Biopsychology: Neurons and Synaptic Transmission

Nervous system- Micro level

• contains about 100 billion nerve cells called neurons (80% located in brain alone)

• cells that relay information around the brain and nervous system by using electrical impulses and chemicals called neurotransmitters

• Electrical impulses travel from one end of a neuron to another and release a chemical known as a neurotransmitter

• if they aren’t working this will affect our behaviour in multiple ways

Structure of a neuron

• dendrite

• nucleus

• axon

• myelin sheath

• nodes of Ranvier

• terminal buttons

Sensory neuron (unipolar)

• carry messages from the PNS to the CNS

• they only transmit messages and hence is unipolar

• tell the brain about the external & internal environment by processing info from 1 of 5 sets of sensory receptors which is converted into neural impulses

• in the brain these impulses are translated into sensations we can appropriately react

• have long dendrites and short axons

relay neuron (multipolar)

• most common type of neuron in the CNS

• allow sensory and motor neurons to communicate and connect with each other (carry nerve impulses between neurons)

• they are multipolar as they send and receive info from many sources

• aren’t found in other parts of the nervous system as they only carry messages from one part of the CNS to the other (just brain, spinal cord and visual system)

• have short and stubby dendrites and axons

Motor neuron (multipolar)

• connect the CNS to effectors such as muscles and glands

• multipolar as they send and receive info from many sources

• project their axons outside the CNS to directly or indirectly control muscles and glands

• form synapses with muscles and when stimulated release neurotransmitters to trigger a response in the muscle (contracts)

• strength of these contractions depends on the rate of the nerve impulses (inhibitors can cause muscle relaxation)

• short dendrites and long axons

Synaptic transmission (part 1)

when the dendrite picks up the message it sends an impulse through the cell body and along the axon to the terminal buttons

Synaptic transmission (part 2)

once the action potential has arrived at the terminal buttons at the end of the axon it needs to be transferred to another neuron

to achieve this it must cross the synaptic gap

Synaptic transmission (part 3)

at the end of the terminal buttons are the synaptic vesicles that contain and store neurotransmitters

these NT’s are chemical messengers that convert the impulse to a chemical message that’s transferred to the next neuron

Synaptic transmission (part 4)

as the impulse travelling to the end of the neuron reaches the synaptic vesicle they release the NT then crossing the synaptic gap

Synaptic transmission (part 5)

as the NT diffuses across the synapse it binds to specialized receptors on the surface of the next cell (on it’s dendrites) that recognise it and match that particular cell

Synaptic transmission (part 6)

once the next cell is activated the receptor molecules produce either an excitatory effect (strengthens; adrenaline) or inhibitory effect (weakens; serotonin) at a post synaptic level

Synaptic transmission (part 7)

synaptic transmission is completed by a process called reuptake, this is where NT is taken back up/ recycled by the pre synaptic neuron

enzymes break down remaining left in the synapse