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The Nerveous System, Neurocrines, Cerebral Cortex, Receptors, Sensory…
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Axonal transport
Fast axonal transport
Anterograde transport, from cell body to axon terminal.
Retrograde transport, from axon terminal to cell body.
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Resting membrane potential determined primarly by
:check: K+ concentration gradient
:check: Cell's resting permeability to K+,Na+,and Cl-
Changes in membrane's permability result in ion movement
:check: Movement creates an electrical signal
:check: Very few ions move to create large changes in membrane potrentials
First, cell membrane of the neuron sligthly permeable to Na+, somewhat it increases Na+ permeability and takes the ions inside. Moving down its electrochemical gradient. The addition of positive Na+ to the intracellular fluid depolarizes the cell membrane and create an electrical signal.
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Gated channels control ion permeability
:check: Mechanically gated, chemically gated, voltage gated ion channels.
Treshold voltage varies from one channel type to another
:check: Activation rates vary
:check: Inactivation rates vary
:check: Variable strength
:check: Used for short distance communication
:check: Depends on initial stimulus, can be summed
:check: Very brief, large depolarizations
:check: Rapid signaling over long distances
:check: All-or-none phenomenon, cannot be summed
:check: Conduction is the high speed movement of a action potential along an axon
When there is a stimulus coming from pre-synaptic neuron then it leads to depolariziation.
Depends on:
:check: Current leak
:check: Cytoplasmic resistance
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:one: Resting membrane potential.
:two: Depolarizing stimulus.
:three: Membrane depolarizes to treshold. Voltage gated Na+ and K+ channels begin to open.
:four: Rapid Na+ entry depolarizes cell.
:five: Na+ channels close again and slower K+ channels open.
:six: K+ moves from cell to extracellular fluid.
:seven: K+ channels remain open and additional K+ leaves celli hyperpolarizing it.
:eight: Voltage gated K+ channels close, less K+ leaks out of the cell.
:nine: Cell returns to resting ion permeability and resting membrane potential.
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To stop cycle, slower Na+ channel inactivation gate closes
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Larger neurons conduct action potentials faster
Conduction is faster in mylinated neurons
:check: Resistance of axon membrane to ion leakage out of the cell (Saltatory conduction between nodes of Ranvier)
:chech: Demyelinating diseases cause loss of myelin (MS vs. Guillain-Barre syndrome)
Larger diaeter axons offer less resistance to current flow
Saltatory conduction
Myelination prevents ion from getting out
So that action potential can travel long distances between node of Ranviers
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Hyperkalemia brings neuron closer to treshold
Increased blood K+ concentration, brings the membrane closer to treshold. Now a stimulus that would normally be subtreshold can trigger action potential
Hypokalemia moves neuron further from treshold
Decreased K+ concentration hyperpolarizes the membrane and makes the neuron less likely to fire an acrion potential in response to a stimulus thhat normally be above the treshold
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Neurons communicate at synapses
Electrical synapses
:check: Pass electrical signals through gap junctions.
:check: Signal can be bi-directional
:check: Migth be advantageus for fast transmission
Chemical synapses
:check: Use neurotransmitters that cross synaptic
:check: Mostly our nervous system utilizes chemical synapses
:check: Little bit of more control
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From choline and acetyl CoA In axon terminals
Binds cholinergic receptors
Nicotinic receptors (On skeletal muscles and in autonomic division of PNS and CNS)
Agonist: Nicotine
Antagonists: curare, a-bungarotoxin
Muscarinic receptors
In CNS and on target cells for outonomic parasympathetic division of PNS
G protein-coupled receptors
Agonist: muscarine
Antagonist: atropine
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:one: An action potential depolarizes the axon terminal
:two: The depolarization opens voltage gated Ca2+ channels and Ca2+ enters the cell
:three:Calcium entry triggers exocytosis of synaptic cesicle contents
:four: Neurotransmitter diffuses across the synaptic cleft and binds with receptors on the postsynaptice cell
:five: Neurotransmitter binding initiates a response in the postsynaptic cell
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Slow synaptic potentials involve G-protein coupled receptors and second messengers
Fast synaptic potentials involve opening of ion channels
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:one: Glutamate binds to AMPA and NMDA channels
:two: Net Na+ entry through AMPA channels depolarizes the postsynaptic cell.
:three: Depolarization ejects Mg2+ from NMDA receptor-channel.
:four: Ca2+ activates second messenger pathways.
:six: Paracrine from postsynaptic cell enhances glutamate release
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In 4 weeks forebrain almost has the same size with the other sides
After 6 weeks forebrain becomes recognizably bigger.
In 11 week forebrain quite larger than other parts
At birth, the cerebrum has covered most of the other brain regions.
We have grey matter and white matter in the CNS. Grey matter usually unmyelinated neural cells. Color is coming from myelin sheets.
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:two: Cerebrospinal fluid
has two main pruposes, psycial protection and chemical protection
Fluid washing the brain and cleaning.
From Chroid Plexus CFS is flow to subarachnoid space.
Cerebrospinal fluid is reabsorbed into the blood at fingerlike projections of the arachnoid membrane called villi.
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:three: The blood-brain barrier
Not a psyical barrier. Isolates brain from harms that blood containing.
Astrocyte forming tight junctions aroud vessels.
Making researcher work harder because blood cannot reach brain inside
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:check: Neurons need a constant supplay of oxygen and glucose
:check: Brain recieves 15% of blood pumped by heart
:check: Oxygen passes freely across blood-brain barrier
:check: Membrane transporters move glucose from plasma into the brain interstilial fluid
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Dorsal root carries sensory (afferent) information to CNS
Cell bodies are combined in dorsal root ganglion.
Ventral root carries motor (efferent) information to muscles and glands
Dark matter is inside dorsal and ventral horn
White matter in the spinal cord consist of tracks of axons carrying information to and from the brain
Ascending - carry to brain
Descending - sending to brain
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Cerebral Cortex
Sensory areas
(Perception)
Motor areas
(Skeletal muscular movement)
Association areas
(Integration of information and direcion of voluntary movement)
Basal Ganglia
Control of voluntary movement
(Parkinson's disease)
Limbic System
Link between cognitive functions and emotions
Reasoning, some emotional responses (such as fear)
Amygdala
(Emotion, memory)
Hipoccampus
(Learning, memory)
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Medulla oblongata
Important for involuntary functions
Pons
Kind of a integration center. Coordinating the breathing
Mid Brain
Important for the eye movement and hearing, some reflexes.
Thalamus
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:one: Activates sympathetic nervous system
:two: Maintains body temperature
:three: Controls body osmolarity
:four: Controls reproductive functions
:five: Controls food intake
:six: Interacts with limbic system to influence behavior and emotions
:seven: Influences cardiovascular control center in medulla oblongata
:eight: Secretes trophic hormones that control release of hormones from anterior pilutiary gland
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:star: Primary sensory cortex
:star: Sensory association area
Sensory information from skin, muscoskeletal system, viscera, and taste buds
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Visceral Stimuli:
:check: Blood pressure
:check: Distension of gastrointestinal tract
:check: blood glucose concentration
:check: Internal body temperature
:check:Osmolarity of body fluids
:check:pH and oxygen content of blood
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:two: Free nerve endings detect light,temperature and pain
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Stimulus energy converted into information processed by nervous system
Ion channels or second messengers initiate
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Sensory modality
Which sensory neurons are activated and where neurons terminate in brain
Location of the stimulus
Which receptive fields are activated
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:one: Primary neuron response is proportional to stimulus strength
:two: Pathway closes to stimulus inhibits neighbors
:three: Inhibition of lateral neurons enhances perception of stimulus
In the same duration of the stimulus, senory system has different adaptation properties
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Nociceptors initiate protective responses
No pain receptors in the CNS
Activation is a reflexive protective response (Integrated in spinal cord)
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Nociceptors from several locations converge on a single ascending tract in the spinal cord. Pain signals
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:a: In absence of input from C fibers, a tonically active inhibitory interneuron suppresses pain pathway
:b: With strong pain, C fiber stops inhibiton inhibition of the pathway, allowing a strong signal to be sent to the brain
Pain can be modulled by simultaneous somatosenory input.
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:one: Ligands activate the taste cell
:two: Various intracellular pathways are activated
:three: Ca2+ signal in the cytoplasm triggers exocytosis or ATP formation
:four: Neurotransmitter or ATP is released
:five: Primary sensory neuron fires and action potentials are sent to the brain
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:one: Sound waves strike the tympanic membrane and become vibrations
:two: The sound wave energy is transferred to the three bones of the middle ear, which vibrate
:three: The stapes is attached to the membrane of the oval window. Vibrations of the oval window create fluid waves within the cochella
:four: The fluid waves push on the flexible membranes of the cochlear duct. Hair cells bend and ion channels openi, creating an electrical signal that alters neurotransmitter release
:five: Neurotransmitter release onto sensory neurons creates action potentials that travel through the cochlear nerve to the brain
:six: Energy from the waves transfers across the cochlear duct into the tympanic duct and dissipated back into the middle ear at the round window.
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Retina contains all the photoreceptors
Optic disk (blind spot) region where optic nerve and blood vessels leave the eye
Fovea region of sharpest vision
Macula center of the visual field
Optic chiasm region that nerves cross
Cillary muscle controls the shape of the lens
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Photoreceptors:
Rods are function for black and white and at nigth, more common
Cones are responsible for color vision
Taking information to bipolar cells
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Control smooth muscle, cardiac muscle, many glands, and some adipose tissue
Mostly involuntary
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The hypothalamus, pons and medulla initiate autonomic, endocrine, and behavioral responses
Most internal organs under antagonistic control
One autonomic branch is excitatory, and the other branch is inhibitory.
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Vagus nerve contains about 75% of all parasympathetic fibers
Sensory information from internal organs to brain
Output from brain to organs
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Instead of making one junction, they are releasing neurotransmitter from varicosities to larger area
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:one: Action potential arrives at the varicosity
:two: Depolarization opens voltage gated Ca+2 channels.
:three: Ca+2 entry triggers exocytosis of synaptic vesicles
:four: NE binds to adrenergic receptor on target
:five: Receptor activation ceases when NE diffuses away from the synapse.
:six: NE is removed from the synapse
:seven: NE can be taken back into synaptic vesicles for re-release
:eight: NE is metabolized by monoamine oxidase (MAO)
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Neuroendocrine tissue
Modified sympathetic ganglion
Secrete epinephrine (neutohormone) into the blood
Chromaffin cell is kind of modified postganglionic sympathetic neuron
The neuromuscular junctions contain nicotinic receptors
The somatic motor pathway contains one long myelinated motor neuron.
At the end of the motor neuron axon branches out
One single motor neuron can control many different muscle fibers.
ACh receptors take information
ACh receptors trigger Na+ intake and depolarize the muscle fiber.
