Biology: Chapter 4 Flashcards
Neurons
specialized cells capable of transmitting electrical impulses and then translating these electrical impulses into chemical signals
Soma
-cell body
-Nucleus is located here as well as endoplasmic reticulum and ribosomes
Dendrites
-appendages emanating directly from the soma
-Receive incoming messages from other cells
-The information received from the dendrites is transmitted through the cell body before it reaches the axon hillock
Axon Hillock
-integrates incoming signals
-Plays an important role in action potentials (transmission of electrical impulses down the axon
-Signals arriving from the dendrites can either be excitatory or inhibitory
-This sums up these signals, and if the result is excitatory enough, it will initiate an action potential
Axon
long appendage that terminates in close proximity to a target structure
Myelin sheath
-fatty membrane that insulates nerve fibers to prevent signal loss or crossing signals
-Maintains the electrical signal within one neuron
Myelin
increases the speed of conduction in the axon
Oligodendrocytes
produces myelin in the central nervous system
Schwann cells
produces myelin in the peripheral nervous system
Nodes of Ranvier
exposed areas of the axon membrane in which there is a break in the myelin sheath
Nerve terminal/synaptic bouton (knob)
-end of the axon
-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
small space into which the terminal portion of the axon releases neurotransmitters, which bind to the dendrites of the adjacent neuron (the postsynaptic neuron)
Synapse
nerve terminal, synaptic cleft, and postsynaptic membrane
Astrocytes
nourish neurons and form the blood-brain barrier
Ependymal cells
line the ventricles of the brain and produce cerebrospinal fluid
Microglia
phagocytic cells that ingest and break down waste products and pathogens in the CNS
Action potential
-relay electrical impulses down the axon to the synaptic bouton
-all or nothing
-ultimately cause the release of neurotransmitters into the synaptic cleft
Resting potential
-net electrical potential difference that exists across the membrane
-created by movement of charged molecules across that membrane
-about -70 mV in neurons
Potassium leak channels
-allow the slow leak of potassium out of the cell
-Potassium concentration is much greater inside of the cell compared to outside. Concentration difference makes it favorable for potassium to move to the outside of the cell
-As potassium leaks out, the outside of cell becomes slightly positively charged
-A negative charge then builds up inside of the cell so potassium is drawn back in
Equilibrium potential of potassium
-no more net movement of potassium because same amount is being drawn in and leaking out
-around -90 mV, the negative is assigned due to convention, and because a positive ion is leaving the cell
Sodium leak channels
-allow the slow leak of sodium into the cell; causes a buildup of electrical potential
-Sodium concentration is much greater outside of the cell compared to inside. Favorable for sodium to move into the cell
Equilibrium potential of sodium
around 60 mV and is positive because sodium is moving into the cell
Na+/K+ ATPase
continually pumps sodium and potassium back to where they started (potassium into the cell and sodium out) to maintain their respective gradients and maintain a resting potential
Depolarization (axon hillock)
-caused by excitatory input
-raises the membrane potential from its resting potential
-If the axon hillock receives enough excitatory input to be depolarized to the threshold value (between -55 mV and -40 mV), an action potential will be triggered
Hyperpolarization (axon hillock)
-caused by inhibitory input
-lowers the membrane potential from its resting potential and thus makes the neuron less likely to fire an action potential
Summation
the additive effect of multiple signals
Temporal summation
-multiple signals are integrated during a relatively short period of time
-A number of small excitatory signals firing at nearly the same moment could bring a postsynaptic cell to threshold
Spatial summation
-the additive effects are based on the number and location of incoming signals
-A large number of inhibitory signals firing directly on the soma will cause more profound hyperpolarization than the depolarization caused by a few excitatory signals firing
Absolute refractory period
no amount of stimulation can cause another action potential to occur
Relative refractory period
there must be 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
Impulse propagation
the act of an action potential traveling down the axon and initiating neurotransmitter release
Saltatory conduction
the signal “hops” from node to node in order to avoid nodes of Ranvier
Presynaptic neuron
the neuron preceding the synaptic cleft
Postsynaptic neuron
the neuron after the synaptic cleft
Effector
postsynaptic cell if a neuron signals to a gland or muscle, rather than another neuron3
3 ways to remove neurotransmitters from the synaptic cleft
-neurotransmitters can be broken down by enzymatic reactions
-neurotransmitters can be brought back into the presynaptic neuron using reuptake carriers
-neurotransmitters may simply diffuse out of the synaptic cleft
Sensory neurons
transmit sensory information from sensory receptors to the spinal cord and brain
Motor neurons
transmit motor information from the brain and spinal cord to muscles and glands
Interneurons
found between other neurons and are the most numerous of the three types; located predominantly in the brain and spinal cord and are often linked to reflexive behavior
Central nervous system (CNS)
composed of the brain and spinal cord
White matter
-consists of axons encased in myelin sheaths
-lies deeper than the grey matter
Grey matter
consists of unmyelinated cell bodies and dendrites
Peripheral nervous system (PNS)
-made up of nerve tissue and fibers outside of the brain and spinal cord
-connects the CNS to the rest of the body
-can be divided into somatic and autonomic nervous system
Somatic nervous system
-consists of sensory and motor neurons distributed throughout the skin, joints, and muscles;
-transmit information through afferent fibers
Autonomic nervous system
-independent of conscious control
-generally regulates heartbeat, respiration, digestion, and glandular secretions; manages involuntary muscles associated with internal organs and glands
-also helps regulate body temperature
-contain preganglionic neurons in which the soma is in the CNS, and its axon travels to a ganglion in the PNS, it then synapse on the cell body of a postganglionic neuron which then stimulates the target tissue
Parasympathetic nervous system (rest and digest) (autonomic nervous system)
-conserves energy
-Associated with resting and sleeping states and acts to reduce heart rate and constrict the bronchi
-Also responsible for managing digestion
-Acetylcholine is the neurotransmitter responsible for responses and is released by both preganglionic and postganglionic neurons
-The vagus nerve is responsible for much of the parasympathetic innervation of the thoracic and abdominal cavity
Sympathetic nervous system (fight or flight) (autonomic nervous system)
-activated by stress
-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
-single synapse between the sensory neuron that receives the stimulus and the motor neuron that responds to it
-the knee-jerk reflex
Polysynaptic reflex arc
-there is at least one interneuron between the sensory and motor neurons
- the withdrawal reflex
