Neurons Flashcards
What are neurons?
- Provides the nervous system with its means of communicating
- They’re nerve cells that process and transmit messages through the nervous system, using electrical and chemical signals
What do neurons consist of?
- Cell body
- Dendrites
- Axon
- Myelin sheath
- Nodes of Ranvier
- Terminal buttons
Describe dendrites as a part of the neuron
- At one end of the neuron and receives signals from other neurons or the sensory receptors
- Connected to the cell body
Describe the cell body as part of the neuron
- Contains the nucleus, control centre of the neuron
- From the cell body, impulse is carried along to axon
Describe the axon as part of the neuron
Impulse is carried, where it terminates at the axon terminal.
Describe the myelin sheath as part of the neuron
- An insulating layer that forms around the axon
- Allows nerve impulses to transmit more rapidly along the axon. If myelin sheath is damaged, impulses slows down.
Describe nodes of Ranvier as part of the neuron
- Gaps between myelin sheath
- The impulse jumps across these leading to increased speed
Describe terminal buttons are part of the neuron
- The end of the axon
- Communicate with the next neuron across the synapse gap via synaptic transmission
What is action potential?
- Neurons must transmit info both within the neuron and from one neuron to the next.
- The dendrites receive info. This is passed down to the cell body and on to the axon. Once info has arrived at the axon, it travels down its length in the form of an electrical signal, action potential.
What are the 3 types of neurons?
- Sensory neuron
- Relay neuron
- Motor neuron
What are sensory neurons?
- Carry nerve impulses from sensory receptors to the brain and spinal cord.
- Sensory neurons convert info from sensory receptors into neural impulses. When it reaches the brain, they’re translated into sensations.
- Some info doesn’t reach the brain and terminates at the spinal cord, allowing reflexes to occur quickly.
What are relay neurons?
Allows sensory and motor neurons to communicate with each other
What are motor neurons?
- They form synapses with muscles and control their contraction. When stimulated, motor neurons releases neurotransmitters that bind to receptors on the muscle and trigger movement.
- When the axon of the motor neurons fires, the muscle with which it has formed synapses with contracts.
- Strength of muscle contraction depends on the rate of firing.
- Muscle relaxation is caused by inhibition of the motor neuron
What big are neurons?
Vary in size from less than 1mm-1 metre
Where are the 3 types of neurons located?
- Motor: in the CNS, their long axons may be in the PNS, allowing control of muscles
- Sensory: in the PNS. Sends info to the brain, some neurons end in the spinal cord.
- Relay: make up 97% of neurons, mostly in the brain and spinal cord
Describe the structure of sensory neurons
- They have a cell body with two stems on either side.
- One side receives information and the other passes it on.
- Each stem ends in small branches (dendrites) which spread out and connect with other cells.
Describe the structure of motor neurons
Their cell body may be in the CNS, but their long axon is in the PNS, where it divides into a spread out set of short dendrites, called the motor end plate, which connects with the muscles.
Describe the structure of relay neurons
- Entirely surrounded by dendrites. It passes messages to other neurons within the CNS.
- They make sensory connections between each other and allows the other 2 neurons to communicate.
