3.1 Nerve Cells

Structure of neurons

Cell body:

  • contains nucleus

  • controls functioning of cell

  • contains cytoplasm with organelles

  • mitochondria, ER, ribosomes, Golgi body

multipolar, white matter

Dendrites:

  • short extensions of the cytoplasm

  • usually from cell body

  • carry nerve impulses into cell body

Axon

  • single extension of cytoplasm

  • carry nerve impulses into cell body

  • contains branches that end at the axon terminal

Myelin Sheath

  • fatty layer covering axons

  • act as an insulator

  • protects axons from damage

  • speeds up movement of nerve impulse

  • formed by cells called Schwann cells (not present in brain/spinal cord)

  • outer layer of Schwann cells are called the neurilemma which helps repair damaged fibres

  • gaps in the myelins sheath = Nodes of Ranvier

  • not all neurons contain myelin sheath

  • amount of axon present determines colour of nervous tissue

  • white matter = long axons, lots of myelin

  • grey matter = short axons (more cell bodies), less myelin

Synapses

  • junction between 2 neurons

  • occurs between axon terminal of one neuron and dendrite of other

  • no physical touching!

  • neurotransmitters are used

Types of Neuron (Function)

Sensory (afferent or receptor neurons)

  • carry messages from receptors/sense organs (tongue) to CNS (brain/spinal cord)

Motor (efferent or effector neuron)

  • carry messages from CNS to effectors (muscles, glands, etc)

Interneurons (association, relay or connector neurons)

  • link sensory and motor neurons


Types of neuron (structure)

Multipolar

  • 1 axon and multiple dendrites from cell body

  • most common

  • found in brain, spinal cord and skeletal muscles

Bipolar

  • 1 axon and 1 dendrite

  • axon and dendrites may be branched at ends

  • found in eye, ear and nose


Pseudounipolar

  • 1 axon - then divides into 2

  • 1 ends in axon terminals, the other in dendrites

  • found mostly in sensory neurons, carrying messages to spinal cord

  • info travels faster because it doesn’t need to go through cell body