Structure and Function of Neurons Flashcards
(14 cards)
what are neurons
neurons are cells that are specialised to carry info through the body
there are 100 billion neurons (nerve cells) in the human nervous system, 80% of which are located in the brain
by transmitting signals electrically and chemically, these neurons provide the nervous system with its primary means of communication
outline the structure of a neuron
neurons vary in size from less than a millimetre to up to a metre depending on their function, but they all share the same basic structure
the cell body (soma) includes a nucleus, which contains the genetic material of the cell
branch like structures called dendrites protrude from the cell body. these can only receive signals from other neurons or sensory receptors
the axon carries the impulse away from the cell body and down the length of the neuron.
the axon is covered in a fatty layer of myelin sheath (except relay neurons) which protects the axon and speeds up electrical transmission of the impulse.
if the myelin sheath was continuous this would have the reverse effect and slow down the electrical impulse. thus, the myelin sheath is segmented by gaps called nodes of ranvier. these speed up the transmission of the impulse by forcing it to ‘jump’ across the gaps along the axon
at the end of the axon are terminal buttons (axon terminals) which communicate with the next neuron in the chain across a gap known as the synapse through synaptic transission (or connect directly to organs)
three main types of neurons
sensory
relay
motor
sensory neurons
carry messages from the PNS to the CNS (brain/spinal cord)
found in receptors such as the eyes, ears, tongue and skin
tell the rest of the brain about the external and internal environment by processing information taken from one of the 5 senses
when these nerve impulses reach the brain, they are translated into ‘sensations’, such as vision, hearing, taste and touch
however, not all sensory information travels as fair as the brain, with some neurons terminating in the spinal cord; this allows for reflex actions to occur quickly without delay if sending impulses to the brain
structure of sensory neurons
unipolar
short axon
long dendrites
connected to a receptor cell
relay neurons
between sensory input and motor output/response
connect the sensory neurons to the motor or other relay neurons
carry messages from one part of the CNS to another
most common type of neurons, found in the brain/spinal cord and allow sensory and motor neurons to communicate with each other
structure of relay neurons
multipolar
short axon
short dendrites
no myelin sheath
motor neurons
found in the central nervous system (CNS)
carry messages from the CNS to directly or indirectly control muscle movement by connecting the CNS to effectors
when stimulated, motor neurons release neurotransmitters (chemical messengers) which bind to receptors in the muscle and trigger a response which leads to muscle movement
muscle relaxation is cause by inhibition of the motor neuron
structure of motor neurons
multipolar
long axon
short dendrites
connected to effector (muscle)
explain how the neurons in the nervous system work together
- stimulus (eg heat)
- sensory neurons (eg pain receptor) are triggered, which sends a signal through the PNS to the CNS (brain/spinal cord)
- sensory neurons pass the signal to a relay neuron (found all over the CNS)
- relay neurons allow mental processes to occur, relating to what the danger is, how severe it is, and how to respond
- when the brain has decided that action is required, the relay neuron sends a signal to the motor neurons
- the motor neurons communicate with effectors like muscles and glands, so the response can occur (eg. contract muscles/pull away)
draw/label a neuron
x
draw/label a sensory neuron
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draw/label a relay neuron
x
draw/label a motor neuron
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