Compendium 8 Flashcards
List functions of the nervous system
Maintaining homeostasis Receive sensory input Integrate information Motor output Establish and maintain mental thinking
What are the structural divisions of the nervous system
Central nervous system- brain and spinal cord
Peripheral nervous system - somatic, autonomic, enteric
- All have sensory and motor input and output
- autonomic motor output divided into parasympathetic (rest and digest) and sympathetic (fight or flight)
What is a nerve
Bundles of axons and their sheaths
What is a ganglion
Collection of cell bodies located outside the CNS
What is a plexus
Extensive network of axons or cell bodies
Explain autonomic nervous system
Action occurs subconsciously (involuntary)
Action potentials in motor neutrons travel go cardiac muscle, smooth muscle and glands
Two neuron system: one from CNS to autonomic ganglion, other from autonomic ganglion to effector
Cell bodies located in both CNS and autonomic ganglion
Explain somatic nervous system
Actions taking place with conscious thought (voluntary)
Action potential in motor neutrons travel to skeletal muscles
Single neuron system
Cell bodies located inside CNS
Explain enteric division of nervous system
Found in digestive tract (controls digestive tract movement)
Interpreted with autonomic subdivision of PNS
Difference between motor and sensory
Motor- away from CNS (the action)
Sensory- toward CNS (stimulus)
Describe neurons
Structural unit of CNS
Receive stimuli, transmit action potentials via axons and dendrites
Consists of cell body (soma), axon, dendrites
Describe dendrites
Short cytoplasm extensions, usually highly branched, emerge from cell body
Receive info from cells, other neurons, environment and direct towards cell body
Can contain dendritic spines to increase SA
Describe cell body
Only one large one
Contains nucleus, nucleolus, other organelles
Describe axon
Extends from cell body through axon hillock, then have initial segment, both of these make up the trigger zone (where an action potential is generated)
Can have branches coming off can axon collaterals which can lead to other cells or same cell body in which it extends from
End of axon called axon terminal or presynaptic terminal which contain terminal buttons or synaptic knobs
Transmit info away from cell body
Functional classification of neurons
Sensory
Motor
Interneurons
Structural classification of neurons
Multipolar, unipolar, bipolar
Explain multipolar neurons
Many dendrites
Single axon
Most neurons in CNS
All motor neurons (cell body in horns of grey matter of spinal cord)
Explain unipolar neurons
One process (axon from cell body divides into T shape one side with sensory receptor, other travels to CNS)
Most sensory neurons
Sensory receptors pick up info rather than dendrites
Explain bipolar neurons
One axon
One dendrite
Rare- only in special sense organs
What are neuroglia
Supporting cells in CNS and PNS
CNS: astrocytes, ependymal cells, microglia, oligodendrocytes
PNS: Schwann cells, satellite cells
Explain astrocytes
Form supporting framework for blood vessels and neurons (communication)
Help maintain blood brain barrier
Respond to tissue damage in CNS - create barrier around damage tissue so it can health faster and stop inflammation to healthy tissue, also limit axon regeneration of injured neurons
Explain ependmyal cells
Line central cavities of brain and spinal cord
Can be squamous, cuboidal or columnar shaped
Can be ciliated
Cavities filled with CSF - cells form lining and cilia assists in movement of fluid
Explain microglial cells
Monitor health surrounding neurons using their extensions
If detect injury, inflammation, unwanted substances then will turn phagocytic and move to affected neuron cell/unwanted substance and destroy it
Explain oligodendrocytes
Wrap around axon forming insulating covering called myelin sheath
Explain Schwann cells
Also called neurolemmocytes
Wrap around axon to form myelin sheath
Explain satellite cells
Provide support and nutrition to cell bodies in ganglia
Protect cell bodies from harmful substances
Difference between myelinated and unmyelinated axons
Myelinated: contain myelin sheath, have nodes of ranvier which are sections that don’t contain myelin sheath
Unmyelinated: no myelin sheath, may have one Schwann cell or oligodendrocytes covering more than one axon
What is the purpose of a myelin sheath
Insulates, stops charges leaking out of axon, protects axon from damage, can speed up action potentials
What is grey matter
Cell body and dendrites
Brain outer cortex and nuclei
Inner part spinal cord
Ganglion
What is white matter
Axons
Deeper nerve tracts of brain
Outer part spinal cord
Nerves
What is the method of communication in the nervous system
Action potential - an electrical signal transferring information from one part of neuron to the next
When ions flow across membrane it causes change in charge (one side more negative, one more positive) which is called a membrane potential
What characteristics of the cell membrane allow action potentials to be generated
1) difference in ionic conc (mostly K and Na) across membrane
- number positive and negative ions in extracellular and intracellular fluid is considered electrically neutral as one same side, the number of positive and negative ions is around the same so charges cancel out –> doesn’t mean charge across whole membrane is neutral
2) ability of membrane to permeable to ions
- action potential results from movement of ions
- cannot occur unless membrane permits this
What are non-gated ion channels
Also called leak channels
Open so ions can leak through at any time
Each leak channel is specific to a certain ion
Cell membrane has more K than Na leak channels
No signal required
What are ion-gated channels
Requires signals to open, three types:
1) ligand gated: open when ligand/chemical binds to them (e.g. Neurotransmitter or hormone)
2) voltage gated: open in response to membrane potential change (voltage)
3) other gated: open in response to stimuli
Explain the establishment of resting membrane potential
RMP: difference in charge across the cell membrane in a resting cell caused by Na/K pump and K leak channels
- inside cell more negative than outside cell
- RMP=-70mV
K is naturally abundant on intracellular side therefore leak through leak channels to extracellular fluid (down conc. gradient), the accumulation of K on extracellular side makes extracellular more positive
Same for Na which is naturally more abundant on extracellular side, however, less of them and their leak channels so no big difference to charge is made
Na/K works against conc. gradient to send 3 Na ions outside and bring 2 K inside which ensures large conc. gradient is maintained
What three processes change the resting membrane potential
Depolarisation: when membrane potential becomes more positive e.g. Could go from -70mV to -30mV
Hyperpolarisation: when membrane potential becomes more negative
Repolarisation: membrane potential returns to normal
What is a graded potential
Can lead to action potentials if the stimulus is strong enough
Short lived, localised (occur in one part of membrane) changes in membrane potential
Magnitude proportional to stimulus strength (strong stimulus = greater voltage change)
Often occurs in dendrites or cell body
Able to SUMMATE: effect produced by one gradient potential is added to effect produced by another graded potential (allows ions channels to open)
Decremental: not able to transfer info over long distance (hence start of action potential)
When does an action potential occur
When a graded potential summates and membrane potential reaches a threshold of -55mV
Occurs in trigger zone of axon as it contains a large number of voltage ion chnanels
List the path of an action potential
Resting membrane potential: all gated na and k channels are closed, K leak channels open so intracellular more negative, Na/K pump working
Depolarisation: once threshold reached, cell becomes more positive, Na gated channels open so Na moves inside cell, K gated channels closed so K remains in abundance in cell
Repolarisation: Na gated channels close, K gated channels open and K moves out of cell down conc. gradient so intracellular becomes more negative, less to negative membrane potential
Hyperpolarisation/afterpotential: Na gated channels closed, k gated channels slowly close so K continues to leave cell to create afterpotential, membrane potential becomes very negative
Resting membrane potential: Na and k gated channels closed, RMP re-established by Na/K pump, k lead channels continue to help re-establish RMP
What is the all of none principle
Graded potential must reach threshold (-55mV) for action potential to be generated
If doesn’t reach then RMP returns to normal until next stimulus
What is the refractory period
Occurs when part of a neuron generates an action potential, so neurons cannot respond to another stimulus at same sight
Absolute refractory period: stages of depolarisation and repolarisation which can’t have any interruptions (Na channels open)
Relative refractory period: stage where most voltage gated Na channels are closed, an action potential can occur but has to be a strong stimulus
How do action potentials travel along unmyelinated fibres
Depolarisation of one part of neuron causes Na to move inside cell which creates current that will depolarise the area adjacent to it
Occurs along the whole length of the fibre
Following depolarisation each segment of axon becomes repolarised
How do action potentials travel along myelinated fibres
Action potential generated at one node of randier which creates current that rapidly jumps to next node – called saltatory conduction
Continues along whole axon length very fast as skips large segments of axon
What occurs at a synapse
An action potential is transmitted to another neuron, cell, muscle, effector gland, ect.
Electrical synapses - current
Chemical synapses - chemicals e.g. Neurotransmitters and hormones
List steps of transmission across a chemical synapse
1) action potential arrives at pre-synaptic terminal
2) calcium channels open and calcium ions move down conc. gradient and diffuse into cell to act on vesicles
3) vesicles containing neurotransmitters, move to presynaptic membrane and fuse with it
4) neurotransmitters released into synaptic cleft via exocytosis
5) neurotransmitters diffuse across cleft
6) neurotransmitters bind to receptors of ligand gated Na channels on postsynaptic membrane
7) ion channels open allow diffusion of ions into post synaptic cell (Na moves in) - change in charge may trigger graded potential and so on
8) neurotransmitter removed from synapse by enzyme activity (must be removed or Na will keep entering cell and cause overstimulation)
Enzyme activity includes: released from receptor on post synaptic membrane and diffuse away from synapse, broken down by enzymes or remains whole, reabsorbed by pre synaptic membrane so can be reused when another impulse arrives
Effect of drugs and alcohol
Antidepressants block reuptake of neurotransmitters (feel good ones) by presynaptic membrane so will continue to stimulate post synaptic neuron producing positive moods and emotions
Neurotransmitters have different effects depending on where they are released e.g. Can prevent neuron from being stimulated in one part or cause it to be active in another
-alcohol increases activity of inhibitory neurotransmitters in brain so brain function is slower as inhibitory input to brain is increased
Describe the spinal cord
Facilitates transfer info from PNS to CNS and back
Protected by vertebral canal, CSF and meninges
Outer= white matter, inner = grey matter
Anterior an posterior of spinal cord have indentations that look like they split the cord in half
- anterior median fissure
- posterior median sulcus
White matter divides into 3 columns- dorsal (back), ventral (front) and lateral (side)
Grey matter divided into horns - dorsal, ventral, lateral
Middle of two halves called COMMISSURES which connects grey and white matter together
Hole right in centre called central canal which contains CSF
Rootlets branch directly off spinal cord which merge to from dorsal root at back and ventral root at front which merge to from spinal nerves (31 pairs arise)
Explain sensory input through neurons in spinal cord and spinal nerves
Sensory receptor stimulated and stimulus travels along sensory neuron through spinal nerve to cell body in dorsal root ganglion
Then through rest of dorsal root to dorsal horn in grey matter
Can then cross synapse to an interneuron and then motor neuron of straight to a motor neuron
-synapse w/ interneuron will pass to somatic motor neuron and to skeletal muscle
-no interneuron will be to automatic motor neuron and then to smooth muscle or glands
Explain motor output through neurons in spinal cord and spinal nerves
Once in motor neuron will travel through ventral root and then through body to effector
What do horns of spinal cord mostly contain
Dorsal horns = interneurons
Ventral horns= some neurons but mostly cell body of somatic motor neuron
Lateral horns= cell body of automatic motor neuron
What is a reflex
Automatic response to a stimulus that requires no contours thought
Can be somatic or autonomic
Homeostatic mechanism
Explain reflex arc
The 5 components of a reflex make up a reflex arc:
1) sensory receptor
2) sensory neuron
3) internuron
4) motor neuron
5) effector
The FUNCTIONAL UNIT of the nervous system
Simplest arcs don’t contain interneurons and are called monosynaptic (ones that do called polysynaptic)
There are 3 types : stretch (monosynaotic), Golgi tension, withdrawal
Explain stretch reflex
Receptor stimulated so signal sent via sensory neuron to spinal cord
Action potential synapses with motor neuron which sends action potential to effector muscle or gland
Action potential is also sent to brain so it is aware something has occurred, however, response initiated by lumbar region of spinal cord and not the brain
Common in knee, ankle, Achilles, tricep
Example autonomic reflex - light shine in eyes
Eye light shinned in would constrict (direct reflex), however, other eye would too (called consensual reflex) as brain communicates and links are made between nerves controlling each eye
What is a reaction
Have control over
Slower than a reflex -require conscious thought
Can become a learned behaviour e.g. Quicker responses through repetition
E.g. Burning hand on hot stove
