Neural Control Mechanisms
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(sensory) Carry impulses toward CNS
carry impulses away from CNS
to skeletal muscles - consciously controlled
PNS consist of:
consists of the nerves and ganglia outside of the brain and spinal cord
Autonomic Nervous System:
to organs, smooth muscle, cardiac muscle, not consciously controlled.
ENS = _____
Glial supporting cells:
____ brain cells.... occupy... ____
10% brain cells r neurons occupy 50% extns
List some glial cells
- Schwann cells
- Ependymal cells
ASTROCYTES (GLIAL CELL)
Forms blood brain barrier
Regulates extracellular fluid around neurons
Responsible for myelin formation in CNS.
Non-neural cell that forms myelin sheath in PNS.
type of glial cell that acts as macrophage
glial cell that lines internal cavities of the brain and produces cerebrospinal fluid
Type of neuroglia in CNS:
- Ependymal Cells
Type of neurological in PNS:
Satellite cells & Schwann cells
1 axon may have as much as 500
Neural growth and regeneration steps:
- Precursor stem -->
- Differentiate ->become Neurons & Glial Cells
- Neurons Migrate ->
- Processes become dendrites & axon
- 50-70% Apoptosis
- Regeneration Occurs
Functional anatomy of neuron:
Axon (Nerve Fiber)
Node of Ranvier
- Axon (Nerve Fiber)
- Axon Hillock
- Collateral Axon--Node of Ranvier--Axon Terminal Branch--Schwann Cell----Myelin Sheath--Soma--Terminal End Knob--Bulb--Trigger Zone
Definition of Synapses
Chemical + Electrical
What is the synaptic cleft usually bridged by?
Functional Clasification of neurons (3)
sensory, motor, and interneurons
- sensory = afferent
What three broad classes of channels do the neural cell membrane contain?
- Ligand-gated channels
- Voltage-activated channels
- Leak Channels
The directed transport of organelles and molecules along nerve cell axons.
- can be from the cell body
- towards the cell body
Grey Vs White Matter
- Grey Matter vs White Matter
- -Neural Cells *Axons connect 2 NeuralCells
- -Forms Cerebral Cortex *White kuz Myelin S.
- -Thalamus/Ganglia Also GM *Glia cells
- -Makes up Outer Surface * Inner Parts
Electrical potential is the difference.....
difference in charge and is measured in mV
The movement of electrical charge is called:
Hindrance of electrical charge movement is called:
Potential is the difference.......
Difference between two amount of charges influenced by # of charged particles and how close they are
Equilibrium potential for an ion is described by the
E=RT/zF in Cout/Cin
Resting membrane potential
Uneven distribution of ions across the membrane caused by 3 things
What are some things that cannot pass out of the membrane?
- Negatively charged proteins
- Organic Phosphates
What is determined by permeability of the membrane?
- Electrical charge across membrane
- Magnitude of resting membrane potential
What are the four channels in neurons we are most worried about in this class?
What is an action potential and what causes it?
A nerve impulse conducted on an excitable membrane, takes the movement of only a few ions to create large change in potential.
What causes an Action Potential?
- -Nerve impulse on excitable membrane
- -Stimulus that causes depolarization to threshold.
- -Takes generation potenrtial of ~15-30mV
- -~55-45mV, Stimulates opening NA+ gates
- (ions rush in aka influx)
- -Inside becomes positive so NA+ gates open
- (positive feedback loop)
- NA+ gates start closing(K/NA ATPase Pump)
- -K+ voltage gates open later
- (neg feedback loop)
- -Once threshold surpassed the AP full sized
- -Re polarization
- -K+ gates start closing
- -Refactory Period
- -Resting Potential
Graded Potential are... that occur mostly in....
Depolarizations or Hyperpolarizations that occur in dendrites,
- Characteristics of graded potential
- -Exitatory or inhibatory
- Excitatory=neurotrans+mem.recep. stimulate opening of NA+ ligand-dependent channels causing local current flow.
- Current flow --> Trigger Zone
- Opens Na+ Voltage-dep gates if threshold
Absolute Refractory Period
Relative Refractory Period
- Absolute Refactory period:
- is the interval during which a second action potential absolutely cannot be initiated, no matter how large a stimulus is applied.
- Relative Refactory Period:is the interval immediately following during which initiation of a second action potential is inhibited but not impossible.
Xyclocaine or novacaine prevent....
Prevent NA+ gates from openning!
Propagation or conductance of AP
- -Depolarization in one area stimulates depolarization in adjacent area.
- -Direction is away from the area of stimulus
- (One way due to ARP)
What does velocity depend on?
Where do AP occur?
- Fiber Diameter
- Myelination:Unmylinated: Slower
- Mylinated: Faster
AP occurs only at the axon/nodes of ranvier
Graded Potential and Action Potential
- Graded.P Action .P
- -Amplitude varies w/size -All or None
- -Can b Summed -Cannot B Summed
- -No refactory period -Has Refactory Period
- -Dec w/dist -Constant value deploarization
- -Duration varies -Duration is constant
- w/initiating cond
- -Depolari/Hyperpolari -Depolarization only
- -Initiated by receptor, -Initiated by G.P
- neurotr(synapse), or spontaneously.
- Mechan. depends on -Depend Voltage-gated
- Ligand-gated chans
What is resting membrane potential usually at?
When does Hyperpolarization occur?
- When below resting membrane potential.
- (below -70 ex: -80)
If threshold is higher than -70mV in AP does that mean the peak will be higher as well?
- Peek is usually at around +60 mV and thats when inactivation gates close, K+ voltage gates open, and depolarization occurs.
Can another action potential occur in the midst of one occuring?
- Only during the Absolute Refactory Period few mili seconds.
This is due to Na+ Gates that are closed & inactivation gates are not yet reset.
Assures one way travel of AP by preventing backward conduction.
WHat are the two kinds?
Specialized junctions between neurons where electrical activity of the presynaptic neuron influences postsynaptic neuron
- Two Kinds:
- Chemical - Most common type
- Electrical - Called electrotonic
Receptors have two parts:
- Binding component - Binds 2 neurotransmitter.
- Ionophore component - Is inside &opens chans
Anatomy of synapse
- Presynaptic neuron->
- Synaptic Cleft ->
- Postsynaptic Neuron ->
Presynaptic neuron releases neurotransmitters which diffuse across synaptic cleft and attach to specific receptors in the post-synaptic membrane.
- Allow for fast or inhibatory transportation in nervous system.
- Can take neuron away from threshold (hyperpolorization)
- Or take post synaptic neuron towards towards threshold
- Neurotransmitter binds to metabotropic
- results in release of G-protein from receptor
- Post synaptic receptor on phospho lipid bilaye
- Neurotransmitter binds to Ionotropic receptor causing an openning of ion channel
- CHanges shape and allows Sodium ions in.
quickly depolarizes or hyperpolarizes post synaptic neuron.
Types of terminal end knobs
- Discrete synapses: One area of contact
- Diffuse: Several areas of contact
Synapses can be:
- Excitatory: produce brief action potential to +
- Inhibatory:produce brief action potential to -
Functional Aspect of synapses:
How signal is transmitted neuron to neuron in ACH synapse.
Depolarization in pre-synaptic neuron causes opening of voltage-sensitive Ca2+ channels.
- Ca diffuses into terminal end knob -> -Calmodulin Activated
- -Protein Kinase
- -phosphorylates synapsins or SNARE -proteins which stimulate vessicles to attach to attachment sites or docking proteins
- -release contents into cleft = Exocytosis
- -Neurotr. diffuse across cleft/bind to proteins in post synaptic density neuron.
- -Achesterase: enzyme that brks down ACH
- -receptors open receptor-operated chan to allow in Na+
Postsynaptic ACH receptors may be....
What are the five major groups neurotransmitters can be divided into?
- Low Molecular Weight Neurotransmitter
- Biogenic Amines or Momoamines
- Amino Acid Transmitters
- Neuropeptides (Large molecules)
- Nitric Oxide Neurotransmitters
Iontropic vs Metbroactive
Ionotropic receptors form an ion channel pore.
Metabotropic: G-Protein coupled receptor
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