NEURONS // CHAPTER 2 (WHAT ARE NEUROTRANSMITTERS? ( Neurotransmitters are…
NEURONS // CHAPTER 2
TYPES OF NEURONS.
They relay sensory information to other interneurons or motor neurons in CNS. They exist only in the CNS. Sensory and motor do not directly connect.
- Afferent neurons.
- They receive and carry sensory information.
- Transmit the information to the central nervous system.
- They take sensory info (from specific sensory receptor cells) from the senses to the spinal cord and hence the brain.
- Efferent neurons.
- Carry messages from the central nervous system to the effectors (cells in the muscles, organs, glands).
- They carry motor info (messages) from brain to muscles, organs and glands via spinal cord.
- Perform the important function of making the connection between sensory and motor neurons, which DO NOT CONNECT DIRECTLY!
E.G. touch a pin, sensory neurons carry info from PNS to CNS, interneurons receive and process info, message sent back to body via motor neuron to move hand.
- An axon is a single, tubelike extension that transmits neural information to other neurons (or cells in muscles and glands).
- Axons vary in length. Some axons extend over a metre from your spine to your big toe, others are as small as the width of a single hair.
- A dendrite is an extension of a neuron that detects and receives information from other neurons.
- Most dendrites have little ‘outgrowths’, called dendritic spines.
- Each spine provides a site with receptors where a neuron can receive information from a neighbouring neuron.
- A neuron may have from one to 20 dendrites, each dendrite may have from one to many branches, and the total numbers of spines on the branches may be in the hundreds or thousands.
- Myelin is a white, fatty substance that surrounds and insulates the axon.
- Without the myelin sheath, interference from the activity of other nearby axons may occur.
- Messages travel much faster through neurons wrapped in myelin than unmyelinated neurons.
o here are small branches at the end of an axon called axon collaterals.
o At the end of the collaterals are axon terminals. Each axon terminal has a small knob-like swelling at its tip called a terminal button.
o The terminal button is a small sac that stores and secretes neurotransmitter (chemical) that is made by the neuron.
o Neurotransmitter Synapse 3D Animation
WHAT IS A NEURON?
- A neuron is an individual nerve cell that is specialised.
- They receive, process and transmit information.
- Neurons not only communicate with each other, but also with muscles and glands.
- They are the ‘building blocks’ of the brain and nervous system.
- Excitatory neurotransmitter in the CNS.
- Activates the postsynaptic neuron.
- Involved in perception, learning, memory, thinking and moving.
EXCITATORY: ACTIVATES THE POSTSYNAPTIC NEURON.
THE SPINAL REFLEX.
- The spinal cord can initiate some simple responses on its own, independent of the brain.
- Spinal reflexes (aka. Reflex arc.): unconscious involuntary and automatically occurring response to certain stimuli without any involvement of the brain.
- The immediate response at the spinal cord enables faster reaction time, a fraction of a second before the sensory information reaches the brain.
- A spinal reflex involving a withdrawal reaction is believed to be an adaptive response.