Chapter 11- Nervous System Flashcards
2 major control systems to maintain homeostasis
Nervous system- works faster but effects are short lived. AP via neurons.
Endocrine system- takes longer to respond but effects last longer. Works by sending hormones through blood stream to target organs
Homeostatic regulation by the nervous system is dependent on
The systems ability to detect, interpret, and respond to changes
Functions of nervous system
-receiving sensory input. Monitor external and internal stimuli
-integrating information. Brain and spinal cord receive and initiate response.
-controlling muscles and glands
-maintain homeostasis
-establish and maintain mental activity. Consciousness, thinning, memory, emotion
Major divisions of nervous system
Central - brain and spinal cord receive (integration function)
Peripheral - all nerves leading and coming into CNS.
Division of peripheral nervous system
Afferent (sensory) - brings info into CNS
Efferent (motor) - takes info out to body organs
efferent division of peripheral nervous system
-somatic - from CNS to skeletal muscle. Voluntary. Single neuron system - one from spinal cord to muscle
-autonomic - from CNS to smooth, cardiac, and glands. Involuntary to maintain homeostasis.
Di
Difference in neuron systems bc somatic and autonomic
Somatic is a single neuron system with no gaps or ganglion. Neuron goes straight to the muscle.
Autonomic involves two ganglion neurons that connect CNS to organ. Allows for more regulation and modulation of autonomic responses.
Divisions of autonomic nervous system
Sympathetic - fight or flight
Parasympathetic - rest and digest
Enteric - (less discussed) consist of plexuses that are responsible for controlling digestive tract
Difference in function between CNS and PNS
CNS is for processing strimuli and initiating response
PNS detects stimuli (sensory receptors) and transmits info two and from the CNS.
The bear and the man scenario with the nervous system
- Afferent Sensory receptors in PNS detect bear and send info to CNS
- CNS processe and integrates the info to determine appropriate response
- PNS then uses efferent pathways to send info via the somatic system (to get skeletal muscle to run) and the autonomic system (to pump heart, prep organs for running, pump adrenaline)
Sensory receptors
Ending of neurons or seperate cells that detect such things as temperature, pain, touch, pressure, light, sound, odor
Nerve
A bundle of axons and their sheaths that connect connects CNS to sensory receptors, muscles, and glands.
12 pair cranial. 31 pair spinal.
Neuroglia
Cells that support and protect neurons. DO NOT transmit APs. More numerous than neurons in nerve tissue.
Neurons
Individual nerve cells that receive stimuli and transmit APs
Basic neuron structure
Cell body or soma
Dendrites
Axon
Neurons lack centrioles and are therefore unable to undergo mitosis
Dendrites of neuron
input part of neuron. cytoplasmic exfensions where axons of other neurons can form a synapse. Impulses sent to soma
Cell body or soma of a neuron
- contains rough ER broken into Nissl bodies. Primary site of protein synthesis for neuron.
Axon
Send AP away from soma
Axon hillock (cone structure btwn soma and axon) is where the threshold must be reached to AP in the axon
End of axon branches out to presynaptic terminals which are at the synapse to another neuron, muscle cell or gland
Terminals hold synaptic vesicles that contain neurotransmitter
May branch to form collateral axons which increase the # of APs
Axolemma
Cell membrane of an axon that can carry an AP
Interneuron
Within CNS from one neuron to another
Structural classification of neuron
Multipolar - one axon and many dendrites - most neurons in CNs
Bipolar- one axon one dendrite - sensory in special senses
Unipolar - cell body and axon with two branches extending to CNS and peripheral with sensory receptors. Most sensory neurons are unipolar.
Neuroglia of the CNS types
Astrocytes
Ependymal cells
Microglia
Oligodendrocytes
Astrocytes
Star shaped cells that wrap around and cover blood vessels. Making up the blood brain barrier to keep brain chemistry constant. (Keeps toxic substances out but allows diffusion to regular CSF)
Ependymal cells
Line the ventricles of brain and central canal of spinal cord. Found in choroid plexus and produce CSF. Have cilia to move CSF.
Microglia
Specialized macrophages that respond to inflammation. Phagocytize necrotic tissue, microorganisms, and foreign substances that invade the CNS
Oligodendrocytes
Wrap around one or more axons to form myelin sheath. (Destruction of this is hallmark of MS)
Purpose of myelination
Protects and electrically insulates axons from one another and also speeds up the action potential propagation down the axon.
Has gaps called nodes of ranvier. Allows for faster propagation by allowing jumps called saltatory conduction.
Neuroglia of PNS
Schwann cells
Satellite cells
Schwann cells
Wraps around only one axon many times to form myelin sheath. Mainly phospholipid
Satellite cells
Surround neuron cell bodies in sensory ganglia to provide nuteruents and support. Also play a role in protecting neurons from heavy metal poisons.
Unmyelinated axons
Not all axons are myelinated
Ganglion
Collection of neurons in the PNS
Nuclei
Collection of neuron cell bodies in the CNS
Plexus
An extensive breadline network of axons and in some cases neuron cell bodies in the PNS
Gray matter
Unmyelinated axons, cell bodies, dendrites, Neuroglia. Integrative functions
White matter
Myelinated axons. Form Nerve tracts to take info from one arte in the CNS to another
Arrangement in grey and white matter in the spinal cord vs the brain
In the brain- the inner is white and the outer is grey
In the spinal cord- the grey is central in a butterfly shape and white is the outer
Basal nuclei
Largest nuclei in the brain and controls motor function. Disrupted during Parkinson’s
Potential difference
Unequal distribution of charge exists between immediate inside and immediate outside of cell. -70mV - 90 mV
Voltage gates Na channels are sensitive to what
Changes in extracellular ca2+ concentration
As ca2+ decreased outside cell..
Na gates open and membrane continues to depolarize from influx of Na. Overexcites the nervous system and could lead to tetany of muscles
Hi Ca outside cell
Na gates close and membrane depolarizes or becomes hyperpolarized. Could lead to sluggish nervous system
Trousseau’s sign
Muscle cramps, spasms or tremors
Can occur anywhere
Due to low calcium levels (hyocalcemia)
- as concentration in extracellular fluid drops, this affects the nervous system sending impulses to skeletal muscles
Graded potentials result from
Ligands binding to receptors
Changes in charge across membrane
Temp changes
Mechanical stimulation
A sub threshold stimulus. Resulting as a localized change over a small portion of the membrane
Graded potentials
Could be depolarization or hyper. May or may not cause action potential due to summation (adding together from
Increased frequency). Spread over plasma membrane in a decreasing fashion bc they do not propogate down the entire length of the axon (therefor no neurotransmitter is used) — unless it becomes strong enough to be an AP
Refractory period
Sensitivity of area of membrane to further stimulation decreases for a time
Absolute (between de and repolarization)- completely insensitive to another stimulus
Relative- can generation an action potential but it takes a stronger than threshold stimulus due to its more negative state
The frequency of APs is determined by
The strength of the stimulus (sets the frequency) and the absolute refractory period (the limiting factor)
Velocity refers to
How fast the APs travel down the membrane
Myelination (myelinated are faster) and diameter of axon (larger diameter is faster)
What direction to action potentials go
From cell body down axon in one direction to the synapse. Because previous site now under refractory period.
Electrical synapse
Gap junctions connected by tubular proteins called connexons that allow for AP to pass from one to the other.
Found in cardiac and smooth muscle. Important where contractile activity among a group of cells is important.
Chemical synapses
Presynaptic terminal with synaptic cleft and post synaptic membrane. Uses neurotransmitters in terminal to bind to ligan gated terminals and allow for flow of ions.
Neurotransmitters other than acetylcholine and how is it broken down
Norepinephrine: recycled within presynaptic neuron or diffuses away from synapse. MAO breaks it down.
Serotonin is taken back up into presynaptic terminal by special reuptake molecules
Purpose of MAO and SSRIs
MAO inhibitor keeps Ne in cleft, elevating mood
SSRIs keep seretonin in cleft, elevating mood
Post synaptic potential
Depends on which gates are open
Excitatory - depolarization occurs and response is stimulatory (Na)
Or inhibitory - hyperpolarization and response inhibitory (Cl and K)
Axoaxonic synapses
Many synapses of the CNS are the connection of one axon of one. Wut on synapses directly to the terminal end of the axon of another neuron
Presynaptic inhibition
Modulator reduce amount of neurotransmitter released from
Presynaptic terminal (endorphins do this to block pain)
Presynaptic facilitation
Amount of neurotransmitter released from presumptive terminal increases
Organization of neurons in CNS
Convergent pathways- from input- many neurons converge to synapse in a. Smaller number of neurons
Divergent pathways - from input- smaller number of neurons synapse onto a larger number of neurons
Oscillating- outputs cause reciprocal activation
