Unit 4 Learning Objectives(Chapters 12-16) Flashcards
Describe the major functions of the nervous system.
Employs electrical and chemical means to send messages from cell to cell
In combination with the endocrine system, it maintains internal coordination.
-Receives information about changes in the body and external environment
-Processes this information, relates it to past experiences, and determines appropriate response
-Issues commands to muscles and glands cells to carry out such a response
Describe the basic pathway of the nervous system in order from beginning to end
1) Sensory receptor detects a stimulus
2) Sensory (afferent) neuron
3) Integrating center: central nervous system
4) Motor (efferent) neuron
5) Effector: responds (muscle or gland)
List the parts of the nervous system that constitute the CNS and those that constitute the PNS.
- CNS: brain and spinal cord (enclosed by meninges, the cranium, and vertebrae)
- PNS: rest of the nervous system except the brain and spinal cord; composed of nerves & ganglia
Differentiate between the somatic and autonomic divisions of the nervous system.
1) Somatic (voluntary) nervous system:
- Motor neurons to skeletal muscle tissue
- Only 1 motor neuron is used
- Somatic reflexes: involuntary muscle contractions
2) Autonomic (involuntary) nervous system”
- Motor neurons to smooth & cardiac muscle, endocrine glands, & exocrine glands
- 2 motor neurons used
- Autonomic/visceral reflexes; involuntary responses
Differentiate between the sympathetic and the parasympathetic divisions of the autonomic nervous system.
1) Sympathetic division: Tends to arouse body for action
- Motor neurons originate from thoracolumbar region
- “Fight or flight” responses; “E” responses (excitement, emergency, exercise)
2) Parasympathetic division: Tends to have calming effect
- Motor neurons originate from craniosacral region
- “Resting and digesting” responses; SLUDD (salivation, lacrimation, urination, digestion, defecation)
Describe three functional properties found in all neurons.
1) Excitability (irritability)
Respond to environmental changes called stimuli; produce an electrical signal
2) Conductivity
Conduct the electrical signal to other cells
3) Secretion
When an electrical signal reaches the end of nerve fiber, the cell secretes a chemical neurotransmitter that influences the next cell
Define the three basic functional categories of neurons.
1) Sensory (afferent) neurons
Detect stimuli & transmit information toward CNS
2) Interneurons (association neurons)
Lie entirely within CNS; connects motor and sensory pathways
Makes decisions (integrating center)
About 90% of all neurons
3) Motor (efferent) neuron
Send signals out to muscles and gland cells (the effectors)
Identify the parts of a neuron including soma (cell body), axon, and dendrites.
1) Soma: control center of neuron
Also called neurosoma or cell body, it has a nucleus with one nucleolus
Cytoplasm contains mitochondria, lysosomes, Golgi complex, inclusions, extensive rough ER and cytoskeleton.
Inclusions include things like glycogen, lipid droplets, melanin, and lipofuscin pigment (produced when lysosomes digest old organelles)
Cytoskeleton has dense mesh of microtubules and neurofibrils (bundles of actin filaments) that compartmentalizes rough ER into dark-staining Nissl bodies
No centrioles, no mitosis. However, extreme longevity.
2) Dendrites: branches that come off the soma
Receives signals from other neurons; the more dendrites the neuron has, the more information it can receive
3) Axon (nerve fiber)
Originates from axon hillock and transmits signals away from soma
Only one (or none) per neuron
Mostly unbranched except for axon collaterals
Axolemma may be enclosed by myelin sheath
Describe multipolar, bipolar, unipolar, and anaoxic neurons
1) Multipolar neuron
One axon and multiple dendrites
Most common type; makes up most neurons in the CNS
2) Bipolar neuron
Has one axon and one dendrite
3) Unipolar neuron
Has one single process leading away from soma
Sensory cells from skin and organs to spinal cord (somas in dorsal root ganglia)
4) Anaxonic neuron
Has many dendrites but no axon
The most common type of neuron shape is what?
Multipolar
Define the terms ganglion, nerve, tract, and synapse.
1) Ganglion: a knot-like swelling in a nerve where neuron cell bodies are concentrated; found in the PNS.
2) Nerve: bundle of nerve fibers (axons) wrapped in fibrous connective tissue; spinal versus cranial nerves. Found in the PNS.
3) Tract: The CNS equivalent of a nerve; it is a bundle of axons, which are often myelinated.
4) Synapse: The junction between two neurons, or between a neuron and muscle tissue.
Explain how neurons transport materials between the cell body and the tips of the axon.
- Proteins made in soma need to be transported to axon & axon terminal to repair axolemma and to transport organelles; they do this via a two-way passage: anterograde (away from soma) and retrograde (toward soma)
- These two types of transport use microtubules (to guide materials along axon) and motor proteins (kinesin and dynein) that carry materials “on their backs” while they “crawl” along microtubules.
Name and describe the 4 types of cells in the CNS that aid neurons
1) Oligodendrocytes
Form myelin sheaths in CNS that speed signal conduction using arm-like processes
2) Ependymal cells
Line internal cavities of the brain; secrete and circulate cerebrospinal fluid (CSF)
3) Microglia
Wander through CNS looking for debris and damage, and get rid of it via phagocytosis.
4) Astrocytes
Most abundant glial cell in CNS; covers brain surface and most nonsynaptic regions of neurons in the gray matter (framework)
Forms blood-brain barrier using perivascular feet
Absorbs excess neurotransmitters and ions
Astrocytosis or sclerosis; when neuron is damaged, astrocytes form hardened scar tissue and fill in space
Name and describe the 2 types of cells in the PNS that aid neurons
1) Schwann cells
Produce a myelin sheath around axons similar to the ones produced by oligodendrocytes in CNS
Also assist in regeneration of damaged fibers
2) Satellite cells
Surround the somas in ganglia of the PNS
Provide electrical insulation around the soma
Regulate the chemical environment of the neurons
Similar in function to astrocytes.
Describe the myelin sheath that is found around certain nerve fibers, and explain its importance.
- Serves as insulation around a nerve fiber (axon)
- Formed by oligodendrocytes in CNS and Schwann cells in PNS
- Consists of the plasma membrane of glial cells
- 20% protein and 80% lipid
- MUCH faster than unmyelinated axons, which is why it’s so critical.
Discuss the 3 cell types from which brain tumors typically originate.
- Meninges (protective membranes of CNS)
- Metastasis from other tumors in other organs
- Glial cells (mitotically active throughout life)
Describe gliomas and discuss whether or not neurons are a major source of tumors
1) Gliomas: grow rapidly and are highly malignant
Blood–brain barrier decreases effectiveness of chemotherapy
Treatment consists of radiation or surgery
2) Mature neurons undergo very little mitosis, so not typically a cause of tumors
Describe the problems with the degenerative disorder Multiple Sclerosis
- A degenerative disorder of the myelin sheath; oligodendrocytes and myelin sheaths in the CNS deteriorate
- Myelin is replaced by hardened scar tissue
- Nerve conduction disrupted (double vision, tremors, numbness, speech defects)
- Onset between 20 and 40 years
- Cause may be autoimmune triggered by virus
Describe the problems with the degenerative disorder Tay-Sachs disease.
- A hereditary disorder of infants of Eastern European Jewish ancestry
- Abnormal accumulation of glycolipid called GM2 (ganglioside) in the myelin sheath disrupts conduction of nerve signals
- Caused by dysfunctional lysosomes
- Symptoms include blindness, loss of coordination, and dementia
- Fatal before age 4
Explain how certain damaged nerve fibers regenerate, and what regeneration requires
1) Steps of regeneration:
- Fiber distal to the injury degenerates
- Axon stump sprouts multiple growth processes
- Schwann cells, basal lamina and neurilemma form a regeneration tube
2) Only peripheral nerve fibers can regenerate and only if:
- the soma is intact
- some neurilemma remains
Describe what 2 factors will increase the conduction speed of nerve fibers.
1) Diameter of fiber
Larger fibers have more surface area and conduct signals more rapidly
2) Presence or absence of myelin
Myelin further speeds signal conduction
Explain why a cell has an electrical charge difference (voltage) across its membrane.
It’s the result of 3 combined factors:
1) Ions diffuse down their concentration gradient through the membrane
2) Plasma membrane is selectively permeable and allows some ions to pass easier than others
3) Electrical attraction of cations and anions to each other
Explain how ion channels affect neuron selective permeability.
〖𝐍𝐚〗^+/𝐊^+ pump moves 3 Na^+ out for every 2 K^+ it brings in. This exchange of 3 positive charges for only 2 positive charges contributes about −3 mV to the cell’s resting membrane potential of −70 mV. It works continuously to compensate for Na+ and K+ leakage.
Contrast the relative concentrations of sodium and potassium ions inside & outside of a cell.
Na+ is more concentrated outside of the cell (ECF) K+ is more concentrated inside the cell (ICF).
Describe the characteristics of local potentials, and explain how stimulation of a neuron causes a local electrical response in its membrane.
1) Local (graded) potentials are defined as changes in membrane potential of a neuron occurring at & nearby the part of the cell that is stimulated
- Short distances; die out quickly
- On dendrites and cell bodies
2) Sodium gates open in response to chemicals, light, heat or mechanical stimulation
- Size of signal depends on stimulus strength
- This leads to the membrane doing one of two things:
depolarize: leads to an action potential or
hyperpolarize: prevents an action potential
Describe the three changes in membrane potentials (depolarization, repolarization, hyperpolarization) that can occur.
1) Depolarization: the inside of the membrane becomes less negative. Will reverse polarity. Can lead to an electrical impulse.
2) Repolarization: the membrane returns to its resting membrane potential
3) Hyperpolarization: the inside of the membrane becomes more negative than the resting potential; inhibits an electrical impulse.
Compare and contrast the properties and location of local potentials and action potentials.
- Action potentials follow an all-or-none law; if threshold is reached, neuron fires at its maximum voltage. If threshold is not reached, it does not fire. This is not a property of local potentials.
- Action potentials do not get weaker with distance, whereas local potentials do
- Action potentials are irreversible; once started, it goes to completion and cannot be stopped. However, local potentials are not irreversible.
Discuss the sequence of events that must occur for an action potential to be generated.
- Arrival of current at axon hillock depolarizes membrane
- Depolarization must reach threshold: critical voltage (about -55 mV) required to open voltage-regulated gates
Define threshold and refractory period.
1) Refractory period: the period of resistance to stimulation.
2) Threshold: the critical voltage (about -55 mV) required to open voltage-regulated gates
Explain how different intensities of sensations can occur.
All nerve action potentials are identical in strength, so different intensities of sensations result from:
1) the frequency of the stimulus
2) the number of neurons stimulated
Explain the two ways (continuous and saltatory) a nerve signal is conducted down an axon.
1) Saltatory conduction:
- Myelinated fibers conduct signals with saltatory conduction; the signal seems to jump from node of Ranvier to node of Ranvier
- Very fast
2) Continuous conduction:
- Unmyelinated fibers have voltage-gated channels along their entire length
- Produce action potential the entire length of the axon
- Chain reaction continues until the nerve signal reaches the end of the axon; the nerve signal is like a wave of falling dominos.
- The refractory membrane ensures that the action potential travels in one direction
List the structures that comprise a chemical synapse
Presynaptic neurons have synaptic vesicles with neurotransmitter and postsynaptic have receptors and ligand-regulated ion channels
List the sequence of events at the chemical synapse.
1) Nerve impulses reach the axonal terminal of presynaptic neuron and open Ca2+ channels
2) Neurotransmitter is released from synaptic vesicle into synaptic cleft via exocytosis (because of the Ca2+)
3) Neurotransmitter crosses synaptic cleft and binds to receptors on postsynaptic neuron
4) Postsynaptic membrane permeability changes, causing an excitatory (EPSP) or inhibitory (IPSP) effect
Compare and contrast chemical and electrical synapses.
1) Electrical:
- Spreads through gap junctions
- Faster
- Two-way transmission
- Can’t make decisions
2) Chemical:
- One-way transmission
- From a presynaptic neuron to a postsynaptic neuron; does not use gap junctions.
- Uses neurotransmitters
- Can make decisions.
- Slower than electrical synapses.
Contrast an excitatory postsynaptic potential (EPSP) with an inhibitory postsynaptic potential (IPSP).
EPSPs depolarize the cell, whereas IPSPs hyperpolarize the cell.
Discuss the relationship between a neurotransmitter and its receptor.
The same neurotransmitter can have completely different effects on different receptors; the postsynaptic membrane permeability will change, but it can cause either an excitatory (EPSP) or inhibitory (IPSP) effect depending on the receptor’s postsynaptic potential.
Describe the events of cholinergic synaptic transmission in proper chronological order.
1) Nerve impulses reach the axonal terminal of presynaptic neuron and open Ca2+ channels
2) ACh (the neurotransmitter) is released into synaptic cleft via exocytosis
3) ACh crosses synaptic cleft and binds to receptors on postsynaptic neuron
4) Postsynaptic membrane permeability changes, causing an excitatory (EPSP) or inhibitory (IPSP) effect
List the six chemical categories of neurotransmitters.
1) Acetylcholine
2) Amino acids
3) Monoamines
4) Purines
5) Neuropeptides
6) Gasses.
Explain the 3 ways in which the stimulation of a postsynaptic cell can be stopped
1) Diffusion
move down concentration gradient away from synapse
2) Enzymatic degradation
Ex: acetylcholinesterase and monoamine oxidase
3) Uptake by neurons or glia cells
neurotransmitter transporters
Explain how a neuron “decides” whether or not to generate action potentials.
The balance between EPSPs and IPSPs using summation enables the nervous system to make decisions
Differentiate between temporal summation and spatial summation.
1) Temporal summation: occurs when a single synapse generates EPSPs so quickly that each is generated before the previous one fades
2) Spatial summation: occurs when EPSPs from several different synapses add up to threshold at an axon hillock
- An example of facilitation; a process in which one neuron enhances the effect of another
Describe the problems and treatments of the degenerative disorder of Alzheimer Disease.
1) Problems:
- It’s the 6th leading cause of death in United States
- Symptoms include memory loss for recent events, moody, combative, lose ability to talk, walk, and eat
- Show deficiencies of acetylcholine
- Diagnosis confirmed at autopsy
- Atrophy of gyri (folds) and formation of abnormal proteins
- Blocks normal synaptic function
2) Treatment:
- Trying to find ways to clear or halt the production of abnormal proteins
- No prevention or cure: SHIELD (sleep, handle stress, interact with others, exercise, learn new things, diet (mind diet)
State the four principal functions of the spinal cord.
1) Conduction: nerve fibers conduct information up (ascending) & down (descending) spinal cord; white matter
2) Neural integration: neurons receive input from sources, integrates it, and decides appropriate output (e.g., bladder control) – white or gray matter?
3) Locomotion: groups of neurons that coordinate repetitive sequences of contractions for walking
4) Reflexes: involuntary responses to stimuli
Describe the gross anatomy of the spinal cord and spinal nerves.
- Spinal cord is shaped like a flattened cylinder
- Arises from the brainstem
- Extends from foramen magnum to L1-L2
- Growth of cord stops at approximately age 5
- Gives rise to 31 pairs of spinal nerves
Describe the meninges, from superficial to deep, that enclose the brain and spinal cord.
1) Dura mater: most superficial
2) Arachnoid mater: middle
3) Pia mater: most deep
- Subarachnoid space is located between arachnoid and pia mater; circulates CSF.
- Epidural space is the space above the dura mater
Contrast the relative position of gray matter and white matter in the spinal cord compared to the white and gray matter in the brain.
The relationship between white and gray matter in the brain and spinal cord is inverse:
- In the brain, the cortical white matter is deep to gray matter
- In the spinal cord, gray matter is deep to white matter.
Trace the ascending pathway followed by nerve signals traveling up and down the spinal cord, and describe the functions of the neurons involved
- Ascending tracts carry sensory signals up the spinal cord
- Uses three neurons from origin (receptors) to destinations in the sensory areas of the brain
1) First neuron: detect stimulus and transmit signal to spinal cord or brainstem (Receptor to spinal cord or brainstem)
2) Second neuron: from spinal cord/brainstem continues to the thalamus (Spinal cord or brainstem to thalamus)
3) Third neuron: carries the signal the rest of the way to the sensory region of the cerebral cortex (Thalamus to cortex).
Trace the descending pathway followed by nerve signals traveling up and down the spinal cord
- Descending tracts: carry motor signals down brainstem and spinal cord
- Involve two motor neurons called upper and lower motor neurons
- Decussation of somatic neurons cross in Medulla oblongata
List the definitions of ascending versus descending tracts, decussation, and contralateral versus ipsilateral.
- Ascending: carry sensory information up
- Descending: carry motor information down
- Decussation: crossing midline so that brain senses and controls contralateral side of body
- Contralateral: when the origin and destination on opposite sides of the body
- Ipsilateral: when the origin and destination on the same side of the body; does not decussate
Explain how decussation occurs in sensory and motor pathways and predict how decussation impacts the correlation of brain damage.
- Decussation means that the sensory and motor tracts cross from one side of the brain as they travel from the top to bottom (and vice versa).
- This is why, for example, if you damage the right side of your brain you may have trouble coordinating/moving the (contralateral) left side of your body.
Describe the effects of Polio, which destroys somatic motor neurons.
- Caused by the poliovirus (spreads by fecal contamination of water)
- Destroys motor neurons in brainstem and anterior horn of spinal cord
- Signs of polio include muscle pain, weakness, and loss of some reflexes
- Followed by paralysis, muscular atrophy, and -respiratory arrest
What two diseases discussed in class destroy somatic motor neurons?
Polio and ALS
Describe the effects of ALS, which destroys somatic motor neurons.
- Known as Amyotrophic lateral sclerosis (ALS) or Lou Gehrig disease
- Destruction of motor neurons and muscular atrophy
- Sclerosis (scarring) of lateral regions of the spinal cord
- Astrocytes fail to reabsorb the neurotransmitter glutamate from the tissue fluid; accumulates to toxic levels
- Early signs: muscular weakness; difficulty speaking, swallowing, and using hands
- Sensory & intellectual functions remain unaffected
Describe the anatomy of nerves and ganglia
Ganglia: a cluster of neurosomas outside the CNS enveloped in an endoneurium (continuous with nerve)
Nerves: a cord-like organ composed of numerous nerve fibers (axons) bound together by connective tissue
Discuss how the structures root, nerve, ramus, plexus, tract and ganglion relate to one another
Ganglia are continuous with a nerve, and found near both the posterior (dorsal) and anterior (ventral) roots of spinal nerves; they’re called posterior root ganglion and anterior root ganglion.
A nerve is a bundle of axons found in the peripheral nervous system, and a bundle of axons found within the central nervous system are called tracts.
The portion of the nerve outside the vertebra divides into rami (singular ramus) distal branches.
In any other region besides the thoracic region of the spine, the anterior rami of nerves give rise to plexuses.
Describe the differences between the anterior and posterior roots of the spine
Anterior (ventral) root: contains motor neurons.
Posterior (dorsal) root: contains sensory neurons.
Describe where the 31 pairs of spinal nerves are located
8 cervical (C1–C8) (First cervical nerve exits between skull and atlas, others exit at intervertebral foramina) 12 thoracic (T1–T12) 5 lumbar (L1–L5) 5 sacral (S1–S5) 1 coccygeal (Co1)
What nerve(s) does the cervical plexus contain?
Phrenic nerve
What nerve(s) does the brachial plexus contain?
Axillary nerve, radial nerve, median nerve, and ulnar nerve
What nerve(s) does the lumbar plexus contain?
Femoral and obturator nerves
What nerve(s) does the sacral plexus contain?
Sciatic and pudendal nerves
Define reflex and explain how reflexes differ from other motor actions.
- Reflexes: defined as quick, involuntary, stereotyped reactions of glands or muscle to stimulation
- Unique characteristics of reflexes:
1) Reflexes require stimulation: not spontaneous actions, but responses to sensory input
2) Reflexes are quick: involve few, if any, interneurons and minimum synaptic delay
3) Reflexes are involuntary: occur without intent and are difficult to suppress
4) Reflexes are stereotyped: occur essentially the same way every time
Describe the general components of a typical somatic reflex arc.
Somatic receptors: In skin, muscles, or tendons Afferent (sensory) nerve fiber Integrating center Efferent (motor) nerve fiber Effectors: skeletal muscles
Give an example of a stretch reflex
The knee-jerk (patellar) monosynaptic reflex.
List the major subdivisions of the brain
Cerebrum Cerebellum Brainstem Midbrain, pons, medulla oblongata Diencephalon Hypothalamus, Thalamus, & Epithalamus
Differentiate between rostral and caudal
Rostral: toward the forehead
Caudal: toward the spinal cord
Describe the locations of the brain’s gray and white matter.
-Gray matter: neurosomas, dendrites, and synapses
Forms cortex (surface layer over cerebrum and cerebellum)
Forms nuclei deep within brain
-White matter: bundles of myelinated axons
Lies deep to cortical gray matter, opposite relationship in the spinal cord
Composed of tracts, or bundles of axons, that connect one part of the brain to another, and to the spinal cord
Define and identify the meninges, and describe their function
- Meninges: three connective tissue membranes that envelop the brain
- Lie between the nervous tissue and bone
- As in spinal cord, they are the dura mater, arachnoid mater, and the pia mater
- They protect the brain and provide structural framework for its arteries and veins
