Chapter 12 Bio 251

Nervous system

Nervous system

maintains internal coordination in the body

Central nervous system (CNS)

consists of the brain and spinal cord, which are enclosed and protected by the cranium and vertebral column, It promotes most of the decision-making function of the nervous system

Peripheral Nervous System (PNS)

consists of the rest of the nerves and is composed of nerves and ganglia

Nerve

A bundle of nerve fibers wrapped in fibrous connective tissue

Ganglion

a knot-like swelling in a nerve where the cell bodies of the PNS neurons are concentrated

Two divisions of the PNS

Sensory and Motor

Sensory (afferent) Division

carries signals from various receptors to the CNS. Informs the CNS of stimuli within and around the body

Somatic Sensory Division

carries signals from receptors in the skin, muscles, bones and joints

Parasympathetic division

Part of the ANS, calms the body down, stimulates digestion

Entric Plexus

lines the wall of the digestive tract, is composed of more neurons than the spinal cord, enables different regions of the digestive tract to communicate with each other and coordinate their motility and secretion

Effectors

Cells and organs that carry out signals from motor neurons

Sensory (Afferent) Neurons

are specialized to detect stimuli such as light and heat and transmit information about them to the CNS

Interneurons

lie entirely within the CNS. They receive signals from many other neurons and carry out the processing and storing information in the nervous system, 90% of neurons are these

Motor(efferent) Neurons

Part of the ANS, arouses the body for action

Cell body a.k.a. neurosoma, soma or perikaryon

the control center of the neuron

Entric Plexus

lines the wall of the digestive tract, is composed of more neurons than the spinal cord, enables different regions of the digestive tract to communicate with each other and coordinate their motility and secretion

Properties of Neurons

Excitability, conductivity, and secretion

Sensory (Afferent) Neurons

are specialized to detect stimuli such as light and heat and transmit information about them to the CNS

Interneurons

lie entirely within the CNS. They receive signals from many other neurons and carry out the processing and storing information in the nervous system, 90% of neurons are these

Motor(efferent) Neurons

send signals mostly to muscle and gland cells away from the CNS

Cell body a.k.a. neurosoma, soma or perikaryon

the control center of the neuron

Neurofibrils

bundles of actin filaments which compartmentalize the rough ER

Chromatophilic substance

dark staining regions of the rough ER made of neurofibrils

Neurites

extensions that reach out to other cells

Dendrites

branch-like extensions of a neuron that receive signals from other neurons and transmit them towards the cell body. They play a crucial role in the process of neural communication and information processing in the brain.

Axon hillock

the part that separates the axon from the dendrites

Axon (Nerve Fiber)

processes that conduct impulses away from the cell body and communicate with other neurons via synapses

Axon collaterals

branches near the cell body

Axoplasm

the cytoplasm of the neuron

Axolemma

the cell membrane of the neuron

Terminal Arborization

a term for an extensive complex of fine dendrite branches

Axon Terminal (Terminal Bouton)

forms a synapse within the next cell of a signaling pathway

Multipolar neurons

have one axon and multiple dendrites. This is the most common type and includes most neurons of the brain and spinal cord

Bipolar Neurons

one axon and one dendrite, examples include olfactory nerves

Unipolar neurons

have a single process leading away from the cell body. They carry signals to the spinal cord in sensory neurons such as touch and pain

Anaxonic Nerves

has multiple dendrites but no axons. They communicate locally through dendrites and don’t produce action potentials

Axonal Transport

the two-way passage of proteins, organelles and other materials along an axon

Anterograde transport

Movement away from the cell body

Retrograde Transport

Movement towards the cell body

Neuroglia or Glial Cells

Help protect the neurons and make them function

Oligodendrites

resembles an octopus, creates the myelin sheath in brain and spinal cord

Ependymal Cells

resembles cuboidal epithelium but exhibit root-like processes. Produces Cerebral spinal fluid

Cerebral Spinal Fluid

a liquid that bathes the CNS and fills its integral cavities

Microglia

small macrophages that develop from monocytes, probes the tissue for cellular debris or other problems. They become concentrates in areas damaged by infection, trauma, or stroke

Astrocytes

covers the entire brain surface and most sympathetic neurons in the gray matter. nourishes neurons, forms BBB, promotes formation of synapses and neural circuitry. Form scar tissue to replace damaged nervous tissue

Schwann Cells

envelop axons of the PNS, makes the myelin sheath, also aid in the regeneration of damaged axons

Satellite Cells

surround the nerve cell bodies in ganglia of the PNS. They provide insulation around the cell body and regulate the chemical environment of neurons

Myelin sheath

Consists of spiral layers of insulation around an axon, is formed by Schwann Cells of the PNS and Oligodendrites of the CNS

Myelination

Production of the myelin sheath, begins on the 14th week of fetal development and ends in late adolescence

Neurolemma

Thick outer shell of the myelin sheath

Node of Ranvier or Myelin sheath Gap

The gap in between the myelin sheath

Mitial segment

the short section of an axon between the axon hillock and the first glial cell

Trigger zone

stimulated by the mitial segment, it initiates a nerve signals

Step 1 of Nerve Regeneration

When an axon is cut, the portion distal to the injury can’t survive because it is incapable of protein synthesis. distal portion of Schwann Cells and axon degenerates. Macrophages clean up tissue debris at the point of injury and beyond

Step 2 of Nerve Regeneration

Cell body exhibits abnormalities. The cell body swells, the ER breaks and the nucleus moves off center. The axon stumps sprouts multiple growth processes while the severed distal ends shows degeneration of its axon. Muscle fibers deprives of their nerve supply exhibits shrinkage

Step 3 of Nerve Regeneration

Near the injury, the Schwann cell neurolemma, endoneurium and basal lamina form a regeneration tube. The Schwann cells produce CAM molecules and nerve growth fibers that enable a neuron to regrow to its original destination

Step 4 of Nerve Regeneration

The regeneration tube guides the growing sprout back to the original target cells, reestablishing synaptic content

Step 5 of Nerve Regeneration

When contact is established, the nerve cell body shrinks and returns to its original appearance, and the reinnervated muscles regrow

Electrical Potential

a difference in the concentration of charged particles between one point and another

Current

A flow of charged particles from one point to another.

Polarization

When a neuron has voltage to it

Resting Membrane Potential (RMP)

The charge difference across the plasma membrane

Depolarization

Any such case in which the voltage shifts to a less negative value

Local Potential

A short range change in voltage

Grading

Potentials that vary in magnitude according to the strength of the stimulus

Hyperpolarization

makes the cell membrane more negative

Action Potential

a more dramatic change produced by voltage-gated ions channels in the plasma membrane and only occur where there is a high enough density of voltage-gated channels

Threshold

the minimum voltage needed to open voltage-gated channels

Refractory Period

The period of resistance to restimulation of an action potential

Absolute refractory Period

Lasts from the start of the actional potential until the membrane until the membrane returns to the resting potential

Continuous Conduction

Uninterrupted wave of electrical excitation along the axon

Nerve Signal

a traveling wave of excitation produced by self propagating action potentials

Step 1 of action potential

When the local current arrives at the axon hillock, it’s a polarizes the membrane at that point, and has a steadily rising local potential

Step 2 of action potential

The local potential must rise to a critical voltage of -55 mV which is the minimum needed to open the voltage gated channels.

Step 3 of action potential

The neuron fires, an action, potential, sodium channels, quickly open potassium channels, close more slowly. A positive feedback loop causes the membrane voltage to rise up more rapidly

Step 4 of action potential

As the rising potential pasa, 0 mV, sodium channels become closed in the voltage peaks automatically

Step 5 of action potential

By the time voltage peaks, potassium channels are fully open. Potassium. I am Snow exit the cell. The outflow repolarize the membrane.

Step 6 of Action Potential

Hyperpolarization can occur

Step 7 of Action Potential

Sodium and potassium channels, switch places across the membrane during an action potential. During hyper polarization, the membrane voltage gradually returns to the resting membrane potential because of the sodium diffusion into the cell.

Synapse

The point where an axon terminal meets the next cell in the line

Presynaptic neuron

The place where the signal arrives and releases neurotransmitters

Postsynaptic Neuron

Where the neuron responds to the signals and neurotransmitters of the presynaptic neuron

Electrical Synapses

Where adjacent cells are joined by gap, junctions, and ions, diffuse, directly from one cell into the next. They have quick transmission and synchronizes the activity of local suites of neurons.

Chemical Synapses

Integrate information and make decisions to the communication of neurotransmitters. There are also the site of learning and memory.

Synaptic Cleft

The gap or one neuron meets another

Synaptic Vessicles

The place where neurotransmitters are stored

Active Zone

Places where they are ready to release neurotransmitters on demand

Postsynaptic Density

Receive Neuro transmitters through ion channels and receptors

Acetylcholine

It is in a class by itself. Is form from acetic acid and choline

Amino acids

Nero transmitters, which includes pricing, glutamate, asked, and y-aminobutyric acid

Monoamines

Synthesized from amino acids by the removal of the -COOH group, they retain the -NH2

Catecholamines

It’s a group of mono means, consist of epinephrine, norepinephrine, and dopamine

Purines

Serving as Nero transmitters include adenosine and ATP

Gasses

Nitric oxide and carbon monoxide, they are synthesized as needed, rather than being stored in the synaptic vesicles and diffuse out of the axon terminal

Neuropeptides

chains of 2 to 40 amino acids like cholecystokinin and endorphins. They are stored in secretory granules and can function as hormones

Cholinergenic synapse

Employs acetylcholine as its neurotransmitter

GABA-ergic synapses

Employs GABA as their neurotransmitters

Adrenrgic synapses

Employees transmitters like epinephrine

Synaptic delay

This is the time from the arrival of a single signal at the axon terminal of a parasympathetic cell to the beginning of an action potential in the postsynaptic cell

Excitatory postsynaptic potential

Any voltage that makes some neuron more likely to fire