Senses

Question 1

What is the overview of the pathway of senses?

Answer 1

Physical/chemical environment 
Reception
Transduction
Encoding/transmission
Perception

Question 2

What are labelled lines?

Answer 2

One pathway per modality

Meaning each sense has only one pathway

Question 3

How are senses recieved?

Answer 3

Properties (e.g. location) of stimuli are mapped onto brain structures e.g. retinotopic, chemotopic and tonotopic maps

Question 4

How can the intensity of coding stimulus be activated?

Answer 4

It can be encoded by either spike rate and the number of axon receptors being activated

Question 5

What are the different pathways of the senses?

Answer 5

Visual Pathway
Auditory pathway
Olfactory (smell) pathway
Gustatory (taste) pathway

Question 6

Describe some features of the eye?

Answer 6

Optic nerve - blind spot, that carries nerve imulses to the brain
Ciliary muscle - changes the thickness of the eye lens
Cornea - transparent layer that protects the eye and helps focus light on the retina - refraction
Iris - ring of muscle controlling the amount of light entering
Lens - focuses light on to the retina
Pupil - hole that allows light through
Retina - light senstive cells recieve the light rays and they are converted to neural signals

Question 7

What is used in phototransduction?

Answer 7

The retina - which is made up of rod and cone cells

Question 8

Information about cone cells?

Answer 8

High in the fovea
Iodopsin pigment - 3 types: blue, green and red sensitive
Each one is connected to a separate bipolar neurone
High visual acuity
Low sensitivity in low light

Question 9

Information about Rod cells?

Answer 9

High in the side eye
Rhodopsin pigment 
Many rod cells are connected to each bipolar neurone
Low visual acuity
High sensitivity in low light

Question 10

What is the retina made up of? How do they generate a nerve impulse?

Answer 10

Choroid
Rod and cone cells
Biopolar cells
Ganglion cells

Light changes the protein conformation of the receptor
G-protein is activated - binding GTP
This decreases second messenger and there is a decrease in Na+ conductance from the ion channels = action potential

Question 11

What is the visual pathway in mammals?

Answer 11

Retina
Optic nerve
Optic chiasm
Optic tract
Lateral geniculate nucleus (in the thalamus)
Projection fibres (optic radiation)
Primary visual cortex of cerebral hemispheres

Question 12

What is the stimulus in the audition pathway?

Answer 12

Stimulus - pressure, waves and air

Sound is actually a series of changes in are pressure which form a wave

Question 13

What is the ear made up of?

Answer 13

External ear
Middle ear - tympanic cavity, auditory ossicles
Internal ear - cochlea

Question 14

What does the middle ear do?

Answer 14

This amplifies the waves
Transmit pressure waves in air into pressure waves in liquid
This results in ~22x greater force at the oval window

Question 15

What does the Cochlea do?

Answer 15

Vibration causes the organ of corti to move up and down
It is the inner hair cells (sterocillia) within the organ of corti that when perturbed = mechano-electrical transduction
Movement of the hair K+ channel opens = depolarisation
Which then opens Ca2+ channels = neurotransmitter release onto spiral ganglion cells
These axons form the auditory nerve

Question 16

What is tonotopy?

Answer 16

The spatial arrangement of where sounds of different frequency are processed in different areas of the brain

Question 17

What is the auditory pathway in mammals?

Answer 17

Cochlea - stimulation of hair cells leads to AP
Cochlear neucleus (brainstem)
Inferior colliculus
Medial geniculate nucleus (in the thalamus)
Primary auditory cortex (temporal lobe)

Question 18

Give an overview of the olfactory (smell) pathway?

Answer 18

Olfactory sensory neurons are located in the olfactory epithelium which lines the nasal cavity below cribriform plate
Odourants enter nasal cavity & dissolve in mucus secretion
Dissolved odourants bind to receptors on the cilia of olfactory sensory neurons

Question 19

How does transduction happen in the olfactory pathway (smell)?

Answer 19

All receptors are metabotropic and initiated a second messenger model:
Odourants bind to G-protein coupled receptors on cilia
Activation = production of cAMP
This leads to depolarisation as:
cAMP binds to and opens cation (Ca2+ & Na+) channels
Ca2+ opens Cl- channels -> Cl- efflux

Question 20

What happens in encoding and transmission in the olfactory pathway (smell)?

Answer 20

Olfactory sensory neurons send their axons through the cribriform plate to synapse in the olfactory bulb (the 1st stage of olfactory processing)
Signals are then sent directly to many brain areas

Question 21

What are the signal targets within the brain in the olfactory pathway (smell)?

Answer 21

It targets cortical and subcritical structures directly

Projects directly to emotion (amygdala) and memory (hippocampal) centres

Question 22

Give an overview of the gustatory system (food)?

Answer 22

Majority of ‘taste’ comes from smell, texture, visual appearance
First step is break down of food by enzymes in saliva to solubilise

Question 23

What are the different sections of the tongue?

Answer 23

Circumvallate papillae – largest, contain many thousands of taste buds, located at posterior
Foliate papillae – elongated structure, contain hundreds of taste buds, lie along posterior lateral edge
Fungiform papillae – smallest, contain one or two taste buds, widespread across anterior portion and tip of tongue

Taste buds localised to these three types of papillae
Throughout the tongue it has sweet, sour, bitter and salty taste buds (all spread out)

Question 24

How does fast transduction take place?

Answer 24

Dissolved molecules interact with receptors
Triggers membrane depolarisation & action potential firing
Accompanied by increase in intracellular calcium which initiates transmitter release
Transmitters excite afferent nerve fibres

Question 25

What do different neurones of the gustatory pathway project to in the brain?

Answer 25

1st order neurons project to medulla
2nd order neurons project to thalamus
3rd order neurones project to gustatory cortex