Anatomy Exam 3

what are the two cell types that makes up neural tissue?

neurons and neuroglial

what are the functions of the nervous system?

• Sensory function

• Integrative/Associative function

• Motor function

sensory function

Gathers information about the internal and external environment (sense organs, nerves) and Relays this information to the spinal cord and the brain

Integrative/Associative function

Processes and integrates the information

motor function

Responds, if necessary, with impulses sent via nerves to muscles, glands, and organs

which type of neurons is only in the central nervous system?

interneurons

central nervous system consists of?

brain and spinal cord

peripheral nervous system consists of?

cranial and spinal nerves

what is the organization of the nervous system?

receptor > sensory NS > CNS > motor NS > effector

dendrites

The message (impulse) receiving end of a neuron

axon hillock

where impulses originate

Anterograde impulse transmission occurs from ___________________ to ________________.

cell body; axon terminals

multipolar neurons

• many processes

• most neurons of CNS

bipolar neurons

• two processes

• sense organs

unipolar neurons

• one process

• ganglia

sensory neurons

• afferent, ascending

• carry impulse to CNS

• most are unipolar

• some are bipolar

interneurons

• link neurons

• integrative

• multipolar

• in CNS

motor neurons

• efferent, descending

• multipolar

• carry impulses away from CNS

• carry impulses to effectors

satellite cells

Regulate microenvironment of neurons

astrocytes

helps regulate the microenvironment and form the blood-brain barrier

Regulate microenvironment of neurons; scar tissue in CNS

schwann cells

Myelination of axons; structural support for non-myelinated axons

Oligodendrocytes

Myelination of axons; structural framework

microglia

Phagocytes of the CNS

ependymal cells

Assist in producing and controlling composition of CSF

What is the resting membrane potential of a neuron?

-70 mV

passive channel

• ALWAYS open

• Also called ‘leak’ channels

• always allow K+ through

active gated channels

open or close in response to signals

mechanical channel

respond to distortion of membrane

ligand-gated channel

• Binding of a chemical molecule, e.g., ACh on MEP (motor endplate)

• Present on dendrites, soma, sometimes on axons

voltage-gated channel

• Respond to changed in electrical potential

• Found on excitable membranes, e.g., axons, sarcolemma

depolarization

• membrane potential becomes more positive than its resting potential

• Na⁺ ions move into the neuron, making the inside more positive

repolarization

• A membrane returning to its resting potential from a depolarized state

• K+ ions leaving the cell making the inside more negative

hyperpolarized

membrane potential becomes more negative than its resting potential

extra K+ leave the cell

all or none

the neuron fires a full action potential or it doesn’t fire at all

threshold

the minimum membrane potential needed to trigger that action potential

absolute refractory period

time when threshold stimulus does not start another action potential (Na+ channels inactivated)

relative refractory period

time when stronger threshold stimulus can start another action potential (Na+ channels restored, K+ channels begin closing)

what are the steps in action potential?

1) depolarization 2) repolarization 3) hyperpolarization 4) return to resting potential

local graded potential

• Caused by various stimuli

• weaken rapidly

• Uses ligand-gated Na+ channels

• Can be summed (so that an action potential threshold is reached; change in membrane potential stimulus strength

• Starting point for an action potential

action potential

• continuous propagation

• What keeps the action potential going in ONE DIRECTION

• Absolute refractory period

myelin

• acts as an insulator and increases the resistance to flow of ions across neuron cell membrane

• produced by Schwann cells and oligodendrocytes

_______________________________________________conduction/transmission is ______

times faster in __________________________ neurons.

impulse; 20x; non-myelinated nerves

Multiple sclerosis damages _______________ of _______________________ nerves resulting in slowed responses.

myelin sheath; CNS nerves

what are the steps of chemical synaptic transmission?

1. Action potential arrives at the axon terminal.

– The electrical impulse travels down the axon to the synaptic end bulb.

2. Voltage‑gated Ca²⁺ channels open.

– The depolarization causes calcium ions (Ca²⁺) to enter the axon terminal from the extracellular fluid.

3. Ca²⁺ entry triggers neurotransmitter release.

– Calcium causes synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitters by exocytosis.

4. Neurotransmitter diffuses across the synaptic cleft.

– The chemical messenger moves across the gap to the postsynaptic membrane.

5. Neurotransmitter binds to receptors on the postsynaptic membrane.

– This binding opens ion channels, producing a graded potential (either excitatory or inhibitory).

6. Neurotransmitter effects are terminated.

acetylcholine

involved in control of skeletal muscle actions

stimulates skeletal muscle contraction at neuromuscular junction

Norepinephrine

• creates a sense of feeling good

• low levels may lead to depression

• may excite/inhibit autonomic nervous system actions depending on receptors

dopamine

• creates a sense of feeling good

• deficiency in some brain areas associated with Parkinsons disease

serotonin

• primarily inhibitory

• leads to sleepiness

• actions is blocked by LSD

• enhanced by selective serotonin drugs

Excitatory Post Synaptic Potentials (EPSP)

• depolarizes membrane of postsynaptic neuron

• action potential of postsynaptic neuron becomes more likely

inhibitory postsynaptic potential (IPSP)

• hyperpolarizes membrane of postsynaptic neuron

• action potential of postsynaptic neuron becomes less likely

summation

• EPSPs and IPSPs are added together

• Summation can be temporal (One presynaptic neuron release ntx repeatedly) or spatial