Topic 6.5Nerves, Hormones and

Homeostasis

IB Biology

Nervous System

Central Nervous System (CNS):

brain and spinal cord relays messages, processes and

analyzes information

Peripheral Nervous System (PNS)

peripheral nerves: cranial and spinal (outside CNS)

connects sense organs to CNS connects CNS to muscles and

glands

Peripheral Nervous System

Sensory division (from receptors to CNS)Motor division (from CNS to effectors)

Somatic: voluntary Autonomic: involuntary

Sympathetic: “fight or flight” Dilates pupil/relaxes lens Inhibits digestion Increases heart rate Dilates bronchioles Stimulate liver: glycogen →

glucose Relaxes bladder

Parasympathetic: opposite - conserves energy (“rest and digest”)

NeuronsSpecialized cells that carry electrical impulses

Motor Neuron

node of Ranvier

Neurons under a microscope

Nerve bundle

•Myelin sheath is made of Schwann cells wrapped around the axon

•Myelin: insulating material

•Demyelination = myelin is destroyed e.g. multiple sclerosis

Spinal cord

Types of NeuronsSensory Neurons: transmit electrical impulses from sensory receptors to the CNSRelay Neurons (Interneurons): move impulses inside the CNSMotor Neurons: take impulses from CNS to effectors (glands/muscles)

Sensory Neuron

Motor Neuron

Reflex

How the impulse is transmittedImpulse begins when a neuron is stimulated by another neuron or by the environmentElectrical impulse moves in one direction:

Dendrites → Cell Body → AxonSynapse: gap between 2 neurons Neurotransmitters send the signal to the following neuronNo myelin = 5-25m/sWith myelin = 10-120m/s

How the impulse is transmitted

Neuron not transmitting an impulse: membrane has an electrical potential (voltage) called resting potential

Caused by the imbalance of K + and Na + across the membrane (Na + /K + pumps) = polarization

Electric difference (voltage): -70mV

When there is a stimulus...

Na+ gates open = Na + enter the cellElectrical potential of the cell changes

depolarization (normal charge is reversed) = +30mV

Action potential is recordedNa + channels closeK + channels open

repolarization occurs (charges back to normal)

K + channels stay open longer hyperpolarization = -85mV

(refractory period = prevents one impulse to catch up with another)

Stimulus = self-propagating

http://outreach.mcb.harvard.edu/animations/actionpotential.swf

The SynapseSynapse = gap between neuronsAction potential cannot cross gap: neurotransmitters carry the impulseNeurotransmitters: stored at the end on axons (glutamate, GABA, acetylcholine, norepinephrine, dopamine, serotonin, nitric oxide, etc)1)Voltage Ca+2 gated ions open → calcium flows inside neuron2)Calcium help vesicles fuse with membrane → neurotransmitters are released3)These bind with neuroreceptors 4)Voltage gated ions are activated = depolarization5)Impulse is passed on to post-synaptic neuronNeurotransmitters = broken by enzymes and reabsorbed by pre-synaptic neuron

Endocrine SystemEndocrine glands produce hormones that travel in the bloodTarget tissue respondsResponse affects the gland = NEGATIVE FEEDBACKBody maintains its internal conditions stable = HOMEOSTASIS-Blood pH, Temperature, Water balance, Glucose concentration, CO2 concentration

Negative Feedback

Negative Feedback 2

Control of Body TemperatureHypothalamus controls body temperature, preventing cooling/overheatingSkin arterioles: vasoconstriction (prevents heat loss) ; vasodilation (more blood near surface – heat is transferred out)ShiveringHairs with erector muscle Sweat glands

Control of Blood GlucosePancreas is an endocrine glandIt releases insulin (- cells) and glucagon (- cells)Receptors present on liver cellsNegative feedback occurs

Diabetes mellitusGlucose builds up in blood = cells lose water (a lot of urine is produced)Glucose appears in urine Type I: juvenile

- no insulin is produced because - cells are destroyed (autoimmune)Type II: adult

- reduced sensitivity to insulin / less receptors