Lecture 5 - The senses Flashcards
1
Q
What are the 5 senses?
A
- touch/ somatosensation
- vision
- taste
- audition (hearing)
- smell/ olfaction
2
Q
What is sensation?
A
the registration of physical stimuli from the environment by the sensory organs
3
Q
What is perception?
A
- the interpretation of sensations by the brain
- our version of reality is our perception of the sensory world
4
Q
What is somatosensation?
A
information about what happens on the surface of the body and inside it
5
Q
How is the physical stimulus converted into an electrical signal?
A
- Sensory receptors have specialised dendrites that will open ion channels if stimulated by the appropriate external stimulus
- For example, a feather rubs a hair on the skin, the dendrite of a touch receptor is wrapped around the hair so that when the hair moves the dendrite is stretched, this opens stretch sensitive Na channels on the dendrite causing depolarization
6
Q
How does the signal get to the brain?
A
Pain and temperature are carried in different pathways to the brain compared to touch and pressure
7
Q
What are the 3 components of somatic (body) sensation?
A
- touch (mechanical stimulation)
- pain (heat, chemical or mechanical stimulation)
- limb proprioception (muscles, joint stimulation)
8
Q
Somatic sensation?
A
- Signals from the body pass to the spinal cord and onto the brain via the thalamus where they are processed by the opposite side of the brain in the somatosensory cortex
- Pain is carried by unmyelinated axons, whereas other somatosensory neurons are myelinated
- Stimulation of non-pain receptors block pain, that is why ‘rubbing it better’ works = ‘gate control theory of pain’
9
Q
What is a receptive field?
A
- Each receptor responds to stimulus that fall within a small area of the body = its receptive field
- For example, the receptive field of a touch neuron is the portion of skin that stimulates all dendrites of that receptor neuron
- The size of the receptive field is an important factor in determining sensitivity of a sensory system: receptor neurons with smaller receptive fields allow greater sensitivity
- Glabrous (non hairy) skin is much more sensitive to touch
- Sensory receptors indicate how strong a stimulus is by the number of action potentials they fire
- Stronger stimuli produce more action potentials per unit time than weaker stimuli – frequency coding
10
Q
What regions of the brain are involved with processing the 5 senses?
A
- vision = occipital/ temporal/ parietal
- hearing = temporal
- touch = parietal
- taste = frontal
- smell = frontal
11
Q
Olfaction (smell)?
A
- Scent (odorants) interacts with chemical receptors
-> Chemicals dissolve in the mucosa and interact with the cilia - Changes in the membrane potential are mediated by metabotropic ion channels
12
Q
Neurons?
A
- respond to a range of odours, and summed activity over a range of neurons allows perception of a particular smell
- this is controlled by 350 strong gene family that allows discrimination of 10,000 different smells
13
Q
What happens when an odour enters a nostril?
A
- Odours entering one nostril are processed by the same side of the brain.
- Unlike other senses smell signals bypass the thalamus and go directly to the amygdala & pyriform areas
- From here one projection goes to the limbic system (emotional response to odours), another projects to the thalamus to the orbitofronal region (conscious perception of odours)
- Olfactory receptor cells are also used to detect pheromones - chemicals that are not perceived consciously as smells, but do nevertheless influence behaviour in respect to attraction
14
Q
Taste?
A
- taste stimuli are chemicals that are detected by taste receptors on the tongue
- different taste receptor neurons detect the 4 basic tastes: salty, sour, sweet and bitter
- taste preference is genetic too
- the surface of the tongue has papillae
- papillae contain taste buds –overall around 10,000
- each taste bud contains multiple taste cells with microvilli that detect tastants
- the opening of ion channels on the microvilli leading to membrane potential changes
15
Q
What is the taste pathway?
A
- Cranial nerves 7 (facial), 9 (glossopharangeal) and 10 (vagus) group together to form the main gustatory nerve.
- The nerve first travels to the nucleus of the solitary tract in the brainstem, then to the thalamus
- It divides into two pathways, one for sensation, one for an emotional and hormonal response
