Exam 2: Chapters 39-41 (Bio2)

Neural signaling

the process by which an animal responds to a stimulus

Neural Signaling Steps:

Reception --> Transmission --> Integration --> Response

Reception (in neural signaling)

performed by neurons and specialized sensory receptors

Transmission (in neural signaling)

sending of a message from one neuron to another; or, from one neuron to a gland or muscle

Integration (in neural signaling)

sorting and interpretation of neural messages & determination of the appropriate response

Response (in neural signaling)

the output or action resulting from the integration of neural messages

Three functional classes of neurons

Afferent neurons

Interneurons

Efferent neurons

Afferent neurons

associate with sensory neurons

transmit stimuli from sensory receptors to interneurons

Interneurons

type of neuron that connect sensory and motor neurons

in the integrating center, process and modify info

Efferent neurons

carry signals indicating a response away from the interneuron to the effectors (muscles or glands) (e.g., motor neuron)

Neuron cell structure

Cell body

Dendrites

Axon

Axon hillock

Axon terminal

Myelin sheath

Node of ranvier

Cell body

contains the nucleus and most organelles

ganglia

Clusters of cell bodies outside the CNS

(eg. dorsal root ganglia)

nuclei

Clusters of cell bodies within the CNS as gray matter

(eg. basal nuclei of the brain)

Dendrites

highly branched structures which receive signals and transmit them toward the cell body

Axon

conducts signals away from the cell body toward another neuron (or an effector)

Axon hillock

axonal segment between the cell body and the axon

Axon terminals

button-like swellings located at the ends of the axons

Neuronal circuit

a typical neural circuit contains an afferent (sensory) neuron, one or more interneurons, and an efferent neuron

in vertebrates, afferent and efferent neurons form the peripheral nervous system (PNS)

interneurons form the central nervous system (CNS), consisting of the brain and spinal cord

Peripheral nervous system (PNS)

made up of afferent and efferent neurons

Central nervous system (CNS)

includes the brain & spinal cord, consists mostly of interneurons

Neural networks

combined neural circuits that interconnect parts of the nervous system

Glial cells (neuroglia)

several types of non-neuronal cells which serve to support the function and survival of neurons (provide nutrition and support)

Astrocytes

located in the vertebrate CNS, covers the surface of blood vessels; physically supports neurons; and, helps maintain ion concentrations of the interstitial fluid

Oligodendrocytes

wraps around CNS axons to form insulating myelin sheaths

Schwann cells

wraps around PNS axons to form insulating myelin sheaths

Synapse

location where a neuron makes a communicating connection with another neuron (or an effector) either via

(a) direct electrical flow; or,

(b) through a chemical neurotransmitter

How many synapses can an individual interneuron form

up to 100,000 synapses

presynaptic cell

The axon terminal which delivers the signal

postsynaptic cell

The dendrite or effector which receives the message

Electrical synapses

the plasma membranes of the pre- and post-synaptic cells are in direct contact

i. Gap junctions allow ions to flow directly between two cells

ii. Allow rapid signal conduction, but difficult to regulate

iii. Egs., cardiac muscle, retina of the eye and pulp of a tooth

Chemical synapse

pre- and post-synaptic cells are separated by a narrow synaptic cleft

i. When an electrical impulse reaches the axon terminal, neurotransmitter is released into the synaptic cleft

ii. Neurotransmitter diffuses across the cleft and binds to a specific receptor in the postsynaptic cell membrane

iii. If enough neurotransmitter binds, the postsynaptic cell generates a new electrical impulse

iiii. Some neurotransmitters are excitatory; while other are inhibitory

Membrane potential

a separation of positive and negative charges across the plasma membrane that produces an electrical potential (voltage)

a. The Na+/K+ pump in the membrane actively removes Na+ from the cytoplasm and brings K+ into the cell

b. Resting membrane potential is produced due to the membrane being more permeable to K+ than to Na+; and, large anionic species being unable to cross the cell membrane

c. Resting membrane potential is -50 to -70mV

Phases of an action potential

threshold

depolarization, repolarization, hyperpolarization

Threshold

for depolarization to occur, the membrane segment must be 10-20mV more positive than resting potential (~55mV)

Depolarization

once threshold is reached, voltage-gated Na+ channels open, and a large amount of Na+ enters causing the cell to depolarize up to +30mV

Repolarization

as Na+ channels are inactivated, K+ channels open allowing K+ to escape the cell and causing the membrane to shift to negative

Hyperpolarization

the K+ channels are slower to fully close which results in more than necessary K+ escaping the cell, and overshooting the resting potential by 10mV to -80mv.

action potential

a series of depolarization events that occur sequentially down the length of an axon.

refractory period

The turning off of Na+ channel activation by inactivation gates creates an absolute refractory period for Na+ channels which keeps the impulse moving forward

(a period when the action potential cant be triggered again)

Nernst-Goldman

equation that can be used to calculate the membrane potential based on the membrane's permeability to specific ions; and, based on the concentration of K+, Na+ and Cl- ions both inside and outside the cell

Tetrodotoxin

Na+ channel blocker which prevents Na+ from entering the cell and keeps the cell more negative than usual (-80mV vs -70mV); the result is typically paralysis

Hyperkalemia

condition in which there is too much K+ in the body which causes the potential to become less negative and makes the neuron more likely to fire (ie., closer to threshold)

The action potential doesn't convey magnitude, instead the:

Strength of a stimulus is based on the frequency of action potentials

(Action potentials are simply on, or off.)

In an unmyelinated axon, the rate of conduction _________ as the diameter of the axon increases

increases

what does myelination do

increases the speed of axon conduction

Saltatory conduction

the mechanism by which myelination permits the “hopping” of action potentials from one Node of Ranvier to another

Voltage-gated Na+ and K+ channels located exclusively at the nodes facilitate saltatory conduction

Process of neurotransmitter release

1. Action potential arrives at an axon terminal of a presynaptic neuron

2. Ca2+ enters the axon terminal

3. Neurotransmitters released by exocytosis

4. Neurotransmitters diffuse across the synapse

5. Neurotransmitters bind to membrane receptors on postsynaptic cell

6. The neurotransmitter stimulates the opening or closing of ligand-gated ion channels

i. Note: ligand is the molecule to which a receptor binds

Neutransmitter

sends information from one neuron to another

a. Some axon terminals release a single type of neurotransmitter; whereas others release several different types

b. Also, excitatory and inhibitory receptors can bind to the same type of neurotransmitter

5 classes of neurotransmitters

1. Acetylcholine

2. monoamines

3. Amino acids

4. Neuropeptides

5. Gaseous neurotransmitters

Acetylcholine

mostly excitatory (eg., neuromuscular junctions)

enables muscle action, learning, and memory

Monoamines (neurotransmitters) include:

dopamine, norepinephrine, serotonin

Norepinephrine

excitatory or inhibitory (eg., CNS interneurons)

helps control alertness and arousal

Dopamine

excitatory (eg., CNS interneurons)

A neurotransmitter associated with movement, attention and learning and the brain's pleasure and reward system.

Serotonin

inhibitory or modulatory (eg., CNS interneurons)

Affects mood, hunger, sleep, and arousal

Selective serotonin reuptake inhibitors

increase serotonin activity in the brain by maintaining levels in the synaptic cleft.

Amino acids (neurotransmitters) include:

Glutamate and GABA

Neuropeptides (neurotransmitters) include:

substance P, endorphins, enkephalins

Gaseous neurotransmitters include:

nitric oxide

Glutamate

A major excitatory neurotransmitter; involved in memory

GABA

inhibitory (many CNS pathways)

Endorphins

inhibitory (modulates pain response)

linked to pain control and to pleasure.

Enkephalins

inhibitory (modulates pain response)

reduce pain

Substance P

excitatory (affects pain perception)

Nitric oxide

modulatory (involved in the PNS)

regulate blood pressure, help immune system

Erectile dysfunction drugs such as Viagra affect this neurotransmitter

Nitric Oxide

Excitatory and Inhibitory pathways

Excitatory pathways produce graded potentials that potentiate an action potential, while inhibitory pathways produce graded potentials that suppress it

Excitatory postsynaptic potential (EPSP)

a change in membrane potential that pushes the neuron closer to threshold

Inhibitory postsynaptic potential (IPSP)

a change in membrane potential which pushes the neuron farther from threshold (hyperpolarizes it)

Two types of summation

temporal and spatial

temporal summation

The process by which multiple excitatory postsynaptic potentials (EPSPs) from a single neuron combine over time to increase the likelihood of reaching the threshold for action potential generation in a postsynaptic neuron.

spatial summation

The process by which multiple synaptic inputs from different locations on a neuron combine to produce a greater postsynaptic potential, leading to increased likelihood of action potential generation.

An IPSP and EPSP of equal strength and near proximity can _________

cancel each other

examples of cnidarians

jellyfish/anemone

examples of echinoderms

starfish

nervous system of cnidarians

- possess nerve net

- No distinctions between dendrites and axons

- Impulses conducted in all directions from the point of stimulus

Nerve net

loose mesh of neurons organized within a radial symmetry

found in cnidarians

nervous system of Echinoderms

Radial Nerves: bundles of axons enclosed in connective tissue

Nerve ring: surrounds a centrally located mouth

Nerves

bundles of axons enclosed in connective tissue

Nerve ring

nervous system of echinoderms; surrounds a centrally located mouth

Platyhelminths examples

flatworms

nervous system of Platyhelminths

- A pair of ganglia (clusters of neurons) at its head-end

- Cephalization: formation of a distinct head region containing a control center

- two or more longitudinal nerve cords (CNS) run the length of the body

- nerve nets serve as the PNS

- Eyespots house photoreceptors which detects changes in light

Cephalization

formation of a distinct head region containing a control center

Arthropods examples

insects

Nervous system of arthropods

- Head region with brain (dorsal and ventral pairs of ganglia)

- Sensory structures such as antennae and complex eyes

- Ventral nerve cord enlarges into a pair of ganglia within each body segment

Mollusca examples

includes cephalopods like octopus

nervous system of Mollusca

- Most cephalization of any invertebrate

- Paired ganglia connected by many nerves

- Octopus possess complex, lobed brains with defined sensory and motor regions

Chordata examples

vertebrates: fish, reptiles, humans, mammals, amphibians

invertebrates: soft bodied marine mammals ect.

(dont need to know all of those, just know what vertebrates are)

Nervous system of chordata

- Vertebrate CNS consists of a brain and spinal cord

- PNS consists of all nerves and ganglia that connect CNS to rest of the body

- Brain and nerve cord are hollow, fluid-filled structures

- Head contains specialized sensory organs connected directly to brain via nerves

In humans, the peripheral nervous system (PNS) is subdivided into:

afferent PNS

efferent PNS

Afferent PNS

transmits sensory information from their receptors

Efferent PNS

carries nerve impulses to effectors

effectors

-produces a response

e.g.muscle contracts to move hand away from stimulus or gland squeezes and releases hormone into blood.

Efferent PNS divided into:

Somatic nervous system (SNS)

Autonomic nervous system (ANS)

Somatic nervous system (SNS)

the part of the peripheral nervous system that controls voluntary movement of skeletal muscles

Autonomic nervous system (ANS)

the part of the peripheral nervous system that controls the glands and the muscles of the internal organs (such as the heart)

Major structures associated with the PNS in vertebrates:

- 31 pairs of spinal nerves

- 12 pairs of cranial nerves

The autonomic nervous system (ANS) controls involuntary processes such as

digestion, sweat gland activation; contraction of smooth muscle

Understand the following diagram

Autonomic neuronal circuits feature

1st preganglionic neuron with cell body located in the CNS

2nd postganglionic neuron which extends from the ganglion to the effector