Chapter 4: The Nervous System Flashcards
Neurons
Transmit electrical impulses and then translates those electrical impulses into chemical signals.
Cell body of a neuron
The cell body (soma) of a neuron contains the cells nucleus, The endoplasmic reticulum, and ribosomes.
Dendrites of a neuron
Appendages emanating from the soma of the cell body of a neuron which receive incoming messages from other cells.
Axon hillock of a neuron
The information received from the dendrites is transmitted through the cell body before it reaches the axon hillock, which integrates the incoming signals.
Action potential of a neuron
The transmission of electrical impulses down the axon.
Axon of a neuron
The axon is a long appendage that terminates in close proximity to a target structure (muscle, gland, another neuron).
Myelin of a neuron
Insulation of most mammalian nerve fibers. Fatty membrane to prevent signal loss or crossing of signals. The myelin sheath maintains the electrical signal within one neuron. Myelin also increases the speed of conduction in the axon.
Production of myelin
Myelin is produced by OLIGODENDROCYTES in the central nervous system and SCHWANN cells in the peripheral nervous system.
Dendro- -dendron mean “TREE”
Nodes of Ranvier (rawn-vee-ay)
Small breaks in the myelin sheath at certain intervals along the axon. Critical for rapid signal conduction.
Nerve terminal (synaptic bouton or knob)
Located at the end of the axon, the structure is enlarged and flattened to maximize transmission of the signal to the next neuron and ensure proper release of neurotransmitters.
Neurotransmitters
Chemicals that transmit information between neurons.
Synaptic cleft
A small space into which the terminal portion of the axon releases neurotransmitters which bind into the dendrites of the adjacent neuron (the postsynaptic neuron). Neurotransmitters released from the axon terminal traverse the synaptic cleft and bind to receptors on the post synaptic neuron.
Synapse
Together, the nerve terminal, synaptic cleft, and postsynaptic membrane are known as the synapse.
Nerve
Multiple neurons bundled together in the peripheral nervous system.
Three kinds of nerves
Sensory, motor, or mixed
Refers to the type or types of information they carry. Mixed nerves carry both sensory and motor information.
Tracts of neurons
In the central nervous system, axons may be bundled together to form tracts. Unlike nerves, TRACTS ONLY CARRY ONE TYPE OF INFORMATION. The cell bodies of neurons in the same tract are grouped into NUCLEI.
Nerve tracts are bundles of nerve fibers that connect the nuclei of the central nervous system
Multiple sclerosis (MS)
A common demyelinating disorder. The myelin of the brain and spinal cord is selectively targeted. The body mounts an immune response against its own myelin, leading to the destruction of its insulating substance called myelin (demyelination).
Because so many different kinds of neurons are demyelinated, patient who have MS experience a wide variety of symptoms, including weakness, lack of balance, vision, problems, and incontinence.
Other cells in the nervous system
Astrocytes: structural support, wound repair, ion regulation
Ependymal cells: form the blood brain barrier
Microglia: mediate immune response in CNS.
Oligodendrocytes (produces myelin in CNS), and Schwann cell (produces myelin PNS).
Glial cell, or neuroglia
Glial cells play both structural and supportive roles. Neurons must be supported by and myelinated by other cells. Most abundant in central nervous system. Oligodendrocytes (myelinate axons of the CNS) and Schwann cells (myelinate axons of the PNS) are considered glial cells.
Astrocytes
Nourish neurons and form and regulate the blood brain barrier.
Ependymal cells
Line the ventricles (each of the four connected fluid-filled cavities in the center of the brain) of the brain that produce cerebrospinal fluid, which physically supports the brain and services a shock of absorber.
Microglia
Phagocytic cells that ingest and breakdown waste products and pathogens in the central nervous system (CNS). Microglia are the primary immune cells of the central nervous system. Macrophages resident in the CNS.
Oligodendrocytes (CNS) and Schwann cells (PNS)
Produce myelin around axons.
Oligodendrocytes are brain cells that produce myelin in the CNS.
Schwann cells are glial cells that support and protect axons of the PNS by creating myelin sheath.
Action potentials
An all or nothing message used to relay electrical impulses down the axon to the synaptic bouton. Ultimately cause the release of neurotransmitters into the synaptic cleft.
Resting membrane potential
Net electric potential different that exist across the cell membrane, created by a movement of charged molecules across the membrane. The inside of the neuron is negative relative to the outside. The two most important ions involved in generating them and maintaining the resting potential or potassium (K+) and sodium (Na+).
Potassium leak channels
Facilitate the OUTWARD movement of potassium across the cell membrane. As potassium continually leaks out of the cell, the cell loses a small amount of positive charge, leaving behind a small amount of negative charge and making the outside of the cell slightly positively charged.
Equilibrium potential of potassium
As potassium leaves the cell, negative charges buildup inside the cell. This eventually causes an equilibrium where potassium is both leaving and entering the cell at the same rate. This is known as the equilibrium potential of potassium.
Sodium leak channels
There is a driving force pushing sodium INTO the cell across sodium leak channels, this causes a buildup of electrical potential.
Resting membrane potential
The balance of the net effect of sodium and potassium equilibrium potentials. Neither Ion is ever able to established its own equilibrium, so both ions continue leaking across the cell membrane.
Na+/K+ ATPase
Enzyme that continually pump sodium and potassium to where they started: potassium into the cell and sodium out of the cell, to maintain the respective gradient. More ATP spent on this enzyme to maintain these gradients than for any other single purpose.
Maintenance of resting membrane potential
Two kinds of input a neuron can receive
Exititory input (excites a neuron to pass on a signal) and inhibitory (work to prevent a neuron from firing) input.
This distinction truly comes at the level of the neurotransmitter receptors.
Excitatory input
Excitatory input causes depolarization and that makes the neuron more likely to fire an action potential. Raises the membrane potential from its resting potential.
Inhibitory input
Causes hyperpolarization that makes the neuron less likely to fire an action potential. Lowers the membrane potential from its resting potential.
GABA (gamma-aminobutyric acid) is a great example of inhibitory input of a neurotransmitter. GABA is a neurotransmitter.
Threshold value
If the axon hillock receives enough excitatory input to be polarized to the threshold value, an action potential will be triggered.
Membrane potential versus time during an action potential
Impulse propagation
For a signal to be conveyed to another neuron, the action potential must travel down the axon and initiate neurotransmitter release.
The synapse
Example of enzymatic removal of a neurotransmitter from the synaptic cleft
Acetylcholesterase will breakdown acetylcholine via enzymatic action.
Reuptake carriers
Neurotransmitter being brought back into the presynaptic neuron. Example being re-uptake of serotonin (5-HT) and norepinephrine (NE).
Major divisions of the nervous system
The spinal cord and it’s four regions
Part of the central nervous system, that extends downward from the brainstem and convey divided into four regions:
Cervical, thoracic, lumbar, and sacral
Consist of white and gray matter.
Pathway of information in a sensory neuron in the spinal cord
The sensory neuron brings information in from the periphery and enter on the dorsal, or back, side of the spinal cord. This information from the sensory neuron runs through the dorsal root ganglia, as the name suggests is in the dorsal side. Motor neurons exit the spinal cord, ventrally, or front side, of the body.
Peripheral nervous system (PNS)
Connect the central nervous system to the rest of the body, and can itself be subdivided into the somatic and autonomic nervous systems. Made up of nerve tissue and fibers outside the brain and spinal cord. 31 pairs of spinal nerves and 10 of the 12 pairs of cranial nerves.
Parasympathetic nervous system role
The main role of the parasympathetic nervous system is to conserve energy. Associated with resting and sleeping states and act to reduce heart rate and constrict the bronchi, manages digestion by increasing peristalsis and exocrine secretions.
ACETYLCHOLINE IS THE NEUROTRANSMITTER RESPONSIBLE FOR PARASYMPATHETIC RESPONSES IN THE BODY AND IS RELEASED BY BOTH PREGANGLIONIC AND POSTGANGLIONIC NERVE NEURONS.
Vagus nerve (cranial nerve x)
Responsible for much of the parasympathetic innervation of the thoracic and abdominal cavity.
Sympathetic nervous system roles.
Activated by stress whether it’s a mild stress or emergency. Closely associated with rage and fear, also known as fighter flight reactions.
Increases heart rate, redistributes blood to muscles of locomotion, increases blood glucose concentration, relaxes the bronchi, decreases digestion and peristalsis, dilates the eyes to maximize light intake, releases epinephrine into the bloodstream.
Monosynaptic reflex arc
There is a single synapse between the sensory neuron that receives the stimulus and the motor on that responds to it.
The classic example is the knee-jerk reflex. When the patellar tendon is stretched, information travels up the sensory (afferent presynaptic) neuron to the spinal cord, where it interfaces with the motor (efferent postsynaptic) neuron that causes contraction of the quadriceps muscle.
