Biology Chapter 4 The Nervous System

Neurons

specialized cells capable of transmitting electrical impulses and translating them into chemical cells

Neuron Cell Body Contents

nucleus, ER, ribosomes

Neuron Dendrites Function

receive incoming messages from other cells

Neuron Axon Hillock Function

integrate incoming signals

Action Potentials Function

all-or-nothing message to relay electrical impulses down axon to nerve terminal

Axon Function

terminates in close proximity to target structure

Myelin Function

insulate nerve fibers to prevent signal loss or crossing of signals

How does myelin affect conduction?

increases speed

What produces myelin?

oligodendrocytes in CNS and Schwann cells in PNS

Myelin Sheath Function

maintains electrical signal within one neuron

Nodes of Ranvier

expose axon membrane

Nerve Terminal

end of axon that maximizes transmission to next neuron

Neurotransmitters

chemicals transmitting information between neurons

Synaptic Cleft

space between neurons where NT release

Synapse Contents

nerve terminal, synaptic cleft, postsynaptic cleft

Nerve Description

multiple neurons bundled in PNS

Classes of Nerves

sensory, motor, mixed

Ganglia Composition

clustered cell bodies of neurons of same type

Tracts Description

axons bundled together in CNS that carry one type of information

Nuclei Description

group of cell bodies of neurons of same tract type

Glial Cells

structural and supportive cells

Types of Glial Cells

astrocytes, ependymal cells, microglia, oligodendrocytes

Astrocytes Function

nourish neurons and form blood-brain barrier

Blood-Brain Barrier Function

controlling transmission of solutes from blood stream to nervous tissue

Ependymal Cells Location

line ventricles of brain

Ependymal Cells Function

produce cerebrospinal fluid to support brain and nerves as shock absorber

Microglial Function

phagocytic cells ingest and break down waste products and pathogens in CNS

Oligodendrocytes Location

CNS

Schwann Cells Location

PNS

Oligodendrocytes and Schwann Cells Function

produce myelin around axons

Resting Membrane Potential

net electric potential difference across cell membrane

What is resting membrane potential voltage?

70 mV

What ion is on the inside of a neuron and what is its concentration?

potassium 140mM

What ion is on the outside of a neuron and what is its concentration?

sodium 4mM

Potassium Leak Channel Function

allow slow leak of potassium outside of the cell

Equilibrium Potential of Potassium

potential difference causing potassium to enter and reenter cell at equal rates

Sodium Leak Channel

slow leak of sodium into cell causes build-up of electric potential

Equilibrium Potential of Sodium

potential difference causing sodium to enter and reenter cell at equal rates

Depolarization

excitatory input causes membrane potential to increase from resting and making it more likely to fire an AP

What is the depolarization threshold to fire AP?

\-55 to -44 mV

Hyperpolarization

inhibitory input causes membrane potential to decrease from resting and make it less likely to fire AP

Summation

postsynaptic neuron receiving signals from many presynaptic neurons being added together

Temporal Summation

multiple signals integrated during relatively short period of time

Spatial Summation

additive effects based on number and location of incoming signals

Where is the majority of sodium during depolarization?

outside

Where is the majority of potassium during hyperpolarization?

inside

Describe the process of an action potential

stimulus → threshold → voltage-gated Na+ open → Depolarization → Na+ close, K+ open, AP → repolarization → N+/Ka+ ATPase pump → hyperpolarization

Electrochemical Gradient Function

promote migration of sodium into the cell

Absolute Refractory Period

no amount of stimulation can cause another action potential to occur

Relative Refractory Period

must be greater than normal stimulation to cause an action potential because membrane is starting from potential that is more negative than resting value

Saltatory Conduction

electrical signal jumps across nodes of Ranvier to travel down axon

What does an increased stimulus do to the frequency and potential difference?

increase frequency, does not affect potential difference

Presynaptic Neuron

neuron preceding synaptic cleft

Postsynptic Neuron

neuron after synaptic cleft

Effector

neuron signals to gland/muscle

What happens to NT after an AP?

exocytosis of NT to diffuse across the cleft and bind to postsynaptic receptors to pass messages between neurons

Ligand-Gated Channel

NT receptor that will be de- or hyperpolarized

G Protein-Coupled Receptor

NT receptor will cause changes in levels of cAMP or influx of Ca

What are three mechanisms that can remove NT from the cleft?

ACh breakdown, reuptake carriers, gaseous signaling molecules

Sensory/Afferent Neurons

transmit sensory info from receptors to spinal cord and brain

Motor/Efferent Neurons

transmit motor info from brain and spinal cord to muscles and glands

Interneurons

between other neurons and most numerous

Where are interneurons located?

predominately in brain and spinal cord

What behavior are interneurons linked to?

reflexive behavior

What does the CNS consist of?

brain and spinal cord

White Matter of Brain

axons encased in myelin sheaths, deeper than grey matter in brain

Grey Matter of Brain

unmyelinated cell bodies and dendrites

Vertebral Column Function

transmits nerves at the space between adjacent vertebrae

What matter is deeper in the spinal cord?

grey

Describe the movement of neurons in the spine

sensory from periphery → dorsal spine → dorsal root ganglia → motor neurons from ventral spine

What is the PNS made of?

composed of nerve tissue and fibers outside brain and spinal cord

Somatic Nervous System

sensory and motor neurons distributed throughout skin, joints, and muscles

Autonomic Nervous system

regulated heartbeat, respiration, digestion, temperature, and glandular secretions; manages involuntary muscles

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What neurons transmit messages from the spinal cord in the ANS?

preganglionic and postganglionic neuron

Preganglionic Neuron

soma in CNS, axon travels to PNS

Postganglionic Neuron

pre synapses to affect target tissue

Sympathetic Nervous System

fight or flight

Parasympathetic Nervous System

rest and digest

Reflex Arc

neural circuits controlling reflexive behavior

Monosynaptic Reflex Arc

single synapse between sensory neuron that receives stimulus and motor neuron that responds

Knee-Jerk Reflex

patellar tendon stretches, info travels up sensory neuron to spinal cord where it interfaces with motor neuron contracting quadriceps muscles

Polysynaptic Reflex Arc

at least one interneuron between sensory and motor neurons

Withdrawal Reflex

step on nail, does monosynaptic movement, but also steps back on opposite leg for balance

Glands Function

secrete hormones

Hormones

signaling molecules secreted directly into bloodstream to travel to distant target tissue

What are the three types of hormones?

peptides, steroids, amino acid derivatives

Peptide (hormones)

made of AA, range in size from small to large

Can peptide hormones pass through the plasma membrane?

no, they must bind to an extracellular receptor

What kind of messenger are peptides?

first that triggers second

What second messengers do peptides trigger?

cAMP, IP3, calcium

Signaling Cascade (peptide hormone)

connection between hormone at surface and effect brought by second messengers in cell

Amplification (peptide hormone)

binding of single peptide hormone to membrane-bound receptor produces a signal that increases in strength through signaling cascade

Peptide Hormone Characteristics

water-soluble, travel freely in blood stream, do not require carriers, rapid but short lived effects

Steroids (Hormones)

derived from cholesterol and produced primarily by gonads and adrenal cortex

Steroid Characteristics (hormone)

nonpolar, easily cross cell membrane, conformational changes, slow but long lived effects, not water soluble, must be carried by proteins in blood

Dimerization (steroid hormone)

pairing of two receptor-hormone complexes

Amino Acid Derivatives (hormones)

derived from one or two AA, usually with few additional modifications

Amino Acid Hormones

epinephrine, norepinephrine, triiodothryonine, thyroxine

Catecholamines (epinephrine and norepinephrine)

bind to G protein-coupled receptors while thyroid hormones bind intracellularly

Direct Hormones

secreted and act directly on target tissue