Brooker Bio 1 Chapter 41 1-4

neurons

Cells that send and receive electrical and chemical signals to and from each other and other cells

Net movement

Concentration gradiant + permeable membrane = net movement by diffusion. if equal K+ conccentration in and out of cell = no net movement.

Saltatory conduction

Action potential seems to leap from node to node. actually action potentials are sped up, conduction process , taking less time to travel from node to node, eliciting new action potentials only at nodes.

Central Nervous System

Brain, nerve cord, extends through the vertebral column - spinal cord.

action potentials

Electrical events that carry a signal along an axon. Occurs in an all or nothing fashion. Rapid depolarization of a cell caused by positive feedback in voltage gate ion channels. depolarization of one part causes adjacent membrane parts to cross the threshold and depolarize too. Action potentials take time to spread down the axon.

EPSP Excitatory postsynaptic potential

Excitatory because the depolarization of the postsynaptic cell membrane brings the membrane potential closer to the threshold potential that would trigger an action potential.

Interneurons

Forms a connection between other neurons in the CNS. Forms complex connections with many other cells.

reflex arc

Knee jerk response is an example. Allows an organism to respond rapidly to inputs from sensory neurons. Evolutionarily oldest and most important feature of the nervous system.

Peripheral Nervous System

Neurons and projections off plasma membranes outside of but connect with spinal cord.

depolarization

Occurs when the cell membrane becomes less polarized, that is, its negative inside the cell relative to surrounding fluid. When a neuron is stimulated by an electrical or chemical stimulus, one or more types of gated membrane channels open, and Na+ ions diffuse into the cell, bringing with them their positive charge. This makes the new membrane potential somewhat less negative than the resting membrane potential. Neurons have special sodium channels that open only when the cell starts to depolarize.

repolarization

Once Na+ channels are inactivated, the continued action of Na+/K+ -ATPase pump begins the process of repolarization. The enzyme going to break down ATP consumes energy, moves stuff where it wants to go. Exchanges Na+ for K+. 3 Na+ outside, get 2 K+ back in. *The evolution of K+ channels with a slower opening time thanNa+ was a key event that led to the formation of nervous systems.

refractory period

Period where the membrane cannot produce another action potential (absolute) or is resistant to H (relative). Where it peaks and comes back down. The process continues and the action potential moves down the axon.

Neuroscience

Study of the nervous system

membrane potential

The difference between the electric charges along the inside and outside surfaces of a cell membrane.

equilibrium potential

The electrical gradiant would favor movement of K+ from left to right, but the concentration gradiant would favor movement from right to left.. The opposing forces create an electrochemical equilibrium in which there is no net diffusion of K+ in either direction. In living cells the membrane potential at which this occurs for a particular ion at a given concentration gradiant is equilibrium potential.

Chemical synapse

a chemical called a neurotransmitter is released from the axon terminal and acts as a signal from the presynaptic to the postsynaptic cell. slower than electrical synapses. Allow for complex modulation of the post synaptic cell.

dendrite

a single projection from a cell body that provide a larger surface area for contacts with other neurons.

glia - astrocyte

cells that surround neurons. provide metabolic support. also involved in forming blood brain barrier.

axon terminal

convey electrical or chemical messages to other cells, such as other neurons or muscle cells.

sensory neurons (afferent)

detect or sense information from outside world. also detect internal body temp and blood pressure. bypass the cell body and projects to CNS.

electrical synapse

directly passes electric current from the presynaptic cell to the postsynaptic cell rapidly.

axon

extension of the cell body that transmits signals along its length to neighboring cells. typically neurons have a single axon wrapped in myelin. Thicker axons increase the speed of conduction. Very thick axons are often found controlling escape or startle responses. (e.g. squid siphon) Can be as fast as 100m/sec or slow as a cm per sec.

Schwann cells

glial cells that form myelin that travel outside brain and spinal cord

IPSP Inhibitory postsynaptic potential

hyperpolarizes the postsynaptic membrane reducing action potential. Can be caused by Cl- channels.

netflow

if it can pass through membrane into cell, net flow - more going in than out. Concentration changes.

myelin sheath

insulating layer of specialized cells wrapped around axons. a sheath of myelin is an alternative solution to speeding up conduction. Electric signal jumps bit to bit, node to node.

oligondendrocytes

myelin producing glial cells in vertebrates

nodes of ranvier

non insulated gaps along the sheath

hyperpolarization

occurs when the cell membrane becomes more polarized, that is, more negative on the inside. i.e. increased diffusion of K+ out of the cell would make the charge along the inside of the cell membrane more negative than it normally is at the resting membrane potential.

Voltage Gated ion channels

open and close in response to changes in voltage across the membranes. Responsible for graded potentials and action potentials.For a cell to communicate using electrical signals, it must be able to change its membrane potential rapidly. This is accomplished using gated ion channels.

ligand gated ion channels

open and close when ligands, molecules such as neurotransmitters bind to them. responsible for graded potentials and action potentials.

electrochemical gradiant

the direction an ion moves depends on electrochemical gradiant., the combined effect of both and electrical and chemical concentration gradiant.

resting membrane potential

the membrane potential of an unstimulated cell not sending action potentials. determined by the ions located along the inner and outer surface of the plasma membrane.

axon hillock

the part of the axon closest to the cell body.

reuptake

to end the synaptic signal, neurotransmitter molecules in the synaptic cleft are broken down by enzymes or transported back into the terminal of the presynaptic cell and repackaged into vesicles for reuse. Drugs that block the reuptake process are used to treat depression etc. SSRIs. boost serotonin in the brain.

motor neuron (efferent)

transmit signals away from CNS and elicit a response that depends on the type of cell receiving the signal. Causes movement. motor nerve impulse is around 100 meters/second. Impulse moves from brain out to muscles. faster than diffusion (red dye in pool analogy) slower than electricity in a wire.