the senses and their receptors (VESTIBULAR ETC)

Question 1

what are the two types of the nervous system ?

Answer 1

. CNS - brain and spinal cord

. PNS - nerves that branch off spinal cord and extend to all parts of body

Question 2

what is the difference between sensory and motor neuron?

Answer 2

. sensory ( afferent ) - carry signals from the outer parts of your body (periphery) into the central nervous system.
. motor ( efferent) - carry signals from the central nervous system to the outer parts

Question 3

how many senses do we have and what are they divided into ?

Answer 3

. 9 senses divided into
1. 4 somatic senses from general body tissues ( skin , muscle , joint , organ )
. touch ( texture , pressure )
. thermal / temperature ( warm , cold)
. pain ( tissue damage )
. kinesthesis / proprioception ( muscle tension , joint position )

2. 5 special senses from specific body tissues : eye , ears , nose , mouth and head
   . vision , hearing/audition , smell/olfaction , taste/gustation
   . vestibular ( head position and movement )

Question 4

what are the 5 main receptors and their response to different types of stimuli ?

Answer 4

1. mechano - receptors : distortion / displacement of the receptor cell membrane
   e. g. touch , kinesthesis , hearing
2. thermostatic - receptors: thermal changes to body core or skin temperature
   e. g. thermal
3. chemo - receptors : molecules that contact the receptor membrane
   e. g. smell/olfaction
4. noci - receptors : foe pain , noxious stimuli respond to tissue damage
   e. g. pain
5. photo - receptors : photons captured by light-sensitive pigments
   e. g. vison/sight

Question 5

what is the function of somatic and olfactory sensory receptors ?

Answer 5

. all sensory receptors perform the same basic function which is converting a particular stimulus into electrical activity ( transduction )

. all types of somatic and olfactory receptors generate action potential when transducing their stimuli because they are attached to axons belonging to sensory neuron which is always nearly known as ganglion cell which send electrical impulses to the CNS

Question 6

what is the function of other sensory receptors ?

Answer 6

they are separate from their sensory neuron and axons , transduction by theses receptors generates changes in their membrane potential and release neurotransmitters at their synapses with the sensory neuron which sends action potential via their axons to the CNS

Question 7

what are the somatic sensory receptors and their function ?

Answer 7

. merkel’s disc - responsible for texture
. free nerve ending - thermal or pain
. meissner’s corpuscle light pressure
. pacinian corpuscle - vibration and deep pressure
. ruffini corpuscle - skin stretch

Question 8

what are the three types of proprioceptor ?

Answer 8

1. muscle spindles - muscle stretch
2. golgi tendon organs - muscle tension/contraction force
3. ruffini ending - also in ligaments for joint stretch / position

Question 9

what is proprioceptor ?

Answer 9

a sensory receptor which receives stimuli from within the body, especially one that responds to position and movement.

Question 10

what are the 2 types of photoreceptors in the eye ?

Answer 10

.Rods are responsible for vision at low light levels (scotopic vision).Cones are active at higher light levels (photopic vision)
.they contain light sensitive photo-pigments
. they have synapse
. they are the most common receptors in human body ( 125 mill per eye )

Question 11

what is the function/structure of mechano - receptors ( hair cells ) for hearing and the vestibular senses ?

Answer 11

structure - 1 kinocillium
40-60- stereocillia ( stick up on top of hair cells )

function :
distortion/bending of the cilia especially the kinocillium leads to transduction : change in membrane potential in receptor hair cells , leads to more synaptic vesicle which causes an change in neurotransmitter release onto the ganglion cell axon reporting information to the brain.

Question 12

what is the function of the vestibular system ?

Answer 12

. forms the basis of our ( unconscious ) sense of head position and motion. it is key to maintaining our balance and posture.

balance involves other modalities
. vision , especially of the ground plane
. tactile and kinesthetic receptors in the body and limbs especially in contact with supporting surfaces e.g. ground
. but these are not sufficient without vestibular information about the head position with respect to gravity and head movement ( especially its acceleration and deceleration )

Question 13

what is the kinesthesis sense ?

Answer 13

It involves being able to detect changes in body position and movements without relying on information from the five senses.

Question 14

where is the vestibular apparatus found ?

Answer 14

is found in the inner ears inside the cranial cavity , housed in hard ( petrous ) part of the temporal bones

Question 15

what are the 5 parts of the inner ear ?

Answer 15

1. convoluted shell of bone - bony labyrinth
2. containing a fluid perilymph
3. suspending a convoluted connective tissue membrane - membranous labyrinth
4. which supports the sensory hair cells
5. bathed in another fluid - endolymph

Question 16

what is the vestibular system ?

Answer 16

is part of the inner ear that provides the leading contribution to the sense of balance and spatial orientation for the purpose of coordinating movement with balance

Question 17

what are the 3 sensory parts of the ear ?

Answer 17

. cochlea ( hearing )
. vestibule ( containing the utricle and saccule )
. 3 semi - circular canals

the utricle and saccule and the 3 other semi-circular canals make up the vestibular apparatus

Question 18

what does the utricle and saccule respond to ?

Answer 18

they respond to linear head acceleration and deceleration of which gravity is a special example

Question 19

what does the semi-circular canal respond to ?

Answer 19

respond to angular head acceleration and deceleration

Question 20

what is a special property of vestibular hair cells ?

Answer 20

they are bi-directional signallers
. at rest they are tonically active releasing an excitatory neurotransmitter producing a steady action potential firing rate in the nerve innervating it

Question 21

what happens when the stereocilia bend towards the kinocilium ?

Answer 21

this causes an excitation/depolarisation in the hair cell , increasing its neurotransmitter release and the nerve firing rate this is because bending the stereocilia towards the kinocilium opens potassium channels in the hair cell membrane so potassium ions enter it from the endolymph and causes depolarisation , causing an increase in excitatory neurotransmitter release

Question 22

what happen when the stereocilia bend away from the kinocilium ?

Answer 22

this causes an inhibiting/hyperpolarizing the hair cell reducing its neurotransmitter release and the nerve firing rate this is because bending the stereocilia away from the kinocilium closes potassium channels in the hair cell and it becomes negatively charged causing a decrease in excitatory neurotransmitter release

Question 23

what are cilia attache by ?

Answer 23

the cilia are attached by myosin threads so that bending them physically opens or closes the potassium channels

Question 24

what is the anatomy of the utricle and saccule ?

Answer 24

. hair cells are concentrated in a region called the macula
. with the head upright , hair cells at right angle
utricle hair cells = vertical
saccule hair cells = horizontal
. tips of their cilia embedded in a gelatinous otolitic membrane
. studded with numerous calcite crystal stones ( otoconia ) that increase the membrane’s weight

Question 25

how do utricle hair cells respond to head motion ?

Answer 25

. linear acceleration/deceleration forwards-backwards

.when you start to walk , inertia causes the heavy otolithic membrane to get left behind so hair cells bend backwards

. when you suddenly stop inertia causes the heavy otolithic membrane to keep going hair cells bend forwards

Question 26

how do saccule hair cells respond to head motion ?

Answer 26

. linear acceleration/deceleration up-down ( bobbing when you walk )

Question 27

how do utricle and saccule respond to head position ?

Answer 27

. utricle and saccule hair cells are bent in different ways
. they act as 2D cartesian x,y coordinate system because gravity acts as a linear head accelerator so utricle can bend towards kinocilium and excited but saccule may be inhibited

Question 28

what is the anatomy of the semi-circular canals ( sccs)

Answer 28

. 3 organised at right angle to each other x,y,z
. hair cells are located in an expanded ampulla at one base of each canal
. they sit on a ridge with their cilia embedded in a gelatinous slab( cupula) which completely blocks the canal and acts like a swing door
. all their kinocilium face in only one direction

Question 29

how do sccs respond when the head is static ?

Answer 29

the hair cells are not bent and the vestibular nerve afferents fire at a steady resting rate

Question 30

how do sccs respond with abrupt head turn ?

Answer 30

the sccs rotate in same direction but their endolymph gets left behind due to inertia and acts as an accelerator pushing cupula to swing in opposite direction bending toward the kinocilium results in hair cell excitation and increased firing

bending away causes inhibition and reduced firing

Question 31

how do sccs respond when head stops abruptly ?

Answer 31

the endolymph keeps going due to inertia pushing the cupula in the opposite direction so if scc was excited by the initial turn its now inhibited and vice versa

Question 32

how do the 3 pairs semi-circular canals respond to different directions of angular head acceleration ?

Answer 32

by acting as 3D cartesian ( x,y,z) coordinate system
1.horizontal side to side ( no )
mainly horizontal canal
2. vertical backwards-forwards (yes)
anterior and posterior canals
3. tilt side to side ( maybe )
all 3 canals in each ear

Question 33

how does the CNS determine the direction of head motion ?

Answer 33

. from the relative excitation or inhibition of the 3 SCCs in each inner ear

Question 34

what happens when you abruptly turn your head to the left ?

Answer 34

. this causes relative endolymph fluid movement to right in the horizontal sccs in both left and right ear
. the cilia bent to left scc are excited by this while those in the right scc are inhibited and the anterior and posterior SCC in both ears are unaffected and remian at rest

Question 35

what are the 2 reflex eye movement generated by vestibular signals ?

Answer 35

1. vestibular - ocular reflex
   . stabilizes visual world on the retina
   . to compensate for angular head acceleration
   . generated by the semi-circular canals
   . both eyes move in opposite direction
   . disorder ( oscillopsia ) - everything is in motion

2. eye - righting reflex
. improves foveal fixation of the visual world
. to compensate for head tilt
. generated by the utricle and saccule 
. both eye rotate in opposite direction

Question 36

how does the vestibular ocular reflex work ?

Answer 36

. when you move your head to the right , this activates right scc and left scc is inhibited , this send signals to the brain which then sends signals to the eye muscle to make them move in opposite direction to compensate so you dont get oscillopsia
. when you move your head to left , left scc excited and excitation of extraocular muscle on the other side , compensating eye movement

Question 37

what are some example of vestibular dysfunctions ?

Answer 37

. motion sickness/nausea - conflicts vestibular vs visual motion signals

. viral inner ear infections / labyrinthitis
inflammation generates convection currents in endolymph fluid mimicking head motion causing vertigo/dizziness

. meniere’s disease
unknown cause : membrane rupture with mixing of endo and peri lymph generating toxins damaging to hair cells
. vestibular apparatus and cochlea affected : vertigo , vomiting , inability to stand and major hearing loss and howling tinnitus