Neurons and synaptic transmission

What are neurons ?

• There are 100 billion neurons in the human nervous system, 80% of them are located in the brain

• Neurons are cells that carry rural information throughout the body

• There are three types of neurons- sensory, motor and relay

• neurons consist of a cell body , dendrites and an axon

• Dendrites at one end of a neurons recieve information signals from other neurons or sensory receptors

• Dendrites are connected to the cell body which is the control centre of thee neuron

• From the cell body the impulse is carried along the axon terminal

• In many nerves there’s is an insulating layer that forms around the axon, called the myelin sheath which allows nerve impulses to transmit

What are sensory neurons ?

• they send information from the PNS towards the CNS such as vision, taste and touch

• They are found in various locations in the body such as ears and eyes

• They convert information from these receptors into neural impulses

• When the impulses reach the brain they are translated into sensations so the organ can react properly

what are relay neurons ?

• they allow motor and sensory neurons to communicate with each other

• They are located between the brain and the spinal cord

• They have short dendrites and axons

what are motor neurons ?

• Located in the CNS

• They control muscles and glands

• They form synapses with muscles ad control their contractions

• When stimulated the motor neuron releases neurotransmitters that bind their receptors on the muscle and trigger a response which leads to muscle movement

• The strength of the muscle contraction depends on the rate of firing of the axons of the motor neurons that control it

• Muscle relaxation is caused by inhibition of motor neurons

What is a synapse ?

• The junction where two neurons meet is known as the synapse

• A synapse consists of the presynaptic knob which is a swelling at the end of the presynaptic neurons it contains vesicles which hold neurotransmitters

• The synaptic cleft this is the space between the axon of one neuron and the dendrites of another where the electrical signal is turned into a chemical messenger that can be directed by the next neuron

• The postsynaptic membrane- the membrane recieves a signal and binds their receptors on neurotransmitter from the presynaptic neuron

What happens during synaptic transmission ?

1) a signal begins as an electrical impulse (an action potential) within the presynaptic neuron

2) when the electrical impulse arrives at the end of the axon on the pre synaptic knob, chemical messengers are released from structures called vesicles ate the presynaptic membrane

3) neurotransmitters are released into the synaptic cleft as a chemical substance from the presynaptic after the action potential has occurred

4) neurotransmitters diffuse across the synaptic cleft and temporarily bind with receptor sites on the postsynaptic membrane

5) this action stimulates the postsynaptic neuron to generate another electrical impulse that the travels down the axon of the postsynaptic neuron

6) the neurotransmitter molecules are then destroyed by enzymes or recycled to prevent continued stimulation of the second neuron, which could cause repeated impulses to be sent

7) the re absorbed neurotransmitter may be used again by the presynaptic neuron

What is action potential ?

An electrical impulse which is a trigger from which neurons fire and conduct signals to stimulate the process of synaptic transmission

What are excitatory neurons ?

the nervous system’s on switch. The more excitatory neurons there are the more likely the cell is to fire

They bind with neurotransmitters to cause an electrical charge in the membrane of the cell causing it to fire

What are inhibitory neurons ?

the more inhibitory neurons there are the less likely the cell is to fire.

• when binding with a post synaptic receptor it results in the cell being less likely to fire

• Associated with calming of the mind and inducing sleep.