PSYB65H3 Chapter Notes - Chapter 3: Dendritic Spine, Axon Hillock, Sensory Neuron
Chapter 3 Notes: What are the Functional Units of the Nervous System?
3.1 Cells of the Nervous System
- Cells use proteins to play a dynamic role in our behaviour
- Were it not for the discovery of different stains that can highlight the features of brain cells, their complexity and connections
would remain unknown
- Cajal’s Neuron Theory: neurons are the functional units of the nervous system, it is the interactions between neurons that enables
behaviour
- 3 Subdivisions of a neuron:
o Cell Body/Soma: core region of cell; contains nucleus and other organelles for making proteins
o Dendrites: branching extensions of a neuron’s cell membrane that greatly increases the surface area of cell and collects
information from other cells
o Axon: root or single fibre of a neuron that carries messages to other neurons
- Human nervous system contains over 100 billion neurons
Neurons: The Basis of Information Processing
- Neurons acquire information from sensory receptors, pass the information to other neurons, and make muscles move to produce
behaviour
- Neurons encode memories and produce our thoughts and emotions
- They regulate body processes (i.e. breathing, heartbeat, body temperature, etc.)
- Specific function can be assigned to an individual neuron, but it is more likely that they work in groups of hundreds to many
thousands
- Neurons are essence of plasticity: i.e. are able to produce new branches and lose old ones (making and losing connections with
each other)
- Longevity of neurons: most CNS neurons on with us for life and re never replaced, if the brain or spinal cord is damaged, the
neurons that are lost are not replaced, and functional recovery is poor; PNS neurons can often be lost and replaced.
Structure and Function of a Neuron
– Dendritic Spines: protrusion from a dendrite that greatly increases the dendrites surface area and usual point of dendritic contact
with axons of other cells
o Neuron has 1-20 dendrites
o Dendrites collect information, spines are the point of contact
– Each neuron has only a single axon to carry messages
– The axon begins ar one end of the cell body at an expansion known as the axon hillock, it then branches out into one or many
axon collaterals
o Axon Hillock (little hill): juncture of a soma and axon where the action potential begins
o Axon collateral: branch of an axon
o Axon collaterals usually emerge in right angles
o Lower tip of axon may divide into a number of smaller branches (teleodendria)
– Terminal Button (end foot): knob at the tip of an axon (teleodendria) that coveys information to other neurons, sits very close to a
dendritic spine or some other part of another cell
– Synapse: junction between one neuron and another that forms the information-transfer site between neurons
Three Types of Neurons
1. Sensory Neuron: neuron that carries incoming information from sensory receptors into the spinal cord and brain
- Simplest neurons structurally
- Bipolar neuron: sensory neuron with one axon and one dendrite
- Somatosensory neuron: brain cell that brings sensory information from body to spinal cord
o Connects directly to the axon; cell body sits on one side of the pathway
2. Interneuron: association neuron interposed between a sensory neuron and a motor neuron; constitutes most of neurons of the
brain in mammals
- Link sensory and motor neurons
- Stellate (star-shaped) Cell: small interneuron with many dendrites, its axon is difficult to see
- Pyramidal (pyramid-shaped) Cell: distinctive interneuron found in the cerebral cortex (Carries information from cortex to the
brain and spinal cord); has a long axon, and two sets of dendrites: one from apex of cell body and other from its sides
- Purkinje Cell: distinctive interneuron found in the cerebellum, extremely branched dendrites (like a fan), carries information from
cerebellum to brain and spinal cord
3. Motor Neurons: neurons that carry information from brain and spinal cord to make muscles contract
- Extensive networks of dendrites, large cells bodies, and long axons that connect to muscles
- Located in the lower brainstem and spinal cord
- All efferent neural information must pass through to reach the muscles
Neural Networks
- Long extensions carry information to distant parts of the nervous system (neurons that project for long distances are large relative
to other neurons)
- Short extensions are engaged in local processing
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Document Summary
Cells use proteins to play a dynamic role in our behaviour. Were it not for the discovery of different stains that can highlight the features of brain cells, their complexity and connections would remain unknown. Cajal"s neuron theory: neurons are the functional units of the nervous system, it is the interactions between neurons that enables behaviour. Human nervous system contains over 100 billion neurons. Neurons acquire information from sensory receptors, pass the information to other neurons, and make muscles move to produce behaviour. Neurons encode memories and produce our thoughts and emotions. They regulate body processes (i. e. breathing, heartbeat, body temperature, etc. ) Specific function can be assigned to an individual neuron, but it is more likely that they work in groups of hundreds to many thousands. Neurons are essence of plasticity: i. e. are able to produce new branches and lose old ones (making and losing connections with each other)
