1-4: Synaptic transmission; structure + function of neurons; nervous and endocrine system

What is synaptic transmission?

the way that neurons communicate with each other. It involves a message being passed chemically between neurons (sensory, relay or motor)

What is happening at step 1?

the electrical signal reaches the end of the presynaptic neuron and it arrives at the terminal button to be passed onto the postsynaptic neuron

What is happening at step 2?

the electrical signal causes the vesicles to release the neurotransmitters they are carrying into the synaptic cleft ( the gap between the neurons)

What is happening at step 3?

the neurotransmitter crosses the synaptic cleft and makes its way to the postsynaptic neuron. It can only enter the postsynaptic neuron if it fits into the receptor cells (complementary) e.g the neurotransmitter dopamine can only fir into the dopamine receptor sites

What is happening at step 4?

the neurotransmitter enters the receptor site and causes an electrical message down the postsynaptic neuron, ready to be passed on to the next one. Any neurotransmitters that are left in the synapse might be broken down (by enzymes) or reabsorbed by the reuptake channel so it can be used again

What are the two possibilities of what a neurotransmitter can be?

either excitatory or inhibitory

What is an excitatory neurotransmitter?

one that binds to the receptor sites and increases the chance of the post-synaptic neuron continuing the message to the next neuron as it makes it more likely to fire

What charge does an excitatory neurotransmitter create?

a positive charge

What is an example of an excitatory neurotransmitter?

adrenaline

What is an inhibitory neurotransmitter?

one that binds to the receptor sites and decreases the chances of the post-synaptic neuron continuing the message to the next neuron as it makes it less likely to fire.

What charge does an inhibitory neurotransmitter create?

a negative charge

What is an example of an inhibitory neurotransmitter?

serotonin

Define summation.

a process which decides whether a post-synaptic neuron will fire (pass on the message). This happens by weighing up the amount of inhibitory neurons compared to the excitatory neurons

What will happen if there are more excitatory neurotransmitters than inhibitory?

the post-synaptic neuron will fire

What do sensory neurons do?

Carry information from sensory receptors in the PNS to the CNS

What do relay neurons do?

Connect sensory and motor neurons within the CNS (or to other relay neurons)

What do motor neurons do?

Carry signals from the CNS to effectors (muscles/glands)

What structural features do sensory neurons have?

Long dendrites, short axon

What structural features do relay neurons have?

Short dendrites, short axon

What structural features do motor neurons have?

Short dendrites, long axon

Show the overall structure of a neuron

What does the cell body do?

it carries the nucleus

What does the nucleus do?

it contains genetic material (DNA)

What do dendrites do?

receives electrical signals from nearby neurons

What does the myelin sheath do?

protects the axon and speeds up electrical signals

What does the node of Ranvier do?

speeds up electrical signals

What does the terminal button/axon terminal do?

communicates to a nearby neuron

What does the axon do?

carries the message through the neuron

no myelin sheath on relay neuron

What is the nervous system?

a specialised network of nerve cells in the human body. It has two main functions - to collect, process and respond to information in the environment and to co-ordinate the organs in the body

What are the two main divisions of the nervous system?

Central nervous system (CNS) and peripheral nervous system (PNS)

What structures make up the CNS?

Brain and spinal cord

What is the brain?

all the decision making takes place here. At the base of the brain is the brain stem which controls basic functions. (relay neuron is found here)

What is the spinal cord?

a long structure running down our back. It carries incoming and outgoing messages between the brain and body. (relay neuron is found here)

What is the role of the PNS?

receives and sends messages to the CNS

What are the two divisions of the PNS?

Somatic nervous system (SNS) and autonomic nervous system (ANS)

What is the somatic nervous system?

we have control over this system. It controls our muscle movement and receives information from sensory receptors

What part of the SNS do we not have control over?

our reflexes

What is the autonomic nervous system?

We have no control over this system. It co-ordinates important functions such as breathing, heart rate and digestion.

What are the two branches of the autonomic system?

Sympathetic (arousal) and parasympathetic (rest/digest)

What happens in the body during sympathetic action (fight or flight)

• heart rate and breathing increases

• pupils dilate

• salivation stops

• intestine/gut action stops

• rectum contracts

What happens in the body during parasympathetic action (rest and digest)?

• heart rate and breathing decreases

• pupils constrict

• salivation resumes

• intestine/gut action resumes

• rectum relaxes

Define fight or flight.

immediate physiological response of an animal when in danger. The body becomes physically ready to fight the threat or run away from it (flight).

What happens when our brain detects a threat in the activation of fight or flight response?

our hypothalamus identifies the threatening event (perhaps someone jumped out at you) and tells the sympathetic division of the ANS to act

What happens for adrenaline to be released?

the ANS changes from it normal resting state (parasympathetic) to a state of arousal (sympathetic). This releases adrenaline into the bloodstream

What happens during the fight or flight response?

physiological changes occur because of the adrenaline. Your heart rate increases, your pupils dilate (expand), digestion stops and saliva production is stopped. All these changes are designed to help us confront the threat (fight) or run away (flight)

What happens once the threat has passed?

The ANS changes from the state of arousal (sympathetic) back to resting (parasympathetic). Your heart rate slows down, your pupils constrict, digestion and saliva production resumes. This is the ‘rest and digest state’

What is the endocrine system?

a collection of glands that produce hormones which regulate our metabolism, growth, tissue function, sexual function, reproduction, sleep, mood and more

How do hormones travel?

Through the bloodstream to target organs with specific receptors

What is the hypothalamus?

a small area in the centre of the brain, located above the pituitary gland

What is the pituitary gland?

the ‘master gland’. It is located in the brain

What is the thyroid gland?

a gland located at the front of the neck

Where is the pancreas located?

in the abdomen part of the digestive system

Where is the adrenal gland located?

on top of the kidneys. The cortex is the outer layer of the gland and the medulla is situated within the gland

What are the ovaries?

part of the female reproductive system

What are the testes?

part of the male reproductive system

What hormone does the pituitary gland produce?

none

What is the function of the pituitary gland?

controls hormone secretion in other glands

What hormone does the hypothalamus produce?

none

What is the function of the hypothalamus?

controls functioning of the pituitary gland

What hormone does the thyroid gland produce?

thyroxine

What is the function of the thyroxine?

controls heart rate and metabolic rate

What hormone does the pancreas produce?

insulin and glucagon

What is the function of insulin and glucagon?

stimulates the release and absorption of glucose

What hormone does the adrenal cortex produce?

cortisol

What is the function of cortisol?

controls cardiovascular and anti-inflammatory functions

What hormone does the adrenal medulla produce?

adrenaline and noradrenaline

What is the function of adrenaline and noradrenaline?

prepares the body for fight and flight response

What hormone do the ovaries produce?

oestrogen

What is the function of oestrogen?

regulates female secondary sex characteristics

What hormone do the testes produce?

testosterone

What is the function of testosterone?

regulates male secondary characteristics

What is the SAM pathway?

sympathetic and adrenal medulla

This is the immediate fight or flight response which causes part of the adrenal glands to release adrenaline. Adrenaline causes the responses listed previously e.g increased heart rate

What is the HPA axis?

hypothalamic + pituitary + adrenal cortex

This is the longer-term stress response (not part of fight or flight). At the same time as the signal is sent to the adrenal medulla, a signal is sent to the hypothalamus, which then sends a signal to the pituitary gland which creates the release of the hormone cortisol from the adrenal cortex. Cortisol deals with longer-term stress e.g release of glucose into the blood to provide energy to sustain fight or flight