KEY OUTCOMES

extend knowledge of coordination and regulation of the living organism.

understand the significant contribution of the nervous system to homeostasis.

extend the understanding of signal transduction in cells with particular reference to neurons.

gain an overview of interactions of the nervous and the endocrine systems.

Case Study – Optic Nervereading page 167

• glaucoma is one of the most frequent causes of blindness in dogs

• the optic nerve comprises a million or more nerve fibres from neurons in the retina of the eye

• damage to the optic nerve can have serious consequences with respect to vision ability.

Tasks

Quick Check 1 & 2

The Nervous System- Structural Classification reading pages 170-172

When classified according to structure, the nervous system has two subdivisions.

1. The central nervous system (CNS)consists of the brain and the spinal cord

acts as the integrating and command center of the nervous system

interprets incoming information and issues instructions based on past experience and current conditions

2. The peripheral nervous system (PNS)the part of the nervous system outside the CNS

consists mainly of nerves that extend from the brain and spinal cord

The Nervous Systemreading pages 170-172

SpinalCord

Brain

Nerves

Central Nervous System

Peripheral Nervous System

Peripheral Nervous Systemreading pages 170-171

Has two parts – the SENSORY DIVISION and MOTOR DIVISION.

1. Sensory (Afferent) division: transmits sensory information about the external and internal environments to the CNS.

2. Motor (Efferent) division: transmits information away from the CNS.

Each part is either externally stimulated (somatic) or internally

Sensory: Somatic Sensory (external stimuli)/ Visceral Sensory (internal stimuli)

Motor: Somatic Motor (skeletal muscles)/ Autonomic Nervous System (internal muscles and glands)

Structure Of The Nervous System

Nervous System

Central Nervous System CNS

Peripheral Nervous System

Brain

Spinal Chord Somatic Sensory Neurons

Visceral Sensory Neurons

Somatic Motor Neurons

Automatic Motor Neurons

SENSORY DIVISION

MOTOR DIVISION

Sensory (Afferent) Nervous System

The Sensory Nervous System has two parts:

1. Somatic Sensory Neurons carry information to the CNS from the external

environment via the senses.

2. Visceral Sensory Neurons carry information to the CNS from the internal

environment (ie organs such as the heart)

• The sensory (afferent) nervous system sends information from receptors to the CNS.

Muscle

MotorNeuron

Interneuron

Skin receptors

SensoryNeuron

Brain

Motor (Efferent) Nervous System

The Motor (Efferent) Nervous System has two parts:

1. the Somatic Nervous System transmits messages to skeletal muscles. It is also known as the voluntary nervous system.

2. the Autonomic Nervous System transmits messages to smooth muscle, cardiac muscle and glands. It is also known as the involuntary nervous system.

• the motor division of the PNS sends information from the CNS to the muscles and glands.

Lets Look more closely at the Motor (Efferent) Nervous System

AUTONOMIC NERVOUS SYSTEM

INVOLUNTARY – CNS to EFFECTORS

Autonomic System

The Autonomic system has two parts: • Sympathetic• Parasympatheitic

Function: Control involuntary functions• heartbeat• blood pressure• respiration• perspiration• digestion

• Can be influenced by thought and emotion

• “ Fight or flight” response

• Release adrenaline and noradrenaline

• Increases heart rate and blood pressure

• Increases blood flow to skeletal muscles

• Inhibits digestive functions

CENTRAL NERVOUS SYSTEMBrain

Spinalcord

Dilates pupil

Stimulates salivation

Relaxes bronchi

Accelerates heartbeat

Inhibits activity

Stimulates glucose

Secretion of adrenaline,nonadrenaline

Relaxes bladder

Stimulates ejaculationin male

Sympatheticganglia

Salivaryglands

Lungs

Heart

Stomach

Pancreas

Liver

Adrenalgland

Kidney

PARASYMPATHETIC

• “ Rest and digest ” system

• Calms body to conserve and maintain energy

• Lowers heartbeat, breathing rate, blood pressure

CENTRAL NERVOUS SYSTEMBrain

Spinalcord

Stimulates salivation

Constricts bronchi

Slows heartbeat

Stimulates activity

Contracts bladder

Stimulates erectionof sex organs

Stimulates gallbladder

Gallbladder

Contracts pupil

PARASYMPATHETIC

Summary Of Autonomic DifferencesSummary Of Autonomic Differences

Autonomic nervous system controls physiological arousal

Sympatheticdivision (arousing)

Parasympatheticdivision (calming)

Pupils dilate EYES Pupils contract

Decreases SALiVATION Increases

Perspires SKIN Dries

Increases RESPiRATION Decreases

Accelerates HEART Slows

Inhibits DIGESTION Activates

Secrete stresshormones

ADRENALGLANDS

Decrease secretionof stress hormones

Neurons

Neurons (Nerve Cells)reading pages 172-175

• nerve cells or neurons are the basic structure of the nervous system

• a typical neuron has:• a nucleus within the cell body • dendrites: highly branched extensions of the cell body that receive and then

carry information towards the cell body• an axon: an extension that carries information away from the cell body

• three types of neurons exist including:• sensory (affector) neurons• connecting (inter) neurons• motor (effector) neurons

• the presence of the myelin sheath (on affector and effector neurons) increases the rate at which a nerve impulse is conducted along the axon.

TasksSee figure 6.8 a, b and cBiozone 97-98

Neurons

These extensions from the cell body vary in length, from microscopic, to just over a meter in some neurons. In humans, the longest ones reach from the lumbar region to the big toe.

– Neuron processes that convey incoming message towards the cell body are dendrites

– Those processes that conduct impulses away from the cell body are axons

– All axons branch profusely at their terminal end, forming thousands of axonal terminals

– These terminals contain hundreds of tiny vesicles that contain chemicals called neurotransmitters

– Each axonal terminal is separated from the next neuron by a tiny gap called the synaptic cleft

– Such a functional junction is called a synapse

Cells of the nervous system. (a) A typical sensory neuron (b) A typical motor neuron (c) Structure of a nerve (d) A typical connector or inter neuron

Relationship between different kinds of neurons.

Task:

See figure 6.8: copy and label

Nerve Impulses -Summaryreading page 174

• as an impulse moves along an axon, the permeability of the membrane changes so that positive Sodium ions (Na+) move into the neuron through ion channels

• the change in permeability moves along the neuron

• Sodium ions (NA+) move into the neuron causing achnage in polarity (from negative to positive). Potassium ions (K+) move out of the neuron (momentarily). When Na+ and K+ are momentarily together inside the neuron, the charge is positive

• after a nerve impulse has passed along the membrane, the original distribution of ions across the membrane is restored

• the larger the axon’s diameter, the faster the impulse moves along it

• the presence of myelin increases the speed of an impulse

• an unstimulated nerve is said to have ‘resting potential’ an activated nerve has ‘action potential’ (the wave being the action potential)

See figure 6.10 (not error on stimulated axon)

Task

Biozone page 100

Transmission of Impulses Along a Neurone

Nerve Impulse Transmission

Cells are set up as electrically polarized.– They are in “resting state”– Ready to do work.– A more + charge outside the cell than inside– Created by Na+/K+ pumps

Nerve Impulse Transmission

ACTION POTENTIAL

– These resting neurons are easy to knock off balance

– Electrical, chemical, or mechanical stimulus can move them to an action state.

– Once the “threshold” level is met, signal is sent.

Myelination

Schwann Cells

– Act as insulators to the nerve

– Lipo-protein based

– Separated by Nodes of Ranvier

Node of Ranvier

Myelination cont

Schwann Cell

– Speed up conduction of impulse

– Depolarization skips from one node to another.

Synapse

• Receptor site receives neurotransmitters• Neurotransmitters change permeability of membrane.• Ions flood into membrane setting off a action potential

in post-synaptic cell.

The Structure of a Synapse.

Transmission between neurons

SynapseThe location between a neuron and its effector (nerve, muscle, gland.)

Not in physical contact with effector.

When signal reaches the synaptic cleft it releases Neurotransmitters (NT).

NT Diffuse across cleft to receptor sites on post-synaptic site.

Signal Transduction Across A Synapse

Neurotransmitters Substancereading page 175-178

• are produced at the ends of axons and are packaged in vesicles (on the end of axons only!)

• diffuse across the synapse and attach to receptors on the postsynaptic membrane

• stimulate another neuron or effector• last for a very short time only (enzymes produced by

muscles tissue inactive the substances for example)

Example: acetycholine

Communication by Neurohormonesreading pages 176-177

• are chemicals released directly into the blood

• travel to a target organ where the signal is transduced and the receptor cells respond

• neurons in the hypothalamus of the brain has several different neurohormones. These are released into the blood and travel to the pituitary cells, both anterior and posterior, where they exert their effect

Examples: thyrotropin-releasing hormone (TRH) signals anterior pituitary cells to producethyroid stimulating hormone (TSH);

This is an example of the nervous and endocrine systems interacting together

See figure 6.14 & 6.15

Signals and Receptors

• signal transduction is the process by which a cell converts one kind of signal into another by a series of relay molecules

• signals initiating transduction include:• hormones• neurotransmitters• neurohormones• environmental stimuli (i.e light)

• cellular responses to transduction include:• activation of a gene- protein production• alteration of cellular activity, such as

• increased cellular secretions• Changes in cell permeability• Increased rates of chemical reactions

Networks of nerve cellsreading page 178

• neuron pathways are of two kinds: diverging or converging

• diverging pathway: a single axon of one neuron branches and links up wit a larger number of postsynaptic neurons.

• converging pathway: many persynaptic nerves cone together to influence a smaller number of synaptic neurons, ultimately one.

• one advantage of the convergence system is that one cell can have multiple signals that influence an outcome.

Figure 6.16 (next page)

ReflexReflex

Simplest of neural Simplest of neural responses.responses.

Involves as little Involves as little as 3 neuronsas 3 neurons

Shortens link Shortens link between stimulus between stimulus and response.and response.

Reflex ArcReflex Arc

Sensory NeuronSensory Neuron

InterneuronInterneuron

Motor NeuronMotor Neuron

Create reflex arcCreate reflex arc

Reflex Arc

ReflexReflex

Acts in an “emergency response”Acts in an “emergency response”

Cuts time of response.Cuts time of response.

Communication by Communication by neurohormonesneurohormones

From the previous slide, it is evident that From the previous slide, it is evident that neurotransmitters signal other cells directly. However neurotransmitters signal other cells directly. However there are neurons that send signals via there are neurons that send signals via neurohormonesneurohormones

Some neurons release chemicals called neurohormones into the blood. The blood carries the appropriate signal to the target organs that then respond.

Communication by Communication by neurohormonesneurohormones

These These neurohormonesneurohormones are released into the are released into the blood, which then travel to the target organ blood, which then travel to the target organ which receives the signal thus resulting in a which receives the signal thus resulting in a response from the receptor cell. For example, response from the receptor cell. For example, the hypothalamus of the brain has several the hypothalamus of the brain has several different kinds of neurons each producing a different kinds of neurons each producing a different kind of neurohormone. These are different kind of neurohormone. These are released into the blood and travel to the cells of released into the blood and travel to the cells of the anterior or posterior pituitary where they the anterior or posterior pituitary where they exert their effect.exert their effect.

Example of Communication by Example of Communication by neurohormonesneurohormones

Neurons in the hypothalamus in Neurons in the hypothalamus in the brain secrete neurohormones the brain secrete neurohormones [e.g. [e.g. thyrotropin-releasing thyrotropin-releasing hormone (TRH)hormone (TRH)] into blood ] into blood capillaries that become associated capillaries that become associated with the pituitary. Signals received with the pituitary. Signals received by cells of the pituitary are by cells of the pituitary are transduced and the pituitary transduced and the pituitary responds by producing a hormone responds by producing a hormone as instructed [in this case as instructed [in this case thyroid-thyroid-stimulating hormone (TSH)stimulating hormone (TSH)]. This ]. This hormone enters the bloodstream hormone enters the bloodstream and is transported to its target cells and is transported to its target cells [in this case the [in this case the thyroid glandthyroid gland].].

Impeded Nerve Functionreading page 178-182

• when adverse events impinge on facets of the hormonal and nervous systems, their normal functioning can be brought to a halt.

• example: thyroid gland. Over activity shows excessive amounts of thyroxin are produced.

• toxins can overwhelm the neuron transmission.

• poisonous animals produce toxins to paralyse their prey or rebuff predators.

Task

Quick Check 6-11 page 182

The Central Nervous Systemreadings page183-187

• the brain and spinal cord together form the central nervous system.• the brain plays a major role in homeostasis.• a living brain has continuous electrical activity• the distinct areas are visible in sections of a spinal cord.

Tasks

Quick Check 12-15

Comparing Nervous And Endocrine Systems.

Nerve Action Endocrine system

is faster Is slower

shorter lived more sustained(longer acting)

Why?

• Nerve action is due to electrical impulses, which travel very quickly (up to 200metres per second)

• Transmitter substance is active at a synapse for a fraction of a second only and then is inactivated

Why?

• endocrine hormones travel from their production site via the bloodstream to their target cells

• Hormones must be metabolised before their actions stop and inactivation time can take hours or days.

Case Studies of Homeostasisreadings pages189-195

• Blood Glucose control• Maintaining core temperature• Maintaining water balance

Control of Blood Pressurereading page 190

(draft)

• figure 6.31 page 190• blood pressure is under nervous and hormonal control.• if a change in blood pressure occurs, events take place that

counteract the initial change. • a fall in blood pressure is followed by events that lead to a

restoration of normal blood pressure.

Maintaining Core Temperaturereading page 191-192

(draft)

• fig. 6.32, page 191.

• when a person is exposed to the cold, the body responds in several ways to maintain a stable core temperature.

Maintaining Water Balancereading page 192-193

(draft)

• fig. 6.33 page 193• vasopressin and renin both play a role in conservation of water.• kidneys are the major organs that control water balance.

Tasks • Complete Biochallenge page 196.• Complete Chapter Review questions 197 – 198.