PHYL 141 (FINAL) EXAM 3

What makes up the central nervous system?

brain and spinal cord

What makes up the peripheral nervous system?

-sensory and motor neurons
-muscle contractions, organ and glandular functions
-everything else, all nerves other than brain and spinal cord

division of PNS that sends sensory signals toward the CNS

afferent division

division of PNS where motor signals exit the CNS and carry toward effectors (muscles, glands, and adipose tissue)

efferent division

sensory structures that either detect changes in the environment or respond to specific stimuli; may be neurons or specialized cells of other tissues

receptors

controls skeletal muscle contractions

somatic nervous system

contractions under conscious control; ex: raising a glass of water to your lips

voluntary

contractions that may be simple, automatic responses or complex movements, but they are controlled at the subconscious level, outside your awareness

involuntary

automatically regulates smooth muscle, cardiac muscle, glandular secretions, and adipose tissue at the subconscious level; includes a parasympathetic and sympathetic division

autonomic nervous system (visceral motor system)

extensive network of neurons and nerve networks in the walls of the digestive tract

enteric nervous system

dendrites

detect signals; tend to be excitatory

cell body

processing occurs; tend to be inhibitory

axon

carries out action potentials & branches into telodendria

telodendria

ends in axon terminals

axon terminals

play a role in communication with another cell

anaxonic

difficult to discern, if present; rare in humans

bipolar

rare; occur in special sense organs

unipolar (pseudounipolar)

most sensory (afferent) neurons (which transmit impulses toward CNS)

multipolar

most motor (efferent) neurons (which transmit impulses from CNS to the rest of the body)

usually pseudounipolar neurons that transmit impulses toward CNS

sensory (afferent) neuron

usually multipolar neurons that transmit impulses from CNS to the rest of the body

motor (efferent) neuron

an axon that carries sensory information to the CNS

afferent fiber

an axon that carries impulses away from the CNS

efferent fiber

monitor the outside world and our position within it

somatic sensory neurons

monitor internal conditions and the status of other organ systems

visceral sensory neurons

collection of neuron cell bodies in the PNS

ganglion

sensory receptors that monitor the digestive, respiratory, cardiovascular, urinary, and reproductive systems, and provide sensations of distention (stretch), deep pressure, and pain (pain, pressure)

interoceptors

sensory receptors that provide information about the external environment in the form of touch, temperature, or pressure sensations and the more complex senses of taste, smell, sight, equilibrium (balance), and hearing (being full, full bladder)

exteroceptors

monitor the position and movement of skeletal muscles and joints (body position, balance, movement)

proprioceptors

cells of the CNS and PNS that support and protect neurons; specialized support roles; 50% of your brain; outnumber neurons 10:1

neuroglia

CNS neuroglia

astrocytes, oligodendrocytes, microglia, ependymal cells

PNS neuroglia

satellite cells and schwann cells

-most abundant glia
-forms blood-brain barrier (BBB)
-CNS

astrocytes

-protect against invaders
-dispose of pathogens, debris, and waste
-CNS

microglia

-line cavities in CNS
-produce cerebrospinal fluid (CSF)
-cilia circulate CSF in cavities
-CNS

ependymal cells

-support and wrap CNS neurons with myelin (helps to protect and aids in functions of neurons)
-CNS

ogliodendrocytes

-surround and protect cell bodies of PNS neurons
-PNS

satellite cells

-wrap themselves around axons
-produce layers of myelin
-PNS

schwann cells

filtering mechanism of the capillaries that carry blood to the brain and spinal cord; created by astrocytes

blood-brain barrier (BBB)

fluid bathing the internal and external surfaces of the CNS; secreted by the choroid plexus; made and circulated by ependymal cells; floats and cushions CNS tissue; allows circulation and waste removal; produced by filtering plasma through the blood through the BBB

cerebrospinal fluid (CSF)

-an insulating sheath around an axon; consists of multiple layers of neuroglial membrane; significantly increases the speed at which an axon potential travels along the axon
-made by ogliodendrocytes in the CNS
-made by schwann cells in the PNS

myelin

are all axons myelinated?

no

-progressive destruction of myelin sheaths in both the PNS and CNS
-result is a loss of sensation and motor control that leaves affected regions numb and paralyzed

demyelination

contains high concentrations of sodium ions (Na+) and chloride ions (Cl-)

extracellular fluid (ECF)

contains high concentrations of potassium ions (K+) and negatively charged proteins

intracellular fluid (cytosol)

-difference in electrical potential between the inside and outside of a cell
-caused by unequal balance of ions and charged molecules on either side
-the more imbalance on one side, the harder it is to cause further imbalance (it will start to push back)
-a cell's electric "charge"

membrane potential

-the membrane potential of a normal cell under homeostatic conditions
-ions move through leak channels

resting membrane potential

-typically generated at axon hillock
-a sequence of ion movements and electrochemical changes in excitable cells

action potential

changes in the membrane potential that cannot spread far from the site of stimulation

graded potential

the membrane potential at which there is no net movement of a particular ion across the plasma membrane

equilibrium potential

the sum of the chemical and electrical forces acting on an ion across the plasma membrane

electrochemical gradient

in a typical cell at rest, there is a higher potassium (K+) concentration ________ the cell

inside

in a typical cell at rest, there is a higher sodium (Na+) concentration ________ the cell

outside

in a typical cell at rest, there is a higher chloride ion (Cl-) concentration ________ the cell

outside

resting membrane potential of a neuron

-70mV

threshold for an action potential

-55 - -60mV

passive ion channels; always open

leak channels

active channels that open or close in response to specific stimuli

gated ion channels

open or close when they bind to specific chemicals or ligands

chemically gated (ligand gated) ion channels

open or close in response to changes in the membrane potential

voltage gated channels

open or close in response to physical distortion of the membrane surface (such as when pressure is applied due to the touch of a hand); deals with senses

mechanically gated channels

-open at -55mV
-activation gate opens on stimulation, letting sodium ions into the cell
-inactivation gate closes to stop the entry of sodium ions
-found along the axon

voltage gated sodium (Na+) channels

-open at +30-40mV

voltage gated potassium (K+) channels

-resets an action potential
-powered by ATP
-exchanges 3 intracellular sodium ions for 2 extracellular potassium ions
-pumps sodium to the outside, brings potassium in

sodium potassium exchange pump

any shift from the resting membrane potential toward a less negative potential

depolarization

the process of restoring the normal resting membrane potential after depolarization

repolarization

an increase in the negativity of the resting membrane potential (the loss of positive ions)

hyperpolarization

-the membrane potential at which an action potential begins
-typically -55 - -60mV

threshold

-in an unmyelinated axon, an action potential moves along by ________
-slow because there re always voltage gated Na+ channels opening, and more Na+ rushing into the cell

continuous conduction (propagation)

-an action potential in a myelinated axon moves by ________
-faster because the new influx of Na+ renews the depolarized membrane

saltatory conduction (propagation)

specialized site where a neuron communicates with another cell

synapse

-direct link via gap junctions
-fast
-action potentials in one neuron can trigger action potentials in other connected neurons

electrical synapse

-involve neurotransmitters
-slow
-easy to control
-one neuron sends chemical signals to another cell

chemical synapse

separates presynaptic and postsynaptic cells in a chemical synapse

synaptic cleft

chemical compounds released by one neuron to affect the membrane potential of another

neurotransmitters

sends a message in a chemical synapse

presynaptic cell/neuron

receives a message in a chemical synapse

postsynaptic cell/neuron

order of events at a cholinergic synapse

synapse that releases ACh (acetylcholine)

cholinergic synapse

-most widespread neurotransmitter
-released at:
1) neuromuscular junctions involving skeletal muscle fibers
2) many synapses in the CNS
3) all neuron-to-neuron synapses in the PNS
4) all neuromuscular and neuroglandular junctions in the parasympathetic division of the ANS

acetylcholine

-affects mood, appetite, and sleep
-usually inhibitory
-antidepressants/SSRIs

serotonin

-inhibits the reabsorption of serotonin by axon terminals which leads to increased serotonin concentration at synapses (over time, the increase may relieve the symptoms of depression)
-side effects: anorexia and insomnia

fluoxetine (prozac)

-emotion, attention, pleasure
-"reward system": links stimuli with positive feelings
-aids in learning, encourages behavior
-dark side: addiction and impulsive behavior

dopamine

-death of cells that normally produce dopamine
-symptoms: tremor, hypokinesia, rigidity, dementia
-treatment with L-DOPA

parkinson's disease

-increases heart rate and alertness
-"fight or flight"

norepinephrine

synapses that release norepinephrine

adrenergic

-amino acid
-primary excitatory neurotransmitter
-alter ion movement across the membrane

glutamate

-primary inhibitory neurotransmitter
-ex: xanax

gamma-aminobutyric acid (GABA)

cause depolarization and promote the generation of action potentials

excitatory neurotransmitters

cause hyper polarization and suppress the generation of action potentials

inhibitory neurotransmitters

causes the membrane potential to move towards the threshold; depolarization in a postsynaptic cell

excitatory postsynaptic potential (EPSP)

causes the membrane to move away from the threshold; hyperpolarization in a postsynaptic cell

inhibitory postsynaptic potential (IPSP)

-dominated by the cell bodies of neurons, neuroglia, and unmyelinated axons
-outside of spinal cord

white matter

-contains large numbers of myelinated and unmyelinated axons
-inside of spinal cord

gray matter

how many pairs of spinal nerves are there?

31

how many pairs of cranial nerves are there?

12

cervical enlargement

nerves that supply upper limbs

lumbosacral enlargement

nerves that supply lower limbs

conus medullaris

main spinal cord doesn't reach coccyx

cauda equina