3: Nervous system Flashcards
Define homeostasis
the process by which the body maintains a relatively stable internal environment.
What are the 3 systems that maintain homeostasis
1- sensory function (detects and sends)
2- Integrative function (analyses, interprets and generates a response)
3- motor function (issues output)
Define general sensory receptors
located in the skin, skeletal muscles, tendons, joints and visceral organs. Include; thermoreceptors nociceptors mechanoreceptors
What does the general sensory receptor thermoreceptors detect?
detect changes in the temperature
What does the general sensory receptor nociceptors detect?
detect painful stimuli
what are the three types of mechanoreceptors and what do they detect
tactile- touch, pressure and vibration
Baroreceptors- blood pressure
proprioceptors- changes in body position (proprioception)
Where are special sensory receptors located?
eyes, ears, mouth and nose
What are some examples of special sensory receptors
photoreceptors- detect light (vision)
Chemoreceptors- detect chemical solutions (taste and smell)
Mechanoreceptors called hair cells (detect hearing and balance)
What are the two divisions of the nervous system?
CNS and PNS
CNS structures and functions
structure= brain and spinal cord Function= control centre that performs integration
- controls emotions, behaviours and personality
- performs intellectual (cognitive) functions
- stores memories
PNS structures and functions
structure= contains sensor receptors, cranial, spinal and peripheral nerves.
Cranial nerves structure and function
branch primarily innervate structures of the head and neck.
Spinal nerves structure and function
Spinal nerves branch to form the peripheral nerves that innervate all parts of the body below the head.
What are the two divisions of the peripheral nervous system?
sensory (afferent)
- conveys sensory input from receptors to the CNS
motor (efferent)
- converts the motor output from CNS to muscles or glands
What are the two divisions of the motor division?
autonomic and somatic
Describe the somatic nervous system and what it controls.
conveys somatic motor output from CNS to skeletal muscles
Voluntary= skeletal muscle movement involuntary= skeletal muscle movements (smoatic reflexes)
Describe the somatic nervous system and what it controls.
conveys autonomic motor output from CNS to glands, cardiac and smooth muscles
controls involuntary activities
e. g.
- heart rate
- respiration (respiratory air flow)
- blood vessel and pupil diameter
- digestion of food
- urination and defecation
- perspiration and salivation
What are the two functions of the autonomic nervous system
sympathetic
parasympathetic
Describe the sympathetic division
“fight or flight”- activities
- activated the body functions that support physical activity and inhibits those that don’t.
- increases heart rate, respiratory air flow, blood flow to skeletal muscles and sweat gland activity.
- dilates pupils
- inhibits digestive function
- inhibits urination and defecation
Describe the parasympathetic division
“rest and digest”- activities
- conserves energy and promotes the body’s housekeeping functions
e. g. - stimulates digestive function, urination and defecation
- constricts pupils
- decreases heart rate
- decreases respiratory flow
What are the two key components of the nervous system
- neuroglia
- neurons (nerve cells)
Define neuroglis
“nerve glue”
support neuron development and function, nourish, protect, insulate and structurally support neurons
Most brain tumours are made of neuroglia.
6 main types
What are the three basic functions of the nervous system?
1- detect chnages (stimuli) occuring inside and outside the body
2- respond to these changes by altering the activities of organ systems
3- coordinate the activities of all organ system
What are the four main types of effectors
- skeletal muscles
- cardiac muscles
- smooth muscles
- glands
Define neurons
the basic structure of the nervous system.
Function: communication.
- when stimulated they generate electrical signals called graded potentials and action potentials to conduct sensory and motor information from one part of the body to another.
high metabolic rate
- Needing a high supply of oxygen and glucose for survival.
unable to divide and replace themselves if destroyed.
What are the 4 main components of a neuron
- Dendrites
- cell body
- axons (fiber)
- axon terminals
Describe dendrites
Structure= finger-like trees at the top of a nerve.
Function= main receptive (or input) region
- act as sensory receptors- detect stimuli
Large surface area= allows them to detect stimulus and receive info effectively.
convert info they receive to graded potentials which they send to cell body
Describe the cell body
contains nucleus and organelles
- crecieves info, intergrates and sends incoming information to the axon
Describe the axon (aka fibre)
The conducting region.
“conducting region” that generates (initial segment) and conducts action potentials to convey information from the initial segment to the axon terminal.
- can be mylinated
Axon hillock
conducting region between cell body and axon
Describe myelin
structure= white and fatty function= speeds up transmission
produced by schwann cells and oligodendrocytes
What diseases are associated with mylein damage
Loss of myelin slows myelin conduction and can determinate so much that conduction stops.
Aka multiple sclerosis
Define nodes of ravier (internodes)
gaps in the myelin
Describe the axon terminal
synapses with another cell
=secretory region
- releases neurotransmitters (chemicals that carry info to another cell)
- contain synaptic vesicles which store and release neurotransmitters (chemical that carry info)
Where are nuclei (nucleus) and ganglia (ganglion) located and what are they?
nuclei (nucleus)= CNS
ganglia= PNS
- they are clusters of neuron cell bodies
What is the function of nuclei (nucleus)
Function= integration
- Analyse and interpret sensory input
- Analyse and decide on a motor response.
Some nuclei located in the brain
- Store memory - Determine personality - Regulate emotion - Perform intellectual function - Produce hormones
neuron axions are bundled to form what in where?
Tract in the CNS
- conduct sensory and motor info through spinal cord and different areas of the brain.
Nerves in the PNS
-conduct sensory input to CNF and motor output away from CNS
What are the three strutural clasifications of neurons and where are they found
Bipolar
(cell body in the middle, unmylenated)
- rare (in special sense organs e.g. ear, eye)
unipolar
(detached cell body)
- PNS
multipolar
(regular looking)
- CNS and PNS
Structure and function of sensory neurons
S= uniploar F= sensory input from receptors to CNS
Structure and function of interneurons
S= multipolar F= conduct information within CNS
Structure and function of motor neurons
S- multipolar
F= conduct motor output away from the CNS to a muscle or gland
lower motor neuron= somatic motor output
pre and post ganglionic= autonomic output
The basic principle of RMP
opposite changes attract so energy is required to keep them apart. aka. potential energy
stored/potential energy= measured in V or mV
Define membrane potential
the potential energy that is separating the
internal negative
and the
external positive changes
When does a change in membrane potential occur
when an ion k+ leaves or Na+ goes into the cell changing the charge strength.
this creates an electrical signal
summary= ions flow across the plasma membrane of a neuron- membrane potential (voltage) changes- electrical signal generated
What must a neuron do they generate an electrical signal
their plasma membrane must;
- exhibit a resting membrane potential (RMP)
- contain protein channels that allow specific ions to diffuse down their concentration gradient.
What are the two main types of channels that let K+ and Na+ ions though to change membrane potential?
leakage channels= always open, the small number allowed to cross
Gated channels= stimulated to open and close, large numbers allowed to cross
summary= when a stimulus opens gated ion channels, multiple/large number of ions move across
What are the three types of gated channels?
chemically gated
mechanically gated
voltage-gated
Explain simulation and location of chemically gated channels
open in response to chemical signals
e.g. neurotransmitter binds to a channel causing it to open. This means ions are free to cross
location= along plasma membrane of dendrites and cell bodies
Explain simulation and location of mechanically gated channels
open in response to mechanical stimulation
e.g. touch, vibration and pressure
location= along the plasma membrane of dendrites
Explain simulation and location of voltage gated channels
Open and close response to voltage changes or changes in membrane potential.
Location= along the plasma membrane od the axon and axon terminals.
What gated channels are on the membranes of;
dendrites
cell bodies
axons and axon terminals
Dendrites: mechanically and chemically gated channels
Cell body: chemically gated
Axon and axon terminals: voltage gated channels
Define resting membrane potential (RMP)
= the voltage across the plasma membrane of a resting (unstimulated) cell
it exists because of an uneven distribution of positive ions across the plasma membrane creates a charge difference across the membrane.
ECF= overall positive
ICF= overall negative
what is the aprox RMP
-70mV
Compare the ECF to ICF in terms of charge
ECF= high concentration of Na+ ions
- more +ve ions
- overall positive charge
ICF= hugh concr=entration of K+ ions
- less +ve ions
- overall negative charge
Depolarisation=
the membrane becomes less negative
- means it moves from -70 towards 0.
D= depolarise= decrease negativity
sodium gated channels open letting Na= (more positive) into the less negative ICF—– this decreases the RMP to -60 e.g.
Hyperpolarisation=
membrane becomes more negative
when a stimulus opens K+ gated channels allowing a great number of K+ ions into the ECF, the ICF becomes more negative (loses positive K+ ions)
RMP= more negative e.g. - 70mV to -80mV
What happens to the RMP when hyperpolarisation and depolarisation occurs
hyper= more negative depola= less negative
Explain graded potentials
- Small changes in membrane potential (de or hyperpolarisation)
- Occur in dendrites or cell body when stimulus opens the chemically mechanically gated channels.
- Short stimulus
- strong stimulus= bigger change in membrane potential= further signal will travel
Explain how a graded potential leads to an action potential
- once stimulated by chemical or chemical stimulant on cell body or dendrite occurs, a graded potential is created. The short burst is send to the initial segment. the stronger the stimulus= treating RMP change= signal will travel further
- AP depolarises initial segment to -55mV = threshold
- this stimulates voltage-gated Na+ channels to open
- this generates AP
Actions potential is generated if a stimulus is so loge the graded potential has enough strength to travel to the imitial segment wich depolarises the initial segment to -55mV= threshold which then stimulates voltage gated Na+ channels to open this then generates action potential.
What are some properties of action potentials?
- long distance
- originate at initial segment
- involve voltage-gated channels
- self propelling aka. fist AP triggers 2nd AP triggers 3rd AP
Action potential are generated by what three consecutive changes in the membrane potential?
depolarisation
depolarisation
hyperpolarisation
Describe depolarisation
once at -55mV, voltage gated chnannels open to let even more Na+ past to get it +30mV
- occurs at -55mV (membrane has got less natuage when Na+ channels have opened up and Na+ comes in)
- axon interior becomes less negative
- membrane potential shifts from -55mV to +30mV
Desctibe repolarisation
- occurs when membrane hits +30mV
- voltage gated Na+ channels close and voltage gated K+ channels open to ket K+ out of the ICF
- loss of K+ ions makes the RMP move closer to -70mV
Describe hyperpolarisation
as the membrane aproaches -70mV it closes vo;tage gated channels however they are slow to close so K+ continue to flow into ECF
- axon interior becomes more negative e.g. -70mV to -90mV
- when K+ channels close, the movement of Na+ and K+ through leakage channels and ATPase pump resotres RMP back to -70mV
Explain continuous conduction
- occurs in unmyelinated axons
- AP generated at voltage-gated channels along the axon
- slow conduction (< 2m/s)
Explain saltatory conduction
- occurs in myelinated axons
- action potentials generated at nodes of ravier
- very fast >100m/s
- signals skip and leap down axons via nodes od ravier
How does localised anesthetic impact action potentials
- blocks sodium gated channels so no pain or sensation can be conducted to the brain
- block pain transmission by blocking Na+ gated channels. Therefor no Na+ entering axon so no depolarisation occurs.
Define a chemical synapse
A junction that mediates the transfer of information from one neuron to another or neuron to a muscle or gland.
presynaptic neuron- post synaptic neuron through synaptic cleft via neuro transmitters
Steps of information transfer
1- action potential arrives at axon terminal and depolarises
2- depolarisation stimulates voltage gated Ca2+ channels (on the membrane) to open and Ca2+ to enter the terminal
3- Ca2+ entrance triggers synaptic vesicles to release neurotransmitters into synaptic cleft
4- neurotransmitters diffuse across the synaptic cleft and bind to chemically gated channels on the post synaptic membrane of cell body or dendrite.
5- binding of neurotransmitter opens chemically gated channels- influx of Na+ into ICF=depolarisation= graded potential created (excitatory postsynaptic potential- EPSP)- EPSP travels and depolarises at initial segment of post synaptic neuron to threshold 9-55mV= action potential generated
- info successfully transmitted
Describe the 3 terminations of synaptic transmission
1- neurotransmitters diffuse away from synaptic cleft
2- are degraded by enzymes in synaptic cleft
3- NT’s re-enters axon terminal and is destroyed by enzyme or reused, aka re uptake
