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