Nervous System(intro) Flashcards
What are the different parts of the CNS and PNS
CNS: brain + spinal chord, PNS: Nerves (Cranial and Spinal)
What are the 3 general functions of the nervous system? What does each one do?
Sensory, Integrative and Motor.
-Sensory: Detect changes and sends those changes as messages to the brain
-Integrative: Processing and prioritization of information; may generate motor response.
-Motor: Sends info to motor effectors
Organization of the sensory system
Afferent, Somatic and Autonomic.
-Afferent: Signals travel from tissue to NS
-Somatic: Detect touch, temp, pain etc.
-Autonomic: Unconscious stuff.
Organization of Motor System
Efferent, Somatic, Autonomic.
-Efferent: Signals travel from CNS to effectors
-Somatic: Send signals to skeletal muscle
-Autonomic: Send info to viscera
What are the traits of the neuron?
-Excitable to electrical signals.
-Transmit signals to other cells.
-Secrete neurotransmitters.
-Neurons live for very long and don’t reproduce
Structure of Neuron
Dendrites, cell body and axons
Dendrite (definition)
Short branches that detect stimuli
Axon (definition)
Long branches that release neurotransmitter.
-Axon Hillock
-Axon Collaterals
-Synaptic knob/terminals
-Synaptic vesicles
Nerve (definition)
Bundle of axons from brain to spinal chord
transmit impulses to brain or spinal chord
Structural classifications of neurons
-unipolar: One axon extends from cell
body, Axon splits into central and
peripheral processes
-Bipolar: One dendrite and one axon
extend from cell body, sensory neurons for special
senses
-Multipolar: One axon extends from cell
body, Most common.
Neuroglia
-Support and protect neurons.
CNS Neuroglia:
-Astrocytes
-Ependymal cells
-Microglia
-Oligodendrocytes
PNS Neuroglia:
-Neurolemmocytes,
aka “Schwann cells”
-satellite cells
Myelination
Lipid wrapped around axolemma. Speeds up transmission of impulse.
Oligodendrocytes
Central nervous system myelination. Each one wraps around several axons and acts as glue to stabilize them. Neurofibril nodes are found between each segment of myelin.
Synapse
The point where neurons transmit information to another neuron/effector cell
Neurolemmocytes
Peripheral nervous system myelination. Wraps around axolemma of single axon; cytoplasm and nucleus squeezed to surface forming neurilemma. Neurofibril nodes are found between each segment of myelin.
Presynaptic neuron
The neuron that sends signals (neurotransmitters) across the synapse to the postsynaptic neuron
Synaptic cleft
Small fluid filled gap between neurons.
Postsynaptic neuron
Receives signals
Events at the synapse
- Neurotransmitters released from vesicles of axon terminals
- Neurotransmitters diffuse across synaptic cleft and bind to the postsynaptic cleft.
- Neurotransmitter binds to receptors, initiating postsynaptic action potential.
Electrical synapse
Pre- and postsynaptic neurons bound by gap junctions
-Connected cytoplasm
-Fast; no synaptic delay
-Cardiac and smooth muscle
Chemical synapse
-Presynaptic neuron releases neurotransmitter
-postsynaptic neuron responds to neurotransmitter
Segments of the neuron
Receptive, initial, conductive, transmissive
Neuron pumps
Active transport
move substances against concentration gradient
Sodium and potassium pumps, Calcium pumps
Neuron channels
-Pores in membrane that allow ions to move down concentration gradient
Leak channels
Part of Neuron channels (passive transport); always open, continuous diffusion.
Chemically-gated channels
Part of Neuron channels (active transport); opens when a neurotransmitter binds to receptor
Voltage-gated channels
Part of Neuron channels (active transport); opens when membrane charge changes
What protein does the entire membrane have?
Na+-K+ pumps and Na+ and K+ leak channels
What protein does the receptive segment have?
Chemically gated K+ and Cl- channels
they also respond to neurotransmitter of pre synaptic neuron
What protein does the initial segment have?
Voltage-gated Na+ and K+ channels
what protein does the Transmission segment have?
Voltage gated Ca2+ channels and Ca2+ pumps
What is the resting membrane potential?
Neurons at rest have a charge of -70mv internally
Process of potential at the receptive segment
- Dendrites receive chemical signal from presynaptic neuron
- Neurotransmitters then bind to chemically gated ion channel (CGIC) and the channel opens, Na+, K+ or Cl- pass through
- change in voltage determined by chemical
- Must reach -55mv to initiate action potential
Local potential
Local potentials are electrical signals that occur in the nervous system when a stimulus causes a change in the membrane potential of a cell. Size of signal is proportional to the strength of the stimulus itself
Graded potential
Graded potentials are small changes in the membrane potential of a neuron that are caused by sensory input or synapses
Summation
The process that determines whether or not an action potential will be generated by the combined effects of the excitatory and inhibitory signals. Occurs on axon hillock (initial segment)
Temporal summation
A single presynaptic neuron repeatedly releases neurotransmitter
Spatial summation
Multiple presynaptic neurons stimulate receptive region simultaneously
All or none law
If threshold reached, action potential will be generated and propagated down axon
* If threshold not reached, voltage-gated channels remain closed, no action potential
* All action potentials propagated with same intensity, even with values greater than threshold
Depolarization
- At rest, voltage-gated ion channels are closed
- As Na+ enters, the voltage-gated ion channels open
- Na+ crosses the axolemma, creating a positive current
- after Na+ goes through the channel closes
- steps 1-4 repeat across adjacent regions of axons
Repolarization
Returns to negative potential as K+ leaves cell
1. Depolarization causes K+ channels to open
2. K+ diffuses out of the cell causing negative membrane potential
Continuous conduction
- Occurs on unmyelinated axons
- Charge opens voltage-gated channels, which spreads to adjacent
region and opens more channels sequentially
Saltatory conduction
- Occurs on myelinated axons
- Faster and requires less ATP to maintain RMP
- Action potential occurs only at neurofibril nodes, where the axon’s
voltage-gated channels are concentrated - Action potential propagated from node to node to terminals
Refractory period
- The time after an action potential during which the neuron cannot produce another action potential
Neurotransmitters
Released by presynaptic neuron; trigger response in target cell
I. Include: acetylcholine, dopamine, serotonin, epinephrine, etc.
Functional classifications of neurotransmitters
Effect:
-Excitatory (cause EPSP’s)
-Inhibitory (cause IPSP’s)
Action
-Direct: bind to CGIC’s
-Indirect: bind to G-proteins and second messengers
Neuronal pools
Groups of neurons arranged in specific patterns
Converging circuits
Input converges at a single postsynaptic neuron
Diverging circuits
One presynaptic neuron sends information to multiple postsynaptic
neurons
Reverberating circuits
Uses feedback to produce repeated, cyclical activity
Parallel-after-discharge circuits
Signal transmitted simultaneously along several paths to
postsynaptic neuron
