BIO 140 ch 17-19

Dendrite

"Branch of" Branchlike parts of a neuron that are specialized to receive information.

Compare/Contrast:

------------------

Characteristics of:

-----------------------------------------

How do neurons work?

1. Neuron receives stimulus at dendrites 2. electrical signal gets sent from the dendrites through the axon to the axon terminal 3. Neurotransmitters get released into the synapse (space/gap between cells) 4. the NT diffuse across the synapse and bind to receptors on the dendrites of the next neuron, stimulating an action potential or nerve impulse along its axon

Sequence and direction of action potential within the neuron

1. Stimulus-gated Na+ (sodium) channels open. 2. Voltage-gated Na* channels open when the threshold is reached. As more Na+ enters through the channels, the membrane DEPOLARIZES further 3. At +30 mV (PEAK) voltage-gated Na+ channels close 4. REPOLARIZATION begins with voltage-gated K+ (potassium) channels open. allows OUTWARD diffusion of K+ 5. brief period HYPERPOLARIZATION, resting potential is restored by the sodium-potassium pump and ion channels to their resting state sodium channels (Na+) allow ions to ENTER the cell (outside) potassium channels (K+) allow ions to LEAVE the cell (inside)

Results of an impulse reaching a synapse

= Electrical - continues through to connecting cell by gap junction. Chemical - action potential activates neurotransmitters to release from synaptic knob, which cross the synaptic cleft and bring a response by the post synaptic neuron. Excitatory (depolarize), Inhibitory (hyperpolarize)

First primary effect of a stimulus on a neuron

??

Reflex arc actions

A signal conduction route to and from the CNS. Most common is the three neuron arch. Feed back loop!!!

Relative vs. absolute refractory periods

Absolute Refractory period - 0.5 ms after membrane surpasses the threshold potential, it will not respond to any stimulus, no matter how strong. Relative refractory period - few ms after absolute refractory period- when membrane is repolarizing and restoring the resting membrane potential. Membrane will respond to very strong stimuli.

Afferent vs. efferent fibers

Afferent vs. efferent fibers Afferent (sensory) fibers transmit nerve impulses to the spinal cord or brain. Efferent (motor) fibers transmit nerve impulses away from the brain or spinal cord. Toward muscles or glands.

Where neurotransmitters bind

After release into the synaptic cleft, neurotransmitters interact with receptor proteins on the membrane of the postsynaptic cell, causing ionic channels on the membrane to either open or close. When these channels open, depolarization occurs, resulting in the initiation of another action potential

Nervous system organization & major divisions

CNS, PNS, Afferent, Efferent, SNS, ANS, Sympathetic, Parasympathetic, Visceral

ANS effectors

Carry information to the autonomic nervous system or visceral effectors which are mainly involuntary tissues.

Main chemical classes of neurotransmitters

Class I: Acetylcholine Class II: Amines - (serotonin, histamine, dopamine, norepinephrine) Class III: Amino Acids - (glutamate, GABA, glycine) Class IV: other small molecules ex: Nitric Oxide (NO), ATP and Adenosine

Major functions of muscles

Contractility - Shorten/contract which allows muscle tissue to pull bones and create movement.

Pathway for impulse conduction in a neuron

Convergence: more than one presynaptic axon synapses with a single postsynaptic neuron (funneled into a single pathway) Divergence: single presynaptic axon synapses with MANY DIFFERENT postsynaptic neurons (allow one pathway to be split or copied and sent to different destinations.

Endoneurium

Delicate layer of reticular fibrous connective tissue

Sequence of transmission of an electrical impulse through a neuron: (D-SAINTS) 1. ___ 2. SOMA 3. AXON HILLOCK 4. __ 5. NODE OF RANVIER 6. TERMINAL ARBORIZATION 7. __ Dendrites, Internodes, synaptic knobs

Dendrites, Internodes, synaptic knobs

The role of dendrites

Distal end of dendrites or sensory neurons can receive stimuli from the intiating nerve signals. Some have dendritic spines which serve as connection points for other neurons.

Excitatory vs. inhibitory neurotransmitters

Excitation when a stimulus triggers the opening of additional Na+ channels, allowing the membrane potential to move toward zero (depolarization) Inhibition when a stimulus triggers the opening of additional K+ channels, increasing the membrane potential (hyperpolarization)

Schwann cell

Found in the PNS ( *comedic drum snare*) support nerve fibers and sometimes form the myelin sheath around them. Can also be a type of cell called "Satellite Cell"

Nodes of Ranvier

Gaps in the myelin sheath of the axons of peripheral neruons. Action potentials can 'jump' from node to node, thus increasing the speed of conduction (saltatory conduction).

Ependymal cell

Glial cell which lines fluid filled (ventricle) cavities of brain and spinal cord.

Functional regions (zones) of neuron

Input -dendrites and cell body; Summation - axon hillock; Conduction - axon; Output - telodendria and synaptic knobs

Synaptic knob & its location

Located at the end of a branch. It is the knob , the cleft then the plasma membrane.

Neuron damage and repair

Mature neurons are incapable of cell division; limited capacity to repair; if cell body and neurilemma intact it can repair 1) Distal portion of axon degenerates 2)Macrophages clean debris 3) Remaining Schwann Cells (neurolemna) for pathway from injury point to effector. 4) New Schwann cells are products by mitotic division within this tunnel maintaining a path for regrowth to axon

Unipolar vs. multipolar neurons

Multipolar neurons have only one axon but several dendrites. Most neurons in the brain and spinal cord. Unipolar neurons have a single process extending from the cell body which branches to form a central process (to CNS) and peripheral process (away from CNS) These form an axon.

Acetylcholine

Neurotransmitter in a class of its own. Created by neurons combining Acetate and choline. Can bind to synaptic receptors ( related to acetylcholesterase?) Can be excitatory (Skeletal muscle) or inhibatory (neuromuscular junctions of cardiac muscle)

Polarization vs. depolarization vs. hyperpolarization

Polarized membrane -a membrane that exhibits a membrane potential Depolarized membrane -Excitation when a stimulus triggers the opening of additional Na+ channels, allowing the membrane potential to move toward zero (depolarization) Hyperpolarized membrane -Inhibition when a stimulus triggers the opening of additional K+ channels, increasing the membrane potential (hyperpolarization)

Primary functions of the nervous system

Provides a means to control and integrate many different functions performed by tissues , organs and cells with in the body it also unifies body functions. Made of brain/spinal cord/nerves.

Saltatory conduction

Saltatory conduction (from the Latin saltare, to hop or leap) is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials.

Formation of the myelin sheath

Schwann cell (made up of mostly phospholipid myelin); densely wraps around axon (peripheral nerve fiber) to form a thick myelin sheath. outer layer- cytoplasm (called neurilemma); extension of OLIGODENDROCYTES also wrap around axons to form myelin sheaths

Sensory vs. motor neurons

Sensory (afferent) neurons transmit nerve impulses to the spinal cord or brain. Motor (efferent) neurons transmit nerve impulses away from the brain or spinal cord. Toward muscles or glands.

Types of Neurons

Sensory - carries signals for sense organs to CNS Motor - carries signals from CNS to muscles and glands Interneuron - connects sensory and motor neurons

Microglia

Small usually stationary cells found in the CNS. These usually enlarge and carry on phagocytosis when brain tissue is inflammed or degenerating.

Oligodendrocyte

Smaller astrocytes with fewer processes " Cell with few branches" . Clustered around nerve cell or in rows between nerve fibers in the brain/spinal column. The hold nerve fibers together and produce parts of the fatty myelin sheath.

Type of muscle tissue without T-tubules

Smooth

Spatial vs. temporal summation

Spatial summation - the sum of the local potential teaches the threshold potential, voltage-gated channels in the axon membrane open, producing an action potential. Temporal Summation - when synaptic knobs stimulate a postsynaptic neuron in rapid succession, their effects can add up over a brief period of time to produce an action potential.

Astrocyte

Star shaped glia cell found only in the CNS. They are the LARGEST and MOST ABUNDANT type. Long points extend through brain tissue attach to both neurons and capillaries of the brain.

Axon hillock

The axon hillock is a specialized part of the cell body (or soma) of a neuron that connects to the axon. The axon hillock is the last site in the soma where membrane potentials propagated from synaptic inputs are summated before being transmitted to the axon. Acts as the summation zone by adding nerve impulse arriving from the cell body.

Cell body

The largest part of a nerve cell containing a nucleus , cytoplasm and various organelles. AKA "perikaryon" which means surrounding the nucleus.

Acetylcholine

The neurotransmitters secreted at the motor end plates of skeletal muscles

Sarcolemma

The plasma membrane of a muscle fiber

Quantity of glia cells vs. neurons

There are more glia cells than neurons. Glia cells surround neurons and have various roles supporting neuron functions. Glia 900 billion. Neurons 100 billion in brain.

Synaptic knobs

Tiny bulge at the end of a branch terminal or presynaptic neuron axon. contains many small sacs with neurotransmitter molecules which are released into the synaptic cleft (between knob and plasma membrane of neuron)

The sequence of cross bridge formation and myofilament movement will be repeated as long as calcium ions are present (T/F)

True

When cross bridge form and the muscle fibers contract, the actin myofilament slides past the myosin myofilament (T/F)

True

Neuromuscular junction and its components 1) The motor end plate makes up part of the

Type of connection called a synapses, and is characterized by a narrow gap, or synaptic cleft, across which neurotransmitter molecules transmit signals; Synaptic knob, Synaptic cleft, Synaptic vesicle, Junctional folds, Acetylcholine (ACh), ACh receptor, Acetylcholinesterase (AChE) 1) Neuromuscular junction

Characteristics of cardiac muscle

Wall of heart, pumps blood, involuntary, striated, nucleus-single (sometimes double) near center of the cell, sarcoplasmic reticulum- less extensive than in skeletal muscle, intercalated disks (gap junctions and desmosomes), contraction style-syncytium of fibers compress the heart chambers in slow, separate contractions-autorhythmically????????

Single unit and multiunit smooth muscle

Where is single unit smooth muscle tissue found? -- Visceral organs, esp. digestive tract - Acts as single unit (all contract together) Where is multi-unit smooth muscle tissue found? - Eyes (pupils); blood vessels - Act as multiple units (contract separately)

Gray matter vs. white matter

White matter - bundles of myelinated fibers of the nervous system. PNS - myelinated nerves CNS - myelinated tracts. Grey matter- cell bodies and unmyelinated fibers.

Myelin

a fatty substance that helps insulate neurons and speeds the transmission of nerve impulses

Neurofibrils

a fibril in the cytoplasm of a nerve cell, visible by light microscopy ????

Location of interneurons

a neuron that transmits impulses between other neurons, especially as part of a reflex . Can be excitatory or inhibatory?

Interneuron

a neuron that transmits impulses between other neurons, especially as part of a reflex arc

Syncytium

a single cell or cytoplasmic mass containing several nuclei, formed by fusion of cells or by division of nuclei.

Axon

a single process extending from the axon hillock. Conducts nerve impulses away from cell body. Distal ends are synaptic knobs.

Local potential

a small change in the resting membrane potential of a neuron caused by a stimulus that opens a ligand-regulated sodium gate in the membrane of a neuron.

Muscle irritability

aka excitability; the ability of muscle cells to respond to nerve stimuli; (neuromusclular junction)

Treppe 1) During which phase of the twitch contraction is there a triggering of the release of calcium ions into the sarcoplasm?

aka the staircase phenomenon; it's a gradual, steplike increase in the strength of contraction that can be observed in a serious of twitch contractions that occur about 1 second apart. Three distinct phases 1) the latent period 2) the contraction phase 3) the relaxation phase 1) Latent phase

Chief function of T-tubules

allow for electrical signals to move deeper into the cell used for calcium delivery, in SKELETAL and CARDIAC muscle; tubules extend transversely across the sarcoplasm or tunnels into muscle cells

Contralateral vs. ipsilateral reflex arcs

arcs lie between interneuron synaptic knobs and motor neuron dendrites. The receptors and effectors are located on the same side of the body. Contralateral receptors and effectors are located on the opposite sides of the body. Ipsi - Receptors/Effectors same side contra-Receptor and Effector are on opposite sides

Ions required for cross-bridging

calcium ions

Pathways of the ANS

consists of motor neurons that control smooth muscles, cardiac muscles, and glands. Sympathetic-prepares body to deal with immediate threats "fight or flight" parasympathetic- coordinates the bodies normal resting activities aka rest and repair division

The human nervous system

coordinates body's responses to internal and external stimuli/changes - stimulus: anything that causes a response Central nervous system - Brain - Spinal Cord Peripheral nervous system - sensory pathways OR motor pathways (somatic/voluntary or autonomic/involuntary) in autonomic: sympathetic division: arousal + energy production "fight or flight" parasympathetic division: calming + back to maintenance "rest and digest"

Neurons

electrically excitable cell that receives, processes, and transmits information through electrical and chemical signals. These signals between neurons occur via specialized connections called synapses. Neurons can connect to each other to form neural networks. - Cell body (soma) contains the nucleus; most of the metabolic activities of the cell take place in the cell body -Dendrites - receive messages from the environment or from other neurons - Axons - carries messages away from the cell body -Axon terminals - release neurotransmitters (little chemicals) which send messages to the next cell Myelin sheath (Schwann cell) - insulating membrane surrounding the axon. increases speed of impulses - Nodes of Ranvier - gaps between myelin sheaths

Influences on the strength of muscle contraction

force of contraction depends on number of cross bridges attached

Components of the BBB

helps maintain the environment of the brain. Formed by Astrocytes wrapping their "feet" around the capillary wall. Can help regulate ion flow in and out of blood. Large molecules that are may cross slowly or not at all while small molecules can ( O2 , Co2 , water )

Trigger for opening stimulus-gated channels

ion channels that open in response to a sensory stimulus or a chemical stimulus from another neuron. Many located in the membrane of the neurons input zone - dendrites and soma. (Na+, K+,)

Mobilizing contractions Most body movements are ? contractions A contraction in which the tension within the muscle remains the same, but the length changes is called a/n ? contraction

is an ISOTONIC contraction; because it causes the body to move. Aka dynamic tension due to the fact the muscle is moving.

Stimulus effects & phases of action potential

nervous system uses the frequency of nerve impulses to code for the strength of a stimulus - not changes in the magnitude of the action potential

Relative sizes and quantities of neuroglia

neuroglia aka "glia" meaning "glue"-Smaller in size and darker-staining nuclei, Make up about half the mass of the brain; How much do neuroglia outnumber neurons? relatively same number of each but some areas have a 4:1 ratio or 11:1 ratio.

Type of nervous tissue dedicated to muscles

neuromuscular tissue

Reflex arc ( 2 and 3 neurons)

neuron patterns. A signal conduction route to and from the CNS. Most common is the three neuron arch. Feed back loop!!! 2 neuron-arc = afferent and efferent 3 neuron arc = feedback loop (most common)

Synapse

place where signals are transmitted from on neuron, called PRESYNAPTIC NEURON, to another neuron, called the POSTSYNAPTIC NEURON

Major components of a synapse

place where signals are transmitted from one neuron, called PRESYNAPTIC NEURON, to another neuron, called the POSTSYNAPTIC NEURON

Neuron external charges & internal charges

positive charge - outside the membrane negative charge - inside the membrane

Type of muscle tissue responsible for peristalsis

single unit smooth

Isotonic vs. isometric contractions

skeletal muscle contractions are either isometric, in which the muscle does not change its length, or isotonic, in which the muscle changes its length without increasing tension. ... Once the load is exceeded, contraction can then be used to shorten the muscle and move the load.

Graded strength principle

skeletal muscles contracting with varying degrees of strength at differnet times.

Impulse conduction with & without nodes of Ranvier

with nodes - Leap, move faster. Without nodes, slower