WEEK 5: Nervous System 1 Flashcards
What 3 organs are included in the nervous system
- brain and spinal cord
- receptors of sense organs (eyes, ears, etc.)
- nerves that connect to other systems
What two type of cells are in nervous tissue
-neurons for intercellular communication
- neuroglia (glial cells)
->essential to survival and function of neurons
->preserve structure of nervous tissue
What are the 2 Anatomical divisions of the nervous system
- Central nervous system
- Peripheral nervous system
What is the Central nervous system (CNS), contains, functions
-brain and spinal cord
-comprises nervous tissue, connective tissue, blood vessels
-functions to process and coordinate sensory data from inside and outside body
-motor commands control activities of peripheral organs (e.g., skeletal muscles)
-higher functions of brain include intelligence, memory, learning, and emotion
What is the Peripheral nervous system (PNS), contains, functions
- includes all nervous tissue outside CNS and ENS, cranial nerves and spinal nerves
- delivers sensory information to the CNS
- carries motor commands to peripheral tissues
What are peripheral nerves+functions
- bundles of axons with connective tissues and blood vessels
- carry sensory information and motor commands
- cranial nerves connect to brain
- spinal nerves attach to spinal cord
What are the 4 Functional divisions of the PNS
afferent division
efferent division
receptors
effectors
What is the afferent division
- carries sensory information
- from receptors in peripheral tissues and organs to CNS
What is the efferent division
- carries motor commands
- from CNS to muscles, glands, and adipose tissue
What are receptors
- detect changes or respond to stimuli
- may be neurons or specialized cells
- may be single cells or complex sensory organs (e.g., eyes, ears)
What are effectors
target organs that respond to motor commands
What 2 systems make up the efferent division of PNS
Somatic nervous system (SNS)
Autonomic nervous system (ANS)
What is Somatic nervous system (SNS)
- controls skeletal muscle contractions
- both voluntary and involuntary (reflexes)
What is Autonomic nervous system (ANS)
- controls subconscious actions, contractions of smooth and cardiac muscle, and glandular secretions
- sympathetic division has a stimulating effect
- parasympathetic division has a relaxing effect
What is Enteric nervous system (ENS)+functions
- 100 million neurons in walls of digestive tract
- as many or more than in spinal cord
- use the same neurotransmitters as the brain
- initiates and coordinates visceral reflexes locally without instructions from cns
- can be influenced by ANS
What are neurons + function
- basic functional units of the nervous system
- send and receive signals
- function in communication, information processing, and control
What 4 strucutres are in a neuron cell body(soma)
- large nucleus and nucleolus
- perikaryon (cytoplasm)
- mitochondria (produce energy)
- RER and ribosomes (synthesize proteins)
What are the 2 Cytoskeletons of perikaryon
- neurofilaments and neurotubules
->similar to intermediate filaments and microtubules - neurofibrils
->bundles of neurofilaments that provide support for dendrites and axon
What are nissl bodies
- dense areas of RER and ribosomes in perikaryon
- make nervous tissue appear gray (gray matter)
What are dendrites?+functions
- short, highly branched processes extending from cell body
- dendritic spines
-> fine processes on dendrites
-> receive information from other neurons
->80–90% of neuron surface area
What is a axon+function
- single, long cytoplasmic process
- propagates electrical signals (action potentials)
What is the axoplasm+contains
- cytoplasm of axon
- contains neurofibrils, neurotubules, enzymes, and organelles
What are the 6 structure of the axon
axolemma
initial segment
axon hillock
collaterals
telodendria
axon terminals (synaptic terminals)
What is axolemma
- plasma membrane of the axon
- covers the axoplasm
What is initial segment
base of axon
What is axon hillock
thick region that attaches initial segment to cell body
What is collaterals
branches of the axon
What is teldendria
fine extensions of distal axon
What is axon terminals (synaptic terminals)
tips of telodendria
What is Axonal (axoplasmic) transport
- movement of materials between cell body and axon terminals
- materials move along neurotubules within axon
- powered by mitochondria, kinesin, and dynein
What are the 4 structural classifications of neurons
- anaxonic neurons
- bipolar neurons
- unipolar neurons (pseudounipolar neurons)
- multipolar neurons
What are anaxonic neurons, location
- small
- all cell processes look similar
- found in brain and special sense organs
What are bipolar neurons, location
- small and rare
- one dendrite and one axon
- found in special sense organs (sight, smell, hearing)
What are unipolar nuerons (pseudounipolar neurons),
- axon and dendrites are fused
- cell body to one side
- most sensory neurons of PNS
What are multipolar neurons
- have one long axon and two or more dendrites
- common in the CNS
- all motor neurons that control skeletal muscles
What are 3 Functional classifications of neurons
- Sensory neurons
- Motor neurons
- Interneurons
What are Sensory neurons (afferent neurons)+ function
- unipolar
- cell bodies grouped in sensory ganglia
- processes (afferent fibers) extend from sensory receptors to CNS
What are 2 types of sensory neurons + their functions
- Somatic sensory neurons
->monitor external environment - Visceral sensory neurons
->monitor internal environment
What are 3 types of sensory receptors
interoceptors
exteroceptors
proprioceptors
What is interoceptors
- monitor internal systems (e.g., digestive, urinary)
- internal senses (stretch, deep pressure, pain)
What is exteroceptors
- monitor external environment (e.g., temperature)
- complex senses (e.g., sight, smell, hearing)
What is proprioceptors
monitor position and movement of skeletal muscles and joints
What are motor neurons (efferent neurons)
- carry instructions from CNS to peripheral effectors
- via efferent fibers (axons)
What are two types of motor neurons + functions
- Somatic motor neurons of SNS
->innervate skeletal muscles - Visceral motor neurons of ANS
->innervate all other peripheral effectors
->smooth and cardiac muscle, glands, adipose tissue
What 2 fibers does the axons divide into when signals from CNS to visceral effectors cross autonomic ganglia
Preganglionic fibers
Postganglionic fibers
What are interneurons, location, functions, involved in…
- most are in brain and spinal cord
- some in autonomic ganglia
- located between sensory and motor neurons
- responsible for distribution of sensory information
-> coordination of motor activity - involved in higher functions
memory, planning, learning
What is neuroglia
- support and protect neurons
- make up half the volume of the nervous system
- many types in CNS and PNS
What are 4 Types of neuroglia in the CNS
astrocytes
ependymal cells
oligodendrocytes
microglia
What are astrocytes
- maintain blood brain barrier
- provide strcutural support
- regulate ion, nutrient+dissolved gas concentrations
- absorb and recycle neurotransmitters
- form scar tissue after injury
What are ependymal cells
- line ventricles (brain)+central canal
- assist prod ,circulating, monitoring cerebrospinal fluid
What are oligodendrocytes
- myellnate cns axons
- provide strucutral framework
What are microglia
- remove cell debris, waste, +pathogens by phagocytosis
What is neuroligia in the pns and the two types
- insulate neuronal cell bodies and most axons
->Satellite cells
->Schwann cells
What are satelite cells
- surround nueuron cell bodies in ganglia
-regulate o2+co2, nutrient + neurotransmitter lvls around ganglia
What are schwann cells
- surround all axons in pns
- responsible for myelination of peripheral axons
- participate in repair process after injury
Describe the 3 stages of formation of myelin sheath
- schwann cells suround poriton of axon within a groove of its cytoplasm
- begins to rotate around axon
- as it rotates, myelin is wound around axon in multiple layers, forming tightly packed membrane
What is resting membrane potential
the membrane potential of a resting cell
- membrane permeability varies by ion
- cells have selectively permeable membranes
- size of potential diff between neg+pos ions measured in mV
- resting MP= -70mV
What is Graded potential
- temporary, localized change in resting potential
- caused by a stimulus
What is an action potential
- is an electrical impulse produced by graded potential
- propagates along surface of axon to synapse
- begin at initial segment of axon
- do not diminish as they move away from source
- affect an entire excitable membrane
What are the 3 concepts of resting membrane potential
- extracellular fluid (ECF) and intracellularfluid (cytosol) differ greatly in ionic composition
- extracellular fluid contains high concentrations of Na+ and Cl−
- cytosol contains high concentrations of K+ and negatively charged proteins
Describe the 5 Passive processes acting across cell membrane
- current
- resistance
- chemical gradients
- electrical gradients
- electrochemical gradient
What is a current passive process
movement of charges to eliminate a potential difference
What is a resistance passive process
- how much the membrane restricts ion movement
- if resistance is high, current is small
What is a passive chemical gradient
concentration gradients of ions (Na+, K+)
- high intracellular conc of K+=move out of cell thru K+ leak channels
- high extracellular conc of Na+=ions move into cell thru Na+ leak channels
- ion movement driven by chemical gradient
What is a passive electrical gradient
- charges are separated by cell membrane
- cytosol is negative relative to extracellular fluid
- K+ ions leave rapidly than Na+ enter = plasma membrane more permeable to K+
- more + charges outside plasma membrane
- neg charged protein molecules inside cannot cross membrane = more neg charges in cytosol = electrical gradient
What is a passive electrochemical gradient
- sum of chemical and electrical forces acting on an ion across the membrane
- a form of potential energy
What is the equilibrium potential
- membrane potential at which there is no net movement of a particular ion across cell membrane
- K+ = −90 mV
- Na+ = +66 mV
Describe the electrochemical gradients for potassium
- at RMP, chemical/elec gradients oppose K+ ions = forcing them out of cell
- is plasma membrane was freely permeable to K+, outflow would continue until -90mV
Describe the electrochemical gradients for sodium
- at RMP, chem/elec gradients for Na+ are combined
- net electrochemical gradients force Na+ into cell
-if plasma membrane was freely permeable to Na+, inflow would conntue to +66mV
What is the active process across the membrane and describe
- Sodium–potassium exchange pump
- powered by ATP
- ejects 3 Na+ for every 2 K+ brought in
- balances passive forces of diffusion
- stabilizes resting membrane potential (−70 mv)
- when ratio of Na+ entry to K+ loss through passive channels is 3:2
Why does the RMP exist
- cytosol differs from extracellular fluid in chemical and ionic composition
-plasma membrane is selectively permeable
Why does membrane potential change in response to temporary changes in membrane permeability
- results from opening or closing of specific membrane channels
- in response to stimuli
What two 2 chemical are the primary determinants of membrane potential
Na+ and K
Describe Passive ion channels (leak channels)
- are always open
- permeability changes with conditions
Describe Active ion channels (gated ion channels)
- open and close in response to stimuli
- at resting membrane potential, most are closed
What are 3 types of active channels
- chemically gated ion channels
- voltage-gated ion channels
- mechanically gated ion channels
What are chemically gated ion channels, location
- also called ligand-gated ion channels
- open when they bind specific chemicals (e.g., ACh)
- found on cell body and dendrites of neurons
What are Voltage-gated ion channels, location
-respond to changes in membrane potential
- found in axons of neurons and sarcolemma of skeletal and cardiac muscle cells
- activation gate opens when stimulated
- inactivation gate closes to stop ion movement
What are Mechanically gated ion channels, location
- respond to membrane distortion
- found in sensory receptors that respond to touch, pressure, or vibration
What are graded potentials, examples
- changes in membrane potential that cannot spread far from site of stimulation
- produced by any stimulus that opens gated channels
- e.g a resting membrane is exposed to a chemical, chemically gated Na+ channels open, sodium ions enter cell
membrane potential rises (depolarization)
What is repolarization
when the stimulus is removed, membrane potential returns to normal
What is hyperpolarizaiton
- results from opening potassium ion channels
- positive ions move out, not into cell
->opposite effect of opening sodium ion channels - increases the negativity of the resting potential
What are 4 characteristcs of graded potentials
- membrane potential is most changed at site of stimulation; effect decreases with distance
- effect spreads passively, due to local currents
- graded change in membrane potential may involve depolarization or hyperpolarization
- stronger stimuli produce greater changes in membrane potential and affect a larger area
What is the all-or-none principle
- any stimulus that changes the membrane potential to threshold
->will cause an action potential - all action potentials are the same
->no matter how large the stimulus - an action potential is either triggered or not
Describe the steps of an action potential
- stimulus intiates action potential =. large graded depolarization
- opens voltage gated sodium ion channels
- occurs at threshold (-60mV)
- plasma membrane becomes more permeable to Na+
- Na+ ions into ytosol = rapid depolrization occurs
- inner membrane surface has more pos ions than neg ions = + membrane potential
- at +30Mv, Na+ inactivated voltage gated channels close = sodium channel inactivation
- coincides w opening of K+ ion channel
- potassium moves out of cell= membrane potential falling = repolarization begins
- Voltage-gated K+ channels begin to close as membrane reaches normal resting potential
- K+ continues to leave cell
- membrane is briefly hyperpolarized to −90 mV
- all voltage-gated K+ channels finish closing = resting membrane potential is restored
- action potential is over
What is the refactory period
- from beginning of action potential
- to return to resting state
- during which the membrane will not respond normally to additional stimuli
What is an Absolute refractory period
- all voltage-gated Na+ channels are already open or inactivated
- membrane cannot respond to further stimulation
What is an Relative refractory period
- begins when Na+ channels regain resting condition
- continues until membrane potential stabilizes
- only a strong stimulus can initiate another action potential
What is propogation
moves an action potential along an axon in a series of steps
What are 2 Types of propagation
- Continuous propagation
- Saltatory propagation
What is continuous propagation of action potentials
- occurs in unmyelinated axons
- affects one segment of an axon at a time
Describe the steps of continuous propagation of action potentials
- Action potential develops at initial segment
->depolarizes membrane to +30 mV - Local current develops as na+ ions entering spread away from voltage gated channels
->depolarizes second segment to threshold - Action potential occurs in second segment
- initial segment begins repolarization
- Local current= sodium ions enter 2nd segment = depolarizes segment, repeats
- action potential travels in one direction (1 m/sec)
What is Saltatory propagation of action potentials
- occurs in myelinated axons
- faster than continuous propagation
requires less energy - myelin prevents continuous propagation
-local current “jumps” from node to node - depolarization occurs only at nodes
Describe the steps to Saltatory propagation of action potentials
- action potential occurs at initial segment
- local current prod a graded depolarization bringing axon membrane at next node to threshold
- action potential occurs at this node
- local current prod a a graded depolarization bringing axon membrane at next node to threshold
