Nervous System Flashcards
What are the two main divisions of the nervous system?
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
What are neurons?
Conducting cells
Transmit nerve impulses
Are bundled into tissues called nerves in the PNS and tracts in the CNS
What are glial cells?
The glial cells surround neurons and provide support for and insulation between between them
They are the most abundant cell type in the CNS
Schwann cells are a type of glial cell
What are the three types of neurons?
Sensory neurons
Interneurons
Motor neurons
What do sensory neurons do?
Gather information from the sensory receptors (senses) and transmit these impulses to the CNS
What do interneurons do?
Only I’m the CNS, they are the link between the sensory and motor neurons, they process incoming sensory information and relay to motor neurons
What do motor neurons do?
Transmit info from the CNS to the muscles, glands, and other organs
What are the parts of a neuron? (7)
Dendrites Cell Body (Soma) Axon Myelin Sheath Schwann Cells Nodes of Ranvier Neurilemma
What are dendrites in a neuron?
Receive information from receptors or other neurons
What is the cell body (soma) in a neuron?
Contains nucleus and other organelles
What is the axon in a neuron?
Longest cytoplasmic extension from the cell body
What is the myelin sheath in a neuron?
Made up of fatty protein and acts as insulation/protection and speeds up nerve impulse
What are Schwann cells in the neuron?
They are part of the myelin sheath and are wrapped around the axons
What is the difference between white matter and gray matter?
White matter has Schwann cells that produce myelin sheath
Gray matter is unmyelinated
What are the nodes of ranvier in the neuron?
Areas between sections of myelin
Impulse jumps from one node to another, speeding up impulse transmission
What is neurilemma in neurons?
Only present on some neurons (PNS mostly)
Allows for regeneration after damage
Not on neurons in gray matter (CNS) therefore damage is permanent
What is an action potential?
A temporary shift (from negative to positive) in the neurons membrane
It’s caused by ions suddenly flowing in and out of the neuron
Gated sodium and potassium channels open once an action potential has been triggered
These gates open and closes depending on the voltage difference across the cell
What is resting potential?
It is negative inside (-70 mV)
There is lots of sodium ions outside the cell
This is a polarized state
A sodium-potassium pump maintains this by pumping 3 sodium out for every 2 potassium in
What is depolarization?
Makes the cell less polar
A stimulus causes the polarity to change, sodium gates open and sodium rushes in
The intercellular fluid goes from -70 mV to +40 mV
Before an impulse is generated the threshold potential must be reached
What is repolarization?
The neuron must be returned to its original polarity
The sodium gates snap shut, stopping the inward rush of positive ions. At the same time the potassium gates open, letting potassium into the cell
More potassium in the cell means the cell loses positively charged ions and returns back towards resting state
What is hyperpolarization?
Makes the cell more negative than its typical resting membrane potential
The potassium gates take a really long time to shut and continue to let potassium in
This means the cell temporarily hyperpolarizes or gets more negative than its resting state (-95 mV)
As the potassium channels shut, the sodium-potassium pump works to re-establish the resting state
What is the refractory period?
During this time it is impossible to send another action potential
The sodium gates snap shut, inhibiting sodium from entering the neuron, which would start an action potential
What is the threshold level?
If depolarization reaches the threshold level it triggers the action potential
If it doesn’t reach that point, then the neuron remains at rest
What is an all-or-none response?
Action potential are an all or none response
This means that an action potential is either triggered or it isn’t, like flipping a switch
A neuron will always send the same size action potential
What is a synapse?
How neurons “talk” to each other
The point of communication between two neurons or between a neuron and a target cell
What are the four actions that occur in a synapse?
- Action potential arrives
- Vesicle fuses with plasma membrane
- Neurotransmitter is released into synaptic cleft
- Neurotransmitter binds to receptor
Describe the effects of excitatory neurotransmitters.
Trigger ion channels
Sodium and calcium can enter the cell
Results in more positive membrane potential
If excitatory signals are strong enough an action potential can occur
Describe the effects of inhibitory neurotransmitters.
Trigger potassium channels to open
Potassium flows out of cell
Results in a more negative transmembrane potential (hyperpolarization)
Because the cell is in hyperpolarization it cannot have an action potential (refractory period)
What is temporal summation?
Occurs when multiple signals from one neuron occur close enough in time to combine and trigger an action potential
What is spatial summation?
The effect of triggering an action potential in a neuron from one or more presynaptic neurons
What does the neurotransmitter acetylcholine do?
It’s an excitatory neurotransmitter at neuromuscular junction
Can be either excitatory or inhibitory in other places
What does the neurotransmitter cholinesterase do?
An enzyme that breaks down acetylcholine
Removes acetylcholine from receptors to allow the membrane to repolarize
What does the neurotransmitter norepinephrine do?
Can be either inhibitory or excitatory
Found in both the CNS and PNS
Causes wakefulness
What does the neurotransmitter GABA (gamma-aminobutyric acid) do?
It causes an inhibitory response
Found in the CNS
Associated with motor behaviour
What is the function of the meninges in the brain?
Membranes that protect the brain
Surround the brain and spinal cord
What is the function of the cerebrospinal fluid in the brain?
Is the “shock absorber”
Circulated between the innermost and middle membranes of the brain and spinal cord
What is the function of the cerebrum in the brain?
Muscular control and balance
The largest and most highly developed part of the human brain
Stores sensory information and imitators voluntary motor activities
What is the function of the cerebral cortex in the brain?
The outer layer of the cerebral hemispheres
divided into four lobes
A thin layer of gray matter that makes humans so smart