The Central Nervous System and Neurons

What is the Central Nervous System?

Is made up of the brain and spinal cord. It collects, processes and responds to information in the environment. It also coordinates the workings of different cells and organs in the body.

What is the brain?

The source of conscious awareness and decision making. It has two hemispheres connected by a corpus callosum and has contralateral control of the body.

What is the spinal cord?

Is a tube like extension of the brain and is connected to the brain via the brain stem. It is responsible for reflex actions (e.g. removing your hand off a hot plate) and passes message between the PNS and CNS.

What is the Peripheral Nervous System?

The PNS transmits messages to and from the CNS.

• Autonomic Nervous System (ANS): Governs vital automatic functions e.g breathing and heart rate

• Somatic Nervous System (SNS): Controls muscle movement and receives information from sensory receptors.

Neurotransmitters

Chemical messengers released from vesicles that relay signals from one neuron to another by diffusing across a synaptic cleft. E.g. Dopamine

Sensory Neuron

Carry messages from sensory receptors (e.g. temperature receptors in our skin) along the PNS to the CNS.

Relay Neuron

Connect sensory neurons to motor neurons or to other relay neurons. They are only found in the CNS.

Motor Neurons

Carry messages from the CNS to the nerves along the PNS to the effectors (muscles and glands)

What is an action potential?

The method by which electrical impulses travel down the axon of a neuron to stimulate the release of neurotransmitters.

Describe the process of synaptic transmission

1. The neuron is depolarised triggering an action potential to travel down the axon of the neuron and stimulate the movement of neurotransmitters.

2. Once at the axon terminal, the vesicles release the neurotransmitters into the synaptic cleft.

3. The neurotransmitters diffuse across the synapse and bind to receptors on the post-synaptic neurons.

4. Remaining neurotransmitters that do not bind to the receptors on the post-synaptic neurone are uptaken by uptake pumps or are broken down by enzymes