Transcript Nervous system

Nervous system
Nervous system
Basic unit: Neurones
 Sensory neurones
receptors  CNS
 Motor neurones
CNS  effectors
 Association neurones
linking sensory & motor
neurones
A neuron
Sensory neurone
Motor neurone
Association neurone
Neurones
Cell body
Dendrites
sense organ/ other
neurones  cell body
Axon
cell body  other
neurones/ effectors
Nerve fibre coverings
Neurilemma, Schwann
cells, Myelin sheath
3 classes of neurons
A neurone postsynaptic to one cell can be presynaptic
to another
Resting Membranes Potential
The nerve fibre is at rest
+ve outside, -ve inside
Diffusion i.e. K+ diffuses outward
 Active transport i.e. K+ in & Na+ out by
Na- K pump
Ions
Na+
K+
Inside
16
100
Outside
140
4.4
Action Potential
Stimulation of an axon by an electrical impulse
change in the potential across the axon
membrane ( -70mV  +40mV)
 Depolarization + Repolarization +
hyperpolarization
An action potential
I. Resting State
Neither Channel is open
II. Depolarization
Na+ gates open but K+
channels remain closed
Na+ flows inward
membrane potential+ve
III. Repolarization
Na+ channels but K+
channels open
K+ moves outward
membrane potential -ve
IV. Hyperpolarization
Na+ channels close but
K+ channels remain
open
further K+ moves
outward
membrane potential
further -ve
All- or- none Law
Strong enough
stimulation ( above
THRESHOLD )
Depolarization
Not strong enough
stimulation ( below
THRESHOLD)
Nothing
Refractory period
~ 1 ms
the period of membrane depolarization
the period when the axon can’t conduct
another impulse
Speed of impulse conduction
Myelinated vs non-myelinated nerve
Rate of impulse transmission in myelinated
fibre > that of non- myelinated fibre
Diameter of fibre
 fibre diameter,  speed
Body temperature
 temp.,  speed
Synapes
The junctions between neurones
 Presynaptic membrane ~ attachment of
vesicles, release of neurotransmitter
Synaptic vesicle ~ contain neurotransmitter
i.e.acetylcholine, noradrenaline
Synaptic cleft ~ small gap
 Postsynaptic membrane ~ receptor sites
 Mitochondria ~ resynthesis of
neurotransmitter
Electro-chemical transmission I
The nerve
impulses travel
along the axon of
synaptic neurone
Electro-chemical transmission II
 arrival of nerve
impulses at axon
of presynaptic
neurone, 
permeability of
presynaptic
membrane to Ca+
Electro-chemical transmission III
Synaptic vesicles fuses
with presynaptic
membrane & rupture
Neurotransmitters are
released into the
synaptic cleft
Electro-chemical transmission IV
Neurotransmitters
diffuses across cleft

Neurotransmitters
attach to receptor sites,
 permeability of
postsynaptic membrane
Electro-chemical transmission V
Local depolarization is
triggered
↓
Nerve impulse
propagate in
postsynaptic axon
Fate of neurotransmitters
Cholinesterase break
down the
neurotransmitters
choline & ethanoic
acid
Choline is reabsorbed &
resyntheisied to recycle
new neurotransmitter
again
Neuromuscular Junction
~ motor end- plate
synapse between the nerve terminals of a
motor neurone & the muscle fibre
deep fold  surface area
the muscle fibre responses by contraction
Motor end-plate
Nervous system
Central Nervous System
(CNS)
 Brain +Spinal cord
Peripheral Nervous
System (PNS)
 Cranial nerves +
spinal nerves
Autonomic Nervous
System (ANS)
Sympathetic +
parasympathetic
Central Nervous System (C.N.S.)
Spinal cord
 transmit impulses  brain
 act as reflex centres
 Central canal
 Grey matter
 Meninges
Spinal nerve
Spinal
cord
Reflexes
Reflex is  innate
 automatic response
involving parts of the body rather
than the whole
Reflex arc = receptor + sensory neurone +
association neurone + motor neurone+
effectors
Types of reflex action I
Inherited reflexes
 no need of learning & experience
 polysynaptic reflex  sensory + association
+ motor neurones
e.g. The withdrawal reflexes
 monosynaptic reflex  sensory + motor
neurones
e.g. Knee-jerk action, iris-pupil reflex,
balancing, breathing rate & blood pressure
Types of reflex action
Conditioned reflex action
 a result of learning & experience
 e.g. typing, playing piano, cycling,
swimming
 promote survival
Properties of reflexes
Certain stimulus  same response
No prior thought or planning for the response
Involuntary and fast in action response
Keeping body from harms   survival
Reflex action vs voluntary action
 Reflex action
~ not involve cerebrum
~ unconscious,
involuntary &
automatic
~ same stimulus same
response
~ fast
~ spinal cord & medulla
oblongata
 Voluntary action
~ involve cerebrum
~ conscious, voluntary &
not automatic
~ same stimulus 
different response
~ slow
~ cerebrum
Central Nervous System
Brain
a. Brainstem
~ medulla + pons + midbrain
b. Cerebellum
c. Cerebrum
~ cortex + basal ganglia + thalamus +
hypothalamus + other areas
Cerebrum
Dicephalon
Midbrain
Pons
Medulla
oblongata
Cerebellum
Spinal cord
Meninges & cerebrospinal fluid
Meninges ~ 3 layers  protective membranes
Cerebrospinal fluid ~ fluid inside the brain &
between the inner two layers of meninges
Blood  CSF  Brain ventricle

surrounding
Central canal
the brain &
of spinal cord
spinal cord


reabsorbed into
capillaries
Functions of CSF
Protect & support the
brain & spinal cord
maintain uniform
pressure
as cushion & shock
absorber
as medium for
exchanging
Flow of
CSF
Frontal lobe
Parietal lobe
Occipital
lobe
Temporal
lobe
Cerebrum
Right + left hemisphere ( connected by Corpus
callosum )
Functions:
 higher mental processes
 initiation & control of the voluntary muscle
contraction
 perception
Function of cerebrum
Decorticate animals
Frog ~ behaves
normally
Dog ~ blind, no senses
of smell& hearing but
able to walk & swallow
Human ~ no breaths &
swallow, no learning &
no voluntary action
 die quickly
Hypothalamus
Thermoreulartory centre
~ heat gain vs heat loss centres
Neuro- secretion
~ Thyroid stimulating hormone releasing
hormone, ADH
Interoreceptors & co-ordinator
Hypithalamus
Cerebellum
Impulse from
Impulse from eyes & ear
muscle & joints
Cerebellum
indicate body position
Provide ‘i’ about the
head position
Impulses from the cerebellum
Influence the contraction of skeletal muscle
Balance
Medulla oblongata I
Continuous with spinal cord
 Cardiac centre
Cardiac centre


parasympathetic nerve fibre
Sympathetic nerve fibre


+


The rate & force of heart beat, cardiac activity
Medulla oblongata II
 Respiratory centre
Excess CO2 or deficiency O2 in blood


Phrenic nerve(+)
Intercostal nerve (+)


diaphragm activity
contraction of ICM


Vigorous breathing movement ( depth & rate)
Medulla oblongata III
 Vasomotor centre
Stimulation  arterial baroreceptors or emotions

vasomotor centre in medulla

Autonomic nervous system (ANS)

Responses  Blood vessels constriction or dilation
Medulla oblongata IV
 Autonomic reflex centres
Irritating substances are
present in the stomach or
respiratory tract

Reflex centre in medulla oblongata

Reflex actions of vomiting, coughing & sneezing
Peripheral Nervous System (PNS)
12 pairs cranial nerves
+ 31 pairs spinal nerves
Spinal nerves: emerge
from spinal cord
Cranial nerves: emerge
from brain
Connect the brain &
spinal cord with
receptors & effectors
Autonomic Nervous System (ANS)
Sympathetic nerves + parasympathetic nerves
Antagonistic system
 Sympathetic system ~ “fight or flight” action
  heart rate, dilates bronchi & arteries to
muscle but constrict arteries to gut,
glycogen glucose, adrenaline
 Parasympathetic system~ conservation
opposite to sympathetic system
ANS
Antagonistic characters
Sympathetic system
 dilation of pupil
  secretion of tear
  secretion of saliva
  heart beat
 arteries constrictBp
  gut movement
 bronchi dilate
 bladder relax
  sweat
Parasympathetic system
 pupil constrict
 normal secretion of tear
 secretion of watery
saliva
  heart beat
 arteries dilate  Bp
  gut movement
 bronchi dilate
 bladder contract
Symp. Vs Parasymp.
Origin: spinal nerve
Diffuse effect
Neurotransmitter:
Noradrenaline
Prepare for stress;
excitatory homeostatic
effect
Ready for emergency
Origin: cranial nerve/
spinal nerve
Localised effect
Neurotransmitter:
acetylcholine
Maintain in steady state;
Inhibitory homeostatic
effect
Conservation
Interrelation of CNS & ANS
Visual interpretation as danger

CNS

ANS


nerve ending
adrenal medulla


adrenaline effectors  blood streamadrenaline
Nervous system
Hormonal system
Hormones
Synthesized by
endocrine gland
Carried in blood to
target sites
 Steroid
 Protein
 Fatty acids
Mechanism of Hormone action
Cell membrane level
~ facilitate/ inhibit
transport substances
into the cell
Enzymes system level
~ second messenger
Cellular organelles level
~ influences electron
transport chain
Gene level
Mechanisms of hormones secretion I
Nervous control
 Adrenaline
danger eye optic nerve CNS(fear)
ANS sympathetic nerve adrenal
medulla Adrenaline
 Oxytocin
sucking on nipples spinal nerve CNS
pituitary gland oxytocin
Mechanism of hormone secretion II
 Antidiuretic hormone (ADH)
Bp baroreceptors
 ADH


hypothalamus  posterior pituitary


 Bp baroreceptors
 ADH
Mechanism of hormone secretion III
Hormonal control
 Negative feedback mechanism
 TSH  stimulation to Thyroid gland 
 thyroxin   stimulation pituitary gland
  TSH
~ maintain a constant concentration of thyroxin
in blood
Mechanism of hormone secretion IV
 Positive feedback
LH  stimulation to ovary  
oestrogen  LH …..
~ but its continued release is prevented by the
later release of progesterone
Endocrine Glands
Ductless gland ~ hormones are released
directly into blood instead of passing a duct
Glands
External Hormone
secretion
Pancreas Pancreatic Insulin &
juice
glucagon
Testis
Sperms
Male sex
hormones
Ovary
Eggs
Female sex
hormones
Endocrine Glands
Pituitary gland
Thyroid gland ~ thyroxine (T4)
Pancreas ~ exocrine & endocrine
~ glucagon& insulin
Parathyroid gland ~ parahormone
Adrenal gland
Pituitary gland
Situated at the base of the brain
Has 2 portions: anterior pituitary & posterior
pituitary
Produces a lage number of hormones
Receive information form hypothalamus
Hypothalamus
Pituitary gland
Hormones secreted by the pituitary gland
Thyroid stimulating
hormone
Adrenocorticotrophic
hormone
Follicle stimulating
hormone
Luteinizing hormone
Prolactin
Growth hormone
Antidiuretic hormone
Oxytocin
Thyroid gland
Found in the neck clost to the larynx
Produces thyroxine(T4)
Parathyroid glands
Embedded in the posterior surface of thyroid
glands.
Produce parathormone which maintains the
level of Calcium.
Parathormone increases the absorption of
calcium from the gut.
Adrenal glands
Situated above each kidney.
Have 2 parts: adrenal cortex and adrenal medulla.
Produces hormone:
~ cortisol
~ aldosterone
~adrenaline
~ norepinephrine
Pancreas
In a loop of the small intestine just below the
stomach.
Has both exocrine and endocrine functions.
α-cell produces glucagon → ↑blood glucose;
glycogen → glucose
β-cell produces →↓blood glucose;
glucose →glycogen
Nervous vs Hormonal System
Similarities
 Co-ordinate various activities
 Message : receptors  effectors
 Most important controlling organ are in the
head: brain & pituitary gland
 Reciprocal pattern of control:
Sympathetic vs parasympathetic
-ve feedback vs +ve feedback mechanism
Endocrine vs Nervous control
Endocrine
 Not obey All-or-none
Law
Transmission via blood
vessels
Slow & gradual action
Long lasting effect
Wide spread influence
Exact response
Master: pituitary gland
Nervous
 Obeys All-or-none Law
Transmission via nerve
fibres
Quick action
Short-lived effect
Localized influence
Widespread response
Master: nervous system
Significance of endocrine system
 As simple transmitter of information
 As limit control
 As reciprocal or -ve feedback system
 As evoking ‘Explosive reaction’ by +ve
feedback control