26 The nervous system Flashcards
what are the two subdivisions of the peripheral NS?
autonomic NS
somatic NS
what are the two subdivisions of the somatic NS?
sensory neurones
motor neurones
what is the function of the somatic NS?
conscious control of skeletal muscle
what is the neurotransmitter associated with the somatic NS?
acetylcholine (ACh)
what is the function of the autonomic NS?
subconscious control, allowing reaction to the environment and internal changes and appropriate behaviour modification
what is the difference in myelination between somatic NS neurones and autonomic neurones?
somatic myelinated completely
autonomic myelinated only CNS -> ganglion (not ganglion -> receptor)
what is the pre-ganglionic neurotransmitter in the autonomic NS?
acetylcholine (ACh)
what is the neurotransmitter used in the
- parasympathetic
- sympathetic
divisions of the autonomic NS?
parasympathetic = acetylcholine (ACh)
sympathetic = noradrenaline (NAdr)
outline functions of the parasympathetic NS
digestion/movement of food through gut
slows h.r.
dilates arteries and arterioles
contracts circular muscles in iris –> pupil constricts
erector pili relax –> hairs lie flat
outline functions of the sympathetic NS
slows movement of food through gut
increases h.r.
constricts arteries and arterioles
contracts radial muscles in iris –> pupil dilates
erector pili contract –> hairs stand erect
in which division of the autonomic NS are the ganglia linking neurones found within the target organ?
parasympathetic
sympathetic’s are close to the spinal cord
what is the role of the cerebrum?
conscious thought/reasoning
emotional understanding
language
contralateral control
what is the role of the corpus callosum?
hemispheric communication
what is the role of the cerebellum?
muscle co-ordination
non-voluntary movement (i.e. reflexes)
what is the role of the medulla oblongata?
autonomic control of:
- heart rate
- breathing rate
- blood pressure
- peristalsis
what is the role of the hypothalamus?
homeostasis
osmoregulation
production of hormones secreted by the posterior pituitary gland
production of releasing factors to stimulate hormone secretion from the anterior pituitary
what is the role of the
- posterior
- anterior
pituitary gland?
posterior = storage and secretion of hormones produced by the hypothalamus
anterior = production and secretion of hormones
what is an axon?
a single elongated nerve fibre extending away from the cell body
what is a dendrite?
a short extension of cell and cytoplasm to increase the surface area of the neurone for receiving impulses from other neurones
what is the structure and function of the myelin sheath?
layers of plasma membrane produced by Schwann cells
wrap the axon and make it impermeable to Na+/K+
what is the function of the Nodes of Ranvier?
small (2 - 3 um) gaps every 1 - 3 mm along the axon
sites of depolarisation allowing saltatory conduction –> faster conduction of nerve impulses
what is the resting potential?
when a neurone is not transmitting an impulse or action potential
~ -60 mV
why is the resting potential of the interior of a neurone negative compared to its outside negative?
Na+/K+ channels and pump open/working
interior of cell has large inorganic ions
outline the procedure of an action potential
1) resting potential
2) depolarisation
- stimulus energy causes Na+ channels to open
- Na+ ions enter down e-chem gradient
- p.d. of membrane reverses
- more Na+ channels open (voltage-gated) (+ve feedback)
3) action potential
- +40 mV reached
- Na+ channels close / voltage-gated K+ channels open
- membrane returns to resting potential
4) repolarisation
- ionic balance restored by pump
- refractory period
5) hyperpolarisation
- K+ channels too slow to close
- ∴ overshoot of p.d. beyond -60 mV
- pump restores resting potential
what is the definition of a refractory period?
the period in which no further action potentials can be generated
what is the purpose of the refractory period?
prevents action potential from going in reverse
controls frequency
in cardiac muscle, refractory period = diastole –> allows time for chambers to refill
outline the process of propagation of a nerve impulse
Na+ diffuse sideways along axon
Na+ channels in next region open
Na+ diffuse in –> depolarisation
what is saltatory conduction?
when an action potential ‘jumps’ from one node to another
what are the advantages of saltatory conduction?
increases transmission speed
conserves energy - fewer ion pumps/channels
what are the factors affecting the speed of action potential transmission?
temperature: more Ek of ions –> faster diffusion
axon diameter: larger = faster transmission (less resistance)
what is a synapse?
a junction between two neurones, or between a neurone and an effector
what are the specialised features of the synaptic knob?
many mitochondria
lots of SER
voltage-gated Ca2+ channels
outline the process of synaptic transmission
a.p. reaches pre-s knob
depolarisation causes Ca2+ channels to open
Ca+ diffuse in
synaptic vesicles triggered to fuse with pre-s 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 Na+ enter, depolarisation ∴ a.p. triggered
what happens to the neurotransmitter after synaptic transmission?
must be removed to prevent stimulus being maintained
broken down by enzymes in cleft
products reabsorbed by pre-s knob by endocytosis
reformed using ATP and packaged into vesicles for next use
what is an EPSP?
{excitatory post-synaptic potential}
increased likelihood of a.p. occurring in post-synaptic neurone - membrane potential –> less negative
what is an IPSP?
{inhibitory post-synaptic potential}
decreased likelihood of a.p. occurring in post-synaptic neurone - membrane potential –> less negative
what is the role of synapses?
ensures impulses are unidirectional
allows synaptic divergence
allows synaptic convergence
what is summation?
the effect of combined neurotransmitters
what are the two types of summation?
spatial:
- lots of pre-s connected to one post-s
- accumulation of NT in synapse
- a.p. triggered in single post-s
temporal:
- NT released several times - builds up in quick succession
- a.p. triggered
what is the function of reflex arcs?
to allow rapid responses to prevent harm to the body
outline the plantar reflex
indicates brain/spinal cord damage
bottom of foot poked - normal: flex down ; abnormal: flex up
outline the pupillary light reflex
indicates damage to brain/optic nerve
light shone in both eyes - should constrict to same degree
what are the advantages of reflex arcs?
involuntary
do not need to be learnt
extremely fast
what is the definition of acquired brain injury?
any brain injury that occurs after birth
what are the two types of brain injury?
traumatic - involves a severe blow to the head (e.g. RTC/mugging)
non-traumatic - no severe blow (e.g. stroke/infection)
how does a stroke occur?
blood vessel supplying brain becomes blocked
OR
blood vessel ruptures and bleeds into brain (subdural haematoma)
when is a person considered ‘dead’?
when there is no activity in the brain stem
how could drugs be used to treat Alzheimer’s?
cholinesterase inhibitors –> prevent hydrolysis of ACh
∴ increased ACh concentrations
∴ increased functioning/restoration of lost functioning
what are the actions of non-steroidal anti-inflammatory drugs (NSAIDs)?
inhibit inflammation response
reduce pain
reduce fever
what are the causes and symptoms of Parkinson’s?
loss of dopamine producing cells
leading to increased muscle tension
leading to joint rigidity and slow movement
how could therapeutic drugs be used to treat Parkinson’s?
levodopa –> metabolised to dopamine
dopamine agonists –> mimic dopamine
monoamine oxidase inhibitors –> inhibition of enzymes that break down dopamine
what is the effect of alcohol on the NS?
inhibition of neurotransmission across synapses –> loss of motor skills and co-ordination
binds to a number of synaptic receptors
what is the effect of heroin on the NS?
an opioid - converted to morphine in brain and binds ti opioid receptors
leading to clouded cognitive function, and reduced h.r./b.r.
what is the effect of marijuana on the NS?
THC - similar to anandamide (a natural cannabinoid)
temporarily releases dopamine
THC not broken down quickly and blocks GABA
what is the effect of methamphetamines on the NS?
affect excitatory synapses in neurones by increasing dopamine released at synapses
slow to be broken down ∴ effect of dopamine prolonged
what is the function of the limbic system?
long term memory creation, behaviour and emotions
influences endocrine system and autonomic NS
what is the effect of excess dopamine on the limbic systems?
dopamine released by hypothalamus for reward-motivated behaviour/actions and creates desire for it to be repeated
ongoing dopamine activity activates limbic system and changes brain to state of dependency
what is the definition of addiction?
when a tolerance to a substance builds up so that more of it is required to produce the same effect
what is the definition of dependency?
when a substance is required by the body for normal functioning
give an example of a biochemical reaction to drug use
increased enzymes required to break down drug
reduction in sensitivity of synapse
what are the reasons that might cause someone to develop an addiction?
social (i.e. peer pressure)
emotional (e.g. anxiety issues)
depression/malfunctioning
what are the consequences of addiction?
can become dominant in life
reduces ability for basic functions
can lead to criminal behaviour
what are the costs to society of addition?
healthcare costs
costs of criminal activity
policing and customs to prevent trafficking
loss of abuser’s contribution to economy
social breakdown as behaviour detoriorates
