around great veins
- Detects core body temperature
*cold receptors > warmth receptors


REGULATION OF BODY TEMPERATURE (Central Temperature sensor)

Anterior Hypothalamic - Preoptic Area


• integrates the Central and Peripheral Temperature Sensory Signals and determines if body needs heat generating or heat losing mechanism

Posterior Hypothalamic


Detected Temperature compared with Set-point Temperature

• Detected Temp Set-Point Temperature: Initiate Heat Loss Mechanisms