Cells of the nervous system

neurons

cells with specialized projections that transfer information throughout the body via an electrochemical process

how many neurons are in the brain?

100 billion

electrochemical signals in a neuron

Once a neuron has been stimulated by some sort of stimulus, it generates an electric potential that travels down the length of the cell

glial cells

support cells that modulate neurotransmission

microscopes

invented in 16th century

bacteria detection

1680

cell theory

in 1830s scientists proposed that all organic beings are composed of individual cells

golgi staining method

invented in 1873 and still used today: viewed the neuron

sensory and motor neurons

discovered in 19th century

sensory neurons spinal cord entrance

dorsal spinal cord

motor neuron spinal cord entrance

ventral spinal cord

law of specific nerve energies

1833: our perceptions are defined by specific nerve pathways stimulated rather than nature of physical stimulus itself

synapses

1897: described the spaces between neurons as synapses

reflexes

1897: description of how reflexes work

neuron cells

located in both the CNS and PNS: communication within nervous system and with organs, muscles, and glands

glial cells: astrocytes

located in CNS: maintain neural environment

glial cells: oligodendroglia

located in the CNS: produces myelin

glial cells: microglia

located in CNS: scavenge debris and defend against foreign substances

glial cells: Schwann cells

located in PNS: produces myelin

glial cells: Satellite cells

located in PNS: maintains neural environment

cell structure smallest to largest

atom, molecule, cell, organism

how do we classify neurons?

classified based on number of neurites

what are neurites?

projections such as dendrites and axons

sensory neurons

connected to sensory structures in body

motor neurons

connected to body structures involved with movement ex. muscles

interneurons

neurons connected to other neurons

synapse joining together

neuron + neuron = chemical neurotransmitter released at the synaptic cleft/ terminal buttons when a signal needs to be passed in order to excite, inhibit, or modulate

synapse type: axodendritic

excitatory

synapse type: axosomatic

inhibatory

synapse type: axoaxonic

regulating

neurotransmitters must be

present in the presynaptic membrane, released with depolarization, and received by specific receptors

how many known neurotransmitters are there?

over 100

what are neurotransmitters?

endogenous chemicals that allow neurons to communicate with each other throughout the body

acetylcholine

muscle contractions in PNS

glutamate

excitation of CNS

GABA

inhibits CNS activity

dopamine

motor control, brain reward system

epinephrine

excites heart: fight or flight response

norepinephrine

attention, alertness, mood

serotonin

inhibits nervous system

substance p

excites: perception of pain, inflammation in response to injury

absolute refractory period

the time after a neuron fires when it is unresponsive because sodium channels are inactivated

relative refractory period

time when a neuron will respond to another stimulus, but that stimulus must be stronger than normal due to sodium channels being in recovery mode

neuron damage: PNS

axotomy

neuron repair: PNS

axons have better ability to regenerate slowly (about 1 inch a month)

neuron damage: CNS

axotomy

axotomy

cutting or crushing of an axon that causes Wallerian degeneration

axon damage: CNS

glial cells rush to help and buildup as scar tissue (axons in CNS have poor ability to regenerate)

afferent communication

nerve cells carry info bottom up, body to brain, sensory, ascending

efferent communication

nerve cells carry info top down, brain to body, motor, descending

similarities of neurons and other cells

membrane, nucleus, cytoplasm, mitochondria, and other organelles

unique features of neurons compared to other cells

have specialized projections, communicate through an electrochemical process, can be very long (several feet at times)

pre synaptic

sending cell: sends cell across synapse

post synaptic

receiving cell: receives cell sent over synapse

action potential

rapid sequence of changes in voltage across membrane

step 1: loaded neuron (polarization)

there is energy potential due to concentration gradient and electrical gradient

resting membrane potential

-70 mV charge: more potassium (K+) inside, more sodium (Na+) outside, chloride (cl-) makes -70 mV charge

step 2a: chemical firing

neurotransmitter released from synaptic vesicle (at terminal button) to find receptor site)

step 2b: electrical firing (depolarization)

equaling of concentration and electrical gradients, protein channels open (Na+ rushes in via passive transport, triggers an action potential and depolarization)

step 3: reloading (repolarization)

concentrations and electrical gradients re - established, active transport: Na+ is pumped out

intellectual disabilities

sub average intelligence (< 70 IQ), occurs before age 18, substantial limitations in functioning, educational struggles, fewer, longer, or thinner dendritic spines

brain tumor types

benign (44%) and malignant (56%)

metastatic brain tumor

starts in other parts of body then spreads to brain

glioma

brain or spinal cord mass

neuroma

forms on branches of 8th nerve

astrocytoma

cancer in brain or spinal cord

oligodendroglioma

growth of cells that starts in the brain or spinal cord

schwannoma

slow growing tumor that arises from Schwann cells and wraps around motor and sensory nerves

medulloblastoma

cancerous brain tumor that starts in lower back part of brain

meningioma

tumors that develop from meninges membrane that covers spinal cord and brain

Amyotrophic lateral sclerosis (ALS)

also known as Lou Gehrig’s disease, nervous system disease that affects nerve cells in brain and spinal cord, withers upper and lower motor neurons, muscle weakness, 90% unknown etiology, not inherited, onset 40 - 60 years old, 3-5 year life expectancy

multiple sclerosis (MS)

numbness and weakness, multiple scarring of white matter in brain, spinal cord, and optic nerves, autoimmune disorder of unkown cause, myelin around axon is damaged

myasthenia gravis (MG)

condition where communication between muscles and nerves break down, causes weakness and fatigue, ACh receptors blocked by antibodies, affects women in 30s and men in 50s

gullian barre syndrome

rapid progressive demyelinating PNS disease, immune system mistakenly attacks peripheral nervous system which disrupts the network of nerves that carries signals from the brain and spinal cord to the rest of the body, autoimmune in nature, progressive paralysis over 1 month, then patients recover