Chapter 4 – Key Terms
action potential change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibers
All-or-Nothing law a principle that if a single nerve fiber if stimulated, it will always give a maximal response and produce an electrical impulse of a single amplitude
ascending tract central nervous system fibers carrying sensory information from the spinal cord or periphery to the brain
autonomic nervous system (ANS) functional division of the nervous system that is responsible for homeostatic reflexes that coordinate control of cardiac and smooth muscle, as well as glandular tissue
axon single process of the neuron that carries an electrical signal (action potential) away from the cell body toward a target cell
axon hillock tapering of the neuron cell body that gives rise to the axon
axon terminal end of the axon, where there are usually several branches extending toward the target cell
cauda equina bundle of spinal nerve roots that descend from the lower spinal cord below the first lumbar vertebra and lie within the vertebral cavity; has the appearance of a horse’s tail
central nervous system (CNS) anatomical division of the nervous system located within the cranial and vertebral cavities, namely the brain and spinal cord
cerebellum region of the adult brain connected primarily to the pons that developed from the metencephalon (along with the pons) and is largely responsible for comparing information from the cerebrum with sensory feedback from the periphery through the spinal cord
cerebral cortex outermost layer of gray matter in the brain, where conscious perception takes place
cerebral hemisphere one half of the bilaterally symmetrical cerebrum
cerebrum region of the adult brain that develops from the telencephalon and is responsible for higher neurological functions such as memory, emotion, and consciousness
dendrite one of many branchlike processes that extends from the neuron cell body and functions as a contact for incoming signals (synapses) from other neurons or sensory cells
depolarization change in a cell membrane potential from rest toward zero
descending tract central nervous system fibers carrying motor commands from the brain to the spinal cord or periphery
excitable membrane cell membrane that regulates the movement of ions so that an electrical signal can be generated
glial cell one of the various types of neural tissue cells responsible for maintenance of the tissue, and largely responsible for supporting neurons
graded potential change in the membrane potential that varies in size, depending on the size of the stimulus that elicits it
hypothalamus major region of the diencephalon that is responsible for coordinating autonomic and endocrine control of homeostasis
initial segment first part of the axon as it emerges from the axon hillock, where the electrical signals known as action potentials are generated
integration nervous system function that combines sensory perceptions and higher cognitive functions (memories, learning, emotion, etc.) to produce a response
longitudinal fissure large separation along the midline between the two cerebral hemispheres
lower motor neuron second neuron in the motor command pathway that is directly connected to the skeletal muscle
membrane potential distribution of charge across the cell membrane, based on the charges of ions
motor unit motor neuron and the group of muscle fibers it innervates
myelin lipid-rich insulating substance surrounding the axons of many neurons, allowing for faster transmission of electrical signals
neuron neural tissue cell that is primarily responsible for generating and propagating electrical signals into, within, and out of the nervous system
neurotransmitter chemical signal that is released from the synaptic end bulb of a neuron to cause a change in the target cell
node of Ranvier gap between two myelinated regions of an axon, allowing for strengthening of the electrical signal as it propagates down the axon
peripheral nervous system (PNS) anatomical division of the nervous system that is largely outside the cranial and vertebral cavities, namely all parts except the brain and spinal cord
process in cells, an extension of a cell body; in the case of neurons, this includes the axon and dendrites
propagation movement of an action potential along the length of an axon
recruitment increase in the number of motor units involved in contraction
repolarization return of the membrane potential to its normally negative voltage at the end of the action potential
response nervous system function that causes a target tissue (muscle or gland) to produce an event as a consequence to stimuli
resting membrane potential the difference in voltage measured across a cell membrane under steady-state conditions, typically -70 mV
sensation nervous system function that receives information from the environment and translates it into the electrical signals of nervous tissue
soma in neurons, that portion of the cell that contains the nucleus; the cell body, as opposed to the cell processes (axons and dendrites)
somatic nervous system (SNS) functional division of the nervous system that is concerned with conscious perception, voluntary movement, and skeletal muscle reflexes
stimulus an event in the external or internal environment that registers as activity in a sensory neuron
synapse narrow junction across which a chemical signal passes from neuron to the next, initiating a new electrical signal in the target cell
synaptic end bulb swelling at the end of an axon where neurotransmitter molecules are released onto a target cell across a synapse
thalamus region of the central nervous system that acts as a relay for sensory pathways
thermoreceptor type of sensory receptor capable of transducing temperature stimuli into neural action potentials
threshold membrane voltage at which an action potential is initiated
upper motor neuron first neuron in the motor command pathway with its cell body in the cerebral cortex that synapses on the lower motor neuron in the spinal cord