Ch. 1 - Nerve Cells & Impulses

neurons, glia

human nervous system is comprised of two types of cells: ______ & _____

separate

individual cells of the nervous system are structurally ________

dendrite

• receive neurotransmitters

• bring information into the neuron

• some contain dendritic spines (greater surface area = more information)

cell body

• soma

• contains nucleus

• metabolic work of the cell

nucleus

contains: endoplasmic reticulum, golgi apparatus, mitochondria, and chromosomes

• regulates all cell function

axon

• begins with axon hillock

• transmits nerve impulse (action potential)

myelin sheath

insulating material that speeds transmission

node of ranvier

interruptions in the sheath

• allows for saltatory conduction

axon terminal

end point of the axon

• releases neurotransmitters at the synapse

synapse

gap between pre-synaptic neuron and post-synaptic neuron

vertebrae motor neuron

soma in the spinal cord receives excitation from other neurons

• conducts impulses along its axon to a muscle or gland

vertebrae sensory neuron

specialized at one end to be highly sensitive to a particular type of stimulation (touch, light, sound, etc)

afferent

bringing info into a structure

efferent

carrying info away from a structure

intrinsic

• interneurons

• neurons whose dendrites and axons are completely contained within a single structure

astrocyte

dilates blood vessels to direct nutrients to areas of high activity

• help synchronize activity of the axon

microgila

• removes waste material, viruses, and fungi from the brain

• also removes dead, dying, or damaged neurons

oligodendrocytes, Schwann cells

____________ (central nervous system) and _____ ____ (peripheral nervous system) build the myelin sheath that surrounds and insulates certain vertebrae axons

axons, dendrites

after embryonic development most _____ and _______ differentiate into neurons (smaller number differentiate into astrocytes and oligodendrocytes)

blood-brain barrier

mechanism that surrounds the brain and blocks most chemical from entering

• immune system destroys damages or infected cells throughout the body

• neurons in brain generally do no regenerate

certain beneficial chemicals have difficultly passing into the brain (ex: chemotherapy for brain cancer)

nerve impulse

electrical message transmitted down the axon of a neuron

• does not travel directly down the axon

• regenerated at points along the axon (nodes of Ranvier) so that it is not weakened

speed of nerve impulses range from less than 1 m/s to 100 m/s

resting potential

state of the neuron prior to sending a nerve impulse

• membrane maintains an electrical gradient known as polarization

• - charge inside membrane (-70 millivolts)

• higher conc. of Na+ outside of cell

• higher conc. of K+ inside of cell

neuron membrane

• membrane is selectively permeable

• Na, K, Ca, Cl

• during a resting potential:

  • Na+ channels are closed

  • K+ channels are partially closed (slow passage of potassium)

  • both passive channels (rely on gradients to move ions when open)

threshold of excitation

a level above which any stimulation produces a massive depolarization (action potential)

depolarization

decreasing the polarization

hyper-polarization

increasing the polarization

polarization

difference between the electrical charge of two places

regenerated

at each node of Ranvier (unmyelinated sections of the axon) the action potential is ________

salatory conduction

“jumping” of the action potential from node to node (rapid conduction of impulses)

absolute refractory period

first part of the period, membrane cannot produce an action potential

relative refractory period

second part of the period; a stronger than usual stimulus would be required to trigger an action potential

all-or-none law

it either fire or doesn’t (no such thing as a small action potential vs. a big action potential)

• amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it