2. Nervous System Flashcards
What is the major function of the Nervous System?
Control center (maintain homeostasis by coordination and communication) e.g. collect information, process information, generate responses
What comprises the Central Nervous System (CNS)?
Brain, spinal cord
What comprises the Peripheral Nervous System (PNS)?
Composed of nerves that connect the brain or spinal cord with the body’s muscles, glands, and sense organs
e.g. cranial nerves, spinal nerves, ganglia
Organization: Afferent (sensory)
To CNS
e.g. somatic, visceral, special
Organization: Efferent (motor)
From CNS
- Somatic Nervous System
- Autonomic Nervous System
- Sympathetic Division
- Parasympathetic Division
e. g. somatic motor, autonomic motor (sympathetic, parasympathetic, enteric)
What is the structure of a neuron?
- Cell body
- Dendrite
- Axon
- Initial segment
Myelinated axon
- Schwann cell
- Node of Ranvier: speeds up the conduction velocity
What is the functional classification of neurons (3 classes)?
- Afferent neuron
- Efferent neuron
- Interneuron
What are the glial cells of CNS?
- Oligodendrocyte
- Astrocyte
- Microglia
- Ependymal cell
Neuron
The basic cell type of both systems; “nerve cells”
What the most numerous cells in the CNS?
Glial cells
Astrocytes
Support cells, control extracellular environment of neurons
Microglia
“Immune system” of CNS
Ependymal cells
Ciliated; involved with production of CSF and CSF movement
Oligodendrocytes
Form the myelin
What are examples of membrane potentials?
- Ohm’s Law
- Resting membrane potential
- Graded potentials
- Action potentials
What is Ohm’s Law?
I = V/R I = current: the movement of electrical charge V = potential: voltage difference between two points R = resistance: hindrance to movement through an opening or substance
How can electrical force increase?
- Increases with quantity of charge
2. Increases as distance of separation between charges decreases
What is the membrane potential?
An electrical “charge” (voltage difference) across the plasma membrane; charged positively outside in respect to inside of the cell
What is resting membrane potential?
The electrical “charge” (voltage difference) across the plasma membrane at resting (with no stimulus), which ranges from -40 to -90 mV
What is the Equilibrium Potential for K+?
The membrane potential at equilibrium due to K+ movement in a hypothetical situation
e.g. -90 mV
What is the Equilibrium Potential for Na+?
The membrane potential at equilibrium due to Na+ movement in a hypothetical situation
e.g. +60 mV
Why is the resting membrane potential close to EK+?
Because at resting, PK+ is high and PNa+ is low
Generation of Resting Membrane Potential
- Concentration difference (for Na+, K+) is set due to 3 Na+ to 2 K+ exchange ratio by sodium-potassium pump
- Permeability difference between Na+ and K+ (PK+ is much greater than PNa+)
If the K+ concentration in the extracellular fluid (ECF) is elevated, what would happen to the magnitude of the membrane potential?
Become less negative
If the membrane permeability to sodium ion (Na+) is elevated, what would happen to the magnitude of the membrane potential?
Become less negative
If a cell once viable is no longer able to generate ATPs (i.e. cell death), what would happen to the magnitude of the membrane potential?
Become less negative
What do some cells (nerve and muscle cells) have that are “gated” by signals?
Ion channels that are gated by signals
e.g. voltage current, chemicals, mechanical force (“excitability”)
What happens when these ion channels become “activated”/”excited”?
These ion channels open up, increasing the permeability of the membrane to a specific ion
After increasing membrane permeability, what will this ion movement result in?
Ion movement will result in a change in membrane potential
** Can be hyperpolarized (more negative) or depolarized (less negative), depending on the signal
Depolarization
The potential moving from RMP to less negative values
Repolarization
The potential moving back to RMP
Hyperpolarization
The potential moving away from RMP in a more negative direction
Graded Potential
- Dissipates with distance
- Either depolarized or hyperpolarized
- Magnitude can vary (“graded”)
e. g. receptor potential, pacemaker potential, synaptic potential
Action Potential
- A very large and rapid change in membrane potential that propagates along the full length of the axon
- Has a threshold (all-or-none response)
- Reversal of the polarity takes place
- The mechanism the nervous system uses to communicate over long distances
Explain the time course of an action potential (7 steps)
- Steady reasing membrane potential is near Ek, Pk is greater than PNa due to leak of K+ channels
- Local membrane is brought to threshold voltage by a depolarizing stimulus
- Current through opening voltage-gated Na+ channels rapidly depolarizes the membrane, causing more Na+ channels to open
- Inactivation of Na+ channels and delayed opening of voltage-gated K+ channels halts membrane depolarization
- Outward current through slowly closing voltage-gated K+ repolarizes the membrane back to a negative potential
- Persistent current through slowly closing voltage-gated K+ channel hyperpolarizes membrane toward Ek; Na+ channels return from inactivated state (without opening)
- Closure of voltage-gated K+ channels returns the membrane potential to its resting value
Behavior of Voltage-Gated Ion Channels: Na+ Channel
Fast responder (3 states) e.g. closed, open, inactivated
Behavior of Voltage-Gated Ion Channels: K+ Channel
Slow responder (2 states) e.g. closed open
The sodium ion results in what state and why?
Influx of Na+ results in depolarization
The potassium ion results in what state and why?
Efflux of K+ results in repolarization
Refractory period
Refractoriness ensures the unidirectional transmission of active potential
The mechanisms for “refractory” period are due to..
“Ion channel” behavior
Why is saltatory conduction in myelinated axons have faster traveling of AP in comparison to unmyelinated axons?
Due to “jumping” effect from one node to the next which increases the direction of action potential propagation
Graded Potential (overview)
- Amplitude varies with size of initiating event
- Can be summed
- Has no threshold
- Has no refractory period
- Amplitude decreases with distance
- Duration varies with initiating conditions
- Can be a depolarization or hyperpolarization
- Initiated by environmental stimulus (receptor) by neurotransmitter (synapse), or spontaneously
- Mechanism depends on ligand-gated channels or other chemical or physical changes
Action Potential (overview)
- All-or-none: once membrane is depolarized to threshold, amplitude is independent of the size of the initiating event
- Cannot be summed
- Has a threshold that is usually about 15 mV depolarized relative to the resting potential
- Has a refractory period
- Is conducted without decrement; depolarization is amplified to a constant value at each point along the membrane
- Duration is constant for a given cell type under constant conditions
- Is only a depolarization
- Initiated by a graded potential
- Mechanism depends on voltage-gated channels
How is the polarity across the membrane established? List the 3 main factors determining the polarity of cell membrane, and describe the role of each.
- Concentration difference for sodium and potassium across the membrane
- Greater flux of K+ out of the cell than Na+ into the cell due to a greater permeability to K+ than to Na+
- Na+/K+ -ATPase pump
What is curare (alkaloid)?
A deadly arrowhead poison used by indigenous peoples of South America, causing death in human and animals by asphyxiation
Explain the process of poisoning by curare.
- Curare binds to nicotinic ACh receptor
- Endogenous ACh fails to bind its own receptors
- The Na+ channels fail to open
- No depolarization takes place at the N-M junction
- Skeletal muscle fails to contract (e.g. diaphragm)
What are the mechanisms of neurotransmitter release?
- Action potential reaches terminal
- Voltage-gated Ca2+ channels open
- Calcium enters axon terminal
- Neurotransmitter is released and diffuses into the cleft
- Neurotransmitter binds to postsynaptic receptors
- Neurotransmitter removed from synaptic cleft
Postsynaptic Potential: Excitatory Postsynaptic Potential (EPSP)
Depolarizing graded potential
Postsynaptic Potential: Inhibitory Postsynaptic Potential (IPSP)
Hyperpolarizing Graded Potential
Temporal vs. Spatial Summation: How are they summated?
Temporal: Graded potentials are summated in time
Spatial: Graded potentials are summated in space
Cholinergic (ACh)
Neurotransmitter; synthesized from the amino acid, tyrosine
e.g. dopamine (DA), norepinephrine (NE)
What are the receptors for Cholinergic (ACh)?
- Nicotinic
2. Muscarinic
What are the receptors for NE, Epi?
- Alpha-adrenergic
2. Beta-adrenergic
What are 3 examples of neurotransmitters?
- Cholinergic (ACh)
- Dopaminergic (DA)
- Adrenergic (NE, Epi)
How is the brain divided (3 divisions)?
- Forebrain (cerebrum, diencephalon)
- Brainstem (midbrain, pons, medulla oblongata)
- Cerebellum
* cerebral ventricles (I, II, III, IV)
Cerebrum: What are the motor areas?
- Primary motor cortex: precentral gyrus (frontal lobe)
- Premotor cortex (skilled motor activities)
- Broca’s area (motor speech area)
Cerebrum: What are the sensory areas?
- Primary somatosensory cortex: postcentral gyrus or parietal lobe
- Somatosensory association area: comprehensive understanding of an object (e.g. size, texture)
- Visual cortex: occipital lobe
- Auditory cortex: temporal lobe
Cerebrum: What are the association areas?
- Prefrontal cortex: intellect, cognition, recall, personality
- Language areas: Wenicke’s area (left hemisphere)
Grey vs. White matter: What is its coloration and what does it mostly house?
Grey matter: grey coloration, houses mostly cell bodies
White matter: light coloration, houses mostly myelinated fiber tracts
Cerebrum: Cerebral White Matter | What fibers are associated?
Deep to the gray matter of the cortex
- Commissural fibers (between hemispheres, corpus callosum)
- Association fibers (within a hemisphere)
- Projection fibers (from cerebral cortex to lower brain)
Cerebrum: Subcortical Nuclei | What autoimmune disorder is associated?
Basal ganglia (stopping, starting movement) e.g. Parkinson's disease: depletion of dopamine in substantia nigra which terminates in basal ganglia (globus pallidus)
Limbic System: What are its components?
- Frontal lobe
- Temporal lobe
- Hippocampus
- Hypothalamus (functional brain system)
Limbic System: What are its functions?
Functions in learning, emotional experience and behavior (e.g. psychosomatic illness), long term memory (LTM)
Diencephalon: Thalamus
Synaptic relay station from all sensory inputs, 12 nuclei
Diencephalon: Hypothalamus
Main visceral control center, center for emotional responses and behavior; crucial to overall body homeostasis
e.g. regulates anterior pituitary gland function, water balance and thirst, food intake, reproductive system, circadian rhythms, and temperature; involved in control of ANS in brainstem,
Diencephalon: Epithalamus
- Pineal gland: melatonin production (an output of the biological clock)
- Choroid plexus: CSF formation
Brainstem: What does it consist of and what does it contain?
- Consists of fiber tracks (ascending, descending)
- Contains “reticular formation” (RAS): controls arousal of the brain (sleep-wake cycle)
Brainstem: Midbrain
Corpora quadrigemina
- Superior colliculi (visual reflex)
- Inferior colliculi (auditory reflex)
Brainstem: Pons
- Pontine nuclei
2. Cell body for cranial nerves
Brainstem: Medulla Oblongata
- Cardiovascular center
- Respiratory center
- Other centers (vomiting, hiccuping, swallowing, coughing, sneezing)
Cerebellum: What does it consist of and what is its function?
- Consists of 2 hemispheres and vermis
- Function: coordination of movement, balance, posture, some types of learning
What is the function of the spinal cord?
Major reflex center
Spinal Cord: ventral view
- Gray matter (cell bodies)
- White matter (fiber tracts)
- Dorsal roots (sensory)
- Dorsal root ganglia
- Ventral roots (motor)
- Spinal nerves
Spinal Cord: dorsal view
- Spinal cord trauma (e.g. paresthesias, paralysis)
e. g. of Paralysis: paraplegia (transection at T1-L1) vs. quadriplegia (transection at C1-8)
How many pairs of cranial and spinal nerves are there in the PNS?
12 pairs of cranial nerves; 31 pairs of spinal nerves
What is the functional division of PNS?
- Somatic division: consists of a single neuron between CNS and skeletal muscle cells, innervates skeletal muscle, can lead only to muscle excitation
- Autonomic division: has 2-neuron chain (connected by a synapse) between CNS and effector organ, innervates smooth and cardiac muscle, glands, and GI neurons, can be either excitatory or inhibitory
What are the cranial nerves?
- Olfactory: from receptors in smell
- Optic: from receptors in eye
- Oculomotor: alters lens shape for near or far vision
- Trochlear: moves eyeball downward and laterally
- Trigeminal: chewing muscles
- Abducens: moves eyeball laterally
- Facial: facial expression
- Vestibulocochlear: from receptors in inner ear
- Glossopharyngeal: swallowing and parotid salivary gland
- Vagus: pharynx, larynx, smooth muscle
- Accessory: neck skeletal muscles
- Hypoglossal: tongue skeletal muscles
Somatic vs. Autonomic Nervous System: Effector Organs
Somatic: skeletal muscle
Autonomic: smooth/cardiac muscles, glands, other cells
Autonomic Nervous System: Sympathetic vs. Parasympathetic Division
Parasympathetic: “rest & digest”
Sympathetic: “fight-or-flight”
Protection of the Brain: What are its components?
- Skull
- Meninges (dura mater, arachnoid mater, pia mater)
- Cerebrospinal fluid (CSF)
- Blood-brain-barrier (BBB)
Cerebrospinal Fluid (CSF): How is it produced and what does space does it fill?
- Produced by choroid plexus in ventricles
- Fills the subarachnoid space and circulates
Blood-Brain Barrier (BBB)
- Most impermeable capillaries in the body (tight junctions formed by astrocytes)
- Highly selective transport system (for glucose, some essential amino acids)
- Lipid-soluble molecules freely penetrate (O2, CO2, alcohol, nicotine, caffeine)
