SCB 204 - Lecture Quiz 1

What are the major nervous system functions?

1. Controls perceptions and experiences

2. Directs voluntary movement

3. Forms consciousness, personality, learning, and memory

4. Regulates many aspects of homeostasis (with endocrine system)

What are the anatomical divisions of the nervous system?

1. Central nervous system (CNS)

2. Peripheral nervous system (PNS)

What is the central nervous system composed of?

Brain and spinal cord

What is the peripheral nervous system composed of?

Nerves

What are the functional divisions of the nervous system?

1. Sensory functions

2. Integrative functions

3. Motor functions

What is the peripheral nervous system divided into?

1. Sensory (afferent) division

2. Motor (efferent) division

What does afferent mean?

Carrying toward

What detects information (sensory stimuli) in the sensory (afferent) division?

Sensory receptors

What does somatic mean?

Body

What does the somatic sensory division consist of?

• Neurons carry signals from skeletal muscles, bones, joints, and skin

• Special sensory neurons that transmit signals from the organs of vision, hearing, taste, smell, and balance

What does visceral mean?

Organs

What does efferent mean?

Carrying away

What is the somatic motor division also known as?

Voluntary motor division

What is the visceral motor division also known as?

Involuntary motor division or autonomic nervous system (ANS)

What is the histology of the nervous system?

Mostly nervous tissue with epithelial and connective tissue

What are neurons?

A type of excitable cells responsible for sending and receiving signals

What do neurons consist of?

1. Cell body

2. Dendrites

3. Axon

What are the functions of dendrites and axons?

Allow communication with other cells

Which direction is retrograde axonal transport?

Toward the cell body

Which direction is antegrade axonal transport?

Away from the cell body

What are the functional regions of neurons?

• Receptive - Receive signals

• Conducting - Propagate signals

• Secretory - Secret chemicals

How are neurons structurally classified?

1. Multipolar

2. Bipolar

3. Pseudounipolar

What processes do axons split into?

1. Peripheral axon

2. Central axon

What are the functional classifications of neurons?

Based on the direction information is carried

• Sensory neurons

• Association neurons

• Motor neurons

What are the neuronal components?

• Nuclei

• Ganglia

• Tracts

• Nerves

What are the functions of neuroglia?

• Maintaining environment around neurons

• Protecting neurons

• Assisting in proper functioning of neurons

Neuroglia retain the ability to divide …

• Unlike neurons

• Fill in the gaps left by dying neurons

What are the 4 types of neuroglia in the central nervous system?

1. Astrocytes

2. Ogliodendrocyres

3. Microglia

4. Ependymal cells

What are the 2 types of neuroglia found in the peripheral nervous system?

1. Schwann cells

2. Satellite cells

What is the function of schwann cells?

Myelinate certain axons in the PNS

What is the function of satellite cells?

Surround and support cell bodies

What produces myelin sheaths?

Oligodendrocytes (CNS) and schwann cells (PNS)

What are the 2 main classes of ion channels?

1. Leak channels

2. Gated channels

What is the stimulus for opening/closing a leak channel?

None, always open

What are the 3 types of gated channels?

1. Ligand-gated channels

2. Voltage-gated channels

3. Mechanically gated channels

What is the stimulus for opening/closing a ligand-gated channel?

Binding of a ligand (chemical) to a channel receptor

What is the stimulus for opening/closing a voltage-gated channel?

Voltage charges across the plasma membrane

What is the stimulus for opening/closing a mechanically gated channel?

Mechanical deformations of the channel (by stretch, pressure, etc.)

What is the resting membrane potential?

• Forms from separation of charges across a membrane

• Potential is called a voltage and is a type of electrical gradient

• The electrical gradient across the cell membrane is the membrane potential (Vm)

• Voltage of inner membrane is negative relative to outer membrane

• Negative voltage is present when cell is at rest and called resting membrane potential

• Cell is polarized in this state

What determines the diffusion of ions (electrochemical gradients)?

1. Concentration gradient

2. Electrical gradient (membrane potential)

What are the changes in membrane potential?

• Depolarization

• Repolarization

• Hyperpolarization

What are local potentials also known as?

Graded potentials

What are local or graded potentials?

• Small local changes in the membrane potential of a dendrite or cell body

• May be depolarizing or hyperpolarizing

What are the types of local potentials?

• Graded - Some produce a larger change in membrane potential than others

• Reversible - When the stimulus that caused the ion channels to open stops, the neurons return to resting potential

• Decremental - The change in membrane potential is small and the current generated is lost across the membrane over short distance

What are action potentials?

The uniform, rapid depolarization and depolarization of the membrane potential

• Change in membrane potential causes a response (action)

What are nervous system action potentials generated by and sent along?

Generated by a trigger zone and sent along axons to another neuron, muscle fiber or gland

What are the 3 general phases (events) of an action potential?

1. Depolarization

2. Repolarization

3. Hyperpolarization

What is the refractory period?

Neurons are limited to how often they can fire action potentials

What is the refractory period divided into?

1. Absolute refractory period

2. Relative refractory period

What are the differences between local and action potentials?

Local

• Graded

• Reversible

• Decremental

Action

• Not graded (uniform)

• Irreversible

• Non-decremental

What is propagation of action potentials?

• Must be propagated along the axon

• Movement creates a flow of charged particles or current

• Action potentials are self-propagating

• Propagation occurs in one direction

• Propagation forms the nerve impulse

What is conduction speed (the rate of propagation) determined by?

1. Diameter of axon

2. Presence or absence of myelin sheath

What are the 3 main classes of axons by conduction speed?

A, B, and C

What are neuronal synapses?

Structure that neurons use to communicate with other neurons

What are the 3 types of neuronal synapses?

1. Axodendritic

2. Axosomatic

3. Axoaxonic

How do axodendritic synapses occur?

As neuronal synapses (connections) between an axon and a dendrite

How do axosomatic synapses occur?

As synapses (connections) between an axon and a cell body

How do axoaxonic synapses occur?

As synapses (connections) between an axon and another axon

What do presynaptic neurons do?

Send messages from its axon

What do postsynaptic neurons do?

Receive messages from its dendrite, cell body, or axon

What are the major differences between the neuromuscular junction and neuronal synapses?

Neuromuscular junction

• Muscle fiber receives input from a single axon

• Only acetylcholine excites muscle fiber

• Action potential in neuron triggers an action potential in a muscle fiber

Neuronal synapses

• Neurons may receive input from thousands of axons

• Several neurotransmitters may excite or inhibit postsynaptic neuron

• A postsynaptic neuron may require input of 100 or more pre-synaptic neurons

What is synaptic transmission?

The transfer of chemical or electrical signals between neurons at a synapse

What are the 2 types of neuronal synapses?

1. Electrical

2. Chemical

What is the function of electrical synapses?

Programmed behaviors (breathing)

What is the majority type of synapses in the nervous system?

Chemical synapses

What are the characteristics of chemical synapses?

• Unidirevtional

• Chemical signal

• Synaptic delay

How are the receptors of chemical synapses linked to ion channels?

Directly or indirectly

What are the events at a chemical synapse?

1. Action potential in presynaptic neuron triggers Ca2+ channels in axon terminals to open

2. Influx of Ca2+ causes synaptic vesicles to release neurotransmitters in the synaptic cleft

3. Neurotransmitters bind to receptors on the postsynaptic neuron

4. Ion channels open leading to a local potential and possibly an action potential

What are the 3 ways to stop (terminate) a synaptic transmission so response can be stimulated again?

1. Diffusion and absorption of the neurotransmitter - Neurotransmitters diffuse away from the synaptic cleft and are returned to the presynaptic neuron

2. Degradation in the synaptic cleft - Neurotransmitters are degraded by enzymatic reactions in the synaptic cleft

3. Reuptake into the presynaptic neuron - Neurotransmitters are taken back into the presynaptic neuron

What are metabotropic receptors?

• Most interact through intracellular enzymes called G-proteins that form a 2nd messenger that opens/closes a channel

• Longer lasting and more variable than ionotropic receptors

What are the 4 groups of neurotransmitter?

1. Acetylcholine (ACh)

2. Biogenic amines (monoamines)

3. Amino acid neurotransmitters

4. Neuropeptides

What are acetylcholine neurotransmitters?

• Found in cholinergic synapses

• Mostly excitatory

• Degraded by acetylcholinesterase into acetic acid and cholin

What are some examples of biogenic amines (monoamines)?

• Catecholamines - Norepinephrine, epinephrine, and dopamine (from tyrosine) and excitatory and inhibitory

• Serotonin - From tryptophan and involved in mood regulation

• Histamine - From histidine and has diverse functions

What are some examples of amino acid neurotransmitters?

• Glutamate - Excitatory, opens a Na+ or Ca++ channel to produce EPSPs

• Glycine - Inhibitory, opens Cl- channels to produce IPSPs

• Y-aminobutyric acid - Inhibitory, opens Cl- channels to produce IPSPs

What are some examples of neuropeptides?

• Substance P - functions in pain and temperature

• Opioids - Depressants including endorphins, enkephalins, and dynorphins for pain relief

• Neuropeptide Y - Involved in feeding behaviors

What are postsynaptic potentials?

Local potentials in post synaptic membrane

How does the membrane potential of the postsynaptic neuron move in EPSPs?

Closer to the threshold

What happens when ion channels open in an EPSP?

Leads to a local potential and possibly an action potential

How does the membrane potential of the postsynaptic neuron move in IPSPs?

A small hyperpolarization moves it away from the threshold

What are the steps of synaptic transmission?

1. Action potential - An action potential reaches the axon terminal of the presynaptic neuron

2. Synaptic transmission - Ca2+ channels open in the presynaptic neuron; neurotransmitters are released from synaptic vesicles and bind to receptors on the postsynaptic neuron

3. Postsynaptic potentials - Neurotransmitters trigger and EPSP/IPSP moving the membrane potential of the postsynaptic neuron either closer to or farther from the threshold

4. Termination of synaptic transmission - Neurotransmitter concentration in the synaptic cleft decreases and synaptic transmission is terminated

What is neural integration?

A postsynaptic neuron evaluates all the information

What are the 2 types of summation?

1. Temporal summation

2. Spatial summation

How must EPSPs occur for summation to occur?

In rapid succession which brings the trigger zone to threshold

What occurs in spatial summation?

Simultaneous EPSPs from multiple neurons bring the trigger zone to threshold

What are the functional groups of neurons?

• Neuronal pools - networks that perform a common function

• Neural circuits - Functional groups of which neuronal pools are organized

What are the 2 basic types of neural circuits?

1. Diverging

2. Converging

What are the 2 types of diverging circuits?

1. Amplifying circuits - Input neuron in the brain sends signals to multiple muscle fibers

2. Multiple tracts - Input neuron in the spinal cord sends signals to different parts of the brain

What are multiple tracts?

Characteristics of sensory information sent from spinal cord neurons to different neuronal pools in the brain

What are converging circuits?

• The opposite of a diverging circuit

• Multiple input neurons from sensory receptors converge onto a neuron in the brain