axons
Action Potential and Axon Conduction
- Resting membrane potential provides and immediate source of power (it can cause a rapid change)
- Hyperpolarize - makes membrane potential more negative
- Depolarize - makes membrane potential less negative
o Depolarization reaches a threshold, at this threshold you cause a massive electrical change (Action Potential aka Impulse aka Spike)
- Threshold - generally 15mV above resting membrane potential
o Threshold for a neuron is around -70 less 15 = -55mV
- All-or-none law
o Size of action potential for a given neuron is always the same regardless of the size of the stimulus that initiated it
- Information about Magnitude
o Conveyed by frequency of action potentials (#/sec [Hz])
- Alternative to Action Potential:
o Graded Potential - passive change occurs
o Signal gets smaller and smaller as it moves on - such as some neurons found in the eyes
Molecular Basis of Action Potential
- Depolarization
o Results in sodium membrane "channels" or "gates" begin to open
- At threshold, the number of open channels overcomes the sodium-potassium pump
o The channels have a time-limit and once open will automatically close after ½ msec.
- Sodium current makes membrane potential positive, and at peak, sodium channels close and potassium channels open
- Now, potassium channels open and potassium ions rush out (triggered by threshold, but have a delay to open so open after the sodium channels)
- Brief hyperpolarization (voltage surpasses -70mV) while sodium potassium pump restores ion distribution
- These voltage-dependant (activated) channels define the action potential
- Sustained activity leads to an increase in extra-cellular potassium (typically picked up by astrocytes)
- Glial cell (astrocytes) transports excess potassium to nearby arteries causing a dilation of the artery wall
o More active areas need more oxygen and glucose, so the movement of the potassium to the arteries, cause them to dilate and thus allow more volume of blood (and nutrients) to the area
- Refractory period - period when the cell is resistant to the generation of further action potentials
o Restricts the firing rate of the cell
- Two phases of the refractory period:
o Absolute - no firing regardless of the size of the stimulus
o Relative - threshold is higher than normal
Conduction of the Nerve Impulse
- Action potential is regenerated at each adjacent patch of the membrane (because of diffusing sodium from generation of action potential)
- Cannot move backwards - seen as a wave rather than distinct action potentials because the patches are so small, and it moves so fast
- Called the propagation of the action potential
- Slower than conduction of electricity down a copper wire (1-10m/sec vs. 300million m/sec)
- Axons with myelin sheaths are faster (120m/sec)
o Myelin sheath insulates the axon, so that sodium ions cannot pass into or out of the cell
o Sodium can cross at Nodes of Ranvier to generate a new action potential
o From one Node to the next, a graded potential regenerates a new action potential at the next node
o Called "salutatory conduction"
Neurons conduct impulses through electrical and chemical signals. When a neuron is activated, an electrical signal called an action potential travels down the length of the cell's axon. At the end of the axon, neurotransmitters are released into the synapse to signal the next neuron in the pathway.
When a nerve cell undergoes its function of secreting a hormone, changes occur in its outer cell membrane that allow electrically-charged ions to move in and out of the cell in a step-wise fashion along the full extent of the nerve.
Dendrites.
Neurones
Neurons transmit nerve impulses/ electric impulses throughout the body.
Functionally, neurons come in three varieties; motor neurons, sensory neurons and interneurons. Motor neurons conduct motor impulses from the CNS to the muscles. Sensory neurons conduct motor impulses from the rest of the body to the CNS. Interneurons connect the sensory to the motor so we can respond to incoming sensory stimuli.
Neurons conduct electrical impulses in the brain. Neuroglia are cells that support the neurons. These cells undergo mitosis where neurons do not. Brain tumors are formed from neuroglia cells because they mitosis.
Glial cells do not conduct electrical impulses (as opposed to neurons, which do). The glial cells surround neurons and etc
Axons conduct the nerve impulses. Dendrites receive the impulses. Possible the impulses go through the dendrites faster, though the synaptic cleft may slow this pathway. Dendrites are much shorter than axons.
Myelinated neurons conduct impulses faster than unmyelinated neurons.
in a spasm
Neurons transmit nerve impulses/ electric impulses throughout the body.
Dendrites conduct impulses toward the cell body in a neuron. Dendrites receive incoming signals and pass them on to the cell body for further processing.
Efferent neurons (sometimes called motor neurons) transmit signals from the CNS to the effector cells.
Motor neurons are the neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue. These types of nerves are what make up the Autonomic nervous system, which regulates the bodies involuntary functions.
Motor neurons
A very basic explanation would say that axons are the structures of neurons that conduct electrical impulses ("messages") away from the cell body, and that dendrites are the structures of neurons that conduct electrical impulses toward the cell body.
TRUE. Neurons with myelin (or myelinated neurons) conduct impulses much faster than those without myelin.
Functionally, neurons come in three varieties; motor neurons, sensory neurons and interneurons. Motor neurons conduct motor impulses from the CNS to the muscles. Sensory neurons conduct motor impulses from the rest of the body to the CNS. Interneurons connect the sensory to the motor so we can respond to incoming sensory stimuli.
Another name for an efferent neuron is a motor neuron. These neurons carry signals from the central nervous system to muscles, glands, and other effector organs in the body, enabling them to respond to stimuli.
Neurons conduct electrical impulses in the brain. Neuroglia are cells that support the neurons. These cells undergo mitosis where neurons do not. Brain tumors are formed from neuroglia cells because they mitosis.