Chapter 6

Coordination and regulation: nervous systems

The nervous systemCentral nervous system (CNS)

Peripheral nervous system (PNS)

Brain & Spinal cord

Peripheral nervous system (PNS)Two parts:

Sensory (afferent) division: transmits sensory information about the internal & external environment to CNS Somatic sensory neurons: carry information to the CNS

from the external environment via the senses Visceral sensory neurons: carry information to the CNS

from the internal environment Motor (efferent) division: transmits information away

from CNS (to muscles & glands = effector organs) Somatic nervous system: voluntary nervous system –

controllable (skeletal muscles) Autonomic nervous system: involuntary nervous system

(smooth muscle, heart muscle & glands Parasympathetic / Sympathetic

The nerve cell (neuron) affector neuron / sensory neuron effector neoron / motor neuron connecting neuron / interneuron

A typical neuron is made up of:• Cell body (cell organelles)• Dendrites (highly branched)• Axon (1mm -1m in humans) with myelin sheath

Connecting CNS & PNS

A nerve impulse Action potential: a short-lasting event in

which the charges across the axon membrane of a cell rapidly rise and fall, following stimuli.

All or nothing (threshold)

Communication by neurotransmitters Once a neuron has been stimulated, it

transmits the nerve impulse along its axon. The impulse is carried along a small gap (synaptic cleft) by neurotransmitters.

Neurotransmitters are produced at the end of the axon and packaged in vesicles.

Communication by neurotransmitters II

Action Potential => influx of Ca ions which stimulates release of Neurotransmitters (NTM)

NTM diffuse across the synapse to pass on the message chemically (inhibitory or excitatory) Mitochondria supply energy for NTM formation and packaging

Message received by dendrites or membrane receptors Enzymes break down NTM for reabsorption NTM stimulates / inhibits the opening of protein

channels Specific receptors receive NTM which allows ion

channels open, Na floods in, depolarisation occurs and the next action potential can begin

(Noradrenaline)

Communication by neurohormones Neurons release hormones into blood which

travel to target organ Example:

Hypthalamus (TRH) -> Pituitary (TSH)-> thyroid glands

Networks of nerve cells Diverging pathway Converging

pathway

From 1 to many from many to 1

1 AP splits & travels many AP combined to 1

through many other nerves

Fig. 6.16 p.178

Summation of Action potentials

Toxins can overwhelm neurotransmission Toxins interfere on both sides of the neuro-

muscular junction, which can lead to paralysis

Antitoxins can react with toxins to destroy their normal abilities

Venom: poison from a snake (mixture of toxins)

Antivenom: reacts with venom to destroy its normal abilities

p. 180/181

Central nervous system (CNS) Brain:

Cerebrum (surface: cerebral cortex) Sensory & Motor Cortices

Thalamus (receives sensory info) Hypothalamus (regulates release of hormones) Brain stem & Medulla oblongata

Meninges:membranes that surround CNS

Cerebro Spinal Fluid (CSF):Between Meninges and CNS tissue

Having a brain wave Electroencephalogram (EEG)

shows brain activity and is measured using electrodes No electrical activity on an EEG means the brain is

dead and life will cease without machines helping an individual to breathe

PET scans (positron emission tomography): detects the amount of glucose being used by

different parts of the body CAT scans (computerised axial tomography)

special form of x-ray that takes many 'sliced' images which can be built up to give and overall picture

Spinal cord Grey matter: nerve cell bodies White matter: axons of these cells

Vertbral column: protective bone tissue surrounding the spinal cord

• made of disks called vertebra• and cartilage in between to absorb shocks

Nerves and hormones: a comparison

Homeostasis: nerves & hormones acting together