Nervous System(intro): anna edited 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 CNS
-Somatic: sensory: Bones and Detect touch, temp, pain etc.
-Autonomic: sensory: Unconscious stuff, (visceral/organs)
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) and parts
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
Single axon wrapped in what
endoneurium
Multipolar
- One axon extends from cell body
- Most common.
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
sensory neurons
Afferent and Unipolar
Interneurons
- Receive and process information
- Most common
- Multipolar
- CNS
Motor neurons
Efferent and Multipolar
Neuroglia
-Support and protect neurons
Astrocyte
- CNS Neuroglia
- helps form the blood brain barrier
Ependymal Cell
- assists in production and circulation of cerebrospinal fluid
- CNS
Microglial cell
- CNS
- phagocytic cell
oligodendrocyte
- Myelinates CNS axons
- CNS
Satellite cell
- PNS
- electrically insulates PNS cell bodies
Neurolemmocyte
- myelinates PNS axons
- PNS
Fascicles
- groups of axons
- wrapped in perineurium
Entire nerve wrapped in what
epineurium
Myelination
Lipid wrapped around axolemma. Speeds up transmission of impulse.
Synapse
The point where neurons transmit information to another neuron/effector cell
Presynaptic neuron
releases neurotransmitters
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 amount of chemicals
- Must reach -55mv to initiate action potential
Local potential
shift of membrane potential in a localized area of the cell, threshold level not reached
Graded potential
shift in membrane potential that declines with distance from the source: threshold level not reached
Excitatory Postsynaptic Potentials (EPSPs)
Depolarization: influx of Na+
Inhibitory Postsynaptic Potentials (IPSPs)
Hyperpolarization- efflux of K+ or influx of Cl-
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
Positively charged electrical current passing along axon to synaptic knobs
- 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
3. steps 1-2 repeat in adjacent regions as impulse moves
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
release of neurotransmitter
- action potential reaches synaptic knob
- Calcium ion channels open and it enters the synaptic knob and binds with proteins
- synaptic vesicles release neurotransmitter into synaptic cleft
- neurotransmitter attach to receptors on next neuron
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
