neurophysiology 1.2

estimates of neurons in humans

• cerebral cortex

  • 16 billion neurons

• rest of the brain

  • < 1 billion neurons

• cerebellum

  • 69 billion neurons

• spinal cord

  • 1 billion neurons

*adult human brain contains around 86 billion neurons

nervous system is composed of two kinds of cells?

• neurons

• glia

neurons

receive + transmit info

Camillo Golgi

discovered a way to stain neurons w/ silver salts

concluded: the brain is like mesh, w/o seperate cells

Santiago Ramon y Cajal

concluded: nerve cells remain separate instead of merging into one another

mitochondrion

aerobic energy metabolism; performs metabolic activities providing energy that the cell uses for all activities

*animal cell

plasma membrane

control of material exchanges, mediation of cell-environment interactions

*animal cell

endoplasmic reticulum

network thin tubes that synthesize new protein molecules

involved in isolation, modification, transport of proteins + other substances

nucleus

contains chromosomes

ribosomes

synthesize new protein molecules

why would a weakened mitochondrion affect the brain more than other organs?

the brain uses energy more than any other organ

motor neuron

receives signal thru its dendrites + moves the impulses along the axon to a muscle

*has soma in spinal cord

sensory neuron

highly sensitive to a specific kind of stimulation (ie touch); sensory info is transmitted to spinal cord

dendrites

branching fibers; surface lined w/ synaptic receptors

*comes from Greek word meaning tree

dendritic spines

short outgrowths that increase the surface area available for synapses

cell body (soma)

contains nucleus, ribosomes, mitochondria

axon

sends signal to other neurons, organs, or muscles

*thin fiber

myelin sheath

insulating material (covering most vertebrae axons but NOT invertebrae axons)

nodes of Ranvier

gap in myelin sheath

presynaptic terminal

specialized ending of neuron’s axon that releases chemical messengers (NTs) into synaptic cleft

*end bulb or button

a neuron can have many _______, but it only has one _______.

dendrites; axon

afferent axon

bring info into structure

efferent axon

carries info out of structure

Every sensory neuron is an _______ to the nervous system, and every motor neuron is an ________ from the nervous system.

afferent; efferent

tip to remember diff*

afferent - admit

efferent - exit

interneuron

cell’s dendrites + axons are entirely contained within a single structure

*intrinsic neuron

how does the structure of a dendrite differ from that of an axon?

• axons are longer + their diameter is constant

• dendrites no longer than a few mm long + it tapers toward its end

which animal species would have the longest axons?

the largest animals; giraffes and elephants

of the three types of neurons (sensory, motor, intrinsic), which would have the shortest axons?

interneurons; bc they are contained entirely within one part of the brain so their axons are short

glia

support, protect, nourish neurons

*means glue

types of glial cells

• astrocytes (star-shaped)

  • shields neuron from chemicals + helps axons send messages in waves

• microglia

  • act as part of the immune system, removing viruses+ fungi from the brain

  • proliferate brain damage + remove dead/damaged neuron

• oligodendrocytes

  • in brain + spinal cord, build myelin sheaths surrounding + insulting certain vertebrae axons

• schwann cells

  • in periphery of body, build myelin sheats surrounding + insulating certain vertebrae axons

• radial glia

  • guide migration of neurons + their axons + dendrites during embryonic development

blood-brain-barrier

excludes most chemicals from vertebrate brain

tripartite synapse

hypothesis that the tip of an axon releases chemicals that cause the neighboring astrocyte to release its own chemicals »» modifying the message to the next neuron

active transport

a protein-mediated process that expends energy to pump glucose, amino acids, omega-3-fatty acids, + several vitamins from blood

A loss of ________ leads to _________.

microglia; seizures

which type of glia synchronize the activity of a related group of axons?

astrocytes

which type of glia cell removes dead neurons + prunes ineffective synapses?

microglia

Most cells use a variety of carbohydrates + fats for nutrition, but vertebrate brain cells depend almost entirely on ______.

glucose

thiamine

body needs to break down glucose

*vitamin B

korsakoff’s syndrome

prolonged thiamine deficiency leading to death of neurons + marked by memory impairments

Identify one major advantage + disadvantage of having a blood-brain-barrier.

• advantage: keeps out many viruses + harmful chemicals

• disadvantage: keeps out most nutrients

which chemicals cross the BBB passively?

molecules that dissolve through fats enter passively; so do water + several ions that the membrane has specific channels for

how do glucose + amino acids cross the blood-brain-barrier?

the membrane has proteins that actively transport glucose + amino acids into the brain

Santiago Ramon y Cajal clearly demonstrated which of the following?

• the nervous system is composed of separate cells

• neurons pass chemicals to communicate at junctions called synapses

• brain damage can produce highly specialized behavioral deficits

• the organization of the brain is substantially the same in all mammalian species

the nervous system is composed of seperate cells

which part of the neuron has the chromosome?

• axon

• cell body

• dendrite

• synapse

cell body

what do the mitochondria do?

• provide energy for the cell

• produce the myelin sheath that surrounds an axon

• surround + insulate the synapses

• create the BBB

provide energy

how do dendrites differ from axons?

• dendrites are covered w/ myelin

• dendrites are long + cylindrical

• dendrites have branches

• dendrites are short + tapered

dendrites are short + tapered

what do dendritic spines do?

• they synthesize proteins

• they increase the SA available for synapses

• they hold the neuron in position

• they metabolize fuels to provide energy for the rest of the neuron

they increase the SA available for synapses

what does an afferent axon do?

• it controls involuntary behavior

• it controls voluntary behavior

• it carries output from a structure

• it brings info into a structure

it brings info into a structure

which of the following is a function of astrocytes?

• they conduct impulses over long distances

• they create new neurons to replace those lost in brain damage

• they synchronize the activity of a group of neurons

• they build myelin sheaths that surround + insulate axons

they synchronize the activity of a group of neurons

which of the following is a function of microglia?

• they remove dead cells + weak synapses

• they build myelin sheaths that surround + insulate axons

• they conduct impulses over long distances

• they synchronize activity for a group of neurons

they remove dead cells + weak synapses

why are chemotherapy drugs ineffective against brain cancers?

they can’t cross the BBB

which of these chemicals cross the BBB by active transport?

glucose and amino acids

what is the brain’s main source of fuel?

• glucose

• glutamate

• proteins

• DNA

glucose

why does the brain need thiamine?

• to metabolize glucose

• to build the BBB

• to build myelin sheaths

• to use at the synapses

to metabolize glucose

under what conditions do the intestinal bacteria produce more inflammatory chemicals?

• during sleep

• when the temperature of the environment is increasing

• after any larger than average meal

• under stressful conditions that might lead to depression

under stressful conditions that might lead to depression