nervous system

What is the nervous system?

includes all neural tissue in the body

What are the two kinds of neural cells?

neurons and neuroglia

What are neurons?

cells that send and receive signal

What are neuroglia (glial cells)?

cells that support and protect neurons

What are the two divisions of the nervous system?

CNS and PNS

What composes the CNS?

brain and spinal cord

What composes the PNS?

all neural tissues outside the CNS

What are the divisions of the PNS?

afferent and efferent

What is the afferent division?

bring sensory information to CNS from receptors in peripheral tissues

What neurons are involved in the afferent division?

sensory neurons

What is the efferent division?

carries motor commands from CNS to effector tissues like muscles and glands

What neurons are involved in the efferent division?

motor neurons

What are the two divisions of the efferent division?

somatic and autonomic

S.A.M.E. stands for?

sensory (afferent) and motor (efferent)

What is the somatic nervous system?

controls voluntary and involuntary skeletal muscle contractions

What is the autonomic nervous system?

controls smooth muscle, cardiac muscle, and glandular secretions at the subconscious level

What two divisions can the autonomic nervous system be divided into?

sympathetic (fight or flight) and parasympathetic (rest and digest)

What does the cell body of a neuron contain?

nucleus and perikaryon

What is the perikaryon?

cytoplasm of neuron that contains organelles

What are the other structures of the neuron?

dendrites, axon, and telodendria (synaptic terminals)

What is gray matter made up of?

neuron cell bodies

What makes it gray?

nissl bodies

What are nissl bodies?

clustered areas of ribosomes and rough ER

In the CNS, what are the collections of neuron cell bodies?

nuclei and cerebral cortex (gray matter)

In the PNS, what are the collections of neuron cell bodies called?

ganglia (gray matter)

What are the collections of neuron axons called in the PNS?

nerves

What are the two nerves in the PNS?

cranial nerves and spinal nerves

What are cranial nerves?

connected to the brain/brainstem

What are the spinal nerves?

connected to the spinal cord

What are the collections of neuron axons in the CNS?

tracts (white matter of CNS)

What makes white matter white?

myelin sheath

What is the synapse?

site where a neuron communicates with another cell

What two cells are involved in the synapse?

postsynaptic cell: receives message
presynaptic cell: sends message

What could presynaptic cells possibly be?

neurons

What could postsynaptic cells possibly be?

neurons, muscle fibers, or gland cells

What are neurotransmitters?

chemicals that when released communicate between presynaptic and postsynaptic cells

Where are neurotransmitters produced?

cell body

How are neurotransmitters transported and what is the type of transportation called?

vesicles and axoplasmic transport

What are the types of axoplasmic transport?

anterograde and retrograde

What is the difference between anterograde and retrograde?

anterograde: toward the synaptic knob
retrograde: toward the cell body

What are the four structural classifications of neurons?

anaxonic, bipolar, unipolar, and multipolar

What are the differences between the different types of neurons?

anaxonic: found in brain
bipolar: found in special sensory organs (sight, smell)
unipolar: most sensory neurons of PNS
multipolar: skeletal muscle motor neurons, common in CNS
What are the three functional classifications of neurons?

What are the three functional classifications of neurons?

motor, sensory, and interneurons

What are the two types of sensory neurons?

somatic and visceral

What are visceral sensory neurons?

monitor internal environment

What are somatic sensory neurons?

monitor external environment

Where are the cell bodies of sensory neurons found? Where are the dendrites and axons found?

cell bodies found in sensory ganglia and processes (dendrites and axons) extend from sensory receptors to CNS

What are proprioceptors?

monitor joint and muscle position

What are the motor neurons responsible for?

the somatic nervous system and autonomic nervous system

Where are the cell bodies of motor neurons found? Where are their axons found?

cell bodies found in CNS (gray matter) and axons travel from CNS to periphery

What are interneurons aka association neurons?

they are responsible for distributing sensory info and coordinating motor info

Where are interneurons located?

brain, spinal cord, and some ganglia

What are interoceptors?

internal organ sensation, blood pH and O2

What are exteroceptors?

touch, temperature, taste, smell, hearing

What are the three types of sensory receptors?

interoceptors, exteroceptors, proprioceptors

What is neuroglia?

cells that support and protect neurons

What are the functions of neuroglia?

preserve physical and biochemical structure of neural tissue and are essential to survival and function of neurons

What are the four neuroglia cells in the CNS?

ependymal, oligodendrocytes, astrocytes, and microglia cells

What are the two neuroglia cells in the PNS?

satellite and schwann cells

What are ependymal cells?

they produce cerebrospinal fluid and monitor/circulate CSF

Where are ependymal cells found?

line the ventricles and central canal

What are astrocytes?

they maintain the blood-brain barrier by acting as gatekeepers for substances entering the CSF/interstitial fluid

What is another function of astrocytes?

they provide structural framework for the neurons of the CNS

Where are astrocytes found?

they cover the surface of all capillaries in the CNS

What are oligodendrocytes?

extensions containing myelin which wrap around neuron axons in order to conduct action potentials much faster

What do the unmyelinated axons and neuron cell bodies make up?

gray matter of CNS

What color does the myelin make?

it makes the white matter of the CNS

What is the difference between internodes and nodes?

axons are myelinated at internodes and axons are unmyelinated at nodes

What are microglia?

they engulf, phagocytize cellular debris, waste products, and infective organisms

Where are microglia found?

they are able to move through CNS

What are satellite cells?

regulate the environment around neurons, very similar to astrocytes in the CNS

Where are satellite cells found?

surround neuron cell bodies in ganglia of PNS

What are schwann cells?

they myelinate sections of a single axon or surround sections of many unmyelinated axons

What do the neurons of neuroglia perform?

they perform all communication, information processing, and control functions of the nervous system

What is the resting potential for a neuron?

-70mV

What are the relative ions outside and inside the cells of a neuron?

high number of Na+ outside cell and high number of K+ and negative proteins inside the cell

What is the net charge inside the cells of the neuron?

net negative charge inside the cell

What is the chemical gradient (direction) of the Na+ and K+ ions?

Na+ wants to rush in cell and K+ wants to rush out

Which channels are passive channels?

Na+ and K+ channels are always open

What helps maintain the resting potential of the cell if the Na+ and K+ channels are always open?

sodium/potassium pump (pump 3Na out of cell and 2K in cell)

What are the three gated channels?

chemically-gate channels, voltage-gated channels, and mechanically-gated channels

What are chemically-gated channels?

open or close when they bind specific chemicals (dendrites and cell body)

What are voltage-gated channels?

open or close in response to changes in transmembrane potential (axon)

What are mechanically-gated channels?

open or close in response to physical distortion

What are graded potentials?

a local change in transmembrane potential that may or may not result in an action potential

What causes graded potentials?

any stimulus that opens gated ion channels

What do graded potentials cause?

they can cause depolarization (shift toward more +) or hyperpolarization (shift toward more -)

What causes depolarization?

sodium channels opening

What causes hyperpolarization?

potassium channels opening

What are action potentials?

propagated changes in transmembrane potential that spread across an excitable membrane

How do action potentials travel?

they are chain reactions that moves along entire length of axon

What is the threshold voltage at the axon hillock?

-60mV

What happens once the threshold is reached?

an action potential occurs

What are the steps of the action potentials?

1) local depolarization to diffusion of Na+ ions
2) threshold is reached: opening of activation gates on voltage-gated sodium channels
3) Na+ rushes into axon causing rapid depolarization
4) at +30mV, Na+ inactivation gates on voltage-gated channels close and voltage-gated K+ channels open
5) K+ rushes out of the axons causing rapid repolarization
6) at -70mV, the voltage-gated K+ channels start closing (hyperpolarization)
7) passive channels allow ions to diffuse and the sodium/potassium pump runs resulting in the shift back to resting potential

How does neurons return to resting potential?

passive channels and the sodium/potassium pumps

What is a refractory period?

period of time during an action potential when another action potential cannot or is unlikely to occur

What are absolute refractory periods?

no action potential possible

Why are action potentials not possible in the absolute refractory period?

voltage-gated Na+ channels are either open or are inactivated

What are relative refractory periods?

action potentials are possible but requires larger stimulus

Why are action potentials possible in relative refractory periods?

Na+ channels are in normal resting state but K+ channels are open, or membrane is hyperpolarized