Section 4 Flashcards
General func. of the nervous system, their branches, and examples (4)
- controls internal environment; parasympathetic (autonomic nervous system); ex. altering hormone release
- voluntary movement; somatic nervous system; ex. direct movement
- spinal cord reflexes; afferent division (sensory); ex. yanking hand away when touched something HOT
- memory and learning; autonomic;
Components of periphery: stimulus, nerve sig. pathway, response of spindles and GTO; include stretch reflex
Stimulus: muscle over-stretching
Nerve sig. path: annulospiral neve fiber; sends impulse to thru dorsal root to spinal cord producing a shortening reflex of muscle
Resp. spindles: detects and responds by shortening length of extrafusal muscle fibers
Resp. GTO: sensors discharge to depress motor neuron activity to reduce force output
Org. of nervous system
CNS
Afferent (sensory)
PNS
Efferent (motor)
Autonomic (involuntary)
Sympathetic
Parasympathetic
Somatic (voluntary)
CNS descrip.
consists of the brain and spinal cord
- brain (incl. retinas)
- spinal cord
- integrative/control centers
Afferent (sensory)
division of CNS
somatic and visceral neurons
conducts impulses from receptors to CNS
PNS
Consists of nerves that transmit information to and from the CNS
- cranial nerves 3-12
- spinal nerves
Efferent (motor)
division of PNS
motor neurons
conducts impulses from CNS to effectors
Autonomic
division of efferent
involuntary
conducts impulses from CNS to cardiac muscle, smooth muscle, and glands
ex. sweating
Somatic
division of efferent
voluntary
conducts impulses from the CNS to skeletal muscle
ex. flexing
Sympathetic
division of autonomic
prepares fro excitement (HR increase)
“fight or flight”
Parasympathetic
division of autonomic
relax and digest (HR decreases)
Unipolar
a neuron that only has one neurite extending from the cell body
Are sensory neurons uni or multipolar?
Unipolar b/c sensory neurons only carry sensory processes and conduct impulses from receptor toward CNS.
Multipolar
a neuron that possesses a single axon and many dendrites to allow info from other neurons to be received.
Are somatic motor neurons uni or multipolar?
Multipolar b/c they conduct impulses from CNS to multiple receptors (skin, skeletal muscles, joints, tendons)
Describe what is meant by excitability
-ability to receive and respond to a stimulus.
Impulse (stimulus) arrives at NMJ
ACh releases saclike vesicles in terminal axons w/in synaptic cleft.
ACh changes elec. neural impulse into chem. stimulus and combines w/ transmitter-receptor complex in postsynaptic membrane.
This change in elec. property of postsynaptic membrane triggers end-plate potential that spreads from motor end-plate to extrajunctional sarcolemma of muscle.
This causes AP to travel to muscle fibers for contraction
Key components of neuron controlling skeletal muscle (6)
Cell body Dendrites Axon Myelin Sheath Schwann cells Nodes of Ranvier
Cell body
aka Soma
Contains the nucleus
Connect dendrites
Found in spinal cord grey matter
Dendrite
brings info TO cell body
consists of short neural branches that receive impulses through numerous connections and conduct them toward cell body
Axon
takes info AWAY from cell body
extends from cord to deliver the impulse to muscle
Myelin Sheath
bilayer lipoprotein membrane that wraps around axon, encasing larger nerve fibers
Acts as an electrical insulator that encloses the axon
ex. plastic coating elec. wires
Schwann Cells
produce the myelin sheath
covers bare axon and spirals around it
Nodes of Ranvier
a 1-2mm gap between the myelin sheath
placed between adjacent Schwann cells
allows impulses to jump from node to node
permits depolarization of axon
Polarized
the electrical difference across a membrane resulting in resting membrane potential (cell is in active at -70 mV)
Application: a cell at rest has more Na+ ions inside than K+ outside ions
Depolarized
loss of polarization; process of reversing the charges across the cell membrane (inside turns +, outside turns -), causing AP.
occurs during Na+ influx into cell
Application: Na+ channels open causing rapid influx of Na+ into cell, changing the charge inside cell to -55 mV (threshold for AP), which causes AP.
Influx
movement of substance (ions) INTO cell
Application: Na+ channels open and Na+ rushes into cell (depolarization)
Efflux
movement of substance (ions) OUT of cell
Application: Na+ channels close and K+ open (overshoot). K+ moves OUT of cell, restoring charge inside cell to -70mV (repolarization).
Electrochemical gradient
electrical difference between inside and outside of cell.
can be viewed as a source of potential energy.
ions move across membrane (up and down gradient) depending on their gradient level (chemical) and charge (electrical).
Graded Potential
change in membrane potential by EPSP or IPSP.
Few Na+ channels open so small amt. of Na+ rushes in resulting in slight depolar. (EPSP) or hyperpolar. (IPSP).
Size of GP depends on strength of EPSP or IPSP.
Threshold
membrane voltage that graded potential becomes action potential.
Action Potential
begins as a graded potential.
when enough stimulus from EPSP occurs, depolar. of +15 to +20 mV, increasing RMP (-70mV) to threshold -50mV to -55mV.
Ex. Na+ influx = depolarize cell to +40mV > repolar. begins: Na+ ch. close, K+ ch. open; efflux of K+ and RMP -70mV is restored.
What is the role of Na/K exchanger?
maintain RMP by shuttling Na+ in/out and K+ in/out of cell
Temporal SUMmation
adding together graded potentials (GP) in TIME.
if 2 GP separated by enough time, they won’t have any effect on each other and will decay. If they happen at similar times, they add to each other (SUMmation), which eventually can add up enough for depolar.
Spatial SUMmation
adding together GPs in SPACE.
if 2 GPs happen far enough away from each other, they may have no effect on each other and decay. If happen closer, they add to each other (SUMmation), which eventually can add up enough for depolar.
Ex./In. input from synapse closer to axon will create larger GP than input from synapse further from axon.
Excitatory Postsynaptic Potential (EPSP) on target cell
graded potential that pushes postsynaptic neuron toward threshold (increase charge inside cell; depolarization), making AP more likely
Inhibitory Postsynaptic Potential (IPSP) on target cell
GP that push postsynaptic neuron further from threshold (hyperpolarization), making AP harder to achieve
Propagation (2)
how an impulse travel down neuron.
Myelin sheath
Diameter of neuron
Propagation during AP: Myelin sheath
axons with myelin sheaths conduct impulses (AP) faster than non-myelinated (nodes of ranvier) by leaping from one myelin to the next (saltatory conduction)
Propagation during AP: Diameter of neuron
speed of neuron down axon is also determined by the diameter of the neuron. Larger = faster because there’s less resistance to local current flow
Voltage
potential energy available by separate charges
Current
flow of electricity
Resistance
ability to resist current.
ex. membrane w/ closed channels = more resistance; membrane w. open channel = less resistance
3 types of channels. Which includes the Na and K channel and ACh receptor?
Ligand-gated: neurotransmitter/hormone (ACh receptor channel)
Mechanically gated: stretching/pressure
Voltage-gated: voltage change (Na and K channel)
Impact exercise has on nervous system while aging (4)
Improved cognitive function
Improved blood flow to brain
Increases brain levels of growth factors that promote optimal function of neurons
Protection against various diseases and stroke
Disorders that effect the NS (5)
Multiple Sclerosis Amyotrophic Later Sclerosis Parkinson's Disease Dystonia Spinal Muscle Atrophy
Multiple Sclerosis
Immune system attacks myelin and destroys sheath. Results in general fatigue, muscle weakness, poor motor control, loss of balance, and depression.
Exercise improves functional capacity, qual. of life, lower depression
Amyotrophic Later Sclerosis
motor neurons die. Starts in hands, feet, legs and continues into chewing, swallowing, and breathing; impacts body until paralysis. No cure, rapid progression, total paralysis and death.
Parkinson’s Disease
Results in decreased dopamine which inhibits muscular activity to aid in control of muscular activity (tremors, shaking). Treated by drugs that stimulate dopamine production.
Dystonia
involuntary muscle contractions that cause repetitive twisting movements. Cause not fully understood, but believed to have something to do with the basal ganglia in the brain
Spinal Muscle Atrophy
genetic disease affecting the part of the nervous system that controls voluntary muscle movement. Caused by a deficiency of motor neuron protein SMN.
What happens when slow and fast muscles are cross innervated?
Cross innervation can change the characteristics of fast and slow twitch muscles (i.e. fast twitch very slowly being turned to slow twitch, vis versa).
