Unit 11: Key terms
Nervous System
controls perception and experience of the world, directs voluntary movement, seat of consciousness, personality, learning, and memory, regulates aspects of homeostasis with the endocrine system (respiratory rate, blood pressure, body temp, etc.)
Anatomical Divisions of the Nervous System
divided anatomically into central nervous system (CNS) and peripheral nervous system (PNS)
Central Nervous System (CNS)
brain and spinal cord
Peripheral Nervous System (PNS)
cranial nerves, spinal nerves and their branches
Functional Divisions of the Nervous System
Sensory, Integrative, Motor
Sensory (afferent division)
gathers information about internal and external environments: somatic, visceral
Somatic Sensory Division (special sensory division)
carry signals from skeletal muscles, bones, joints, and skin, also from organs of vision, hearing, taste, smell, and balance
Visceral Sensory Division
transmit signals from viscera (heart, lungs, stomach, kidneys, and urinary bladder)
Integrative functions
analyze and interpret incoming sensory information: determine an appropriate response, 99% of integrated sensory information is subconsciously disregarded as unimportant, remaining sensory stimuli that CNS does respond to leads to motor response
Motor functions
actions performed in response to integration by motor (efferent) division of PNS: subdivisions into somatic and autonomic divisions by organs that neurons contact
Somatic motor division
neurons transmit signals to skeletal muscle: voluntary control
Autonomic nervous system (ANS)
neurons carry signals to thoracic and abdominal viscera critical for maintaining homeostasis
Neurons
excitable cells responsible for sending and receiving signals as action potentials, most consist of 3 parts
Receptive Region
dendrites and cell body
Conducting Region
axon
Secretory Region
axon terminal
Cell body (soma)
most metabolically active region, manufactures all proteins needed for whole neuron
Nissl bodies
both free ribosomes and rough endoplasmic reticulum (protein synthesis)
Golgi apparatus
vesicular transport
Mitochondria
supply energy required in the cell body
Cytoskeleton
microtubules, structural support and chemical transportation between cell body and axon
Neurofibrils
intermediate filaments extending into neuron processes
Dendrites
short, branched processes: receive input from other neurons, which they transmit toward the cell body as electrical impulses: each neuron may have multiple dendrites
Conductivity
the ability of cells to transmit electrical impulses
2 forms of electrical changes
local potentials, action potentials
Local potentials
travel short distances
Action potentials
travel entire length of axon
The resting membrane potential
thin layer of negativity charged ions exists in cytosol on inside of cell, thin layer of positively charged ions exist on outside of cell, typical neuron has resting membrane potential (RMP) at -70mV
Voltage
electrical gradient established by separation of charges between two locations (across plasma membrane)
Membrane potential
electrical potential across cell membrane, source of potential energy for cell
Polarized
cell is polarized when voltage difference across plasma membrane does not equal 0mV
Ion channels
ions cannot diffuse through components of the plasma membrane, and must rely on specific protein channels
Leak channels
always open, continuously allow ions to flow down concentration gradients between cytosol and ECF
Gated channels
closed at rest, open in response to specific stimulus
Ligand-gated channels
open in response to binding of specific chemical (ligand) to a specific receptor
Voltage-gated channels
open in response to changes in voltage across membrane
Mechanically-gated channels
open or close in response to mechanical stimulation (pressure, stretch, or vibration)
Sodium-potassium ion pump
most important ATP-consuming pumps, moves 3 sodium ions out and 2 potassium ions into cells per ATP hydrolyzed, maintains a high concentration of sodium in extracellular fluid and lower concentration in cytosol: opposite true for potassium
Repolarization
when cell returns to resting membrane potential
Local potentials
small local changes in potential of neuron's plasma membrane, triggers for long-distance action potentials, may cause one of two effects
Depolarization
positive charges enter cytosol, make membrane potential less negative (change from -70 to -60mV)
Hyperpolarization
either positive charges exit or negative charges enter cytosol makes membrane potential more negative (change from -70 to -80 mV)
Graded potentials
local potentials are sometimes called this, vary greatly in size, reversible
Action potentials count.
uniform, rapid depolarization and repolarization of membrane potential, only generated in trigger zones (axolemma, axon hillock, and initial segment of axon)
All-or-none principle
refers to an event (action potential) that either happens completely or does not occur at all
Neuronal action potential phases
depolarization, repolarization, hyperpolarization
Depolarization phase
membrane potential rises towards zero, then becomes positive briefly
Repolarization phase
membrane potential returns to a negative value
Hyperpolarization phase
membrane potential temporarily becomes more negative than resting membrane potential
Conducted (propagated)
action potentials must do this, along entire length of axon to serve as long-distance signaling service
Action potential propagation
down axon is nerve impulse
Synapse
where neuron meets target cell (neuronal synapse if another neuron) can be electrical or chemical
Electrical synapse
occurs between cells electrically via gap junctions, in areas of brain responsible for programmed automatic behaviors (breathing), in cardiac and visceral smooth muscle to allow for coordinate muscle activity
Chemical synapses
make up the majority of synapses in the nervous system, more efficient than electrical synapses, convert electrical signals into chemical signals, and no signal strength is lost (as at electrical synapses)
Axon
each neuron has only one axon (nerve fiber) can generate and conduct action potentials
Axon hillock
where axon originates
Axon collaterals
branches extending from main axon
Telodendria
small branches arising from axon
Axon terminals or synaptic bulbs
arise from telodendria, components that communicate with a target cell
Axolemma
plasma membrane surrounding axon and its cytoplasm (axoplasm)
Multipolar neurons
single axon and multiple dendrites, over 99% of all neurons
Bipolar neurons
one axon and one dendrite and cell body between them, eye and olfactory epithelium (nasal cavity)
Pseudounipolar neuron
only one fused axon, extends from cell body, divides into 2 processes, one carriers sensory information from sensory receptors to cell body, other carriers sensory information from cell body to spinal cord
Sensory (afferent) neurons
carry into toward CNS, neuron cell bodies in PNS receive info from sensory receptors and relay information via axons to brain or spinal cord, usually pseudounipolar or bipolar
Interneurons (association) neurons
relay info within CNS between sensory and motor neurons, most neurons in body, multipolar, communicates with many other neurons
Motor (efferent) neurons
carry info away from cell body in CNS to muscles and glands, mostly multipolar
Neuroglia (neuroglial) cells
provide structural support and protection for neurons also maintain their environment, able to divide and fill in space left behind when neuron dies
4 types of neuroglial cells in CNS
astrocytes, oligodendrocytes, microglia, ependymal cells
2 types of neuroglial cells in PNS
Schwann cells, Satellite cells
Astrocytes
large star-shaped cells, many processes terminating in end-feet, functions include: anchor neurons and blood vessels in place, transport of nutrients and gases between blood vessels and neurons, formation of blood-brain barrier, repair damaged brain tissue by rapid cell division
Oligodendrocytes
also in CNS, radiating processes with flattened sacs, wrap around axons of nearby neurons to form myelin
Microglia
small, scarce cells, activated by injury into wandering phagocytic cells within CNS, ingest disease-causing microorganisms, dead neurons, and cellular debris
Ependymal cells
ciliated cells, line hollow spaces within CNS, manufacture and circulate cerebrospinal fluid
Schwann cells
encircle axons in PNS to provide them with myleination
Satellite cells
surround cell bodies of neurons in PNS, provide supportive functions
Myelin sheath
layers of the plasma membrane of Schwann cell or oligodendrocyte in PNS and CNS respectively
Myelination
neuroglial cells wrap multiple layers of membrane (myelin) around axon, insulates axon (prevents ion movements), increases speed
Internodes
segments of axon covered by neuroglia
Node of Ranvier
gap between adjacent neuroglia, where myelin sheath is absent
Myelin sheath white matter
composed of myelinated axons, appear white
Myelin sheath gray matter
composed of neuron cell bodies, unmyelinated dendrites and axons, appear gray