Neurons and Neural Transmission

Psychology

What is a neuron?

• cells of he nervous system that communicate with each other, as well as muscle and gland cells

What is the structure of a neuron?

• cell body (soma)

• Nucleus

• Dendrites

• Axon

• Myelin sheath

• Axon terminal

What is the cell body (soma)?

• structure containing a nucleus that controls the activities of the neuron

• Processes information received by dendrites

What is the dendrites?

• extensions of the cell body that receive neurotransmitters from presynaptic neurons and convert them into electrical nerve impulses that are conducted towards the cell body

What is the axon?

• long projection of a neuron that conducts electrical nerve impulses and carries them away from the cell body

What is the axon terminals?

• enlarged end points of axon branches that store neurotransmitters and release them into the synaptic cleft

What is the myelin sheath?

• fatty covering of the axon that acts as an insulator, protecting axon from stimuli that could interfere with electrical nerve impulse transmisson

What is Nerogenises?

The process of growing neurons

What is the process of neurogenesis?

1. Producing new neurons

   • the creation of new neurons from neural stem cells

2. Growing new branches

   • development of new dendrites or axon terminal branches

3. Establishing connections

• forming connections between existing neurons to create neural circuits

What are the three main types of neurons?

Sensory

Motor

Interneurons

What do sensory neurons do?

process sensory information from the sense organs and carry the sensory messages to the spinal cord and brain (CNS)

• Carry nerve impulses from receptor to CNS

• Have long dendrites, and short axons

What do motor neurons do?

carry motor messages from the spinal cord and brain (CNS) to the muscles, glands and organs of the body.

• carry nerve impulses from CNS to an effector gland (muscle or gland)

• Short dendrites and long axons

What do interneurons do?

Act as a connection between sensory and motor neurons.

They transfer messages from the sensory neurons to motor neurons within the CNS

• found completely in CNS

• Provide link writhing CNS between sensory and motor neurons

• Short dendrites, long or short axons

What are the three types of neurons (according to structure)

Unipolar

• 1 axon

Bipolar

• 1 axon, 1 dendrites

Multipolar

• multiple dendrites and a single axon

Process of Neural Transmission (long)

• Neurotransmitters within Nervous System that as as chemical messengers, allowing neurons to communicate info

• Neurotransmitters DO NOT travel through the entire neuron. Only located in the Synapse

• Electrical nerve impulses travels on only one direction, from dendrites to the cell body, where it is converted into an action potential

• Action potential rapidly continues down the axon to axon terminals

• Upon reaching axon terminals, triggers release of neurotransmitters into synaptic cleft, and attach to receptor sites on dendrites of the postsynaptic neuron

• Dendrites then convert neurotransmitters into electrical nerve impulses that travels to cell body

What are neurotransmitters?

molecules found within the NS that act as chemical messengers

What is the synapse?

segment comprised of the action terminal of a presynaptic neuron, the synaptic cleft and the dendrites of a postsynaptic neuron

What is a presynaptic neuron?

neuron that transmits a signal into the synapse

What is the synaptic cleft?

space between 2 neurons

What is a postsynaptic neuron?

neuron that receives a signal from the synapse

What is an action potential?

electrical impulse that travels along the axon of neurons towards the axon terminals where it causes the release if neurotransmitters into the synaptic cleft

What is an electrochemical signal?

The combination of electrical nerve impulses and neurotransmitters found within and between neurons

Process of Neurotransmission (simple)

NEUROTRANSMISSION IF AN ELECTRO-CHEMICAL PROCESS

1. Electrical nerve impulses (action potential) travel to the axon terminal in the presynaptic neuron

2. Action potential triggers neurotransmitter release from vesicles in the axon terminal

3. Neurotransmitters diffuse across the synaptic cleft

4. Neurotransmitters bind to receptor sites on the dendrites of the postsynaptic neuron

5. Dendrites converts neurotransmitters into electrical nerve impulses which travel to the cell body

How are neural impulses transmitter/ what is the electro-chemical signal?

1. Resting state

   • neuron maintains negative charge inside, relative to outside

2. Depolarisation

   • stimulus causes sodium channels to open, positive ions flow in

3. Action potential

   • if threshold is reached, electrical signal travels down axon

4. Depolarisation

   • potassium channels open, restoring negative internal charge

What are receptors?

specialised proteins on postsynaptic neuron that bind to specific neurotransmitters

What happens at the synapse? Stage 1

1. Axon terminals connect with receptors on neighbouring dendrites

What happens at the synapse? Stage 2

2. When hit with electrical impulse (action potential), axon terminals of sending neuron release neurotransmitters

What happens at the synapse? Stage 3

3. Neurotransmitters travel across tiny gap called synapse and attach to receptor sites on target dendrites of receiving neuron

What happens at the synapse? Stage 4

4. Attached neurotransmitters generate action potential in receiving neuron’s short dendrites (neural impulse has been transmitted)

What happens at the synapse? Stage 5

5. Most neurotransmitters return to their original axon terminal, a ‘re-uptake’ process

What happens at the synapse? Stage 6

Other neurotransmitters are broken down by enzymes and need to be replenished.

By: -food, excessive sleep

Affected: drugs, toxins, emotional states

What happens at the synapse (simple)

1. Release

   • neurotransmitters are released into synaptic gap

2. Binding

   • neurotransmitters bind to receptors

3. Signal

   • Postsynaptic neuron is excited or inhibited (depending on the emotion etc..)

4. Removed

   • excess neurotransmitters are removed

What is he direction of transmission?

Electrical never impulse travels ONE WAY

From dendrites down to axon

Once reached axon terminals, causes release of neurotransmitters

What is the role of the synapse?

allows neural transmission to occur by converting electrical nerve impulses from one neuron into chemical signal and then back into electrical