Lecture 3 - Simple neural circuits and memory

Question 1

Intracarnial meaning

Answer 1

Inside the cranium

Question 2

Intracranial self-stimulation

Answer 2

ICSS appears to produce a pleasurable effect in animals experimented on including humans

ICSS activates dopaminergic pathways including the nucleus accumbens and VTA (ventral tegmental area)

Electrodes implanted in chronically depressed patients soon became controversial

Around 50% of the neurons in the VTA are dopaminergic. The VTA projects to a number of regions including the nucleus accumbens and prefrontal cortex

The human reward system (e.g. VTA and nucleus accumbens) is activated by a wide range of reinforcers including food, sex, money, drugs, beauty and humour!
Drugs like cocaine and amphetamines are known dopamine agonists, one of the things that they are doing is activating this system so you are artificially getting activation of the system. So you are artificially getting stimulation of a system that is in place to ensure that you find behaviours that will enhance you survival such as eating, having sex and drinking are pleasurable through the natural means of dopamine

Recent pre-clinical and clinical trials suggest that deep brain stimulation DBS in areas including the nucleus accumbens may be effective in moderating treatment resistant depression
Note - they would try other treatment options first, this is the final option available because it is so extreme

Question 3

Areas where dopamine transmission is very important?

Answer 3

Ventral tegmental area and the nucleus accumbens

Question 4

Simplest behaviour producing network is the …

Answer 4

reflex

Question 5

Nervous system relies on the operation of networks of neurons to produce

Answer 5

Complex behaviour

Question 6

The reflex

Answer 6

a simple automatic response to a stimulus

Question 7

The reflex operators without

Answer 7

conscious control

i.e. stereotyped, subconscious, unlearned

Question 8

Reflex examples

Answer 8

eye blink, swallowing, pupil dilation/contriction, piloerection, photic sneeze (10% of population, going from dark to light which results in a sneeze) or withdrawn reflex

Question 9

What level do reflexes occur?

Answer 9

Occurs at the level of the spinal cord to ensure that they are fast as there is no need for higher level processing which would take more time and this therefore frees the brain up to do much more important tasks

Question 10

All commands to muscles are communicated through…

Answer 10

There are several million neurons concerned with the generation of movement but all of the commands to muscles are communicated through approx 400,000 alpha motor neurons

Question 11

Monosynaptic stretch reflex

Answer 11

Reflex that works to maintain posture, corrects posture when you are leaning too far forward or back for example
One synapse
This is the reflex that doctors check when they are hitting your knee cap
Sensory stretch receptors pick up on the stretching of the muscle and sends it to the spinal cord via a neuron which synapses with the alpha motor neuron causing this signal to come back from the alpha motor neuron to tell the muscle to contract because something has happened i.e. it sends a signal to cause the reflex therefore your leg will kick out

Question 12

Synaptic excitation

Answer 12

excitatory synapse is a synapse in which an action potential in a presynaptic neuron increases the probability of an action potential occurring in a postsynaptic cell.

Question 13

Synaptic inhibition

Answer 13

a specialized type of junction at which activity from one neuron (in the form of an action potential) reduces the probability of activity in an adjacent neuron by initiating an inhibitory postsynaptic potential.

Question 14

Polysynaptic reflex

Answer 14

Very important for fluid movement and movement around a joint

Involves more than one synapse

THe stretch receptor does not only send a signal to the alpha motor neuron from the muscle that the signal is coming from but also sends a signal through an inter neuron ( a neuron sending a signal internal to the spinal cord, short distance) and its a signal to the alpha motor neuron that controls the flexor muscles to relax

Question 15

Grasping reflex

Answer 15

babies when you put your finger in their hand they grasp

Question 16

Suckling reflex

Answer 16

when you stroke a baby’s face it causes them to turn as if they are ready to suckle

Question 17

Grasping and suckling - why not display these reflexes when older?

Answer 17

Inhibited by maturing brain but may be disinhibited - this reflex has been suppressed as the nervous system develops, so you do not normally see them except in cases where you remove the suppression such as brain damage or extreme intoxication i.e. these cause disinhibition

Question 18

Vestibulocular reflex (VOR)

Answer 18

modifiable, monitors your head movement so that you eyes move in the opposite direction and therefore you maintain a steady gaze

Question 19

rooting reflex

Answer 19

touch a baby on its cheek will cause it to turn its head towards the direction of the touch in order to orient its mouth towards a breast or bottle

Question 20

Define reflexes

Answer 20

Automatic, inborn behaviours that occur in response to a specific stimuli