Module 3 Chapter 13 & 14 Organization of the Neural Function and Somatosensory Function, Pain, Headache, and Temperature Flashcards
What are the two major cell types found in the nervous system? What are their basic functions?
Neurons - functioning cells of the nervous system. They are excitable and conduct impulses.
Neuroglial cells - protect and provide metabolic support for the nervous system.
CNS - components
The central nervous system is the control center for the body. It is made up of the brain and spinal cord.
PNS - components
The peripheral nervous system is the information highway, connecting the bodies parts with the brain. Transmits sensation, movement impulses, and many other things between the two.
Afferent VS efferent
These two pathways are found in both the PNS and CNS.
Afferent pathways are incoming, sensory pathways. Transmit information to the brain.
Efferent pathways are outgoing, motor pathways. Transmit information from the brain.
Parts of neuron
There are three main parts of a neuron.
1. Cell body
2. Dendrites - these are long branching extension of the nerve cell. Send and receive information from surrounding cells.
3. Axons - conduct nerve impulses. Long, unbranched.
Astrocytes
A type of neuroglial cell that plays a role in forming the blood-brain barrier. The blood brain barrier prevents toxic material from enter the brain.
These are the most prevalent neuroglial cells. Play a role in potassium uptake, scar tissue formation, gliosis, and communication with capillaries.
Oligodendrocytes and Schwann cells
These are two types of neuroglial cells. They play the role of forming myelin.
What is myelin/myelin sheaths? What does it do?
Myelin is a lipoprotein. It is primarily lipid substance that coats the neuron cell processes. The presence of myelin increases velocity of nerve impulse conduction (makes neurologic processes faster).
What is the white matter?
The white matter is the myelin sheaths. The primary lipid composition gives these structures a whitish color.
Microglia
Small phagocytic neuroglial cells.
What are the neuroglial cells of the PNS? What do they do?
Satellite - form a basement membrane to prevent the diffusion of large particles
Schwann cells - create myelin
White Vs Gray matter
White - myelin sheaths (tract system)
Gray - cell body
The autonomic nervous system
Considered part of the PNS system. Plays a role in blood vessel relaxation vs constriction, blood pressure, temperature, digestion, bowel and bladder function, respiration, and metabolism. Strongly tied to emotions.
- The sympathetic nervous system - “Fight or flight”. Hormones secreted from the adrenal glands on top of the kidneys result in activation of the sympathetic nervous system in times of stress. Results in:
- Increased BP, vasoconstriction, pupillary dilation, shunting of blood from skin into the heart and brain, constriction of the GI and Gu sphincters, increase in blood sugar. All these adaptations are to prepare the body for critical, life and death situations. - The parasympathetic nervous system has opposite effects. It promotes digestion, elimination, pupillary constriction gland secretion.
Somatic nervous system
Sensory and motor nerves
Metabolic requirements of the brain
The brain receives 15-20% of the total, resting CO.
Consumes 20% of oxygen.
Cannot store oxygen like other areas of the body, so when blood flow is cut off the results are immediate.
The brain without oxygen
The brain takes a hefty amount of the body’s total oxygenation to perform it’s functions. The brain has no oxygen or glucose reserve. The brain without oxygenation quickly fails and irreversible damage occurs within seconds.
Neurons
1. Division
2. Replacement
3. Plasticity
4. Requirements
- Neurons cannot divide.
- Neurons that die due to aging or injury cannot be replaced.
- Plasticity - the neurons ability to assume the functions of damaged neurons. How neurologic function can continue at the same level post injury and throughout the aging process.
- Neurons require a constant supply of oxygen and glucose to continue functioning. Vulnerable to hypoxia and hypoglycemia.
Plasticity of neurons
Neurons have the ability to assume the role of other neurons that are damaged or injured.
The Circle of Willis
Redundant way for the brain to receive blood supply. Promotes collateralization as well.
Anterior Cerebral artery
Frontal lobes
Middle cerebral artery
Frontal lobe and lateral surfaces of the temporal and parietal lobes.
Which cerebral artery is most frequently affected during strokes? How does this present and why?
The middle cerebral artery is the most commonly affected during strokes. This presents with the common symptoms of a stroke - trouble with speech, movement, and sensation. That is because the middle cerebral artery supplies blood to the frontal (movement/Wernicke), parietal (sensory), and temporal (speech) lobes.
Posterior cerebral artery
Supplies blood to temporal and occipital lobes
Choroid Plexuses
Where CSF is made. A collection of arteries and veins that come in close proximity and function to filter plasma to make CSF.
Function of CSF
Cushion and nourishes the brain
Hydrocephalus
Excessive accumulation of CSF
Ependymal Cells
One of the glial cells. Plays a role in filtering the blood for CSF.
How does the brain get blood flow?
The brain gets blood flow from the internal carotids and the vertebral arteries.
The circle of Willis ensures adequate flow to all parts of the brain. Does this by ensuring redundant flow is available for the brain tissue.
How does CO2 affect blood flow to the brain?
CO2 is a powerful vasodilator. Under conditions where there is adequate circulating volume, increased CO2 in the body will improve blood flow to the brain.
Synapse
1. Types
How neurons communicate. There is a presynaptic and postsynaptic cleft.
1. Electrical - the quicker form of passing information between neurons. Ions passing through the gap junctions allow action potentials to quickly pass along impulses.
2. Chemical - slower, more common. Communicate across the synaptic cleft via neurotransmitters. Two types - excitatory and inhibitory.
Excitatory VS Inhibitory and how they work
These are types of chemical synapses.
Excitatory function via depolarization.
Inhibitory function via hyperpolarization.
Where are synapses primarily located?
Thousands of synapses are located on the dendrites of the neurons.
What are neurotransmitters?
Substances that excite, inhibit, or modify neuron responses. Ach, norepinephrine, and epinephrine are examples.
Cholinergic receptors VS adrenergic receptors
Cholinergic receptors - activated by Ach. Part of the PNS system.
Adrenergic receptors - activated by norepinephrine and epinephrine. Part of the sympathetic nervous system.
What are interneurons?
connect the sensory (afferent) and motor (efferent) parts in the spinal cord
What two neurological conditions are associated with destruction of myelin? Describe these conditions.
- GBS - the immune system attack myelin layer. Happens in the PNS which results in ascending muscle paralysis as the demyelination works peripherally and then results are seen more centrally.
- MS - loss of myelin layer in the CNS. Symptoms are seen with brain and spinal symptoms.
Types of Sensory/Afferent innervation
- General somatic
- Special visceral
- General visceral
Types of Motor/Efferent Innervation
- General visceral
- Pharyngeal
- General somatic
Two important spinal reflexes
- Withdraw reflex - introduction to an offending stimulus result in withdrawal of the affected limb, typically by flexion. Takes precedence over other reflexes.
- Myotatic or stretch reflex - a reflex to maintain propriocception.
Where does interpretation of objects and events occur in the brain?
Interpretation of objects and events occur in the temporal lobe.
What important structures are located in the diencephalon?
- Thalamus
- Hypothalamus
Meninges
Pia
Arachnoid
Dura mater
These are spaces that are in place to protect the brain.
Dura Mater
Outer most meninge. Lines the inside of the skull.
Arachnoid mater
Middle meninge. Contains blood vessels.
Pia Mater
Inner most meninge
3 potential spaces for bleeds
- Epidural - outside the dura, typically arterial
- Subdural - between the dura and arachnoid. Typically, venous in origin. Can be acute or slow bleed.
- Subarachnoid - deep within the arachnoid. Filled with CSF.
What does the autonomic nervous system control? Examples?
The autonomic nervous system controls smooth muscles. Its effects on the body are unconscious and are in response to activities. Two different branches.
- Heart rate
- Blood pressure
- Intestinal motility
What receptors are activated with activation of the sympathetic nervous system? Where do these neurotransmitters come from?
Adrenergic receptors are activated. The adrenal medulla releases the neurotransmitters epinephrine and norepinephrine which causes vasoconstriction, increased heart rate, pupillary dilation, shunting of blood from other organs to the muscles and brain.
Beta 1 and Beta 2 receptors
Sympathetic nervous systems receptors
What is the somatosensory system?
The somatosensory system provides the central nervous system with sensory information such as temperature, positioning, pain, and touch.
What are the three major types of sensory neurons?
- General somatic afferent neurons - these are located throughout the body and let the CNS know about pain, touch, and temperature.
- Special somatic afferent neurons - these are located in muscles, tendons, and joints.
- General visceral afferent neurons - provide the CNS with sensations of fullness and discomfort from visceral structures.
Nociperception
Pain sensation
What four sensory modalities are communicated via the somatosensory system?
- Temperature
- Pain
- Positioning
- Touch
First-order neurons
The neurons that detect sensory information.
Second-order neurons
The neurons that communicate the detected sensory stimuli through the spinal cord to the thalamus.
Third-order neurons
Relay information from the thalamus to the cerebral cortex.
What order neurons are a part of the ascending pathways?
The second-order neurons. They communicate with various reflex and sensory pathways in the spinal cord and travel to the thalamus.
What order neurons are associated with central prcoessing in the thalamus and cerebral cortex?
Third-order neurons. They relay information from the thalamus to the cerebral cortex.
These order neurons are found in the periphery and communicate sensations (pain, temperature, positioning, and touch) with the CNS.
First-order neurons
What composes the sensory unit?
The sensory unit is composed of the dorsal root ganglion and its peripheral branch and central axon.
Dorsal root ganglion fibers and their differing functions.
- Type A - myelinated. The fastest of the fibers. Transmits cutaneous pressure and touch sensation.
- Type B - myelinated. Slightly slower. Transmits cutaneous and subcutaneous mechanoreceptors.
- Type C - unmyelinated. Slowest. Transmit heat/cold sensation and heat/cold pain.
The discriminative pathway
1. What is its function?
This is one of the two somatosensory pathways leading from the spinal cord to the thalamus area.
Crosses at the base of medulla.
- Controls perception, arousal, and motor control.
The anterolateral pathway
1. What is its function?
This is one of the two somatosensory pathways leading from the spinal cord to the thalamus.
1. Provides sensory information such as pain, thermal sensations, crude touch.
What is the somatosensory cortex? Where is it?
This is an area located in the parietal lobe that allows the full localization, judgement of intensity, and interpretation of the meaning of stimuli. Specifically, this area is located in the parietal lobe up against the central sulcus.
What is the limbic system?
The emotional component of the pain response. Helps control emotions and behaviors. Located around the thalamus.
What neurologic systems are triggered by pain?
- The limbic system - deals with the emotional aspect of pain
- The brain stem - autonomic nervous system response
First-order nociceptive pathways
Second-order nociceptive pathways
Third-order nociceptive pathways
First-order - detect stimuli that threaten the integrity of innervated tissues.
Second order - process nociceptive information.
Third order - project pain information to the brain.
A fibers VS C fibers
The A fibers are myelinated, fast fibers that transmit mechanical or thermal stimuli.
The C fibers are unmyelinated. These slow fibers (slow wave) transmit chemical or persistent mechanical and thermal stimuli.
The C fibers are at fault for the feeling of chronic pain due their slow nature.
Both of these fibers are used to transmit pain stimuli to the brain.
What is the neospinothalamic tract?
This is one of the two pathways within the spine that transmit pain to the brain. This is the faster moving tract that transmits bright, sharp, or stabbing pain. Travel via the myelinated alpha fibers.
What is the paleospinothalamic tract?
This is one of the two spinal pathways for pain to reach the brain. It is a slower conducting pathway due to the use of C fibers. Determines sensations such as diffuse, dull, aching, and other unpleasant stimuli commonly associated with chronic or visceral pain.
What are the opioid peptides and how do they relate to pain?
The opioid peptides are similar to neurotransmitters in that they transmit information. Considered endogenous analgesic mechanism.
- Enkephalins
- Endorphins
- Dynorphins
Pain threshold
The point at which a stimulus becomes painful
Pain tolerance
The maximum intensity or duration of pain that a person is willing to endure before they want something to be done about the pain
Allodynia
Pain from noninjuries stimuli to the skin
Hypoesthesia
Numbness or reduced sensation of touch. Seen after nerve injury or stroke.
Hyperesthesia
Increased cutaneous sensitivity of the skin. Neuropathy. Commonly seen after nerve injury or stroke.
Paresthesias
Burning, numbness, and tingling
Analgesia
The absence of pain from a normally painful stimulus
Neuralgia
Pain that is caused by an irritated or damaged nerve. Pain can be described as severe lightning-like or throbbing pain. Brief.
Trigeminal Neuralgia
Most common neuralgia. Affects the trigeminal nerve leading to facial and jaw symptoms - lightning like throbbing pain. Brief but repetitive episodes.
Temporomandibular Joint Pain (TMJ)
1. Symptoms
2. Cause
3. Treatment
Common cause of head pain - facial, headache, or earache
Caused by imbalance of joint movement because of poor bite, bruxism, or joint problems.
Treated with NSAIDs
Migraine
Pulsatile, throbbing, unilateral headache that lasts 1-2 days and is aggravated by routine physical activity. Aggravated by light and sound.
Migraine with VS without aura
Migraine w/o aura is a pulsatile, throbbing, unilateral headache that lasts 1-2 days. The pain is aggravated by light, sound, and physical activity.
Migraine with aura has the same features but with reversible visual, sensory, and speech components. These temporary components include flicking lights, seeing spots, loss of vision. Pins and needles, numbness. These aura symptoms precede the headache and can last from 5 minutes to an hour.
Rarely do people experience auras preceding each migraine.
What are the first line treatment options for migraine headaches?
- ASA
- Acetaminophen
- ASA + Caffeine
- Antiemetics
- NSAIDs
Cluster headache
Usually felt behind one eye - histamine related. Oxygen can relieve pain sometimes.
Sinus headache
Pain behind the browbone and/or cheekbones
Tension headache
Tight band around the head. Associated with muscle tension.
What controls temperature in the body
Hypothalamus
What are some ways the body responds to a decrease in temperature? What about an increase in temperature?
The body responds to a decrease in temperature by inducing shivering where skeletal muscle contractions increase the body temperature. The body also induces vasoconstriction to move the warm blood supply farther away from the cold environment and closer to the vital internal organs.
The body responds to an increase in temperature by sweating, where evaporation works to cool the skin. The body also vasodilates which allows the warm blood to move closer to the skin.
Shivering
1. What controls it?
2. How much does it affect the body?
3. What else is affected?
Shivering is controlled by the hypothalamus in response to cold temperatures. It can cause a decent increase in body temperature. Shivering also increases oxygen consumption.
What causes goose bumps?
Goosebumps are caused by the contraction of the pilamotor muscles. Their contraction reduces the surface area for heat loss.
Pyrexia
Fever
Fever VS hyperthermia
Fever is caused by the displacement of the set point of the thermoregulatory system in the hypothalamus.
Hyperthermia does not involve a change to the set point, instead the body’s mechanisms at cooling it down are insufficient.
Prostaglandin
Hormone-like substances that the body produces in response to stress. Help control inflammation, blood flow, and blood clots.
Pyrogens
Fever inducing substances. Broken down into exogenous or endogenous.
Exogenous pyrogens
Bacteria toxins, bacteria products, microorganisms.
Presence of exogenous pyrogens causes the release of endogenous pyrogens. What are these endogenous pyrogens? What do they do to bring about fever?
- Phagocytic cells of the immune system phagocytize the exogenous pyrogens. They then release pyrogenic cytokines that are transported to the hypothalamus.
What does the hypothalamus do in response to pyrogenic cytokines being presented to it?
The hypothalamus induces an increase to the thermostatic set point. This means that the hypothalamus increases the thermostat. The heat kicks on via shivering, erection of the pilomotor muscles, and vasoconstriction.
Neurogenic Fever. Typical causes?
Fever that has its origin in the CNS. Trauma, intracerebral hemorrhage, or increased intracranial pressure.
What are the benefits of fever?
- Many microorganisms live at a set temperature. If the thermostat is raised, these organisms cannot continue.
- Enhances immune function:
- T lymphocyte proliferation
- Boosts antiviral immunity
How does a fever affect oxygenation? By what degree? What other signs and symptoms are associated with fevers?
For every 1 degree of temperature increase there is a corresponding 7% BMR increase. This increases the workload on the heart which increases oxygen consumption.
Fever is often accompanied by anorexia, leukocytosis, and malaise.
Confusion, tachycardia, and tachypnea can also be seen commonly.
At what point does heat cause damage to the body?
41 degrees C or 105.8 degrees F causes nerve damage and convulsions
What are the tiers of hyperthermia? What causes these? What are the differences?
Least - heat cramps - caused by loss of salt from sweating. Results in skeletal muscle cramping.
Middle - heat exhaustion - gradual loss of salt and fluids. Thirst, fatigue, nausea, oliguria, GI flu symptoms, delirium. Still sweating.
Severe - heatstroke - tachycardia, hypervent, dizzy, weak, n/v, convulsions, coma.
What is malignant Hyperthermia? Mechanism of action? What symptoms besides hyperthermia are seen? Associated with? Treatment?
An autosomal dominant metabolic disorder in which heat generated by uncontrolled skeletal muscle contraction produces severe and potentially fatal hyperthermia.
Other symptoms include muscle rigidity, tacy, acidosis, shock.
Abnormal release of calcium in the cell results in sustained hypermetabolic rates. This generates lots of heat.
Associated with anesthesia. Succinylcholine.
Treat with cooling measures. Muscle relaxers to stop the calcium release.
Who is at greatest risk for hypothermia?
Infants due to a lower surface area. Their temperature can drop .3 degrees per minute in cold environments.
No shivering mechanism in place.
Axons
The part of the neuron that sends electrical impulses toward the brain or toward the periphery
Dendrites
The part of a neuron that communicates with other adjacent neurons
