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Major functions of the CNS, PNS
& basic functions.
- -Brain & spinal cord.
- -Receives & sends out signals through PNS.
- -Afferent neurons send to CNS
- -Efferent neurons transmit messages from CNS to effector cells. (Muscles, Glands)
Structue & Functions of Neurons
- -Receivess incoming info & Transmits signals to cell body.
- Cell Body
- -Contains nucleus, other cellular organelles
- -Integrates incoming signals.
- -Extensions from cell body / Carry outgoing info.
Brain and spinal cord
Receives and sends out signals through PNS
Afferent Neurons sens to CNS
Efferent Neurons transmit msssgs from CNS to EFFECTOR cells. (Muscles, glands)
Receives incoming info & transmits signals to cell body.
Contain nucleus, Other cellular organelles
Integrated incoming signals.
Extensions from cell body /
Carry outgoing info.
Delivers signals to synapse
Narrow space etween Presynaptic cell & Post Synaptic Cell.
Post Synaptic Cell
Cell that receives the signal.
3 main Glial Cells in the CNS
Forms myelin sheaths
Lay down mylin on CNS neurons
Links neurons w Blood vessels
Helps form Blood Brain Barrier
Regulate levels of extracellular ions and neurotransmitters.
Immune Cells in the CNS
Removes damaged cells and foreign invaders.
What causes electrical signaling in Neurons
Changes in ION permeability by opening or closing ion channels.
Variable Strength Signals
Lose Strength a they travel
Occurs in dendrites & Cell body
**Small changes in voltage caused by opening of a few channels**
CONSTANT strength signals
DOES NOT lose strength as they travel
Occurs in AXONS
Travels long distance
LARGE CHANGES caused by openings of MANY channels as it moves down the axon.
What leads to loss of strength of graded potentials?
- Current Leak
- -Across membrane
- Cytoplasmic Resistance
- -As travels through cytoplasm.
Current Leak (Graded Potential)
Cytoplasmic Resistance (Graded Potential)
Travels through Cytplasm
Where on the Neuron does action potential begin?
- Stimuli open channels on dendrites,
- Cell Body causes graded potentials.
2 Ways to speed up conduction of action potentials along neuron?
- Large Diameter Axons
- -Have less resistancy.
- Myeinated Axons
- -Signal travels faster.
Jump in actions potentials
Increased rate of flow by 50-fold
Nodes of Rhanvier
Areas of NO myelin.
Name demyelinated pathology,
How it can affect Neural Transmission
Results in loss of Myelin.
Slowing of conduction o action potentials down neuron.
Transmission of signal from one cell to another.
Direct passing of current to post synaptic cell.
Found in some CNS cells.
**Cardiac, & Smooth muscle**
Neurotrasnmitters are released from presynaptic cell.
Binds to receptors on postsynaptic cells & causes response.
How to distinguish a strong VS weak stimulus?
-Increased frequency of action potentials
-Releases more neutotransmitters NT
What happens to NT once its released into synaptic cleft?
Rapidly removed from synaptic cleft.
How do we remove NT from synaptic cleft?
It is removed by
HOW Spatial and Temporal Summation of graded potentials is used to signal a post-synaptic cell.
- Spatial Summation
- -How many diff presynaptic neurons are stimulated by it.
- Temporal Summation
- -How QUICKLY the presynaptic cells stimulate the post synaptic cell.
What is meant when we say that sensory receptors "TRANSDUCE" stimuli?
Sensry receptors transduces (Converts stimulus signal into (Electrochemical) info into graded potentials called RECEPTOR POTENTIALS.
Another term for sensory neurons
- Afferent Neurons
- -Project to CNS (Brain & Spianl Cord)
How does convergence give rise to a large receptive field?
If many Primary Sensory Neurons synapse on one Secondary Neuron in CNS then you have a large receptive field.
-Becomes less sensitive
-Allowing multiple subthreshold stimuli to reach threshold.
Will more sensitive areas of the skin have bigger or smaller secondary receptive fields?
More sensitive= Smaller receptive fields.
Which sense projects directly to the cortex w -out first going to the thalamus?
Which portions of the brain do most sensory neurons synapse prior to entering the cortex?
- -known as relay station.
What are the 4 properties of a stimulus?
Intensity- How strong?
Duration- How long?
How does the CNS decipher the actions potentials into meaning?
- -What type of stimulus determined by which cortical region.
- Location of stimulus
- -Each cortical region has a topographical organization that reveals position: (Auditory neurons use timing)
- -Determined by frequency of action potentials.
- -Duration of action potential.
Example of Tonic Receptor
Fire rapidly at first then slow down
Maintain firing for things that need constant monitoring,
Ex: Pressure, & Proprioreceptors.
Example of Phasic Receptors
Stops firing if signal stays the same
Sensitive to changes in stimuli
Absolute Refractory Period
-Na+ inactivation gate is closed
Prevents action potntial from traveling backwards.
More stimulus needed to reach Action Potential.
Neuron is more likely to fire.
Chemical Neuron Antagonist
Chemical Neuron Agonist
Major NT for Pain
Does release of NT from a presynaptic cell always cause excitation in the post synaptic cell?
Needs enough NT to reach 55 at trigger Zone.
Spatial vs Temporal Summation
- - Many signals adding together to make stronger.
- -One signal = more frequent.
2 examples of senses that use neurons as receptors
Sends out signal to secondary messanger.
2 Ex. of senses that use specialized non neural reseptor cells that synapse onto sensory neurons.
Somatosensory Pathways for pain and Proprioception
- - Ear, Equillibrium, POSITION
Afferent synapse in spinal cord.
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