Unit 2: Neuron Structure/Function Flashcards
Two types of nervous tissue cells
Neurons (sends signals)
Neuroglia (cellular division)
Astrocytes
Type neuroglial
- help form blood brain barrier
- Allows certain substances to pass while harmful things are kept out
Ependymal cells
Type of neuroglial
- creates cerebral spinal fluid
- Located in brain and spinal chord
Microglia
Type of neuroglial
- provide protection
- engulf microbes or clear debris from dead cells
Oligodendrocytes
Type of neuroglial cell
- In the CNS: produce myelin sheaths
Schwann cells
Type of neuroglial
- in the PNS and form the myelin sheaths for PNS Neurons
- Surround the axon and increase the speed of conduction
Four characteristics of neurons
- Extreme longevity
- Amitotic (not capable of division)
- High metabolic rate (constant need for oxygen and glucose)
- Irritability (capable of responding to stimulation)
Structure of neurons
- Central cell body (axon) and dendrites (axon terminals)
- Entire cell is surrounded by a cell membrane
Axon hillock
- Connects the cell body or soma to the axon
- Thickened area
- Also called the trigger zone
Axon terminals
Responsible for releasing neurotransmitters into the synapse so that communication can continue between two neurons
Myelin sheath
Fatty and insulating material that covers the axons of the neurons
Includes: Oligodendrocytes Schwann cells Nodes of ranvier Saltatory conduction
The synapse
Space or gap between an axon terminal and another neuron effector
Neurotransmitter
Released into this synapse and then binds to a specialized receptor
- Chemical that carries the nerve message.
- Released from the axon terminal (not the dendrite)
Neuromuscular junction
Name for the synapse between a nerve cell and the skeletal muscle fiber that it supplies
Dendrites
Contain receptors for neurotransmitters
2 ways to classify neurons
- Number of processes they have
- Direction of action potential conduction
Three number of processes
- Multipolar: Many dendrites and one axon
- Bipolar: one dendrite and one axon
- Unipolar: One process from the cell body that divides into 2 processes
3 directions of neurons
- Afferent or sensory neurons: From the body into the CNS
- Interneurons: connect neurons within the central nervous system
- Efferent or motor neurons: Convey info out of the CNS into the body
Cns
Central nervous system
Voltage gated channels
Present on the axon cell membrane, normally kept closed unless there is a change in voltage
Depolarization
Charge goes toward positive
Happens when Na+ enters the axon
Hyper polarization
Charge goes more negative
This happens when K+ leaves the axon
Propagation if action potentials
The action potential travels down the axon, toward the axonal terminals
Two types of propagation
Saltatory conduction
Continuous (local) conduction
Describe a neuron at rest
Negative charge inside
High concentration of Na+ inside
Phase of action potential
Depolarization: Na+, charge goes to +30mV, into axon
Repolarization: K+, back down to -70mV, out of axon
Action potential
A brief reversal of membrane potential
Synaptic transmission
Where one neuron meets the next neuron or where a neuron meets a muscle cell
Presynaptic events
Action potential travels down the axon and gets to the axonal terminal
Postsynaptic events
Ligand gated channels - Channels for either Na+, K+ or Cl- that are found on the dendrites if neurons
Events of presynaptic process
- Action potential arrives
- Ca++ channels open
- Ca++ enters presynaptic neuron
- neurotransmitters released
- Neurotransmitter binds to receptors
- ligand gated Na+ channels open
- removal of neurotransmitters by reuptake
Cell body/soma
Contains nucleus of the cell or neuron
Nodes of ranvier
Gaps or spaces do not contain myelin and allow the action potential to propagate or move faster
Neuron action potential sequence of events
- Depolarization graded potential occurs in response to a stimulus
- Na+ channels open
- Na+ flows into axon
- -70mV to +30 mV
- K+ channels open
- K+ flows out of axon
- +30 to -70
