Properties of Cells in Nervous System Flashcards
Terms:
- Neurons = ?
- Glia = ?
Properties of Cells in Nervous System
Terms:
(a) Neurons:
- Receive and process information and generate output.
(b) Glia:
- Provide mechanical and metabolic support
How do Neurons process and transmit information = ?
Properties of Cells in Nervous System
Electrical signaling in Neuron:
(a) Electrical signaling is the fundamental neuronal process that underlies all aspects of the brain function.
- Neurons process and transmit information via the generation of electrical signals.
- This is the basis for rehabilitation lies at the cellular level.
A typical neuron has four main components:
- What are they = ?
Properties of Cells in Nervous System
Structure of a Neuron:
(a) A typical neuron has four main components:
(1) Cell body / Soma: Synthesizes large variety and quantity of protein used as neurotransmitters.
(2) Dendrites: Branchlike extensions that arise from the cell body.
- Receive information from other neurons (= “input sites” for the cell)
(3) Axon: Extends from soma.
- Output unit of the cell
- Sends information to other neurons, muscle cells or glands (“output unit” of cell).
- Arises from a specialized region of the cell, called axon hillock.
(4.a) Presynaptic terminals (part of the synapses): Transmitting element of the cell.
(4.b) Synapse: Site of communication between neurons, and between a neuron and a muscle or a gland.
(4.c) Synapses have three elements:
- 1- Presynaptic terminals: Finger like projections (= transmitting element of the cell).
- 2- Synaptic cleft: Space between neurons.
- 3- Post-synaptic terminals.
Organelles within the cell body = ?
*Structure and function (5)
Properties of Cells in Nervous System
Cell body: Synthesizes large variety and quantity of protein used as neurotransmitters
(a) Organelles
- Nucleus: Control center, contains genetic material
-
Endoplasmic reticulum -
Rough (called Nissl substance): Synthesizes and transports proteins. - Endoplasmic reticulum -Smooth: releases calcium for signaling and synthesizes and transports lipids.
- Golgi apparatus: Packages the neurotransmitter.
- Mitochondria: Converts nutrients into energy source
Notes:
- Golgi apparatus and nucleus are restricted to soma of the neuron.
- Microtubules / Neurofilaments / Microfilaments: Long protein strands- responsible for maintaining unique neuronal shape
Direction of Information - Flow of Neurons:
- Three functional groups include= ?
Properties of Cells in Nervous System
Direction of Information - Flow of Neurons: Three functional groups (based on direction of information flow):
(1) Afferent neurons = Carry sensory information from the outer body toward the CNS).
- - Sensory neurons
(2) Efferent neurons = Relay commands from the CNS to smooth and striated muscles and to glands.
- - Motor neurons
(3) Interneurons
Axon:
On many neurons outside the CNS, the axon is surrounded by a white, fatty substance known as myelin.
- Myelin is formed by = ?
Properties of Cells in Nervous System
Axon:
(a) On many neurons outside the CNS, the axon is surrounded by a white, fatty substance known as myelin that is formed by Schwann cells.
- Nodes of Ranvier are indentations between adjacent Schwann cells.
Site of communication between neurons, and between a neuron and a muscle or a gland = ?
Properties of Cells in Nervous System
Synapse:
(a) Site of communication between neurons, and between a neuron and a muscle or a gland.
(b) Synapses have three elements:
- 1- Presynaptic terminals: Finger like projections (= transmitting element of the cell)
- 2- Synaptic cleft: Space between neurons.
- 3- Post-synaptic terminals
Axoplasmic transport:
- What is it = ?
- What are the two directions associated with axoplasmic transport = ?
Properties of Cells in Nervous System
Axoplasmic Transport:
(a) Cellular mechanism that transports substances along an axon is axoplasmic transport.
(b) Two directions:
- (1) Anterograde: Moves substances / neurotransmitter from the soma down the axon toward the presynaptic terminal.
- (2) Retrograde: Moves substances from synapse back to the soma.
(c) Axonal transport appears to slow with ageing process… (Neurodegenerative disease, Alzheimer’s disease)
How is information transmitted through a neuron = ?
- A. axon , dendrite , synapse , cell body , axon
- B. dendrite , synapse , cell body , axon , dendrite
- C. synapse , dendrite , axon , cell body , synapse
- D. synapse , dendrite , cell body , axon , synapse
Properties of Cells in Nervous System
How is information transmitted through a neuron ?
- D. synapse , dendrite , cell body , axon , synapse
Vertebrae neurons are classified into two groups = ?
Properties of Cells in Nervous System
Types of Neurons:
(a) Vertebrae neurons are classified into two groups, based on the number of processes that directly arise from cell body;
(1) Bipolar: Have two primary processes that extend from the cell body.
- Dendritic root
- Axon
(2) Multipolar: Have multiple dendrites arising from many regions of the cell body and an axon.
- Most common (e.g., Purkinje cells in the cerebellum – 150,000 synapses)
- Specialized to receive and accommodate huge amount of synaptic inputs to their dendrites
A subclass of bipolar cells, neurons having two axons and no true dendrites = ?
Properties of Cells in Nervous System
Types of Neurons - Bipolar Cells:
(a) Pseudounipolar cells, a subclass of bipolar cells, neurons having two axons and no true dendrites:
- Peripheral axon: transmit signals from the periphery to cell body.
- Central axon: conduct signals into the spinal cord.
Characteristics of Neurons:
- What do neurons use to receive, integrate and transmit information from thousands of other neurons = ?
Hint: Two
Properties of Cells in Nervous System
Characteristics of Neurons:
(a) Neurons function to receive, integrate and transmit information from thousands of other neurons using
- Electrical signals, and
- Chemical messengers.
Characteristics of Neurons:
- How do neurons distinguish from most other cells by = ?
Properties of Cells in Nervous System
Characteristics of Neurons:
(b) Neurons distinguish from most other cells by
- bioelectrical properties and,
- intercellular communications.
Greater in Extracellular Fluid or Intracellular Fluid:
- Na+ = ?
- K+ = ?
- Ca2+ = ?
- Cl- = ?
- HCO3- = ?
- pH = ?
- Osmolarity = ?
Properties of Cells in Nervous System
Greater in Extracellular Fluid or Intracellular Fluid:
(a) Na+ (mEq/L)
- Extracellular Fluid = 140
- Intracellular Fluid = 14
(b) K+ (mEq/L)
- Extracellular Fluid = 4
- Intracellular Fluid = 120
(c) Ca2+, ionized, (mEq/L)
- Extracellular Fluid = 2.5
- Intracellular Fluid = 1x10^-4
(d) Cl- (mEq/L)
- Extracellular Fluid = 105
- Intracellular Fluid = 10
(e) HCO3- (mEq/L)
- Extracellular Fluid = 24
- Intracellular Fluid = 10
(f) pH
- Extracellular Fluid = 7.4
- Intracellular Fluid = 7.1
(g) Osmolarity (mOsm/L)
- Extracellular Fluid = 290
- Intracellular Fluid = 290
Neurons function via rapid changes in the electrical potential across the cell membrane.
- What is an electrical potential = ?
Properties of Cells in Nervous System
Transmission of Information by Neurons:
(a) Neurons function via rapid changes in the electrical potential across the cell membrane.
(b) Electrical potential: distribution of ions creates a difference in electrical charge (+ or -) on each side of the cell membrane
Four types of membrane channels = ?
Properties of Cells in Nervous System
Membrane Channels:
(a) Channels are specialized to serve as openings through the membrane.
- When open, ions diffuse through the channel.
- ‘ Gated ’ membrane channels open in response to a stimulus and close when the stimulus is removed
(b) Four types of membrane channels allow ions to flow across the membrane:
(1) Modality-gated channels:
- Open in response to mechanical forces (stretch or touch), temperature changes or chemicals; specific to sensory neurons.
(2) Ligand-gated channels:
- Open in response to a neurotransmitter binding to the surface of a channel receptor on a postsynaptic cell membrane
(3) Voltage-gated channels:
- Open in response to changes in the electrical potential across the cell membrane.
(4) Leak channels:
- A small number of ions leak at a slow, continuous rate.
- Non-Gated membrane channel.
Electrical potential:
- Three types of electrical potentials in neurons are essential for transmitting information = ?
Properties of Cells in Nervous System
Electrical potential:
(a) Three types of electrical potentials in neurons are essential for transmitting information:
- (1) Resting membrane potential
- (2) Local potential
- (3) Action potential
Electrical Potentials:
- When a neuron is not transmitting information, the value of electrical potential across membrane is called = ?
- Value = ?
Properties of Cells in Nervous System
Resting membrane potential:
(a) When a neuron is not transmitting information, the value of electrical potential across membrane is called RMP.
(b) It’s a steady state, with no net flow of ions across the membrane.
(c) Unequal distribution [negative inside and positive outside] of ionic charge across the membrane is essential for neurons to be excitable.
- Inside of the neuron contains more negative charges than the outside ( -70mV / -90mV )
Sudden, brief changes in membrane potential can occur and be depolarized or hyperpolarized.
- Depolarized = ?
- Hyperpolarized = ?
Properties of Cells in Nervous System
Changes From Resting Membrane Potential:
(a) Sudden, brief changes in membrane potential can occur: depolarized or hyperpolarized.
(a.1) Depolarized:
- The membrane potential becomes less negative than the resting membrane potential.
- Increases the likelihood that the neuron will generate a transmittable electrical signal and is excitatory.
(a.2) Hyperpolarized:
- The membrane potential becomes more negative.
- Decreases the neuron’s ability to generate an electrical signal, and is inhibitory.
Local Potential
Aplitude strength can be increased and potentials integrated via:
- Temporal summation = ?
- Spatial summation = ?
Properties of Cells in Nervous System
Local Potential:
(a) Amplitude decreases with distance traveled.
(b) Strength can be increased and potentials integrated via temporal and spatial summation.
- Temporal summation: combined effect of a series of small potential changes that occur within milliseconds of each other.
- Spatial summation: process by which either receptor or synaptic potentials generated in different regions of the neuron are added together
(b) Via summation, sufficient number of potentials occurring within a short period cause significant changes in membrane potential.
Action Potential
Threshold stimulus intensity = ?
Properties of Cells in Nervous System
Action Potential:
(a) Threshold stimulus intensity
- Stimulus intensity that is sufficient to produce an action potential
(b) Unlike local potentials (graded in amplitude and duration), AP is All-Or-None
- Every time sufficient stimuli are provided, an action potential will be produced.
- Stronger stimuli produce action potentials of the same voltage and duration as the minimally sufficient stimuli.
(c) APs transmit information over longer distances because they are actively propagated
Refractory Period
- Absolute refractory period = ?
- Relative refractory period = ?
- What do both promote = ?
Properties of Cells in Nervous System
Refractory Period:
(a) Some channels become inactivated immediately after opening an action potential and require specific amount of time before it can be activated again for another action potential.
- Absolute refractory period: Another action cannot be stimulated.
- Relative refractory period: If greater depolarizing current is applied then next action potential can be initiated
(b) Refractory period promotes forward progression of the action potential and prevents backward flow
Events following stimulation of a sensory receptors = ?
Properties of Cells in Nervous System
Propagation of Action Potential
Once an AP is generated, the change in electrical potential = ?
Properties of Cells in Nervous System
Propagation of Action Potential:
- Once an AP is generated, the change in electrical potential spreads passively along the axon.
- Generation of new action potential is repeated along the length of the axon
Function of myelination = ?
Properties of Cells in Nervous System
Myelination:
(a) Myelination: A sheath of proteins and fats surrounding an axon
(b) Function:
- Provides insulation
- Prevents the leakage of current across the axonal membrane
- Increases the speed of AP propagation and the distance a current can passively spread
(c) Thicker myelin leads to faster conduction and greater chances for AP propagation
Small patches which lack myelin = ?
Properties of Cells in Nervous System
Nodes of Ranvier:
(a) Small patches which lack myelin
- Distributed every 1 to 2 mm along the axon and contain high densities of Na+ and K+ channels
(b) Specialized for active propagation of an action potential by allowing ion flow across the membrane
- AP spreads rapidly along a myelinated region, slows when crossing Nodes of Ranvier
- Saltatory conduction: quick node-to-node jumping of AP down a myelinated axon
Glial Cells
Types = ?
Properties of Cells in Nervous System
Glial Cells - Glia are categorized by size and function:
(1) Macroglia (large)
- Astrocytes
- Oligodendrocytes
- Schwann cells
(2) Microglia (small)
(3) Glial stem cells
Glial Cells
Where are astrocytes found in the CNS = ?
- Job = ?
Properties of Cells in Nervous System
Astrocytes:
(a) Star-shaped macroglial cells found throughout the CNS, primarily in gray matter because of close association with neuronal cell bodies, dendrites and synapses.
- Can be stimulated by signals from adjacent neurons or by mechanical changes (shape or pressure).
- Role in cell signaling
Glial Cells - Astrocytes
Functions = ?
Properties of Cells in Nervous System
Function of Astrocytes:
(a) Help maintain normal neuronal signaling by acting as scavengers
- Taking up extra K+ ions in the extracellular environment, regulating ionic concentration gradient.
- Removing chemical transmitters from the synaptic cleft between neurons, and
- Cleaning up other debris in the extracellular space
(b) Connect neurons with capillaries via end-feet, providing nutrition.
(c) Participate in the formation of scars to fill in cavities following an injury
(d) Assist in formation of new synapses and circuits
Glial Cells - Oligodendrocytes & Schwann Cells
- Form = ?
- Found primarily in = ?
Properties of Cells in Nervous System
Oligodendrocytes and Schwann Cells:
(a) They form myelin sheath (axonal insulation) and are found primarily in white matter.
- Oligodendrocytes myelinate neurons in the CNS.
- Schwann cells myelinate neurons in the PNS.
- Subject to immunological insults in certain neurological conditions, causing demyelinating diseases, such as multiple sclerosis (MS) and Guillain-Barre syndrome (GBS)
Glial Cells
Which cell, act as the ‘immune system’ of the CNS = ?
Properties of Cells in Nervous System
Microglial Cells:
(a) Are special type of phagocytes that resides in the CNS
(b) Microglia act as the immune system of the CNS
- Activated during development of the nervous system and following injury, infection, or disease
- Proteins in dying cells attract microglia to the site; microglia clean up and remove debris, important for healing following stroke, brain injury etc.
Glial Cells
Which type of glial cells are activated during development of the nervous system and following injury, infection, or disease = ?
Properties of Cells in Nervous System
Microglial Cells:
(a) Are special type of phagocytes that resides in the CNS
(b) Microglia act as the immune system of the CNS
- Activated during development of the nervous system and following injury, infection, or disease
- Proteins in dying cells attract microglia to the site; microglia clean up and remove debris, important for healing following stroke, brain injury etc.
Glial Cells
Which Glial cells are immature and undifferentiated cells = ?
Properties of Cells in Nervous System
Glial Stem Cells:
(a) Glial stem cells are also found throughout the developing and adult brain
- These cells are immature and undifferentiated cells.
- Retain the capacity to proliferate and generate additional precursors or differentiated glia and, in some cases, neurons
(b) Characteristics include the ability to:
- Self-renew; differentiate into most types of glial cells and neurons
Neuroinflammation
Neuroinflammation response is mediated by = ?
Properties of Cells in Nervous System
Neuroinflammation - Beneficial and Harmful Effects:
(a) Neuroinflammation:
- The response of the CNS to infections, diseases and injuries
- Response is mediated by reactive microglia and astrocytes.
(b) Beneficial effect:
- When reactive microglia clean up and remove debris;
(c) Harmful effects:
- Microglia and astrocytes become excessively activated.
- Death of neurons and oligodendrocytes, inhibition of neural regeneration.
- Correlation between abnormal glial activity and neural damage in stroke.
Neuroinflammation
- Beneficial effects = ?
- Harmful effects = ?
Properties of Cells in Nervous System
Neuroinflammation - Beneficial and Harmful Effects:
(a) Neuroinflammation:
- The response of the CNS to infections, diseases and injuries
- Response is mediated by reactive microglia and astrocytes
(b) Beneficial effect:
- When reactive microglia clean up and remove debris;
(c) Harmful effects:
- Microglia and astrocytes become excessively activated
- Death of neurons and oligodendrocytes, inhibition of neural regeneration
- Correlation between abnormal glial activity and neural damage in stroke
Clinical Considerations - Myelin
Damaged myelination slows and impedes = ?
Properties of Cells in Nervous System
Clinical Considerations - Myelin:
- Critical to conduction of information in the CNS
- Damaged myelination slows and impedes the conduction of AP in the CNS
- Such as multiple sclerosis or the PNS (e.g., Guillain-Barre syndrome)
What am I = ?
- Autoimmune disorder
- Oligodendrocytes are destroyed
- Women more affected
- Impaired sensation
- Speech difficulties
- Spasticity
- Gait difficulties
Properties of Cells in Nervous System
Multiple Sclerosis:
(a) Damage to myelin sheath in brain and SC
- Immune system disorder (autoimmune disorder)
- Oligodendrocytes are destructed
- Patches of demyelination
- Plaques
- Women more affected
(b) Signs and symptoms:
- Lack of coordination and balance
- Impaired and/or double vison
- Impaired sensation (paresis/ paralysis)
- Speech difficulties
- Spasticity (increased reflexes (UMN))
- Gait difficulties
(c) Notes:
- Diagnosis is difficult; variable symptoms, MS usually manifests with one sign that may completely resolve.
- 20% present with visual symptoms as the first symptom but 80% will have visual symptoms at some point
Multiple Sclerosis (MS)
Four types = ?
Properties of Cells in Nervous System
Multiple Sclerosis:
(a) Onset common between 20 and 40 years; women are three times more frequently affected
(b) Four types of MS, all named according to the course of disease progression:
(1) Relapsing/remitting (most common - 85%):
- Alternate between relapse(s) /remissions
- Relapse - New signs/sxs appear & old signs worsen.
- Remission - Full or partial recovery
- Without treatment, most cases transition to secondary progressive.
(2) Secondary progressive:
- Continuous decline with fewer or no relapses.
(3) Primary progressive (10%):
- Steady functional decline from time of onset
(4) Progressive relapsing (5%):
- Progressive Relapsing
- Steady functional decline with relapse/ partial remissions
- Function never fully recovers in remissions
