Nervous System (Ch 10 only)

Cell Types of Neural Tissue 1. Neurons

classified by structure Bipolar

two processes EX:eyes, ears, nose

Unipolar one process EX:ganglia

Multipolar many processes EX:most neurons of CNS

classified by function

Sensory neurons afferent (bringing impulse into the CNS) most are unipolar some are bipolar

Interneurons link neurons multipolar CNS only

Motor Neurons efferent (bringing impulse out from CNS) multipolar

carries impulses to effectors (thing receiving impulse) 2. Neuroglial cells

PNS Schwann cells

produce myelin found on peripheral myelinated neurons which speeds transmission (unrelated but axon diameter also speeds transmission)

Satellite cells support clusters of neuron cell bodies

CNS Astrocytes

scar tissue formation mop up excess ions, etc induce synapse formation connect neurons to blood vessels

Oligodendrocytes myelinating cell

Microglia Phagocytic cell

Ependyma ciliated line central canal of spinal cord and ventricles of brain

Divisions of the Nervous system

Sensory Division → picks up info then delivers to CNS Motor Division → carries info to muscles and glands

Somatic → carries info to skeletal muscle Autonomic → carries info to smooth muscle, cardiac muscle, and glands

Functions of Nervous System (SIM) 1. Sensory function → sensory receptors gather info for CNS 2. Integrative Function → sensory used to create sensations, memory, thoughts, and

decisions 3. Motor Function → decisions are acted upon/ impulses are carried to effectors

Neuron Structure

Myelination of Axons

White matter contains myelinated axons

Gray Matter contains unmyelinated structures: cell bodies/dendrites

Synaptic Transmission nerve impulses pass from neuron to neuron at synapses neurotransmitters are released when impulse reaches synaptic knob

Impulse Processing

1. Neuronal Pools → how interneurons are organized in CNS; groups of neurons that synapse with each other and work together to perform a common function

a. each pool receives input from other neurons and generate output to other neurons

2. Convergence → axons originating from different parts of NS leading to the same neuron exhibit

a. can amplify an impulse

b. facilitation → impulse from a single neuron in CNS may be amplified to activate enough motor units needed for muscle contraction

3. Divergence → impulses leaving a neuron pool Resting Membrane Potential

inside is negative relative to outside Na is on outside/ K is on inside

polarized membrane due to distribution of ions maintained Na+/K+ pump (diffusion = no energy needed)

Local Potential Changes

caused by various stimuli → temp. change, light, pressure, etc. environmental changes affect the membrane by opening a gated ion channel (Active

Transport)

hyperpolarized → membrane potential becomes more negative depolarized → membrane potential becomes less negative graded → local potentials are graded meaning the degree of change in resting potential is directly proportional to the intensity of the stimulation summation → can lead to threshold stimulus that starts an action potential Action Potential

at rest membrane is polarized threshold stimulus reached sodium channels open and membrane depolarizes potassium leaves cytoplasm and membrane repolarizes

(a=rest ­70 mV b=reaching threshold 30 mV c=repolarization

All-or-None Response

if a neuron responds at all, it responds completely nerve impulse is conducted whenever a stimulus of threshold intensity or above is

applied to an axon all impulses carried on an axon are the same strength

Refractory Period 1. Absolute

time when threshold stimulus does not start another action potential 2. Relative

time when stronger stimulus can start another action potential Saltatory Conduction

action potentials occur only at nodes in myelinated neurons (appear to jump from node

to node) Synaptic Potentials

EPSP (excitatory postsynaptic potential) graded depolarizes membrane of postsynaptic neuron action potential of postsynaptic neuron becomes more likely

IPSP (inhibitory postsynaptic potential) graded hyperpolarizes membrane of postsynaptic neuron action potential of postsynaptic neuron becomes less likely

EPSP + IPSP = summation greater EPSP = greater action potential probability

Neurotransmitters

Green Boxes and Clinical Applications

1. Migraines Symptoms → pounding headache, waves of nausea, sometimes shimmering

images in peripheral field, and extreme sensitivity to light/sound Possible Causations → sudden exposure to bright light, eating particular

foods, lack of sleep, stress, high altitude, stormy weather, and excessive caffeine/ alcohol intake

70% of sufferers are women (hormonal) Results from changes in the diameters of blood vessels in the face head

and neck ii. Types

Classic

10 ­ 15% experience can last 4 ­ 6 hours begins with light in peripheral vision

Common lacks an aura can last 3 ­ 4 days

Familial Hemiplegic (rare) hereditary paralyzes one side of the body for a few hours to a few days may cause loss of unconsciousness

iii. Treatments Triptans → mimic serotonin Aspirin/Ibuprofen → usually enough Wild Rhubarb extract Antidepressants, anticonvulsants, and drugs to treat high blood pressure

2. Multiple Sclerosis (MS) i. myelin coating becomes inflamed and is eventually destroyed leaving hard scars

called scleroses scleroses block underlying neurons from transmitting messages muscles that stop receiving impulses, stop contracting, and then

experience atrophy ii. Symptoms → begins as blurred vision, numb legs/arms

following symptoms vary depending on what neurons are affected 70% first notice symptoms in ages 20 ­ 40 eventually become paralyzed women are twice as more likely to develop this; caucasians are more

often affected than other races more common in temperate zones of Europe, SA, and NA

iii. Diagnosis → MRI scans (track development of lesions) hypothesized that certain infections in certain individuals stimulate T cells

(a type of white blood cell) in the periphery cross blood brain barrier and attack cells producing myelin

virus may lie behind misplaced immune attack that is MS iv. Treatments

drugs to treat urinary problems antidepressants short term steroids are used to shorten the length of acute disabling

relapses 3 main long term drugs

Beta interferon an immune system biochemical adapted as a drug decreases # of attacks by ⅓ + can slow progression may cause flu­like symptoms

Glatiramer Acetate 4 linked amino acids (found in myelin basic protein) fools T­cells into attacking this and dampening

inflammation may protect axons can slow relapse rate

Mitoxantrone anti­inflammatory drug halts immune system’s attack on CNS myelin can slow relapse rate

3. Normal Myelin development i. myelin beings formation during 14th week of prenatal development ii. by birth, many axons are not completely myelinated iii. when child starts walking, all myelinated axons begin to develop sheaths iv. continues into adolescence

Tay­Sachs Disease excess myelin seriously impairs NS hereditary defect in a lysosomal enzyme causing neurons to be

buried in fat symptoms → gradual loss of sight, hearing, and muscle function

starts around 6 months old; death by 4 years 4. Neuromas

when peripheral nerve is severed, it is very important the two cut ends be connected asap

so that sprouts of the axon can more easily reach the tubes formed by the basement membranes and connective tissues on the distal side of the gap

gaps > 3mm are prone to neuromas

composed of sensory axons and is painfully sensitive to pressure can complicate a patient’s recovery following limb amputation

5. Factors Affecting Impulse Conduction a # of substances alter axon membrane permeability EXAMPLE 1 → calcium ions are required to close sodium channels in axon

membranes during an action potential Calcium deficiency → Tetanus/Tetany

spontaneous impulses that travel through skeletal fibers and cause spasms

can be caused by maternal Calcium taken in pregnancy/ decreased vitamin D/ prolonged diarrhea

EXAMPLE 2 → potassium ions Potassium increase → Convulsions

can cause the resting potential of nerve fibers to be less negative (partially depolarized)

threshold is reached with less intense stimulus than usual as a result of very excitable fibers

Potassium decrease → muscle paralysis resting potentials of nerves may become so negative that action

potentials are not generated EXAMPLE 3 → anesthetic drugs

Procaine → decreases permeability of sodium ions in the tissue fluids surrounding an axon prevents nerve impulses from passing through

blocks touch and pain 6. Opiates in the Human Body

Opiate drugs → morphine, heroin, codeine, and opium potent painkillers derived from poppy plant easier to tolerate pain and mood elevation

Endorphins body’s natural opiates peptides resemble opiate drug; influence perception of pain + mood discovered in 1971 at Stanford University and the John Hopkins School of

medicine exposed mammalian brain tissue to morphine (which was

radioactively labeled) bound to receptors on membrane of nerve cells that transmit pain

why would it bound to those places unless there was already a natural signal?

explained why some people who are addicted to opiate drugs experience withdrawal pain

body stops producing endorphins because of the perceived excess of endorphins in the body

7. Drug Addiction Timeline → 3,500 yr. old egyptians used opium, 1600’s Chinese relied on opium,

Japan and Europe discovered addictive nature of nicotine, during American civil war morphine was used as painkiller and cocaine was later introduced to relieve veterans addicted to morphine, 1960s LSD was used for psychotherapy, and PCP was an anesthesia before being used in the 1980s

Role of Receptors when drug alters activity of a neurotransmitter on postsynaptic neuron, it

halts/enhances synaptic transmission Antagonist → drug that blocks neurotransmitter from binding Agonist → drug that activates a receptor, triggering action

potential/ helps a neurotransmitter bind many addictive substances bind to the receptor for Dopamine in a region

called nucleus accumbens with repeated use, # of receptors it targets can decline (tolerance) EXAMPLE 1 → Amphetamine

enhances norepinephrine → controls arousal, dreaming, and mood

EXAMPLE 2 → Cocaine blocks reuptake of norepinephrine + binds to molecules that

transport dopamine EXAMPLE 3 → Valium

GABA agonist

causes relaxation and inhibits seizures + anxiety by helping GABA → an inhibitory neurotransmitter used in ⅓ of the brain synapses

Nicotine binds postsynaptic receptors that normally bind the neurotransmitter ACH alters receptor so that positive ions enter the cell triggering dopamine

release heavy smoker = stimulation of excess receptors to accumulate and soon

become nonfunctional (tolerance)