Midterm #1 Main Topics (also look at diagrams on D2L) Flashcards
Directions
Medial:
Horizontal, moving towards the middle
Lateral:
Horizontal, moving away from the middle
Dorsal: above
Ventral: below
Anterior: front
Posterior: behind
Proximal: close to body
Distal: further from body
Horizontal vs. Frontal vs. Sagittal
Frontal (aka Coronal): separates the front from the rest
Sagittal: Separates the left and right
Horizontal: x- axis
Directions/Orientation
Contralateral: opposite side
Ipsilateral: Same side
Major Divisions of Nervous System
Central Nervous System (CNS)
- brain and spinal cord
Peripheral Nervous System (PNS)
- nerves
Protection for CNS
Bone: skull and spinal cord
3 Meninges
Dura mater: outermost, tough membrane.
Arachnoid layer: web-like
Pia mater : innermost layer of protection,
attached to the brain
Cerebrospinal fluid (CSF)
Supports or ‘cushions’ the brain.
Found in sub-arachnoid layer and 4 ventricles
Ventricles
Ventricles are filled CSF
Central Aqueduct transports CSF across the ventricles
Peripheral Nervous System Separates Into…
Autonomic:
- regulates internal organs and involuntary organs
Somatic:
- controls voluntary movements and interacts with external environment
Autonomic Separates into…
- Sympathetic: fight or flight
- Parasympathetic: rest and digest
Efferent vs Afferent nerves
Efferent: information exiting the NS
Afferent: information to the NS
12 Cranial Nerves
Olfactory - smell
Oculomotor - eye movement and pupil reflex
Trigeminal - face sensation and chewing
Facial - face movement and taste
Glossopharyngeal - throat sensation, taste, and swallowing
Accessory - neck movement
Optic - vision
Trochlear - eye movement
Abducens - eye movement
Vestibulocochlear - hearing and balance
Vagus - movement, sensation, and abdominal organs
Hypoglossal - movement, sensation, and abdominal organs
Major Brain Divisions
Developing:
Telencephalon and Diencephalon ➡️ Forebrain (matured)
Mesencephalon ➡️ Midbrain (matured)
Metencephalon and Myelencephalon ➡️ Hindbrain (matured)
More Detailed Divisions
Forebrain (major division):
- Lateral
(ventricle) - Telencephalon
(subdivision) - Cerebral cortex, Basal ganglia, Limbic system
(principle structures) - Third
(ventricle) - Diencephalon
(subdivision) - Thalamus, Hypothalamus
(principle structures)
Midbrain (major division):
- Cerebral aqueduct
(ventricle) - Mesencephalon
(subdivision) - Tectum tegmentum
(principle structures)
Hindbrain (major division):
- Fourth
(ventricle) - Metencephalon
(subdivision) - Myelencephalon
(subdivision) - Cerebellum, Pons, Medulla oblongata
(principle structures)
Hindbrain Divisions
Myelencephalon:
- medulla ➡️ life support functions ➡️ damage = death
- reticular formation ➡️ ‘gate keeper’; can admit or block sensory info
Metencephalon:
- pons ➡️ ‘bridge’; main connection b/w cortex and cerebellum, role in sleep, dreaming
- cerebellum ➡️ ‘little brain’
Midbrain Divisions
Mesencephalon:
Tectum (dorsal surface):
- superior colliculus ➡️ vision
- inferior colliculus ➡️ audition
Tegmentum (ventral surface):
- 3 colourful structures
- periaqueductal gray ➡️ analgesia
- substantia nigra ➡️ sensorimotor
- red nucleus ➡️ sensorimotor
Forebrain Divisions
Diencephalon:
Thalamus
- relay centre from senses to the cortex.
- all senses stop here except for olfaction.
Hypothalamus
- located below thalamus
- homeostasis: internal balance
Cerebral Cortex
The very top of the brain
It has many foldings and convolutions to increase surface area
Sulci: small grooves
Fissures: larger sulci
Gyri: bumps/ bulges
Longitudinal fissure – a groove that
separates right and left hemisphere
Parts of the Neuron
Soma: cell body of the neuron, contains the nucleus
Dendrites: branch-like structure that receives messages from other neurons
Axon Hillock: located between cell body and axon. Integration site before signal
goes down the axon
Axon: The long, thin cylindrical structure that conveys information from the soma
of a neuron to its terminal button
Node of Ranvier: gaps between section of myelin
Terminal buttons: The bud at the end of a branch of an axon
Synapse: A junction between the terminal button of an axon and the body/dendrites of another neuron
Cytoskeleton
(helps give a neuron its shape: Scaffolding)
Microtubules: Long ‘pipes’ running down the axon
Neurofilament:
- consists of wound rope-like subunits
- very strong
Microfilaments:
- most densely found in the neurites (axons and dendrites)
- plays a role in changing shapes of a cell (actin)
Glia Cells
Support & nourish neurons
Outnumbers neurons 10:1
Four types: Oligodendrocytes, Schwann Cells, Astrocytes, Microglia
Oligodendrocytes
Produce myelin: the fatty sheath that covers the axon
Can myelinate multiple axons in Central Nervous System (CNS).
Can produce up to 50 segments of myelin.
Not all axons are myelinated
Schwann Cells
Produce myelin in peripheral nervous system (PNS)
Only myelinates a single nerve.
Digest dead axons and provide process for regrowth.
Astrocytes
Largest glia, star-shaped
Many functions:
- surround neurons and contact blood vessels via end-feet.
- provides physical support.
- provides nourishment
Microglia
Involved in response to injury or disease
Protect the brain from invading micro-organisms
Membrane Structure
Phospholipids are the molecules that make up the cell membrane.
They have three sections.
2 hydrophobic tails: will not dissolve in water
1 hydrophilic head: will dissolve in water
Phospholipid Bilayer
Cell membrane is semi-permeable
Protein Synthesis
DNA→ mRNA: Transcription
RNA→ Protein: Translation
Amino acids are the building blocks of proteins
Ion distribution creates Resting Membrane
Potential
Ions, charged particles, are unevenly distributed
4 Ions Contributing:
- Sodium (Na+)
- Chloride (Cl- )
- Potassium (K+)
- Negatively charged proteins: synthesized within the neuron found primarily within the neuron
Factor of Resting Potential - Random Motion
Particles move down their concentration gradient
From areas of high concentration to area of low concentration
Even distribution
Factor of Resting Potential - Electrostatic Pressure
Like forces repel, opposites attract
Even distribution
Factor of Resting Potential - Selective Permeability
Some ions can pass through others cannot
Uneven distribution
Factor of Resting Potential - Sodium-Potassium Pump
Moves 3 Na+ out for every 2K+ in
Uneven distribution
Neuron Equilibrium Equations
To calculate the equilibrium of one ion -> Nerst equation
All relevant ions -> Goldman equation
Resting membrane potential: -70mV
Action Potential
“All or nothing”
Mechanical or chemical (neurotransmitter) input causes depolarization of the cytoplasm when sodium enters the cell (stretching of ion channels, or gated ion channels)
Lots of sodium outside, not as much inside – it floods in and makes the inside more positive in charge
If the potential reaches –55mV, an AP is triggered
Na+ is concentrated outside the cell
Depolarization caused by Na+
influx when channels open (voltage-gated)
K+ is concentrated inside the cell, so moves outward. It takes longer for K+ channels to open compared to Na+ channels!
Refractory period caused by efflux of K+ (because delay in channel opening) - cell becomes temporarily hyperpolarized
Refractory Periods
Absolute refractory period:
sodium channels inactivate when the membrane becomes strongly depolarized. They cannot be activated again, and another action potential cannot be generated until the polarization becomes low enough
Relative refractory period:
the membrane potential stays hyperpolarized until the voltage-gated potassium channels close. An action potential can be generated but requires a stronger depolarization to do so
Saltatory Conduction
Ions cannot flow in and out of the cell across fatty tissues, and so they flow directly towards the next node without activating ion channels until they reach
an “open space” (which takes time)
Myelin allows current to spread further between nodes, and speeds up AP conduction
Chemical Messengers
Electrical and chemical synapses
Neurotransmitter families
- Cholinergic, catecholaminergic, serotonergic, amino acids
Receptor families
- G-proteins, transmitter-gated channels
Pharmaceuticals
- Agonists, antagonists
Types of Synapses
Electrical
- Occur at specialized sites called gap junctions
- Membranes of two cells are very close together (3nm); the gap contains proteins called connexins
- Allow direct transfer of ionic current from one cell to the other (very fast)
Chemical
- Presynaptic and postsynaptic membranes are separated by a 20- 50nm cleft (10x the width of gap junctions)
- Many specialized components on both sides help to convert chemicals (i.e., neurotransmitters) from the presynaptic neuron into electrical signals on the postsynaptic side (a much slower process)
Electrical Synapses
6 connexins = 1 connexon
2 connexons = 1 gap junction channel
Each gap junction channel bridges the cytoplasm of two cells. Ions and small molecules can travel in both directions.
Many gap junction channels create one “gap junction”
Fast and reliable! Cells connected this way are “electrically coupled”
PSPs generated at a single gap junction are very small, but neurons form gap junctions with many cells – many PSPs generated at the same time can add together to generate an AP
Chemical Synapses
The cleft is filled with fibrous proteins that act as a “glue” to hold the two cells together
Presynaptic side:
- Site of release is called an active zone
- Contains many synaptic vesicles that hold neurotransmitters (produced in the cell body and then transported to the presynaptic site)
- Contains voltage-gated calcium channels
Postsynaptic side:
- Protein clusters known as postsynaptic density contain neurotransmitter receptors
- This is where the chemicals (neurotransmitters) bind and become translated into a change in membrane
potential (electricity) - The postsynaptic response varies depending on what kind of receptor is activated (ionotropic vs metabotropic)
Chemical Synapses: Presynaptic Activity
Action potential arrives at the presynaptic terminal
Voltage-gated calcium channels are opened in response to changing cell potential – calcium enters the presynaptic cell rapidly
Calcium influx triggers synaptic vesicle exocytosis
Vesicles are recycled back into the cell via endocytosis
Chemical Synapses: Postsynaptic Activity
Neurotransmitters are like a “key in a lock” - you need the right key to activate each receptor
Transmitter-Gated Ion Channels:
- Transmitters trigger conformational change that opens a pore between subunits
- Consequences depend on which ions can pass through the channel
- Not as selective as voltage-gated channels (e.g., ACh activated channels allow passage of both Na+ and K+)
G-protein Coupled Receptors:
- Slower and longer-lasting effects than transmitter-gated ion channels
- More steps involved
- Receptors activate g-proteins
- G-proteins activate effector proteins
(ion channels or enzymes)
Ionotropic Receptors: EPSP/IPSP
Excitatory Postsynaptic Potential (EPSP):
- If the open channels are permeable to Na+ then the net effect is to depolarize the postsynaptic cell (i.e., take the cell closer to triggering an action potential)
Examples: ACh-hated and glutamate-gated ion channels
Inhibitory Postsynaptic Action Potential (IPSP):
- If the open channels are permeable to Cl then the net effect is to hyperpolarize the
postsynaptic cell (i.e., take the cell further from triggering an action potential)
Examples: GABA and glycine-gated ion channels
EPSP Summation
Not every EPSP triggers an action potential. Most EPSPs are very small (A)
Spatial summation (B) occurs when many nearby synapses each generate an EPSP to generate a larger depolarization when added together
Temporal summation (C) occurs when a synapse fires multiple times in short succession (before the cell has time to repolarize)
IPSP Shunting
If the resting membrane potential is already - 65mV, no IPSP will be visible (membrane potential already = reversal potential for Cl)
So what effect is the IPSP having on cell signaling?
When an EPSP depolarizes the cell membrane and the current flows towards the soma, the current may pass by an active inhibitory synapse
Positive current here will flow out of the cell,
redirecting the excitatory potential away from the soma
The inhibitory synapse acts as a “shunt” and prevents an action potential from being generated
Neurotransmitter Families
Cholinergic:
- Present at neuromuscular junction
- Produced by all motor neurons in the spine and brainstem
- Examples: Acetylcholine
Catecholaminergic:
- Tyrosine is the precursor of all catecholaminergic neurotransmitters
- Regulate movement, mood, attention, and visceral function
- Examples: dopamine, norepinephrine, epinephrine
Serotonergic:
- Tryptophan is the precursor of
serotonergic neurotransmitters
- Plays a role in regulating mood, emotional behaviour, and sleep
- Examples: serotonin
Amino Acid:
- Literally amino acids (building blocks of proteins)
- Very small
- Examples: glutamate (excitatory), glycine, GABA (inhibitory
Other:
ATP
- excitatory
Endocannabinoids
- retrograde messengers
Nitric Oxide
- gaseous, membrane permeable
Receptor Agonists vs. Antagonists
Like neurotransmitters, many drugs bind to receptors to exert an effect on the nervous system
Agonists
- Bind to receptors and imitate the actions of neurotransmitters
- Effect looks similar to response to naturally-occurring neurotransmitter release
- Example: nicotine (binds to ACh receptors, mimics ACh function – muscle activation)
Antagonists
- Binds to receptors and inhibits (antagonizes) their function
- Blocks the action of naturally-occurring
neurotransmitters
- Example: curare (binds to ACh receptors, prevents ACh function at the neuromuscular junction – paralysis)
