Chapter 11: Nervous Tissue Flashcards
Functions of Nervous Tissue
- Gather Information- receptors detect change (stimuli)
- Integration- analysis of stimuli
- Activation of Effectors- perform response
Function of Nervous Tissue: Gather Information
receptor: a neural structure that detects changes in the environment called stimuli
Function of Nervous Tissue: Integration
analysis of stimuli (what is their significance/ meaning)
-formulation of appropriate response(s)
Function of Nervous Tissue: Activation of Effectors
to perform the response generated during integration
Central Nervous System (CNS)
- brain spinal cord
- perform integration (non-stop)
Peripheral Nervous System (PNS)
-contains all neural structures outside brain + spinal cord
-send information TO and FROM the CNS
ex:
to from
environment –> CNS –> effectors
l l
sensory division motor division
send info to CNS conducts info from CNS
Motor Division of PNS has 2 Branches:
- Somatic
2. Autonomic
PNS Motor Division Branch: Somatic
communications with “voluntary effectors” (effectors you can consciously control)
-skeletal muscles
PNS Motor Division Branch: Autonomic
communications with “involuntary effectors” (effectors you can not consciously control”
- cardiac muscles, smooth muscle, glands
- sympathetic- mobilizes body systems during activity
- parasympathetic- conserves energy; promotes house-keeping functions during rest
Cells In Nervous Tissue?
- Neurons- send receive chemical + electrical “messages” (non-stop)
- Glia (neuroglia)- support + take care of neurons
Examples of Glia In The Central Nervous System (CNS): Astrocytes
- Astrocytes- connect CNS neurons to blood stream
- feed neurons
- move neuron waste in blood
Examples of Glia in The Central Nervous System (CNS): Oligodendrocytes
- Oligodendrocytes- from myelin sheaths which help speed transmission of electricity through a neuron
Examples of Glia In The Peripheral Nervous System (PNS): Schwann Cells
Schwann cells- form myelin sheath
Characteristics of Neurons
- Irritable- easily stimulated (in producing responses)
- Amitotic- cant divide (don’t do mitosis)
- long lived
- Very Metabolically Demanding- require large + constant amounts of glucose and oxygen
Parts of a Neuron: Cell Body (Soma)
part of the neuron that directly surrounds the nucleus
- biosynthetic center of cell (any chemical that the neuron makes has to be in the cell body then shipped to where needed)
- “decision maker” for neuron because it contains nucleus
Part of a Neuron: Dendrite
“branches”
- contain large concentrations/ densities of neurotransmitter receptors
- input regions- (bringing information to the cell body)
Part of a Neuron: Axon
(comes out of a cone-shaped structure called a hillock)
-send electrical impulses called Action Potentials from its Axon Hillock to its Axon Terminals (end of neuron) to release neurotransmitters
axon= output region
Classifying Neurons: based on a # of processes
- multipolar neuron- more than 2
- bipolar- 2
- unipolar-1
Classifying Neurons: based on activity
- sensory- send info toward CNS
- motor- send info from CNS
- interneurons- perform integration
Neurophysiology (how neurons work):
Voltage
A separation of charge with respect to a barrier
- when opposite charges are separated (by barrier), energy is STORED
- allowing opposing charges to contact one another RELEASES energy
Membrane Potential
the voltage occurring at the plasma membrane’ measured in milliVolts (mV)
(neurons use plasma membrane as a barrier)
Resting Potential; Resting Membrane Potential (RMP)
the membrane potential of a neuron at “rest” ( a neuron that is not currently sending or receiving information) [-70 mV] (charge of inside of the cell compared to the outside)
Establishment + Maintenance of RMP
How is the cell -70mV?
- at “rest”, Na+ (sodium) is diffusing INTO a neuron and K+ (potassium) is diffusing OUT. However, more k+ is diffusing out than Na+ is diffusing in.
- because more (+) charge is diffusing out than is diffusing in, the inside of the membrane behaves as if its -70 mV compared to the outside.
(Na+ and K+ diffusion produce (establish) RMP) - Na+ and K+ ions must continue to diffuse in order for the neurons membrane potential to be maintained
- Proteins called Sodium-Potassium Pumps spend ATP to actively transport “diffused” Na+ and K+ back to their high-concentration areas
(move sodium and potassium back to their original place to start again like a loop)
-Sodium Potassium Pumps maintain membrane potential by making sue that Na+ and K+ continue to diffuse
Changing Membrane Potential
depolarization- more (+)
hyperpolarization- more (-)
These are made to occur through the opening of Voltage-Gated Ion Channels (open in response to voltage)
Depolarization
making membrane potential more positive
to depolarize, open gated Na+ channels
Na low
————–
Hyperpolarization
making membrane potential more negative
to hyperpolarize, we would open K+ channels (allowing (+) to leave the cell
K+ high (high to low) diffuse into the outside
————-
K+ low
Membrane Potential changes as a neuron sends 2 kinds of electrical “messages”:
- Graded Potential-share info among itself
2. Action Potential- talk to other cells
Membrane Potential changes with 2 kinds of electrical messages: 1. Graded Potential
“Short Distance” messages sent from one part of a neuron to another part of that same neuron
(ex: dendrites tell soma (cell body) about messages they’ve received)
Membrane Potential changes with 2 kinds of electrical messages: 2. Action Potential
sent from the axon hillock to axon terminal
-cause terminals to release neurotransmitters
Action Potential
a quick reversal in membrane potential from rest (RMP) (-70mV) to +30mV and back
-releases the energy needed for the terminals to release neurotransmitters
Events of the Action Potential
- A stimulus depolarizes (+) the neuron to Threshold (-55mV)
- At Threshold, voltage-gated Na+ channels open
-neuron depolarizes to +30mV as Na+ enters neuron
ENERGY is released - At +30mV:
-Na+ entry stops
-Na+ gates begin to close
-voltage-gated K+ channels open and membrane potential hyperpolarizes (goes back down) - K+ gates open longer than needed to reach RMP(resting membrane potential) producing an undershoot
An Action Potential is created at the ____, this action potential must be propagated to the ______
- Axon Hillock
2. Axon Terminals
Propagation of an Action Potential
- At hillock, as Na+ enters, energy is released
- This energy makes the next part of the axon reach threshold; Na+ enters
- This releases energy that makes the next part of axon reach threshold + causes Na+ to enter
- These events continue until an action potential reaches the terminals
An Action Potential is an “All or Nothing” event
- Threshold is reached at the axon hillock, and an action potential propagates all the way to the terminals as fast as possible or,
- Threshold is not reached + nothing happens
Because all of a Neurons Action Potentials are propagated at the same speed, a neuron alters its ______ to convey information about stimulus strength
Firing Frequency
(each neuron sends action potentials as fast as they can go (maximum speed))
ex: where there is dim light they send a lower frequency + at bright light they send a higher frequency
Firing Frequency is limited by
Refractory period
Absolute Refractory Period
Period of time during which sodium gates are open and a neuron cant fire
-a neuron can not be made to fire while its sodium gates are open
(gates open at threshold), (from threshold back to Resting membrane potential (RMP))
-as soon as sodium channel is closed it can fire again
Relative refractory Period
during the “undershoot” a neuron can be made to fire, but only if it receives a suprathreshold stimulus (bigger stimulus)
-whether or not it fires is relative whether you can do the extra cost
Factors influencing propagation speed
- Axon Diameter
2. Presence of myelin
Factors influencing propagation speed
1. Axon Diameter
Thicker axons offer less resistance to the flow of electricity (thicker, the more faster)
-ex: electricity flows like a milkshake, easier to drink a milkshake through a thicker straw)
Factors influencing propagation speed
2. Presence of Myelin
-myelin insulating an axon, helping keep electrical charge within the axon
(does not let electricity escape, action potentials travel farther)
-unmyelinated axon; without myelin its electrical charge spills outside the axon; travels shorter
Synapse
point of communication between 2 excitable cells
2 Types:
-electrical
-chemical
Electrical Synapse
a membrane junction like an intercalated disc allows electricity to flow easily between cells
-fast, bidirectional (right to left, left to right)
Chemical Synapse
makes use of chemicals called neurotransmitters
- unidirectional (one cell is the sender, the other is the receiver)
- presynaptic cell (sender)
- postsynaptic cell (receiver)
Transmission at a Chemical Synapse
when axon gets to terminal
- An action potential reaches an axon terminal
- Action potential causes Voltage-Gated Calcium Channels to open, and Calcium enters the terminal
- Calcium causes organelle, Synaptic Vesicles to release neurotransmitters
- Neurotransmitters diffuse across the Synaptic Cleft to postsynaptic cell
- Neurotransmitters open gated ion channels in postsynaptic cell
- This causes postsynaptic cell to create Graded Potentials which are sent to the postsynaptic soma (cell body)
Excitatory Postsynaptic Potential (EPSP)
If neurotransmitters open gated Na+ Channels in postsynaptic cell, that cell creates a depolarizing graded potential called a Excitatory Postsynaptic Cell
-bringing closer to threshold
Inhibitory Postsynaptic Cell (IPSP)
If neurotransmitters open gated K+ channels, an inhibitory postsynaptic cell is created
-pulled away from threshold (inhibition)
EPSP’s + IPSP’s travel to the postsynaptic soma (axon hillock)
if they cause the hillock to reach threshold, the hillock fires
ESPS and IPSP are summated
-added up
ex: -70mV RMP
+12mV EPSP 1
-8mV IPSP
+7mV EPSP 2
————————————–
-59mV
(wont fire action potential, did not reach threshold(-55mV)
