Neuronal Cell Types

Central nervous system (CNS)

Consists of the brain and spinal cord. Integrates, processes and coordinates sensory data and motor commands

Peripheral nervous system (PNS)

Includes all the nervous tissue outside the CNS and ENS. Made up of all the somatic and autonomous nervous systems

Enteric nervous system (ENS)

Network of neurons and nerve networks which line the digestive track. Has as many neurons as the spinal cord and uses neurotransmitters found in the brain

Axons

Long projections which propagate electrical signals

Axoplasm

Cytoplasm of an axon

Axolemma

Plasma membrane of axon

Axon hillock

Portion of the neuron which joins the cell body to the axon

Collaterals

Braches along the length of the axon

Telodendria

Fine branches of the axon which end at a synaptic terminal

Synaptic terminal

Where a synapse is

Dendrites

Small tree like protrusions that protrude from the cell body of the neuron

Dendritic spines

Small protrusions from dendrites which make up 80-90% of a neurons total surface area

Axoplasmic transport

Movement of material between the cell body and the axon, is bidirectional simultaneously

Kinesin

Molecular motor which actively transports material during anterograde flow

Dynein

Molecular motor which actively transports material during retrograde flow

Anterograde flow

The flow of materials from the cell body to the axon

Retrograde flow

The flow of materials from the axon to the cell body

Structural classification

Classified based on how the neuron is structured

Functional classification

Classified based on the job the neuron carries out

Sensory neurons

Unipolar neurons which extend between a sensory receptor in the PNS and the CNS

Somatic sensory neurons

Monitor stimuli from the external environment

Visceral sensory neurons

Monitor internal stimuli from organs and internal environment within the body

Interoceptor

Classification of sensory neuron. Monitors the digestive, respiratory, cardiovascular, urinary and reproductive systems, provide info about distension, deep pressure and pain

Exteroceptors

Classification of sensory neuron. Provide into about the external environment through touch, temperature, pressure, taste, smell, sight, balance and hearing

Proprioceptors

Classification of sensory neuron. Monitor the position and movement of skeletal muscles and joints

Motor neurons

Carry instructions from the CNS to peripheral tissues, organs and organ systems

Somatic motor neurons

Innervate skeletal muscles, full conscious control

Visceral motor neurons

Innervate everything else. Typically, these neurons will connect to a second of this neuron which is then connected to the target tissue

Interneuron

Connect sensory and motor neurons, mostly contained within the brain and spinal cord, distribute sensory info and coordinate motor activity

Neuroglia

Highly specialised cells and require support from other cell types to ensure they function effectively. Provide a supportive framework for nervous tissue

Astrocytes

Found in the CNS. Maintain the blood brain barrier (BBB). Create a 3D framework for the CNS. Reparation of damaged nervous tissue. Guiding neuron development. Controlling the interstitial environment

How astrocytes maintain the BBB

The feet of astrocytes form a blanket around capillaries and secrete chemicals responsible for maintaining the selective permeability characteristics of the BBB

How astrocytes create a 3D framework for the CNS

The extensive cytoskeleton of the astrocytes provides a structural framework for neurons in the brain and spinal cord

How astrocytes repair damaged nervous tissues

There is limited regeneration in the CNS, however, astrocytes will move to a site of injury to stabilize the tissue and prevent further injury

How astrocytes guide neuron development

In embryonic brain development, they direct the growth and formation of connections of developing neurons

How astrocytes control the interstitial environment

Adjusts the composition of interstitial fluid: by regulating the concentration of Na+, K+, CO2, by providing a rapid-transit system for moving nutrients, ions and dissolved gasses between neurons and capillaries, by controlling the volume of blood blow through capillaries, by absorbing and recycling some neurotransmitters, by releasing chemicals to modulate communication across axon terminals

Ependymal cells

Found in the CNS. Line the central canal and ventricles, form simple columnar epithelium, monitor and produce cerebrospinal fluid

Oligodendrocytes

Found in the CNS. Responsible for creating the myelin sheath around the axons of the neurons. Multiple work together to myelinate an axon, each one will myelinate multiple axons

Myelin sheath

Insulative coating found around neurons

Nodes of Ranvier

Gaps in the myelin sheath

Microglia

Found in the CNS. Work as immune cells by engulfing debris, waste and pathogens

Satellite cells

Found in the PNS. Support cells, analogous to astrocytes in the CNS. Regulate the interstitial fluid around the neurons in the same manner astrocytes in the CNS do

Schwann cells

Found in the PNS. Similar to oligodendrocytes, myelinate the axons of the PNS. Multiple Schwann cells are needed to myelinate one axon. A Schwann cell only myelinates one axon. Some Schwann cells are non-myelinating, they engulf small segments of multiple neurons

Presynaptic neuron

The neuron that is passing the synapse to the postsynaptic neurons

Postsynaptic neuron

The neuron that is receiving the synapse from the presynaptic neuron

Gap junctions

The area between two neurons where an electrical synapse passes

Connexins

Proteins which form pores between the membranes of the presynaptic and postsynaptic neurons allowing ions to move between the two neurons during electrical synapses