Lecture 10: Behaviour, Motivation, Emotion, and the Brain

Olfaction

• Olfactory epithelium contains receptor cells and support cells, receptor cells send cilia into the olfactory mucosa

• Airborne chemicals dissolve in the olfactory mucosa and interact with the cilia

• Activation of metabotropic receptors leads to the opening of sodium channels and subsequent change in membrane potential

Olfactory pathways

• Odorant comes in through the olfactory mucosa

• The olfactory receptors are within the nasal/olfactory epithelium

• The cilia get moved from the odorants and cause an action potential or activate the glomeruli

• The glomeruli in the olfactory bulb synapse at the mitral cells which feed the rest of the brain that information

• The pyriform cortex is an input to the hippocampus (you have a smell and right away you have a memory -  its because there's a direct link between the olfactory bulb and your hippocampus)

• Olfaction is the only sensory input that doesn't only go the thalamus first

Gustation

• Taste receptors are found within taste buds on our tongue

• Five different taste-receptor types (sweet, sour, salty, bitter, and umami)

• Gustatory stimuli interact with microvilli located on the tips of receptors to open ion channels and alter the membrane potential

• Taste buds connect to cranial nerves 7 (facial), 9 (glossopharyngeal), and 10 (vagus)

Gustatory pathways

• cranial nerves 7,9, and 10 form the main gustatory nerve (the solitary tract) from which two paths emerge:

  1. the perception of flavour to the thalamus, the somatosensory cortex, gustatory cortex, and the orbital frontal cortex

  2. whereas the more basic behaviours of feeding go to the hypothalamus and amygdala

Regulatory motivated behaviour

Some things we just have to do for homeostasis, how hypothalamus seems to be the key for that (eating, sleeping, sweating - basic and unconsicous behaviours that we have to do to keep a balance)

Non-regulatory motivated behaviour

Don't need these to live, related to the frontal lobe (cognitive control is coming from)

• no homeostasis, curiosity driven activities (sexual activity, aggression, reading)

Hypothalamic inputs

1. Visceral input that we get from the vagus nerve (blood pressure and gut distension - taste), solitary tract made up of those cranial nerves

2. Reticular formation in brain stem, getting info from the spinal cord related to our sleep wake cycle (skin temperature)

3. Retinohypothalamic pathway = info comes into the retina to the suprachiasmic nucleus (within the hypothalamus) to help keep our circadian rhythms in check - retina is another example of input to the hypothalamus)

4. Circumventricular nuclei - The parts around the ventricles that don’t have a blood brain barrier (3 parts that don’t - ex: area postrema = induces vomiting when senses toxins in the blood)

5. Limbic and olfactory systems also provide input (amygdala, hippocampus, olfactory cortex project to hypothalamus, regulating behaviours such as eating and reproduction)

Hypothalamus outputs

1. Sends outputs to the pituitary gland

   - Stress response (HPA axis = hypothalamic-pituitary-adrenal -> hypothalamus being that hormones and endocrine system control)

2. Lateral region of hypothalamus contains both nuclei and tracts connecting brain stem to forebrain (speaks to all parts of the brain)

3. Medial tract contains the medial forebrain bundle (MFB) connecting the brain stem with parts of the limbic system (DA - reward)