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Title: human physiology - the nervous system
Description: a summary explaining the physiology of the nervous system
Description: a summary explaining the physiology of the nervous system
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Human physiology
Controlled conditions within limits = maintain health and maintain homeostasis
Endocrine system = sensor of response
...
Homeostasis is automatic – continuous
- No signals from the brain
- Electrical, response is rapid,
Nervous system – tissue
...
(react to changes within
receptors)
- interpreting and remembering those changes
-Reacting to changes with effectors
...
Special parts of the nervous system:
- Brain
- Cranial nerves
- Spinal cord
- Spinal nerves
- Ganglia
- Enteric plexuses and sensory receptors
...
12 pairs of cranial nerves – emerge from the base of the brain through foramina of the skull
...
Spinal cord = connects to the brain though the foramen magnum of the skull and is encircled
by the bones of the vertebral column
...
Ganglia – located outside the brain + spinal cord, small masses of nervous tissue, containing
pulmonary cell bodies of neurones
...
Enteric plexuses help regulate definitive system
...
Functions of the nervous system
The sensory function of the nervous system is to sense changes in the internal and external
environment through sensory receptors
3 types of sensory receptors – Afferent (sensory) membranes – analyse sensory info and
makes decision using it
...
2 divisions
- CNS – central nervous system (brain and spinal cord)
- PNS – Peripheral nervous system
...
- Connects CNS to muscles
Neurones
Functional unit of neurones system
Have the capacity to produce action potentials = electrical energy
Cell body – single nucleaus with prominent nucleolous
...
Dentrites – input of info
...
Dendrites – receiving/input portion of a neurone
...
Eg bicep
Neurological cells
-Half volume of CNS
- smaller cells than neurones
- 50 x more neurones
-cells can divide
4 types of CNS - astrocytes
- Oligodendrytes
- Microglia
- Ependymal
Cell type in PNS – schwaan
Dendrites
- Conduct impulses towards the cell body
- Short, highly branched + unmyelinated
- Surfaces specialised for contact with other neurones
Axons
-
Conduct impulses away form the cell body
Long, thin and cylindrical processes of cell
Impulses arise from initial segment ( trigger zone)
Swollen tips called synaptic end bulbs contain vesicles
filled with neurotransmitters
...
The sheath electrically insulates the axon and increases speed of the nerve impulse
conduction
...
Gaps are called Ranvier
...
-Myelin – jelly roll like wrapping is made of lipoprotein
...
Unmyelinated fibres
- Slow, small diameter fibres
- Only surrounding by neurilemma but no myelin sheath
wrapping
...
Nucleus = mass of nerve cell bodies and dendrites inside the cell
...
communicate with 2 types of electrical signals:
- action potentials that can travel long distances
- graded potentials that one local membrane changes only
...
Ion channels - gated ion channels
3 channels:
these respond to voltage changes, ligands (chemical)
and mechanical pressure
...
2 types of ion channels:
Always open channels:
-
leaking (non gated) channel
gated channels
nerves have more K+ than Na+ leakage channels
...
Therefore, resting potential of -70mV in nerve tissue
...
Electrical signals in neurones
...
Communicate with 2 different electrical signals:
- Action potentials that travel long distances
...
in living cells a flow of ions channels occurs through ion channels in the cell membrane
...
Voltage gated channel:
Voltage gated k+ channels close
...
2
...
Chemical stimulus opens the channel
Cation channels open and acetylcholine binds and opens the channel
...
(overall
is generally neutral)
Only a very thin shell of charge difference is needed to establish a membrane potential
...
This produces
one molecule of energy (1 ATP)
- at a steady state, active fluxes of Na + K balance the ‘leak’
fluxes
...
e electrical force = chemical gradient
Vk ≈- 60mV log [k+]in
[k+] out
this is known as the Nernst equation
...
ion gradients
2
...
(refer to pic below) due to boundary conditions of ions
inside the cell
...
in conclusions:
1
...
2
...
3
...
-
Large permeability to k+
Please refer below to the picture explaining the general pattern
...
Axons – undergo the action potential to
deliever the information, typically a neurone
transmitter from axon terminals
...
Graded potentials
Small dendrites from resting potential of -70mV
...
For the graded potential, the signals are graded, meaning
they vary in size depending on strength of stimulus and
localised
...
source of stimuli:
How graded potentials arise
-
mechanical stimulation of membranes with mechanical
gated ion channels (remember this means pressure etc)
chemical stimulation of membranes with ligand gated ion
channels (remember this is like neurotransmitter)
Remember this was discussed earlier on
...
Remember DEpolarisation is opposite of ‘Down’and then you can recal that
HYPERpolarisation is opposite of ‘High’
...
remember size of graded potential can be large or small depending on the size of stimuli
they are proportional:
- graded potential size = size of stimuli
as action potentials move down the neurone, it starts to decrease in size
...
Generation of an action potential
...
These eventually decrease and reverse the membrane potential (make it more positive –
depolarisation)
...
During action potential – Na+ and K+ gates open and close in a sequence
...
e the positive/negative – ness of the membrane
...
Don’t be that stupid person – always remember a stronger stimulus WILL NOT cause a larger
AP, it will only increase the frequency of the impulses
...
When the Na+ ion channels open, Na+ rushes in and causes depolarisation
...
These are going to be explained below:
Depolarisation phase of the action potential
1
...
2
...
They cannot move back
out of the cell
...
This makes the cell more positive inside (it was originally negative)
4
...
Known as positive feedback
...
Repolarisation phase of the action potential
1
...
2
...
When the k+ channels open, the Na+ channels close
...
The outflow of K+ ions quickly returns the membrane to the resting membrane
potential of -70mV
...
5
...
6
...
Refractory period -Absolute
1
...
2
...
3
...
Large fibres have refractory periods of 0
...
s
Refractory period – Relative
1
...
2
...
3
...
Propagation of the Action Potential
...
An action potential spreads (this is known as propagation) over the surface of axon
membrane
...
Na+ flows into cell during depolarisation, however because the k+ channels are
slower in opening (we mentioned this earlier) the Na+ ions move across the
membrane to adjacent channels and changes the membrane potential
...
This causes the channels to open and Na+ to be released out the cell
...
Continuous conduction – unmyelinated fibres
- Step by step depolarisation of each portion of the length
of the axolemma
...
(remember voltage
gated ions react to change in membrane potential
...
Encoding stimulus intensity
Frequency of impulses – we mentioned this earlier, the frequency of action potentials will
increase following greater pressure
...
sensory neurones – the number of sensory neurones activated (remember you activate
sensory receptors by external or internal changes) is proportional to the pressure applied
...
Title: human physiology - the nervous system
Description: a summary explaining the physiology of the nervous system
Description: a summary explaining the physiology of the nervous system