The Nervous System Flashcards
Neuron Anatomical Terms
Soma; dendrite; axon hillock; axon; myelin sheath, nodes of Ranvier; axon terminal
Soma (Cell body)
The “cell body” of a neuron and is the location of the nucleus, ER, and ribosomes.
Dendrite
The appendages emanating directly from the soma. Receives incoming messages from other cells, which is then transmitted to the cell body.
Axon Hillock
Portion of the axon which integrates incoming signals from the cell body and transmits action potentials (electrical impulses) down the axon.
Axon
The long appendage emanating directly from the cell body which terminates in close proximity to target structures (e.g. muscles, glands, other neurons etc…). Responsible for directing action potentials (electrical impulses) away from the cell body.
Myelin Sheath
The layer of dielectric (electrically insulating) material that encapsulates the axon of the neuron. Responsible for:
- preventing signal loss or crossing of signals
- electrical signal maintenance
- increasing speed of conduction
Note:
- produced by oligodendrocytes in CNS
- produced by Schwann cells in PNS
Nodes of Ranvier
Small breaks in the myelin sheath that are uninsulated and, therefore, are capable of generating electrical activity.
Axon Terminal (Synaptic Bouton)
The enlarged and flattened terminus of the axon responsible for maximizing neurotransmission to the next neuron and ensure proper release of neurotransmitters.
Neurotransmitters
The endogenous chemicals that transmit signals across a synapse from one neuron to another target neuron. They are released from synaptic vesicles in synapses into the synaptic cleft, where they are received by receptors on other synapses.
Synthesized from simple precursors such as amino acids
Synaptic Cleft
The small space that exists between two neurons. It is here that the terminal axon of the presynaptic neuron releases neurotransmitters which bind to the dendrites of the postsynaptic neuron. If the neuron signals to a gland or muscle, rather than a neuron, the postsynaptic cell is termed an effector.
Synapse
The process by which neurotransmitters released from the axon terminal of a presynaptic neuron transverse the synaptic cleft and bind to the dendrites of the postsynaptic neuron.
Neurons
Specialized cells capable of transmitting and translating electrical impulses into chemical signals.
Nerves
Bundles of neurons located in the PNS. Nerves may be sensory, motor or mixed, which refers to the types of information they carry. Cell bodies of neurons of the same type are clustered together into ganglia.
Tracts
Bundles of neurons found in the CNS. Unlike nerves, tracts only carry one type of information. Cell bodies of neurons in the same tract are grouped into nuclei.
Astrocytes
Nourish neurons and form the blood-brain barrier, which controls the transmission of solutes from the bloodstream into the nervous tissue
Ependymal Cells
Line the ventricles of the brain and produce cerebrospinal fluid, which physically supports the brain and serves as a shock absorber
Microglia
Phagocytic cells that ingest and break down waste products and pathogens in the CNS
Resting Membrane Potential
The Na+/K+ ATPase pump maintains a resting membrane potential of -70 mV by moving 3
Na+ ions out of the cell for every 2 K+ ions moved into the cell.
Excitatory Input
Causes depolarization, a process that occurs when the voltage-gated Na+ channels open, allowing Na+ to rush into the cell. This process makes the neuron more likely to fire an action potential.
Inhibitory Input
Causes hyperpolarization, the process that occurs when voltage-gated K+ channels open, allowing K+ to rush out of the cell while allowing Cl- to rush into the cell via Cl- channels. This process makes the neuron less likely to fire an action potential.
Internal vs. External Environment of Neuron
Internal: [K+] > [Na+]; net negative charge
External: [K+]
Threshold Value of Action Potential
-55 mV to -40 mV; occurs when the cell is depolarized to trigger an action potential
Temporal Summation
The addition of multiple signals near each other in TIME.
Spatial Summation
The addition of multiple signals near each other in SPACE.
Refractory Period
Following hyperpolarization of an axon. A period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation. There are two types:
- absolute refractory period
- relative refractory period
Absolute Refractory Period
No amount of stimulation can cause another action potential to occur.
Relative Refractory Period
There must be a greater than normal stimulation to cause an action potential because the membrane is starting from a potential that is more negative than its resting value.
Release of Neurotransmitters at Synaptic Cleft
Once an action potential reaches a nerve terminal, voltage gated Cl- channels open, allowing calcium to flow into the cell. Sudden increase of intracellular calcium triggers fusion of membrane-bound vesicles containing neurotransmitters with the cell membrane at the synapse, causing exocytosis of neurotransmitters
Electrical vs Chemical Transmission
Electrical: Within a neuron, electricity is used to pass signals down the length of the axon.
Chemical: Between neurons, chemicals (neurotransmitters) are used to pass signals to subsequent neurons, glands, or muscles.
Regulation of Neurotransmission
Neurotransmitters must be removed from the synaptic cleft. Three mechanism exist:
- breakdown of neurotransmitters by an enzyme
- reuptake of neurotransmitters into presynaptic neuron via reuptake carriers
- diffusion of neurotransmitters out of synaptic cleft
Name the 3 kinds of neurons in the nervous system.
- Sensory Neurons (afferent)
- Motor Neurons (efferent)
- Interneurons
Sensory (Afferent) Neurons
Transmit sensory information from receptors to the spinal cord and brain. Thus afferent means ascend in the spinal cord.
Motor (Efferent) Neurons
Transmit motor information from the brain and spinal cord to muscles and glands. This efferent means exit the spinal cord to the rest of the body.
Interneurons
Found between other sensory and motor neurons and are the most predominant. Located primarily in the brain and spinal cord and are often linked to reflexive behavior
Division of the Nervous System
CNS:
- > brain
- > spinal cord
PNS:
- > somatic
- > autonomic -> sympathetic; parasympathetic
Central Nervous System (CNS)
Composed of the brain and spinal cord.
- the brain consists of white and grey matter
- the spinal cord extends downward from the brainstem and is divided into four divisions: cervical, thoracic, lumbar, and sacral
White Matter
Portion of the brain that consists of myelin sheaths. Lies inside grey matter.
Grey Matter
Portion of the brain that consists of unmyelinated cell bodies and dendrites. Lies outside of the white matter.
Peripheral Nervous System (PNS)
Composed of nerve tissue and fibers outside the brain and spinal cord. The PNS thus connects the CNS to the rest of the body and can itself be subdivided into the somatic and autonomic nervous systems.
Somatic Nervous System
Subdivision of the PNS and consists of sensory and motor neurons distributed throughout the skin, joints and muscles.
Note:
- sensory neurons transmit through afferent fibers
- motor neurons transmits through efferent fibers
Autonomic Nervous System (ANS)
Subdivision of the PNS that regulates heartbeat, respiration, digestion, and glandular secretions. ANS manages the invite Gary muscles associated with many internal organs and glands.
Mnemonic: Autonomic means automatic means independent of conscious control
How do neurons interconnect the CNS and PNS?
Interconnection via preganglionic and postganglionic neurons. The soma of the preganglionic neuron is in the CNS, and its axon travels to a ganglion in the PNS. Here it synapses on the cell body of the postganglionic neuron, which affects the target tissue.
Parasympathetic Nervous System
“Rest-and-digest” through conservation of energy. Associated with rest and sleep cycles and responsible for:
- constricting pupils and bronchi
- stimulating saliva, peristalsis, exocrine secretion, and bile release
- slowing heart rate
- contracting bladder
Sympathetic Nervous System
“Fight-or-flight” via energy consumption. Activated by stress and associated with fear and anger. Responsible for:
- increasing heart rate and blood glucose concentration
- redistribution of blood to muscles
- dilation of bronchi and pupils
- decreasing digestion and peristalsis
- release of epinephrine into bloodstream
Reflex Arcs
Control reflex behavior. Utilize the ability of interneurons in the spinal cord to relay information to the source of stimuli while simultaneously routing it to the brain. There are two types of reflex arches:
- Monosynaptic Reflex Arch
- Polysynaptic Reflex Arch
Monosynaptic Reflex Arch
The sensory (afferent, presynaptic) neuron fires directly onto the motor (efferent, postsynaptic) neuron.
Polysynaptic Reflex Arch
The sensory neuron may fire onto a motor neuron as well as interneurons that fire onto other motor neurons.
