Nervous System - Cell Biology Semester 2
What are the areas of the nervous system
The CNS is made up of the brain and the spinal cord but wont branch out from the spinal cord
The PNS contain cranial and spinal nerves as well as ganglia, these bracnh oiut from the spinal cord to the rest of the body
The ganglia is a collection of neuroanl cells in the dorals roots outisde the spinal cord
Who was phineas gage
He had an iron rod stake through his frontal lobe of the brain where he survived but lost an eye as well as had a major personality change
Discovered the frontal lobe of the brain is involved in personality traits
What is the Function of the nervous system
To control and coordinate the finction throughout the body and can allow response to internal and external stimuli
How does the nervous system work
It can detect change internally ansd externally to the body
Respond to external changes
Receive and interpret sensory infomation
Stimulate muscles and glands
What is the nervous system made up of
made of neurones that are made of:
Axon - Direct stimulus away from the cell body and there is 1 output but mnay input so many dendrute but 1 axon
Dendrites - Direct stimulation towards the cell body
Axon Hillock- Is full of volatge gated sodium ion channels used o trigger an actionn potential from cell body to the axon
What are the supporting cells for the CNS
Gilial Cells will help to glew the CNS together:
Astrocytyes = Growth support + trophic resposne
Oligodendrocyte = Support myelin sheath production
Microglia = Support form of immune response for CNS
Ependymal cells = Secrete cerebral spinal fluid
What do Schwann cells do
These are found in the PNS and there job is to:
Myelin shyeath formation
Carry out grwoth suppoort and the immune response as well
But they dont secrete cerebral spinal fluid
What are the areas of the nervous system
Grey matter is made up of cell bodies of neurone and the White Matter is made up of the axons and where they reside
Whar are the 4 divisions of the brain
Cerebrum , Diencephalon, Brain Stem and the Cerebellum
What is the cerebrum made up of
It is made of the frontal lobe, parietal lobe, temporal lobe and the occipital lobe
There are also Sulci that is the infolding of the cerebral hemisphere that then form valley between the Gyri
The Gyri are the ridges of the infolded cerebral cortex and is doen to allow the packing of more brain material in the skull
What are the functions of the different areas of the cerebrum
The frontal lobe is used to control the motor functions
The Pareietal lobe is used to control the sensory fucntions
The occipital lobe will control the vision functions
The temporal lobe will control the auditory functions
What does each cerebral hemisphere do
Each one will receive snesory impulses from the opposite side of the body and each cerebral hemisphere will dispathc motor impulses to the opposite side of the body
The left dominat brain people are better at languages and maths
Right dominant brai8n people will be better visual, spatial and creative skills
What does the Diencephalon do
It contain the thalamus which is a major relay station for all sensory information that come into the cortex from below in the spinal cord and brain stem
The Hypothalamus is used for homeostasis and autonomic response system
Whar are the component of the brain stem
It is the most primitive area of the brain and attach the spinal cord and cerebellum to the cerebrum
There are 3 divisions:
- MidBrain for reflex and eye movement
Pons for major relay between cerebellum and cerebrum
Medulla Oblongata is the control centre for the involuntary functions like heart rate and blood pressure
What is the cerebellum
There are 2 hemispheres thath connect direct to the brain stem
The function is to coordinate the motor activity for smooth and well timed movements as well as our balance
What does the spinal cord do
It will create a 2 way impulse conduction pathway and reflex centre that will reside within the vertebral column and is protected by meninges and CSF
How do Meninges protect the CNS
They enclose the brain and spinal cord and their respective blood vessels
There are 3 protective layers whihc are the Dira which is superfical and the strongest that is in contact with the bone
Arachnoid is adhered close to the dura and is web like
Pia is the deepest layer and is in direct contact with the CNS
What is the CSF and BBB
CSF is the cerebrospinal fluid produced by the choroid plexusw that ciurculate in the subarachnoid space
BBB is blood brain barrier and is made of endothelial cells and astroctyes- it will prevent free diffusion into the brain barrier or larger molecules and only allow lipid soluble molecules to enter to enter the brain
What is an action potential
A brief change in electrical potentials across the cell membrane that involves the movement of Na+ and K+ in response to a stimuli and will cuase nerve impulses
What is the resting potential
It is -70mv anxd is the difference between the electrical potential in and out of the cell. This is the state where the cell sits when therev is no stimuli and so the neurones are not being excited by stimuli and is maintained by passive K channels
How is the resting potential maintained
By passive potassium channels that allow K+ to diffsue through them
Alxo by Na/K ion channel what will pump out 3Na+ ions and then at the same time pull in 2 K+ ions , this is done by single AYP hydrolysis for energy and can be blocked by the toxin ouabain
How does the action potential start
Due to a transient increase in intracellular Na+ due to volgate gated Na+ ion channles will open and the K+ wil close so cause membrane depolarsiation
How does an action potential start - seven steps
S1 - The membrane is at rest so there is greater K+ permability in the membrane
S2- Membrane is passibly depolarised due to a small stimuli that cause Na+ movement into the membrane so electrical potnetial increases
S3- Membrane reaches threshold for activation of Volatge gated Na channels and cause an all or nothing response so it cant be stopped as Na+ flood into the membrane
S4 - There is a + feedback loop that cause more Na+ to enter the membrane so keep depolarising and get more +
S5- Reach Na + EM so then the Na+ channel inactivate and reopen rectifier K+ channels
S6- Na+ channels inactivate and K+ channels fully open so repolarise the membrane to beyond -70 so get hyperpolarisation - allows the refractory period
S7- Get back to resting potential so only us Na/K ion pump
What is the refractory period
These happen immediatly after the action potential spike and it is where the membrane is not excitable as all the Na+ ion channels are closed so there is no action potential able to be generated for a short amount of time. This is beneficial due to mean that the action potential are only unidirectional and travel in one way
How does Rapid signal transduction occur
There is a + feedback loop that is activated by volatge gated ion channels that will keep increasing the membrane depolarisation
There is propagation of voltage change over the membrane surface
Myelination will increase reation of Rout/Rin so then greater conductivity velocity in a mylinated axon
How is myelin made
It is made by schwann cells in the peripheral nerves in the PNS and then in the CNS it is made by the oligodendrocytes cells
What does myelination allow
There will be rapid action potential transmission with zero signal loss
Also be smaller axon diameters and so the singal is able to jump from node to node via the node of ranvier and the singal can only occur at exposed axonla membrane
Get Saltatory conduction where the singal will jump between the node of ranvier that have many Na+ channels
What are unmyelinated axons
These are usually sensory fibres and axons like pain and temperature
There are adjacent active and inactive regiosn that exchange charge to then depolarise the next section of the axon to threshold for new action potential to then start and continue the sigal
Action potential are 1 direction due to refractory period and this is called continuous conductions
They have a larger axon diameter but a slower speed of conduction compared to myelinated axons
What is a Synapse
These are electrochemical communication between 2 or more neurons that occur via synapses between axons and dendrites or at a neuromuscular junction
What are the steps for a synapse to work
S1= The neurotransmitter must be synthesized them stored in vesicles in the pre synaptic knob so they can be released when the action potential arrives
S2- When the action potential arrrives the neurotransmitters are released, this happens due to Ca2+ ion channels will open and so Ca2+ will enter the pre-synaptic knob leading the vesicles to then fuse with the membrane and release the ACH to the synaptic cleft
S3= The neurotransmitters are released into the synpatic cleft and diffuse across and bind to complimentary receptors on the post synaptic knob
S4= This then cause the action potential to keep going down the neurones from the post knob and then enzyme will inactivate the ACH to prevent constant stimulation and dont occupy the receptpors all the time
What will neuron excitability convey properties of neurons
Input and output of relaitionships
Transmission of signals
Plasticity- this is needed for learning and memory mechanism we use
Clinical implication in terms of epilepsy
What is neuronal excitability
It is the ability of a neurone to respond to a stimuli and it will be influenced by:
Resting membrane potential and Voltage gated ion channels
What is the resting membrane potential
It is the difference in voltage across the plasma membrane of a neurone when the neurone is at rest and not being stimulated
The resting potential for a human is -70mv so the inside of the neurone is njegative compared to the outside of the neurone
Why is there a negative permeability
This is due to selective permeability:
In a practial with KCL solution there are equal K+,Cl- and so when K+ ion channels are added it will mean that K+ diffuse down concentration gradient to the ECM to make the ECM more + and the ICM more -
This will lead an electrical charge where the K+ are being attracted back to the ECM due to more - area
The resting potential is then generated when there is a balamce between the electrical gradient and the concentration gradient so there is no net movement of ions
How to predict the equilibrium potential
The nernst equation = RT/zf x log e [K+]out/ [K+]in
R = gas constant
T= temperature
Z= Valence of the ion
F= Faraday constant which is the electrical charge on 1 mole of the univalent ion
What did Hodgekins and Huxley do
They determined what ions set the resting potential of a neurone by working on squid axons as they are bigger
Their base theory was that resting membrane is proportional to the equilibriumm potential of K+ so the EM is proportional to any change in log[K+ out]
But it is not directly proportinal due to other ions that have a role in setting the resting membrane potential
How do potasium leak channels come about
There is selective permeability to K+ at rest and have very high permeability
The channels are open at rest and dont let any other ions through so then K+ will leave due to electrical gradient so isndie is less +
But there are Na+ ions outside and they will enter due to the electrical gradient via sodium leak channels
The membrane potential is -70 closer to the K equilibrium potential at -90 than the Na one which is +60
This then mean that the membrane potential is a weighted average of the difference in ion potential
What is the Goldmann equation
61.5 x logP[K+out] + P[Na+out] + p[Cl-in] /
P [K+in] + P[Na+ in ] + P[Cl- out]
What is the membrane potential generated from
The difference in ion concentrations inside and outside of the cell and ion pumps are used to maintain the concentration gradient
Membrane Selective permeability
What does the Na+/K+ ATPase pump do
It is an ion pump that need energy so undergo ATP hydrolysis
At the same time it will pump out 3Na+ out of the cell and then pump 2K+ into the cell at the same time
This is so Na+ can continue to move down its concentration gradient into the cell and so there is a K+ concentration for then K+ to then enter the cell
What can the Na+/K+ pump be inhibited by
By Ouabain that will cause membrane depolarsiation and so the resting membrane will be destroyed due to no functional ion pump
Why are the ions not at equilibrium at resting potential
This is due to the ions moving in a certain direction like Na due to the large difference between the resting membrane potential and the electro potential of Na so the Na want to enter the cell and have a high energy state
This can be used to open voltage gated Na ion channels when the neurone wants to be excited
This will then cause the Na+ to flood into the cell and depolarise the cell and if threshold is met then will cause an action potential
What is excitatory postsynaptic currents + Postsynaptic potential
These are minature responses due to only 1-2 vesicles are released
The currents are through ligand gated ion channels / neurotransmitters
They will cause the membrane to become depolarised
What are Inhibitory postsynaptic current+ Postsynaptic potentials
This is where the current will only flow through inhibitory neurotransmitter activated channels
These will then sumate to reduce the neuronal excitabiloty by hyperpolarising the membrane due to K+ move out the cell and Cl- enter the cell, so then lower chance of an acrtion potential being generated
What is the peripheral nervous system made up of
It is everything else but the CNS= Brain and Spinal cord
It uses sensory afferent divison to come towards the CNS and uses motor efferent divisons to move away from the CNS
What is the motor efferent divison made up of
It is made up of the visceral motor divison + Somatic motor division
The somatic divison is related to the body wall and limbs so the things that are controlled by the skeletal muscles
Viscerla divison will be related to the internal organs and is controlled by the autonomic nervous system
What is the autonomic nervous system made of
It is needed for the maintanece of homeostasis and made up of 2 divisions called the parasymnpathetic for rest and dogestion and then the synpathetic division used for fight or flight response
How is the ANS controlled
It is continueously active under normal conditions due to both having discreet and independent function
They are both controlled by the hypothalamus to respond to stimuli
The hypothalamus is able to function even if it is disconnected from the brain
How are the ANS and the endocrine system linked together
They will together control the Blood circulation, activity of the gastrointestinal tract and then also body temperature
What are the mechansims of the ANS for endocrine control
The ANS will target the visceral muscles so will need to innervate the smooth muscles, cardiac muscles and the gland of internal organs
It is involuntary process
They are both made up of a 2 neurone chain for both the sympathetic and the parasympathetic, these are made of pre ganglion neurones that are in the CNS + a post ganglion neuronen that sit outside the CNS
The pre is myelinated and the post in unmyelinated
What is the parasympathetic system
This is the craniosacral and is used for resting and digestion
It will conserve body energy and maintain body activities at basal low levels to maintain homeostasis
What is the parasympathetic system used for
Pupillary constriction, glandular secretion, increase digestive tract mobility, smooth muscles activity to remove faeces and urine
The preganglion neuron come from the brain stem and from S2-S4 craniosacral
What is the sympathetic system
It will activate the body under condtions of emergency and under levels of stress
During excersize it will also activate to then cause vasoconstriction so then blood is moved from the skin and digestive tract to the heart, brain and skeletal muscles
What does the sympathetic system do
Pupil dilation, heart rate increade and blood glucose will increase, then also dilation of the bronchioles to induce sweating
Pre ganglion neurone come from the lateral hrons of the L1-L2 thoracolumbar spinal cord
How are the parasympathetic and synpathetic system similar
They both secrete ACH onto post ganglion neurone that have nicotinic receptros to then cause an action potential outside of the CNS
How are the autonomic and somatic nervous system different
Somatic cells are all heavily myelinated due to the ACH cause rapid neurone transmission to a neuromuscular junction where the motor neurone will direct contact the muslce via a synpase
The autonomic system have 2 neuronss chain and wilol direct contact with the smooth or cardiac muscles via a synpase
What is the spinal cord and the spinal nerves
There are 31 pairs made up of:
8 cervical nerves, 12 thoraic nerves, 5 lumbar nerves, 5 sacral nerves and 1 coccygeal nerve
During development the bone of the vertabrate column will elongate more than the spinal cord but the nerves will exit from the appropriate intervertabral space
The more posterior nerves run down the inside of the vertabral canal forming the cauda equina
The nerves that will innverate the limbs form the plexi where all the spinal cords nerves come together to operate the limbs
What is the spinal nerve made up of
Grey matter is the dense part of the neurones and the white matter are the myelinated axons
Each spinal nerve has roorts that join together to form the mixed spinal nerves that are bioth motor and sensory
Each spinal nerve segment gives rise to a pair of spinal nerves
What does each pair of spinal nerves have
Axons of motor neurons that will innervate muscles as well as sensory axons that innervate defined area of skin
Also contain sympathetic neurones for body structure in the body wall to regulate temp
Peripgeral nerves in the head are cranila from the brain stem that can be motor, sensory or both
What do dermatomes and myotomes do
Provide both sensory and motor supply of an adjacent muscles
The adjacent muscle mass is the myotome and the cutaneousn supp,ly of an area of skin is the dermatome
What is the reflex arc
A reflex is an involuntary rapid motor response to a stimuli
Arc - Receptor, sensory neuroen integration centre, motor neurone then effector so no need for CNS amd the brain
What is a motor unit
A motor neurone and all the skeletal muscle it will innervate/effect
The finer the movement then the fewer the motor neurones and the firbes and spread through the muscle so single stimulation can cause weak contraction
Several motor units have to stimulate together to cause large muscle contraction