BIOL 66- Ch 7: The Nervous System: Neurons and Synapses

Two divisions of nervous system

Central and Peripheral

Nervous system

consist of trillions of cells in brain, spinal cord, periphery (on the side, not central)

Nervous System- Function

major control system; rapid electrical signals for communication; chemical communication- neurotransmitters; maintain homeostasis in physio variable; sensation, movement

Nervous System- Within neuron

conduct electricity

Nervous System- between neuron

communication

CNS components

Brain and spinal cord

PNS divisons

PNS- somatic, autonomic- parasympathetic, sympathetic

PNS- Nerves

groups of neurons in PNS; 12 pairs of cranial nerves and 31 pairs of spinal nerves; carry sensory and motor info

PNS- Afferent

carries sensory info to CNS; affects what will happen

PNS- Efferent

carries motor info from the CNS to effector cells; effect a change

Interneuron (Association Neuron)

connects neuron with in the CNS; integration and connection

PNS- Somatic nervous system

control skeletal muscle; voluntary movement

PNS- Autonomic nervous system

control smooth and cardiac muscle, and glands; automatic function; 2 divisions, parasympathetic and sympathetic

ANS- Parasympathetic

peace; rest and digest

ANS- Sympathetic

stimulate; fight or flight

Neuron

nerve cell, basic structural and functional unit; carries information in the form of electrical signals that move along the cell and to adjacent cells

Neuron- Electrical signal in…

Electrical signal (action potential) in neuron causes it to release a neurotransmitter to communicate with other cells

Glial Cells

glue of the nervous system; supporting cells, help neurons function; account for half the cells in human CNS; surround soma, axon, and dendrites

Dendrites

receive information from other neurons, typically neurotransmitters, resulting in graded potentials (electrical)

Graded potential

graded charge in membrane potential; ex: the change varies in size

Axons

Undergo action potential to deliver information, typically neutrotransmitters, from the axon terminals to other neurons or cells

Schwann cells

form myelin, a fatty sheath, on PNS axons

Oligodendrocytes

form myelin on CNS axons

Myelinated vs Nonmyelinated

myelinated neurons conduct action potential more rapidly than nonmyelinated neurons

Resting membrane potential

RMP of neuron is -70mV; neurons rest and conduct electricity

Electricity and NS- due to…

ion concentration gradients, leak channel in membrane, and sodium-potassium pump in membrane

Electricity and NS- Due to ion concentration gradients

more Na+ outside cell, K+ inside cell, Cl- outside cell, and fixed anion in cell

Ion gating and polarization- Ion Gating

opening and closing of gated ion channels in axon; changes permeability and polarization

Ion gating and polarization- Depolarization

membrane potential becomes more positive due to positive ions enetering cell; excitatory can result in action potential

Ion gating and polarization- Hyperpolarization

membrane potential becomes more negative due to positive ions leaving cell when K+ channels open or negative ions entering; inhibitory

Ion gating and polarization- Repolarization

return to the RMP when K+ channels are open and then start to close

Ion gating and polarization

Na+ channels are gated, closed at rest; K+ channels are either gated (at rest) or leak, so greater permeability to K+ at rest due to leak channels

Ion gating and polarization- Initial Depolarization

caused by neurotransmitter binding to receptors on dendrite, graded potential

Initial Depolarization process

Depolarization to -55 mV, the threshold potential causes voltage-gated Na+ channels to open in axon; Na+ rushes into neuron, potential becomes more positive, action potential= +30mV; Na+ channels are quickly inactivated; K+ channels open and K+ exits neuron. Hyperpolarization and then repolarization; K+ channel closes

Ion gating

at RMP, Na+ channel is close, depolarization opens the channel, the channel is inactivate during refractory period

Threshold potential

-55 mV

Action Potential

depolarization to 30 mV; rapid in axons; threshold potential must be met to occur; Na+ channel open, Na+ rushes in depolarizing neuron and AP occurs; slow opening K+ channels, K+ exits cell, hyperpolarizing and repolarizing; Na+/K+ pumps help restore RMP

Absolute Refractory Period

membrane cannot produce another AP because Na+ channels are inactivated

Relative Refractory Period

occurs when K+ channels are open and neuron is hyperpolarized; requires stronger stimulus to reach threshold

Conduction of AP

in unmyelinated axon, AP causes neaby Na+ channels to open, depolarizing the adjacent axon where another AP occurs; Propagation of the AP from is typically one-way due to absolute refractory period following the moving AP

Salatory Conduction

in myelinated axon, APs jump from one node Ranvier to another. ion channels are abundant at the node

Synapse

junction between neuron and effector cell, where presynaptic neuron influences electrical and chemical activity of postsynaptic neuron or effector cell (in muscle or gland)

Presynaptic Neuron

neuron undergoing APs in its axon, send the excitatory or inhibitory message (NT) to another neuron via synapse

Postsynaptic Neuron

neuron that receives the message from another neuron via the synapse. either excited (depolarized) or inhibited (hyperpolarized) by this message

Neurotransmitters

chemical messengers release from presynaptic neurons to cause a response in postsynaptic neuron

Neurotransmitters- Excitatory

depolarizes neurons due to Na+ or Ca2+ entry; EPSP

Neurotransmitters- Inhibitory

hyperpolarizes neuron due to Cl- entry; IPSP

EPSP

excitatory postsynaptic potential

IPSP

inhibitory postsynaptic potential

Neurotransmitters- Acetylcholine (ACh)

release by cholinergic neurons; skeletal muscle excitation (movement), autonomic functions both sympathetic and parasympathetic

Neurotransmitters- Catecholamines

released by adrenergic neurons; based on tyrosine (AA); dopamines, norepinephrine, and epinephrine; mood, states of consciousness, movement, blood, pressure regulation and more