neurones

what is a nerve made up of

a bundle of neurones

sensory, relay and motor neurones structures

sensory, relay and motor neurones comparison

cell body

• contains nucleus

• carries genetic code for production of neurotransmitters

• dense group of ribosomes and ER

• NISSL granules

• site of protein synthesis to make neurotransmitter

• sensory neuron cell bodies in dorsal root ganglia

• motor neuron cell bodies in spinal cord or brain

axon

• transmit action potential away from the cell body

• can be over 1 m in length

• 10 µm diameter

• allows for rapid transmission of impulse

• reduces the number of synapses required which are the area of slower transmission

• contains axoplasm and usual cell organelles

dendrite

transmits action potential towards cell body

dendron

allow communication with other neurones

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phospholipid bilayer with many protein ion channels

schwann cells

• thin cells which have wrapped themselves around the neurone

• have a higher than usual phospholipid content in their membranes and fewer ion channels, increasing electrical insulation of the neurone

myelin sheath

the enclosing layer created by schwann cells

nodes of ranvier

regions of uninsulated membrane where ion movement occurs to create action potential

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• Point at which neurotransmitter is released from neurone to transfer the action potential to another neurone

• Point at which neurotransmitter is released from neurone to transfer the action potential to a muscle

sensory neurone

• cell body positioned in a ganglia just outside of the CNS

• transmit nerve impulse from sensory receptor to the CNS.

• at the CNS it may sign up with a relay or motor nuerone

motor neurone

• transmit nerve impulses from the CNS to an effect (muscle or a gland)

• cell body in the CNS

relay neurone

• connect sensory and motor neurones

• totally within the CNS

myelinated neurones

• covered by myelin sheaths

• happens when schwann cells wrapped around neurone creating myelin sheath

• schwann cell plasma membranes have a higher than usual phospholipid content with few ion channels, therefore iron movement can only occur at the nodes of ravier

  • this electrically insulate the neurone

what are sensory receptors

• Specialised cells

• Can detect changes in our surroundings [stimulus]

• Initiate a nerve impulse.

• Are transducers.

• Are specific to a stimulus

what are transducers

• a cell that converts on store of energy to another

• stimulus converts to nerve impulse → electrical energy

receptors and the energy changes they detect

pacinian corpuscle

• detects pressure changes on skin

• changes deform the layers of connective tissue

  • pushes against the nerve ending

  • initiates a nerve impulse.

• is sensitive to changes in pressure, so if the pressure becomes constant it will stop initiating nerve impulses

  • explains why you stop feeling clothes soon after you put them on