‘YOU’ You are ‘YOU’ because of your NERVOUS SYSTEM kidneyHeart NERVOUS SYSTEM, not because of your kidney or Heart or……………… HUMAN NERVOUS SYSTEM HUMAN NERVOUS SYSTEM controls all Human behavior

All BEHAVIOR Human Nervous System All BEHAVIOR is determined by the Human Nervous System GENETICS ENVIRONMENT HNSMALFUNCTION DISTURBANCE OF BEHAVIOR NEURAL NETWORK BRAIN

HUMAN NERVOUS SYSTEM NEURAL NETWORK NEURAL NETWORK NEURONS PRECISELY CONNECTED WITH EACH OTHER SENSORY SYSTEM MOTOR SYSTEM SENSORYRECEPTORSSENSORYRECEPTORS EXTERNALENVIRRONMENTEXTERNALENVIRRONMENT MOTOROUTPUTMOTOROUTPUT MUSCLESMUSCLES HUMANBEHAVIORHUMANBEHAVIOR INFORMATION PROCESSING INFORMATION STORAGE SENSORY CODING REFLEX ACTION OR DELAYED ACTION

Functional Unit of the Brain

1. Resting Membrane Potential is a potential difference that exists across the membrane of a all cells. 2. Electrotonic Potential is a voltage signal that is produced by passive changes in resting membrane potential of a cell (neuron or muscle). 3. Action Potential is a voltage signal (an impulse) that is produced by a sudden and a transient reversal of resting membrane potential of an excitable active cell (neuron or muscle).

The magnitude of potential depends on the degree of separation of the opposite charges - 70mV Resting Membrane Potential MEMBRANE OUT IN mV Hyperpolarization - 50mV Depolarization or Hypopolarization

Electrotonic Potentials (EPSP) OR Hypopolarization (IPSP)

ACETYLCHOLINE NICOTINIC RECEPTOR (CHANNEL)

(Secretory granules)

At some excitatory synapses, closing of K + or Cl - channels or both may cause ecxitation of the postsynaptic cell

At some inhibitory synapses, K + channels open and hyperpolarize the postsynaptic cell

In cells with longer time constant the signals decay slowly and therefore EPSPs have more time and better chance of integration – a process called “Temporal summation”. In cells with shorter time constant the signals rapidly decay and therefore EPSPs have poor chance of integration. 63% τ

In cells with longer length constant the signals spread to longer distances with minimal decay, and therefore EPSPs have better chance of integration – a process called “Spatial summation”. In cells with shorter length constant the signals spread to smaller distances, because of rapid decay and therefore EPSPs have poor chance of integration.

Graded Potential

Local circuits cross the membrane only at the nodes of Ranvier.  Current density is greater.  Depolarisation is more rapid & threshold is reached more quickly  CV is raised  The AP appears to jump from node to node rather than propagate smoothly along the axon.  This process is Salatatory Conduction (Lat. saltere = to jump).  Local circuits can travel along the cytoplasm for several internodal lengths and still be strong enough to depolarise a node of Ranvier to threshold. Thus if one or more nodes are blocked, propagation is still possible over the inactive region. The axon has a large Safety Factor.