The Neuron

Fast Facts. A neuron is a cell. A group of neurons = A nerve! Three different types of neurons: sensory (afferent), motor (efferent) and connector neurons. Neurons conduct electrical impulses.

The Nucleus Contains the neurons DNA. Controls activity of the cell.

Cell Body. Contains the nucleus.

The Dendrites. Receives electrical impulse from neighboring neurons. Carries electrical impulse towards the cell body.

The Axon. Carries electrical impulse away from cell body.

Myelin Sheath Cover the axon and work like insulation which allows them to move more quickly.

Node of Ranvier Un-myelinated segments of the the neuron. Allowing nutrients and waste products to enter/leave the neuron.

Schwann Cell. Schwann cells are the cells that lay down the protective myelin sheath around the axon. Each Schwann cell protects one length of axon, around which it twists as it grows.

Axon Terminal A complex terminal formation which the axon where an electrical impulse is passed into a synapse.

Synapse Two neurons do not make direct contact! Where they meet, there is a very small gap called a synapse. The impulse needs to cross this gap to continue on its journey to, or from, the CNS. This is done by means of chemicals which diffuse across the gap between the two neurons using neurotransmitters.

Types of Neuron Motor Neuron. 2. Sensory Neuron. 3. Connector Neuron (or interneuron). Sensory neuron: Takes the sensory information (prick of the pin) from the receptor towards the spinal cord. Cell body found the dorsal root ganglion. Connector neuron: Solely found in the CNS – brain and spinal cord. These connect sensory neurons and motor neurons with each other and other CNS neurons. No myelin sheath (found in grey matter) and no extended axon. Motor neuron: Takes the motor information from the CNS to the effector (muscle/gland/tissue) Cell body found in grey matter of spinal cord.

This is a motor neuron

This is a sensory neuron

This is a connector neuron

Grey v White Matter.

Process of Neural Transmission.

What are neurotransmitters? The electrical signals cannot travel from one neuron to the next directly. The signal crosses the gap called the synaptic cleft, between cells in chemical form. In response to the movement of sodium as part of a nerve impulse, one neuron releases chemicals called neurotransmitters in response to an action potential (nerve impulse). The chemicals travel across the synapse and stimulate an action potential in the next neuron. These chemicals are known as neurotransmitters.

Neurotransmitter Effects Variation results in Dopamine Motor control, arousal, motivation, pleasure, attention. Low levels = ADHD and Parkinson’s. High levels = schizophrenia. Serotonin Mood, appetite, sleep, impulsive/aggressive behaviour. Low levels = depression and anxiety disorders. Acetylcholine   Attention, learning, memory, muscle stimulation. Low levels = Alzheimer’s. Noradrenalin Flight/flight. (Increased heart rate, increased glucose in blood stream, increase oxygen to brain/muscles). Low levels associated with depression. Endorphins Involved in pain relief and feelings of pleasure and contentedness

The Spinal Cord Add in 6 – central canal. White matter Dorsal root ganglion Grey matter Ventral root.

The Spinal Cord.

Sensory neuron Motor neuron Connector (relay) neuron Receptor Stimulus Effector

The Spinal Reflex. Ask students to annotate “relay neuron” to interneuron. Focus on cell body locations.