Nervous System

• Works with endo and imm syst to maintain homeo.

3 Functions-->

1. Sensory input through sens recep.

2. Integration in CNS.

3. Motor output, sig from CNS alter eff cell behav.

• Nerves between CNS and rest body making PNS.
• Nerves sending info to CNS= afferent.
• Taking info from= efferent.
• Interneur connect sens in to motor out.

Neural circ 

Cone snail prod neurotox inducing paralysis/sensors detect prey, send info to brain and triggers release toxin coated tooth.

Neurons

• Cell body (soma) contains nuc
• Covered in dendrites
• Highly branched
• Receives messages
• Pass to cell body by elec sig
• Axons carry out mess from neu to other cells
• Connects to cell body by axon hillock
• Imp transmission nerve sig
• Axons covered insulating myelin 
• Axon ends= synapses
• Sig neu to others by chem (neurotrans)

Cell sends sig= Pre syn

Responds= Post syn

Sensory-> peripheral ends detect stim

Inter-> Complex dendrites + axons

Motor-> Comp dend but less comp ax

Supporting Cells

Astrocytes= structural/reg composition CNS fluid and neur.

Oligodendrocytes + Schwann cells= Form myelin sheathes.

Microglia= Imm

Nerves

Sig alt volt memb poten (Vm) across nerve memb.

Volt change caused by move ions across memb through specialised ion chan.

Ion chan open and close when responding to sig and Vm change.

Vm changes allow nerves sig each other

Why memb poten?

Caused by asymmetric distrib ions across memb (due to K+ and Na+ pumps and chan)

K+ cation in.         Na+ out

Prot/Phos anion in.      Cl- out

• Na+K+ ATPase moves Na+ out and K+ in
• More open K+ chann
• Allow K+ efflux and min Na+ in--> causes charge asymm 
• Memb poten = -70mV

Nerve imp= result change in memb poten

Nerve and musc Vm can change (excitable cells)

Unexcite state- Resting poten

Vm changes result from open gated ion chann.

Open/close in response to chem or volt change.

Graded potentials (small volt changes)

On dend, neurotrans stim Vm change.

Hyperpolar= dec voltage

Depolar= inc volt (can cause threshold potetial reached)

Mag change of poten depends on stim strength.

Large= more neurotrans/opens more chann.

Action Poten

Threshold poten(20mV more + than RP) exceeded which causes allor nothing AP.

Volt gate ion chann in APs

Na+ and K+ chann responsible for APs.

K+ chann- single volt sensi gate (closed in rest state,open slow depolar)

Na+- 2 volt sensi gates (acti gate closed rest state opens fast depolar/inact gate open in rest state close slow depolar)

APs

Rest state= Na and K chann closed (Vm -70mV)

Stimuli open some Na chann and more open when GP exceeds thresh (grad depolar caused may cause AP)

Rising phase AP= Na chann fully open allowing Na+ ions in cell/K+ chann most close but open slow.

Vm more + --> Na+ chann inact gates close/K+ chann open allow K+ efflux…