Special senses

Question 1

General senses

Answer 1

Receptors are scattered through the body. E.g touch, pressure, pain, vibration, tem

Question 2

Special senses

Answer 2

have a special organ/structure with distance receptor cells devoted to it and all localised in the head region

Question 3

Importance of sensory systems

Answer 3

The ability to sense changed in the environment and in the body allowing survival
Survival depends on:
- Sensation: the awareness of changed in the internal and external environment
- Perception: the conscious interpretation of those stimuli
How we interpret sensation determines how:
- we develop physically, cognitively
- our memories are formed
- we interact socially
- we become unique

Question 4

Simple organisms e.g Hydra

Answer 4

• Respond to light, pH and nutrient presence
• basic nerve connections and primitive histology
• hydra defy standard sensory receptor modelling
• Show endogenous activity when kept in a homogenous environment

Question 5

General principles in higher animals
Receptor cells
Purpose

Answer 5

• specialised receptor cells are distributed throughout eukaryotic organisms
• purpose: to convert physical or chemical signal into electrical signal so that is can be used as an action potential
• electrical signals travel PNS to CNS

Question 6

Afferent

Answer 6

Signals received and processed by CNS

Question 7

Efferent

Answer 7

Signals from CNS elicit appropriate response in body

Question 8

Free nerve endings

Answer 8

Non-encapsulated
Pain and thermoreceptors
Light tough and hair follicle e receptors

Question 9

Encapsulated nerve endings

Answer 9

Pacinian (lamellar) corpuscles for touch and pressure
Tactile corpuscles for discriminative touch
Muscle spindles: proprioceptors respond to muscle stretch

Question 10

Specialised receptor cells e.g.

Answer 10

Photoreceptor cells in the retina of the eye respond to light stimuli - rods
Tastebuds

Question 11

Sensory receptors process

Answer 11

Stimuli in the environment activate specialised receptor cells in the PNS –> integration in brain –> send motor output to effectors
Different types of stimuli are sensed by different types of receptor cells

Question 12

How are receptor cells classified

Answer 12

Structurally by cells type, position and function

Question 13

General arrangement of neurones in ascending tracts: first order neuron

Answer 13

Has the receptor
Synapses to second order neutron
In grey matter of spinal cord or in medulla oblongata

Question 14

General arrangement of neurones in ascending tracts: second order neuron

Answer 14

interneuron
crosses over to other side
Decussation
Ascends to thalamus

Question 15

General arrangement of neurones in ascending tracts: this order neuron

Answer 15

Axons pass to somatosensory cortex

There the sensory information is received and interpreted = perception of peripheral stimulus

Question 16

Ascending tracts

Answer 16

Afferent signals travel towards brain for processing

Question 17

Descending tracts

Answer 17

efferent signals from CNS to elicit appropriate response elsewhere in body

Question 18

Spinal cord

Answer 18

• Ascending and descending tracts located in specific areas of the spinal cord
  Allocated pathways for different senses so that the brain knows where the stimuli is coming from
  Different nerve tracts lead to different parts of the brain
  Tracts are symmetrical

Question 19

Ascending pathways
Dorsal 
Tracts
Conscious 
Sub-conscious

Answer 19

Somatosensory signals travel along three main pathways on each side of spinal cord:
Dorsal column pathway: Spinothalamic tract and spinocerebellar tract
Conscious information: dorsal column,ns, fasciculus gracilis, fasciculus cuneatus, spinothalamic tracts
Subconscious: spinocerebellar

Question 20

Descending Pathways

Answer 20

Descend from brain to effector region - motor neurone to create effect
In the pyramidal pathways of the spine

Question 21

Sensory receptors (2)

Answer 21

Stimuli in the environment activate specialised receptor cells in the PNS –> integration in brain –> send motor output to effects
Different types of stimuli are sensed by different types of receptor cells
Receptor cells classified structurally by cell type, position and function

Question 22

Exteroceptors

Answer 22

Respond to stimuli arising outside of body
Receptors in skin for touch, pressure, pain and temperature
Most special sense organ

Question 23

Interceptors (visceroceptors)

Answer 23

Respond to stimuli arising in internal viscera and blood vesseld
Sensitive to chemical changes, tissue stretch, and temp changes

Question 24

Proprioceptors

Answer 24

Respond to stretch in skeletal muscles, joints, ligaments, and connective tissue covering of bones and muscles
Inform brain of one’s movements

Question 25

Mechanoreceptors

Answer 25

Stretching of cell membrane opens ion channels Respond to physical stimuli like touch, pressure, vibration and stretch. Balance, sounds, muscle length and tension, joint position and movement

Question 26

Thermoreceptors

Answer 26

Allows ions to enter cell, eliciting generator potential Several proteins that detect temperature Sensitive to changes above or below normal body temp Free nerve endings, mainly in skin, lining oral cavity and on tongue

Question 27

Chemoreceptors

Answer 27

Chemicals bind to specific receptors on cell membrane | Respond to chemicals (smell, taste, blood chemistry) = external (nose) or internal

Question 28

Photoreceptors

Answer 28

Initiate chain of reactions to cause breakdown of 2nd messenger molecule and closure of ion channels Always has an influx of ions to get the membrane potential Respond to light energy

Question 29

Osmoreceptors

Answer 29

Respond to solute concentrations of body fluids

Question 30

Nociceptors

Answer 30

Free nerve ending chemoreceptors that respond to tissue-damaging stimuli In the brain the signals are perceived as pain Sensitive to pain-causing stimuli (extreme heat or cold, excessive pressure, inflammatory chemicals) - have different properties in terms of where

Question 31

Neuronal communication after detection

Answer 31

For sensation to occur, the stimulus must excite a receptor and the action potential must be created This action potential must reach the CNS. The transmission of a nerve impulse across a synapse is by means of a chemical called a neurotransmitter

Question 32

Neurons characteristics

Answer 32

Long-lived (>100) Hugh metabolic rate - depends on continuous supply of oxygen and glucose Plasma functions in electrical signalling and cell-to-cell interaction during development

Question 33

Chemical synapses

Answer 33

- Neuron secrete neurotransmitter that binds to specific receptors in cell membrane of second neuron - most common way in which neurones communicate - axon terminal contains packets of neurotransmitter e.g. acetylcholine - electrical signal to chemical signal and then back to an electrical signal when it reached the next neuron

Question 34

Signal transmission at synapse

Answer 34

1. AP arrive at axon terminal 2. Voltage-gated Ca2+ channels open 3. Ca2+ enters cell – communicates with the synaptic vesicles to begin the transfer 4. Ca2+ signals to vesicles 5. Vesicles move to membrane 6. Vesicles dock and release neurotransmitter by exocytosis 7. Neurotransmitter diffuses across synaptic cleft and binds to specific receptors 8. Binding of neurotransmitter to receptor activated signal transduction pathway

Question 35

Sensory transduction

Answer 35

Physical energy --> electrical energy electrical energy produced by receptor = receptor potential Stimulus acts by affecting opening/closing of channels or affects calcium levels inside separate cell

Question 36

Graded potentials and special senses

Answer 36

- a receptor potential is a graded response to a stimulus that may be depolarising or hyperpolarising - receptor potentials have a threshold in stimulus amplitude that must be reached before a response is generated - graded means the amplitude of the receptor is proportional to the size of the stimulus - the transduction process couple's stimulus detection to the opening or closing of ion channels

Question 37

Stimulus intensity: frequency or recruitment

Answer 37

- the more intense stimuli produce higher frequency of action potentials - stimuli of increasing intensity activate, or recruit, greater number of receptors

Question 38

What happens in the brain

Answer 38

- any given neurone usually received signals from many other neurons - special sense pathways can form complex neural pathways when they enter the brain - when groups of neurones synapse there can always be integration