Nervous System Flashcards
Two parts of Nervous System
-CNS (brain, spinal chord)
-Peripheral NS (all other neurones that connect CNS to rest of the body)
Two parts of PNS
-Somatic nervous system
-Autonomic nervous system
Function of somatic NS
under conscious control, voluntary actions
single neurone links SNS to effector
Neurones are myelinated along axon
NT released by motor neurones= acetylcholine
Function of Autonomic NS
under subconscious control, involuntary actions eg (heartbeat)
2 neurones link CNS and effectors- connected via ganglion
Myelinated until ganglion, unmyelinated after
pre ganglionic NT= ach
ANS further divided into:
Parasympathetic NS (decreases activity)
postganglionic NT: ach
Sympathetic NS (increases activity)
postganglionic NT: noradrenaline
Parasymoatehtic NS nerve
Vagus nerve
Sympathetic NS nerve
sympathetic nerve
5 regions of the brain
cerebrum, cerebellum, medulla oblongata, hypothalamus, pituitary gland
Cerebrum role
-consists of 2 hemispheres
-controls conscious thoughts, language, emotional responses etc
cerebellum
controls muscle coordination, balance & posture, reflexes
Medulla oblongata
Controls autonomic activities in body eg. heart rate, breathing rate, blood pressure etc
Hypothalamus
homeostasis
osmoregulation
Production of hormones which are then stored in the posterior pituitary gland
Pituitary gland function
-Posterior: stores & secretes hormones produced by hypothalamus
-Anterior: produces & secretes hormones
What is an axon
singular elongated nerve fibre
Transmits nerve impulses AWAY (a for axon) from cell body
Importance of myelin sheath
Made of Schwann cells WRAPPED AROUND AXON
Insulate the axon
Makes it impermeable to Na and K ions, SO ions cannot pass in and out of neurone
There are small gaps- Nodes of Ranvier
These gaps are sites of depolarisation
Enable saltary conduction
Therefore faster conduction of the nerve impulse
Action potential def
the change in electrical potential with the passage of an impulse along the membrane of a neurone
what is resting potential
when a neurone is not transmitting an impulse or action potential
outline the procedure of an action potential
- Resting Potential (-70mV)
Established by Na/K pump. 3 Na out, 2 K in - Depolarisation
Stimulus causes Na voltage gated channels to open
Na diffuse into cell
Inside more +, even more Na channels open (+ feedback - Action Potential (+30 mv)
Na channels close, K channels open
Membrane starts to return to resting potential - Repolarisation
Na/K pump restores ionic balance
Time for depolarisation- refractory period - Hyperpolarisation (dip)
Overshoot of K
Membrane potential is less than -70
Pump restores resting potential
What is the purpose of the refractory period
- prevents action potential from going in reverse
-eg. cardiac muscle, refractory period allows time for chambers to refill
Why do action potentials travel faster in myelinated
-Depolarisation can only occur at nodes of Ranvier
-with myelinated, action potential jumps to the next adjacent node
-so speed of action potential transmission is sped up
Factors affecting speed of action potential transmission
-Temp (more kinetic energy)
-Axon diameter (less resistance)
what is a synapse
region between 2 neurones
impulses are transmitted across synapses using diffusion of NT
types of NT
-excitatory: depolarisation, triggers AP
-inhibitory: hyper polarisation, prevents AP
Feature of synaptic knob
many mitochondria & SER
voltage gated Ca2+ channels
outline the process of synaptic transmission
Action potential reaches pre-s knob
Depolarisation causes Ca channels to open
Ca ions flow in
Synaptic vesicles triggered to fuse with pre-membrane
NT released via exocytosis into cleft
NT binds to specific, complementary receptors on post-s membrane
Na+ channels on post-s membrane open
If sufficient open, to overcome threshold value, action potential is generated
what happens to NT after synaptic transmission
NT broken down by enzymes in the cleft
products reabsorbed by pre-s knob by endocytosis
reformed using ATP & packaged into vesicles to be used next time
Why do synapses only allow transmission in one direction
Ca ions are only present at the presynaptic membrane
Excitatory postsynaptic potential
Increases likelihood of AP occurring
NT causes membrane to become more positive closer to the threshold value
Inhibitory postynaptical potential
decreases likelihood of AP occurring
NT causes membrane to become more negative & further away from threshold value
Summation & control
Sometimes NT quantity is low and not enough to excite postsynaptic membrane to a threshold value
-Spatial summation: when several pre-synaptic neurones connect to 1 post-synaptic neurone
-Temporal summation: several sub threshold build up in synapse until quantity is high enough to trigger action potential
what is a reflex
rapid, involuntary response to a stimuli to prevent harm to body
what is the plantar reflex
bottom of foot poked
normal: flex down
abnormal: flex up- indicated spinal cord damage
pupillary light reflex
both pupils should constrict to the same degree- if otherwise, possible damage to optic nerve
Advantages of reflexes
involuntary
Rapid
Do not have to be learnt
aquired brain injury
any brain injury after birth
how does a stroke occur
blood vessel supplying brain becomes blocked
or
blood vessel ruptures & bleeds into the brain
when is a patient considered dead
when there is no activity in the brain stem
how could drugs be used to treat alzeihmers
-Cholineesterase inhibitors
-Prevent breakdown of Ach to choline
-inc Ach conc
-inc functioning
Causes and symptoms of Parkinson’s
due to loss of brain cells that produce dopamine
results in joint rigidity and slow movement
drugs which could be used to treat Parkinson’s: levodopa, dopamine agonists
addiction
uncontrolled, compulsive behaviour
tolerance builds up- inc quantities required to produce the same effect
suggest why a person taking heroin may develop a psychological dependency
drug induces a false feeling of well-being
so persons falls into the habit of taking drug to feel good
