The nervous system is divided into what parts?

central nervous system (CNS) and peripheral nervous system (PNS)

The CNS is made up of

the brain and spinal cord

The PNS is made up of

the cranial and spinal nerves and sensory receptors

What subdivisions is the PNS further divided into based on the direction impulses travel?

sensory (afferent) pathway and motor (efferent) pathway

sensory (afferent) pathway

receptors that detect stimuli and the neurons that carry info TO the CNS (incoming)

motor (efferent) pathway

neurons that carry impulses FROM the CNS (outgoing)

What are the two parts of the efferent pathway?

somatic nervous system (SNS) and the autonomic nervous system (ANS)

SNS

mostly voluntary- includes the neurons sending info to the skeletal muscles

ANS

always involuntary- includes sending info to smooth and cardiac muscles. Divided into sympathetic and parasympathetic divisions.

What are the two main parts of the cells in the nervous system?

a)neurons
b)neuroglia

neurons

the functional unit of the nervous system, excitable cells that produce and conduct electrical signals and release chemicals for regulation and communication called neurotransmitters.

neurotransmitters (NT)

chemicals used to regulate and communicate

neuroglia

(glial cells) support neurons

The structure of a neuron includes:

a)cell body
b)axon hillock
c)processes (axons and dendrites)

cell body

has one nucleus, rough ER, and ribosomes to make proteins

axon hillock

thick base of the cell body

dendrites

carry impulses TO the cell body, often branched

axons

carry impulses AWAY from the cell body. a single long process that starts at the axon hillock. branches at its end to form axon terminals whose tips are filled with NT.

How are neurons classified by function?

a)afferent neutons
b)efferent neurons
c)interneurons

interneurons

make up about 90% of all neurons in the body, connect sensory and motor neurons

How are neurons classified by structure?

multipolar

several dendrites and one axon; most common

bipolar

has one dendrite and one axon

unipolar

has one process that splits into an axon and dendrite; rare

Which glial cells are in the CNS?

astrocytes, oligodendrocytes, microglia, and ependymal

Which glial cells are found in the PNS?

Schwann and satellite

astrocytes (CNS)

star shaped cells that form the blood-brain barrier by covering brain capillaries in the brain.

oligodendrocytes (CNS)

form a myelin sheath around multiple axons which send signals faster

microglia (CNS)

found near blood vessels and are phagocytic

ependymal cells (CNS)

line the inside of the spinal cord and produce cerebrospinal fluid

satellite cells (PNS)

flat cells that surround cell bodies in ganglia to provide support

Schwann cells (PNS)

wrap around axons of PNS neurons and produce a myelin sheath

myelination

most PNS axons are myelinated, only some are in the CNS

nodes of Ranvier

unmyelinated gaps along an axon; nodes are in contact with the extra cellular fluid (ECF)

white matter

made up of myelinated axons

gray matter

made up of everything else (cell bodies, dendrites, axon terminals, unmyelinated axons, and neuroglia)

excitable cells

change their membrane potential when they are stimulated which creates an electrical signal

resting membrane potential (RPM)

occurs when all ions inside and outside of the membrane are in equilibrium; RPM = -70 in neurons

Na+ is high _____ the cell and the membrane is ________ permeable to Na+.

outside, barely

K+ is high ______ the cell and the membrane is ________ permeable to K+.

inside, highly

One pump cycle moves ____ Na+ out and ____ K+ in.

3, 2

Ion channels

Allow ions to pass thorough the membrane
types: i)leakage channels
ii)gated channels
a)chemically-gated
b)voltage-gated

Leakage channels

are always open and create a slow leak

Gated channels

must be stimulated in order to open and close

Chemically-gated channels

channel has ligands bound to it which cause the gate to open. The gate closes when there is no ligand present.

Voltage-gated channels

open and close when there is a nearby change in membrane potential (voltage)

Depolarization

the potential is making the inside of the cell less negative than the RMP ex. -60

Repolarization

the potential is making the inside of the cell more negative

Hyperpolarization

the potential is making the inside of the cell more negative than RMP ex. -80

stimulus

starts activity by moving neuron away from its RMP and creates a new potential
types: a)chemical
b)mechanical
c)electrical

Name the types of potentials.

a)graded
b)action

Graded potentials

initiated by a stimulus to either the dendrites or cell body. they can be weak or strong depending on the stimulus. transmitted along the membrane of dendrites/cell body towards the axon hillock.

Action potentials

initiated ONLY if a STRONG graded potential makes it to the axon hillock; spreads along the length of an axon to the axon terminals

Graded potentials _____ as they travel.

weaken

Strong enough graded potentials reach a ___________ which is located on the axon hillock.

trigger zone

Trigger zone

is only activated if the graded potential is strong enough (if GP hits a threshold voltage, TV, of -55mV)

GP < TV, then

there is no response

GP > or = TP, then

the neuron hits threshold and an AP is generated in the axon

In the trigger zone

there is a high concentration of Na+ voltage-gated channels. if threshold is reached: channels open and Na+ rush into cell which causes depolarization and initiates the AP

Action potentials are based on

if the threshold is reached or not; the activity of voltage-gated Na+ and K+ channels

What are the steps of an action potential?

1.resting state
2.depolarization
3.repolarization
4.hyperpolarization

1.Resting State

neuron is at RMP and Na+ and K+ channels are closed

2.Depolarization

stimulus depolarizes the membrane IF stimulus is strong enough, then the AP starts. Many Na+ channels open causing Na+ to rush in (causes depolarization). Few K+ channels open causing a little K+ to leak out. At the peak of depolarization, a second gate on Na+ channels closes (stops depolarization)

3.Repolarization

many K+ channels open and K+ leaves the cell

4.Hyperpolarization

some K+ channels are still open after repolarization and the membrane over shoots RMP (hyperpolarization). Then all K+ channels are closed, Na/K+ pumps restore ions to original position (Na+ out and K+ in). Membrane returns to RMP.

Energy

ATP is needed to fuel Na+/K+ pumps but is not needed to generate an AP (done by diffusion)

How does a neuron respond to stimuli of different intensities?

a stronger stimulus means an increase in the frequency of AP

Refractory Period

recovery period for the neuron after an AP

Absolute refractory period

axon membrane can produce another AP, but requires a STRONGER stimulus than before

Conduction of APs

one AP doesn't occur across the entire axon, only across a small distance (< 1mm). One AP stimulates a new one in the next region of the axon membrane and conduct along the axon to it's end. (Domino Effect)

Saltatory Conduction in myelinated axons

where there is myelin on an axon, channels don't open or close. APs jump from one Node of Ranvier to another; conducts APs 10-50x faster

Synapse

occurs when an AP reaches the end of the axon; allows communication between a neuron and another cell (neuron to neuron or neuron to effector)

Which direction is the transmission of synapse information?

the presynaptic neuron sends info to the postsynaptic neuron or cell

Synaptic cleft

space between presynaptic and postsynaptic neurons

Steps to release a NT

1. an AP arrives at axon terminal
2. voltage-gated Ca2+ channels open and Ca2+ diffuses into axon terminal
3. calcium ions stimulate vesicles to release NT
4. NT crosses the synaptic cleft via diffusion
5. NT binds to the receptors on the postsynaptic cell and causes chemical-gated
6. NT activities stop when:
a) NT reuptakes back into axon
b) NT diffuses away from receptor
c) enzymes degrade the NT