Class 8 - Nervous System

CNS, PNS

2 main nervous systems

CNS

nervous system composed of the brain and spinal cord; integrative and control centers

PNS

nervous system made up of cranial and spinal nerves; communication lines between the CNS and the rest of the body

sensory (afferent), motor (efferent)

two divisions of the PNS

sensory (afferent)

division of the PNS responsible for somatic and visceral sensory nerve fibers; conducts impulses from receptors to the CNS

motor (efferent)

division of the PNS responsible for motor nerve fibers; conducts impulses from the CNS to effectors (muscles and glands)

somatic, autonomic

2 divisions of motor division of the PNS

somatic

nervous system that is responsible for voluntary motor function; conducts impulses from the CNS to skeletal muscles

autonomic

nervous system that is responsible for involuntary movement; conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands

sympathetic, parasympathetic

2 divisions of the autonomic nervous system of the motor division of the PNS

sympathetic

division of the autonomic nervous system that mobilizes body systems during activty

parasympathetic

division of the autonomic nervous system that conserves energy and promotes house-keeping functions during rest

neurons, supporting cells

2 principal cell types of the nervous system

neurons

excitable cells that transmit electrical signals

supporting cells

cells that surround and wrap neurons, insulate, guide young neurons and promote health and growth

astrocytes, microglia, ependymal cells, oligodendrocytes

4 types of supporting cells in the CNS

astrocytes

most abundant supporting cell in the CNS

astrocytes

supporting cell in the CNS that cling to neurons and their synaptic endings, cover capillaries, anchor neurons to their nutrient supplies, guide migration of young neurons, and control chemical environment

microglia

supporting cells in the CNS that are small, ovoid cells with spiny processes; function as phagocytes; monitor neuron health

ependymal cells

supporting cells in the CNS that are squamous to columnar; line central cavities of brain and spinal cord

oligodendrytes

supporting cells in the CNS that are branched and wrap CNS nerve fibers

Schwann cells

supporting cells in the PNS that surround fibers

satellite cells

supporting cells in the PNS that surround neuron cell bodies with ganglia

Schwann cells, satellite cells

2 supporting cells in the PNS

neurons

cells that are composed of a body, axon, and dendrites, are long-lived, amitotic, have a high metabolic rate

no

Are neurons capable of division?

olfactory (smell), hypocampus (memory)

You're born with all the neurons you have except for which 2 types of neurons?

cell body (soma)

part of the neuron that contains the nucleus

Nissl bodies

rough ER in the neuron

axon hillock

area from which axons and impulses originate

tracts

collection of axons in the CNS

nerves

collection of axons in the PNS

axon terminal

branches terminal of the axon

dendrites

receptive regions of the neuron

electrical signaling, cell-to-cell signaling

functions of neurons during development

action potentials

axons generate ___________ _____________

anterograde

movement towards the axon terminal

retrograde

movement away from the axon terminal

neurotransmitters

axon terminals make ______________________

high

Do neurons have high or low metabolic rate?

glucose

the only thing neurons can use to make ATP

PNS

Does CNS or PNS have more myelin?

nodes of Ranvier

spaces between myelin where action potentials occur

nuclei

collection of cell bodies in the CNS

ganglia

collection of cell bodies in the PNS

oligodendrocytes

What are myelinated and unmyelinated fibers formed by?

brain, spinal cord

Where are white matter and gray matter present?

white matter

dense collections of myelinated fibers in the brain and spinal cord

gray matter

mostly soma and unmyelinated fibers in the brain and spinal cord

multipolar, bipolar, unipolar

structural classifications of neurons

sensory (afferent), motor (efferent), interneurons (association neurons)

functional classifications of neurons

sensory (afferent)

neurons that transmit impulses toward the CNS

motor (efferent)

neurons that carry impulses away from the CNS

interneurons (association neurons)

neurons that shuttle signals through CNS pathways

multipolar

structural classification of neuron: most abundant neuron in the body, found in brain and spinal cord, interneurons and motor neurons

bipolar

structural classification of neuron: rare, found in eyes, ears, nose, sensory neurons

unipolar

structural classification of neuron: found in dorsal root ganglia of spinal cord and sensory ganglia of cranial nerves, sensory neurons

action potentials

nerve impulses/electrical impulses that are carried along the axonal length

stimulus

action potentials are always the same regardless of the ___________

all or none phenomenon

actions potentials either happen completely, or not at all

passive/leakage channels

ion channels that are always open

chemically gated channels

ion channels that open when a specific neurotransmitter binds

voltage-gated channels

ion channels that open and close in response to membrane potential

mechanically gated channels

ion channels that open and close in response to physical deformation of receptors

chemical gradient

ion flow from an area of high to low concentration

electrical gradient

ion flow along this towards an area of opposite charge

electrochemical gradient

combination of the chemical gradient and the electrical gradient

-70mV

resting membrane potential of a neuron

depolarization

membrane potential becomes less negative

hyperpolarization

membrane potential becomes more negative

outside

Na+ concentration is higher ___________ the cell

inside

K+ concentration is higher ___________ the cell

100 mV

total amplitude action potentials can reach

no

Do action potentials decrease in strength over distance?

muscle cells, neurons

Action potentials are only generated by what 2 things?

nerve impulse

an action potential in the axon of a neuron

resting stage, depolarization, repolarization, hyperpolarization

4 major steps of action potentials

4 ms

time it takes for an action potential to be generated

threshold

when membrane is depolarized by 15 to 20 mV to reach this

total amount of current flowing through the membrane

What is threshold established by?

weak (subthreshold)

stimuli that are not relayed into action potentials

strong (threshold)

stimuli that are relayed into action potentials

yes

Are all action potentials alike?

yes

Are all action potentials independent of stimulus intensity?

refractory period

the time from the opening of the Na+ activation gates until the closing of inactivation gates

absolute refractory period

prevents the neuron from generating an action potential; ensures each action potential is separate; enforces one-way transmission of nerve impulses

relative refractory period

interval that follows the absolute refractory period; Na+ gates are closed, K+ gates are open, repolarization is occurring; threshold is elevated allowing strong stimuli to increase frequency of action potentials

myelin

insulates the neuron and keeps conductance from leaking

bare plasma membrane

place on a neuron (such as a dendrite) where the impulse diminishes over time due to current leaks across the membrane

unmyelinated axon

type of axon where the impulse slows because voltage-gated Na+ and K+ channels must regenerate the action potential at each point along the axon

myelinated axon

type of axon where the impulse happens quickly because myelin keeps current in the axon; action potentials jump rapidly from one node of Ranvier to another

saltatory conduction

type of conduction in myelinated axons where the impulse jumps rapidly from node to node on the axon

multiple sclerosis (MS)

autoimmune disease that mainly affects young adults

visual disturbances, weakness, loss of muscular control, urinary incontinence

symptoms of multiple sclerosis (MS)

multiple sclerosis (MS)

autoimmune disease where nerve fibers are severed and myelin sheaths in the CNS become nonfunctional; short-circuiting of nerve fibers occurs

hold symptoms at bay, reduces complications, reduces disability

affects multiple sclerosis (MS) treatment has

no

Can multiple sclerosis (MS) be cured?

synapse

junction that mediates information transfer from one neuron to another neuron or to an effector cell

presynaptic neuron

conducts impulses toward the synapse

postsynaptic neuron

transmits impulses away from the synapse