NERVOUS SYSTEM

Neural network that coordinates voluntary and involuntary actions between different body parts

Function

  1. Sensory input
  2. Integration
  3. Motor output

Cephalization in invertebrates
brain as centre for integration and formed from concentration of neuron in head region

  • appears in planarian, annelid, arthropod and molusk

CNS & PNS in vertebrates

CNS ( brain & spinal cord )
receives sensory input from PNS, integrates and initiate motor output

PNS ( nerves branching out from CNS )
carries sensory information to CNS and sends command to glands and muscle

Somatic NS
regulate voluntary action

Autonomic NS
regulate involuntary actions

Sympathetic division
promotes responses at relaxed state

Parasympathetic division
promotes responses at active state

Neurons


  • structural and functional unit of nervous system
  • communicate in the form of nerve impulse

consist of: 1. dendrites

  1. cell body
  2. axon

Types of neurons

Interneurons

Motor neurons

Sensory neurons

Receptor Mechanism

  • stimulus energy converted to membrane potential
  • weak stimulus energy is amplified
  • signals from receptor integrated through summation of graded potential

Type of sensory receptor

Thermoreceptor
cold and hot stimulus

Chemoreceptor
transduces chemical signal into receptor potential

Nocireceptor
stimulated by pain from ext & int source

Electromagnetic receptor
detects electromagnetic energy

Mechanoreceptor
stimulated by pressure, touch, stretch,motion and sound

Photoreceptor
determines how organism perceives environment through vision

Generation and conduction of the action potential

Resting Potential
state of neuron when no impulse is conducted

  • potential is due to unequal distribution of ions

Action potential
rapid change in polarity across axonal membrane as nerve impulse occurs

  • 2 gated ion channel ( K+ and NA+ )
  • axon will depolarise threshold level in all-or-none manner

Membrane potential
an electrical potential difference exist between inside and outside of the cell and is measured by mV between two points

  • cycle of nerve stimulation : RP -> Threshold level -> AP -> Refractory period

Depolarisation & Repolarisation

Depolarisation

  • sodium gates open, Na flow into axon
  • inside axon change from -ve to +ve

Repolarisation

  • Potassium gates open, K+ flows out of axon
  • inside of axon change from +ve to -ve

Propagation of an action potential
in unmyeliated axon, action potential travels down an axon one section at a time

  • action potential moved on, previous section undergoes refractory period, Na gates are closed
  • after refractory period, NA-K pump restores previous ion distribution by pumping Na outside and K inside

Saltatory conduction
in myelinated axon, gated ion channels that produce action potential are concentrated at nodes of Ranvier

Neurotransmitter and synaptic transmission

Neurotransmitter ( ACh, NE)
carries transmission across synapse and is stored in synaptic vesicles

NE - dreaming, waking, mood in CNS

ACh- excites skeletal muscle but inhibit cardiac muscle
excitatory or inhibitory effect on smooth muscles/glands

Serotonin - thermoregulation, sleeping, emotion and perception

is removed from cleft once initiated response to prevent continuous stimulation/inhibition of postsynaptic membranes

Synapse -region of close proximity

a neuron can have many synapse all over its dendrites and clell body

excitatory neurotransmitter- signal drives neuron closer to threshold

inhibitory transmitter - signal drives neuron away from threshold

Synaptic Integration

  1. too many excitatory signal, axon transmit nerve impulse
  2. both excitatory and inhibitory, signals will be prohibited by axon from reaching threshold and firing