Chapter 12

functional units

nourish and protect neurons

• Spinal cord + brain
• intergrates and coordinates sensory and motor information

All neural tissue outside CNS

carries sensory info from receptors toward CNS

Carries motor commands from CNS to effectors

controls skeletal muscle contractions

Controls smooth/cardiac muscle contractions

activiated during times of danger

Activated during times of NO danger

Contains large nucleus, cytoplasm (perokaryon) and Nissl Bodies (RER [rough endoplasmic reticulum] + ribosomes)

• Branched processes from the soma
• carry impulses toward soma

• Long cytoplasmic processes with smaller branches (telodendria) ending in synaptic terminals
• May branch into collaterals
• Cytoplasm (axoplasm) and membrane (axolemma)
• Base is axon hillock
• Carry information away from soma

• synapse is where pre and post synaptic cells communicate thru release of chemicals across spaces called synaptic clefts
• Neuron - Neuron (typical synapse)
• Neuron - Gland (neuroglandular synapse)
• Neuron - Muscle (neuromuscular synapse)

• small, no defined axon/dendrites
• unknown function

• small, cell body in middle, two distinct processes
• found in eyes, ears

• cell body to side, axon/dendrites are continuous
• very long (~1m)
• found in PNS

• cell with axon, two or more dendrites
• very long (~1m)
• found in CNS

• Unipolar
• Axons (afferent fibers) that extend between the receptor and CNS

• Multipolar
• Axons (efferent fibers) extend between CNS and effectors

• Multipolar
• Distribute information between the sensory neruon and motor neuron

• line central canal and vetricles of the brain
• secretes and moves CSF

• large and numerous
• cell extensions surround capillaries
• maintain blood/brain barrier

remove cell debris and pathogens

• lipid-rich pads wrap axons to form a myelin sheath
• sheath insulates and speeds up action potential

surround cell bodies of PNS neurons

• lipid-rich pads wrap axons to form a myelin sheath
• lightly wrap unmyelinated axon

• Step 1: fragmentation of axon myelin occurs in distal stump
• Step 2: schwann cells form cord, grow in cut, and unite stumps, macrophages engulf disintergrating axon and myelin
• Step 3: Axon sends buds into network of Schwann cells and then starts growing along cord of schwann cells
• Step 4: Axon continues to grow into distal stump and is enclosed in schwann cells

• limited due to numerous neurons and scarring
• some released chemicals (of the inflammatory response) block axon regrowth

when positive and negative charges are held apart

transmembrane potential is a potential difference across the membrane

movement of charges to eliminate potential difference

• membrane restricts ion movement
• creates resistance to current

• potential difference at rest is -70mV
• inside has more K⁺ and negative proteins
• outside has more Na⁺ and Cl^-
• K⁺ move through leak channels faster than Na⁺ moves in (negative proteins stay in cell) so inside is negative and outside is positive

• high concentration of K⁺ inside and high concentration of Na⁺ outside
• drives Na⁺ in and K⁺ out

• high negative charge inside and high positive charge on the outside
• drives sodium ions in and potassium ions in

• drives potassium ions out of cell
• less than chemical gradient alone due to opposing electrical gradient

• drives sodium ions into the cell
• greater than chemical gradient alone due to the aid of the electrical gradient

• uses ATP to pump 3 sodiums out and 2 potassiums in
• along with leak channels, the pump maintains resting potential of a cell

Always open

open and close

open/close in response to chemicals

open/close in response to changes in the transmembrane potential

open/close in response to physical stimulation

• changes in transmembrane potential that do not spread far from the point of stimulus
• occur at axon hillock, can lead to action potential

shift in resting potential toward a more positive potential

the process of restoring resting potential

increase in negative aspect of the resting potential

• changes in the transmembrane potential that affects the entire excitable membrane
• occur at the axon

• need stimulus large enough to reach threshold (+10mV) which opens voltage regulated sodium ion channels
• actional potential properties are independent of the stimulus strength

• stimulus causes depolarization to threshold
• sodium ion channels open and sodium ions move in (depolarization)
• sodium ion channels inactivated
• potassium channels open and potassium ions move out (repolarization)
• more potassium ions move out (hyperpolarization)
• potassium ion channels close
• sodium/potassium ion pump and leak channels restore resting potential

time from beginning of action potential until the resting potential is stabilized

• from the time when sodium ion channels open until sodium ion channel inactivation ends
• membrane does not respond to second stimulus

• from when sodium ion channels regain their resting condition until transmembrane potential stabilizes
• membrane responds to greater than normal second stimulus

repeated action potential along entire membrane (axon)

• action potential spreads along unmyelinated axon
• Step 1 - an action potential develops in the initial segment, transmembrane potential depolarizes
• Step 2 - local current depolarizes the adjacent portion
• Step 3 - an action potential develops at this location and the initial segment enters refractory period
• Step 4 - a local current depolarizes the adjacent portion of the membrane and the cycle is repeated

• action potential spreads along myelinated axon (faster)
• the same steps happen but it happens node to node (skips over internode) causing it to be faster

increased diameter decreased resistance

• largest, myelinated, action potential = 140m/sec
• deliver very important information

• smaller, myelinated, action potential = 18m/sec
• delivers less urgent info

• smallest, unmyelinated, action potential = 1m/sec
• delivers least urgent info

• movement of the action potential along an axon
• moves from presynaptic cell to a postsynaptic cell

pre and postsynaptic cell have direct contact via gap junction

• pre and postsynaptic cell do not have direct contact (synaptic cleft inbetween)
• neurotransmitter released at synapse

causes depolarization and action potential

causes hyperpolarization and prevents action potential

• acetylcholine released
• neuron-neuron synapses in CNS and PNS and neuromuscular junctions
• action potential arrives, synpatic knob depolarizes, calcium ion channels open, calcium enters
• entry of calcium ions causes acetylcholine release into synapse which binds receptors of postsynaptic membrane
• postsynaptic membrane depolarizes
• acetylcholinesterase digests acetylcholine

result in changes in postsynaptic cell membrane permeability

released at adrenergic synapses in CNS and ANS with excitatory effects

released in CNS with inhibatory role that helps control precise movements

released in CNS with effects on emotions and attention states

released at CNS with effect of reducing anxiety

• affect neurotransmitter release or postsynaptic cell response
• peptide opioids for pain control

integration process at axon hillock which determines action potential generation

graded potential at postsynaptic membrane in response to neurotransmitters

graded depolarization at postsynaptic membrane

graded hyperpolarization at postsynaptic membrane

integrated effect of all graded potentials at membrane

add stimuli in quick succession

simultaneous stimuli having cumulative effects

• bring neuron transmembrane potential closer to threshold
• dur to summation of EPSPs or drugs