Unit 2 Flashcards
What is the nervous system?
Network of nerve cells that uses a rapid means of communication to adapt the body to external stimuli and coordinates internal processes.
What are afferent neurons?
Neurons that send impulses from the receptor to the brain (At the brain).
What are efferent neurons?
Neurons that send impulses from the the brain to the receptor (Exit the brain).
What is the autonomic nervous system divided into?
Sympathetic and parasympathetic nervous system.
What is the nervous system divided into?
Central nervous system and peripheral nervous system.
What is the main function of the somatic nervous system?
Voluntary control of body movements via skeletal muscles.
What is the main function of the autonomic nervous system?
Involuntary control of body movements via visceral organs.
What is a neuron?
A functional communicating cell that transits nerve impulses.
A typical neuron contains what three structures?
- Cell body
- Dendrites
- Axons
What is myelin?
An insulating sheath that contains phospholipids which act as protection and insulation. Also conducts faster impulses along the axon.
What are Nodes of Ranvier?
Part of the axon not covered by myelin.
What is a synapse?
The gap between neurons which impulses pass by diffusion of a neurotransmitter.
What is a sensory neuron?
Afferent neurons that send information into the CNS from the receptors.
What is a motor neuron?
An efferent neuron that transmits information from the CNS to the effectors (muscles and/or glands).
What are interneurons?
Neurons located within the CNS and are involved with integration.
How is a membrane potential across the membrane produced?
A membrane potential occurs when there is an unequal distribution of ions occurs between the inside and outside of the cell, which also creates an unequal charge distribution.
Extracellular fluid contains more ___ and ___.
Sodium and chloride. Outside cell more positive.
Intracellular fluid contains more ___ and ___.
Potassium and negatively charged proteins. Inside cell more negative.
How many more times permeable is the membrane to potassium?
The membrane is 40 times more permeable to potassium. Thus, potassium can move outward and sodium slightly inward. The outside becomes positive and inside becomes negative.
What three forces are involved in maintaining the membrane potential?
- Chemical or concentration force
- Electrical force
- Na-K pump
Explain the chemical or concentration force.
The chemical or concentration force is caused by the concentration gradient.
Explain the electrical force.
The electrical force is the attraction and repulsion between charges.
Explain the Na-K Pump.
Maintains the electrical and chemical gradients.
One way it does this:
Step 1. Sodium binds to receptor site on enzyme that’s in the membrane
Step 2. ATPase binds to enzyme and breaks off a phosphate which provides energy to change the shape of the pump
Step 3. Brings sodium inside of cell
Step 4: Potassium bonds to receptor site on enzyme
Step 5: Rechanges pump to original shape
Step 6: Potassium released outside of cell
What is a nerve impulse?
Changes in membrane potentials that form electrical signals that travel down an axon.
What is depolarization?
Membrane potential becomes LESS NEGATIVE. Can be caused by an increase in sodium ion permeability (Na+ going into cell).
What is repolarization?
Membrane returns to resting state. Can be caused by an increase in potassium ion permeability (K+ going out of cell cell).
What is hyperpolarization?
When the membrane potential becomes more polarized or MORE NEGATIVE. Can be caused by an increase in chloride ion or potassium ion permeability (Cl- or K+ goes into cell).
What two types of electrical signals in the neuron are there?
- Graded potential
- Action potential
Where do graded potentials occur?
In the membranes of dendrites and cell body membranes.
Where do action potentials occur?
Start at the axon hillock, then axon, then axon terminals (knobs).
Describe the strength of graded potentials.
Strength of depolarization and hyperpolarization varies depending on the stimulus strength.
The stronger the stimulus, the stronger the depolarization and hyperpolarization.
What kind of transmission do graded potentials have?
Passive transmission. The signal or graded potential weakens with distance.
Describe the strength of action potentials.
All-or-nothing. Action potential is generated to its maximum strength or doesn’t fire at all.
What kind of transmission do action potentials have?
Action transmission or propagation. Where the strength of the action potential at the end of the axon is the same strength as the beginning. It doesn’t fade or weaken with distance.
Describe the refractory period of graded potentials.
There are no refractory periods.
Describe the refractory period of action potentials.
Refractory lasts about 10 milliseconds.
What is a refractory period?
A period of neuron insensitivity to another stimulation that prevents the creation of a second action potential.
What is an absolute refractory period?
No additional action potential can be generated.
What is a relative refractory period?
An additional action potential may be generated if the stimulus is increased.
What happens to the millivolts (mV) level for depolarization of action potential?
It goes from -70 mV to +30 mV.
Na+ ion gates open causing increased Na+ permeability 600x. This causes an influx of Na+ into the cell, making cell more positive.
What happens to the millivolts (mV) level for repolarization of action potential?
It goes from +30 mV to -70 mV.
Na+ ion gates close and K+ ion gates open to increase K+ permeability 10x. This causes an efflux of K+ into the cell, making cell more negative.
What happens to the millivolts (mV) level for hyperpolarization of action potential?
It becomes more negative than -70 mV.
Speed of action potential is influenced by two things:
- Diameter of axon
- Presence of myelinated axon
What is a neuromuscular junction?
Synaptic gap between muscles.
What is a neuroneural junction?
Synaptic gap between two neurons.
There are three types of neuroneural junctions:
- Axodendritic (between axon and dendrite)
- Axosomatic (between axon and cell body)
- Axoaxonic (between axon and axon)
Two types of chemical synapses:
- Neuromuscular junction
- Neuroneural junction
Two ways presynaptic neurons affect likelihood of the postsynaptic neuron to fire:
- Excitatory synapses: increases the likelihood of the postsynaptic neuron to fire
- Inhibitory synapses: decreases the likelihood of the postsynaptic neuron to fire
Events at an excitatory synapse (7 steps):
Step 1: Action potential sweeps into axon terminals or knobs.
Step 2: This depolarization of the membrane opens Ca gates and an influx of Ca, from ECF, into presynaptic knob (voltage-activated).
Step 3: Ca causes vesicular migration to inner membrane of knob and exocytosis of the neurotransmitter.
Step 4: Neurotransmitter diffuses across synapse.
Step 5: Neurotransmitter attaches to the receptors on the postsynaptic membrane that causes permeability changes in the membrane and change in the postsynaptic membrane potential.
Step 6: Na+ ion (influx) and K+ ion (efflux) gates open that cause a small depolarization or excitatory postsynaptic potential (EPSP). Inside becomes more positive.
- Removal of neurotransmitter.
Events at an inhibitory synapse (7 steps):
Step 1: Action potential sweeps into the axon terminals or knobs.
Step 2: This depolarization of the membrane opens Ca gates and an influx of Ca, from ECF, into the presynaptic knob.
Step 3: Ca causes vesicular migration to inner membrane of knob and exocytosis of the neurotransmitter.
Step 4: Neurotransmitter diffuses across synapse.
Step 5: Neurotransmitter attaches to the receptors on the postsynaptic membrane that causes permeability changes in the membrane and change in the postsynaptic membrane potential.
Step 6: Cl- ion (influx) and K+ ion gates open that cause a small hyperpolarization or inhibitory postsynaptic potential (IPSP). Outcome is to become more negative.
Step 7: Removal of neurotransmitter.
What is a summation?
The additive effect of many EPSP’s until threshold is reached thus producing an action potential.
What is a temporal summation?
A type of summation that has multiple volleys of impulses along one knob.
What is spatial summation?
A type of summation where different knobs carry the impulses.
What is an inhibitory postsynaptic potential (IPSP)?
A small hyperpolarization.
A predominance of IPSP’s causes inhibition of the neuron.
What is an excitatory postsynaptic potential (EPSP)?
A small depolarization.
A predominance of EPSP’s causes postsynaptic neuron to fire.
How is acetylcholine synthesized or produced?
Choline Acetyltransferase (CAT) produced ACh
or
Acetyl COA + Choline → Acetylcholine (ACh) + COA
How is acetylcholine degraded or removed?
Degradation by enzyme acetylcholinesterase (ACHE).
Acetylcholine → Acetate + Choline
After degraded, Acetate + Choline are removed from the synapse.
What are two ACh receptors?
- Nicotinic
- Muscarinic
How are catecholamines (an amine) synthesized or produced?
L-Dopa → Dopamine → Norepinephrine
How are catecholamines (an amine) degraded or removed?
- Broken down by monoamine oxidase (MAO) in the membrane of the axonal terminals.
- Broken down by catechol-o-methyltransferase (COMT) on the postsynaptic membrane in the cytoplasm.
- Absorbed (uptake) backed into the knobs.
Name four types of amino acid neurotransmitters:
- Aspartate
- Glutamate
- Glycine
- GABA
Name two types of neuro active peptides:
- Endorphins
- Vasopressin (ADH)
What are five modifications of neuronal activity by drugs:
- Mimic the neurotransmitter (agonists)
- Alters the release of the neurotransmitter
- Influences the receptor site (antagonists)
- Influences the removal of the neurotransmitter
- Influences ion channels or gates
Examples of two drugs that mimic the neurotransmitter (agonists):
Nicotine and muscarine mimic acetylcholine.
Examples of four drugs that alter the release of the neurotransmitter:
Amphetamines increase the release of dopamine and norepinephrine in the brain.
Caffeine increases the release of ACh.
Botox and Botulism inihibits the release of ACh (less skeletal muscle activity).
Examples of drugs that influence receptor site (antagonists):
Curare and Botox block receptor sites for ACh (blocks muscle movement).
Atropine-belladonna block parasympathetic receptors (parasympathetic receptors block sphincter muscles which dilate pupils).
Examples of drugs that influence the removal of the neurotransmitter:
Cocaine reduces uptake of norepinephrine (you have more norepi, which constricts blood vessels).
Nerve gas or Organophosphates block acetylcholinesterase activity.
Amphetamines inhibit monoamine oxidase (MAO).
Examples of drugs that influence ion channels or gates:
Digitoxin (Foxglove plant) inhibits Na-K ATPase
Verapamil blocks calcium channels (lowers blood pressure).
Tetrodotoxin (puffer fish), Saxitoxin (dinoflagellates), and Apamin (honeybee) block ion channels.
What does the blood-brain barrier do?
Prevents the brain from potential injury from toxins.
What are the BBB’s capillary membranes permeable to?
Hydrophobic (lipophilic) molecules such as liquids, gases, and alcohol.
What are the BBB’s capillary membranes impermeable to?
Hydrophilic (lipophobic) molecules unless transport mechanisms are present such as glucose, amino acids, and ions.
What are ascending tracts or sensory pathways?
The pathway of sensory nerves that go from spinal cord to the brain.
What are descending tracts or motor pathways?
A nerve tract in the spinal cord that carries impulses away from the brain.
What is the brain?
The brain is the major processing center of the body.
What are the three main areas of the brain?
- Brain stem
- Cerebellum
- Forebrain.
What are three parts of the brain stem?
- Medulla oblongata
- Pons
- Midbrain
What does the medulla oblongata do?
Functions:
- Controls vital centers of respiration and cardiovascular functions.
- Controls non-vital areas of swallowing, coughing, and sneezing.
- Contains pyramids for the crossing over of fibers coming down from the brain.
What do the pons do?
Controls respiration.
What does the midbrain do?
Controls eye movements and auditory and visual reflexes.
What does the cerebellum do?
- Motor coordination and balance.
- Provides feedback to motor systems.
What is the major area of the forebrain?
The cerebral cortex (gray matter on the outer quarter inch of the brain).
What does the cerebral cortex do?
It is the most complex region of the brain that is involved in mind and intellect. The conscious area of the brain.
What is the left hemisphere of our brain specialized in?
The left side contains language centers (Wernicke’s & Broca’s area), verbal skills, and numerical skills. It also controls the right side of our body.
What is the right hemisphere of our brain specialized in?
The right side contains recognition of visual patterns, expression, and recognition of emotions or artistic abilities. It also controls the left side of our body.
What are the four lobes?
- Parietal
- Occipital
- Temporal
- Frontal lobe
What is the parietal lobe involved in?
Primary sensory (somatosensory) area receives input from receptors.
Sensory homunculus.
Vision (where does it fit in with memories and experiences).
What is the occipital lobe involved in?
Visual processing center.
Radiates anteriorly into temporal lobe and parietal lobe:
- Temporal portion: recognition of what is seen
- Parietal portion: where does it fit in with memories and experiences
What is the temporal lobe involved in?
Vision (recognition of what is seen), hearing, Wernicke’s area for language comprehension.
What is the frontal lobe involved in?
Primary motor area controls voluntary skeletal activity.
Motor homunculus.
What two structures does the basal nuclei and subcortical nuclei have?
Amygdala and hippocampus.
What are the basal nuclei and subcortical nuclei involved in?
Fine motor coordination.
What is Parkinson’s disease and what does it impair?
A disease where there is not enough dopamine. This interferes with fine motor coordination.
What is the thalamus involved in?
It is a sensory relay station to cortex, hypothalamus, etc.
What is the hypothalamus involved in?
This area controls body temperature, thirst, appetite, sexual activity, the pituitary gland, and the autonomic nerves.
What five structures does the limbic system have?
- Hypothalamus
- Thalamus
- Fornix
- Basal ganglia
- Cingulate gyrus of the cortex